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The oculomotor nerve is the third of twelve paired cranial nerves. It controls most of the eye movements (cranial nerves IV and VI also do some), constriction of the pupil, and holding the eyelid open.

The oculomotor nerve arises from the anterior aspect of mesencephalon (midbrain), the oculomotor nucleus originates at the level of the superior colliculus. The muscles it controls are the ciliary muscle (affecting accommodation), and all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle. In addition, it supplies parasympathetic fibres - which originate in the Edinger-Westphal nucleus - to the eye via the ciliary ganglion, and thus controls pupil constriction.