Cranial Nerves
Fila Olfactoria
(bundles of olfactory axons) Once the axon penetrates through the basement membrane, it joins other non-myelinated processes to form the ____________
Recurrent laryngeal nerve
(right side only) - Hooks underneath the right subclavian artery, then ascends towards to the larynx. It innervates the majority of the intrinsic muscles of the larynx.
Extrinsic muscles of the tongue
-Genioglossus (makes up the bulk of the tongue) -Hyoglossus -Styloglossus
Intrinsic muscles of the tongue
-Superior longitudinal -Inferior longitudinal -Transverse -Vertical
Origin of the cranial nerves
12 cranial nerves in total. The olfactory nerve (CN I) & optic nerve (CN II) originate from the cerebrum. Cranial nerves III - XII arise from the brain stem. They can arise from a specific part of the brain stem (midbrain, pons or medulla), or from a junction between 2 parts
Oculomotor Nerve Lesion
3 main anatomical causes of an oculomotor nerve lesion: 1.Increasing intracranial pressure - this compresses the nerve against the temporal bone. 2.Aneurysm of the posterior cerebral artery. 3.Cavernous sinus infection or trauma. Oculomotor nerve is the major nerve supplying the ocular & extraocular muscles. The clinical signs of CN III injury are all associated with the eye: -Ptosis (drooping upper eyelid) - due to paralysis of the levator palpabrae superioris. -Eyeball resting in the 'down & out' location - due to the paralysis of the superior, inferior & medial rectus, & the inferior oblique. The patient is unable to elevate, depress or adduct the eye. -Dilated pupil - due to the unopposed action of the dilator pupillae muscle.
Abducens Nerve
6th paired cranial nerve. It has a purely somatic motor function
Lateral Rectus Muscle of eye
Abducens nerve innervates a single muscle - the lateral rectus, one of the muscles of oculomotion. This muscle takes its origin from the common tendinous ring, & acts to abduct the eyeball (i.e. to rotate the gaze away from the midline)
Sensory Modalities
Afferent
Facial nerve extracranial course
After exiting the skull, the facial nerve turns superiorly to run just anterior to the outer ear. The 1st extracranial branch to arise is:posterior auricular nerve. It provides motor nn to the some muscles around the ear. Immediately distal to this, motor branches are sent to the posterior belly of the digastric muscle & to the stylohyoid muscle. The main trunk of the nerve, now termed the motor root of the facial nerve, continues anteriorly & inferiorly into the parotid gland (note - the facial nerve does not contribute towards the nn of the parotid gland).
Optic Canal
After its formation, the nerve leaves the bony orbit via the _________, a passageway through the sphenoid bone. It enters the cranial cavity, running along the surface of the middle cranial fossa (in close proximity to the pituitary gland)
Course of facial nerve
Anatomically, course of facial nerve can be divided into 2 parts: Intracranial - the course of the nerve through the cranial cavity, & the cranium itself. Extracranial - the course of the nerve outside the cranium, through the face & neck
Palsy of the Abducens nerve
Any pathology which leads to downward pressure on the brainstem (e.g. brain tumour, extradural haematoma) can lead to the nerve becoming stretched along the clivus of the skull. Wernicke-Korsakoff syndrome (caused by thiamine deficiency & generally seen in alcoholics) is a rare cause of sixth nerve palsy. Other causes of abducens nerve damage include diabetic neuropathy & thrombophlebitis of the cavernous sinus - in these cases, it is rare for the abducens nerve to be affected in isolation. Patients will present with diplopia & a medially rotated eye which cannot be abducted past the midline. The patient may attempt to compensate by rotating their head to allow the eye to look sideways.
Posterior Auricular Nerve
Ascends in front of the mastoid process, & innervates the intrinsic & extrinsic muscles of the outer ear. It also supplies the occipital part of the occipitofrontalis muscle.
Sensory Root
At the level of the pons, the sensory nuclei merge to form a ________. The motor nucleus continues to form a motor root. These roots are analogous to the dorsal & ventral roots of the spinal cord
Carotid sinus nerve
At the level of the stylopharyngeus, the ________ arises. It descends down the neck to innervates both the carotid sinus & carotid body, providing information regarding blood pressure & oxygenation respectively
Trapezius
Attachments - Runs from the base of the skull & the spinous processes of the C7-T12 vertebrae to lateral third of the clavicle & the acromion of the scapula. Actions - It is made up of upper, middle & lower fibres. Upper fibres of the trapezius elevate the scapula & rotate it during abduction of the arm. The middle fibres retract the scapula & the lower fibres pull the scapula inferiorly
Sternocleidomastoid
Attachments - Runs from the mastoid process of the temporal bone to the manubrium (sternal head) & medial third of the clavicle (clavicular head). Actions - Lateral flexion & rotation of the neck when acting unilaterally, & extension of the neck at the atlanto-occipital joints when acting bilaterally.
Optic Radiation
Axons from the LGN then carry visual information via a pathway known as the ________. The pathway itself can be divided into: -upper optic radiation -lower optic radiation
Motor branches of facial nerve
Between the stylomastoid foramen, & the parotid gland, 3 more motor branches are given off: 1. Posterior Auricular Nerve 2. Nerve to Posterior Belly of Digastric muscle 3. Nerve to the stylohyoid muscle
Cerebellopontine angle
Both sets of fibres combine in the pons to form the vestibulocochlear nerve. The nerve emerges from the brain at the _________
Nerve to stapedius
Branches of the facial nerve are responsible for innervating many of the muscles of head& neck. All these muscles are derivatives of the 2nd pharyngeal arch. The 1st motor branch arises within the facial canal; the nerve to stapedius. The nerve passes through the pyramidal eminence to supply the stapedius muscle in the middle ear
Olfactory Nerve
CN I
Glossopharyngeal nerve
CN IX, is the ninth paired cranial nerve
Trigeminal Nerve
CN V, is the fifth paired cranial nerve. It is also the largest cranial nerve
Facial Nerve
CN VII -Derivative of 2nd pharyngeal arch
Vagus nerve cardiac innervation
Cardiac branches arise in the thorax, conveying parasympathetic innervation to the sino-atrial & atrio-ventricular nodes of the heart These branches stimulate a reduction in the resting heart rate. They are constantly active, producing a rhythm of 60-80 beats per minute. If the vagus nerve was lesioned, the resting heart rate would be around 100 beats per minute
Sphincter pupillae
Constricts the pupil, reducing the amount of light entering the eye
Ciliary muscles
Contracts, causes the lens to become more spherical, & thus more adapted to short range vision
Motor Modalities
Efferent
Otic Placode
Embryologically derived from the ________ (a thickening of the ectoderm layer), which also give rise to the glial cells which support the nerve
Optic Vesicle
Embryologically, the optic nerve is developed from the _________, an outpocketing of the forebrain. Thus, the entirety of the nerve can be considered part of the CNS & as a consequence, examining the optic nerve (usually performed via ophthalmoscopy) enables an assessment of intra-cranial health to be made
Extracranial lesions
Extracranial lesions occur during the extracranial course of the facial nerve (distal to the stylomastoid foramen). Only the motor function of the facial nerve is affected, resulting in paralysis or severe weakness of the muscles of facial expression. There are various causes of extracranial lesions of the facial nerve: Parotid gland pathology - e.g a tumor, parotitis, surgery. Infection of the nerve - particularly by the herpes virus. Compression during forceps delivery - the neonatal mastoid process is not fully developed, & does not provide complete protection of the nerve. Idiopathic - If no definitive cause can be found, the disease is termed Bell's palsy.
Internal Acoustic Meatus
Facial (CNVII) Vestibulococchlear (CN VIII)
Stylomastoid foramen
Facial nerve then exits the facial canal (& the cranium) via the __________. This is an exit located just posterior to the styloid process of the temporal bone.
Basal Cells
Form the new stem cells from which the new olfactory cells can develop
Nerve of the pterygoid canal
From here, its travels across (but not through) the foramen lacerum, combining with the deep petrosal nerve to form the ___________
Jugular Foramen
Glossopharyngeal (CN IX) Vagus (CN X) Accessory (CN XI)
Parasympathetics of the glossopharyngeal nerve
Glossopharyngeal nerve provides parasympathetic nn to the parotid gland. These fibers originate in the inferior salivatory nucleus of CN IX. These fibres travel with the tympanic nerve to the middle ear. From the ear, the fibres continue as the lesser petrosal nerve, before synapsing at the otic ganglion. The fibres then hitchhike on the auriculotemporal nerve to the parotid gland, where they have a secretomotor effect.
Hypoglossal Canal
Hypoglossal (CN XII)
Superior and Inferior Ganglia
Immediately outside the jugular foramen lie 2 ganglia (collections of nerve cell bodies) known as the superior & inferior (or petrous) ganglia - they contain the cell bodies of the sensory fibres in the glossopharyngeal nerve
Trigeminal ganglion
In middle cranial fossa, the sensory root expands into the ________. A ganglion (pl. ganglia) refers to a collection of the nerve cell bodies outside the CNS. The trigeminal ganglion is located lateral to the cavernous sinus, in a depression of the temporal bone known as the trigeminal cave.
Terminal branches of the vagus nerve
In the abdomen, the vagal trunks terminate by dividing into branches that supply the esophagus, stomach & the small & large bowel (up to the splenic flexure)
Right & Left Vagus nerves
In the neck, vagus nerve passes into the carotid sheath, travelling inferiorly with the internal jugular vein & common carotid artery. At the base of the neck, the right & left nerves have differing pathways
Posterior vagal trunk
In the thorax, the right vagus nerve forms the _____________, & the left forms the anterior vagal trunk. Branches from the vagal trunks contribute to the formation of the esophageal plexus, which innervates the smooth muscle of the esophagus
Inferior branch of oculomotor nerve
Inferior rectus - Depresses the eyeball Medial rectus - Adducts the eyeball Inferior oblique - Elevates, abducts & laterally rotates the eyeball
Vestibulo-ocular reflex
Information about the position of the head is used to coordinate balance & the vestibulo-ocular reflex. The vestibulo-ocular reflex (aka oculocephalic reflex) allows images on the retina to be stabilized when the head is turning by moving the eyes in the opposite direction. It can be demonstrated by holding one finger still at a comfortable distance in front of you & twisting your head from side to side whilst staying focused on the finger
Nerve to the stylohyoid muscle
Innervates a suprahyoid muscle of the neck. It is responsible for raising the hyoid bone
Nerve to posterior belly of digastric muscle
Innervates a suprahyoid muscle of the neck. It is responsible for raising the hyoid bone.
Muscles of the larynx
Innervation to the intrinsic muscles of the larynx is achieved via the recurrent laryngeal nerve & external branch of the superior laryngeal nerve. Recurrent laryngeal nerve: Thyro-arytenoid Posterior crico-arytenoid Lateral crico-arytenoid Transverse & oblique arytenoids Vocalis External laryngeal nerve: Cricothyroid
Intracranial lesions
Intracranial lesions occur during the intracranial course of the facial nerve (proximal to the stylomastoid foramen). The muscles of facial expression will be paralysed or severely weakened. The other symptoms produced depend on the location of the lesion,& the branches that are affected: Chorda tympani - reduced salivation & loss of taste on the ipsilateral 2/3 of the tongue. Nerve to stapedius - ipsilateral hyperacusis (hypersensitive to sound). Greater petrosal nerve - ipsilateral reduced lacrimal fluid production. The most common cause of an intracranial lesion of the facial nerve is middle ear pathology - such as a tumor or infection. If no definitive cause can be found, the disease is termed Bell's palsy.
