Oculomotor nerve (CN III)

Nervus oculomotorius

NervousNervesHeadLeft and right

View left in 3D View right in 3D

What it is
Leaves the front of the midbrain between the cerebral peduncles, runs forward in the roof and lateral wall of the cavernous sinus beside the pituitary and enters the orbit through the superior orbital fissure.
Function
Moves the eye up, down and inward (superior, inferior and medial recti, inferior oblique), lifts the upper lid (levator palpebrae) and constricts the pupil and focuses the lens via parasympathetic fibres.
Size
About 3 mm thick, 2.5 cm from midbrain to orbit
Clinical note
A complete third-nerve palsy gives a drooping lid and an eye that sits "down and out"; a dilated pupil with it suggests compression by an aneurysm or a herniating temporal lobe - a neurosurgical emergency.

Nearby nervous structures Abducens nerve (CN VI), Amygdala, Oculomotor nerve root (CN III), Olfactory nerve (CN I), Olfactory tract root (CN I), Optic chiasm, Optic nerve (CN II), intracranial part, Optic tract root (CN II), Trigeminal ganglion, Trochlear nerve (CN IV)