Abducens Nerve: Origin, Course,functions and Distributions

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Overview

Abducens Nerve also known as  Abducent Nerve  is the 6th cranial nerve. It is motor and supplies only 1 muscle, the lateral rectus of the eye-ball.

It is named so because it abducts the eye. It’s also termed fan’s nerve, because in ancient times (nonverbal age between the adolescent girls and boys), the boy utilized to call the girls from a party by sending signal via the actions of the Muscle.

It is most vulnerable to damage of all The Cranial Nerves during Raised Intracranial pressure, functional Parts And Nuclei General Somatic Efferent Fibres.

Abducens nerve Origin

They originate from the Abducens nucleus in the pons and supply the lateral rectus muscle of the eyeball.

Abducens nerve course

The Abducent Nerve Originates At The Lower Border of The Pons Opposite The Pyramid of The Medulla The Nerve Runs Upward, Forwards and Laterally Dorsal To The Anterior Cerebellar Artery And Pierces The Dura Mater Over The Clivus Inferolateral To The Dorsum Sellae.

It then Goes through the Medial Wall of The Inferior Petrosal Sinus And Arches Forwards Directly Over The Sharp Ridge of The Petrous Temporal Bone, Under The Petroclinoid Ligament And Enters The Fibro-Osseous Canal (Dorello’s Canal) Created By The Apex of the Petrous Temporal Bone And Petroclinoid Ligament (Gruber’s Ligament).

The nerve subsequently, Enters The Cavernous Sinus By Piercing The Posterior Wall Near The Floor of The Sinus In The Cavernous Sinus, It Runs Forwards Inferolateral To The Internal Carotid Artery The nerve enters the orbit via the superior orbital fissure inside the tendinous ring lateral to 2 sections of oculomotor and nasociliary nerves.

General somatic afferent fibres. They Carry Proprioceptive Sensations from the Lateral Rectus. and terminate In The Mesencephalic Nucleus of The Trigeminal Nerve Course, Relationships and Distribution.

In the orbit, it runs forward, toward the lateral side to go into the orbital surface of the lateral rectus muscle which  it supplies.

Abducens nerve Function

The abducens nerve provides innervation to the lateral rectus muscle – one of the extraocular muscles.

The lateral rectus originates from the lateral part of the common tendinous ring, and attaches to the anterolateral aspect of the sclera. It acts to abduct the eyeball (i.e. to rotate the gaze away from the midline).

Clinical Relevance 

Examination of the Abducens Nerve

The abducens nerve is examined in conjunction with the oculomotor and trochlear nerves by testing the movements of the eye.

The patient is asked to follow a point with their eyes (commonly the tip of a pen) without moving their head. The target is moved in an ‘H-shape’ and the patient is asked to report any blurring of vision or diplopia (double vision).

Abducens Nerve Palsy

Abducens nerve palsy can be caused by any structural pathology which leads to downwards pressure on the brainstem (e.g. space-occupying lesion). This can stretch the nerve from its origin at the junction of the pons and medulla.

Other causes include diabetic neuropathy and thrombophlebitis of the cavernous sinus (in these cases, it is rare for the abducens nerve to be affected in isolation).

Clinical features of abducens nerve palsy include diplopia, the affected eye resting in adduction (due to unopposed activity of the medial rectus), and inability to abduct the eye. The patient may attempt to compensate by rotating their head to allow the eye to look sideways.

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