Dorello's Canal
It then enters the subarachnoid space & pierces the dura mater to run in a space known as __________
Visceral Sensation of vagus nerve
Laryngopharynx - via the internal laryngeal nerve. Superior aspect of larynx (above vocal folds) - via the internal laryngeal nerve. Heart - via cardiac branches of the vagus nerve. Gastro-intestinal tract (up to the splenic flexure) - via the terminal branches of the vagus nerve.
Disorders of vagus nerve
Lesions to the CN X are rare. A lesion to the pharyngeal branches can lead to dysphagia (difficulty swallowing) due to the involvement with the muscles of the pharynx. As CN X innervates the Palatopharyngeus & Salpingopharyngeus muscles a lesion here will cause the Palatoglossal arch to drop leading to Uvula deviation away from the affected side. The CN IX is sensory to the oropharynx & laryngopharynx with CN X being the motor efferents involved in the Gag reflex therefore a lesion in this area will cause a loss of the Gag reflex. Once upon a time a Vagotomy could be done to reduce excess stomach acid production. However with advancements in pharmacological therapy this is no longer necessary.
Foramen Ovale
Mandibular (CNV3)
Disorders of Vagus nerve
Many pharmacological agents can be used to potentiate vagal tone on the heart therefore slowing the heart rate. Beta-blockers, muscarinic agonists & cardiac glycosides such as Digoxin are just a few that can be used. Vasovagal syncope can ensue during a period of emotional stress for example causing a sudden drop in blood pressure & heart rate. Further to this a carotid massage can compress the carotid sinus leading to the perception of a high blood pressure. This will cause CN X to increase its firing leading to a decreased activity of the SA node & AV node. Overall a decreased rate & strength of contraction will ensue & the person may experience syncope. Many congenital heart defects such as a patent ductus arteriosus can irritate the left recurrent laryngeal nerve, leading to dysphonia (hoarse voice)
Foramen Rotundum
Maxillary (CNV2)
Vagus nerve muscle innervation
Most of the muscles of the pharynx are innervated by the pharyngeal branches of the vagus nerve: Superior, middle & inferior pharyngeal constrictor muscles Palatopharyngeus Salpingopharyngeus
Inferior Branch of oculomotor nerve
Motor innervation to the inferior rectus, medial rectus & inferior oblique. Parasympathetic fibres to the ciliary ganglion, which ultimately innervates the sphincter pupillae & ciliary muscles
Superior Branch of oculomotor nerve
Motor innervation to the superior rectus & levator palpabrae superioris. Sympathetic fibres run with the superior branch to innervate the superior tarsal muscle.
Oculomotor Nerve motor
Motor: Innervates a number of the extraocular muscles
Facial nerve
Motor: Innervates muscles of facial expression, posterior belly of the digastric, stylohyoid & stapedius muscles. Sensory: None. Special Sensory: Provides special taste sensation to the anterior 2/3 of the tongue. Parasympathetic: Supplies many of the glands of the head & neck, including the submandibular, sublingual, nasal, palatine, lacrimal & pharyngeal gland.
Special visceral motor (SVM)
Muscles derived from pharyngeal arches
Oculomotor Nerve Sympathetic
No direct function, but sympathetic fibres run with the oculomotor nerve to innervate the superior tarsal muscle
Glossopharyngeal nerve descent
Now extracranial, the glossopharyngeal nerve descends down the neck, anterolateral to the internal carotid artery. At the inferior margin of the stylopharyngeus, several branches arise to provide motor innervation to the muscle
Superior Orbital Fissure
Oculomotor (III) Trochlear (IV) Ophthalmic (CNV1) Abducens (CN VI)
Cribiform Plate
Olfactory (I)
Olfactory Bulb
Once in the cranial cavity, the fibres enter the ________, which lies in the olfactory groove, within the anterior cranial fossa
Motor of trigeminal nerve
Only the mandibular branch of CN V has motor fibres. It innervates the muscles of mastication: medial pterygoid, lateral pterygoid, masseter & temporalis. The mandibular nerve also supplies other 1st pharyngeal arch derivatives: anterior belly of digastric, tensor veli palatini & tensor tympani
Optic Canal
Optic (II)
Nasal Glands
Parasympathetic fibres are also carried to the mucous glands of the nasal mucosa. Post-ganglionic fibres travel with the nasopalatine & greater palatine nerves (branches of V2)
Oculomotor Nerve Parasympathetic
Parasympathetic: Supplies the sphincter pupillae & ciliary muscles of the eye
Trigeminal ganglion divisions
Peripheral aspect of the trigeminal ganglion gives rise to 3 divisions: ophthalmic (V1), maxillary (V2) & mandibular (V3)
Olfactory Nerve Processes
Peripheral olfactory processes (receptors) in the olfactory mucosa. Central processes that return the information to the brain
Lacrimal Gland
Post ganglionic fibres from the pterygopalatine ganglion (derived from the facial nerve), travel with the zygomatic branch of V2 & then join the lacrimal branch of V1. The fibres supply parasympathetic innervation to the lacrimal gland
Lacrimal Gland
Post ganglionic fibres from the pterygopalatine ganglion (derived from the facial nerve), travel with the zygomatic branch of V2 & then join the lacrimal branch of V1. The fibres supply parasympathetic innervation to to the lacrimal gland.
parotid gland
Post-ganglionic fibres from the otic ganglion ganglion (derived from the glossopharyngeal nerve, CN IX), travel with the auricotemporal branch of the V3 to innervate the parotid gland
Submandibular & Sublingual Glands
Post-ganglionic fibres from the submandibular ganglion (derived from the facial nerve), travel with the lingual nerve to innervate these glands.
