The oculomotor nucleus is the motor nucleus of cranial nerve III, lying in the upper midbrain. It controls four of the six muscles that move the eye and the muscle that raises the upper eyelid. It is organised in subnuclei, some of which send fibres to the same eye and some to the opposite eye.
| Location | Upper midbrain at the level of the superior colliculus, in front of the periaqueductal grey, next to the midline and the medial longitudinal fasciculus |
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| Parts |
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| Connections |
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| Blood Supply | Paramedian perforators from the basilar tip and posterior cerebral artery |
Controls eye elevation, depression, adduction and eyelid elevation, working with the other eye movement nuclei to produce coordinated gaze.
A nuclear third nerve lesion differs from a nerve lesion: it causes weakness of the opposite superior rectus and droop of both eyelids, because those subnuclei serve both sides. Small midbrain strokes, demyelination and tumours can cause these patterns. A dilated pupil with a third nerve palsy suggests compression of the nerve rather than a nuclear lesion.
Damage to the oculomotor nucleus causing ipsilateral eye movement weakness, contralateral superior rectus weakness and bilateral ptosis.
A paramedian midbrain infarct causing double vision and drooping eyelids from involvement of the oculomotor nucleus or fascicles.
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