Edinger-Westphal nucleus and oculomotor parasympathetic fibres
Radiation & CN III · Fixed dilated pupil
Preganglionic parasympathetic nucleus of the oculomotor complex in the rostral midbrain at the level of the superior colliculus. It receives bilateral pretectal input and sends its axons in the oculomotor nerve, where the pupillomotor fibres run superficially on the dorsomedial surface of the nerve.
Traced from the start
- Temporal hemiretinaNasal hemiretinaMacula and papillomacular bundle
- Optic nerve (CN II)
- Optic tract
- Pretectal (olivary pretectal) nucleus
- Edinger-Westphal nucleus and oculomotor parasympathetic fibres
Detail
- Transmitter
- Acetylcholine, acting on nicotinic receptors in the ciliary ganglion
- Position in CN III
- Superficial and dorsomedial, so compressed early but spared by microvascular ischaemia of the core
- Course of CN III
- Interpeduncular fossa between the posterior cerebral and superior cerebellar arteries, beside the posterior communicating artery, lateral wall of cavernous sinus, superior orbital fissure
- Other input
- Cortical near-response pathway for the accommodation-convergence-miosis triad
When it goes wrong
Posterior communicating artery aneurysm or uncal herniation compressing the oculomotor nerve
'Surgical' third-nerve palsy: fixed dilated pupil with ptosis and the eye resting down and out; early pupil involvement demands urgent imaging
Microvascular ischaemia of the oculomotor nerve (diabetes, hypertension)
'Medical' third-nerve palsy: ptosis and ophthalmoplegia with the pupil spared, often painful, usually recovering over months
Practise this structure
1 question in the bank tagged Autonomic.