HSF IV Unit II

What do a collection of axial slices make up?

*CT Volume*

What is the name of the parasympathetic ganglion for CN III?

*Ciliary Ganglion*

What is the name of the visceral afferent ganglion for CN X?

*Inferior Vagal Ganglion*

Describe the process of endochondral ossification.

*Mesenchymal Model:* • Stellate-shaped loose mesenchyme w/ long projections and lots of extracellular space • Mesenchyme gradually becomes condensed by proliferating and losing their projections *Cartilage Model:* • Some mesenchymal cells differentiate into chondrocytes • The chondrocytes lay down ground substance and collagen between cells *Formation of Primary Ossification Center:* • Chondrocytes are replaced by osteoprogenitor cells, which then differentiate into osteoblasts • Osteoblasts will form the mineralized portion of bone by replacing the ground substance

Which part of the chondrocranium remains cartilaginous throughout life?

*Nasal Capsule:* • Snout End • In front of crista galli

What is the name of the parasympathetic ganglion for CN IX?

*Otic Ganglion*

What is a pixel and a voxel?

*Pixel:* Grayscale dots, shown in single axial slice *Voxel:* Pixel w/ slice thickness

What is the difference between the *skull* and the *cranium*?

*Skull* = Entire Head Skeleton *Cranium* = Skull w/o Mandible (Lower Jaw)

What are the function(s) of the optic N (CN II)?

*Special sense of vision*

What is the name of the somatic sensory ganglion for CN X?

*Superior & Inferior (Nodose) Vagal Ganglia*

Which cranial nerves carry special sensory innervation?

1, 2, 7-10 *Olfactory:* Smell *Optic:* Vision *Facial:* Taste *Vestibulocochlear:* Hearing/Balance & Equilibrium *Glossopharyngeal:* Taste *Vagus:* Taste

What is the name of the parasympathetic ganglion for CN VII?

1. *Pterygopalatine Ganglia* 2. *Submandibular Ganglia*

What are the different zones at the synchondrosis?

1. *Resting Zone:* • Hyaline cartilage with plenty of extracellular space (filled with ground substance) between them 2. *Proliferative Zone:* • Division of chondrocytes => lined up in columns 3. *Hypertrophic Zone:* • Chondrocytes swell and extracellular matrix is reduced 4. *Degeneration Zone:* • Chondrocytes die and remaining matrix begins to calcify 5. *Ossification Zone:* • Osteoprogenitor cells and capillaries move into the spaces left by the dead chondrocytes • Osteoprogenitor cells differentiate into osteoblasts, which begin forming bone

What are the advantages of CT scan to plain radiography?

1. Much greater ability to visualize "gray tissues." 2. Discrete "slices" of the body can be viewed without superimposing everything 3. A single series of scans (a "volume") can be viewed from any angle. 4. Image parameters (e.g., brightness and contrast) can always be changed. 5. Segmentation and isosurfaces are possible

What are some MRI safety precautions?

1. Patients should remove any metallic items (watches, jewelry) before entering the room with the scanner 2. Removal of extraneous metallic objects ("flying objects")

What are the 4 types of imaging?

1. Plain Radiography 2. Fluoroscopy 3. Computed X-Ray Tomography (CT) 4. Magnetic Resonance Imaging (MRI)

What are the advantages of MRI?

1. Relative to plain radiography, MRI has all of the advantages of CT 2. In many applications, MRI is capable of better imaging of soft tissue than CT • Tissues w/ lots H2O = White • Tissues w/ little H2O = Black 3. Does not use ionizing radiation

What are the 3 types of the cranial nerve ganglia?

1. Somatic Sensory Innervation 2. Parasympathetic Innervation 3. Special Sensory Innervation

Which cranial nerves carry visceral afferents?

9 & 10

What is the basic unit of data for CT?

Axial Slice

REVIEW: What are baroreceptors and chemoreceptors?

Baroreceptors: Stretch receptors that sense changes in BP Chemoreceptors: Monitor balance of O2 and CO2 in blood

Describe UMN and LMN for cranial nerves and spinal nerves.

