Midbrain
Origin · CN III CN IV
The oculomotor nucleus and Edinger–Westphal nucleus lie at the level of the superior colliculus and the trochlear nucleus at the inferior colliculus. III leaves ventrally into the interpeduncular fossa between the posterior cerebral and superior cerebellar arteries; IV leaves dorsally below the inferior colliculus after decussating.
Detail
- Gives rise to
- CN III (ventral, interpeduncular fossa), CN IV (dorsal, only dorsally exiting cranial nerve)
- Neighbours
- Cerebral peduncle (corticospinal tract) ventrally, red nucleus and substantia nigra; posterior cerebral artery supply
When it goes wrong
Ventral midbrain infarct (branch of the posterior cerebral artery) involving the III fascicle and cerebral peduncle (Weber syndrome)
Ipsilateral complete third nerve palsy with contralateral hemiparesis of face, arm and leg
Uncal herniation from a supratentorial haematoma pushing the medial temporal lobe over the tentorial edge onto the midbrain
Ipsilateral dilated fixed pupil first, then full third nerve palsy, falling conscious level and contralateral hemiparesis
Practise this structure
1 question in the bank tagged Brainstem.