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Question

Write short note on retina.


Solution

The retina is the innermost layer. It contains three layers of cells viz., inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types, rod cells, and cone cells.
(i) Rod cells: The rods contain rhodopsin pigment (visual purple), which is highly sensitive to dim light. It is responsible for twilight vision.
(ii) Cone cells: The cones contain iodopsin pigment (visual violet) and are highly sensitive to high-intensity light. They are responsible for daylight and colour visions.
The innermost ganglionic cells give rise to optic nerve fibre that forms the optic nerve in each eye and is connected to the brain. In this region, the photoreceptor cells are absent. Hence, it is known as the blind spot. At the posterior part, lateral to the blind spot, there is a pigmented spot called macula lutea. This spot has a shallow depression at its middle known as the fovea. Fovea has only cone cells. They are devoid of rod cells. Hence, it is the place of most distinct vision.

Biology
NCERT
Standard XI

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