Question

Input to primary visual cortex from the retina follows three basic pathways. Describe them and explain how each is able to process different aspects of visual information.

Answer 1

MECHANISM OF SIGHT:

The mechanism of sight (vision) is as follows:

1: Light enters the eye through the cornea (which acts as an entrnce window for light).

2: Iris and he pupil regulate the amount of ligh enering the eye.

3: The image is then focussed throgh the lens on the retina.

4: The pigmented choroid darkens the interior of the eye, this reduces scattering and reflextion of light.

5: The image then stimulates the receptors present in the rod and cones of retina.

6: This impulses are then carried through optic nerve. The optic nerves of both sides cross at optic chiasma. From the optic chiasma the impulses are carried by optic tract to visual cortex present in the occipital lobe (of brain). Here the image is preceived.

Light transmitting strucures:

1:Aqueous humour:

2:Lens

3:Vitrous humour

Retina:

It is the innermost nervous coat of eye ball and lens immediately deeper to the choroid.

The retina contains:

1. Nerve cells and nerve fibers which are in the inner surface.

2. Some special structures called rod and cones which are on the outer or choroidal surface of retina. These rods and cones received the light and this setsup impulses which are transmitted through optic nerve.

3. Optic disc is the point where the optic nerve leaves the eye ball. This point does not contain retina and It is insensitive to light so this point is called as blind spot.

4. Macula is a smaller area of retina which is situated just lateral to the entrance of optic neve. Macula is exactly opposite to the centre of pupil. Direct or near vision is focussed on macula.