The oculomotor nerve (cranial nerve III) leaves the front of the midbrain, runs forward through the wall of the cavernous sinus and enters each eye socket (orbit) through the superior orbital fissure, where it splits into a superior and an inferior branch. It works four of the six muscles that move each eye, lifts the upper eyelid and narrows the pupil. [1][2]
Lit: the branches of the oculomotor nerve inside the eye socket (its superior and inferior branch, on both sides); the part from the midbrain is not a separate shape in this atlas, so it is not drawn. [3]
Where it starts: the midbrain. Its nucleus lies at the level of the superior colliculus, just in front of the cerebral aqueduct, and the nerve leaves the brainstem in the hollow between the two cerebral peduncles. [1]
The 3D brain needs JavaScript. The text below still says where the oculomotor nerve is and what it does.
Slice
Opens cut by a front (coronal) slice through the oculomotor nerve. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Takes part in: eye movements — see every part of each lit together.
Where it is
It leaves the front of the midbrain from a groove, the oculomotor sulcus, on the side wall of the interpeduncular fossa: the hollow between the two cerebral peduncles. [1]
Its fibres start in two nuclei at the level of the superior colliculus, just in front of the cerebral aqueduct: the oculomotor nucleus (for the muscles) and the Edinger–Westphal nucleus (for the pupil and lens). On their way out they pass through the red nucleus. [1]
Heading forward it passes between two arteries, the posterior cerebral above and the superior cerebellar below, pierces the dura beside the posterior clinoid process and runs through the cavernous sinus, above the other nerves bound for the eye socket. [1]
It enters the eye socket through the superior orbital fissure and there divides: a smaller superior branch that passes over the optic nerve, and a larger inferior branch. These two branches are the parts lit on this model. [1][3]
What it does
The superior branch supplies the superior rectus, which turns the eye up, and the levator palpebrae superioris, which lifts the upper eyelid. [1][4]
The inferior branch supplies the medial rectus (turns the eye in toward the nose), the inferior rectus (turns it down) and the inferior oblique (turns it up and out), and sends a short root to the ciliary ganglion behind the eye. [1][4]
Its parasympathetic fibres, from the Edinger–Westphal nucleus, relay in the ciliary ganglion and work two muscles inside the eye: the sphincter pupillae, which narrows the pupil, and the ciliary muscle, which focuses the lens for near sight such as reading. [1][2]
That makes four of the six muscles that move each eye. The other two have nerves of their own: the superior oblique (trochlear nerve, IV) and the lateral rectus (abducens nerve, VI). All three eye-movement nerves are motor nerves. [2][4]
Connections
From: the oculomotor and Edinger–Westphal nuclei in the midbrain. To: the superior, medial and inferior rectus, the inferior oblique and the eyelid lifter, and (through the ciliary ganglion) the pupil and lens muscles of the same side. [1]
Other names
Cranial nerve III (CN III), third cranial nerve; nervus oculomotorius (Latin). Its two branches are also called the superior and inferior divisions. [1]
Size
On this model the left oculomotor nerve measures about 36 mm front to back, 30 mm top to bottom and 25 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [3]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.