I was at the eye doctor today for my biannual check-up (all good). Since part of the test was a retina scan, I thought I’d refresh my knowledge of rods and cones in the retina. The human retina contains about 120 million rod cells, and 6 million cone cells. Check out the diagram below for a primer on how the retina works.
Biologists are still learning about all the cells and proteins and chemistry involved in vision. For example, in 2008 a team of Japanese researchers discovered a lightning-fast protein involved in the precise interactions between what is called the photoreceptor ribbon synapse and the bipolar dendrites. They promptly named the protein Pikachurin, after Pikachu, the lightning-fast Pokémon creature.
[Source: Arizona State University ‘Ask a Biologist’ https://askabiologist.asu.edu/rods-and-cones]. 1. Light moves through the lens of the eye to the back of the eye, which is the retina. Here, there are millions of rods and cones. 2. When light hits the discs in the outer segment of the rods and cones, the little bits of light (photons) activate the cells. Rods can be activated in low light, but cones require much brighter light (many more photons). Most of the light not absorbed by the rods or cones is absorbed by the epithelial cells behind them. The discs of rods hold rhodopsin and the discs of cones hold photopsin. Both of these photoreceptor proteins are special molecules that change shape when activated by light. This shape change allows the proteins to activate a second special protein molecule that then starts causing other changes involved in sending a visual signal. For the signal to be sent through the cell, charged molecules called ions are let in and out of the cell in an action potential. 3. When the signal reaches the inner end (left side) of the rods and cones, the signal is passed to sets of neural cells. 4. The signal moves through neural cells in the optic nerve. 5. The optic nerve will send this information to the brain, where separate signals can be processed so you see them as a complete image.
biannual check-up (all good). Since part of the test was a retina scan, I thought I’d refresh my knowledge of rods and cones in the retina. The human retina contains about 120 million rod cells, and 6 million cone cells. Check out the diagram below for a primer on how the retina works.