Each pathway consists of 2 neurons: UMN and LMN. *Similarity w/ Spinal Nerve:* 1. UMN are contained wholly within the CNS (brain and spinal cord), no matter what 2. UMN crosses the midline *Spinal Nerve:* UMN: Extends into spinal cord (CNS) LMN: Contained in spinal nerve (PNS) *Cranial Nerve:* UMN: Brain (CNS) LMN: Contained in cranial nerve (PNS)

What is medical radiography?

Electromagnetic rays that are shorter than UV and Visible Light Rays

What are the physic mechanisms of computed X-ray tomography (CT scan)?

Emitter travels around the patient multiple times to compile a series of radiographs. These radiographs are taken in different directions and then the images are reconstructed into a 3D volume.

How do CN VII and CN VIII exit?

Exit through the *internal acoustic meatus* into the temporal bone

How do CN III, IV, and VI exit?

Exit through the *superior orbital fissure* into the orbit

How do CN IX, X, and XI exit?

Exit through the medial part of the *jugular foramen* into the neck NOTE: CN XI's rootlets ascend into the skull through foramen magnum

What do cranial nerves carry?

Like Spinal Nerves... 1. *Somatic Sensory Innervation* 2. *Somatic Motor Innervation* (Lower Motor Neurons) Also... 3. *Special Sensory Innervation* (olfaction,vision, hearing, balance and equilibrium, taste) 4. *Parasympathetic Innervation* 5. *Visceral Afferents*

What is the gray scale in plain radiography?

Radioopaque/White (Tissue absorbs or scatters more radiation. Less exposure of film.) 1. Pb, BaSO4 2. Enamel 3. Bone 4. Soft Tissue: Muscle/Blood/Organs 5. Fat 6. Air Radiolucent/Black (Tissue absorbs or scatters less radiation. More exposure of film.)

What is the disadvantage of 3D reconstruction?

Resolution suffers a bit because viewing the voxels from the side

What is Meckel's Cartilage?

Scaffold that gives rise to the membrane of mandible

What does the basicranium play a role in?

Serves as a scaffold that the facial skeleton can fit around

What is the most important difference between the neurocranium and basicranium?

*Developmental:* Neurocranium: • Intramembranous Ossification • Origin: Mixture of Mesoderm + Neural Crest Cells Basicranium: • Endochondral Ossification • Origin: Entirely Mesoderm

What is the name of the somatic sensory & special sensory ganglion for CN VII?

*Geniculate Ganglion*

What is the name of the *special* sensory ganglion for CN IX?

*Inferior Glossopharyngeal Ganglion*

What are the function(s) of the abducens N (CN VI)?

*Somatic Motor:* Supplies ONE skeletal muscle that moves the eyeball = lateral rectus M

What are the function(s) of the trochlear N (CN IV)?

*Somatic Motor:* Supplies ONE skeletal muscle that moves the eyeball = superior oblique M

What are the function(s) of the accessory N (CN XI)?

*Somatic Motor:* Supplies TWO muscles = trapezius & sternocleidomastoid

What are the function(s) of the hypoglossal N (CN XII)?

*Somatic Motor:* Supplies both *intrinsic & extrinsic muscles of tongue * NOTE: Does NOT carry any special sensory information (taste)

What are the function(s) of the olfactory N (CN I)?

*Special sense of olfaction (smell)*

Where do the sympathetics of the head originate?

*Spinal Cord T1-L2* Most Preganglionic Sympathetic Cell Bodies' Location: *T1* Most Postganglionic Sympathetic Cell Bodies' Location: Superior Cervical Ganglion *C1-4* Side Note: C1-4 paravertebral ganglia fused together

Cranial nerves DO NOT carry...

*Sympathetics* • However, sympathetic axons may hitchhike along with cranial nerve axons, as well as with vessels

What is the name of the somatic sensory ganglion for CN V?

*Trigeminal (Semilunar) Ganglion*

What are the disadvantages of plain radiography?

1. 3D objects are collapsed into 2D (superimposition). Detailed 3D analysis may require more than 1 view. All structures are necessarily included (nothing can be considered in isolation). 2. Difficult to distinguish different soft tissues, which mostly look gray 3. Ionizing Radiation

What are some other cephalic structures derived from neural crest?

1. Connective Tissue 2. Peripheral NS

What are the major uses for fluoroscopy?

1. Evaluation of Joint Function (especially for the TMJ) 2. Swallowing Disorders

What are the disadvantages of CT scan?

