abducens nerve

The abducens nerve (6n), also known as the sixth cranial nerve (CN VI), is a cranial nerve that runs to the muscles of the eye. It is responsible for controlling the lateral rectus muscle, which moves the eye outward (abduction).

The abducens nerve originates from its nucleus in the pontine tegmentum (floor of the fourth ventricle in the brainstem). It has a long intracranial course traveling through the cavernous sinus before entering the orbit through the superior orbital fissure to innervate the lateral rectus muscle.

The sole function of the abducens nerve is to supply motor innervation to the lateral rectus muscle of the eye, enabling abduction — the movement of the eye away from the midline. This movement is essential for horizontal gaze and coordinated binocular vision.

Abducens nerve palsy (CN VI palsy) causes an inability to abduct the affected eye, leading to horizontal double vision (diplopia) with the eyes deviated inward (esotropia). Causes include increased intracranial pressure, microvascular disease (often in diabetes), brainstem tumors, and multiple sclerosis.

The oculomotor nerve (CN III) controls most of the eye's muscles (including the medial rectus, superior and inferior rectus, inferior oblique, and levator palpebrae), whereas the abducens nerve controls only the lateral rectus. CN III also carries parasympathetic fibers for pupil constriction, which the abducens does not.