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Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
less.
In this installment I will discuss the abducens nerve.
The abducens nerve, also known as cranial nerve VI, is a motor nerve responsible for
supplying one of the extraocular muscles of the eye: the lateral rectus muscle.
The lateral rectus muscle abducts the eye, or moves it laterally toward the side of the
head.
The abducens nerve originates in the abducens nucleus, which is located in the pons.
Fibers from the facial nerve wrap around the abducens nucleus, and the combination of the
nucleus and facial nerve fibers creates a bulge in the floor of the fourth ventricle
known as the facial colliculus.
The abducens nerve fibers exit the brainstem at the junction between the pons and medulla
and supply the lateral rectus muscle on the same side of the head.
Neurons from the abducens nucleus also travel through a pathway called the medial longitudinal
fasciculus to the oculomotor nucleus, where they synapse on neurons that control the medial
rectus muscle of the other eye.
The medial rectus moves the eye inward.
This pathway allows for coordination of eye movement, as when your abducens nerve allows
you to look laterally with your left eye, the fibers that travel in the medial longitudinal
fasciculus cause your right eye to look medially.
Damage to the abducens nerve causes impairment in the ability of the eye the nerve supplies
to to move laterally, and a condition called esotropia in which the eye that’s affected
deviates medially.
In this case, the medial deviation is due to the loss of abducens function and the unopposed
action of the medial rectus muscle.
This also leads to diplopia, or double vision.