The table below shows the major differences between rod and cone cells which you can go through quickly to gain an idea of the same. 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. Eyes are one of the primary sense organs found in the human being and other animals.
The role of the eyes is to visualize the object coming in front of us. But the core work is done by the photoreceptors, which are found in the retina of an eye. There are around million photoreceptors present in the human eye, and these cells work by absorbing light and further converting into signals, which triggers the membrane potential and result in visual phototransduction or supporting the vision in the light.
There are various factors like sensitivity, function, deficiency disease, etc. Basis for Comparison Rods Cones Meaning Rods are one of the photoreceptors found in the eye, these have rod-like structure and provides twilight vision. Cones are also photoreceptors present in the eye, they are fewer in number and are of the cone shape. 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. 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.
In addition, several rod cells connect to a single bipolar cell while one cone cell connects to one bipolar cell. Rod cells are involved in peripheral vision while cone cells can only detect the images in the centre of the retina. Hence, this an important difference between rod cells and cone cells.
Another difference between rod cells and cone cells is that rod cells are responsible for monochromatic vision while cone cells are responsible for coloured vision. Photoreceptive pigments is another difference between rod cells and cone cells. Rod cells contain rhodopsin while cone cells contain photopsin. Rod cells are more sensitive and responsible for night vision while cone cells have a poor sensitivity and require bright light for vision.
Thus, this is also a major difference between rod cells and cone cells. More to above, the rod cells possess a poor acuity while cone cells possess a higher acuity. 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. The Receptor Mosaic. This figure shows how the three cone types are arranged in the fovea.
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