Cranial Nerves

CN I: name, sensory or motor, function

olfactory nerve

sensory

smell

CN II: name, sensory or motor, function

optic nerve

sensory

vision

CN III: name, sensory or motor, function

oculomotor nerve

motor

eye movement, accommodation, pupil constriction

CN IV: name, sensory or motor, function

trochlear nerve

motor

superior oblique innervation

CN V: name, sensory or motor, function

trigeminal nerve

both

facial sensation, mastication

CN VI: name, sensory or motor, function

abducens nerve

motor

lateral rectus innervation

CN VII: name, sensory or motor, function

facial nerve

both

facial expressions, anterior 2/3 of taste, lacrimation, salivation (submaxillary and submandibular glands)

CN VIII: name, sensory or motor, function

vestibulocochlear nerve

sensory

hearing, balance

CN IX: name, sensory or motor, function

glossopharyngeal nerve

both

swallowing, salivation (parotid gland), posterior 1/3 of taste, monitoring of carotid sinus

CN X: name, sensory or motor, function

vagus nerve

both

taste, swallowing, palate elevation, talking, thoracoabdominal viscera

CN XI: name, sensory or motor, function

accessory nerve

motor

head turning, shoulder shrugging

CN XII: name, sensory or motor, function

hypoglossal nerve

motor

tongue movement

what are signs of a CN X palsy

uvula deviates away from side of lesion

palate does not elevate

patient reports hoarse voice

what is a sign of a CN XII palsy

tongue deviates towards the side with the lesion

the optic nerve carries ______ info only

sensory

what is the ON composed of

GC axons

path of GC axons that form ON

converge at optic disc, exit sclera through the lamina cribrosa, leave the orbit via optic foramen, travel through optic canal

where does the ON leave the orbit

optic foramen

(nasal/temporal) fibers cross at the _________ to join the fibers in the other eye

nasal fibers cross at the optic chiasm to join the fibers in the other eye

the optic tract contains nasal fibers from the (contralateral/ipsilateral) eye

optic tract contains nasal fibers from the contralateral eye and temporal fibers from the ipsilateral eye

the fibers in the optic tract carry visual information from the (same/opposite) side of the visual field

the fibers in the optic tract carry information from the same side of the visual field

4 destinations of CN II fibers

LGN, pretectal nucleus, superior colliculus, hypothalamus

what do ON fibers that travel to the LGN do

relay visual info to the primary visual cortex (V1)

what do ON fibers that travel to the pretectal nucleus do

responsible for pupil innervation

what do ON fibers that travel to the superior colliculus do

involved in saccade control

what do ON fibers that travel to the hypothalamus do

involved in circadian rhythm

what are the nuclei of CN III and where are they located

right and left nucleus

located in the midbrain at the level of the superior colliculus

what does each nucleus (right and left) of CN III contain

each nucleus has a sub-nucleus and an Edinger-westphal nucleus

role of sub-nuclei of the CN III nuclei

provide voluntary motor control to SR, MR, IR, IO muscles

role of Edinger-Westphal nuclei of the CN III nuclei

provide parasympathetic innervation to the CB and iris sphincter muscles through the ciliary ganglion

the CN III nuclei are connected to which other nuclei, and how

connected to nuclei of CN IV, VI, and VIII via the MLF (medial longitudinal fasciculus)

what 2 structures do the CN III nuclei receive information from

superior colliculus, visual cortex

which CN III fibers project to ipsilateral muscles

fibers of the sub-nuclei that leave for the medial rectus, inferior oblique, and inferior rectus

which CN III fibers project to contralateral muscles

fibers of the sub-nuclei that leave for the superior rectus

what are the only fibers from CN III sub-nuclei that cross

SR fibers

a lesion in the right SR sub-nuclei will result in poor control of what and why

the left SR muscle

the SR CN III fibers are the only CN III fibers that cross the midline (contralateral innervation)

what controls the levator palpebrae muscle of each eye

one central CN III sub-nucleus

a lesion in the levator palpebrae sub-nucleus will result in what and why

sudden onset bilateral ptosis

one sub-nuclei of CN III control the levator palpebrae innervation of both eyes

when the sub-nuclei exit the brainstem, where do they go

cavernous sinus

what kind of innervation do CN III fibers receive in the cavernous sinus, and from where