Pharyngeal branches of vagus nerve
Provides motor innervation to the majority of the muscles of the pharynx & soft palate
Optic Nerve
Second cranial nerve (CN II)
Motor & Sensory of Mandibular nerve
Sensory supply: Mucous membranes & floor of the oral cavity External ear Lower lip Chin Anterior 2/3 of the tongue (only general sensation; special taste sensation supplied by the chorda tympani, a branch of the facial nerve) Lower molar, incisor & canine teeth & associated gingiva Motor Supply: Muscles of mastication; medial pterygoid, lateral pterygoid, masseter, temporalis Anterior belly of the digastric muscle & the mylohyoid muscle (these are suprahyoid muscles) Tensor veli palatini Tensor tympani
General somatic motor (GSM)
Skeletal Muscles
General visceral motor (GVM)
Smooth muscles of gut & autonomic motor
Superior laryngeal nerve
Splits into internal & external branches. The external laryngeal nerve nn the cricothyroid muscle of the larynx. The internal laryngeal provides sensory nn to the laryngopharynx & superior part of the larynx.
Facial Canal
Still within the temporal bone, the roots leave the internal acoustic meatus, & enter into the facial canal. The canal is a 'Z' shaped structure. Within the facial canal, 3 important events occur: Firstly the 2 roots fuse to form the facial nerve. Next, the nerve forms the geniculate ganglion Lastly, the nerve gives rise to the greater petrosal nerve (parasympathetic fibres to glands), the nerve to stapedius (motor fibres to stapedius muscle),& the chorda tympani (special sensory fibres to the anterior 2/3 tongue)
Superior branch of oculomotor Nerve
Superior rectus - Elevates the eyeball Levator palpabrae superioris - Raises the upper eyelid
Sustentacular Cells
Tall cells for structural support. These are analogous to the glial cells located in the CNS
Sensory of trigeminal nerve
The 3 terminal branches of CN V innervate the skin, mucous membranes & sinuses of the face. Their distribution pattern is similar to the dermatome supply of spinal nerves (except there is little overlap in the supply of the divisions)
Medulla Oblangata
The glossopharyngeal nerve originates in the ________ of the brain. It emerges from the anterior aspect of the medulla, moving laterally in the posterior cranial fossa
Basilar membrane
The magnitude of the sound determines how much the membrane vibrates & thereby how often action potentials are triggered. Louder sounds cause the ________ to vibrate more, resulting in action potentials being transmitted from the spiral ganglia more often,& vice versa. The frequency of the sound is coded by the position of the activated inner hair cells along the basilar membrane
Mandibular Division
The motor root passes inferiorly to the sensory root, along the floor of the trigeminal cave. Its fibres are only distributed to the __________
Branches of glossopharyngeal nerve
The nerve enters the pharynx by passing b/w the superior & middle pharyngeal constrictors. Within the pharynx, it terminates by dividing into several branches - lingual, tonsil & pharyngeal
Superior Orbital Fissure
The nerve leaves the cranial cavity via the ________. At this point, it divides into superior & inferior branches. Once within the orbital cavity, both branches innervate accessory structures of the eye
Superior Orbital Fissure
The nerve travels through the cavernous sinus at the tip of the petrous temporal bone, before entering the orbit of the eye through the _________
Trochlear Nerve
(CN IV) the fourth paired cranial nerve. The smallest cranial nerve (by # of axons), yet has the longest intracranial course. Has a purely somatic motor function
Lateral Geniculate Nucleus
(LGN) Each optic tract travels to its corresponding cerebral hemisphere to reach the ____________, a relay system located in the thalamus; the fibres synapse here
Parasympathetic of Trigeminal nerve
The post-ganglionic neuron of parasympathetic ganglia travel with branches of the trigeminal nerve. (But note that CN V is NOT part of the cranial outflow of PNS supply)
Trochlea
The tendon of the superior oblique is tethered by a fibrous structure known as the ________, giving the nerve its name. Although the mechanism of action of the superior oblique is complex, in clinical practice it is sufficient to understand that the overall action of the superior oblique is to depress & intort the eyeball
vestibulocochlear nerve components
The vestibular & cochlear portions of the vestibulocochlear nerve are functionally discrete, & so originate from different nuclei in the brain
Otolith organs
The vestibular apparatus senses changes in the position of the head in relation to gravity. The vestibular hair cells are located in the otolith organs (the utricule & saccule), where they detect linear movements of the head, as well as in the 3 semicircular canals, where they detect rotational movements of the head. The cell bodies of the vestibular nerve are located in the vestibular ganglion which is housed in the outer part of the internal acoustic meatus
Cribiform Plate
They then enter the cranial cavity through the _________ of the ethmoid bone - the roof of the nasal cavity
Oculomotor Nerve
Third Cranial Nerve (CN III) -offers motor & parasympathetic innervation to many of the ocular structures
Pons
Trigeminal (V)
Trochlear nerve palsy
Trochlear nerve palsy commonly presents with vertical diplopia, exacerbated when looking downwards & inwards (such as when reading or walking down the stairs). Patients can also develop a head tilt away from the affected side. They are commonly caused by microvascular damage from diabetes mellitus or hypertensive disease. Other causes include congenital malformation, thrombophebitis of the cavernous sinus, & raised intracranial pressure
Lateral Rectus Muscle
Within the bony orbit, the abducens nerve terminates by innervating the ________
Auricular branch
Within the cranium, the ________ arises. This supplies sensation to the posterior part of the external auditory & canal external ear.
