Head and Neck Written

Special afferent (SA) neurons in cranial nerves I, II, VII, VIII, IX, and X carry sensory information back to the CNS from a variety of highly specialized end organs in the head and neck, including those for: SA: 1,2 + 7,8,9,10

-olfaction (smell). -vision (sight). -audition (hearing). -vestibulation (balance). -gustation (taste).

Ependymal Cells

Ependymal cells line the cerebral ventricles and the central canal of the spinal cord. They form a regular layer one cell thick, and the shape of the cell varies from flattened to column-shaped depending on location. They have cilia at the luminal surface and contact each other with gap junctions and occasional desmosomes. They do not project into the periventricular neuropil. Ependymal cells contain cilia, which contributes to the flow of cerebrospinal fluid. Ependymal cells DO NOT form a diffusion barrier between the brain and the cerebrospinal fluid, such that CSF may pass across the ependymal lining and enter the neuropil to form the interstitial fluid of the brain.

Extrinsic muscles of tongue - alter position

Genioglossus -- protrude Hyoglossus -- retract Styloglossus -- retract Palatoglossus --Pharyngeal plexus (X)

Maxillary Artery (2) Pterygoid (second) part [location: crosses the infratemporal fossa superficial (typical) or deep to the lateral pterygoid muscle] All branches are distributed directly to their targets, which are primarily the muscles of mastication. (4, deep temporal, asserter, pterygoid, buccinator)

- Anterior and posterior deep temporal arteries supply the temporalis muscle - Masseteric artery supplies the masseter muscle - Several pterygoid arteries run to the lateral and medial pterygoid muscles - Buccal artery supplies the buccinator muscle.

Maxillary Artery Mandibular (first) part [location: posterior to lateral pterygoid muscle]: Passes anteriorly between the ramus of the mandible and the sphenomandibular ligament. All branches of this part pass through bone or cartilage to their targets. The branches of this part are: (4, 2 you know, 1 is accessory, other is tympanic)

- Anterior tympanic artery enters the middle ear cavity through the petrotympanic fissure, along with the chorda tympani nerve. - Middle meningeal artery enters middle cranial fossa via the foramen spinosum to the skull and to much of the cranial dura mater. o Clinical correlation: This artery is often damaged in blows to the lateral head, and is typically the cause of epidural hematomas. - Accessory meningeal artery passes up through foramen ovaleto supply the trigeminal ganglion. - Inferior alveolar artery passes with its corresponding nerve through the mandibular foramen into the mandibular canal to supply lower teeth and chin. Before doing so, they give off the mylohyoid artery and nerve to the mylohyoid and anterior digastric muscles.

Anterior Aspect of the Skull

Supraorbital foramen (notch)x, Infraorbital foramen, Mental foramen, Zygomaticofacial foramen (hole on zygomatic) Orbit, Malar prominence (prominence of the cheek), Piriform aperture (nasal opening tear drop), Anterior nasal apertures, Nasal septum, Nasal cavities, Anterior nasal spine, Middle nasal conchae off ethmoid and inferior nasal conchae is its out bone (turbinates), Mouth, Superior/ Inferior alveolar process (arc on teeth) , Mental protuberance (chin), Glabella (center of eyebrows), Nasion (junction between nose and forehead)

Five arteries supply the interior of the nose. All five of these arteries anastamose on the anterior nasal septum. The following arteries provide both lateral and septal branches

Anterior and Posterior ethmoidal (from ophthalamic artery) Sphenopalatine artery (from maxillary artery) +Greater palatine artery (from maxillary artery) Septal branch of the superior labial artery (from the facial artery)The external nose is supplied by the anterior ethmoidal of the ophthalmic a. and septal branch of superior labial facial arteries. Submucosal venous plexus (warms air before entering lung) drains ophthalmic, sphenopalatine, and facial veins. It is im- portant to be aware that these veins also communicate with the cavernous sinus to infection into the cranium.

Choroidal Cells

Choroidal cells are embryonically derived from ependymal cells. They secrete cerebrospinal fluid. There are four plexuses of choroidal cells; one in the each of the lateral ventricles, the third ventricle, and the fourth ventricle. The capillaries of the choroids plexus are fenestrated.

Orbit 2

Orbit Apex - back of eye Mastoid emissary foramenMastoid emissary foramen Optic canal x Roof x Frontal bone x Lesser wing of the sphenoid x Lacrimal fossa x Floor Maxilla x careful mix up with zygomatic Zygomatic bone x Palatine bone (orbital process at apex) (tiny back part) Infraorbital groove and canal (more anterior) Medial wall Maxilla x Lacrimal bone x Ethmoid bone (lateral mass) x Lacrimal groove - ridge of lacrimal bone Nasolacrimal canal near nasal and lacrimal bone Anterior and posterior ethmoidal foramina (on ethmoid before superior orbital fissure) Lateral wall Zygomatic bone x Greater wing of the sphenoid x Superior orbital fissure x Inferior orbital fissure x Zygomatic-orbital foramen medial foramen

Remaining branches arise from the vagus nerve itself..The Vagus Nerve, Cranial Nerve X

Superior Vagal Ganglion 2 -The meningeal branch reenters the skull through the jugular foramen and is distributed to the dura mater of the posterior cranial fossa. Doubt exists whether these fibers originate in the vagus or in upper cer- vical spinal nerves. -The auricular branch (PDF Figs. 20,21) enters the lateral wall of the jugular fossa, runs horizontally through the temporal bone, and emerges behind the auricle through the tympanomastoid fissure. It carries GSA fibers to skin behind the auricle, a portion of the auricle itself, the external auditory meatus, and the outer surface of the ear- drum. -auricular branch. From the jugular fossa, they pass through the temporal bone, emerge through the tympanomastoid fissure, and are distributed to skin behind the ear, over a portion of the auricle, in the floor of the external auditory meatus, and on the external surface of the ear drum, in company with GSA fibers from the facial and glossopharyngeal nerves. -Superior laryngeal nerve. General sensory fibers passing through the internal branch of the superior laryngeal nerve reach the base of the tongue, the epiglottic region, and the laryngeal mucous mem- brane above the margin of the vocal fold. Proprioceptive fibers carry information from the intrinsic laryngeal musculature. -Recurrent laryngeal nerve. General sensory fibers are distributed to the trachea, upper esophagus, and laryngeal mucous membrane below the free margin of the vocal fold. Inferior Vagal Ganglion 3 -The pharyngeal branch, descends between the internal and ex- ternal carotid arteries to reach the outer surface of the middle phar- yngeal constrictor. It contains SVE fibers that traverse the pharyngeal plexus to innervate all muscles of the palate and pharynx except tensor veil palate (med pterygoid V3) and stylopharyngeus (IX). -The superior laryngeal nerve descends deep to the internal and external carotid arteries **External laryngeal nerve with superior thyroid artery, supplying SVE fibers to the inferior pharyngeal constrictor and cricothyroideus*** **Internal laryngeal nerve pierces the posterolateral part of the thyrohyoid membrane to enter the larynx from above and behind. It is distributed to the laryngeal mucous mem- brane above the free margin of the vocal fold, the epiglottis, and the base of the tongue. The nerve supplies this area with GSA general sensory fibers; GVE preganglionic parasympathetic fibers to scattered ganglion cells that innervate regional glands; and SA (taste) fibers. It also carries GSA proprioceptive fibers from the intrinsic laryngeal muscles. -Vagus nerve proper. Below the origins of the recurrent laryngeal nerves, the vagi distribute interoceptive fibers to the heart, lungs, lower esophagus, and abdominal viscera down nearly to the left colic flexure. Other Br 2 -Cervical cardiac branches GVE preganglionic parasympathetic axons that reach the heart through the cardiac plexus. GVA stretch receptors in heart walls and to chemo/baro in aorta/pulm trunk. -The right and left recurrent (inferior) laryngeal nerves slipping into the larynx beneath the lower border of the inferior pharyngeal constrictor. The recurrent nerves carry four fiber types. GSA general sensory fibers are conveyed to the esophagus, trachea, and mucous membrane of the larynx below the margins of the vocal folds (internal laryngeal does above) GVA interoceptive fibers return from the heart and airway. GVE preganglionic parasympathetic fibers reach scattered ganglion cells that regulate tracheal smooth muscle and glands in the lower portion of the larynx, trachea, and upper two-thirds of the esophagus. SVE fibers of recurrent laryngeal do all muscles of layrnx except circa. Inilateral paralysis of the intrinsic laryngeal muscles produces marked hoarseness of the voice. Damage vagus carotid, damage recurrent thyroid/pt, enlargement of lymph node.

The Trochlear Nerve IV GSE only Superior Oblique

carries GSE fibers that provide motor innervation to the extraocular muscle (superior oblique) whose tendon changes its direction by passing through the trochlea, a cartilaginous pulley on the wall of the orbit.

The Facial Nerve VII (5 but GSE!!) GVA/GVE (pterygopalatine/submandibular ganglia) GSA (exteroceptive sense of ear) SA (taste ant tongue and palate) SVE (facial expression br 2)

the great motor nerve of the face, distributes SVE fibers to striated mus culature derived from branchial arch two, including the muscles of facial expression. It also contains: -GVA fibers in the Facial nerve carrying interoceptive infor- mation back from the mucosa of the nasal cavity, oral cavity and palate. These represent the afferent limb of visceral re- flexes involving glands controlled through the pterygopala- tine and submandibular ganglia. -GVE preganglionic parasympathetic fibers to cells of the pterygopalatine and submandibular ganglia. -GSA fibers conveying exteroceptive sensation from a small patch of skin behind the ear, in the floor of the external audi- tory meatus, and on the outer surface of the ear drum. -SA fibers from taste buds of the palate and anterior portion of the tongue.

Maxillary Artery(3) Pterygopalatine (third) part: [location: within pteryogpalatine fossa, which it enters via the pteryogmaxillary fissure] Branches of the artery pair up with those of the maxillary nerve to form typical neurovascular bundles. All bundles then pass through bone to targets. (6, psa,inforb,pharyn,descpal,spheoepal,arteryofcanal)

- Posterior superior alveolar (similar path and target as nerve) - Infraorbital (similar path and targets as nerve) - Pharyngeal (similar path and target as nerve) - Descending palatine artery descends into the upper part of the greater palatine canal and divides into the greater and lesser palatine arteries - Sphenopalatine artery is the terminal, continuing branch of the maxillary artery. It passes through the sphenopalatine foramen into the nasal cavity together with the posterior superior nasal branches of the maxillary nerve. The artery gives off posterior lateral and posterior septal nasal branches that accompany the nerves on the lateral and septal walls of the nasal cavity. - The artery of the pterygoid canal passes posteriorly along the nerve of the pterygoid canal, through that canal. In the canal, the artery anastomoses with a similar branch of the internal carotid artery to form a potentially important link between external and internal carotid systems.

Fascial layers

- Superficial fascia- subcutaneous tissue- contains platysma muscle and cutaneous veins and nerves - Pretracheal fascia o Muscular layer: encloses infrahyoid (strap) muscles o Visceral layer: encloses thyroid (& parathyroids), tra- chea, and esophagus Buccophayrngeal fascia: is the thin, posteriorlamina of the visceral layer of the pretracheal fascia that separates the esophagus from the pre vertebral fascia The RETROPHARYNGEAL SPACE is a potential space between buccopharyngeal fascia and alar fascia. o Alar fascia: anterior lamina of prevertebral lamina (which arises medial to anterior tubercle of the cervical vertebrae PREVERTEBRAL SPACE space lies between the alar fascia anteriorly and the and the prevertebral fascia posteriorly Prevertebral fascia - encloses vertebral column and associated. Muscles (scalenes, etc.) roots of brachial and cervical plexi, sympathetic trunk. Carotid sheath - encloses common and internal carotid arteries, internal. Jugular vein, vagus nerve and fibers of the carotid plexuses

General somatic afferent (GSA) neurons Cell bodies are located in dorsal root ganglia of spinal nerves and sensory ganglia of cranial nerves (no synapse). Each ganglion cell sends a peripheral process out to the sensory ending and a central process into the CNS. GSA: 9,10 General somatic efferent (GSE) neurons provide motor innervation to voluntary, striated, skeletal muscle derived embryonically from paraxial or lateral plate mesoderm. Cell bodies are located in the ventral motor column of the spinal cord and in brainstem nuclei of cranial nerves III, IV, VI, and XII. Their axons pass outward through the appropriate spinal and cranial nerves. GSE: 3*4, 6,12

-Exteroception is the highly developed, well-localized sense of tem- perature, touch, pain, and pressure mediated by receptors in skin and mucous membranes. It is exemplified by the sensation felt over the palp of the index finger and tip of the tongue. -Proprioception is the positional sense returned from muscles, ten- dons, and joints. -General sensation is returned from viscera in the head and neck by cranial nerves IX and X. Although it is poorly localized compared with that carried by the trigeminal nerve, it is classified as GSA.

The Vagus Nerve, Cranial Nerve X, is a vagabond, wandering widely through the head, neck, thorax, and abdomen. Like the Glossopharyngeal nerve, the Vagus also contains five of the six modalities, including:

-GSA fibers carrying poorly localized general sensation from the epiglottic region, larynx, and upper esophagus. Exteroceptive fibers return from the same small area of skin also supplied by the Facial and Glossopharyngeal nerves. In addition, this component includes proprioceptive fibers returning from muscle spindles and other receptors in the laryngeal musculature. These are often overlooked but are of considerable significance during speaking and singing. -GVE preganglionic fibers in the parasympathetic motor pathways to glands of the epiglottic region and to cervical, thoracic, and abdominal viscera. -GVA fibers carrying interoceptive information as the afferent limb of visceral reflexes. -SVE fibers providing motor innervation to striated muscles of the pal- ate, larynx, pharynx, and upper esophagus, which arise from the fourth and sixth branchial arches. ] -SA fibers from taste buds scattered at the base of the tongue, around the epiglottis, and in the upper larynx.

The Vagus Nerve X (5 but GSE!!) GVE (ps motor to glands of epiglottic region), GVA, SVE (palate, larynx, pharynx, upper esophagus 4th/6th br arch), SA (tase of tongue, epiglottis, upper larynx)

-GSA general sensory fibers carrying poorly localized pain, tem- perature, touch, and pressure felt in the lining of the larynx and upper esophagus; exteroceptive fibers from the same small area of skin also supplied by the Facial and Glossopha- ryngeal nerves; and proprioceptive fibers returning from muscle spindles and other receptors in the laryngeal musculature for voice!. These are often overlooked. -GVE preganglionic fibers in the parasympathetic motor path- ways to glands of the epiglottic region and to cervical, tho- racic, and abdominal viscera. -GVA fibers carrying interoceptive information as the afferent limb of visceral reflexes. -SVE fibers providing motor innervation to striated muscles of the palate, larynx, pharynx, and upper esophagus, which arise from the fourth and sixth branchial arches. (However, see cranial nerve XI, below.) -SA fibers from taste buds scattered at the base of the tongue, around the epiglottis, and in the upper larynx.

General visceral afferent (GVA) neurons mediate interoception (knowledge of the internal environment) by carrying sensory information back from viscera. Cell bodies are located in dorsal root ganglia of spinal nerves (T1-L2; S2-S4) and sensory ganglia of cranial nerves 9,10,12 (no synapse). Each ganglion cell sends a peripheral process out to sensory endings in the wall of an organ or blood vessel and a central pro- cess into the CNS. GVA: 9 10 12

-fibers carrying feedback for regulation of physiological re- flexes (distension, chemoreception, etc.) usually retrace the path followed by parasympathetic motor fibers to the organ, while -fibers carrying pain information usually retrace the path fol- lowed by sympathetic motor fibers to the organ. RULE: General visceral sensation (other than pain) doesn't usually reach the level of consciousness. EXCEPTION: Dull, poorly localized sensations of pain, touch, and temperature from viscera in the head and neck are felt consciously. They are carried by cranial nerves IX and X from the middle ear, posterior tongue, pharynx, larynx, and upper esophagus. This input reaches the conscious level and is classified as GSA "general sensory".

Course The Facial nerve, Cranial Nerve VII is intimately related to the temporal bone and middle ear cavity

1. Cerebllopontine angle 2. Cross posterior cranial fossa 3. Enter internal auditory meatus w/ Vestibulocochlear 4. Into facial canal between meatus and stylomastoid foramen 5. Genu: Sharp turn to mastoid antrum behind middle ear cavity to stylomastoid foramen (SVE) facial expression Stapedius Arch II- branch in temporal bone Nervus Intermedius: Vestibulocochlear, SVE VII, and NonSVE VII internal auditory meatus. NonSVE VII = Nervus Intermedius- joins sensory geniculate ganglion on facial nerve at gene Greater Petrosal Nerve: Nervus intermedius -> Greater petrosal nerve -> runs towards Pterygopalatine fossa -> Escapes out of Hiatus for greater petrosal nerve onto middle cranial fossa -> Continues on surface of petrous temporal bone, pass bigeminal ganglion, past internal carotid artery, joins up with deep petrosal nerve from carotid sympathetic plexus to enter pterygoid canal to reach pterygopalatine fossa and ganglion. Chords Tympani: Chords tympanic - leaves lower facial canal to go through the small posterior canaliculus to reach margin of tympanic membrane - cross base of external auditory meatus 0 reenter temporal bone through short anterior canaliculus ending in the petrotympanic fissure to emerge in the infra temporal fossa to join lingual nerve and reach submandibular ganglion and tongue. GSA add to auricular br of vagus nerve.

The Temporal Bone and Middle Ear Cavity

1. Close to Facial, Vestibulochoclear, Glossopharyngeal, Vagus, and Accessory nerves. 2. Facial and Glossopharyngeal all have preganglioninc parasympathetic outflow passing through the temporal bone to reach the pterygopalatine, submandibular, and otic ganglia. 3. Postganglionic sympathetic fibers cross the bone with the internal carotid artery to reach meninges, orbit, nose and palate. 4. Auricle/pinna cartilage, medial bone continous with middle ear.

Nerves of the neck region: Cervical plexus

1. Cutaneous branches emerge from the posterior border of the sternocleidomastoid m. Lesser occipital n. (C2) behind ear Great auricular n. (C2,3) across sternocleidomastoid to angle of mandible Transverse cervical n. (C2, 3) to anterior triangle Supraclavicular nn. (C3, 4) downward over clavicle 2. Motor branches a. Ansa cervicalis - Superior & inferior rami to infrahyoid muscles b. Cervical branch of facial n. (CN VII) to platysma, arises at angle of mandible c. Vagus nerve (X) in carotid sheath behind vessels to mus- cles of larynx and pharynx d. Hypoglossal nerve (XII) to muscles of tongue e. Phrenic nerve (formed by C3, 4, 5) f. Accessory nerve - to sternocleidomastoid and trapezius

The inner ear

1. Embedded in petrous temporal bone consisting of bony labyrinth: cushioning perilymph of anterior/posterior membranous labyrinth: endolymph 2. Posterior membranous labyrinth: Semicircular canal, saccule, utricle of vestibulation. 3. Anterior membranous labyrinth: cochlea. (Ant=Audition)

The muscles associated with the larynx serve to fill the gaps between the cartilages as well as making them move. They can be loosely divided into two broad cate- gories: extrinsic and intrinsic.

1. Extrinsic: These are muscles that insert onto the larynx, but arise else- where. Their actions result chiefly in movements of the entire larynx relative to surrounding structures. Within this group, the extrinsic mus- culature can be divided into two additional categories: Elevators (6)- thyrohyoid, stylohyoid, mylohyoid, digastric, stylopharyngeus, palatopharyngeus. Depressors (3)- omohyoid, sternohyoid, and sternothyroid. 2. Intrinsic: This group contains muscles that pass between the cartilages of the larynx and moves them individually. Of these, there are six pairs named for the cartilages they span. (Netter Pl 81) 1. Cricothyroid: Only external muscle, acts at cricothyroid joint. Lengthen and TIGHTEN the vocal fold. 2. Cricoarytenoids: (Posterior & Lateral), control arytenoid cartilages relative to cricoid cartilage by rotating the arytenoids about avertical axis, which in turn moves the vocal folds toward or away from each other. Posterior cricoarytenoids work together to open the folds. Lateral cricoarytenoids close the folds 3. Thyroarytenoid located within conus elasticus and aryepiglottic fold. Shortens and thickens the vocal folds. 4. Vocalis: Between thyroid cartilage and vocal process of arytenoid cartilages. Fine-tunes the locations at which the folds are tense or loose. 5/6. Transverse and Oblique arytenoid: Abduct the arytenoid muscles to draw the vocal folds closer together. 7 Aryepiglotticus: Lies in free upper border of quadrangular mem- brane between epiglottis and arytenoid cartilages. Gives membrane stiffness and rigidity.

Tonsils: The tonsils are masses of lymphoid tissue distributed near the openings to the oral and respiratory passages.

1. Lingual tonsils located on the posterior 1/3 of the tongue. 2. Pharyngeal tonsils located above and behind the pharyngotympanic tube 3. Palatine tonsils located in the fossa between the palatoglossal and pa- latopharyngeal arches (the fauces. L. Throat) in the oral cavity.

Muscles of the Face he muscles are in the subcutaneous tissue of the face, with origins from either bone or fascia and insertions into skin. Contraction results in a pulling of skin and a change in facial expression. The muscles listed below are organized into muscles of/around the eye, nose and mouth.

