0409 Cranial Nerves I - BX

Question 1

Name the 12 cranial nerves

Answer 1

I Olfactory

II Optic

III Oculomotor

IV Trochlear

V Trigeminal

VI Abducens

VII Facial

VIII Vestibulocochlear

VIIII Glossopharyngeal

X Vagus

XI Accessory

XII Hypoglossal

Question 2

Categorize the cranial nerves in terms of Sensory only, Motor only, or both.

Answer 2

use the mnemonic:

Some Say Money Matters, But My Brother Says Big Brains Matter More.

S= sensory only

M = motor only

B = both

Question 3

How are sympathhetic and parasympathetic neurons integrated into cranial nerves?

Answer 3

Sympathetic input: Superior Cervical Ganglion

Parasympathetic output: cranial nerves III, IV, VII, X have parasympathetic output

(responsible for everything down to left colic flexure)

Question 4

What is special about CN II?

Answer 4

Optic nerve not considered part of PNS,

considered an extension of the brain.

Question 5

Where does CN I exit?

Answer 5

Cribriform plate of ethmoid bone.

Question 6

Name the cranial nerves that control eye movement, where they originate in the brain and where they exit.

Answer 6

III Oculomotor, lateral to mamillary bodies in diencephalon

IV Trochlear, dorsal aspect inferior to colliculi

VI Abducens, pontomedullary fissure, medial to VII

all exit through the superior orbital fissure.

Question 7

Describe the route of transmission through the olfactory nerve.

Answer 7

1. Dendrites of Bipolar cells (chemoreceptor cells) ascend
2. through cribriform plate (above cribriform is known as olfactory bulb)
3. reaches glomerulus
4. mitral cells
5. group of mitral cell axons form olfactory tract
6. ends in ento-rhinal cortex

Question 8

List the following for CNII:

Location of origin and ending,

Exit through skull,

Function,

Special details

Answer 8

Originates: in diencephalon

ends at: optic tract

Exit: through optic canal

Function: sight ONLY (special sensory)

Special Details: only half of fibers cross at optic chiasm, only the medial half of the visual field for each eye crosses.

mapped projections in occipital cortex, central visual field to back, periphery to anterior, superior projects below calcarine fissure, inferior above fissure.

Question 9

Describe what happens to vision in the following lesions:

Damage to left optic nerve

Damage to right optic tract

Tumour in pituitary

Damage to projections below the calcarine fissure

Answer 9

Left optic nerve lesion: vision in only right eye

Damage to right optic tract: right visual field is gone

Tumour in pituitary: medial half of visual field is gone, if severe enough complete vision loss.

Damage to projections: superior portion of visual field gone.

Question 10

Where else do optic tract fibers travel to?

Answer 10

Thalamus,

Superior colliculi

Specifically, Lateral Geniculate Nucleus (LGN) of thalamus

Question 11

Name the muscles innervated by the cranial nerves that control eye movement.

Answer 11

CN III: Superior rectus, inferior rectus, medial rectus, inferior oblique

CN IV: superior oblique

CN VI: lateral rectus

Question 12

How are pure up and down movements of the eyes completed?

Answer 12

Pure up and down movements require a combination of two movments:

UP: superior rectus (up and medial) + superior oblique (down and lateral) Medial and lateral movements cancel out…

Down: Inferior rectus (down and medial) + inferior oblique (up and lateral)

Note: lateral movements are just the medial and lateral rectus muscles.

Question 13

What three major sensory signals does the vestibulocochlear nerve receive?

Answer 13

Static vestibular: from saccule and utricles

Kinetic vestibular: from semicicular canals (3)

Hearing: from cochlea through tectorial membrane

Question 14

Where does CN VIII exit?

Answer 14

It does not exit, enters skull through internal acoustic meatus

stays inside temporal bone

Question 15

How is kinetic vestibular information conveyed to CN VIII?

Answer 15

semicircular canals move during acceleration

endolymph contains jelly-like substance

during acceleration, the canals move but fluid lags behind

hair cells in the cupula detects movement of canal by “brushing” against endolymph

signal travels to vestibular ganglion

Question 16

How is static information conveyed to CN VIII?

Answer 16

through utricles and saccules

hair cells in these structures detect which orientation gravity pulls

thus telling static head position

(continuous signalling) i.e. if a person is lying down, signals continuously tell the person they are lying down.

Question 17

Which part of the brain receives information from CN VIII?

Answer 17

the posterior two vertical gyri of the insula lobe

heschl’s gyrus of temporal lobe

Question 18

Describe the parasympathetic components of CN III

Answer 18

ciliary ganglion receives input from the edinger-westphal nucleus (midbrain strcuture)

from ciliar ganglion, short ciliary nerves carry parasympathetic info to the eyes.

Question 19

What are short ciliary nerves and what information do they carry?

Answer 19

mixed nerve containing sensory, parasympathetic and sympathetic functions.

sensory information carried by short ciliary goes to trigeminal V1 (naso ciliary branch) AFFERENT DIRECTION

Parasympathetic output from ciliary ganglion (pupil constriction)

Sympathetic information from superior cervical ganglion hitchhikes naso-ciliary branch to eye. EFFERENT DIRECTION (pupil dilation)

Question 20

Name the location, exit, and function of CN XII

Answer 20

location: anterolateral sulcus (between pyramid and olives in medulla)
exit: hypoglossal canal near jugular foramen
function: innervation to all intrinsic muslces of tongue

(allows speech, tongue movement)

Innervation to the following EXTRINSIC muscles:

genioglossus (pulls tongue forward), hyoglossus (depresses tongue), styloglossus (retracts tongue)