Optic nerve


The optic nerve is a sensory nerve. Its basic responsibility is to transmit information received from rods and cones in the eye known as photoreceptors, and then deliver this information that is received from the retina. At the back of the eyeball, there is a gathering place for the optic nerves, and here, approximately 125 million nerve fibers which make up the optic nerve congregate.

As a unit, they can then pass through the optic canal and enter the brain through the cranial cavity. Each eyeball has its own optic nerve, and these two nerves then meet at the diencephalon, along the floor, to create a unified nerve known as the optic chiasma.


The optic chiasma serves as a point in intervention, as there are nerve fibers which rise up from the medial half of the individual retinas. They cross over at the point of the optic chiasma and then head over to the brain. Those fibers which rise up from the lateral side of the nerve do not stray from their path and continue their journey toward the brain.

Optic tracts lead to the thalamus, encouraging the optic nerves to pass along the posterior portion of the optic chiasma. Specified thalamic nuclei receive the optic nerve fibers and here, the fibers fuse with the nuclei. While most of the ganglion axon cells are devoid of collaterals, a few of them use theirs to convey the various impulses from the thalamic nuclei to the superior colliculi.

Synapses within the thalamic nuclei become the passageway for synapse between the impulses which are required to pass through the neurons, which eventually lead into the visual cortex. The visual cortex can be found within the occipital lobes.


Optic nerve
Image: Optic Nerve


There are additional synapses that regulate other action and the passage of information. For instance, impulses that are required for the actions of eyeball motor function (moving the eyeball) and other extrinsic forms of motor manipulation are permitted to pass through the nuclei for the oculomotor, abducen, or trochlear nerves. These same nerves support the passage of impulses for neurons to participate in intrinsic eye movement as well.

The entire system is set up to allow the eyeball, and the appropriate neurons, and nerves to respond to light stimuli, which then results in reflexive actions which produce motor responses. The optic nerve is so primitively valuable within the entire process that if the optic nerve is damaged or severed, the eye which relied on that nerve for information relay is now unable to determine sight, and therefore is blinded.
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