1. Muscles associated with the eyes (orbital group): Orbicularis oculi- a large muscle that surrounds the entire orbital orifice. The muscle forms concentric circles from the medial orbital margin, medial palpebral ligament and lacrimal bone and inserts into the skin around the margin of the orbit. Corrugator supercilli- deep to the eyebrows and the orbicularis oculi. Contrac- tion produces vertical lines 2. Muscles associated with the nose (nasal group): Nasalis- largest and best developed of the nasal muscles with two parts Transverse: from maxilla to the nose, the aponeurosis over nose is continuous with fibers from other side. Compresses nasal apertures Alar part: maxilla over lateral incisor tooth to the alar cartilage of nose. Opens nasal aperatures Procerus- arises from the nasal bone and produces wrinkles over the bridge of the nose 3. Muscles associated with the mouth (oral group) Orbicularis oris- completely encircles the mouth, forming the first sphincter of the digestive system Buccinator- muscular component of the cheek Depressor anguli oris- depresses the corner of the mouth Depressor labii inferioris- depresses the lower lip Mentalis -elevates and protrudes the lower lip, the "pouting" muscle Zygomaticus major and minor- the "smile" muscles Levator labii superioris alaeque nasi- the longest named muscle in the human body, used when "snarling" D. Other muscles: Platysma- thin sheet in the superficial fascia of the neck Occipitofrontalis- moves the scalp and wrinkles the forehead ALL of the above muscles are innervated by the Facial Nerve (CNVII)

Pharynx The pharynx is vertically oriented tube of muscles that is "U" shaped in cross section. It is positioned anterior the vertebral column roughly between the C1 through T1 vertebrae, with the bottom of the "U" facing posteriorly. Inferiorly it is contiguous with the trachea and the beginning of the esophagus. The pharynx consists of the muscles, membranes, and other soft tissues that enclose and com- plete the walls of the upper throat. It is anatomically divided into three regions (Netter Plate 66)

1. Nasopharynx: posterior to the nasal cavity; from the base of the skull superiorly to the distal uvula inferiorly 2. Oropharynx: posterior to the oral cavity; from the distal uvula to the apex of the epiglottis 3. Laryngopharynx: posterior to the larynx; from the tip of the epiglottis to the arytenoid cartilage

The brain itself is usually described as having 5 subdivisions. These are (from caudal to rostral) the myelencephalon (the medulla oblongata), the metenceph- alon (pons/cerebellum), the mesencephalon (midbrain), the diencephalon, and the telencephalon. The "brainstem" is a term that includes the mesencephalon, metencephalon and myelencephalon.

1. The Myelencephalon (Medulla Oblongata, or Medulla for short) This is the most caudal part of the brainstem. It is continuous with the spinal cord, and maintains a similar caliber. The medulla has two longitudinal ridges on its ventral aspect - these are the pyramids. The pyramids are axon tracts that pro- gress from the cerebral cortex to the spinal cord. The medulla can be divided into a rostral portion, and a caudal portion based on the presence of a bulge called the olive. This bulge occurs on both sides in the rostral medulla and is present lateral to the pyramid. The CSF-filled space in the caudal medulla is a continuation of the central canal of the spinal cord. As one moves rostrally in the medulla, the central canal ceases to be central and moves dorsally - at rostral medullary level, the central canal opens to the fourth ventricle.

Part of the challenge of understanding larynx anatomy is that its cartilages and muscles have very similar names. However, by knowing the names of the principal cartilages, naming the musculature becomes easy. The larynx possesses eight named elements of its skeleton:

1. The hyoid bone: A U-shaped bone that acts like a clothes hanger for the larynx. This bone is suspended from the styloid processes of the skull by the paired stylohyoid ligaments. The hyoid bone also serves as the defining line between the suprahyoid muscles that insert on it and the infrahyoid muscles that arise from it. 3 Unpaired Cartilages 2. Thyroid cartilage: This is the largest and most superficial of the laryngeal cartilages. It is shaped like an H-shaped shield and forms the "Adams Ap- ple." In males, this cartilage tends to be more prominent than in females. It articulates with the cricoid cartilage by means of two hinge joints. The vocal ligament inserts on its inner anteromedian angle. 3. Cricoid cartilage: This cartilage is described as having the shape of a signet ring, with the "gem" pointing posteriorly. This posterior lamina serves as the platform on which the arytenoid cartilages articulate with a sliding joint. In- feriorly, the cricoid cartilage attaches to the first ring of the trachea. The thyroid and cricoid cartilages are the two principal structures forming the body of the larynx. 4. Epiglottic cartilage: Literally Epi = over, above, Glottis = opening of the larynx. Guards the opening of the trachea. 4 Pairs Cartilages 5 Arytenoid cartilages: These paired, L-shaped or three-sided pyramidal car- tilages sit atop the cricoid cartilages, can rotate, slide forward or laterally ac- cording to the muscle that acts on them. They act as the posterior anchor point for the vocal ligaments. 6. Corniculate cartilage: (L. resembling small horns) paired small horn-shaped bits that sit on top of the arytenoids. 7. Cuneiform cartilage: Small pieces of cartilage that are embedded in the ari- epiglottic folds and act like "sail stays" to stiffen it and resist collapsing in- ward. 8. Cartilagio triticea: (L: rice-grain) Paired, itty-bitty, teenie-tiny, bits of car- tilage embedded in the thyrohyoid ligament.

The membranes and ligaments of the larynx complete the "chamber" and help make it an instrument of vocalization. Like the muscles, these are named chiefly for their cartilaginous attachments.

1. Thyrohyoid membrane 2. Thyrohyoid ligament: thickened median portion of thyrohyoid membrane 3. Cricothyroid membrane (conus elasticus) 4. Vocal ligament 5. Quadrangular membrane: lies within the aryepiglottic folds. The vocal folds connect the posterior aspect of the thyroid cartilage to the poste- rior aspect of the ring of the cricoid cartilage. The resting position of these folds is partway between open and closed, neither fully open to allow breathing nor closed to allow vocalization. The vocal ligament (f) is a fibroelastic thickening within the substance of the true vocal fold. The combined movements of the cartilages and the movements and adjustments of the vocal fold by the musculature permit an extraordinary range of sounds to be created by the membrane.

The middle ear (tympanic) cavity

1. Two holes departing middle ear cavity and bony labyrinth: Fenestra ovals above promontory (knock), Fenestra rotundam below promontory. 2.Pharyngotympanic/auditory tube connects the middle ear to the anterior/inferior nasopharynx. Posterior tube in bone, anterior hemicartilage part can reach the tube (continuous at tubal isthmus). 3. Aditus connects middle ear to posterior mastoid air cells.

Motor aspects of the visceral nervous system in the head and neck General visceral efferent innervation, sympathetic and parasympathetic, is directed to structures at all body segmental levels, but certain basic principles ap- ply to autonomic motor pathways, regardless of their destination. RULE: When considering any visceral motor pathway, it is necessary to: (1) locate the general position of the preganglionic neuron in the CNS. (2) trace the course of the preganglionic axon to its synapse with the ganglion cell. (3) trace the path taken by the postganglionic axon to its peripheral target

1. Two neurons are required to convey a motor signal from the CNS to target cells in the periphery. 2. Ganglion cells send their postganglionic axons to cardiac muscle, smooth muscle, or glands. They receive input from axons of preganglionic neurons located in the CNS. 3. Preganglionic outflow is from a discontinuous cell column in the CNS. -Thoracolumbar neurons (T1-L2 cord segments) provide outflow to sympathetic ganglion cells. -Craniosacral neurons (certain brainstem nuclei and S2-S4 cord segments) provide outflow to parasympathetic ganglion cells.

The human embryo has four pairs of pharyngeal pouches (the fifth does not de- velop). All the pouches are derived from endodermal epithelial lining and give rise to important structures and organs of the body. The derivatives of the pouches (and clefts) do not necessarily give rise to the entire structure or organ, instead most often giving rise to the epithelial components of the organ. Typically, the mesoderm and neural crest cells of the arches form the other tissues of the organ.

1st - The first pouch forms an elongated diverticulum called the Tubotym- panic recess, which is in contact with the epithelial lining of the first pharyngeal cleft. The distal portion of the tubotympanic recess gives rise to the epithelial lining of the middle ear cavity and the proximal portion gives rise to the epithelial lining of the auditory tube. 2nd - The epithelial lining of the second pouch forms buds that extend into the mesoderm layer. The endoderm layer of pouch two forms the epithelial covering of the palatine tonsil. The connective tissue framework of the organ is formed by mesoderm and neural crest. The lymphocytes invade the organ after the frame work has been established. 3rd -The third pouch develops a dorsal wing and a ventral wing. The adult derivatives are as follows: Dorsal part: Inferior parathyroid gland Ventral part: Thymus Both glands disassociate from the pharyngeal wall and migrate caudal and medial. The thymus fuses with the thymus of the opposite side. The inferior parathyroid gland takes a position on the posterior side of the thyroid gland. 4th - The fourth pharyngeal pouch also develops a dorsal and a ventral wing. The adult derivatives are as follows: Dorsal part - Superior parathyroid gland Ventral part - Ultimobranchial body The superior parathyroid gland loses the connection with the pharyngeal wall and attaches to the superior aspect of the migrating thyroid gland. The ultimobranchial body is also incorporated into the thyroid gland as the parafollicular or C-cells of the thyroid gland. The ultimobranchial body is involved in regulation of blood calcium lev- els.

Lymphatics of the Neck Region

A pericervical collar of lymph nodes is formed at the junction of the head and neck. These nodes are drained by lymphatic vessels that enter the superficial cervical lymph nodes, which are located along the course of the external jugular vein. These superficial nodes, then drain to the deep cervical lymph nodes, a collection of lymph nodes that form a chain which courses along the spinal accessory nerve and internal jugular vein. Alternately, the pericervical nodes may drain directly to the deep cervical lymph nodes The deep cervical nodes are divided in to upper and lower groups and two large nodes are singled out in the deep cervical chain: the jugulodigastric (from upper group) and the jugulo-omohyoid nodes (from lower group). Efferent lymphatic vessels from the deep cervical nodes join to form the jug- ular lymphatic trunks, which usually join the thoracic duct on the left side and enter the junction of the internal jugular and subclavian veins (right ve- nous angle) directly or via a short right lymphatic duct on the right.

Muscles of Neck

A. Platysma m. muscle of facial expression inserts into skin B. Sternocleidomastoid and trapezius muscles D. Suprahyoid muscles: elevate hyoid mylohyoid m.: floor of oral cavity geniohyoid m.: floor of oral cavity stylohyoid m.: styloid process to hyoid digastric m. (anterior and posterior belly): mandible and mastoid process of temporal bone to hyoid C. Infrahyoid (strap) muscles. Act on larynx and pharynx, important in swallowing, etc. omohyoid m. (superior & inferior bellies): scapula to clavicle to hyoid sternohyoid m.: manubrium to hyoid sternothyroid m.: manubrium to thyroid cartilage thyrohyoid m.: thyroid cartilage to hyoid

Innervation of tongue Due to the different embryological origins of the anterior 2/3 and posterior 1/3 of the tongue, the innervation of the tongue is varied. Innervation to the tongue re- quires multiple types of innervation (movement, general sense and special sense)

Anterior 2/3 GSA: Lingual n (V3) Special sense (taste): Chorda tympani (VII) Posterior 1/3 GSA and special sense (taste): lingual branch of glossopharyngeal (IX) and internal laryngeal nerve, a branch of vagus (X) Musculature All tongue muscles are innervated by hypoglossal (XII) except palatoglossus, which is actually a palatine muscle supplied by the pharyngeal plexus (IX, X and XI)

Branches of Maxillary Artery AM I A, D P M B, P I S D P P

Anterior Tympanic A (Ptyerotympanic fissure w/Chorda Tympani), Middle Meningeal A (F.S), Inferior Alveolar A ( Manddib For) Mental br), Ascending Meningeal A (F.O.), Deep Temporal A, Pterygoid A, Masseteric A, Buccal A, Posterior Superior Alveolar A (ITF Post Mid Ant Alv For), Infraorbital A, Sphenopalatine A (Lat Nasal, Septal Nasal), Descending Palatine A (Gr/Les Pal For), Pharyngeal A, Ant. Pterygoid A w/ICA

Innervation of Nasal Cavities

Anterosuperior part of the mucosa (V1): Anterior & posterior ethmoidal nerves (branches of nasociliary n), Posteroinferior part of mucosa (V2): Nasopalatine n (br maxillary n) to septum Posterior superior LATERAL NASAL br of greater palatine and inferior lateral nasal nerves (br greater palatine) to lateral wall, External nose: Infratrochlear and external nasal nerves (V1) and infraorbital nerves (V2).

Vasculature of the tongue

Arterial supply comes from the lingual artery, a branch of the external carotid artery., The dorsal lingual arteries supply the root and the deep lingual arteries supply the anterior part of the tongue., The dorsal and deep lingual veins effectively follow the course of their associated arteries, and drain into the internal jugular vein. The lymph from the central and posterior parts of the Anterior 2/3 of the tongue: Tip of tongue drains to the submental group Sides of tongue drain mainly into the submandibular group Central part of tongue drains mainly into the juguloomohyoid group Posterior 1/3 of the tongue: Drains mainly into the jugulodigastric groups

Telencephalon

As in the diencephalon, the entire telencephalon is formed from alar plate neuro- blasts. The mantle zone at the base of each lateral ventricle thickens to form large bilateral gray masses called the basal ganglia. Additional neuroblasts in the mantle zone migrate through the marginal zone (much like in the cerebellum) to form layers of cerebral cortex (gray matter) on the outer surface and white matter be- neath. Eventually, the telencephalon overgrows the lateral aspect of the dienceph- alon and the two embryonic subdivisions fuse. Fiber projections traveling to and from the cortex divide the basal ganglia. Ultimately, continued expansion of the telencephalon results in the progressive appearance of sulci (clefts) and gyri (ridges) on the external surface of the cerebral hemispheres. All major sulci and gyri are present by the seventh month of development whereas many minor sulci and gyri appear after birth.

Carotid system carotid sheath, which also contains the internal jugular vein, vagus nerve, and lym- phatics

At about the level of the larynx the artery divides into the internal and external carotid arteries. This carotid bifurcation is a critical location where blood pres- sure and respiration are monitored. The bifurcation is dilated to form the carotid sinus whose walls contain visceral baroreceptors sensitive to arterial blood pres sure. The carotid body, located close to the bifurcation, monitors blood pO2, pCO2, and pH via a variety of visceral chemoreceptors.

Lateral Aspect of the Skull

Bregma (connection of sutures), Vertex (high point of skull), Zygomatic arch, Temporal process of the zygomatic bone (spine), Zygomatic process of the temporal bone (front part), Mastoid process (pointy part next to styloid), Styloid process (dagger in back), External auditory meatus (most obvious hole), Mandible -Condylar process (part of head), Head (top part inside skull being mandibular notch), Neck (below head) Ramus (master cheek part), Body (chin part), Angle (angle below teeth), Coronoid process (point part under zygomatic), Mandibular notch (notch between condylar head process and coronoid process), Temporomandibular joint (articular disc between condylar process and temporal part of zig), Infratemporal crest of the sphenoid (crest of sphenoid and temporal before it becomes the lateral pterygoid plate), Tuberosity of the maxilla (end of maxilla teeth right before pterygoid plate), Lateral pterygoid plate (pterygoid process of sphenoid bone), Pterygomaxillary fissure - entrance to the pterygopalatine fossa in the temporal bone

Course The Vestibulocochlear Nerve, Cranial Nerve VIII carries special afferent SA fibers from the sensory hair cells of the inner ear

Cerebellopontine angle ( med6,7,8), 8 crosses posterior cranial fossa through internal auditory meatus into petrous part of temporal bone, right below facial SVE and Nervus Intermedium. Superior vestibular + Inferior cochlear divisions with cell bodies in temporal lobe. Vestibular ganglion of Scarpa along course of inferior cochlear. Cochlear ganglion within modiolis bone core of cochlear serial. Peripheral axons pass small pores in bony labyrinth to reach membranous labyrinth. SA fibers for positional sense from vestibular labyrinth and auditory sense from cochlea.

Cerebrospinal fluid

Cerebrospinal fluid (CSF) is a relatively clear, slightly alkaline fluid surrounding the brain and spinal cord in the subarachnoid space and supporting the structure from within the brain through a network of cerebral ventricles. CSF is derived from blood, but it not an ultrafiltrate thereof; it is a secretion since its production involves active transport and requires energy. The CSF contains an ionic compositions similar to that in blood plasma although not in identical concentration- for instance, in CSF the concentration of Na+ is higher and K+ and Ca2+ are smaller. The CSF also contains a lower concentration of glucose and considerably less protein. An adult has only about 125 ml of CSF at one time yet CSF is produced at a rate of 600-700 ml a day, indicating that there is considerable turnover of the CSF. The CSF fills spaces within the brain called the cerebral ventricles. These spaces are lined by specialized cells called ependymal cells. These ventricles are four in number. There are two lateral ventricles, one under each cerebral hemisphere. These ventricles in turn both drain into a third ventricle below and between the hemispheres. The third ventricle drains into a fourth ventricle under the cerebel- lum, and from here the CSF drains into the subarachnoid space to flow around the brain. From the subarachnoid space, the CSF passes into the venous system of the dural sinuses. The arachnoid granulations are structures that operate as one-way valves to allow CSF in the subarachnoid space to enter the dural venous sinuses. The choroid plexus is a highly vascularized organ whose parts are located within the lateral, third and fourth ventricles of the brain. The cells of this organ generate the CSF. It has a core of connective tissue derived from a fold of pia mater, and it is covered on its outer surface by a specialized epithelium of choroidal cells. Its surface is greatly increased by many fine branches that in turn are covered by tiny villi. Each villus contains one large capillary. These capillaries have fenestrations by which the plasma of blood can leak into the extracellular space. Once in that space, the blood plasma is prevented from accessing the ventricle directly because the epithelium of the choroid plexus is connected with tight junctions. The cells thus take up the fluid, modify it, and then secrete it into the ventricle as CSF. Thus, the specialized epithelium of the choroid plexus is responsible for the Blood-CSF Barrier. The buoyant effect of CSF serves to support and cushion the central nervous sys- tem against trauma. Whether CSF serves a nutritive function is in question. Due to the free exchange with the fluid that surrounds the neurons of the brain (extra- cellular or interstitial fluid), the CSF, as part of this fluid compartment, contributes to the intercellular fluid of the brain, carries nutrients, and serves to remove waste products of neuronal metabolism.

Internal carotid artery The internal carotid artery supplies nothing in the external head and neck. Rather, it continues superiorly within the carotid sheath until it reaches the base of the skull. There it travels through a canal in the bone to emerge into the middle cranial fossa. The branches of the internal carotid artery supply the eye, orbit, forehead, pituitary gland, and much of the cerebrum.

Cervical part extends superiorly through the neck from the carotid bifurcation to the base of the skull. o Branches: None Petrous part curves anteromedially through the carotid canal of the petrous part of the temporal bone. o Two small caroticotympanic arteries to tympanic (middle ear) cavity. o Pterygoid artery travels forward with the nerve of the pterygoid canal to meet the pterygoid branch of the maxillary artery Cavernous part travels through the cavernous dural venous sinus. When the artery emerges from its bony canal, its course takes it through the sinus. It takes a sharply curved course: anterior toward the superior or- bital fissure, bends sharply back upon itself, then turns vertically to pierce the roof of the sinus and emerge into the subdural space. o Branches: small branches to surrounding structures (dura, pituitary gland) Cerebral part is the very short segment between the roof of the cavernous sinus and the terminal bifurcation of the artery. o Anterior cerebral artery - supplies medial cerebral hemi- spheres** o Middle cerebral artery - supplies temporal lobe, anterolateral frontal lobe, and parietal lobe** **Clinical correlation: Note that the territories of these vessels are much more complex than indicated here. The clinical impli- cations of these territories are profound, as occlusion of one of these vessels (i.e., a stroke) will affect the functions moderated by these territories of the brain. Posterior communicating artery - joins the middle cereal artery of the internal carotid to the posterior cerebral branch of the basilar artery/vertebral to form a link in the circle of Willis Ophthalmic artery - variable branching pattern. Many of its more important branches travel with branches of the ophthalmic division of the Trigeminal nerve, which you will learn in detail. - CentralarteryoftheretinapassesintotheOpticnerve with which it enters the back of the eye to reach the retina. Clinical correlation: The central artery of the retina is important in clinical examinations because it is the only arterial vessel the phy- sician can see directly (via the ophthalmo- scope). This allows assessment of the gen- eral state of the arterial system. Clinical correlation: This is a true end artery: its occlusion (obstruction) results in instant and complete blindness in the affected eye. -Lacrimalarteryaccompaniesthelacrimalnervetothe lacrimal gland Lacrimal-> Palpebral, Recurrent meningeal, Zygomatic Also supplies palpebral branches to t- per and lower eyelids, sends a recurrent meningeal branch back through the superior orbital fissure to supply the dura, and a zygo- matic branch to accompany branches of the zygomatic nerve -Ciliary arteries accompany the short and long ciliary nerves to the back of the eye. -Muscularbranchestotheextraocularmuscles. -Supraorbital artery travels with the supraorbital nerve onto the forehead. -Anterior and posterior ethmoidal arteries supply the paranasal sinuses and the nasal cavity. -Palpebral branches supply the upper and lower eyelids -Supratrochlear artery runs with the supratrochlear branch of the frontal nerve to the bridge of the nose, glabella, and scalp of the central forehead. -Dorsalnasalarteryistheterminalcontinuationofthe ophthalmic artery. It passes below the trochlea with the infratrochlear branch of the nasociliary nerve, and is distributed to the root and side of the nose. This artery anastomoses with the angular branch of the facial artery, thus forming an important link between internal and external carotid systems.