Split of vestibulocochlear nerve
Within the distal aspect of the internal acoustic meatus, the vestibulocochlear nerve splits, forming the vestibular nerve & the cochlear nerve
Optic Chaism
Within the middle cranial fossa, the optic nerves from each eye unite to form the ________. At the chiasm, fibres from the nasal (medial) half of each retina cross over, forming the optic tracts
5 motor branches of the facial nerve
Within the parotid gland, the facial nerve terminates by bifurcating into 5 motor branches. These innervate the muscles of facial expression: Temporal branch - Innervates the frontalis, orbicularis oculi & corrugator supercilii Zygomatic branch - Innervates the orbicularis oculi. Buccal branch - Innervates the orbicularis oris, buccinator & zygomaticus muscles. Marginal Mandibular branch- Innervates the mentalis muscle. Cervical branch - Innervates the platysma.
Branches of the facial nerve
Within the parotid gland, the nerve terminates by splitting into 5 branches: Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch These branches are responsible for innervating the muscles of facial expression.
Inferior Alveolar Nerve
a branch of V3, travels through the mandibular foramen & mandibular canal. Within the mandibular canal, the inferior alveolar nerve forms the inferior dental plexus, which innervates the lower teeth. A major branch of this plexus, the mental nerve, supplies the skin & mucous membranes of the lower lip, skin of the chin, & the gingiva of the lower teeth. In some dental procedures which require a local anaesthesia, the inferior alveolar nerve is blocked before it gives rise to the plexus. The anaesthetic solution is administered at the mandibular foramen, causing numbness of area supplied by the inferior alveolar nerve. The anaesthetic fluid also spreads to the lingual nerve which originates near the inferior alveolar nerve, causing numbness of the anterior 2/3 of the tongue.
Basilar Skull Fracture
a fracture of the skull base, usually resulting from major trauma. The vestibulocochlear nerve can be damaged within the internal acoustic meatus, producing symptoms of vestibular & cochlear nerve damage. Patients may also exhibit signs related to the other cranial nerves, bleeding from the ears & nose, & cerebrospinal fluid leaking from the ears (CSF otorrhoea) & nose (CSF rhinorrhoea).
Cranial Nerves
a set of 12 paired nerves that arise directly from the brain. 1st 2 nerves (olfactory & optic) arise from the cerebrum, whereas the remaining 10 emerge from the brain stem. Names of the cranial nerves relate to their function & they are numerically identified in roman numerals (I-XII)
Examination of Abducens nerve
abducens nerve is examined in conjunction with the oculomotor & trochlear nerves by testing the movements of the eye. The pt is asked to follow a point with their eyes without moving their head. The target is moved in an 'H-shape' & the pt is asked to report any blurring of vision or diplopia (double vision).
Pontine-Medulla Junction
abducens, facial, vestibulocochlear (VI-VIII)
Chorda tympani
also carries some parasympathetic fibres. These combine with the lingual nerve (a branch of the trigeminal nerve) in the infratemporal fossa. The 2 nerves form the submandibular ganglion. Branches from this ganglion travel to the submandibular & sublingual salivary glands.
Parasympathetic fibers of facial nerve
are carried by the greater petrosal & chorda tympani branches.
Tympanic nerve
arises as the nerve traverses the jugular foramen. It penetrates the temporal bone & enters the cavity of the middle ear. Here, it forms the tympanic plexus - a network of nerves that provide sensory innervation to the middle ear, internal surface of the tympanic membrane & Eustachian tube.
Anatomical Course of Abducens nerve
arises from the abducens nucleus in the pons of the brain, & exits the brainstem at the junction of the pons & the medulla
Hypoglossal Nerve course
arises from the hypoglossal nucleus in the medulla oblongata of the brain. It then passes laterally across the posterior cranial fossa, within the subarachnoid space. The nerve exits the cranium via the hypoglossal canal.
Cochlear component
arises from the ventral & dorsal cochlear nuclei, situated in the inferior cerebellar peduncle
Vestibular component
arises from the vestibular nuclei complex in the pons & medulla
Greater Petrosal Nerve
arises immediately distal to the geniculate ganglion within the facial canal. It then moves in antero-medial direction, exiting the temporal bone into the middle cranial fossa
glossopharyngeal nerve
associated with the derivatives of the 3rd pharyngeal arch Sensory: Innervates the oropharynx, carotid body & sinus, posterior 1/3 of tongue, middle ear cavity & Eustachian tube. Special Sensory: Provides taste sensation to posterior 1/3 of the tongue. Parasympathetic: Provides parasympathetic nn to the parotid gland. Motor: Innervates the stylopharyngeus muscle of the pharynx.
vagus nerve
associated with the derivatives of the 4th pharyngeal arch Sensory: Innervates the skin of the external acoustic meatus & internal surfaces of the laryngopharynx & larynx. Provides visceral sensation to the heart & abdominal viscera. Special Sensory: Provides taste sensation to the epiglottis & root of the tongue. Motor: Provides motor nn to the majority of the muscles of the pharynx, soft palate & larynx. Parasympathetic: Innervates the smooth muscle of the trachea, bronchi & GI tract & regulates heart rhythm
Olfactory Receptor Cells
bipolar neurons which have 2 processes, a dendritic process & a central process. The dendritic process projects to the surface of the epithelium, where they project a number of short cilia, the olfactory hairs, into the mucous membrane. These cilia react to odors in the air & stimulate the olfactory cells. The central process (aka the axon) projects in the opposite direction through the basement membrane.
