Oculomotor nerve

A cranial nerve primarily responsible for eye movement and several key functions in ocular health.

The oculomotor nerve, also known as cranial nerve III, is a motor nerve that innervates several muscles responsible for moving the eyeball and raising the eyelid. It also carries parasympathetic fibers that contribute to the regulation of pupil size and lens shape for proper focusing of light onto the retina.

Terminologia Anatomica

nervus oculomotorius

System

Nervous system

Function

The oculomotor nerve plays a crucial role in controlling the majority of the eye's movements. It enables the upward, downward, and medial (inward) movements of the eyeball through its innervation of four extraocular muscles: the superior rectus, inferior rectus, medial rectus, and inferior oblique. Additionally, the oculomotor nerve is responsible for elevating the upper eyelid via the levator palpebrae superioris muscle, allowing for proper eye exposure. Of paramount importance is its function in autonomic regulation; it provides parasympathetic inputs to the sphincter pupillae muscle which constricts the pupil in response to bright light, enhancing visual clarity and depth of field. It is also responsible for controlling the ciliary muscle, adjusting the lens shape for near vision. A dysfunction in this nerve can lead to conditions like diplopia (double vision), ptosis (drooping eyelid), and anisocoria (unequal pupil sizes).

Location

The oculomotor nerve emerges from the midbrain, specifically from a region known as the oculomotor nucleus. It travels anteriorly and exits the brainstem at the interpeduncular fossa, situated between the two cerebral peduncles. Subsequently, it passes through the cavernous sinus, a cavity at the base of the skull, before entering the orbit via the superior orbital fissure. Once in the orbit, it branches into different paths to innervate the extraocular muscles and the autonomic components that control pupil size and lens curvature.

Did You Know?

The oculomotor nerve is one of the twelve cranial nerves and is vital for nearly all eye movements except those controlled by the lateral rectus muscle and the superior oblique muscle.
Weakness or paralysis of the oculomotor nerve can lead to a droopy eyelid, known as ptosis, and an inability to move the eye normally.
In addition to its motor functions, the oculomotor nerve also plays an essential role in the body's autonomic nervous system by controlling pupil constriction and lens accommodation.