Eyelids

Conjunctival sac -> Palpebral issue -> Palpebral margins -> Medial/Lateral Canthi -> Upper eyelid: Tarsal plate dense CT w/ Superior tarsal muscle (fear eye opening, Horners in cranial sum= pseudoptosis) connected to Levator Palpebrae Superioris(does upward looking, paralysis III ptosis and lateral deviation) Superior and Inferior tarsal plates merge to form medial and lateral palpebral ligament Subcutaneous tissue of eyelid loose for puffy eyelid Palpebral eyelid CN VII: Effector limb of blink reflex (sense via V1 nasociliary) Bells Palsy of VII = Dry eyeget Tarsal glands lubricate and make get sty Effector blink: VII Feeler blink: V1/V2

ANOMALIES AND CLINICAL ASPECTS

Consider the importance of the neural crest cells as we discuss some of these syn- dromes. 1. Pharyngeal/branchial cysts 2. First arch syndrome 3. DiGeorge syndrome. 4. Ectopic thymus, thyroid and parathyroid 5. Thyroglossal cyst

C. PHARYNGEAL CLEFTS: Around the 5th week of the embryonic development, four pharyngeal clefts are present and only one contributes to an adult structure. The dorsal part of the first cleft develops into the lining of the external auditory meatus and tympanic membrane. Due to over growth of the second arch externally it covers the second, third and fourth clefts and merges with the epicardial ridge in the lower part of the neck. This forms a temporary pocket known as the cervical sinus, which normally disappears.

D. PHARYNGEAL MEMBRANES Pharyngeal membranes are found where the epithelia of the cleft and pouch meet each other. The only definitive structure is the tympanic membrane arising from the first pharyngeal membrane.

Spinal Cord

Differentiation of the Wall Initially, the neural tube is comprised of rapidly dividing neural stem cells called the germinal neuroepithelium that are one layer thick. This neuroepithelium is classified as a pseudo stratified epithelium. Following mitosis, the newly born primitive nerve cells, called neuroblasts, migrate to form a second layer that surrounds the germinal neuroepithelium named the mantle (or intermediate) zone. With the establishment of the mantle layer, the germinal epithelium is renamed the ventricular zone (which later be- comes the ependymal layer that lines the fluid-filled cavities of the adult CNS). As cell division continues, the mantle zone becomes progressively thicker and the neuroblasts undergo differentiation into neurons and glia (supportive cells). As the neurons establish connections with one another they send axonal processes away from the lumen. These processes form the outermost layer of the developing neural tube called the marginal zone. Glia soon form the myelin sheaths that sur- round axons in the marginal zone giving the marginal zone a white appearance; this is the white matter of the spinal cord (Fig. 2). The mantle zone, which pri- marily contains cell bodies, is the gray matter of the spinal cord. In the adult spinal cord, the gray matter takes on the shape of a butterfly. Segmental Organization Intraembryonic paraxial mesoderm proliferates to form thickened columns on ei- ther side of the developing neural tube. The columns eventually break up into paired cuboidal masses termed somites. Each somite forms its own sclerotome (skeleton and cartilage), myotome (skeletal muscle) and dermatome (connective tissue dermis of the skin). Along the length of spinal cord, the spinal nerves carry somatic sensory input from, and somatic motor output to, the mesodermal somites in a segmentally organized fashion. Basic Circuitry A population of neural crest cells migrates to either side of the developing neural tube to form the dorsal root ganglia (DRG). During development, neuroblasts with cell bodies in the DRG form two processes. Peripheral processes originate from sensory endings in somatic targets (e.g. skin, joints, and muscles) or in visceral targets (e.g. organs, glands, blood vessels) and are categorized as somatic sensory and visceral sensory, respectively. Peripheral processes travel towards the spinal cord via spinal nerves. Central processes enter the spinal cord as the dorsal roots of the spinal cord. From there, neuroblasts either directly or indirectly (via synap- tic communication with additional neuroblast(s): 1) establish intraspinal reflex circuits, or; 2) ascend through the marginal layer to communicate with higher brain centers. Ascending axons form the ascending white matter tracts. Descending neurons from the cortex and brainstem form the descending white matter tracts. Neurons of the descending tracts synapse directly or indirectly on motor neurons in the ventral horn to modulate motor output. Motor neurons in the ventral horn send efferent axonal projections out through the ventral roots of the spinal cord. Axons of motor neurons then travel in spinal nerves to provide motor innervation to skeletal muscles. This type of motor output is classified as somatic motor. Autonomic visceral motor fibers also exit the ventral horn of the spinal cord.

Dorsoventral Patterning

Dorsoventral patterning along the length of the neural tube is initially established by opposing concentration gradients of signaling molecules expressed by struc- tures surrounding the neural tube (e.g. notochord, ectoderm). Later, regions of specialized glia in both the dorsal and ventral midline of the neural tube itself also contribute to these concentration gradients. During development, a longitudinal groove called the sulcus limitans forms in the lateral walls of the fluid-filled cavities of both the spinal cord and the brain- stem (discussed below). These 'limiting sulci' demarcate the functional division between the dorsal and ventral portions of the neural tube (Fig. 2). Neuroblasts residing in the dorsal neural tube are involved in sensory input and processing and form the alar plate. Alar plate nuclei are categorized as somatic sensory or visceral sensory. Neuroblasts residing in the ventral neural tube are concerned with coordination of motor output and form the basal plate. Basal plate nuclei are categorized as somatic motor or visceral motor. Visceral sensory and visceral motor nuclei are located adjacent to the midline axis, directly dorsal and ventral to the sulcus limitans respectively. Somatic sensory and somatic motor nuclei are located toward the lateral edges of the gray matter. In the gray matter of the de- veloped spinal cord, the alar plates become the dorsal (or posterior) horns and the basal plates become the lateral horns (in thoracic segments) and ventral (or ante- rior) horns.

Induction of the Neural Plate Neural tube defects (NTDs) are a group of congenital anomalies that result from defective closure of the neural tube. NTDs occur in ~1 out of every 1,000 live births in the United States although there is geographical variation in incidence. While a number of teratogens (factors that cause embryonic malformations) are known to cause NTDs, a combination of factors likely contributes to the develop- mental origin of each NTD. Ultrasound and maternal blood and amniotic fluid tests allow for prenatal diagnosis of NTDs. Folic acid taken before conception and throughout pregnancy significantly reduces the incidence of NTDs by ~70%. NTDs may affect both neural tissue and non-neural tissue overlying the spinal cord (e.g. meninges, vertebral arches, skin, muscles). A common NTD is spina bifida, an anomaly involving the nonfusion of the vertebral arches in the lum- bosacral region. There are two types of spina bifida: spina bifida occulta and spina bifida cystica. In spina bifida occulta the vertebral arches fail to grow nor- mally and fuse at the midline. This type of spina bifida typically produces no clin- ical symptoms and is usually marked by a tuft of hair overlying the affected re- gion. In spina bifida cystica, neural tissue and/or the fluid-filled meninges may protrude through the vertebral arch defect. Anencephaly is a cephalic neural tube defect in which the skull does not properly form and the exposed brain tissue be- comes necrotic. A rudimentary brainstem may remain intact; however, the cere- brum is largely absent.

During the third week of development, gastrulation transforms the embryo from a bilaminar to a trilaminar disc. The trilaminar disc is comprised of three germ layers named the ectoderm, the endoderm and the mesoderm, each of which gives rise to specific tissues and organs in the developing embryo. During gastru- lation, a population of mesenchymal cells migrates through the primitive pit to- wards the prechordal plate (the future oropharyngeal membrane) and elongate as a rigid cord along the midline axis called the notochord. Via secretion of neural- inducing factors, the notochord and the paraxial mesoderm (the mesoderm on either side of the notochord) induce the overlying ectoderm to thicken and differ- entiate as the neural plate. The ectoderm of the neural plate is called neuroecto- derm and gives rise to the entire central nervous system (CNS; brain and spinal cord). The formation of the neural plate marks the beginning of neurulation, a process by which the neural plate forms the neural tube (Fig. 1). Following induction, the lateral edges of the neural plate further thicken as neural folds. A specialized population of neuroectodermal cells inhabit the peak of each neural fold named neural crest cells. As the neural folds elevate, the neural plate invaginates at the midline to form the neural groove. Eventually, the neural folds converge at the dorsal midline to form the neural tube. The neural tube separates from the overly- ing surface ectoderm, which will form the epidermis. During this time, the neural crest cells begin to migrate along either side of the neural tube. Neural crest cells migrate to a variety of locations and differentiate into multiple different cell types. Neurulation is complete by the end of the fourth week of development with the closing of two openings on either end of the tube called the rostral and the caudal neuropore. The lumen of the neural tube becomes the cerebrospi- nal fluid-filled cavities of the brain (ventricular system) and spinal cord (central canal).

- Note that cranial nerves attached to the brainstem close to the midline are motor only. (III, IV, VI, XII) -Nerves arising more lateral are either mixed (V, VII, IX, X) or sensory (VIII) - Motor is medial! In the lab take a look at the pontomedullary junction. Is the order of the nerves VI, VII, VIII or is it VIII, VII, VI? ganglia are peripheral and nuclei are central. Ganglia with synapses are GVE motor parasympathetic. Ganglia without synapses are sensory.

Each cranial nerve is associated with its own nucleus, which can be thought of as the site of origin of the nerve. There are motor nuclei (somatic and branchio- motor) and sensory nuclei. GSE Nucleus Oculomotor: Upper Midbrain- Oculomotor III- eye move Trochlear: Lower Midbrain - Trochlear IV -eye move Abducens: Pons - Abducens VI - eye move Hypoglossal - Medulla - Hypoglossal XII - tongue move SVE Nucleus Trigeminal - Pons - Manipular V3 - 1st Branch Mastication Facial - Pons - Facial VII - 2nd Facial Exp Nuc. Ambiguus- Medulla - Glossopharyngeal IX, Vagus X recurrent laryngeal 3rd/4th/6th speech/swallowing Spinal Acceseory Nucleus - Upper Spinal Cord - Sinal Accesory XI - Sternocleidomastoid and trapezius

Muscles of mastication The muscles of mastication are the primary muscles that move the jaw. All of these muscles are derived from pharyngeal Arch 1, so therefore they are all innervated by CN V SVE. Note that none of the listed actions include opening the jaw. Generally, depression of the mandible occurs as a result of gravity. In cases in which the jaw is opened quickly or against resistance, the suprahyoid and infrahyoid muscles can contribute to this movement.

Elevate mandible: Temporals: Temporal fossa -> Ramus of Mandible + Retractor Masseter: Zygomatic Arch -> Ramus of mandible Medial pterygoid: Med. Lateral pterygoal plate -> Ramus of mandible (+ Protrusion/grind) Protract, Swing, Depress chiln, chew: Lateral Pterygoid: Sphenoid + Lat Lat Pterygoid Plate -> Joint of TMJ + Ant condyloid process of mandible

Course The Vagus Nerve, Cranial Nerve X

Emerging from the me- dulla as a series of fine rootlets, the vagus nerve crosses the posterior cranial fossa to exit the skull through the central compartment of the jugular foramen, between cranial nerves IX and XI. In the jugular fossa, the nerve bears its two ganglia. The smaller, superior (jugular) ganglion consists of somatic sensory cell bodies. The much larger, inferior (nodose) ganglion extends well below the base of the skull. It contains general sensory and general visceral sensory neurons and it communicates with the first two cervical spinal nerves and with the superior cervical sympathetic ganglion. From the nodose ganglion, the vagus nerve de- scends through the neck in the carotid sheath, lodged between the internal jugular vein and the internal and common carotid arteries. It enters the thorax and passes downward behind the root of the lung to reach the esophagus. Right and left vagi intermingle in the esophageal plexus, separate imperfectly into posterior and an- terior vagal trunks, and enter the abdomen through the esophageal hiatus.

Early development of the brain - a brief anticipation of Dr. Haydar's lecture on "Neuroembryology"

Even before the rostral neuropore closes late in the fourth week of devel- opment, the cranial region of the neural tube has expanded into three primitive brain vesicles, the: telencephalic vesicles, from the midline -diencephalon. -forebrain, or prosencephalon -midbrain, or mesencephalon, and -hindbrain, or rhombencephalon (so-called for its shape). Each of the five vesicles develops into particular brain regions: telencephalon: cerebral hemisphere, olfactory bulb and tract, and lateral ventricle. -diencephalon: thalamus, hypothalamus, and third ventricle. In addition, the diencephalon gives rise to a number of important outgrowths: -from its roof, the pineal body. -from its floor, the neural (posterior) pituitary. -from its lateral walls, the paired optic diverticula (optic nerves and retinae). -mesencephalon: midbrain and cerebral aqueduct. -rhombencephalon: cerebellum, pons, medulla oblongata, and fourth ventricle.

-The trilaminar tympanic membrane (ear drum) separates the outer and middle ears (oval window). A second round window isolates inner ear.

Ext Aud- Stratified squamous-ConectiveTissue-MucousMembrane - Tympanic Cavity Malleus hammer in epitympanic recess - Incus - Stapes - Footplate of oval window by circumferential annular ligament Air conduction: ossicles, sound waves, mechanical waves, round window bulging inward into bony labyrinth: stimulate auditory hair cells Bone: to perilymph through skull Protect sensory ear: Tensor tympanic: lessens malleus Stapedius: lesses stapes

Pterygoid venous plexus

Extensive venous plexus that is difficult to appreciate in the cadaver. This plexus drains most of the territory that is supplied by the maxillary artery. Importantly, it drains both anteriorly to the facial vein (via the deep facial vein) and superiorly to the cavernous sinus (via emissary veins). Therefore, it is a significant potential connection between the external face and the intracranial dural venous sinuses.

Blood Supply of the Face and Scalp

External carotid branches (Netter plates 33, 35) a. Facial artery provides the major supply to the face. It is a branch off the external carotid artery (ECA). The facial artery passes through the neck and crosses over the mandi- ble to enter the face. It passes along the side of the nose and terminates as the angular artery at the medial corner of the eye. The facial artery gives rise to superior and inferior labial arteries that supply the upper and lower lip and a portion of the nasal septum. The lateral nasal artery is a branch of the facial artery that supplies the skin of the nose. Once the lateral nasal branch is given off, the facial artery continues medially to terminate as the angular artery. b. The superficial temporal artery is a terminal branch of ECA. It supplies the temporal region and scalp and gives off the transverse facial artery deep to the parotid gland, which supplies the cheek. c. The maxillary artery is the larger of the two terminal branches of the ECA. The maxillary artery has many branches, three of which contribute to the arterial supply of the face. The infraorbital artery enters the face through the infraorbital foramen and supplies the upper cheek; the buccal artery enters the face to supply the cheek, and the mental artery enters the face through the mental foramen to supply the chin. Internal carotid branches From the ophthalmic artery: supratrochlear artery- from the supratrochlear notch supraorbital artery- from the supra-orbital foramen The above supply the forehead and anterior scalp dorsal nasal artery zygomaticofacial artery zygomaticotemporal artery

Parotid Glands The bilateral parotid glands are the largest of the salivary glands. The parotid gland is found anterior to the lower half of the ear extending to the lower border of the mandible. The parotid gland is enclosed in a tough capsule called the parotid sheath derived from the investing layer of deep cervical fascia. The parotid duct exits the glandular tissue midway between the zygomatic arch and the corner of the mouth running in a transverse direction. After crossing the medial border of the masseter muscle, the duct turns to enter the buccal fat pad and pierces the buccinators muscle to enter the oral cavity near the second upper molar tooth. The parotid gland has several structures that enter the gland or pass deep to the gland:

Facial nerve- the facial nerve exits the skull, divides into the upper and lower trunks in the parotid gland. The five terminal branches of the facial nerve emerge from the upper, anterior and lower border of the parotid gland. ** The facial nerve does NOT innervate the parotid gland. TZBMC External carotid artery- the ECA enters into the parotid gland where it divides into the terminal branches of the maxillary artery and the super- ficial temporal artery. The superficial temporal artery gives off the trans- verse facial artery in the parotid gland. The transverse facial artery gives off small branches that supply the parotid gland and duct. Retromandibular vein- formed in the parotid gland by the union of the superficial temporal and the maxillary veins. Sensory innervation to the parotid sheath and the overlying skin: provided by the auriculotemporal nerve (a branch of the mandibular nerve- V3) and the great auricular nerve (a branch of the cervical plexus, fibers from C2 and C3) Parasympathetic innervation - provides secretomotor fibers to the gland. Preganglionic secretory fibers arise from the glossopharyngeal nerve (CN IX) to the otic ganglia. The postsynaptic parasympathetic fibers are carried from the otic ganglia to the parotid gland by the auriculotemporal nerve. Sympathetic fibers reduce secretion of the gland and are derived from the cervical ganglia

The Auricular Branch of the Vagus and GSA Fibers in VII, IX, and X.

Facial, Glosso, Vagus GSA exteroceptive to small patch behind ear, auricle, ext aud meatus, outer tympanic membrane. Somatic sensory fibers in the Facial and Glossopharyngeal nerves are added to the auricular branch of the Vagus, with which they emerge through the **tympanomastoid fissure**immediately behind the external auditory meatus.

Extraocular musculature SO is innervated by tro i SOT for LARSchlear

Four rectus muscles diverge from the common tendinous ring to in- sert into the sclera of the eyeball. Superior rectus (CN III) primarily elevates the eyeball. Inferior rectus (CN III) primarily depresses the eyeball. Lateral rectus (CN VI) abducts the eye. Medial rectus (CN III) adducts the eye. The two oblique muscles have different origins and courses. Superior oblique muscle (CN IV) This muscle originates from the sphenoid bone superome- dial to the common tendinous ring, posteriorly in the apex of the orbit. It has a unique course: the muscle belly passes anteriorly along the medial wall of the orbit, then through a fibrous trochlea (Latin: pulley) that is attached to the frontal bone at the anterosuperior aspect of the medial orbital margin. The tendon then passes posteriorly to insert onto the posterol- ateral quadrant of the superior surface of the eyeball. Because the tendon inserts posterior to the midline of the eyeball, this muscle draws the posterior portion of the eye- ball upward, therefore depressing the eye. It also aids with abduction. Inferior oblique muscle (CN III) This muscle originates from the anteroinferior aspect of the medial orbital margin. It passes backward to insert onto the posterolateral quadrant of the inferior surface of the eyeball. This muscle draws the posterior portion of the eyeball downward, therefore abducting and elevating the eyeball. Finally, the levator palpebrae superioris muscle (CN III) is considered an ex- traocular muscle although it does not move the eyeball itself. Instead it moves the eyelid in coordination with upward movements of the eye. Because of its close association with the movement of the eye and the fact that it is innervated by CN III, it is grouped with these mus- cles. The levator palpebrae superioris originates superiorly to the com- mon tendinous ring, inserts into the tarsal plate of the superior eye- lid, and draws the eyelid upward when the eyeball is elevated.

Mandibular nerve (V3) (GSA/SVE) The mandibular nerve is the third major branch of the trigeminal nerve. It arises from the trigeminal ganglion, which lies in the middle cranial fossa immediately superior to the infratemporal fossa. Here it receives the motor root of the trigeminal nerve and descends through the foramen ovale into the infratemporal fossa, where it gives off the following branches: Auriculotemporal nerve Inferior alveolar nerve Lingual nerve Buccal nerve

GSA Auriculotemporal nerve - general sensory from auricle and temporal region and articular sensory from TMJ. Has unique morphology in that it encircles the middle meningeal artery. o Connection with autonomics: Conveys postsynaptic parasympathetic fibers of CN IX from otic ganglion to parotid gland GSA Inferior alveolar nerve - General sensory from inferior dental arcade, vestibular gingiva, lower lip, and chin. It traverses the infratemporal fossa to join with its partner artery to then enter and continue its course within the mandible (mandibular canal). Clinical correlation: Dental anesthesia The inferior nerve block is the most common type of nerve block used for dental procedures. Administration of this nerve block involves entering the oral cavity and directing the needle through the mucosa through the mucosa overlying the ramus into the infratemporal fossa, and then bathing the inferior alveolar nerve in anesthesia. The target of this technique is the inferior alveolar nerve just before it enters the mandibular canal. Due to the proximity of the nerves in the infratemporal fossa, the lingual nerve may also be anesthetized. If this occurs, what will be numbed? GSA Lingual nerve - General sensory from anterior 2/3 of tongue, floor of mouth, and lingual gingivae o Connection with VII: Conveys taste and parasympathetic fibers of the chorda tympani nerve (br. VII) to their synapse at the submandibular ganglion in the floor of the mouth, then on to their targets (see below) Buccal nerve - General sensory from check Direct motor branches to the 4 muscles of mastication, plus nerve to mylohyoid (mylohoyid + anterior belly digastric) - These motor branches are SVE as the associated muscles are derived from a pharyngeal err

To open the jaw, the following movements occur:

Gently opened mouth: First few degrees of opening involves rotation of the heads in the fossae Widely open mouth: Head of mandible and articular disc move anteriorly on the articular surface until the head translates forward to under the articular tubercle, while mandible is simultaneously depressed. Protrusion/retrusion of mandible: Head of mandible and articular disc slide anteriorly/posteriorly on articular surface of temporal bone from the fossa onto the articular tubercle, and back. This is not accompanied by depression/elevation of the mandible. Side-to-side chewing/grinding: Head and disc protrude unilaterally while contralateral head rotates on inferior surface of articular disc

Inferior Aspect of the Skull

Hard palate (whole hard palate), Palatine process of the maxilla (forms ant 2/3 of palatine), Horizontal plate of the palatine bone (the horizontal part of palatine forms last 1/3), Mandible - inner aspect Mandibular foramen (inside mandible behind lingual), Lingula (inner pointy part of mandible), Posterior nasal apertures (choanae; singular = china back of nose), Vomer (shark bone), Pterygoid process of the sphenoid (two plates pointing out of sphenoid), Lateral pterygoid plate (yes), Medial pterygoid plate (yes), Pterygoid hamulus (crest inside pterygoid plates), Greater wing of the sphenoid (only part of spend you see), Temporal bone, Petrous part (part of temporal bone that comes in and has styloid process), Mandibular fossa (for joint), Articular tubercle (bump behind the mandibular fossa), External auditory meatus (big circle on side),Styloid process (point), Mastoid process (edges pointing out), Foramen lacerum (Not a passageway, landmark only! right above the rocket ship, big and obvious), Occipital bone, Basiocciput (front of rocket ship), Occipital condyles (rocket ship wings),External occipital protuberance (Inion), Superior nuchal line, Foramen magnum

Clinical Correlations Larynx

Hyoid fracture: not technically the larynx, but certainly related to it. Medicolegally this is a cardinal sign of throttling, or strangulation. Bruising or ligature marks over the region suggest the possibility of hy- oid fracture. Xray CT Laryngeal fracture: Often the result of traumatic impact to the anterior throat by dashboard or well-placed blow. Dangerous because bruising of these tissues results in inflammatory response (pain, redness, heat, swelling.) Can compromise breathing, swallowing and vocalization. Vagus nerve damage: The position and relationship between the vagus nerve and the larynx put it at risk in thyroid gland surgery. Small nicks or cuts to the nerve have profound sequelae. Remember that this is a BILATERAL innervation meaning that loss of one vagus nerve will handicap function. Unlikely bilateral loss of the vagus places the Pt. in a precarious position with loss of vocalization and compromised respi- ration and swallowing. Laryngeal cancers are common especially among smokers. The epithe- lium below the vocal fold is respiratory epithelium; however, above the vocal fold it's stratified squamous. Regions of epithelial transition are prime locations to develop cancer

Cerebellum

In the metencephalon, neuroblasts migrate from the dorsolateral aspect of the alar plates, eventually growing over the fourth ventricle and fusing at the dorsal mid- line. The deepening pontine flexure compresses the primordial cerebellum ros- trocaudally. Initially, the cerebellum maintains the same basic three-layered or- ganization as the spinal cord. During further development however, neuroblasts migrate from the mantle zone through the marginal zone to form the cerebellar cortex. Discrete populations of neuroblasts within the mantle do not migrate and form nuclei that are located near the ventricular cavity.