Lower optic radiation
carries fibres from the inferior retinal quadrants (corresponding to the superior visual field quadrants). It travels through the temporal lobe, via a pathway known as Meyers' loop, to reach the visual cortex
Upper optic radiation
carries fibres from the superior retinal quadrants (corresponding to the inferior visual field quadrants). It travels through the parietal lobe to reach the visual cortex
Medial Stria
carry the axons across the medial plane of the anterior commissure where they meet the olfactory bulb of the opposite side
Pharyngeal branch
combines with fibers of the vagus nerve to form the pharyngeal plexus. It innervates the mucosa of the oropharynx.
Left Optic Tract
contains fibres from the left temporal (lateral) retina, & the right nasal (medial) retina
Right Optic Tract
contains fibres from the right temporal retina, & left nasal retina
Cranial part of accessory nerve
cranial portion is much smaller & arises from the lateral aspect of the medulla oblongata. It leaves the cranium via the jugular foramen, where it briefly contacts the spinal part of the accessory nerve. Immediately after leaving the skull, cranial part combines with the vagus nerve (CN X) at the inferior ganglion of vagus nerve (a ganglion is a collection of nerve cell bodies). The fibres from the cranial part are then distributed through the vagus nerve. For this reason, the cranial part of the accessory nerve is considered as part of the vagus nerve
Anatomical course of optic nerve
describes the transmission of special sensory information from the retina of the eye to the primary visual cortex of the brain. It can be divided into extracranial (outside the cranial cavity), & intracranial parts
Cochlea
detects the magnitude & frequency of sound waves
Accessory Nerve
eleventh paired cranial nerve. It has a purely somatic motor function, innervating the sternocleidomastoid & trapezius muscles
Mandibular nerve
exits via the foramen ovale entering the infra-temporal fossa
optic nerve
formed by the convergence of axons from the retinal ganglion cells. These cells in turn receive impulses from the photoreceptors of the eye (the rods & cones)
Tonsillar branch
forms a network of nerves, known as the tonsillar plexus, which innervates the palatine tonsils
General somatic sensory (GSS)
general sensation from skin
General visceral sensory (GVS)
general sensation from viscera
Maxillary Nerve
gives rise to 14 terminal branches, which innervate the skin, mucous membranes & sinuses of derivatives of the maxillary prominence of the 1st pharyngeal arch: Lower eyelid & its conjunctiva Cheeks & maxillary sinus Nasal cavity & lateral nose Upper lip Upper molar, incisor & canine teeth & the associated gingiva Superior palate
Ophthalmic Nerve
gives rise to 3 terminal branches: frontal, lacrimal & nasociliary, which innervate the skin & mucous membrane of derivatives of the frontonasal prominence derivatives: Forehead & scalp Frontal & ethmoidal sinus Upper eyelid & its conjunctiva Cornea Dorsum of the nose
Mandibular nerve
gives rise to 4 terminal branches in the infra-temporal fossa: buccal nerve, inferior alveolar nerve, auricotemporal nerve & lingual nerve. These branches innervate the skin, mucous membrane & striated muscle derivatives of the mandibular prominence of the 1st pharyngeal arch
Carotid sinus nerve
gives rise to the _________, which provides sensation to the carotid sinus & body
Gag reflex
glossopharyngeal nerve supplies sensory nn to the oropharynx, & thus carries the afferent information for the gag reflex. When a foreign object touches the back of the mouth, this stimulates CNIX, beginning the reflex. The efferent nerve in this process is the vagus nerve, CNX. An absent gag reflex signifies damage to the glossopharyngeal nerve
vagus nerve course
has the longest course of all the cranial nerves, extending from the head to the abdomen; sometimes referred to as the wandering nerve
Organ of Corti
inner hair cells of the _________ activate ion channels in response to vibrations of the basilar membrane. Action potentials travel from the spiral ganglia, which house the cell bodies of neurons of the cochlear nerve.
Vestibular nerve
innervates the vestibular system of the inner ear, which is responsible for detecting balance
Corneal Reflex
involuntary blinking of the eyelids - stimulated by tactile, thermal or painful stimulation of the cornea. In the corneal reflex, the ophthalmic nerve acts as the afferent limb - detecting the stimuli. The facial nerve is the efferent limb, causing contraction of the orbicularis oculi muscle. If the corneal reflex is absent, it is a sign of damage to the trigeminal/ophthalmic nerve, or the facial nerve.
Left Recurrent laryngeal nerve
it hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx.
