What is the difference between rod and cone

Rods help in seeing objects at night or in low light conditions. This phenomenon is also known as scotopic vision. Cone cells help in seeing during daytime and detecting colours of the objects around us.

This type of vision is called photopic view. These photoreceptor cells have rod-like structures and around the periphery of the retina. These cone-shaped cells are seen in the centre of the retina. Of the total million photoreceptor cells, there are a total of million rod cells. There are 5 million cone-shaped photoreceptors. Rod cells are susceptible to light particles, which is why they can detect objects in low light conditions. Compared to rod cells, they are not sensitive to photon particles.

For instance, a response by cone cells to photons is equal to the response of rod cells to one. Deficiency of pigment in rod cells causes night blindness. Colour blindness is caused if there is a deficiency of cone cell pigment. For medical aspirants, NEET is very significant as it is the gateway for admission to important medical colleges within India.

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Each amino acid is encoded by a sequence of three nucleic acids in the DNA. Before identifying the genetic sequence of human rhodopsin, it was sequences in other animals. Here is shown the comparison between the bovine cow sequence and the human sequence. They are very similar with only a small number of differences the dark circles.

Even when there is a difference it may not be functionally significant. The gene for human rhodopsin is located on chromosome 3. This figure shows the sequence for the S-cone pigment compared to that of rhodopsin.

The S-cone pigment gene is located on chromosome 7. Notice how different they are. This figure shows the sequence of the L- and M-cone pigments compared to each other. These pigments are very similar. Only those differences within the cell membrane can contribute to the differences in their spectral sensitivity. The M- and L- cone pigments are both encoded on the X chromosome in tandem. The 23rd pair of chromosomes determines gender.

For females this pair is XX and for males this pair is XY. We will return to this later on when we discuss color vision and color blindness. This means these cells require more photons for vision. Hence, their vision is called high-light vision photopic vision. There are three types of cone cells in the retina.

They respond to different wavelengths : long — nm , medium — nm , and shorter — nm. Therefore, the cone cells are called L-cones sensitive to the red light , M-cones sensitive to the green light , and S-cones sensitive to the blue light. They have three different types of photopsins and give trichromatic or colour vision. Moreover, each cone cell connects to an individual bipolar cell, increasing the resolution of the image. Rod cells are cylindrically-shaped cells in the retina that respond to dim light.

Cone cells are cone-shaped, visual receptor cells in the retina that are sensitive to bright light and colour. These definitions explains the main difference between rod cells and cone cells. As the names suggest, the outer segment of the rod cells is rod-shaped while the outer segment of the cone cells is cone-shaped. Also, another difference between rod cells and cone cells is that rod cells are comparatively long while cone cells are short.

Besides, only a single type of rod cells occur in the retina while three types of cone cells occur in the retina. Furthermore, the retina contains approximately 90 million rod cells and 6 million cone cells. Moreover, rod cells are distributed through the retina while the cone cells mainly occur in the fovea.

Location Rods are usually located around the boundary of the retina. Cones are usually located in the center of the retina.

Amount Rods are about million photoreceptors out of the total million photoreceptors in the human eye. Cones are 5 million photoreceptors. The outer segment is conical of Cones which contain iodopsin pigment. Colour vision Rods cells do not give colour vision, and they do not have any differentiation. Cones give colour vision, and they are of three types: green, blue, and red.

Lack of the pigment in the cones, known as iodopsin may cause colour blindness. Rods are present in ample amount, at the periphery of the retina of an eye. As the name says, these are rod-shaped photoreceptors and supports the vision during dim light or at night.

Rods contain a pigment known as rhodopsin or visual purple, it is a purplish pigment, which is rich in vitamin A. This pigment is responsible for the night vision and so rods are said to be sensitive to light, and the visual pigment is black-white.

This effect is known as the Purkinje effect.