Inferior Aspect of the Skull 2 Petrosphenoidal fissure, Groove for the auditory (pharyngotympanic, Eustachian) tube (ridge superior to rocket ship), Petrooccipital fissure , Sphenopalatine foramen (anterior hole of ppt), Vaginal process of the sphenoid bone (?), Palatovaginal canal (most medial to medial pteryoid), Temporal bone, Tympanic plate (plate covering auditory meatus), Petrotympanic fissure (line between sphenoid ptero and tympanic plate), Tympanomastoid fissure (?), Tympanic canaliculus (?), Posterior canaliculus for chords tympani (?), Anterior canaliculus for chords tympani (?)

Incisive fossa, Greater palatine foramen front hole , Lesser palatine foramen (foramina) back, Mandible - inner aspect, Mylohyoid line (chin part), Mylohyoid groove (cheek part), Genial tubercles (mental spines inside chin), Digastric fossa (inner two chins), Sphenoid bone, Pterygoid fossa?, Scaphoid fossa?, Spine? Temporal bone, Carotid canal (cervical, external, inferior entrance), Jugular fossa (leading upward to jugular foramen), Stylomastoid foramen- hole behind styloid, Occipital bone, Pharyngeal tubercle (bump on rocket ship), Hypoglossal canal (anterior condylar canal) rocketship, Condylar canal (posterior condylar canal) rocketship, Mastoid emissary foramen (behind the mastoid)

Deep Venous Drainage

Internal jugular vein The internal jugular vein receives drainage of the cranial contents. Blood drains from the cranial contents via the dural venous sinuses (described below) and leaves the cranial cavity through the jugular foramen. At this location the dura is continuous with the internal jugular vein, which then descends in the carotid sheath toward the commencement of the brachiocephalic vein. In its descent through the neck the IJ also receives venous drainage from many of the structures it passes. Drainage within the skull Veins draining the brain cross the subarachnoid and subdural spaces to enter an interconnected system of dural venous sinuses formed within the thickness of the cranial dura mater. These sinuses also receive blood from the orbit, the inner ear, the dura itself, and from an extensive network of diploic veins between the inner and outer layers of the skull. Dural Venous Sinuses Collect blood from the brain, eye, orbit, dura mater, and skull and carry it to the internal jugular veins on its way back to the heart. Structure: The cranial dura mater is a thick sheet of tough connective tissue. The rough outer surface of the sheet, the periosteal dura, serves as the endocranium (periosteum for the inner surface of the skull), and it is continuous with the epicranium (periosteum for the outer sur- face of the skull) through the sutures between individual bones. Therefore, there is no typical epidural space in the normal, unaltered anatomy. The inner surface, the meningeal dura, is smooth and faces the arachnoid mater across the subdural space. This surface follows the gross contours of the brain rather than the contours of the skull. Dural folds are formed where the contours of the outer and inner layers of the dura differ. While the external layer always follows the contours of the skull, the inner surface of the dura may project inward, away from the skull. There are two such folds, one in the sagittal plane between the two hemispheres of the brain, and the other in a more or less transverse plane (Figure 10). These folds do not com- pletely partition the cranial cavity, so they therefore have free inner margins. They also intersect at nearly a right angle, and they share a common continuous interface. The sagittal fold projects inward away from the skull and outer layer of dura along the midsagittal line, from crista galli to foramen magnum. It is subdivided by its intersection with the horizontal fold into the: o Falx cerebri: The upper, larger part of the fold that separates the right and left cerebral hemispheres. ("falx" = sickle shaped) o Falx cerebelli: The lower, smaller part of the fold that separates right and left cerebellar hemispheres. The transverse fold projects inward away from the skull and outer surface of the dura to separate the occipital lobes of the cerebrum from the cerebellum. Because it forms a membrane above the cerebellum, it is called tentorium cerebelli.

Lips and cheeks

Lips Obicularis iris Upper: superior labial branches of facial and infraorbital arteries Lower: inferior labial branches of the facial and mental arteries Upper: superior labial branches of infraorbital nerves (V2) Lower: inferior labial branches of mental nerves (V3) Labial frenula: folds of mucous membrane in the midline of upper & lower lip within oral vestibule Cheeks Buccinator Buccal branches of maxillary artery Buccal branches of mandibular n (V3) Buccal fat pads superficial to buccinator muscles

Maxillary artery The maxillary artery is the larger of the two terminal branches of the external carotid artery. The maxillary artery arises posterior to the neck of the mandible and crosses the infratemporal fossa from lateral to medial to supply many of the deeper structures of the face. It is divided into three parts:

Mandibular (first) part [location: posterior to lateral pterygoid muscle]: Passes anteriorly between the ramus of the mandible and the sphenomandibular ligament. All branches of this part pass through bone or cartilage to their targets. The branches of this part are: Pterygoid (second) part [location: crosses the infratemporal fossa superficial (typical) or deep to the lateral pterygoid muscle] All branches are distributed directly to their targets, which are primarily the muscles of mastication. (4, deep temporal, asserter, pterygoid, buccinator) Pterygopalatine (third) part: [location: within pteryogpalatine fossa, which it enters via the pteryogmaxillary fissure] Branches of the artery pair up with those of the maxillary nerve to form typical neurovascular bundles. All bundles then pass through bone to targets. (6, spa,inform,pharyn,descpal,spheoepal,arteryofcanal)

Posterior Aspect of the Skull

Mastoid emissary foramen (variable and inconstant, behind mastoid process), Condylar canal (lower hole near rock ship farthest from wings posterior condylar canal: an inconstant emissary foramen), External occipital protuberance (inion small point at back of skull), Superior nuchal line (line near external occipital protuberance), Mastoid process (end of mastoid seen from the back), Lambdoidal suture, Lambda (posterior "bregma (site of posterior fontanelle)), Parietal emissary foramen (inconstant, hole off the back saggistal suture near lambda)

Internal Carotid - External Carotid Left - Right External Carotid Anastomoses All branches of the external carotid artery that pass medially to the midline anas- tomose freely across the midline with those of the opposite side.

Medial angle of orbit: Angular Facial + Infraorbital Maxillary External Carotid w/ Dorsal Nasal Ophthalmic Internal Carotid Lateral angle of orbit: Transverse Facial (superficial temporal) + Superficial Temporal External Carotid w/ Palpebral Br of Lacrimal Ophthalmic Forehead and scalp: Superficial Temporal External Carotid w/ Supraorbital + Supratrochlear Ophthalmic Nasal cavity and paranasal sinuses: Sphenopalatine Maxillary a. w/ Anterior and Posterior Ethmoidal Ophthalmic A.

Innervation of the orbit Sensory innervation within and about the orbit is provided by GSA fibers in the trigeminal nerve (CN V). Branches of the ophthalmic di- vision (V1) supply the superior orbit and branches of the maxillary di- vision (V2) supply the inferior orbit. Details of these branches are provided in the CN V resources. The optic nerves are actually tracts of the brain and carry meningeal sheaths (dura mater, arachnoid mater, subarachnoid space, and pia ma- ter), which are continuous with those of the brain. The optic nerve contains Special Afferent (SA) nerve fibers for vision. They enter the orbit along with the ophthalmic artery through the optic foramen. The central artery of the retina, a branch of the ophthalmic ar- tery, runs within the optic nerve and is a true end artery (no anas- tomoses).

Motor to extraocular musculature All of the extraocular muscles are innervated by general somatic efferent (GSE) nerve fibers Oculomotor nerve (CN III) Innervates five of the extraocular muscles. The superior division innervates the levator pal- pebrae superioris and the superior rectus muscles. The inferior division innervates the medial rectus, the inferior rectus, and the inferior oblique muscles. The oculomotor nerve also has a parasympathetic compo- nent (GVE), described below under "D.4. Autonomic inner- vation of the orbit" Lesions of the oculomotor nerve produce lateral strabismus (lack of parallelism of the visual axis) due to nearly com- plete paralysis of one or more ocular muscles. Oculomotor nerve lesions also result in ptosis (drooping) of the eyelid,dilation of the pupil (no parasympathetic opposition to the sympathetic dilatory affect), and inability to accommodate for near vision due to lack of parasympathetic innervation to this mechanism Trochlear nerve (CN IV) Innervates the superior oblique muscle. Lesions produce diplopia (double vision) upon looking down. Abducens nerve (CN VI) Innervates the lateral rectus muscle. Lesions produce medial strabismus (medially deviated eye). The diplopia is minimized when looking toward the side away from the lesion.

Anterior Triangle Borders: Sternocleidomastoid, mandible and midline of the neck. The anterior triangle is further divided into three sets of paired triangles (mus- cular, carotid, submandibular) and one unpaired midline triangle (submittal) Tracheostomy - creation of an airway in the trachea - either above or below the isthmus - usually an elective procedure, but sometimes done emergently Cricothyrotomy - creation of an emergency airway between thyroid and cricoid cartilages Torticollis - torsion or twisting of the neck and elevation of the chin due to shortening of ster- nocleidomastoid m. Goiter - goiter is enlargement of thyroid

Muscular - Borders: hyoid, superior belly of omohyoid, sternocleidomastoid muscle, midline of neck contents: infrahyoid muscles; thyroid and parathyroid glands Carotid - Borders: posterior belly of digastric, superior belly of omohyoid, sternocleidomastoid muscle contents: HYPOGLOSSAL 9 NERVE ANSA CERVICALIS CAROTID SHEATH SYMPATHETIC TRUNK Submandibular - Borders: anterior and posterior bellies of digastric + mandible contents: submandibular gland; FACIAL ARTERY AND VEIN Submental (unpaired)- Borders: 2x anterior belly of bilateral digastric muscles, hyoid bone contents: submental lymph nodes; tributaries of anterior jugular vein

Brainstem Nuclei Basic Organiza- tion Brainstem sensory and motor nuclei lo- cated near the floor of the ventricular cavity largely con- form to a stereotypic arrangement. Bilater- ally, from the mid- line axis outwards to the lateral edge, cra- nial nerve nuclei are organized according to functional modal- ity in the following order: somatic mo- tor, branchial motor, visceral motor, vis- ceral sensory, somatic sensory, special sensory. Two caveats to this organization are: 1) differential growth of the brainstem and migration of the neuroblasts can displace nuclei ventrally, away from the ventricular floor, and; 2) not every type of nuclei is found at all brainstem levels (Fig. 5). c. Additional Nuclei The brainstem contains additional nuclei that are involved in a variety of sensory and motor functions. Many of these nuclei are of particular importance in shaping the external contours and in determining the internal histological staining patterns of the developed brainstem. B. Fiber Tracts Numerous fiber tracts involved in a variety of functions terminate within, or trav- erse, the different levels of the brainstem. These fiber tracts connect the spinal cord, brainstem, brain, and cerebellum.

Neuroblasts migrate from the mantle zone of alar and basal plates to form discrete bilateral columns of sensory and motor nuclei residing near the ventricular lu- men. Unlike in the spinal cord, somites of the head region are limited in number and are primarily responsible for formation and organization of skeletal muscle of the extrinsic eye and the majority of the extrinsic and intrinsic muscles of the tongue. The majority of skeletal muscle in the head is formed and organized within mesodermal outpocketings called branchial arches. Branchial motor output innervates skeletal muscle derived from resident mesenchyme within the branchial arches. These branchiomeric muscles control chewing, facial expres- sions, swallowing, vocalization, and turning the head. The major special sensory nuclei in the brainstem are dedicated to the functions of hearing and balance.

The microglial cell has dense cytoplasm and an irregular shaped nucleus with dense clumped chromatin. The granular endoplasmic reticulum has long and narrow cisterns with fairly dense contents. Small, dark bodies are characteristic. Mi-croglia vary in shape from an amorphous amoeboid form to a branched ramified form depending on the developmental stage of the brain and functional state of the cell. The presence of a glycocalyx, neurotransmitter receptors, ion channels, and receptors to numerous blood-borne molecules on the cell surface of the microglial cell suggests that this cell acts as an immunological sentry, dynamically monitoring the brain parenchyma. Following injury to the nervous system, these cells become activated, migrate to the site of damage, and act as phagocytes and mediators of the inflammatory reaction. In aged brains and in disease states mi- croglia come to contain large amounts of dense inclusions from materials they have phagocytksed. These are the non-excitable cells in the central nervous system and they form a major component in its total composition. They include the neuroglial cells in the brain and spinal cord parenchyma, the ependymal cells lining the cerebral ventricles and the cells of the choroid plexus.

Oligodendrocytes have fewer processes than astrocytes. Ultrastructurally they are moderately dense in appearance and have a round or oval nucleus with clumped heterochromatin. The cisterns of the granular endoplasmic reticulum and the Golgi apparatus frequently appear light in contrast to the dark cytoplasm. Their processes contain conspicuous microtubules. Oligodendrocytes supply my- elin sheaths to axons in the CNS, allowing for saltatory conduction of neuronal action potentials. Each oligodendrocyte produces a number of internodal lengths of myelin, each one on a different axon. It is thought that the myelin sheaths formed by oligodendrocytes may also serve a role in modifying axonal structure and maintaining axonal integrity. Cell loss, oligodendrocyte dysfunction, and/or abnormalities in myelin sheath structure have been implicated in the pathology of many neurological diseases including multiple sclerosis, unipolar depression, and schizophrenia. Astrocytes are star-shaped cells with a small cell body and ramifying extensions. Ultrastructurally they are light in appearance having a nucleus with little hetero- chromatin. Their contours are characteristically irregular. An astrocyte's cytoskel- eton is well developed and is largely comprised of intermediate filaments, most notably glial fibrillary acidic protein (GFAP). Astrocytes are termed protoplas- mic, if found in the gray matter, or fibrous if found in the white matter. The major distinction between protoplasmic and fibrous astrocytes, besides their location, is that fibrous astrocytes have a greater abundance of intermediate filaments in their cytoplasm. Astrocytes best fit the original definition of glial cells as brain "glue". Their cyto- skeleton makes them well suited for providing structural support to neurons. How- ever, astrocyte function goes well beyond structural support. Astrocyte processes surround all blood vessels of the brain and cover the pial surface, forming the "glial limitans". In addition, their processes surround some components of the neuropil, such as neuronal synapses and the nodes of Ranvier, possibly acting as electrical insulators. Astrocytes are known to have neurotransmitter receptors and ion channels on their cell surface suggesting that these cells may have the ability to monitor neuronal activity and subsequently manipulate the microenvironment surrounding neurons. Neighboring astrocytes are often joined via gap junctions, forming a syncytium. Additionally, astrocytes play a role in the brain's response to disease and injury, acting as phagocytes and forming glial scars following le- sions.

Posterior Triangle Borders: Trapezius, sternocleidomastoid, clavicle

Omoclavicular triangle (Subclavian): Borders: inferior belly of omohyoid, clavicle, sternocleidomastoid muscle contents: subclavian artery/vein; suprascapular artery; supraclavicular lymph nodes Occipital triangle - Borders: trapezius, sternocleidomastoid,inferior belly of omohyoid contents: part of external jugular vein; branches of cervical plexus; accessory nerve; trunks of brachial plexus; trans- verse cervical artery; cervical lymph node

The Main Stuff - Good

Parietal, Occipital, Temporal, Frontal, Sphenoid, Maxilla, Zygomatic, Mandible, Nasal, Inferior nasal concha, Lacrimal, Palatine, Vomer, Coronal, Sagittal, Lambdoidal Anterior (end after ethmoid), middle (up to foramen magnum), and posterior cranial fosse, Hypophyseal fossa (pituitary fossa, sella Turcica seat for pit obvious), Nasal cavities, Orbits, Oral cavity, Temporal fossa (outside skull: above zygomatic arch , Infra temporal fosse (inner part below zygomatic arch, Pterygopalatine fossae (innside most will have hole leading to), Paranasal Air Sinuses (all the turbaned area), Frontal , Maxillary, Ethmoidal (anterior, middle and posterior ethmoid air cells small pockets base on same side as cribriform plate), Sphenoidal

Salivary glands

Parotid gland, Parotid duct (pierce the buccinator and enter the oral cavity next to the second superior molar), Parasympathetic (secretory) from glossopharyngeal (IX), which synapses at otic ganglion. Postsynaptic fibers on V3 auriculotemporal n. Sympathetic fibers derived from cervical ganglia through external carotid nerve plexus, and are thought to reduce secretion of gland. Submandibular gland, Submandibular duct: {The lingual nerve loops around but does not supply this duct.} Innervation: Parasympathetic (secretomotor) fibers in chorda tympani [facial (VII)] which synapse in submandibular ganglion and travel to gland on branches of the lingual n and arteries. Sympathetic (vasoconstrictive) fibers from superior cervical ganglion also travel along these vessels, Submittal arteries, Sublingual gland, Innervation:Parasympathetic (secretomotor) fibers in chorda tympani [facial (VII)] which synapse in submandibular ganglion and travel to gland on branches of the lingual n and arteries. Sympathetic (vasoconstrictive) fibers from superior cervical ganglion also travel along these vessels. Blood supply: Submental and sublingual arteries

Functional Components.The Vagus Nerve, Cranial Nerve X -GVE. Preganglionic parasympathetic cell bodies lie in the brain stem. Their axons are distributed widely by many branches of the vagus nerve. 4 SVE - 4th Pharyngeal branch. Pharyngeal plexus to SVE for pharynx and palate (branchial arch four), excepting tensor palati and stylopharyngeus. -Superior laryngeal nerve. Fibers pass through the external branch to innervate cricothyroideus and a portion of the inferior pharyngeal constrictor (branchial arch four). -Recurrent laryngeal nerve. Fibers are distributed to all intrinsic muscles of the larynx (branchial arch six), excepting cricothyroideus; also to striated muscle in the wall of the upper esophagus (caudal pharyngeal wall).

Pharyngeal branch. Preganglionic fibers carry parasympathetic outflow to pharyngeal glands via the pharyngeal plexus. Ganglion cells occur in the wall of the pharynx itself. Superior laryngeal nerve. Preganglionic fibers in the internal branch carry parasympathetic outflow destined for glands on the base of the tongue, over the epiglottis, and in the larynx above the margin of the vocal fold. Ganglion cells lie scattered along the course of the nerve and close to the glands being innervated. Recurrent laryngeal nerve. Preganglionic fibers carry parasympa- thetic outflow for glands in the esophagus, trachea, and larynx below the margin of the vocal fold; also for tracheal smooth muscle. Gan- glion cells lie in the walls of the respective organs. Vagus nerve proper. Below the origins of the recurrent laryngeal nerves, the vagi distribute preganglionic parasympathetic fibers to the heart, lungs, lower esophagus, and abdominal viscera down nearly to the left colic flexure. Ganglion cells lie in the walls of the respective organs.

Sympathetic motor innervation of the head and involves preganglionic outflow from neurons located in the T1-T5 cord segments (mainly T1-T3). Their axons travel out in the corresponding spinal nerves and pass through the white rami communicantes to reach the sympathetic trunk, in which they ascend to synapse in the superior, middle, and inferior cervical sym- pathetic ganglia.

Postganglionic axons from cells of the cervical sympathetic chain are distributed as: -gray rami communicantes to cervical spinal nerves. -branches to certain cranial nerves (9,10,12, IX, X, XII). -branches to the meninges. -direct branches to cervical viscera and the heart. -plexuses on the carotid, subclavian, and vertebral arteries Postganglionic sympathetic outflow is added to branches of the trigeminal nerve in close relation to each of the four parasympathetic motor ganglia. . In all cases this involves axons of cell bodies in the superior cervical sympathetic ganglion, and they have traveled upward into the head through the carotid periarterial plexuses.