Olfactory Mucosa
located in the roof of the nasal cavity & composed of pseudostratified columnar epithelium which contains a number of cells (basal, sustentacular, olfactory receptor cells)
Maxillary nerve
maxillary nerve travels lateral to the cavernous sinus exiting the cranium via the foramen rotundum respectively
Stylopharyngeus
muscle of the pharynx is innervated by the glossopharyngeal nerve & acts to shorten & widen the pharynx, & elevate the larynx during swallowing
Intracranial path of facial nerve
nerve arises in the pons, an area of the brainstem. It begins as 2 roots; a large motor root, & a small sensory root (the part of the facial nerve that arises from the sensory root is sometimes known as intermediate nerve). The 2 roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of the temporal bone. Here, they are in very close proximity to the inner ear
Pterygopalatine fossa
nerve of pterygoid canal then passes through the pterygoid canal (Vidian canal) to enter the pterygopalatine fossa, & synapses with the pterygopalatine ganglion. Branches from this ganglion then go on to provide parasympathetic innervation to the mucous glands of the oral cavity, nose & pharynx, & the lacrimal gland
Extracranial course of hypoglossal nerve
nerve receives a branch of the cervical plexus that conducts fibres from C1/C2 spinal nerve roots. These fibres do not combine with the hypoglossal nerve - they merely travel within its sheath. It then passes inferiorly to the angle of the mandible, crossing the internal & external carotid arteries, & moving in an anterior direction to enter the tongue
Superior Orbital Fissure
nerve then moves along the lateral wall of the cavernous sinus (along with the oculomotor nerve, the abducens nerve, the ophthalmic & maxillary branches of the trigeminal nerve & the internal carotid artery) before entering the orbit of the eye via the ___________
Midbrain-pontine junction
oculomotor nerve (III)
Chorda tympani branch
of the facial nerve is responsible for the taste nn of the anterior 2/3 of the tongue. The nerve arises in the facial canal, & travels across the bones of the middle ear, exiting via the petrotympanic fissure, & entering the infratemporal fossa. Here, the chorda tympani 'hitchhikes' with the lingual nerve. The parasympathetic fibres of the chorda tympani stay with the lingual nerve, but the main body of the nerve leaves to innervate the anterior 2/3 of the tongue.
Mitral Cells
olfactory bulb is an ovoid structure which contains specialized neurons, called ____________
Synaptic Glomeruli
olfactory nerve fibres synapse with the mitral cells, forming collections known as ________. From the glomeruli, second order nerves then pass posteriorly into the olfactory tract
Ophthalmic nerve
ophthalmic nerve travels lateral to the cavernous sinus exiting the cranium via the superior orbital fissure
Trigeminal nerve
originates from 3 sensory nuclei (mesencephalic, principal sensory, spinal nuclei of trigeminal nerve) & 1 motor nucleus (motor nucleus of the trigeminal nerve) extending from the midbrain to the medulla. A nucleus= a collection of nerve cell bodies within the CNS.
Anatomical course of oculomotor nerve
originates from anterior aspect of the midbrain. It moves anteriorly, passing below the posterior cerebral artery, & above the superior cerebellar artery. The nerve pierces the dura mater & enters the lateral aspect of the cavernous sinus. Within the cavernous sinus, it receives sympathetic branches from the internal carotid plexus. These fibres do not combine with the oculomotor nerve - they merely travel within its sheath.
Ciliary Ganglion
parasympathetic fibres travel in the inferior branch of the oculomotor nerve. Within the orbit, they branch off & synapse in the __________. The fibres are carried from the ganglion to the eye via the short ciliary nerves
Right vagus nerve
passes anterior to the subclavian artery & posterior to the sternoclavicular joint, entering the thorax.
Left Vagus nerve
passes inferiorly b/w the left common carotid & left subclavian arteries, posterior to the sternoclavicular joint, entering the thorax.
Terminal branches of glossopharyngeal nerve
pharyngeal branch lingual branch tonsillar branch
Medulla Oblangata
posterior to the olive: glossopharyngeal, vagus, accessory (IX-XI). Anterior to the olive: hypoglossal (XII)
Glossopharyngeal nerve on tongue
provides taste sensation to the posterior 1/3 of the tongue, via its lingual branch
Lingual branch
provides the posterior 1/3 of the tongue with general & taste sensation
Labrinthitis
refers to inflammation of the membranous labyrinth, resulting in damage to the vestibular & cochlear branches of the vestibulocochlear nerve. The symptoms are similar to vestibular neuritis, but also include indicators of cochlear nerve damage: Sensorineural hearing loss. Tinnitus - a false ringing or buzzing sound
Vestibular neuritis
refers to inflammation of the vestibular branch of the vestibulocochlear nerve. Etiology of this condition is not fully understood, but some cases are thought to be due to reactivation of the herpes simplex virus. It presents with with symptoms of vestibular nerve damage: Vertigo - a false sensation that oneself or the surroundings are spinning or moving. Nystagmus - a repetitive, involuntary to-and-fro oscillation of the eyes. Loss of equilibrium (especially in low light). Nausea & vomiting. The condition is usually self-resolving. Treatment is symptomatic, usually in the form of anti-emetics or vestibular suppressants
Motor function of hypoglossal nerve
responsible for motor nn of the vast majority of the muscles of the tongue (except for palatoglossus). These muscles can be subdivided into 2 groups: -extrinsic -intrinsic
Olfactory Tract
runs inferiorly to the frontal lobe. As the tract reaches the anterior perforated substance, it divides into medial & lateral stria
Bowman's Glands
secrete mucous
Lateral stria
sends carries the axons to the olfactory area of the cerebral cortex (aka the primary olfactory cortex)
Primary Olfactory Cortex
sends nerve fibres to many other areas of the brain, notably the piriform cortex, the amygdala, olfactory tubercle & the secondary olfactory cortex. These areas are involved in the memory & appreciation of olfactory sensations
Special somatic sensory (SSS)
senses derived from ectoderm (sight, sound, balance)
Special visceral sensory (SVS)
senses derived from endoderm (taste)
Olfactory nerve
shortest cranial nerve & nerve which transmits special sensory information, allowing us to have a sense of smell. 1 of 2 nerves that do not join with the brainstem, the other being the optic nerve. Similar to the optic nerve also in its structure, as it has a meningeal covering unlike CN III to XII -capable of regeneration. Olfactory nerves are unmyelinated & covered by schwann cells
Spinal part of accessory nerve
spinal portion arises from neurons of the upper spinal cord, specifically C1-C5/C6 spinal nerve roots. These fibres coalesce to form the spinal part of the accessory nerve, which then runs superiorly to enter the cranial cavity via the foramen magnum. The nerve traverses the posterior cranial fossa to reach the jugular foramen. It briefly meets the cranial portion of the accessory nerve, before exiting the skull (along with the glossopharyngeal & vagus nerves). Outside the cranium, the spinal part descends along the internal carotid artery to reach the sternocleidomastoid muscle, which it innervates. It then moves across the posterior triangle of the neck to supply motor fibres to the trapezius.
