Visual Sensory System

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The following information is taken from the one source listed at the end of this response.

RESPONSE:

1. A brief description of the sequential flow of visual information through its respective neural processes in the eye, the brain and spinal cord, and with the input finally resulting in an emotion, a complex action, a verbal statement and a memory.

IT ALL BEGINS IN THE RETINA...

The retina is responsible for converting light into neural signals that can be relayed to the brain. The retina consists of a team of five types of cells whose role it is to collect light, extract basic information about color, form, and motion, and pass the pre-processed image on to centers in the brain. These cell types are photoreceptors, bipolar cells, horizontal cells, amacrine cells, and ganglion cells. They are arranged within the retina in three layers, from the back to the front. An image shining upon the retina traverses the three layers to reach the photoreceptor cells, which absorb the incoming light and transform it into electrochemical signals. Photoreceptors are divided into two subtypes, rods and cones, named for their shape. Rod cells are very sensitive to changes in contrast even at low light levels, but consequently are imprecise in detecting position (due to light scatter) and insensitive to color. Rods are generally located in the periphery of the retina and used for night vision. Cones are high-precision cells that are specialized to detect red, green, or blue light. They are generally located in the center of the retina in a region of high spatial acuity called the fovea. Signals from the photoreceptors pass forward into the next layer of the retina containing horizontal, bipolar, and amacrine cells. These cells form small networks that are able to extract information about form and motion from an image. That information continues to the front of the retina where it is received by a layer of ganglion cells. The ganglion cells send out long, thin fibers that bundle together and plunge back down through the retina and out the back of the eye into the optic nerve, which carries them deep into the brain. The spot where the optic nerve exits the eye is devoid of cells, and forms a blind spot in each eye.

The optic nerves within each eye meet in the front part of the head at a point called the optic chiasm, which functions like a cloverleaf on a highway. All the fibers from the left half of each retina turn towards the right side of the brain, and the fibers from ...