Question

What are photoreceptors of eyes and where are they found? What is the function of these cells?

Answer 1

Photoreceptors are specialised light-sensitive cells present in the retina, the innermost layer of the eyeball. They are of two types:

1. Rods: Rods are more numerous and are found mainly towards the peripheral parts of the retina. They contain the pigment rhodopsin and are highly sensitive to dim light. They help us to see in twilight or darkness, but they do not provide colour vision.

2. Cones: Cones are found mainly near the central region of the retina, especially in the yellow spot or fovea. They contain opsin pigments and function best in bright light. They provide sharp vision and enable us to distinguish colours. Different cones are sensitive mainly to red, green and blue light.

When light falls on the rods and cones, it produces chemical changes in their pigments. These changes generate electrical nerve impulses. The impulses travel through the optic nerve to the visual centre of the cerebrum, where they are interpreted as vision. The fovea, which is densely packed with cones, provides the greatest visual sharpness, whereas the blind spot has no photoreceptors.