Notes

Horizontal cells modulate the output of photoreceptors and play many roles in early visual processing contributing to contrast enhancement, color opponency, and the generation of center-surround receptive fields in cones. In the human retina there are approx. 1 million ganglion cells (per eye), which collect information about the visual world from bipolar and amacrine cells (retinal interneurons). There are many types of amacrine cells that are distinguished based on the way they respond to visual inputs. Then, the layer of photoreceptors responds to changes in membrane potential. Indeed, when the membrane changes potential, photoreceptors release neurotransmitters (All known NTs are present in the retina). Since they need nutrients, they are located closely to blood vessels, i.e., at the back of the eye in humans.