Gross Morphological Changes of the Cranial Neural Tube

Primary and Secondary Vesicles Even before the closure of the neuropores, the cranial neural tube forms three primary vesicles from which the brain develops: the prosencephalon (forebrain), the mesencephalon (midbrain) and the rhombencephalon (hindbrain). During the fifth week, the primary brain vesicles further subdivide to yield five secondary brain vesicles; the prosencephalon divides to form the telencephalon (1) and the diencephalon (2), and the rhombencephalon divides into the metencephalon (3) and the myelencephalon (4). The mesencephalon does not divide (5). Each sec- ondary vesicle has an associated fluid-filled cavity and set of adult neural deriva- tives (Fig.3; Table 1). While dorsoventral patterning is maintained along the length of the neural tube during development (see above), rostrocaudal patterning signals that deter- mine the distinctive identities and functions of the embryonic subdivisions of the brain are complex. To accommodate expansion during vesicle formation (and as a result of head fold- ing) the cranial neural tube undergoes a series of bends or flexures (Fig. 4). The first two flexures can be seen during the three-vesicle stage and occur from the ventral surface of the developing neural tube. They are called the mesencephalic flexure (at the level of the mesencephalon) and the cervical flexure (at the junc- tion of the rhombencephalon and spinal cord). At the five-vesicle stage, differen- tial growth between first two flexures results in a third flexure that occurs in the dorsal surface, between the metencephalon and the myelencephalon. This flexure is called the pontine flexure and it has important consequences for the shape of the rhombencephalon as it causes the walls of the neural tube splay open laterally (Fig. 5). A thin layer of ependymal cells stretches over the dorsal aspect of the fourth ventricle and both the basal and alar plates (still separated by sulcus lim- itans) now reside in the ventricular floor. Ultimately, only the mesencephalic flex- ure persists, accounting for the bend in the adult neuroaxis at the transition be- tween the prosencephalon and the mesencephalon.

The scalp has five layers that are easy to remember by using each letter of the word SCALP SCA proper

S- skin. Composed of thin skin similar to the skin of the body with hair follicles sweat glands, arteries, veins and lymphatic vessels C- connective tissue (dense). This thick layer contains an abundance of arteries, veins and nerves. If the scalp is cut through to this layer profuse bleeding can occur since the dense connective tissue tends to hold the vessels open. A- aponeurotic layer. This layer consists of the occipitofrontalis muscle. The occipitofrontalis has two muscle bellies connected by a tendon (epicranial aponeurosis or gala aponeurosis): 1. The frontal belly is anterior, is attached to the skin of the eyebrows, moves the scalp anteriorly, wrinkles the forehead and raises the eyebrows 2. the occipital bellies arise from the superior nuchal line of the occipital bone and pulls the scalp posteriorly (smoothes the forehead) L- loose connective tissue. This layer separates the scalp proper from the pericranium and facilitates the free movement of the scalp. The loose connective tissue acts as a potential space that can become filled with fluid with injury or infection. P- pericranium. The pericranium is a layer of dense connective tissue that is the periosteum on the outer surface is of calvaria.

Otic ganglion

This parasympathetic ganglion is located just inferior to the foramen ovale within the infratemporal fossa, posterior to the medial pterygoid muscle. Presynaptic parasympathetic fibers from CN IX enter the fossa through foramen ovale, synapse here, then travel with the auriculotemporal nerve (CN V) to the target, the parotid gland.

Innervation of palate Soft Palate Muscles SVE: Pharyngeal br X 1. V3 Medial Pterygoid N. Tensor veli palatini - tenses soft palate; opens pharyngotympanic tube 2. Levator veli palatini - elevates soft palate 3. Palatoglossus - elevates posterior tongue; draws soft palate to tongue 4. Palatopharyngeus - tenses soft palate; pulls walls of pharynx superiorly, anteriorly and medially during swallowing 5. Musculus uvulae - shortens uvula and pulls it superiorly

Sense V2 (nasopalatine, greater palatine & lesser palatine nerves) PS Taste and Mucous of Palate: 7 pterygopalatine ganglion SVE: All muscles of soft palate by pharyngeal br of vagus (executer tensor veil palatineL medial ptyergotd V3) Greater + lesser palatine artery br of maxillary artery Ascending palatine artery - br of facial artery Foramina of hard palate: 1. Incisive fossa (single): Nasopalatine nerves and vessels 2. Greater palatine foramina (bilateral): 3. Lesser palatine foramina (bilateral): Posterior to greater palatine foramina; supply the soft palate and adjacent structures

The Glossopharyngeal Nerve, Cranial Nerve IX tympanic. These fibers represent the preganglionic limb of the parasympathetic motor pathway to the parotid salivary gland. They traverse the tympanic canaliculus and the tympanic plexus in the middle ear cavity. They leave the tympanic plexus as the lesser petrosal nerve, pass through the lesser petrosal hiatus, cross the floor of the middle cranial fossa, and exit through the rear-most part of the foramen ovale. They end by synapsing on cells of the otic ganglion. Postganglionic axons of the parasympathetic ganglion cells en- ter the roots of the auriculotemporal nerve (V3), through which they reach the parotid gland.

Sense pain, temp, touch, pressure of posterior tongue/pharynx/audiotyr tube/middle ear cavity, eardrum/ mastoid air cell complex. Some GSA exteroceptive in small are of ear facial/vagus. -GSA -GVE Preganglionic parasympathetic inner vatic otic ganglion + posterior third tongue ganglions -GVA of carotid body and sinus. -SVE to (stylopharyngeus) derived from the third branchial arch. -SA taste buds of the vallate papillae and posterior part of the tongue. Medulla Oblongata -> Jugular foramen w/ Vagus + Accessory -> Superior no nerve ganglia + Inferior Ganglia and Superior cervical sumapthetic + C1/C2 between IJV/ICA medial to styloid process lateral surface of stylophangeus muscle (9 supplies), nerve + muscle downward between ICA ECA to ender pharynx between superior/middle pharyngeal constrictors. -A contribution to the auricular branch of X arises from the inferior glossopharyngeal ganglion, although its cell bodies lie in the superior ganglion for GSA behind skin ear. -The tympanic nerve also arises from the inferior ganglion, and consists mainly of GSA general sensory fibers for the middle ear cavity, mastoid air cells, and auditory tube. It enters the skull between the jugular fossa and the carotid canal and ascends through the tympanic canaliculus to reach the middle ear cavity. On the medial wall of the cavity, it is joined by postganglionic sympathetic fibers from the plexus on the in- ternal carotid artery; together these elements form the tympanic plexus. Most branches of the plexus distribute GSA fibers and sympathet ics to the mucosal lining of the middle ear cavity, auditory tube, mas-toid air cells, and inner surface of the ear drum. -Lesser petrosal: GVE PS glossopharyngeal through gap in roof of tympanic cavity (hiatus for lesser petrosal nerve) crossing middle cranial fossa- exiting by foramen oval to end in otic ganglion. Post ganglion fibers added to auriculotemporal for parotid. -The carotid nerve leaves the glossopharyngeal between the internal jugular vein and the internal carotid artery. It descends within the carotid sheath, carrying GVA interoceptive fibers to chemoreceptors of the carotid body (blood pO2, pCO2, pH) and baroreceptors of the carotid sinus (blood pressure). -Pharyngeal branches leave the glossopharyngeal nerve between the inter- nal and external carotid arteries. These carry GSA general sensory fibers to the lining of the pharynx via the pharyngeal plexus, formed on the external surface of the middle constrictor along with pharyngeal branches of the vagus nerve and superior cervical sympathetic ganglion -The muscular branch sup- plies SVE fibers to stylopharyngeus. It arises where the glossophayngeal nerve is applied directly to the surface of the muscle.. -Tonsillar branches arise after the glossopharyngeal nerve has entered the pharynx. They carry GSA general sensory fibers to the palatine tonsil, oropharyngeal isthmus, and adjacent soft palate via the tonsillar plexus, formed with branches of the lesser palatine nerves (V2). They also may carry SA fibers to taste buds on the soft palate. -The two terminal lingual branches of the glossopharyngeal nerve distribute GSA general sensory fibers to the posterior third of the tongue; SA fibers to taste buds on the posterior third of the tongue and in the vallate papillae (which lie anterior to the sulcus terminalis); and GVE preganglionic fibers to scattered parasympathetic ganglion cells whose postganglionic axons innervate glands in the posterior third of the tongue. Cell bodies lie in the glossopharyngeal ganglia. Their peripheral axons leave the nerve in five of its branches: contribution to the auricular branch of X within the temporal bone. Exteroceptive fibers travel with the auricular branch to supply skin over a part of the auricle, behind the auricle, and on the posterior wall of the external auditory meatus. tympanic. General sensory fibers pass through the tympanic canaliculus and tympanic plexus to reach the middle ear cavity, auditory tube, mastoid antrum and air cells, and inner surface of the ear drum. pharyngeal. General sensory fibers reach the mucosal lining of the pharynx via the pharyngeal plexus. tonsillar. General sensory fibers pass through the tonsillar plexus to reach the palatine tonsil, tonsillar fossa, and mucosa of the oropharyngeal isthmus and nearby soft palate. lingual. General sensory fibers are distributed to the posterior third of the tongue. lingual branches to taste buds on the posterior third of the tongue and on the vallate papillae. tonsillar branches, which may carry carry fibers to some of the taste buds on the soft palate. muscular branch, providing motor innervation to the stylopharyngeus. Stylopharyngeus is the only muscle to arise from the third branchial arch and, therefore, the only muscle innervated by the glossopharyngeal nerve. It assists in elevating the phar- ynx during swallowing and speech.

Neurovasculature of Larynx

Sensory (internal) Above the vocal fold = internal branch of superior laryngeal n (branch of Vagus) Below the vocal fold = recurrent laryngeal n. (branch of Vagus) Motor: All the intrinsic muscles of the larynx EXCEPT the cricothyroideus are inner- vated by the recurrent laryngeal nerve (branch of Vagus). The external laryngeal branch of the superior laryngeal nerve innervates the crico- thyroids. The blood supply of the larynx is similarly uncomplicated: Superior and inferior laryngeal arteries supply the soft tissues of the larynx. These two trunks are direct branches of the superior and inferior thyroid arteries respectively.

Classification of ganglia in the head and neck Ganglion cells are nerve cell bodies lying outside the central nervous sys- tem, that is they belong to the peripheral nervous system. They may occur singly, in small groups (microganglia), or in clusters large enough to produce significant swellings (true ganglia) along the course of peripheral nerves. Ganglia are to be distinguished from discrete groups of nerve cell bodies lying within the CNS, which are referred to as nerve nuclei

Sensory ganglia include: -dorsal root ganglia of the spinal nerves. These arise from neural crest. -ganglia of the cranial nerves. These arise partly from neural crest and partly from ectodermal placodes. RULE: A sensory ganglion contains the cell bodies of all afferent nerve fibers entering the CNS with the corresponding nerve. EXCEPTION: Some if not all proprioceptive fibers in the trigemi- nal nerve have their cell bodies in the midbrain sensory nucleus of V rather than in the ganglion. B. Motor ganglia all consist of general visceral efferent (GVE) neurons belong- ing to the autonomic nervous system. They are classified according to their loca- tion as: -paravertebral, alongside the vertebral column . These comprise the sympathetic chain ganglia. -terminal, near the termination of the visceral motor outflow pathways (PDF Figs. 3,7). These are parasympathetic microganglia and ganglion cells scattered in or near certain viscera (the tongue, lar- ynx, trachea and esophagus). -parasympathetic motor ganglia. In the head and neck, many parasympathetic ganglion cells never migrate far enough to reach their tar- get organs. Instead, they are arrested en route to form four discrete, named ganglia.

General somatic sensation

Sensory information from the face and scalp is carried back to the trigeminal sen- sory nuclei in the brainstem. The cell bodies of the trigeminal sensory fibers are located in the trigeminal ganglion (except for proprioceptive fibers). Information is then relayed to other regions of the brain. This is an important system. Think of the simple act of splashing cold water on your face in the morning: 1) connections from the various trigeminal nuclei travel to the sensory cortex (so we know what we are doing); 2) fibers travel to the limbic system due to the habit formed by our mothers telling us to wash our faces— conditioning; 3) fibers travel to the reticular formation to wake us up; and 4) fibers travel to the hypothalamus to control vas- oconstriction or vasodilation depending on the temperature of the water

Fiber types in the individual cranial nerves - a summary AS A RULE, resident fibers are those present in a nerve as it joins (enters/exits) the central nervous system.

Seven cranial nerves each have only one resident fiber type. 1,2,8 : Special Afferent (Olfactory,Optic,Vestibulocochlear) 4,6,12: General Somatic Efferent (Trochlear, Abducens, Hypoglossal) 11: Special Visceral Efferent (Spinal Accessory) Two cranial nerves have two resident fiber types. 3: GSE GVE Oculomotor (so both the movers) 5 Trigeminal: GSA SVE (sense the face + move inners) The remaining three cranial nerves have five of the possible six resident fiber types (All be GSE): 7 Facial, 9 Glossopharyngeal, 10/C11: GSA,GVA,GVE,SA,SVE

The five distinct regions of the nasal cavity are listed below along with the sinus or other structure that connect to them.

Sphenoethmoidal recess: opening of sphenoidal sinus Superior nasal meatus: opening of post. ethmoidal air cells Middle nasal meatus: opening of semilunar hiatus FAMM frontal sinus via the frontonasal duct (into the ethmoid infundibulum),opening to the anterior/middle ethmoidal air cells, opening of the maxillary sinus, the maxillary ostium Inferior nasal meatus - opening of the nasolacrimal duct Common nasal meatus - All four spaces listed above drain into this space

Adult derivatives of the subdivisions of the neural tube.

Spinal cord: Spinal cord: Central canal: Spinal Cord Rhombencephalon: Myelencephalon (Caudal 4th, Medulla) + Metencephalon (Rostral 4th, Pons, Cerebellum) Mesencephalon: Mesencephalon: Cerebral aqueduct: Supeior colliculi/Inferior colliculi/Tegmentum Prosencephalon: Di/Telencephalon Diencephalon: 3rd ventical: Epithalmus, Thalamus, SUbthalamus, Hypothalamus, Optic nerve/retina, Posterior pituitary, Pineal Telencephalon: Lateral ventical/Rostral 3rd: Cerebal cortex, basal ganglia, hippocampus, amygdala, olfactory bulb

Patterns of motor innervation and development - a brief anticipation of Mary Ann MacNeil's lecture on the "Development of the Pharyngeal Ap- parts" The first is familiar to you from study of the back and limbs and thorax, abdomen, and pelvis. In this pattern paraxial mesoderm of the somites gives rise to striated voluntary muscle of the vertebral column, body wall, and limbs. The cervical vertebral musculature, infrahyoid muscles, most muscles of the tongue, and the muscles that move the globe of the eye in the orbit arise in this way. They all receive general somatic motor (GSE) innervation. The second pattern, which will be described in detail in the lecture on the Pharyngeal (Branchial) Apparatus, is very different, involving development of many important structures from the wall of the pharyngeal (cranial) region of the foregut (PDF Fig. 14).

Streams of neural crest cells migrate ventrally into the wall of the pharynx, between the surface ectoderm and the foregut endoderm. As the cells prolif- erate, they raise ridges, or arches, which produce irregularities in the epithelial layers. The core of each arch contains: 1. a cranial nerve that has grown in from the brainstem. 2. a bar of cartilage developed from neural crest mesenchyme. 3. an artery also developed from neural crest mesenchyme. 4. a muscle rudiment composed of cells that have migrated in from the paraxial mesoderm but are patterned by neural crest mesenchyme of the arch. (thus SVE) Each branchial (gill, or pharyngeal) arch is closely associated with a particular cranial nerve, which innervates all muscles developed from that arch rudiment. This is an extremely useful organizing principle. 1. Muscles of mastication (chewing) develop from the first arch and are innervated by Cranial Nerve V (Trigeminal). 2. Muscles of facial expression (including platysma) develop from the second arch and are innervated by Cranial Nerve VII (Facial). 3. Stylopharyngeus, a longitudinal muscle of the pharynx, is the only muscle to develop from the third arch. It is the only muscle innervated by the Glossopharyngeal nerve (Cranial Nerve IX). 4. Muscles of the soft palate, pharynx, and larynx develop from the fourth and sixth arches, and are innervated by Cranial Nerve X (Vagus).

Glands in the Neck

Thyroid Gland: Usually comprised of two lobes (right and left)each with a superior and inferior pole Function: Regulate general metabolism Additional features: Isthmus - connection between lobes, tightly attached to 2nd and 3rd tracheal rings Pyramidal lobe - thyroid tissue along tract of descent connects to isthmus toward left Parathyroid glands: Approximately four glands located on the posterior aspect of the thyroid gland which are associated with thyroid by embryonic descent. Function: Control of mineral metabolism

Venous blood returns from the head and neck via the internal jugular, external jugular, vertebral, and inferior thyroid veins. The division between internal and external systems is not as clear-cut as on the arterial side, as there are more com- munications between the internal and external venous systems

Superficial Venous Drainage External Jugular Vein (EJV) The blood of the temporal and posterior auricular regions of the scalp, the external ear, the upper and lower jaws, cranial dura mater, nasal cavity, palate, orbit, and muscles of mastication drain into the external jug- ular vein. While the patterns by which they join can be variable, the external jugular vein typically receives contributions from the following veins: superficial temporal, retromandibular, posterior auricular, maxillary, and facial. The EJV can vary considerably in size. Note that the system drains both directly into the subclavian vein as well as into the internal jugular vein. Vertebral vein in many ways parallels the distribution of the vertebral artery. It drains the scalp of the occipital region, the cervical vertebral column and muscles, as well as nerve roots, spinal dura, and spinal cord. It is formed by contributions from the internal vertebral venous plexus, the occipital vein, and segmental intervertebral veins. It descends through the C1-C6 transverse foramina to enter the brachiocephalic vein. Inferior thyroid vein drains the lower part of the thyroid gland and larynx and the upper part of the trachea and esophagus and drains into the left brachiocephalic vein as it crosses the midline. Clinical correlation: Recall the epidural venous plexus that extends the entire length of the vertebral column, providing a longitudinal pathway for the spread of infections and tumors. At each segmental level it com- municates with the intervertebral veins and thus with the lateral sacral, lumbar, and intercostal veins. In the neck, the plexus is linked with the vertebral, ascending cervical, and deep cervical veins. If cells from tumors of the pelvic viscera, breast, and lung gain access to the venous system, they can be carried to the vertebral plexus and through it reach the vertebral bodies, ribs, sternum, and clavicles. Above, by means of these venous connections through foramen mag- num, they can also be distributed to the intracranial dural sinuses, brain, and skull.

Branches of External Carotid Artery SALFOPSM TC Trunk: Suprascapular a, Transverse cervical a, Ascending cervical a, Inf Thy a, Inf Laryngeal a CC Trunk under anterior scalene: Deep cervical a

Superior Thyroid A (Cricothyroid, Sup Laryngeal), Ascending Pharyngeal A (W/ ICA Carotid canal), Lingual A, Facial A (Submental a, Inf/Sup Labial a, Lat Nasal A, Angular A), Occipital A, Posterior Auricular A, Superficial Temporal (t facial) A, Maxillary A

Intrinsic muscles of tongue - alter shape

Superior longitudinal - thin layer deep to mucous membrane of dorsum Inferior longitudinal - narrow band close to inferior surface Transverse - mediolaterally transverse muscle deep to superior longitu- dinal m Vertical - vertical fibers intersect transverse m Genioglossus -- protrude Hyoglossus -- retract Styloglossus -- retract Palatoglossus --Pharyngeal plexus (X)

Dural venous sinuses are formed where the contours of the outer and inner layers of the dura separate from each other, forming a space between the layers. These spaces act as channels for venous blood.

Superior sagittal sinus - superior edge of falx cerebra Superior sag ->Inferior sag -> Straight sinus -> Confluence of sinuses -> Transferse and sigmoid sinuses -> Jugular foramina -> Internal Jugular Vein Inferior sagittal sinus - inferior edge of falx cerebri; joins with the great cerebral vein to form the straight sinus Occipital sinus Confluence of sinuses Transverse sinuses Sigmoid sinuses - drain into the internal jugular vein Superior petrosal sinus - along edge of tentorium cerebell Inferior petrosal sinus - connects cavernous sinus to IJV Cavernous sinus* The cavernous sinuses are paired venous chambers on either side of the sella tur- cica. They occupy a critical location and have many anatomical relationships and connections of clinical importance. Each cavernous sinus: Contains the hairpin curve portion of the internal carotid artery and the sympathetic nervous plexus on its surface Contains cranial nerve3,4,51,52,6 Is freely connected via valve-free venous channels to the pterygoid venous plexus of the face and the ophthalmic vein of the orbit. o Clinical correlation: These free venous connections allow in fections and other pathology to potentially travel between these regions

External carotid artery SAL FOP SM The external carotid leaves the carotid sheath to supply the external structures of the head, including the face, scalp, cranial dura mater, oral cavity, nasal cavity, larynx, pharynx, and thyroid gland. Note that its distribution in the neck is com- plemented by segmental spinal branches of the vertebral artery and other branches of the subclavian artery in the inferior neck.