CN III fibers get sympathetic fibers from the internal carotid artery plexusw

what does CN III divide into and where

superior and inferior divisions

divides just before it enters the orbit

where does CN III enter the orbit

superior orbital fissure

path of CN III sub-nuclei fibers from the brain to the eye

sub-nuclei fibers join together and enter brainstem > travel closely to posterior communicating artery (ICA branch) > enter cavernous sinus > get ICA plexus sympathetic fibers in cavernous sinus > divide into superior and inferior divisions > enter orbit through superior orbital fissure

what does the superior division of CN III innervate

superior rectus and superior levator palpebrae

what travels with the superior division of CN III, and what does it innervate

sympathetic fibers travel with the superior division and innervate Muller’s muscle of the UL

what does the inferior division of CN III innervate

medial rectus, inferior rectus, inferior oblique

what travels with the inferior division of CN III, and what does it innervate

parasympathetic fibers from the EW nuclei

innervate the iris sphincter and the ciliary muscle

what is the path of the EW nuclei fibers

PS EW nuclei fibers travel with the inferior division of CN III

go to the ciliary ganglion and leave the ganglion as SPCNs

innervate iris sphincter and ciliary muscler

role of EW nuclei fibers

innervate iris sphincter and ciliary muscle with parasympathetic innervation for pupillary constriction and accommodation

what does the CN III innervate

MR, SR, IR, IO

levator palpebrae

CB & iris sphincter (PS innervation)

Muller’s muscle (sympathetic innervation)

what does a complete CN III lesion look like

severe ptosis (levator not being innervated)

eye goes down and out (only LR and SO are getting innervation)

is ptosis more severe in horner’s or CN III palsy, and why

CN III palsy

horner’s is caused by lack of sympathetic innervation, causing muller’s muscle not to be innervated

muller’s is only responsible for 1-2 mm of lid elevation

CN III palsy causes lack of innervation to the levator (via superior division of CN III), which is the main elevator of the eye (causing large ptosis)

where are pupillary fibers of CN III located

on the outside of CN III

pupil-involving CN III palsy should raise suspicion for what and why

aneurysm of the posterior communicating artery (most likely at junction of ICA and PCA)

CN III fibers travel closely with PCA before reaching cavernous sinus

since pupillary fibers are on the outside of CN III, an aneurysm of the PCA will press on the pupil fibers, causing pupil involvement

what is the most likely cause of a pupil-sparing CN III palsy

ischemia of small BVs that nourish inner fibers of CN III (likely due to vascular disease like DM or HTN)

what type of CN III palsy is considered an emergency and why

pupil-involving CN III palsy

most likely caused by a compressive lesion (aneurysm or tumor) of the PCA pressing on the outer CN III fibers

CN rule of fours

CN 1-4 originate above the pons (CN 3 & 4 originate in the midbrain)

CN 5-8 originate in the pons

CN 9-12 originate in the medulla

remember midbrain, pons, medulla

what is the medulla responsible for

autonomic functions

breathing, heartrate, digestion

hearing and balance are the 2 main functions of what nerve

CN VIII: vestibulocochlear

what 2 nerves innervate taste in the tongue, and what part of the tongue

anterior 2/3 of tongue: CN VII (facial nerve)

posterior 1/3 of tongue: CN IX (glossopharyngeal nerve)

what nerve innervates tongue movement, and where will the tongue move if there is a lesion in that nerve

CN XII (hypoglossal nerve)

tongue will move toward direction of lesion

remember tongue toward

what nerve innervates the uvula, and where will the uvula move if there is a lesion in that nerve

CN X (vagus nerve)

uvula will move away from lesion

remember vagus = uVula

what 2 movements are associated with CN XI

CN XI is the accessory nerve

it is associated with head turning and shoulder shrugging

remember accessory nerve = student nerve, turning head and shrugging shoulders like you don’t know something

what are the only 2 nerves with contralateral innervation

nerves innervating SR and SO

CN IV (trochlear nerve)

only the superior division of CN III that innervates the SO

what is the main nerve responsible for mastication (chewing)

