Abducens nerve

The abducens nerve is a nerve that controls the movement of the lateral rectus muscle in humans, responsible for outward gaze. It is also known as the abducent nerve, the sixth cranial nerve, sixth nerve, or simply CNVI. It is a somatic efferent nerve.Dura mater and its processes exposed by removing part of the right half of the skull, and the brain.Superficial dissection of brain-stem. Ventral view.Hind- and mid-brains; postero-lateral view.Figure showing the mode of innervation of the Recti medialis and lateralis of the eye.Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure.Cerebrum.Inferior view.Deep dissection The abducens nerve is a nerve that controls the movement of the lateral rectus muscle in humans, responsible for outward gaze. It is also known as the abducent nerve, the sixth cranial nerve, sixth nerve, or simply CNVI. It is a somatic efferent nerve. The abducens nerve leaves the brainstem at the junction of the pons and the medulla, medial to the facial nerve. It runs upwards and forwards from this position to reach the eye. The nerve enters the subarachnoid space when it emerges from the brainstem. It runs upward between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull through Dorello's canal. At the tip of the petrous temporal bone it makes a sharp turn forward to enter the cavernous sinus. In the cavernous sinus it runs alongside the internal carotid artery. It then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye. The abducens nucleus is located in the pons, on the floor of the fourth ventricle, at the level of the facial colliculus. Axons from the facial nerve loop around the abducens nucleus, creating a slight bulge (the facial colliculus) that is visible on the dorsal surface of the floor of the fourth ventricle. The abducens nucleus is close to the midline, like the other motor nuclei that control eye movements (the oculomotor and trochlear nuclei). Motor axons leaving the abducens nucleus run ventrally and caudally through the pons. They pass lateral to the corticospinal tract (which runs longitudinally through the pons at this level) before exiting the brainstem at the pontomedullary junction. The human abducens nerve is derived from the basal plate of the embryonic pons. The abducens nerve supplies the lateral rectus muscle of the human eye. This muscle is responsible for outward gaze. The abducens nerve carries axons of type GSE, general somatic efferent. Damage to the peripheral part of the abducens nerve will cause double vision (diplopia), due to the unopposed muscle tone of the medial rectus muscle. The affected eye is pulled to look towards the midline. In order to see without double vision, patients will rotate their heads so that both eyes are toward the temple. Partial damage to the abducens nerve causes weak or incomplete abduction of the affected eye. The diplopia is worse on attempts at looking laterally. The long course of the abducens nerve between the brainstem and the eye makes it vulnerable to injury at many levels. For example, fractures of the petrous temporal bone can selectively damage the nerve, as can aneurysms of the intracavernous carotid artery. Mass lesions that push the brainstem downward can damage the nerve by stretching it between the point where it emerges from the pons and the point where it hooks over the petrous temporal bone.