Superior thyroid artery supplies the larynx via the superior laryngeal branch and thyroid gland Ascending pharyngeal artery runs upward on the outer surface of the pharynx, posterior to and parallel with the internal carotid artery to sup- ply the pharynx, palatine tonsil, and auditory tube. o The course is clinically significant, for the artery can be misin- terpreted as a partially patent internal carotid in arteriograms. Lingual artery passes up and forward deep to the hyoglossus muscle. It sends dorsal lingual branches to the posterior part of the tongue, a sublingual artery to the sublingual gland and muscles in the floor of the mouth, and continues onward as the deep lingual artery supplying the remainder of the tongue Facial artery (or external maxillary a) follows a complicated s-shaped course to reach the face. Its course takes it across the lower border of the mandible, where its pulse can be felt against the bone. The artery snakes its way among the muscles of facial expression toward the medial angle of the eye. Along the way, it supplies the following structures: Palatine tonsil, tonsil/softpalate/auditorytube,chin,lips, side of nose, lacrimal sac and eyelids Tonsillar branch, ascending palatine artery, submittal branch, inferior labial superior labial, lateral nasal, angular branch Occipital artery runs up and posteriorly, deep to the digastric muscle and the mastoid process to ultimately distribute across the posterior scalp. It supplies the muscles it crosses in the neck and the posterior scalp. Posterior auricular artery supplies anterior and posterior aspects of the external ear and the adjacent scalp. o Note that the small but important stylomastoid artery travels up and through the stylomastoid foramen to the tympanic cavity and inner ear. This artery typically arises from occipital, but may arise from posterior auricular (1/3 of individuals) The external carotid finally divides into its terminal branches posterior to the ra- mus of the mandible within or deep to the parotid gland. The terminal branches are the superficial temporal artery and maxillary artery: Superficial temporal artery gives off the transverse facial artery within the parotid gland. This artery passes forward onto the face. Su- perficial temporal then ascends to supply the lateral scalp. o The pulsations of superficial temporal can be felt against the posterior zygomatic arch, and pressure can be applied here to control bleeding from scalp wounds. Maxillary artery supplies many of the deeper structures of the face. It passes medially from external carotid toward the midline. It is divided into three parts: Mandibular (first) part - posterior to lateral pterygoid muscle Pterygoid (second) part - crosses the infratemporal fossa superficial (typical) or deep to the lateral pterygoid muscle Pterygopalatine (third) part - within pteryogpalatine fossa, which it enters via the pteryogmaxillary fissure.

Middle Ear 3

Superiorly Tegmen tympani (of petrous temporal bone) Middle cranial fossa inferiorly Entrance to the carotid canal, Jugular fossa, Entrance to the tympanic canaliculus anteriorly Carotid canal, Auditory (pharyngotympanic, Eustachian) tube posteriorly Facial canal (vertical part), Mastoid antrum and air cells laterally, Tympanic membrane (ear drum), External auditory (acoustic) meatus medially Facial canal (horizontal part), Internal Ear (cochlear and vestibular labyrinths), Oval window (fenestra ovals), Round window (fenestra rotundum

Frontal, Zygomatic, Sphenoid, Maxilla, Ethmoid, Lacrimal, and Palatine bones make up the orbit.

Supraorbital foramen: Supraorbital br of Frontal V1 Infraorbital foramen: Infraorbital gr,canal,for br of V2 Optic Canal (optic nerve + ophthalmic artery) connects the orbit to the middle cranial fossa. Superior Orbital Fissure (S/I III, IV, VI, NasoFronLac V1, Opth Vein) connects orbit to the middle cranial fossa Inferior Orbital Fissure (Infraorbital br V2) conencts orbit to the PPF Lamina papyracea separates orbit from ethmoid air cells Superior Nasal Meatus: Post Ethmoid Foramina Middle Nasal Meatus: Frontal, Ant/Med Ethmoid, Maxillary Inferior Nasal Meatus:Lacrim sac->Nasolacrimal canal/duct

DEVELOPMENT OF THE THYROID GLAND

The thyroid gland develops from two sources. 1. Majority of the gland develops from the median thyroid diverticulum. The original site of the diverticulum persists in the adult at the foramen cecum, at the junction of the anterior 2/3 and posterior 1/3 of the tongue. 2. Parafollicular or C-cells which produce calcitonin; these are developed from the ultimobranchial body. The thyroid gland first appears as an epithelial proliferation on the floor of phar- ynx at the foramen cecum of the developing tongue. The thyroid gland "descends" ventral to the gut tube as a bi-lobed diverticulum. As the thyroid gland is migrat- ing, it maintains the connection to the foramen cecum by the thyroglossal duct. The duct will regress and completely disappear, leaving only the foramen cecum as a remnant of the migration. As the thyroid gland descends to its final position anterior to the trachea cells of the ultimobranchial body invade the gland to give rise to the parafollicular cells. The epithelial cells of the pharyngeal floor give rise to the follicular cells involved in produce thyroid hormones.

Autonomic innervation of the orbit Parasympathetic pathways Presynaptic neurons course in the oculomotor nerve (CN III). The preganglionic parasympathetic neurons leave the oculomotor nerve via the parasympathetic (motor) root. They then reach the ciliary ganglion, which is located lateral to the optic nerve. The postganglionic axons of the ciliary ganglion course through the short ciliary nerves to the constrictor pu- pillae muscle for pupillary constriction and to the cil- iaris muscle for accommodation to near vision.

Sympathetic nerves to the orbit arrive in the head via typical pathways for sympathetics in the head: The preganglionic neurons lie in the upper thoracic seg- ments of the spinal cord, gain access to the sympathetic chain via white rami communicantes and course superi- orly along the sympathetic chain to reach the superior cer- vical ganglion, where they synapse. From the superior cervical ganglion, the postsynaptic neu- rons course in the carotid plexus along the internal carotid artery. From the carotid plexus, the sympathetic fibers may reach the eye by a number of routes: The sympathetic fibers continue along the internal ca- rotid artery and the ophthalmic artery to gain access to the orbit and eyeball. In the cavernous sinus, sympathetic fibers may pass to the ophthalmic nerve and its nasociliary branch and then along the long ciliary nerves to the eyeball or, al- ternatively, along the sensory root of the ciliary gan- glion and then along the short ciliary nerves to the eyeball. The function of the sympathetics in the orbit is to inner- vate the dilator pupillae muscle (dilation of the pupil), transmit sensory information from the iris and cornea, and to innervate the superior tarsal muscle (elevation of the eyelid) Injury to the cervical sympathetic chain results in Horner's syndrome. Signs of this syndrome include: Miosis (pupillary constriction) due to unopposed action of the parasympathetic nerves. Ptosis (a slight drooping of the eyelid) due to paralysis of the superior tarsal muscle. Anhydrosis (lack of sweating) Flushing of the skin due to ceasing of the vasoconstric- tive effects of the sympathetic nerves (therefore, vaso- dilation and increased blood flow).

The Blood-Brain Barrier (BBB)

The BBB is a complex of structures that controls the movement of substances from the body's general vascular compartment to the extracellular compartment of the CNS. The barrier was first described to account for the phenomenon whereby certain dyes injected into the circulatory system fail to stain brain paren- chyma, although they pass easily into non-nervous tissue. The blood-brain-barrier is selectively permeable. Some substances do not penetrate into the brain; others do so very slowly, while others, like small ions and sugars, pass through easily. The site of the blood brain barrier is believed to be the endothelial cells of the brain capillaries in which cells are joined by tight junctions. The BBB exists in most of the brain except for few small regions (e.g. the pineal body, the pituitary gland, the area postrema, the subfornical organ), which usually have chemically sensitive neurons. These regions are collectively referred to as "circumventricular organs," and within these regions the capillaries are fenestrated (holes in or be- tween the endothelial cells). The mechanisms by which substances are transported across the blood-brain-bar- rier are diverse. Certain ions are actively transported against a concentration gra- dient, causing considerable differences between the ionic concentrations in blood plasma and brain extracellular fluid. Some metabolites are transported across the endothelial cell wall by identifiable carrier mediated systems. Lipid-mediated penetration is important since this is the mechanism by which certain drugs pen- etrate the barrier. Some plasma solutes that pass into the endothelial cells are de- graded before they can pass out of the endothelial cells into the brain.

The Meninges

The CNS is surrounded by a series of three coverings, classified according to two categories of toughness: the strong and substantial dura mater, and the thin and delicate arachnoid and pia mater, which are often referred to together as lep- tomeninges. In the skull, the dura mater is attached to the periosteum of the inner surface of the cranial bone and is considered to have two layers - an outer perios- teal layer and an inner meningeal layer. In several places around the brain the inner meningeal layer of dura mater folds in on itself and forms specific dural reflections or septa. There are two major reflections (and some minor ones) - one that separates the two cerebral hemispheres called the falx cerebri, and one that separates the inferior and caudal aspect of the cerebrum from the cerebellum - the tentorium cerebelli (or tentorium for short). The dural venous sinuses are en- dothelial-lined channels that form between the two dural layers and exist either where reflections originate (i.e., where the mengineal layer separates from the periosteal layer), or where the meningeal layer turns back on itself. Blood from the cerebral veins empty into the dural venous sinuses, which then convey the blood from the cranial vault to veins external to the skull. The delicate pia mater is attached to the brain and closely follows its contours. Between the pia mater and the dura mater is the arachnoid, which consists of a cellular layer of arachnoid barrier cells closely attached to the dura. The arachnoid layer also contains delicate cellular trabeculae that connect the arachoid layer to the pial layer. These trabeculae have the appearance of spiderwebs and this ap- pearance confers the name arachnoid. The interval between the pia and the arach- noid layers that is bridged by the arachnoid trabeculae is called the subarach- noid space, and it is filled with cerebrospinal fluid. In locations where the arach- noid bridges over large surface irregularities, such as the space between the inferior surface of the cerebellum and the dorsal surface of the medulla, the subarach- noid spaces may be particularly large, forming space called subarachnoid cis- terns. The subarachnoid space is also notable because it is through this space that many of the arterial branches travel on their way to supply the brain. The branches of these arteries get smaller in caliber as they approach their destination and turn and penetrate the pia to enter the brain - these penetrating arterioles retain some of the pia as they enter the brain Of clinical importance are two potential spaces associated with the meninges where blood may collect during a vascular hemorrhage. These spaces do not or- dinarily exist, but may be expressed under certain circumstances. An epidural space exists between the skull and the periosteal dura. Hemorrhaging of blood into the epidural space is most likely to occur when a meningeal artery of the skull is torn. A second potential space, the subdural space, exists within the dura ma- ter, between the meningeal layer of the dura and the cells of the arachnoid mater. Hemorrhaging of blood into the subdural space is most likely to occur following tearing of a cerebral vein where it meets a dural venous sinus. These veins are commonly referred to bridging veins, and they leave the surface of the brain to travel through the meninges to reach the dural venous sinus.

Nerves of the Face and Scalp

The Facial Nerve (Netter plate 24,122) The facial nerve (CNVII) exits the posterior cranial fossa, gives off several branches and then exits the skull through the stylomastoid foramen. A branch passes behind the ear to supply the occipital belly of the occipitofrontalis; another branch innervates the digastric muscle and the stylohyoid muscle. The facial nerve then enters the deep surface of the parotid gland and divides into an upper trunk (temporofacial) and lower trunk (cervicofacial) which forms an anastomotic net- work of nerves called the parotid plexus. The plexus gives rise to five terminal branches of nerves: To Zanz By Mot Car Temporal branches of the facial nerve Zygomatic branches Buccal branches Marginal mandibular branches Cervical branches The Trigeminal Nerve (Netter plate 121) The trigeminal nerve (CNV) divides into three major divisions in the cranial fossa. Each division passes out of the cranial cavity to innervate a part of the face. The trigeminal nerve provides cutaneous innervation to the face and the scalp (excep- tion: a small area covering the lower border of the mandible and parts of the ear which are supplied by cervical nerves) and motor innervation to the muscles of mastication. The three branches of the trigeminal nerve are: 1. Ophthalmic (V1)- carries sensory fibers 2. Maxillary (V2)- carries sensory fibers 3. Mandibular (V3)- carries sensory branches that innervate the skin and motor fibers that innervate the muscles of mastication Sensory innervation to the Scalp Sensory innervation to the scalp is derived from two sources: 1. branches of the trigeminal nerve- supply the scalp anterior to the ears and to the vertex of the scalp 2. anterior rami of cervical spinal nerves- supply posterior to the ears and vertex of the scalp

Innervation Vascular supply to the TMJ is provided by branches of the superficial temporal and maxillary arteries near the joint.

The TMJ sensory fibers primarily travel in articular branches of the auriculotemporal, masseteric, and possibly the lateral pterygoid nerves. All of these branches are of the mandibular division of the trigeminal nerve. These patterns of innervation have important dental clinical considerations for the management of TMJ pain. Proprioceptive awareness of the position of the jaw is crucial for maintenance of appropriate masticatory position and force. The muscle spindles in the muscles of mastication contain afferent fibers to maintain this positional awareness. These fibers have their own nucleus in the brain, as described in the Brainstem 1 notes: "Mesencephalic Nucleus of V: (midbrain & pons, V). This small sensory component of CN V lies in the lateral wall of the rostral end of the fourth ventricle and extends in the lateral wall of the cerebral aqueduct into the caudal midbrain beneath the inferior colliculus. It is best identified in myelin stained sections by visualizing its associated fibers, the mesencephalic tract of V. The neurons of this nucleus are ganglion cells that innervate muscle spindles in the muscles of mastication peripherally and have central axons that innervate alpha motor neurons in the motor nucleus of V. These ganglion cells are anomalous in that they migrated into the developing neurotube from the trigeminal ganglia for reasons that are unknown. As with other muscle spindle afferents, they play a role in controlling the force of the bite as their axons project to the Motor Nucleus of V, producing a monosynaptic stretch reflex (myotatic reflex). They also project to the most rostral part of the spinal nucleus of V, which relays this muscle spindle

Temporal Fossa The temporal fossa is a region on the lateral head that contains the temporalis muscle, one of the primary muscles of mastication. This muscle takes its origin from the bony floor of the fossa and the temporal fascia, the "roof" of the fossa.

The boundaries of the fossa are: Laterally: zygomatic arch Medially ("floor of the fossa"): 4 bones that form the pterion: frontal, parietal, temporal, and greater wing of sphenoid Anteriorly: frontal and zygomatic bones Posteriorly/superiorly: temporal lines on skull Inferiorly: infratemporal crest

The fourth and sixth pharyngeal arch Left side: arch of aorta Right side: right subclavian Left side: left pulmonary artery Right side: right and ductus arterious pulmonary artery

The cartilage component of the fourth and sixth pharyngeal arches derived from lateral plate mesoderm, fuse to form the cartilages of the larynx (with the exception of the epiglottis which develops after the laryngeal cartilages have formed). The muscles of the fourth arch and sixth pharyngeal arch are the: muscles of the soft palate (except tensor veli palatine) muscles of the pharynx (except stylopharyngeus) striated muscles of the esophagus muscles of the larynx The nerve of the fourth arch is the superior laryngeal nerve of the vagus nerve (CN X). The nerve of the sixth arch is the recurrent laryngeal branch of the vagus nerve (CN X).

The second pharyngeal arch: Hyoid and Stapedial arteries

The cartilage of the second pharyngeal arch (also called the hyoid arch) is called Reichert cartilage, derived from neural crest cells and will give rise to the: stapes styloid process stylohyoid ligament lesser horn and upper part of the body of the hyoid bone The muscles of the second pharyngeal arch include: all of the muscles of facial expression stapedius stylohyoid posterior belly of the digastric The nerve associated with the second pharyngeal arch is the facial nerve (CN VII).

The third pharyngeal arch: Common Carotid arteries The fifth pharyngeal arch does not develop in humans.

The cartilage of the third pharyngeal arch is also derived from neural crest cell derived mesenchyme. Ossification of the cartilage forms the greater horns and the lower portion of the hyoid bone. The muscle component of the third pharyngeal arch is limited to the stylopharyn- geus muscle. The nerve of the third pharyngeal arch is the glossopharyngeal nerve (CN IX)

5. The Telencephalon

The cerebral cortex is the primary component of the telencephalon. This sheet of cells is thrown into convolutions with invaginations (sulci) and evaginations (gyri). There are two cerebral hemispheres, one on each side. The cerebral cor- tex is divided into lobes, and each lobe contains multiple and different cortical areas that perform unique and specific functions. In general, the occipital lobe is concerned with vision, the temporal lobe with audition, processing of objects, and memory, the parietal lobe with tactile information and processing of space and action, and the frontal lobe is involved in control and processing of move- ment and higher cognitive processes (many aspects of language, planning, inten- tion). The cortex folds in on itself at the medial aspect of the temporal lobe to form a structure called the hippocampus, which is critical for memory. Deep to the cerebral cortex is the cerebral white matter, which consists of axons traveling to and from the cerebral cortex. This white matter interconnects the re- gions of the cerebral cortex with each other, with areas of the diencephalon and brainstem, and with deep nuclei of the telencephalon that are buried under the cerebral cortex. These deep nuclei are called the basal ganglia. Many of the basal ganglia (caudate, putamen, globus pallidus) are involved in modulating motor commands. An additional basal nucleus (amygdala) processes emotion. A CSF-filled structure called the lateral ventricle exists underneath the cerebral cortex. There are two lateral ventricles - one under each hemisphere. They are roughly C-shaped, with named parts of the lateral ventricle underneath each lobe. The anterior horn is below the frontal lobe, the body of the lateral ventricle un- derneath the parietal lobe, the posterior horn underneath the occipital lobe, and the inferior horn below the temporal lobe. Between the anterior horn and the body, the foramen of Monro emerges to connect with the third ventricle. There is one foramen of Monro on either side

Tongue The structural floor of the mouth is formed by the mylohyoid and geniohyoid muscles, which attach to the hyoid bone and act to depress the mandible.

The tongue is a mobile muscular organ that is partly in the oral cavity and partly in the oropharynx. Its functions include aid in mastication, forming words during speech, oral cleansing, and taste. Parts of the tongue: Root: rests on the floor of the mouth. Body: anterior 2/3 of tongue Apex: anterior end of body

The Abducent Nerve VI GSE only Lateral Rectus

arries the GSE fibers that provide motor innervation to the extraocular muscle (lateral rectus) mainly responsible for abducting the visual axis.

Parasympathetic motor innervation of the head and neck involves preganglionic outflow from cells comprising scattered nerve nuclei in the brain stem. Their axons pass outward in cranial nerves 3,7,9,10 and travel through the cranial nerve plexus to synapse on parasympathetic ganglion cells. True terminal parasympathetic ganglion cells occur in the tongue, larynx, trachea, and lower esophagus. Their postganglionic axons are distributed directly to local targets. Occasional microganglia and parasympathetic ganglion cells lie scattered along the course of branches of cranial nerves IX and X that travel to the posterior part of the tongue and to the pharynx and larynx. Postganglionic fibers continue on in these nerves to reach their destinations There are four discrete parasympathetic ganglia in the head. Each is closely associated with a major branch of cranial nerve V, which is used as a pathway along which to distribute the postganglionic axons to target glands and smooth muscle in the periphery.

The ciliary ganglion is located in the apex of the orbit. Its post-ganglionic fibers are added to the short ciliary nerves (part of the ophthalmic division of V1) to reach the ciliary and sphincter pupillae muscles in the globe of the eye. The pterygopalatine ganglion is located in the pterygopalatine fossa. Its postganglionic fibers are added to branches of the max- illary division of V2, through which they are carried to the lacrimal gland and glands of the nasal cavity and hard and soft palate. The otic ganglion is located in the infratemporal fossa just below the foramen ovale. Its postganglionic fibers are added to the auriculotemporal nerve (a branch of the mandibular V3) with which they reach the parotid salivary gland The submandibular ganglion is located in the floor of the mouth. Some of its postganglionic fibers pass directly to the submandibular salivary gland. Others are added to the lingual nerve (a branch of the mandibular division of V3) to reach the sublingual salivary gland, as well as minor glands in the floor of the mouth and on the anterior part of the tongue

The Accessory Nerve, Cranial Nerve XI, cranial and spinal roots converge on the jugular foramen,, diverge again immediately below the base of the skull, and the cranial root blends with the vagus nerve thus becoming its accessory.

The cranial root arises from caudal portions of the same GVE (parasympa- thetic) and SVE brain stem nuclei associated with the vagus nerve. In fact, many branchial motor fibers distributed to striated muscles of the palate, larynx, and pharynx reach the vagus through the cranial root of the accessory nerve. The spinal root, arising from the upper cervical spinal cord, ascends through the foramen magnum to reach the jugular foramen. After parting from the cranial root high in the neck, it supplies motor fibers to trapezius and sternocleidomastoid SVE!, GSA from spinal roots

Surface of the tongue The inferior surface of the tongue is covered with a thin layer of mucosa, and is connected to the floor of the mouth by a midline fold called the frenulum. The submandibular duct (described below) opens into the sublingual caruncles on both sides of the frenulum. The veins that drain the tongue may be viewed through the thin mucosa.

The curved dorsal surface of the tongue is characterized by a V-shaped groove (terminal sulcus), which delineates the anterior 2/3 (oral part) from the posterior 1/3 (pharyngeal part), which have different embryological origins. The mucous membrane on the anterior part of the tongue is roughened by lingual papillae, which contain taste receptors (taste buds). The posterior part of the tongue has no papillae, but is rough- ened by the presence of lymphoid nodules, known collectively as the lymphoid tonsil.

Diencephalon

The diencephalon is comprised entirely of alar plate neuroblasts that migrate to form three swellings. These swellings are called (from ventral to dorsal) the hy- pothalamus, the thalamus and the epithalamus. With cell proliferation, the thala- mus protrudes into the third ventricle. There are two sulci in the developing di- encephalon- the hypothalamic sulcus divides the hypothalamus from the thalamus and the epithalamic sulcus divides the thalamus from the epithalamus.

4. The Diencephalon

The diencephalon is the division of the brain rostral to the midbrain. It is best appreciated on a mid-sagittal cut through the brain. It consists of two main divi- sions - the thalamus, a collection of nuclei which relays the majority of sensory signals to the cerebral cortex, and below it, the hypothalamus, a collection of nuclei that is responsible for a variety of autonomic and endocrine functions in the service of maintaining body homeostasis. There is one thalamus and one hypothalamus on each side, and they are separated by the third ventricle, which is continuous with the cerebral aqueduct of the mid- brain.

