Human Anatomy - Kotsan I. Ya. 2009

Peripheral Nervous System
Cranial Nerves
Optic Nerve (II)

The Optic nerve (n. opticus) is sensory in function. During Embryogenesis, it develops as an outgrowth of the optic vesicle from the Diencephalon, whereas in phylogenesis, it is associated with the Midbrain, which evolved in connection with photoreceptors—thus explaining its strong structural connections with these Regions of the Brain (Figs. 239, 254). The optic nerve contains somatic sensory fibers that transmit impulses generated by light and color stimuli. Being of cerebral origin, much like the first pair of Cranial Nerves, it lacks a ganglion. The optic nerve consists of axons originating from large ganglion Cells located in the ganglionic layer of the retina. Piercing the Tunics of the Eyeball, these axons emerge from its posterior surface and, unlike the olfactory nerves, converge to form a single optic nerve trunk. Leaving the posterior pole of the eyeball, the optic nerve passes through the optic canal from the orbital cavity into the cranial cavity. Upon entering the cranial cavity, the optic nerve approaches its counterpart from the opposite side, and the two nerves (right and left) form a partial decussation of optic nerve fibers known as the optic chiasm (chiasma opticum).

The lateral fibers of each optic nerve continue on the same side, whereas the medial fibers cross over to the opposite side, where they join the lateral fibers of the contralateral optic nerve to form the optic tract.

Consequently, each optic tract contains fibers originating from the ipsilateral lateral half of the retina and the contralateral medial visual field.

The optic tract curves laterally around the cerebral peduncle and terminates in the subcortical visual centers, which on each side are represented by the lateral geniculate body, the pulvinar of the thalamus, and the nuclei of the superior colliculus of the midbrain tectum.

Fibers emerging from the Cells of the lateral geniculate body and the pulvinar of the thalamus course through the posterior limb of the internal capsule into the cerebral hemisphere, forming the optic radiation, and terminate in the cortex of the Medial surface of the occipital lobe.

Fibers originating from the superior colliculi of the midbrain tectum project to the nuclei of the oculomotor and other cranial nerves, as well as to the tectospinal tract.