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.