Development of the Face

The facial prominences begin to develop at the end of the fourth week. These prominences consist primarily of neural crest cell derived mesenchyme and for the most part have been introduced in the pharyngeal apparatus lecture. The five prominences include: Maxillary prominences (bilateral) Mandibular prominences (bilateral) Frontonasal prominence (single midline prominence) The nasal placodes, thickenings of surface ectoderm, appear on both sides of the frontonasal prominence. The nasal placodes invaginate to form nasal pits. Sur- rounding the nasal pits are lateral and medial nasal prominences. With further proliferation the prominences increase in size, grow medially and compress the medial nasal prominences. The upper lip is formed by the medial nasal prominences and the two maxillary prominences. The maxillary and lateral nasal prominences are separated by the nasolacrimal groove, which becomes an epithelial cord that gives rise to the nasolacrimal duct. The intermaxillary segment forms as the two medial nasal prominences fuse to- gether. The intermaxillary segment gives rise to the Philtrum of the upper lip An upper jaw component Primary palate The secondary palate is derived from the lateral palatine shelves, outgrowths of the maxillary prominences. The palatine shelves form the secondary palate. The incisive fossa is the midline landmark between the primary and secondary palate and is significant in the identification of specific types of cleft palate.

The largest of the pharynx muscles are 3 pairs of thin, concentric muscles that originate from the midline pharyngeal raphe. This thin band of connective tissue forms the posterior anchor of the pharynx and it originates from the pharyngeal tubercle at the base of the skull and extends inferiorly along the midline of the posterior wall of the pharynx.

These three muscles (superior, middle, and inferior pharyngeal constrictors) have characteristic insertions on the bony structures of the neck. The insertions of these muscles leave three pairs of "gaps" in the lateral walls of the pharynx. These are between the: 1. Base of the skull and the upper margin of the superior pharyngeal constrictor 1. Upper gap is completed by pharyngobasilar fascia. 2. Lower margin of the superior pharyngeal constrictor and the upper margin of the middle pharyngeal constrictor 2. The middle gap transmits stylohyoid ligament and the glossopharyngeal nerve (CN IX) and stylopharyngeus muscle. 3. The lower border of the hyoid bone and the upper edge of the thyroid cartilage. 3. The third gap is completed by the thyrohyoid ligament and transmits the internal laryngeal neurovascular bundle. There are several additional muscles associated with the pharynx. They are: 1. The three pharyngeal constrictors mentioned above. All three are inner- vated by the pharyngeal plexus on nerves (Netter plate 124) consisting of autonomic, glossopharyngeal and vagal fibers that form a mat or plexus on the external surface of the constrictors. 2. Stylopharyngeus 3. Salpingopharyngeus 4. Palatopharyngeus

COMPOSITION OF PHARYNGEAL ARCHES: 1. Skeletal elements. 2. Muscle elements with their associated nerve and artery. 3. Cranial nerve. 4. Arterial components The pharyngeal arches have a core of mesenchymal tissue surrounded by surface ectoderm (skin) on the outside and endodermal epithelium on the inside. Neural crest cells, originating in the neuroectoderm, have migrated into each of the phar- yngeal arches and contribute to the skeleton, connective tissue and other tissues of the head and neck region. Each pharyngeal arch contains a skeletal component, a muscle component, a cra- nial nerve component and an artery. In lecture we will go over each component with the exception of the arterial component. The artery of each arch is typically described in a heart development lecture. By the fourth week of development, the stomadeum (the primordial oral cavity) is surrounded by the first pair of pharyngeal arches.

The first pharyngeal arch has two prominences largely formed by migrating neural crest cells: Maxillary arteries 1. the maxillary prominence - the central cartilage of the maxillary promi- nence is the palatopterygoquadrate bar which will completely regress in humans 2. the mandibular prominence- the central cartilage of the mandibular prominence is Meckel's cartilage. Meckel's cartilage does not contribute to the adult mandible, instead provides the framework around which the bone of the mandible will form. Thus, most of Meckel's cartilage will regress, with the exception of the proximal portion which gives rise to the malleus, incus, sphenomandibular ligament and the anterior ligament of the malleus The adult skeletal derivatives of the first arch are the incus, malleus, anterior lig- ament of the malleus, sphenomandibular ligament -all derived from Meckel's car- tilage. Mesenchyme of the maxillary prominence gives rise to the maxilla, zygo- matic bone and the squamous portion of the temporal bone through intramembra- nous ossification. The mandible is formed by intramembranous ossification of the mesenchyme surrounding Meckel's cartilage The muscle components of the first arch are: the four muscles of mastication tensor veli palatine tensor tympani anterior belly of the digastric mylohyoid As the muscle cells of each arch migrate, they carry their nerve component with them. The cranial nerve of the first arch is the trigeminal nerve (CN V).

Infra temporal Fossa The infratemporal fossa is an anatomic space of great importance as it contains the temporomandibular joint, two major muscles of mastication, and is also a significant crossroads for neurovascular structures. Most of these nerves and vessels either enter or exit the infratemporal fossa via foramina in the skull base. Knowledge of these relationships is crucially important to neurological surgeons, neuro-otologists, and craniofacial head and neck surgeons.

The infratemporal fossa lies between the mandible and the lateral surface of the skeletal mid-face (Figure 1). Its boundaries are: Lateral: ramus of mandible Medial: lateral pterygoid plate Anterior: posterior maxilla Posterior: tympanic plate; mastoid and styloid processes Superior: inferior surface of greater wing of sphenoid Inferior: attachment of medial pterygoid muscle to mandible, near the angle of the mandible The infratemporal fossa is the location of most of the muscles of mastication. It also is a region through which numerous important neural and vascular structures pass on their way to their targets: the mandibular branch of the trigeminal nerve and its branches, the maxillary artery and many of its branches, the chorda tympani nerve and otic ganglion, and the pterygoid plexus of veins.

Here is an example of what I am talking about:

The ingestion of food is initiated by opening of the mouth (Vc and VII). Vc opens the jaw and VII parts the lips. Chewing involves moving the jaw (Vc), keeping the lips closed (VII) and movements of the tongue (XII) to keep the food in place between the teeth. Vc also senses the consistency of the food and position of the food in the mouth and thereby affects the force of contraction of the muscles of mastication. Both Vc and VII are also both involved in taste. After we chew, we swallow. This is accomplished mostly by XII, X, IX. The va- gus nerve (X) innervates the muscles of swallowing and unconsciously senses some phases of swallowing. This is aided by IX which also carries sensory infor- mation to the brain and takes part in the perception of taste and control of salivary secretions. - Mandibular and facial movements and sensations are functions of the 1st and 2nd arches (V, VII). - Pharyngeal movement and sensation involved in swallowing are func- tions of the 3rd, 4th, and 6th arches (IX— 3rd arch; X— 4th and 6th arch).

Lacrimal apparatus

The lacrimal gland is controlled by parasympathetic innervation from CN VII which takes a remarkably complex route to arrive at the lacrimal gland: The preganglionic axons travel with the nervus intermedius branch of the facial nerve to the greater petrosal nerve, then via the nerve of the pterygoid canal to arrive and synapse at the ptery- gopalatine ganglion in the pterygopalatine fossa. The postganglionic axons of the pterygopalatine ganglion then travel along the maxillary, zygo- matic and zygomaticotemporal nerves before giv- ing off a communicating branch to the lacrimal branch of the ophthalmic nerve, by which these fi- bers finally reach the lacrimal gland. The lacrimal glands are located in the superior lateral region of the orbit. The lacrimal gland has an intimate relationship with the tendon of the levator palpebrae superioris muscle. The major portion of the lacrimal gland lies above it, while a smaller portion lies be- neath it. Thus, movement of the eyelids tends to "milk" the gland, so that continuous lubrication is provided and the conjunctiva is kept moist. Blinking sweeps tears medially across the eye surface to the me- dial canthus, where a small fold of conjunctiva, the plica semi- lunaris, encloses a triangular area, the lacrimal lake. The plica functions to allow greater movement of the eyeball as otherwise the conjunctiva would attach directly to the eye and restrict move- ment. Bordering the lacrimal lake is a small lacrimal papilla with an apical punctum (hole) at the orifice of the lacrimal canaliculus (small canal). The upper and lower canaliculi drain behind the medial palpebral ligament and then join to drain into the lacrimal sac. The lacrimal sac is the blind upper end of the nasolacrimal duct, which rests in the lacrimal groove of the lacrimal and maxillary bones. The nasolacrimal duct drains into the inferior meatus of the nasal cavity.

Pterygopalatine Fossa 4

lateral wall Pterygomaxillary fissure medial wall Vertical plate of the palatine Sphenopalatine foramen Palatovaginal canal posterior wall Pterygoid process of the sphenoid Pterygoid (Vidian) canal anterior wall Maxilla Inferior orbital fissure roof Greater wing of the sphenoid Foramen rotundum floor Greater palatine canal

Larynx The laryngopharynx is so named because it encompasses the larynx anteriorly and the start of the esophagus posteriorly. It is therefore the location where the common passageway for respiration and eating and drinking is divided into a ded- icated airway (larynx and trachea) and passageway for ingested food and liquid (esophagus).

The larynx (Netter plates 79-82) is a structure composed of cartilage, bone, and associated soft tissues that is a specialized region of the superior-most trachea. It serves multiple purposes including vocalization. It is present in all land verte- brates, but in birds it is called the syrinx and has no vocal cords. Embryologically, it is derived from the mesenchyme associated with pharyngeal arches IV and VI. Also known as "the Adam's Apple" or "Voice Box," it is approximately 5 cm in length and is typically more prominent in males. It lies anterior to cervical verte- brae C3 to C6. The larynx is located anterior to the laryngopharynx. In very simple terms, the larynx serves to connect the lower pharynx with the trachea. It is an elegant apparatus of soft tissues and cartilage that along with other aspects of the respiratory tract contributes to the production of sound. Even though the great apes possess similar anatomical structures, the morphology of their tongue and pharynx prevent "humanoid" vocalizations. While most think of the larynx as the organ of vocalization, it is arguably more important as a valve. Its valvular functions are needed for assisting in rais- ing intra-abdominal pressure during micturition, defecation, coughing, laughing, parturition, and Tibetan throat singing. In addition, the larynx protects the trachea from material passing to the tra- chea during deglutition and regurgitation, while permitting the passage of air dur- ing inhalation and exhalation.

DEVELOPMENT OF THE TONGUE:

The mucous membrane of the tongue develops from two embryological sources: 1. Anterior two-thirds of the tongue develops from three swellings of mesenchyme beneath the endodermal epithelium of the first pharyngeal arch. The line of demarcation between the two parts of the tongue persists as the sulcus terminalis. The muscles of the tongue are developed from myotomes derived from occipital somites. The diverse embryological origin of the tongue explains the diverse nerve supply.

Early development of the nervous system - a review The primitive nervous system is generated in the third and fourth weeks after fertilization, when the neural plate appears as a thickening in the ectoderm overlying the notochord (PDF Fig. 2). The margins of the neural plate rise up into neural folds containing a distinct population of pluripotential cells that will become segregated into the neural crest and, in the cranial region, a number of ectodermal placodes. As the neural folds meet one another in the midline and begin to fuse, they give rise to the neural tube, which comes to lie beneath the reestablished ectoder- mal surface, flanked by paraxial mesoderm. The neural crest cells are also carried downward into the mesoderm, forming for a short time a longitudinal ridge dorsal to the neural tube (hence the name, neural crest). Placodal cells, on the other hand, remain behind as discoid clusters (placodes) in the surface ectoderm.

The neural tube gives rise to the central nervous system (CNS) - that is, to the brain and spinal cord. Its: -lumen persists as the central canal of the spinal cord and the system of brain ventricles. -wall gives rise to the neural substance of the CNS. In the spinal cord and medulla, it is soon organized into a ventral, motor area (the basal plate) and a dorsal, sensory area (the alar plate). These are demarcated by the sulcus limitans, a longitudinal groove or fur- row on either side of the central canal and the fourth ventricle. The neural crest gives rise to a wide variety of cells and tissues, including: -sensory and motor ganglion cells of the peripheral nervous system (PNS). -satellite and Schwann cells of the PNS. -chromaffin cells of the adrenal medulla. -neuromesenchyme of the head region (especially that of the branchial, or pharyngeal, arches) The ectodermal placodes, influenced by appropriate inducing stimuli, give rise to: -the nasal cavities, including sensorineural cells of the olfactory epithelium and cranial nerve I. -the inner ear, including the membranous labyrinth, its sensory recep- tors, and ganglion cells of cranial nerve VIII. -neurons in the ganglia of cranial nerves V, VII, IX, and X. -the adenohypophysis (anterior pituitary gland). -the crystalline lens of the eye.

Orbital vasculature

The ophthalmic artery is a branch of the internal carotid artery (Fig- ure 4), which enters the orbit through the optic canal beneath the optic nerve. It supplies the eyeball through the central artery of the retina. Within the orbit, it winds around the medial surface of the optic nerve in company with the nasociliary nerve. The branches of the artery correspond to the branches of the oph- thalmic division of the trigeminal nerve: ethmoidal, supratroch- lear, supraorbital, and lacrimal. Ophthalmic vein (Figure 4) The superior ophthalmic vein drains the superior regions of the orbit, eyelids, and forehead. It anastomoses with the angular vein, a branch of the facial vein. The inferior ophthalmic vein drains the inferior regions of the orbit and eyelids. It also anastomoses with the angular vein and the pterygoid plexus. The superior and inferior ophthalmic veins leave the orbit via the superior orbital fissure to drain, either separately or by one trunk, into the cavernous sinus. Clinically important: The anastomoses between the angular and ophthalmic veins may result in spread of infection from the eye and nose regions to the cavernous sinus. Inflammatory thrombosis of the cavernous sinus interferes with venous drainage of the retina, thereby resulting in en- gorgement of the retinal arteries, followed by retinal ische- mia and ultimately blindness.Because the ophthalmic, ocu- lomotor, trochlear, and abducens nerves also pass through the cavernous sinus, infection here may result in ophthal- moplegia, mydriasis (dilation of pupil), and sensory deficits in the periorbital regio

Chorda tympani nerve

This branch of VII carries taste fibers from the anterior 2/3 of the tongue and parasympathetic secretomotor fibers to the submandibular and sublingual salivary glands, as well as the mucosa on the floor of the mouth. The parasympathetic fibers synapse in submandibular ganglion in floor of mouth. This nerve passes from its origin through the skull to exit via the petrotympanic fissure in the TMJ to enter the infratemporal fossa. There it joins with the lingual nerve in the superior aspect of the fossa and rides with that nerve for the remainder of its course.

Autonomic fibers: the parasympathetic system Now that we have discussed nuclei and ganglia we can tackle the topic of auto- nomic fibers. Autonomic fibers are cranial nerve fibers associated with both nuclei and ganglia

The parasympathetic fibers innervate the following: 1. Ciliary muscle and constructor papillae muscles 2. Lacrimal and salivary glands 3. SA node of the heart 4. Glands and muscles of the gut tube as far distally as the junction between the mid and hind guts. The parasympathetic fibers originate from 4 motor nuclei in the brainstem: 1. Edinger-Westphal— CN III—Cilary ganglion: Ciliary muscle accommodation, iris, constriction 2. Superior salivatory— CN VII Gr Pet/Chord Tymp— pterygopalatine ganglion: lacrimal, nasal, palate, submandibular, sublingual glands 3. Inferior salivatory— CN IX Lesser Pet.— Otic ganglion: secretomotor parotid gland 4. Dorsal motor nucleus of the vagus nerve— CN X— cardiac and mesenteric ganglia: Heart, foregut, midgut All of these fibers originating from the parasympathetic nuclei are preganglionic fibers. This is where things get confusing. After hitching a ride with their associated cranial nerves, the fibers synapse in the autonomic ganglia.After synapsing in the parasympathetic ganglia, the postganglionic fibers hitch a ride with branches of the trigeminal nerve (V) to reach their final des- tinations. These postganglionic fibers get to their target muscles via branches of V. It's totally confusing: parasympathetic fibers have separate nuclei, they leave the brainstem via branches of various cranial nerves, synapses on gan- glia, and then catch a ride to their target muscles through branches of another cranial nerve!

The Accessory Nerve XI (SVE only) according to the traditional view, consists of cranial and spinal roots. From sep- arate origins they converge on the jugular foramen, through which they pass together. The two roots diverge again immediately outside the skull, and the cranial root blends with the Vagus nerve immediately below the inferior vagal ganglion, thus becoming its accessory. A more modern view, holds that there are no "cranial" rootlets at all, just caudal rootlets belonging to the vagus. Therefore, in terms of motor innervation in the head and neck, it is best to consider X and cranial XI as a single entity.

The spinal root, arising from the upper cervical spinal cord, as- cends through the foramen magnum to reach the jugular foramen. Af- ter parting from the cranial root high in the neck, it supplies motor fibers to Trapezius and Sternocleidomastoid via SVE.

Innervation and vasculature of the teeth

The superior and inferior alveolar arteries, branches of the maxillary artery, supply the teeth. The upper and lower teeth are innervated by the superior alveolar nerve (br. V2) and inferior alveolar nerve (br. V3), respectively.

Temporomandibular Joint (TMJ) At rest, the heads of the mandible sit in the mandibular fossae and the chin is elevated (mouth is closed) by tonic contraction of mandibular retractors and elevators (temporalis, masseter, medial pterygoid). In deep sleep, tonic contraction of retractors and elevators relaxes and gravity causes depression of mandible (mouth opens).

The temporomandibular joints are modified hinge type synovial joints where the right and left heads of the mandible articulate with the skull. These are the joints that allow movement of the mandible relative to the skull, and are the most used joints in the body. Each of these joints permits elevation and depression of the mandible as well as movements of gliding (translation) and a small amount of rotation. The articular surfaces of each joint are the mandibular fossa of the temporal bone and the head of the mandible. The entire joint is wrapped in a loose fibrous joint capsule that attaches to the margins of the temporal articular cartilage and around the neck of the mandible. In addition, the two bony articular surfaces are completely separated by an articular disc, a flexible and elastic cushion between the two bones. This disc separates the joints into superior and inferior synovial cavities (Figure 3). The superior head of the lateral pterygoid muscle attaches to the TMJ joint capsule. Excessive contraction of this muscle during yawning or otherwise widely opening the jaw may cause the muscle to spasm and the heads of the mandible to dislocate anteriorly. Alternatively, dislocation of the TMJ due to a different mechanism (e.g. sideways blow to the chin) may be difficult to reduce due to contraction of this muscle. In addition to the joint capsule, the TMJ is supported by to external ligaments: Sphenomandibular ligament: primary passive support of mandible (along with tonus of muscles of mastication). Connects spin of sphenoid to lingual of mandible. Stylomandibular ligament: thickening of capsule of parotid gland; passes from styloid process to angle of mandible

Lymphatic Drainage of the Head and Neck The thoracic duct begins in the abdomen and passes superiorly through the thorax to terminate at the venous channels in the neck.

The thoracic duct terminates in the junction between the left internal jugular and the left subclavian veins. At that junction, the thoracic duct is joined by the -Left jugular trunk (drains left side of head and neck) -Left subclavian trunk (drains upper body) -Left bronchomediastinal (variable- if present drains left thoracic struc tires) The drainage pattern on the right is similar arrangement and the between the right internal jugular vein and right subclavian vein are: Right jugular trunk (drains head and neck) Right subclavian (drains right upper extremity) Right bronchomediastinal (variable) When discussing the lymphatics of the face and scalp region it is common to in- clude the lymphatics of the neck. It is difficult to separate the regions, which in- clude the following components: Superficial nodes (around the head) Superficial cervical nodes (around the external jugular vein) Deep cervical nodes (around the internal jugular vein Five groups of superficial lymph nodes form a ring around the head and are the primary drainage system of the face and scalp. Occipital nodes Mastoid nodes Parotid and pre-auricular nodes Submandibular nodes Submental nodes Lymphatic flow from these nodes will Drain into superficial cervical nodes (occipital and mastoid) Drain to the deep cervical nodes Superficial cervical nodes These lymphatic nodes are found along the external jugular vein and send lym- phatic fluid to the deep cervical nodes. Deep cervical nodes These nodes are found along the internal jugular vein and divided into upper and lower groups. The most superior node is the jugulodigastric node, the most in- ferior is the juguloomohyoid node. The deep cervical nodes eventually receive all the lymphatic drainage from the head and neck. The lymphatic vessels from the deep cervical nodes empty into the right and left jugular trunks, which empty into the right lymphatic duct on the right side or the thoracic duct on the left. The lymphatics of the occipital region drain to occipital nodes at the base of the skull. Occipital nodes drain into superficial cervical nodes (some lymphatics of the occipital region drain directly to upper deep cervical nodes). The lymphatics from the upper scalp drain to mastoid nodes (which drain to su- perficial cervical nodes) and pre auricular and parotid nodes (parotid nodes drain to deep cervical nodes). Lymph from the lateral part of the face (including eyelids and external nose) drains to the parotid lymph nodes. Lymph from the upper lip and lateral part lower lip drains to the submandibular lymph nodes and lymph from the chin and lower lip drains to the submental lymph nodes. Lymphatic vessels from the pharynx drain into the following nodes Retropharngeal nodes Paratracheal nodes (also receives lymph from the thyroid gland) Infrahyoid node Lymph from the tongue takes four routes: Lymph form the root drains into superior deep cervical lymph nodes Lymph from the medial part of the body drains to the inferior deep cer- vical lymph nodes Lymph from the lateral part of the tongue drains to the submandibular nodes Apex and frenulum drain to submental nodes

Subclavian system - Note that all listed arteries below are paired bilateral structures The subclavian artery gives rise to a number of branches that supply structures in the neck and the head (Figure 7). Most branches supply only external structures of the H&N. The paired vertebral arteries, on the other hand, are half of the major contributors to the internal structures of the cranium (the other half being the paired internal carotid arteries).

