14 August, 2017
How Your Eyes Send Images to the Brain
There are two distinct kinds of cells in the eyes, the cones and the rods. The cones are the cells which are responsible for transmitting color vision to the brain. As InnVista explains, there are three different kinds of cones: green absorbing, red absorbing and blue absorbing. Colors are identified in the brain by examining the relative activity of all three kinds of cones. When colored light hits the pigments in the cones, it generates a chemical signal. This signal then causes a small electrical current to develop in the cone cells and some of the other nerve cells in the retina, which is the beginning of transmitting color images to the brain. Cone cells are concentrated in the middle of the retina and are tightly clustered in a special eye region called the fovea.
Rod cells are used for low light conditions. They do not have the ability to detect colors but they are able to generate signals to the brain when the amount of visible light is very low. As the Veterinary Medicine school at Virginia Tech explains, when light hits rod cells, it causes a compound called rhodopsin within the rod cells to break down. This chemical change causes an electrical signal which is detected by other cells nearby which then transmit the signals to the brain. Rod cells tend to be located at the periphery of the eye, which means that night vision works better with images seen out of the corner of the eye than objects looked at directly.
Signals from the cone and rod cells are passed on to neurons which eventually come together to form the optic nerve. Some of the nerve signals from each eye are sent over to the other side of the brain at a part of the optic nerves called the optic chiasm. This allows signals from both eyes to be used by the brain to give binocular vision. Once the signals are sent to the brain they are processed by the visual cortex, which is located in the back of the head. This part of the brain takes all of the signals from the eye and turns them into images.
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