CN V (trigeminal nerve)

what is the main nerve responsible for lacrimation

CN VII (facial nerve)

what is the main nerve responsible for swallowing

CN IX (glossopharyngeal nerve)

what are 2 other names for V1 (visual cortex) in the brain

Brodmann’s area 17

striate cortex

(this is where the LGN projects visual info)

where does CN III start its course

midbrain

what is the sensory and motor innervation that occurs when you shine light into a patient’s eye to check their pupils

sensory: CN II (ON) brings the light signal to the brain by sending signals to the pretectal nucleus (light response, pupil control), which then signals to the EW nucleus

motor: CN III causes the EW nucleus to send PS innervation to the iris sphincter, causing the pupil to constrict

where do the preganglionic parasympathetic fibers start their course

EW nucleus

what happens when you have a lesion between the pretectal nucleus and EW nucleus and why

Argyll Robertson pupil: pupil does not constrict with light, but constricts with accommodation

pretectal nucleus is responsible for light response, is not able to tell the EW nucleus to signal to iris sphincter when light shines

EW nucleus still works, so can still respond to accommodation

what happens when you have a lesion in the EW nucleus

Adie’s tonic pupil

pupils don’t respond to light and respond slowly to accommodation

where is the lesion most likely located if there is a pupil-involing CN III palsy

junction of ICA and posterior communicating artery

what is the longest cranial nerve

CN IV (trochlear nerve)

location and number of nuclei in CN IV

2 nuclei located in the midbrain at the level of the inferior colliculus

(slightly lower than CN III nuclei located in the midbrain at the level of superior colliculus)

what nuclei are the nuclei of CN IV connected to and how

nuclei of CN III, CN VI, CN VIII via the MLF

path of CN IV nuclei connection to visual cortex

CN IV nuclei use the tectobulbar tract to connect to the superior colliculus, which then connects to the visual cortex

what is the only CN that comes off of the dorsal (posterior) side of the brainstem

CN IV

what is the only cranial nerve to fully decussate

CN IV

contralateral innervation of SO

a patient with a superior oblique palsy will tilt their head (towards/away) from the affected side

away from the affected side

actually tilting their head towards the location of the lesion since a left lesion would affect the right SO

damage to the right trochlear nucleus will cause a _____ palsy, and the patient will tilt their head to the ______

left SO palsy

right

path of CN IV entering the orbit

enters the lateral wall of the cavernous sinus

travels under CN III

enters the orbit above the annulus of zinn through the superior orbital fissure

where does CN IV enter the orbit

superior orbital fissure

anatomical origin of the SO (where muscle attachment is)

lesser wing of the sphenoid

physiologic origin of the SO (functional origin)

trochlea

where are the roots of CN V located and what are they

1 motor root and 1 sensory root

located in the pons

sensory function of CN V

carries sensory info from the face and head, including all orbital structures

3 sensory divisions of CN V and where they provide sensory input

CN V1: sensory info from head to tip of nose

CN V2: sensory info from side of nose to mouth

CN V3: sensory info from head and ear to mandible

what branch of CN V provides sensory and motor input and what does it innervate

CN V3

sensory info from head and ear to mandible

motor info to muscles of mastication

the sensory fibers of CN V travel to the ____ nuclei in the _____ to relay sensory info to the ______

sensory fibers of CN V travel to the sensory nuclei in the pons to relay sensory info to the thalamus

path the sensory fibers of CN V take to relay sensory info

leave face and head structures

enter cavernous sinus

synapse in trigeminal ganglion in the posterior cavernous sinus

travel to the sensory nuclei in the pons

relay sensory info to the thalamus

where do sensory fibers of CN V synapse in the cavernous sinus

trigeminal ganglion in the posterior cavernous sinus

what are the 3 sensory nuclei where sensory fibers of CN V synapse

spinal nucleus

main sensory nucleus

mesencephalic nucleus

spinal nucleus

where CN V sensory fibers synapse in the medulla

gets touch, pain, and temperature info from the ipsilateral face

main sensory nucleus

where CN V sensory fibers synapse in the pons

gets light touch info and discriminates sensation

mesencephalic nucleus

where CN V sensory fibers synapse in the pons

proprioception

what part of the face is herpes simplex keratitis most likely to affect and why

upper eyelid and forehead

HSK can affect any or all branches of CN V1

branches of CN V1

nasociliary nerve

frontal nerve

lacrimal nerve

NFL is #1

function of nasociliary nerve (CN V1)

carries sensory info from the cornea, iris, and tip of nose