Nerve · Head

Abducens nerve

Nervus abducens

One nerve, one muscle, one job: the abducens supplies lateral rectus, the muscle that turns the eye outward. Its nucleus sits in the floor of the fourth ventricle in the pons, raising the small bump called the facial colliculus because the fibres of the facial nerve loop over it on their way out. From there the nerve takes an exposed route — it emerges at the junction of pons and medulla, climbs the steep front face of the clivus, bends sharply forward over the petrous ridge of the temporal bone under a tough band of dura, and is the only cranial nerve to lie loose inside the cavernous sinus itself, right beside the internal carotid artery, rather than embedded in its wall. That long, angled, tethered course over bone is the anatomical reason it is the eye-movement nerve most easily stretched.