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2-Minute Neuroscience: Optic Nerve (Cranial Nerve II)

Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or

less.

In this installment I will discuss the optic nerve.

The optic nerve is a sensory nerve responsible for transmitting information about vision

to the brain.

The nerve begins in the retina as the axons of cells called retinal ganglion cells.

These axons come together to leave the eye at a region called the optic disc and form

the optic nerve.

The optic nerve leaves the eye and extends to a structure called the optic chiasm where

it meets the optic nerve from the other eye.

At the optic chiasm, the optic nerve fibers carrying information from the sides of the

retina closest to the nose cross over to the other side of the brain, while those carrying

information from the sides of the retina closest to the temples remain on the side of the brain

where they are.

After leaving the optic chiasm, the nerve fibers are referred to as the optic tract.

Most of the nerve fibers in the optic tract end in the lateral geniculate nucleus of the

thalamus, and from there the information will be passed on to the visual cortex.

Damage to the optic nerve can occur due to a variety of causes like trauma, tumors, stroke,

or glaucoma.

The deficit that occurs after damage depends on where the nerve is damaged, and involves

some degree of visual defect or anopsia.

If the damage occurs before the optic chiasm, then the patient will experience blindness

in the eye supplied by that optic nerve.

Damage to the middle of the optic chiasm will cause loss of the lateral visual field of

both eyes, due to the way fibers from the nasal side of the retina cross over at this

point.

If the optic tract is damaged, one half of the visual field will be lost in both eyes.