1. Expensive and not always easily accessible. 2. Like plain radiography, it exposes the patient to ionizing radiation. 3. Metal causes artifacts • Ex) Dental fillings explodes into "starburst" artifact that ruins the soft tissue surrounding it

How is the skull divided?

1. Facial Skeleton AKA Viscerocranium OR Splanchnocranium 2. Calvaria (Enclose Brain)

What are the advantages of plain radiography?

1. Fast and relatively inexpensive. Now often entirely digital. 2. Useful for: • Visualizing bone, especially for initial diagnosis of fractures • Visualizing vessels (with contrast media) • Visualizing teeth • Detecting fluid in sinuses • Detecting foreign objects, especially metal

What are the disadvantages of MRI?

1. Like CT, MRI is expensive and not always easily accessible 2. MRI is not well-suited to visualizing mineralized tissues (bones and teeth) 3. Some patients find the experience of having an MRI scan very unpleasant (noise and claustrophobia)

Describe the process of intramembranous ossification.

1. The developing brain is covered by a capsule that is *made of both neural crest and mesoderm*. The space between is only a *potential space*. 2. The capsule differentiates into two layers, the *endomeninx* (internal) and the *ectomeninx* (external), separated by a *potential space*. In doing so, the *mesoderm and neural crest are largely separated* • Endomeninx = Entirely Neural Crest • Ectomeninx = Mesoderm + Neural Crest (Mixture) 3. The ectomeninx and endomeninx both differentiate into 2 layers. • Inner Layer Endomeninx => *Pia Mater* (Entirely Neural Crest) • Outer Layer Endomeninx => *Arachnoid Mater* (Entirely Neural Crest) • Inner Layer Ectomeninx => *Dura Mater* (Little Neural Crest + Mesoderm) • Outer Layer Ectomenix => *Osteogenic Layer* That Gives Rise to Bones of Membranous Neurocranium (Neural Crest + Mesoderm)

What are the different ways you can manipulate CT volumes?

1.) *3D Reconstruction:* Can be cut from different perspectives => Sagittal/ Coronal/Oblique Reconstruction 2.) *Segmentation & Isosurfaces:* Selectively viewing bone, tissue, or vessels by subtracting everything else out then reassembling it back into 3D model

What are the 2 parts of the calvaria?

1.) *Neurocranium:* • Covers the brain from above, in front and back, and on both sides • Small portion supports the brain from beneath (in the front and back). 2.) *Basicranium:* • Supports brain from beneath

What are the function(s) of the trigeminal N (CN V)?

1.) *Somatic Motor:* • ALL Mastication Mm • Tensor Tympani (Middle Ear M) • Part of Soft Palate, • Anterior Digastric & Mylohyoid (2 Suprahyoid Mm) 2.) *Somatic Sensory:* • Eye & Orbit • Nasal Cavity • Oral Cavity (inc. teeth, *anterior 2/3 tongue*) • Skin of Most Head (except back) • Part of External Ear, Ear Canal, & Tympanic Membrane (Eardrum) • Part of Dura Mater

What are the function(s) of the oculomotor N (CN III)?

1.) *Somatic Motor:* • Activates most of the *skeletal* muscles that move the eyeball, as well as the *skeletal* muscle that opens the upper eyelid 2.) *Parasympathetic:* • Activates *smooth* muscles in the eye that constrict the pupil (admitting less light) and focus the eye by acting on the lens

What are the function(s) of the facial N (CN VII)?

1.) *Somatic Motor:* • Facial Expression Mm • Stapedius (Middle Ear M) • Posterior Digastric & Stylohyoid (2 Suprahyoid Mm) 2.) *Somatic Sensory:* • Small Part of External Ear • Parts of Ear Canal & Tympanic Membrane 3.) *Parasympathetic:* • *Glands: Lacrimal, Submandibular, Sublingual* • Nasal & Oral Mucosa 4.) *Special Sensory:* • Taste to *anterior 2/3 tongue* & scattered taste buds on soft palate

What are the function(s) of the vagus N (CN X)?

1.) *Somatic Motor:* • Soft Palate Mm • Pharynx Mm • Larynx Mm 2.) *Somatic Sensory:* • Part of External Ear, Ear Canal, & Tympanic Membrane • Part of Dura Mater • Larynx 3.) *Parasympathetics:* • Thoracic & Abdominal Viscera • Pharynx & Larynx Mucosa 4.) *Special Sensory:* • Taste to the *most posterior part of tongue* and epiglottis 5.) *Visceral Afferent:* • From thoracic & abdominal and probably pelvic viscera • Baroreceptors in aortic arch

What are the function(s) of the glossopharyngeal N (CN IX)?

