Retinal nerve cells help us see in the dark
This image shows a top view of light-sensitive retina tissue found in the back of the eye. The snapshot captures the interactions of nerve cell networks that control your vision when you look around on a moonless night.
Night vision is made possible by photoreceptor cells called rods, which are not shown in this image. Rods initiate a series of communications between other nerve cells, two of which are shown here.
The blue structures are the nerve endings of rod bipolar cells, which receive visual signals from rods at night. The thin green extensions from another type of retinal nerve cell--S1 amacrine cells--have tiny swellings that clutch onto the rod bipolar cells. Where the two nerve cells are in contact, they communicate through chemical signals, or neurotransmitters.
Neurotransmitters are a crucial part of the feedback loop between the rod bipolar cells and S1 amacrine cells. When they receive visual input from rods, rod bipolar cells release a neurotransmitter called glutamate. This signal excites the S1 amacrine cells and stimulates them to release another neurotransmitter called GABA.
GABA in turn curbs the release of glutamate from the rod bipolar cells. The delicate balance of this feedback loop ensures that the signal released by the rod bipolar cells stays within the range that downstream nerve cells can handle.
Image courtesy of Wei Li, Ph.D., chief of the NEI Unit on Retinal Neurophysiology.