The abducens nerve is also known as cranial nerve 6. Like the other eye related cranial nerves, the abducens emerges either side of the midline. It leaves the pontomedullary junction, medial to the facial and vestibulocochlear nerves. As with all eye related cranial nerves (3,4,6) excluding the optic nerve, the nerve leaves the cranial vault via the superior orbital fissure.
The abducens is also known as cranial nerve 6. The name Abducens comes from the word ‘abduct’ meaning move away from the midline. The nucleus of the abducens nerve lies in the floor of the fourth ventricle, on the posterior surface of the pons. The fibers of facial nerve loops around the fibers of the abducens nerve in the pontine tegmentum. The abducens nerve emerges from the pontomedullary junction either side of the midline. The nerve then enters the subarachnoid space and runs in Dorello’s canal, which is bordered superiorly by the petrosphenoid ligament, and inferior laterally by the petrous portion of the temporal bone and the clivus medially. It then runs forwards to eventually reach the cavernous sinus, where it runs close the internal carotid artery in the medial wall. It passes forwards to leave the skull via the superior orbital fissure and innervate the lateral rectus muscle (the muscle that abducts the eye).
The oculomotor nerve nucleus, trochlear nerve nucleus and the abducens nerve nucleus lie within in the brainstem. A tract called the medial longitudinal fasciculus connects them. This ensures that our two eyes move in coordination, so when we are following a moving object we are able to focus on it. When the medial rectus contracts in one eye (oculomotor innervation), the lateral rectus contracts in the other. Hence the eyes move in the same direction.
Lateral rectus palsy- This manifests as an inability to abduct the eye beyond the midline in the affected eye. The eye is able to move to the midline from the adducted position, but is not able to move beyond. Causes include diabetes, brain tumours, and demyelinating diseases. The relatively long course of the abducens nerve makes the nerve vulnerable to injury. Petrous temporal bone fractures can damage the nerve, as can intracavernous aneurysms of the internal carotid artery. Any lesion that causes inferior brainstem movement can also damage the nerve by damaging the point at which the nerve exits the pontomedullary junction, and the point where it arches over the petrous portion of the temporal bone.
Developmental precursor- Basal plate of the pons (metencephalon- secondary brain vesicle)
Muscle supplied- Lateral rectus
Superior Oblique innervated by the fourth cranial nerve (trochlear nerve)
Lateral rectus innervated by the 6th cranial nerve (abducens)
The others are supplied by the oculomotor nerve.
The abducens is the 6th cranial nerve. It arises from the pontomedullary junction either side of the midline. The nerve supplies the lateral rectus muscle (which abducts the eye).
1. Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders, Chapter 1 Head and Neck
2. Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier
3. Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier
4. Elliiot L.Manchell: Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience