Chapter contents
Overview
Sensory transduction
Central course
Primary visual cortex
Retinal deficits
Optic nerve damage
Chiasm damage
Damage posterior to chiasm
| Cranial Nerve II - Optic Nerve | Page 4 of 11 |
Central Course
The optic nerve travels posteromedially from the eye to exit the orbit via the optic canal in the lesser wing of the sphenoid bone.
Upon exiting the optic canal the optic nerve enters the middle cranial fossa where it joins the other optic nerve to form the optic chiasm:
Figure 2-4a. Central course of the optic nerve.
At the optic chiasm approximately 1/2 of the fibers from each optic nerve cross the midline and exit the chiasm in the opposite optic tract.
The fibers of the optic tracts continue posteriorly around the cerebral peduncles of the midbrain with most synapsing in the lateral geniculate nucleus of their respective thalamus. A small portion of the fibers enter the pretectal region of the midbrain and participate in the pupillary light reflex.
Cells of the lateral geniculate nuclei are tertiary sensory neurons which project to the primary visual cortex in the occipital lobe via the optic radiation (geniculocalcarine tract). Note that the axons of the optic radiation fan out to pass above and lateral to the inferior horn of the lateral ventricles enroute to the visual cortex. The fibers that course anteriorly toward the pole of the temporal lobe before turning posteriorly are referred to as Meyer's loop.
Figure 2-4b. Central course of the optic nerve.