1.) *Somatic Motor:* • Stylopharyngeus (Pharynx M) 2.) *Somatic Sensory:* • Pharynx • *Posterior 1/3 Tongue* • Auditory Tube • Middle Ear • Part of Tympanic Membrane 3.) *Parasympathetics:* • *Parotid Gland* 4.) *Special Sensory:* • Taste to *posterior 1/3 tongue* 5.) *Visceral Afferent:* • Baroreceptors in carotid sinus • Chemoreceptors in carotid body

What is the name of the *somatic* sensory ganglion for CN IX?

1.) *Superior Glossopharyngeal Ganglia* 2.) *Inferior Glossopharyngeal Ganglia*

What are the different ways you can manipulate MRI scans?

1.) *Tissue Segmentation* 2.) *Tractography:* Visualize pathways of white matter

What are the 4 functions of sympathetic innervation of the head?

1.) Supplying visceral structures in the skin (e.g., sweat glands and smooth muscle of vessels and of the upper eyelid). 2.) Supplying smooth muscles in the eye itself (causing the pupil to dilate, admitting more light) 3.) Supplying the lacrimal gland, along with nasal and oral mucosa (inhibiting secretion by their glands) and associated vasculature 4.) Causing some secretion by the parotid salivary gland

Which cranial nerves carry parasympathetic innervation?

3, 7, 9, 10

What are the cranial nerves that carry somatic motor innervation?

3-7, 9-12

Which cranial nerves are mixed (*somatic sensory* + somatic motor)?

5, 7, 9, 10

Describe the physics mechanisms behind MRI.

A person contains polarized H2O molecules with polar sides. *Resting State:* Random Orientation *Magnetization (MRI):* H2O molecules use energy to line up in response to external magnetic field. • (-) O => (+) North Pole • (+) H => (-) South Pole *Excitation State:* Application of radio frequencies tilt the H2O molecules from aligned position to an alternative position *Relaxation State:* The radio frequencies are turned off and the H2O molecules snap back into aligned position; emit energy that is then detected

What are the locations of the cranial nerves?

CN I: Olfactory Tracts & Bulbs (Slender set of projections underneath of frontal lobes) CN II: Stalk for pituitary gland CN III, IV: Midbrain (associated with motor Nn that move eyeball) CN V, VI: Pons CN VII, VIII: Side of Brainstem/Pons CN IX , X: Medulla Oblongota CN XI: Proximal Spinal Cord CN XII: Medulla Oblongota

CT & MRI scans...

Can be combined to look at the relationship between bone and soft tissue!

What can the the timing of growth cessation of these synchondroses be used for?

Can be used in forensic anthropology and medicine as a fairly reliable age estimator

How does CN I exit?

Exits through the *cribriform plate* and into the nasal cavity

How does CN XII exit?

Exits through the *hypoglossal canal* into the neck

How does CN II exit?

Exits through the *optic canal* into the orbit

How are postganglionic sympathetics distributed?

Hitchhike with vessels and cranial nerve branches! *No cranial nerves have their own sympathetic components.*

What is MRI weighting?

How the signals processed when energy emitted and brought into detector T1 Weighting: • White Matter (Myelin) & Fat = White • CSF, Compact Bone = Black T2 Weighting: • White Matter (Myelin) & Fat = Dark Gray • CSF = White • Compact Bone = Black

Describe the cartilaginous beginning of the basicranium.

Little islands of cartilage => Grow & fuse => Chondrocranium (cartilaginous model)

When is MRI contraindicated?

MRI may be contraindicated in patients with ferrous metallic objects internally: • Pacemakers • Surgical Staples, Plates, & Screws • Orthopedic Prostheses • Stents • Cochlear Implants

Which cranial nerves carry somatic motor innervation, somatic sensory innervation, or both?

