Oculomotor nerve root (CN III)

Radix nervi oculomotorii

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What it is
Emerges from the interpeduncular fossa on the medial side of the cerebral peduncle, between the posterior cerebral and superior cerebellar arteries. Shown as a short stub on both sides; the nerve continues in the peripheral nervous system.
Function
Motor to four extraocular muscles and the eyelid levator; parasympathetic to the pupil.
Size
Stub about 1 cm; root 2.8 mm thick
Clinical note
A posterior communicating artery aneurysm compresses it here, giving a painful third-nerve palsy with a dilated pupil.

Nearby nervous structures Abducens nerve root (CN VI), Cerebral aqueduct, Hypothalamus, Midbrain, Optic chiasm, Optic tract, Optic tract root (CN II), Pons, Trigeminal nerve root (CN V), Trochlear nerve (CN IV)