I know they’re in the retina, but I don’t fully understand their roles.
The ganglion is the innermost, and these cells send signals to the brain, which result in our vision being “activated”.
The bipolar is the middleman between the starburst and the ganglion cells, and this type is responsible for…? Seems like a translator of some sort?
I fail to understand anything about the starburst cells, though.
In: 1
It’s easiest to go in “order” of neuronal activity to explain this.
Light comes into the eye, through a couple of transparent layers (containing ganglion, bipolar, amacrine, etc. cells), and hits the photoreceptors – rods and cones. Cones, of course, are responsible for vision at higher light levels and are better for color vision, while rods are responsible for vision at low light. The rods and cones hyperpolarize and send a signal back through the layers, starting with…
…**bipolar cells**, which function primarily to transmit signals from the photoreceptors to ganglion and amacrine cells – indeed, they are literally so named because they’re basically linear with two distinct “ends”; they have a cell body that has one axon sticking out of either side (one to receive, one to transmit). You can think of them basically as power lines. Generally they are specific to a type of photoreceptor – either rods or cones. They can transmit data directly to ganglion cells, or first to…
…**amacrine cells**, which are very diverse (there are over 30 types) and perform a wide range of functions. They are intermediate neurons, serving to modulate and pre-process the signal that they will then pass on to the ganglions for transport to the brain. Some amacrine cells (AII amacrine cells), for example, function specifically to transmit signals vertically from rod bipolar cells to ganglion cells, which helps with vision in dim conditions. Another type, A17, has an incredibly spread-out dendritic tree which helps it integrate information horizontally from multiple photoreceptors, and is thought to help amplify signals from thousands of rod bipolar cells to boost vision at very low light levels. **Starburst amacrines** are yet another type of amacrine cell and these play a role in direction sensitivity, i.e. detection of directional motion, by modulating the signal they send to direction-selective ganglion cells (DSGCs, a specialized type of ganglion cell dedicated to motion detection).
Finally, you already had the right idea about **ganglion cells** – they are the main signal output neuron. Ganglion cells receive all of that visual information from the rods/cones that has been modulated and pre-processed by horizontal and amacrine cells, and send it to the brain. In addition, as hinted at earlier, while signal output to the brain is the *primary* function of the ganglion cells, they too have multiple types that can perform several specialized functions, such as motion detection and even acting as a third type of photoreceptor.
[Here is a helpful little diagram](https://upload.wikimedia.org/wikipedia/commons/d/d6/Retina-diagram.svg) to put it all in place spatially, if that helps. Light is coming from the left; rods and cones are at the far right. Bipolar cells transmit the signals to the yellow layer, which contains horizontal cells and the extended dendrites of ganglion/amacrine cells. The modulated signal then gets taken up by the ganglion/amacrine cells for further processing in the purple layer, and then finally the ganglion cells send it off to the brain.
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