Cranial Nerve II - Optic Nerve
Figure 8. Cranial Nerve II – Optic Nerve
This nerve, like the olfactory is exclusively a special sensory nerve and as can be surmised by its name it is involved with the sense of vision. The nerve originates in the retinal ganglion cells which are the third neuron the signal passes through in the retina. These axons gather at an area known as the optic disc in the medial portion of the retina and exit each eyeball as an optic nerve. The optic disc has no light sensing cells so it corresponds to the blind spot of the eye. Having left the eye each of the pair of nerves passes through their respective optic canal. The two optic nerves then join at the optic chiasm where, as one can see in the diagram, the fibers from the medial portion of retina cross the midline and continue with the lateral fibers from the ipsilateral eye as the optic tract through the lateral geniculate body which mediates the “hunter’s reflex” to turn one’s head to better see an object moving in our lateral vision. The signals then pass through the optic radiations to the occipital lobe of the brain for processing.