|MadSci Network: Cell Biology|
Cones cells, and also rod cells, are photoreceptor neurons of the neural retina. During development, before birth in humans, our neural retinas are formed by a supply of cells called neural progenitor cells. These divide and divide to make the number of cells you will need for your functional retina. At some point most of these cells stop dividing and they "choose" their cell fate. That is they start to differentiate into one of the six major neurons of the retina: cones, rods, bipolar cells, amacrine cells, horizontal cells or ganglion cells (ganglion cells have loooong axons that bundle together to make your optic nerve and they stretch all the way to your brain). All of these cells are formed; turning into these different cell types with different jobs. They do not divide again. Then, if your retina is healthy, these cells last your entire life. Therefore, cone cells live as long as you do. That is why losing photoreceptors (cones and rods), due to diabetes effects etc., is such a problem. You cannot grow new ones. DR Ken Mitton, PhD Associate Professor of Biomedical Research Oakland University Eye Research Institute Rochester MI USA.
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