Nerves of the H&N CN I-VI

Question 1

What are the different cranial nerves

Answer 1

CN I - olfactory

CN II - optic

CN III - oculomotor

CN IV - trochlear

CN V - trigeminal

CN VI - abducens

CN VII - facial nerve

CN VIII - vestibulocochlear nerve

CN IX - glossopharyngeal nerve

CN X - vagus nerve

CN XI - spinal accessory nerve

CN XII - hypoglossal nerve

Question 2

What are the branches of the trigeminal nerve and what are their functions

Answer 2

Opthalmic (V1) - sensory

Maxillary (V2) - sensory

Mandibular (V3) - motor and sensory

Question 3

What are the cranial nerves

Answer 3

Nerves that are part of the periphernal nervous system that arise at irregular intervals from CNS segments

Can be general sensory, special sensory, motor and/or autonomic

Question 4

Where do the cranial nerves branch from

Answer 4

Two from forebrain

Two from midbrain

Four from pons

Four from medulla

Question 5

Describe the course of the olfactory nerve

Answer 5

Originates in roof of nasal cavity

Fibres run through cribriform foramina to enter olfactory bulb

Olfactory fibres then form olfactory tract which goes to the temporal lobe

Question 6

What are the functions of the olfactory nerve and how do you test the functions

Answer 6

Olfaction is its function

Test changes/differences in smell and test changes in taste (taste affected by smell)

Test one nostril at a time

Question 7

Describe the course of the optic nerve

Answer 7

Cells within retina generate impulses in response to light

Impulse generates AP which is propagated along optic nerve

Optic nerve exits back of orbit via optic canal where fibres cross and merge at the optic chiasm

Fibres then enter optic tract

AP runs along visual pathway to reach primary visual cortex

Question 8

What can happen to the optic nerve if there is raised ICP

Answer 8

Optic disc can swell as the optic nerve carries an extension of the meninges

Optic disc swelling = papilloedema

Question 9

How do you test the optic nerve

Answer 9

Visual acuity tests - e.g.

• Snellen chart
• Check visual fields
• Test pupillary responses

Question 10

Describe the course of the oculomotor nerve

Answer 10

Originates in anterior midbrain

Runs through lateral wall of cavernous sinus

Runs through superior orbital fissure

Question 11

What are the functions of the oculomotor nerve

Answer 11

Motor functions:

• Innervates most muscles that move the eyeball - extra-ocular muscles
• Innervates muscles of the eyelid - levator palpebrae superioris

PNS functions:

• Innervates sphincter pupillae - constricts pupil
• Innervates ciliary muscles - surround lens

Question 12

Where is the oculomotor at most risk of compression

Answer 12

Between tentorium cerebelli and part of the temporal lobe

Due to raised ICP

Question 13

How do you test oculomotor functions

Answer 13

Inspect eyelids and pupil size - see if pupil is normal or if it is blown

Test eye movements and pupillary reflexes

History of diplopia

Look for down and out position

Look for ptosis

Question 14

Describe the course of the trochlear nerve

Answer 14

Originates from the back of the midbrain

Goes through the lateral wall of the cavernous sinus

Runs through superior orbital fissure

Question 15

What is the function of the trochlear nerve and how do you test it

Answer 15

Innervates superior oblique muscle - moves the eyeball

Test eye movements to test the nerve

Question 16

Describe the course of the trigeminal nerve and its branches

Answer 16

Trigeminal nerve originates in the pons then forms the trigeminal ganglion and splits into:

• Opthalmic division - after ganglion, passes through lateral wall of cavernous sinus -> superior orbital fissure -> orbit
• Maxillary division - after ganglion, passes through lateral wall of cavernous sinus -> foramen rotundum and then pterygopalatine fossa
• Mandibular division - after ganglion, passes through foramen ovale -> infratemporal fossa

Question 17

How do you test the trigeminal nerve

Answer 17

Test sensation in each of its dermatomes

Test muscles of mastication - jaw jerk

Test corneal reflex

Question 18

Which branches of the opthalmic division are vulnerable to damage

Answer 18

Supraorbital and supratrochlear - sensory innervation to forehead and anterior scalp

Question 19

Which branches of the maxillary division are vulnerable to damage

Answer 19

Infraorbital - runs through floor of orbit -> susceptible to injury in orbital floor #

Superior alveolar nerve

Question 20

Which branches of the mandibular division are vulnerable to damage

Answer 20

Inferior alveolar - runs through bony canal in mandible -> susceptible to injury in mandibular #

Lingual

Auriculotemporal

Question 21

What are the symptoms of trigeminal neuralgia

Answer 21

Episodes of sharp shooting pains throughout the trigeminal dermatomes

Usually only one side of the face

Question 22

Describe the course of the abducens nerve

Answer 22

Originates in lower pons - junction between pons and medulla

Runs inwards before passing into cavernous sinus

Runs through superior orbital fissure to enter orbit

Question 23

What is the function of the abducens nerve

Answer 23

Innervates lateral rectus muscle - abducts the eye

Question 24

What is abductor nerve palsy

Answer 24

Where the abducens nerve has been compressed and so the patient cannot look laterally - cannot abduct the eye