Optic nerve

The optic nerve is the nerve that transmits visual information from the retina to the brain.

Anatomy

The optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nervous system as it is derived from an outpouching of the diencephalon during embryonic development. Consequently, the fibers are covered with myelin produced by oligodendrocytes rather than the Schwann cells of the peripheral nervous system. This is an important issue, as fiber tracks of the mammalian central nervous system (as opposed to the peripheral nervous system) are incapable of regeneration and hence optic nerve damage produces irreversible blindness. The fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from whence a major relay inputs into the primary visual cortex.

Related Topics:
Cranial nerve - Central nervous system - Diencephalon - Oligodendrocyte - Schwann cell - Peripheral nervous system - Retina - Primary visual cortex

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The optic nerve is composed of retinal ganglion cell axons and support cells. It leaves the orbit (eye) via the optic canal, running postero-medially towards the optic chiasm where there is a partial decussation (crossing) of fibers from the temporal visual fields of both eyes. Most of the axons of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex. Its diameter increases from about 1.6 mm within the eye, to 3.5 mm in the orbit to 4.5 mm within the cranial space. The optic nerve component lengths are 1mm in the globe, 25mm in the orbit, 9mm in the optic canal and 16mm in the cranial space before joining the optic chiasm. There, partial decussation occurs and about 53% of the fibers cross to form the optic tracts. Most of these fibers terminate in the lateral geniculate body.

Related Topics:
Retina - Ganglion cell - Orbit - Optic canal - Optic chiasm - Temporal - Axon - Lateral geniculate nucleus

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From the lateral geniculate body, fibers of the optic radiation pass to the visual cortex in the occipital lobe of the brain. More specifically, fibers carrying information from the contralateral superior visual field traverse Meyer's loop to terminate in the lingual gyrus below the calcarine fissure in the occipital lobe, and fibers carrying information from the contralateral inferior visual field terminate more superiorly.

Related Topics:
Optic radiation - Visual cortex - Occipital lobe - Meyer's loop

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