Muscles innervated by accessory nerve
sternocleidomastoid & trapezius
cranial meninges
surrounds the optic nerve
Sympathetic fibers with superior branch of oculomotor nerve
sympathetic fibres that run with the superior branch of the oculomotor nerve. They innervate the superior tarsal muscle, which acts to keep the eyelid elevated after the levator palpabrae superioris has raised it
Vagus nerve
the 10th cranial nerve (CN X). Functionally diverse nerve, offering many different modalities of innervation
Hypoglossal Nerve
the 12th paired cranial nerve. Name derived from ancient greek, 'hypo' meaning under, & 'glossal' meaning tongue. The nerve has a purely somatic motor function, innervating the majority of the muscles of the tongue
Anosmia
the absence of the sense of smell. Can be temporary, permanent, progressive or congenital. Temporary anosmia can be caused by infection or by local disorders of the nose. Permanent anosmia can be caused by head injury, or tumors which occur in the olfactory groove (e.g. meningioma). Anosmia can also occur as a result of neurodegenerative conditions, such as Parkinson's or Alzheimer's disease. In these conditions, the anosmia is progressive & precedes motor symptoms but it is not often noticed by the patient. Anosmia is also a feature of a number of genetic conditions such as Kallmann syndrome (failure to start or finish puberty) & Primary Ciliary Dyskinesia (defect in cilia causing it to be immobile
Vestibulocochlear nerve
the eighth paired cranial nerve. Is comprised of 2 parts - vestibular fibres & cochlear fibres. Both have a purely sensory function
Jugular foramen
the nerve leaves the cranium via the __________
Midbrain
the trochlear nerve (IV) comes from the posterior side of the midbrain. It has the longest intracranial length of all the cranial nerves
Cardiac branches of vagus nerve
these innervate regulate heart rate & provide visceral sensation to the organ.
OPTIC NERVE
transmits the special sensory information for sight. It is 1 of 2 nerves that do not join with the brainstem (the other being the olfactory nerve, CN I)
C1/C2 nerve roots
travel with the hypoglossal nerve also have a motor function. They branch off to innervate the geniohyoid (elevates the hyoid bone) & thryohyoid (depresses the hyoid bone) muscles. Another branch containing C1/C2 fibres descends to supply the ansa cervicalis - a loop of nerves that is part of the cervical plexus. From the ansa cervicalis, nerves arise to innervate the omohyoid, sternohyoid & sternthyroid muscles. These muscles all act to depress the hyoid bone.
Cochlear nerve
travels to cochlea of the inner ear, forming the spiral ganglia which serve the sense of hearing
1st pharyngeal arch
trigeminal nerve is associated with derivatives of the _________
Trochlear Nucleus
trochlear nerve arises from the ________ of the brain, emerging from the posterior aspect of the midbrain (is the only cranial nerve to exit from the posterior midbrain). It runs anteriorly & inferiorly within the subarachnoid space before piercing the dura mater adjacent to the posterior clinoid process of the sphenoid bone
Superior Oblique
trochlear nerve innervates a single muscle - the superior oblique, which is a muscle of oculomotion. As the fibres from the trochlear nucleus cross in the midbrain before they exit, the trochlear neurones innervate the contralateral superior oblique
Pituitary Adenoma
tumor of the pituitary gland. Within the middle cranial fossa, the pituitary gland lies in close proximity to the optic chiasm. Enlargement of the pituitary gland can affect the functioning of the optic nerve. Compression to the optic chiasm particularly affects the fibres that are crossing over from the nasal half of each retina. This produces visual defect affecting the peripheral vision in both eyes, known as a bitemporal hemianopia. Surgical intervention is commonly required. To access the gland, the surgeon uses a transspehenoidal approach, accessing the gland via the sphenoidal sinus
Parasympathetic functions
two structures in the eye that receive parasympathetic innervation from the oculomotor nerve: -sphincter pupillae -ciliary muscles
Esophageal hiatus
vagal trunks enter the abdomen via the _________, an opening in the diaphragm
Palatoglosses & soft palate
vagus nerve also innervates the palatoglossus of the tongue, & the majority of the muscles of the soft palate
Vagus nerve taste
vagus nerve has a minor role in taste sensation. It carries afferent fibres from the root of the tongue & epiglottis
Jugular Foramen
vagus nerve originates from the medulla of the brainstem. It exits the cranium via the _______, with the glossopharyngeal & accessory nerves (CN IX & XI respectively).
Vagus nerve innervates GI tract
vagus nerve provides parasympathetic nn to the majority of the abdominal organs. It sends branches to the esophagus, stomach & most of the intestinal tract - up to the splenic flexure of the large colon. The function of the vagus nerve is to stimulate smooth muscle contraction & glandular secretions in these organs. For ex., in the stomach, vagus nerve increases the rate of gastric emptying, & stimulates acid production
Internal Acoustic Meatus
vestibulocochlear nerve exits the cranium via the __________ of the temporal bone
vestibulocochlear nerve
vestibulocochlear nerve is unusual in that it primarily consists of bipolar neurons. Responsible for the special senses of hearing (via the cochlear nerve), & balance (via the vestibular nerve)
Tympanic nerve
when the glossopharyngeal nerve leaves the cranium, the _______ arises. It has a mixed sensory & parasympathetic composition.