3rd cranial nerve

where is the nucleus of the 3rd nerve located?

midbrain

describe the course of the 3rd nerve

Base of periaqueductal grey of midbrain at superior colliculus

Pre-ganglionic parasympathetic n arise from= EWS

Travels ventrally → tegmentum. Passes thru → red nucleus

Exits midbrain → enters subarachnoid space

Passes between posterior cerebral & superior cerebellar arteries

→ Pierces arachnoid around, & rests on tentorium cerebelli

→Enters cavernous sinus - lies in lateral wall

→Enters orbit via superior orbital fissure

→ splits into superior and inferior divisions

Innervates MR, IR, IO (inferior), SR and levator (superior),

Parasympathetic fibres terminate in ciliary ganglion

clinical relevance of the 3rd nerve nucleus

nucleus located in midbrain near 4th nerve nucleus

aetiology of 3rd CNP with pupil involvement

aneurysm of the PCA

where does the subarachnoid space next to

it is lateral to the posterior communicating artery

what is the clinical relevance of the subarachnoid space being lateral to the PCA?

aneurysms of the PCA can cause 3rd CNP with pupil involvement (dilation)

list aetiologies of 3rd CNP with pupil involvement

cysts
schwannomas/angiomas
infection
mass/herniation of tentorium cerebelli

what's a schwannoma?

tumour of schwann cells whcih myelinate nerve fibres causing palsies

what kind of infections can cause 3rd CNP?

meningitis

3rd CNP with pupil sparing aetiologies?

ischaemia
diabetes
hypertension
temporal arteritis
migraine
constrictive type issue
vascular - more common vs space occupying lesions

what type of fibres travel with the 3rd which control pupil constriction?

parasympathetic fibres

where are parasympathetic fibres found in the 3rd?

outer laters

why do space occupying lesions cause 3rd CNP with pupil involvement

compresses the 3rd outer fibres`

why do vascular causes usually not cause a 3rd CNP with pupil involvement

deep vasculature within the nerve allows the nerve to function
constricts supply to nerve
affects OM nerve but less likely to effect parasympathethic fibres as theyre further away

is it immediate or delayed investigation of a 3rd CNP with pupil involvement?

emergency as it could be a space occupying lesion

symptom of an aetiology/space occupying lesion within the cavernous sinus

acute, painful headache

example of vascular lesions affecting the cavernous sinus causing a 3rd CNP

internal carotid artery aneurysm
thrombosis
carotid cavernous fistula

example of tumours affecting the cavernous sinus causing a 3rd CNP

pituitary
meningioma
nasopharyngeal carcinoma

list aetiologies within the cavernous sinus

infection
inflammation
ischaemia
trauma - skull fracture

what is tolosa hunt syndrome and what does it effect

aetiolog affecting cavernous sinus
causes unilateral headaches

would an acquired 3rd CNP be symptomatic or asymptomatic?

symptomatic

if there was a 3rd CNP with the inferior branch, what deviation would you expect to see?

exodeviation as the MR is the main horizontal muscle affected

if there was a 3rd CNP with the superior branch, what deviation would you expect to see?

hypotropic deviaiton as SR is an elevator

if pt has a 3rd CNP with ptosis, what branch is affected?

superior

what is the CHP in a complete 3rd CNP?

unlikely yo get one as there is so many muscles affected and diplopia in so many gazes, they can't get rid of it

CHP in a superior division 3rd CNP

chin elevate

deviation expected in a complete 3rd

exotropia - MR
hypotropia - SR

deviation in a superior CNP

hypotropia/phoria - SR
exo - adduction is horizontal action of SR
usually larger hypo than the exo

how would you assess the 4th function in a complete/inferior 3rd CNP?

put pt in laevodepression

What does the oculomotor nerve innervate?

It innervates most extraocular muscles (superior rectus, inferior rectus, medial rectus, inferior oblique - ps fibres) and provides parasympathetic innervation to the pupil and ciliary body.

What are the motor functions of CN III?

Controls eye elevation, depression, adduction, and eyelid elevation.

What are the parasympathetic functions of CN III?

Controls pupil constriction and accommodation.

What are the key anatomical areas where CN III can be affected?

Subnuclei in the midbrain, subarachnoid space, and cavernous sinus.

What are the main causes of CN III palsy with pupil involvement?

Aneurysms (often posterior cerebral artery), tumors, infections, or cysts affecting nerve fibers.

What are the main causes of pupil-sparing CN III palsy?

Ischemia, often due to vascular conditions like diabetes, hypertension, or temporal arteritis.

What are the typical presentations of complete CN III palsy?

Ptosis, 'down and out' eye positioning, and mydriasis (pupil dilation).

What is aberrant regeneration in CN III palsy?

Abnormal regrowth of nerve fibers causing phenomena like lid retraction on adduction or pupil constriction on eye movement.