Oculomotor nerve (CN III)
Nerve · CN III Motor Parasympathetic
From the oculomotor and Edinger–Westphal nuclei in the midbrain it exits between the posterior cerebral and superior cerebellar arteries, runs beside the posterior communicating artery, enters the lateral wall of the cavernous sinus and passes through the superior orbital fissure as superior and inferior divisions inside the tendinous ring. Motor to four extraocular muscles and levator palpebrae; parasympathetic to the sphincter pupillae and ciliary muscle.
Traced from the start
- Midbrain
- Oculomotor nerve (CN III)
Detail
- Motor
- Superior division: superior rectus, levator palpebrae superioris. Inferior division: medial rectus, inferior rectus, inferior oblique
- Parasympathetic
- Edinger–Westphal nucleus → inferior division → ciliary ganglion → short ciliary nerves → sphincter pupillae (constriction) and ciliary muscle (accommodation)
- Fibre layout
- Pupillomotor fibres run superficially on the dorsomedial surface of the nerve, supplied by pial vessels; the motor core is supplied by the vasa nervorum
- Complete palsy
- Ptosis, eye resting down and out (unopposed lateral rectus and superior oblique), dilated unreactive pupil, loss of accommodation
When it goes wrong
Posterior communicating artery aneurysm expanding against the nerve (surgical, pupil-involving third nerve palsy)
Painful third nerve palsy with a dilated unreactive pupil because the superficial pupillomotor fibres are compressed first; treat as a leaking aneurysm and obtain urgent CT angiography
Microvascular infarction of the nerve core from diabetes or hypertension (medical, pupil-sparing third nerve palsy)
Ptosis and a down-and-out eye with a normal pupil, often with periorbital ache; usually recovers over about three months, but image if the pupil becomes involved or recovery stalls
Uncal herniation or a cavernous sinus lesion stretching the nerve
Pupil dilatation preceding ophthalmoplegia; in the cavernous sinus it is accompanied by IV, VI and V1 signs
Practise this structure
1 question in the bank tagged Extraocular Muscles.