The transverse cervical, suprascapular, and dorsal scapular arteries supply muscles in the posterior triangle of the neck. They are familiar to you from Back and Limbs and Thorax, Abdomen, and Pelvis. Inferior thyroid artery ascends to reach the thyroid gland. o It sends an inferior laryngeal artery into the larynx with the recurrent laryngeal nerve. o It gives off the ascending cervical artery to the prevertebral and anterior scalene muscles. o It also sends segmental spinal branches inward through the intervertebral foramina, supplementing those from the vertebral artery. Deep cervical artery arises from the costocervical trunk and ascends to supply the deep muscles of the back of the neck. Vertebral artery ascends through the transverse foramina of cervical vertebrae C6-C1. o Along the way it sends segmental spinal branches through the interver- tebral formina to supply the vertebral column, meninges, nerve roots, and spinal cord. o At the level of the atlas (C1), it pierces the spinal dura and enters the cranial cavity through foramen magnum. It joins the vertebral artery from the opposite side to form the basilar artery (see Circle of Willis). It is therefore a major contributor to the arterial supply of the brain.

Regions of Larynx Opening of the ventricle bordered above by the free LOWER border of the Quadrangular mem- brane becoming the false vocal fold. The ventricle is bordered BELOW by the upper free margin of conus elasticus becoming the true vocal fold. The ventricle continues laterally and above by the saccule. In the previous figure, the line indicates the level of the ventricle. Above that line to the top of the epiglottis is called the vestibule of the larynx. The space below the ventricle is called the infraglottic cavity.

The ventricles are opening on lateral sides of larynx that is formed by: Vestibular folds above Saccule, a cavity in the middle Vocal folds below. The vocal folds contain the vocal liga- tents The rima glottidis is the ap- erture created by the apposi- tion surfaces of the vocal folds. It is also called the vo- cal aperture. The aryepiglot- tic folds are the membranes between arytenoid and epi- glottis and represent the up- per free border of the quad- rangular membrane. Finally, there are two slopes or chan- nels that are formed by the larynx. The anterior aspect of the epiglottis is secured to median root of the tongue and hyoid bone by the hyoepiglottic ligament. This forms two depressions on either side of the ligament and small bits of food occasionally get stuck there. On either side of the larynx within the folds of the laryngopharynx are modest channels or grooves that direct swallowed ingesta to either side of the larynx rather than directly over the top. This is another place where sharp items occasionally become lodged.

The Arterial Supply of the Brain

There are two sources of blood to the brain. One is called the anterior circula- tion, and it derives from branches of the internal carotid, one on each side. The internal carotid branches into the anterior and middle cerebral arteries at the base of the brain - the anterior turns rostrally towards the front of the brain and the middle has a lateral trajectory. The second source is referred to as the poste- rior circulation, and it arises from the paired vertebral arteries. The vertebral arteries merge to form the basilar artery, which travels towards the front of the brain on the ventral aspect of the brainstem. When it arrives at the base of the brain, it divides into two posterior cerebral arteries. The posterior cerebral ar- teries are joined with the anterior and middle cerebral arteries in an arterial ring called the circle of Willis by two posterior communicating arteries that arise from the internal carotid. The circle is completed by an anterior communicating artery that connects the two anterior cerebral arteries. Unlike other regions of the body, the fluid in the blood cannot have unrestricted access to the brain. The neurons of the brain are very sensitive to the composition of the extracellular fluid, and so this composition must be tightly regulated and stabilized. Moreover, neurons need to be protected and isolated from neurotoxic or neuroactive substances that travel in the blood. This is the function of the blood- brain barrie

3. The Mesencephalon (Midbrain)

This division is characterized by distinct features both on its dorsal and ventral aspects. On the ventral aspect, the pons is replaced by paired cerebral peduncles. These peduncles contain bundles of axons that arise from the cerebral cortex; some of these axons end in the pons, while others continue through the pons to become aggregated as the pyramids. On the dorsal aspect of the midbrain, there are four bumps - the corpora quadrigemia or the tectum. These bumps are di- vided into a caudal pair - the inferior colliculi - and a rostral pair - the superior colliculi. The inferior colliculus is involved in audition, and the superior collicu- lus processes visual signals from the retina. The narrowing of the fourth ventricle in the metencephalon leads to a canal that travels rostrally under the tectum. This is known as the cerebral aqueduct (of Sylvius).

2. The Metencephalon

This division is characterized by two major structures. The cerebellum (little brain) is a folded structure on the dorsal aspect of the metencephalon involved in coordinating movements. The cerebellum is a sheet of cells (gray matter) folded into invaginations (sulci) and evaginations (folia) to increase surface area. On the ventral aspect of the metencephalon, the pyramids of the medulla are replaced by the pons of the metencephalon. Between the cerebellum and the pons is the fourth ventricle, a CSF-filled space. This space narrows rostrally towards the mesencephalon.

5, 7 Trigeminal Facial

V, VII (Autonomic functions in conjunction with taste and smell)

Branches of Trigeminal CNV MFLN, MPDZAI, MDPBMLAAT IX - hiatus less petrosal - otic ganglia - parotid Chords tympani goes through post and ant tympanic canaliculus

V1 SO: Meningeal N, Frontal N (Supratrochlear N Supraorbital N), Lacrimal N (W/ V2 Zygomaticotemporal/Pterygopalatine Ganglion VII + ICA), Nasociliary N (Post Ethmoid N, Ant Ethmoid N (ext/int nasal br), Infratrochlear N, Long Ciliar Sym ICA, Short Ciliary PS CNIII CG) V2 FR: Meningeal N, Pharyngeal N (Palatovaginal Canal), Descending Palatine N (Less/Gr DP), Zygomatic N (IFOF Zygomaticotemporal Lacrimal, Zygomaticofacial), Alveolar N (Post Sup Alveolar Foramina, Mid, Ant Alveolar N), Infraorbital N. (Canal to Palpebral br, Nasal br, Superior Labial br.) V3 FO: Meningeal N, Deep Temporal N, N to Pterygoids, Buccal N, Masseteric N, Lingual N (w/ Chorda Tympani to Submand Gang and Gland and Subling Gland),Inf Alveolar N (Mandibular and Mental Foramen Mental N), Auriculotemporal N, Tensor Ns (tensor tympanic, tensor veli palatini)

Internal Carotid - Subclavian system

Within the skull, the two sets of arteries that supply the brain and dura with oxy- gen-rich blood communicate freely via the Circle of Willis. This circle connects the internal carotid arterial supply with the vertebral arterial supply (Figure 8). The posterior part of the Circle of Willis is formed by the basilar artery (recall this was formed by the joining of the right and left vertebral ar- teries), which runs superiorly through the posterior cranial fossa on the anterior surface of the pons. o The vertebral/basilar arterial system supplies the upper cervical spinal cord, medulla, pons, cerebellum, and inner ear before joining the circle of Willis. The basilar artery ends by dividing into left and right posterior cerebral arteries. The posterior communicating artery connects the posterior cerebral arteries to the middle cerebral artery of the + branches of the internal carotid system. Recall that the internal carotid gives off the middle and anterior cerebral arteries. The circle is completed by the anterior communicating artery, which connects the two anterior cerebral arteries.

9,10,11 Hypoglossal, Vagus, Spinal Accessory

X, IX, XI (Swallowing)

Lateral Aspect of the Skull 2

Zygomaticotemporal foramen (inside temporal arch) Posterior superior alveolar foramina (above teeth in back), Temporal fossa, Temporal lines (superior, inferior curves on outside), Pterion - includes frontal, parietal, squamous temporal, and greater wing of splenoid

The laryngeal apparatus has two principle synovial joints that allow the larynx to change the shape and flexibility of the vocal ligament.

a) Cricothyroid joint: permits a "hinging" of thyroid cartilage on the cricoid like the visor of a helmet. Permits an anterior-posterior rock- ing motion of the thyroid cartilage relative to the cricoid cartilage. Seen in front b) Crico-arytenoid joint: permits a compound motion of the arytenoids. Anterior - posterior sliding, lateral to medial sliding and rotation about the long axis of the arytenoid cartilages.

The Cerebral Hemispheres

a. Rotation Disproportionate growth between the frontal and the temporal poles of the cere- bral hemispheres causes the cerebral hemispheres to appear as if they have rotated, forming a c-shape about a central axis. This central axis is called the insular cor- tex, which is eventually overgrown by the expanding cerebral hemispheres and hidden from view. In the developed brain the cerebral hemispheres cover not only the diencephalon, but also the mesencephalon and the majority of the metenceph- alon. b. C-Shaped Structures The rotation of the cerebral hemispheres is of great importance to the organization of the adult telencephalon. As the hemispheres grow, many structures take on a c- shaped configuration, following the trajectory of the temporal poles as they move first in a caudal and then in a dorsal-rostral direction. One embryonic structure that follows this trajectory is the lamina terminalis. The lamina terminalis begins as a thin midline membrane that separates the two budding telencephalic vesicles at the most rostral aspect of the developing CNS (Fig. 3; Fig. 4). Important fiber bundles called commissures use the lamina terminalis as a bridge to travel be- tween the two cerebral hemispheres. Additional structures that adopt the c-shaped configuration include, but are not limited to, the lateral ventricles, various fiber bundles, and components of the basal ganglia.

Venous drainage is via veins running in parallel with these arteries. The facial vein is the major vein that drains the face. It is formed at the medial aspect of the orbit as the supratrochear vein and the supra-orbital vein merge together to form the angular vein. The facial vein is a continuation of the angular vein past the inferior margin of the orbit.

a. The superficial temporal & maxillary veins join to form the retromandibular vein, which then splits into anterior and posterior branches. b. The facial vein usually joins the anterior division of the retromandibular vein to form the common facial that then drains into the internal jugular vein. Blood Supply to the scalp is from branches of the three branches of the ECA and from the supratrochelar and supra-orbital branches of the internal carotid artery. From the external carotid arteries: Posterior auricular artery Occipital artery Superficial temporal artery The veins draining the scalp form a similar pattern.

The Vestibulocochlear Nerve VIII (SA only!) balance and cochlea hearing

carries SA fibers from sensory hair cells of the vestibular labyrinth (balance) and the cochlea (hearing).

The Olfactory Nerve SA The relationship between the olfactory nerves and the meninges is of clinical importance.

carries SA fibers from the olfactory epithelium in the lining of the roof of the nasal cavity The olfactory neurons are unique in that they also function as the primary receptors for the sense of smell. Each cell possesses a peripheral or sensory process (dendrite) and a central or neural process (axon). The sensory den- dritic processes bear modified cilia projecting into the fluid layer cov- ering the surface of the olfactory mucosa. The central axonal processes are collected into bundles that make up the olfactory nerves themselves. These pass upwards through holes in the cribriform plate of the ethmoid bone to end in the olfactory bulb, an extension of the forebrain. The olfactory tract, connecting the olfactory bulb with the cerebral hemisphere, is not to be confused with the olfactory nerve. The subdural space is prolonged around the bundles of olfactory nerve fibers as they pass through the perforations in the cribriform plate. Consequently, the space is continuous with the connective tissue compartment beneath the nasal epithelium, providing a po- tential route for spread of infections. The subarachnoid space continues for some distance along the nerves into the passageways through the cribriform plate. There- fore, fractures of the plate may result in leakage of cerebrospinal fluid into the nasal cavity (Cerebrospinal rhinorrhea). The subarachnoid space also communicates with tissue spaces and lymphatics in the connective tissue sheaths surrounding bundles of olfactory nerve fibers. This arrangement is thought (but not proven) to provide a pathway for spread of nasopharyngeal infections to the meninges and brain.

The Optic Nerve II SA

carries SA fibers, axons of the retinal gan- glion cells of the eye.Because the neural retina develops as an outgrowth of the wall of the neural tube, the nerve is really a tract of the brain, and it is covered by meninges as far as the back of the eyeball. Upon entering the middle cranial fossa through the optic canal, the nerve exchanges its fibers from the nasal half of the retina with those in the contralateral nerve. The crossing of these fibers, carrying information from the temporal visual fields, forms the optic chiasm, located directly in front of the pituitary gland. The meningeal coverings of the optic nerve are clinically significant. Because the subarachnoid space surrounds the nerve throughout its length, increases in intracranial pressure will push the retinal end of the nerve ("head" of the optic nerve, or "optic disk") for- ward into the back of the eye, a condition visible with the ophthal- moscope. Furthermore, tumors (meningiomas) can arise from the meningeal sheath within the bony optic canal. These may compress the nerve and accompanying blood supply to the neural retina, pro- ducing complete unilateral blindness. Proximity of the optic chiasm and the pituitary gland also can be significant. Compression of the chiasm by an enlarging pituitary tumor causes a unique type of blindness. Input is blocked from the nasal half of each retina. These, however, perceive the temporal visual fields because the pupil/lens complex acts as a pinhole camera and inverts the image before it falls on the retina. Thus, the patient reports loss of vision in the temporal half of both visual fields - a condition termed bi-temporal hemianopsia.

The Oculomotor Nerve III GSE(motor to all but SO/LR eye muscles) GVE (parasympathetic ciliary ganglion)

conveys GSE fibers that provide motor innervation to all but two of the extraocular muscles responsible for moving the visual axis. It also carries preganglionic parasympathetic GVE fibers to the cells of the ciliary ganglion.

The Glossopharyngeal Nerve IX (5 but GSE!!) GVE (otic ganglion),GVA (carotid body/sinus), GSA (snese post tongue, pharynx, aud tube, mid ear, inner ear, exteroceptive of facial), SA (valuate papillae + post taste), SVE (stylopharyngess br 3)

mainly carries poorly localized GSA general sensation (pain, temper- ature, touch, and pressure) from the posterior part of the tongue (glos- sus) and the pharynx, but also from the auditory tube (tympanic, Eu- stachian, or pharyngotympanic tube), middle ear cavity, and inner sur- face of the eardrum. Other GSA fibers return exteroceptive sensation from roughly the same small area of skin supplied by the Facial nerve. The glossopharyngeal nerve also contains four other modalities, including: -GVE preganglionic parasympathetic fibers innervating cells of the otic ganglion. -GVA fibers carrying interoceptive fibers from the carotid body and sinus. -SA fibers returning from taste buds of the vallate papillae and posterior part of the tongue. -SVE fibers to the only striated muscle (stylopharyngeus) derived from the third branchial arch.

General visceral efferent (GVE) autonomic signals require two neurons (pre- and postganglionic) to bridge the gap between CNS and the pe- ripheral target. GVE: 3, 7, 9, 10

provide motor innervation to cardiac muscle, smooth muscle, and glands. A two-neuron chain is required in both sympathetic and parasympathetic pathways. Pregangli- onic cell bodies are located in the ventrolateral gray matter of the spinal cord (segments T1-L2; S2-S4) and in brainstem nuclei associated with cra- nial nerves III, VII, IX, and X. Their axons pass outward through appro- priate spinal and cranial nerves to sympathetic or parasympathetic ganglion cells (synapse). Ganglion cells send their postganglionic axons out to reach peripheral targets.

The Hypoglossal Nerve XII (GSE only)

reaches the tongue (glossus) from below. It supplies GSE fibers to all intrinsic and extrinsic tongue muscles except Palatoglossus, which receives branchial motor (SVE) fibers from X/XI The hypoglossal nerve forms a plexus with the ventral rami of the first three cervical spinal nerves C1C2C3 Branches appear to leave the hypoglossal nerve to supply the gen iohyoid and thyrohyoid muscles, but these actually contain somatic motor (GSE) and sensory (GSA) fibers belonging to the C1 spinal nerve. Additional fibers from C1 leave the hypoglossal nerve as the superior limb of the ansa cervicalis, through which they reach infrahyoid muscles in the anterior triangle of the neck. The ansa, or loop, is completed by its inferior limb, a bundle of fibers from the communication between the C2 and C3 ventral rami. Branches are given off from the loop to supply superior belly of omohyoid (C1), sternohyoid (C1, C2, C3), sternothyroid (C1, C2, C3), and inferior belly of omohyoid (C2, C3). Therefore, intracranial lesions of the hypoglossal nerve affect the tongue but spare the hyoid muscles. However, lesions of the nerve in the neck as it descends toward the hyoid bone affect both tongue and certain of the hyoid muscles. Neck = neck + hyoid issue intracranial: tongue not hyoid because C2,C3 add onto nasa cervicalis

Nasal Cavity 3

roof Nasal, ethmoid, palatine, and sphenoid bones x, Cribriform plate and foramina for olfactory nerves x, Entrance of the sphenoidal sinus x lateral wall (intact) Maxilla, lacrimal,and ethmoid bones; vertical plate of the palatine bone!! x, Nasal conchae (turbinates) - superior, middle, inferior x, Nasal meatus- superior, middle, inferior x, Sphenopalatine foramen (ant of ppt) lateral wall (conchae removed) Frontonasal duct (under superior meatus), Infundibulum (?), Hiatus semilunaris (?), Ethmoidal bulla (?), Maxillary hiatus (?), Nasolacrimal canal medial (septal) wall Vertical plate of the ethmoid connects to vomer, Grooves for olfactory nerves (?), Groove for the nasopalatine nerve (on the nasal septum) floor Palatine process of the maxilla x; horizontal plate of the palatine x, Incisive canal x anterior wall Anterior nasal aperture x posterior wall Posterior nasal aperture (china) x

Special visceral efferent (SVE), or branchial efferent, neurons like gse, SVE: 5,7,9,10,11

rovide motor outflow to voluntary, striated muscles of the jaws, face, palate, lar- ynx, pharynx, and upper esophagus. Cell bodies are located in brainstem nuclei and the upper cervical spinal cord. Their axons pass out through cranial nerves V, VII, IX, X, and XI. Muscles receiving this type of in- nervation cannot be differentiated histologically or functionally from those receiving general somatic efferent fibers. The distinction rests on their embryological origin. These can be designated as Special Visceral Efferent, SVE, Branchial Motor, or Branchial Efferent fibers. RULE: Special visceral efferent fibers are distributed only to branchi- omeric striated muscles - that is to muscles developed within the bran- chial arches (see PDF Figures 14 and 15). Musculature derived directly from paraxial or lateral plate mesoderm receives a general somatic motor innervation.

The Trigeminal Nerve V Ophthalmic, Maxillary, Mandibular GSA (sense face) and SVE (muscles of mastication 1st branch)

the great somatic sensory nerve of the anterior head and face, carries ex- teroceptive and proprioceptive GSA fibers. It is tripartite, having three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3). The nerve also contains SVE fibers providing motor innervation to striated musculature derived from the first branchial arch, including the muscles of mastication. Postganglionic GVE axons of parasympathetic and sympathetic ganglion cells are added to certain peripheral branches of all three di- visions of the Trigeminal nerve for distribution to glands and smooth muscle.

Internal Aspect of the Skull Base Grooves for Middle meningeal artery (medial end of foramen oval to lat), Grooves for Superior sagittal sinus (sag suture inner skull), Grooves for Transverse sinus (transverse ridge inner skull), Grooves for Sigmoid sinus (more narrow from rocket ship), Grooves for Confluence of the sinuses (something in back?) Anterior Cranial Fossa Foramen cecum (front most foramen infant of cribriform), Cribriform plate and foramina for olfactory nerves x Middle Cranial Fossa Sphenoid bone, Optic canal (cranial entrance x), Chiasmatic groove (sulcus grove between front of christmas seat), Superior orbital fissure x, Foramen rotundum (upper foramen right upper optic canal), Foramen ovale (larger hole), Foramen spinosum (smaller hole), Carotid groove (on the body of the sphenoid sides of sella turcica), Temporal bone (petrous part), Tegmen tympani (roof of middle ear cavity), Carotid canal (cranial, internal, superior entrance right before foramen lacer) from petrous apex Posterior Cranial Fossa Temporal bone (petrous part), Internal auditory (acoustic) meatus (and entrance to the Facial canal) Occipital bone Jugular foramen (below in aud meatus), Hypoglossal canal (small canal almost inside rocket ship), Condylar canal (posterior condylar canal, lower part of rocket ship) Petrosphenoidal fissure (lines making up the foramen lacrerum), Petrooccipital fissure (connects foramen lacerum to jugular foramen) Grooves for: Superior petrosal sinus (lower spine coming off sella turcica), Inferior petrosal sinus (??) Middle Cranial Fossa Trigeminal fossa (right behind foramen lacerumfor the trigeminal ganglion), Temporal bone (petrous part, middle cranial fossa), Hiatus and groove for the greater petrosal nerve, Hiatus and groove for lesser petrosal nerve (closer to foramen spinousum) Sphenoid bone (body at base of carotid groove), Entrance to pterygoid (Vidian) canal from middle cranial fossa- unsure!

xAnterior cranial fossa xMiddle cranial fossa xPosterior cranial fossa xHypophyseal fossa (pituitary fossa, sella turcica) Clinoid processes, anterior and posterior (sharp end of wagon, back end of wagon on seat) Dorsal sell (santa christmas seat of sella turcica) Tubercular sell (tubercle handles for saints christmas seat) xFrontal bone Ethmoid bone Crista galli (middle part of cribriform plate) Cribriform plate (net part) Sphenoid bone Lesser wing (part that makes whole front of christmand saddle) Body (central part) Greater wing (lower wing) Temporal bone Squamous part (thin flat part behind zygomatic spine going up) Petrous part (part near ridge of temporal) Petrous ridge (the ridge) Foramen lacer (big hole right next to sella turcia Not a passageway, landmark only!) Occipital bone Clivis (front rocket ship) Foramen magnum