Mmenomic: *S*ome *S*ay *M*ore *M*oney *B*ut *M*y *B*rother *S*ays *B*eing *B*lissful *M*atters *M*ore Olfactory N: Sensory Optic N: Sensory Oculomotor N: Motor Trochlear: Motor Trigeminal: Both Abducens: Motor Facial: Both Vestibulocochlear: Sensory Glossopharyngeal: Both Vagus: Both Accessory: Motor Hypoglossal: Motor

What are the 12 cranial nerves?

Mnemonic: *O*h, *O*nce *O*ne *T*akes *T*he *A*natomy *F*inal, *V*ery *G*ood *V*acations *A*re *H*eavenly I. Olfactory II. Optic III. Oculomotor IV. Trochelar V. Trigeminal VI. Abducens VII. Facial VIII. Vestibulocochlear IX. Glossopharyngeal X. Vagus XI. Accessory XII. Hypoglossal

Where are parasympathetic ganglia located?

Parasympathetic ganglia for cranial nerves are sometimes, but not always, minute structures embedded in the target organs (i.e., thoracic and abdominal organs). But most times, they are often grossly visible located outside of target organs. They are also named.

How does the mandibular nerve (V3) exit?

Passes through the *foramen ovale* into the infratemporal fossa

How does the maxillary nerve (V2) exit?

Passes through the *foramen rotundum* into the pterygopalatine fossa

How does the opthalmic N. (V1) exit?

Passes through the *superior orbital fissure* and into the orbit

What do recent experimental evidence show about *hedgehog genes sonic, indian, and desert*)?

Play important roles in formation and function of synchondroses

What is the basioccipital synchondrosis unique for?

Primary site of postnatal growth in cranial base

What are the somatic sensory ganglia similar to?

Similar to dorsal root ganglia in function, but they have names

What are the function(s) of the vestibulocochlear N (CN VIII)?

Special Senses That Involve Inner Ear: 1.) *Hearing* (cochlear part) 2.) *Equilibrium & Balance* (vestibular part)

What is a unique feature of fluoroscopy?

The *grayscale is reversed* from plain radiography (air is white and dense bone is dark).

What does the position relative to the film do?

The position relative to the film makes a difference. Tissues Closer to Film ("PA"): • Beam moves from posterior (closest to the emitter) to anterior (closest to the film) 1. Sharper 2. Close to true size Tissues Farther to Film ("AP"): • Beam moves from anterior (closest to the emitter) to posterior (closest to the film). 1. Fuzzier 2. Larger than true size

Describe the physics mechanism behind plain radiography.

Transmission of beams of ionizing radiation from emitter and collimator through patient to strike film on the far side of the patient Thinner Substances: X-ray will strike the film and expose it = Black (More Exposed Film) Thicker Substances: X-ray will be reabsorbed = White (Less Exposed Film)

What is fluoroscopy used for?

Used to make X-ray "movies" that the clinician can observe in real time • Emitter + Video Recorder

What are the 3 divisions of CNV?

V1 = Opthalmic Nerve V2 = Maximally Nerve V3 = Mandibular Nerve

What are cranial nerves?

• 12 paired nerves that belong to the peripheral NS • Emerge from the brain and proximal spinal cord • Supply the tissues of the head and neck, as well has supplying some structures in the thorax, the abdomen, and the back

What is *achondroplastic dwarfism*?

• Failure of basicranium to grow sufficiently from front to back => Enlarged Head • Short Long Bones (e.g. limbs) • Normal-Sized Face

What is *alisphenoid*?

• Greater Wing of Sphenoid • Both Types of Ossification • Mixed Origin (Mesoderm + Neural Crest)

Describe the facial skeleton developmentally.

• Intramembranous Ossification (like neurocranium) • Origin: Entirely Neural Crest

Where are the vagal parasympathetic postganglionic cell bodies located?

• NO Ganglion • Embedded in organ walls, as is usual with the vagus nerve in the thorax and abdomen

What are synchondroses?

• Regions of the chondrocranium that do not ossify, at least not initially • Instead, they persist as cartilagenous zones / growth centers between bones

How does the chondrocranium turn into bone?

• Synchondroses Between: Nasal - Frontal - Ethmoid - Presphenoid - Basisphenoid - Basioccipital/Sphenobasilar • At the synchondroses, get *anteroposterior* growth of cranial base • Eventually ossify and growth ceases in a *front-to-back sequence* ("wave") • First to Cease Growth: 6-7 years • Last to Cease Growth: 19-21 years