The Retina

1039 Words Dec 1st, 2013 5 Pages
THE RETINA: RECEPTOR CELLS

The receptor cells are the RODS and CONES. Each consists of: * A process consisting of outer and inner segments. * An external fiber connecting the process with the soma. * A soma or body containing the nucleus. * An inner fiber that resembles an axon and synapses with a bipolar cell.

Rods are extremely sensitive to light and can react to a single photon. The light is absorbed by the pigment rhodopsin and the energy acquired results in decrease in cGMP which in turn causes the closing of Na+ channels. This hyperpolarizes the cell causing a release of synaptic vesicles.
Rhodopsin which can only detect variation in intensity of light resulting in gray level visio

Horizontal
…show more content…
The Meyer’s loop fibers carry information from the lower retina, and thus from the upper part of the visual field to the lower bank of the calcarine fissure.

THE VISUAL CORTEX
The information received by the primary visual cortex is illlustrated in A below: It is inverted and reversed, and the center has high resolution which becomes progressively worse toward the periphery. In addition, there are fewer cones at the periphery, so the image contains less color at the periphery.
The visual cortex reconstructs the image with constant color and resolution.

INFLAMMATION OF THE OPTIC NERVE
Because nearly ½ of the fibers in the optic nerve are from the fovea, inflammation of the nerve will affect color perception and resolution in the central vision in the ipsilateral eye.
LESION OF THE OPTIC NERVE
A lesion that destroys the optic nerve will destroy all input from that retina, leading to monocular visual loss (blindness in that eye).

LESION OF THE OPTIC CHIASM
A lesion of the optic chiasm will destroy the fibers from the medial halves of both retinas where they cross. Remember that the medial half of the retina receives the image from the lateral half of the visual field. Thus a lesion of the optic chiasm will result in loss of the lateral halves of the visual fields, sometimes called “tunnel vision” (bitemporal hemianopia).

LESION OF THE OPTIC TRACT
A lesion of the