In this episode, Leslie tells us about on center, off surround ganglion cells. See how the configuration of rods with respect to the ganglion cell’s receptive field influences the type of response we get when those rods are stimulated.
Transcript of Today’s Episode
Hello and welcome to another episode of Interactive Biology TV, where we’re making biology fun! My name is Leslie Samuel. In this episode, Episode 35, I’m going to talk about a specific type of ganglion cell that we call “on center, off surround ganglion cells.” Let’s get right into it.
I have a ledger over here that shows to the top left that R stands for rods, B stands for bipolar cell, H stands for horizontal cell, and G stands for ganglion cells. Here, I’m starting with a ganglion cell. We’ve look at the way rods connect to ganglion cells via bipolar cells, so I’m going to show that right now. So here we have 4 rods, and you can see those 4 rods here. Those 4 rods are making synapses with bipolar cells, and the bipolar cells are connecting to this ganglion cell. So this ganglion cell connects to 2 bipolar cells that connect to a total of 4 rods.
When we have this configuration with the rod directly connected to a bipolar cell that is directly connected to a ganglion cell, we call this the center of that ganglion cell’s receptive field. So this is the center of the receptive field, so any stimulation that results in activity in these rod cells is considered to be in the center of that ganglion cell’s receptive field.
Then we can have another configuration where we have rods that are connected to bipolar cells, so here we have a rod that’s connected to a bipolar cell that’s connected to a horizontal cell, and then it connects to the ganglion cell. So it goes via a bipolar cell, then a horizontal cell, and that eventually gets connected to this ganglion cell. Since it’s not directly from the bipolar to the ganglion cell, like it is over here, we call this not the center, but the surround. So any stimulation that stimulates these rods is considered to be in the surround of that ganglion cell’s receptive field.
So once again, these rods are considered to be in the center of this ganglion cell’s receptive field because they are connected directly via a bipolar cell to that ganglion cell. These rods, these two, the one over here and the one over here to the left are considered to be in the surround of that ganglion cell’s receptive field because they don’t go directly from the bipolar cell to the ganglion cell. They go via a horizontal cell.
Now, if this ganglion cell is considered to be an on center, off surround ganglion cell, that’s going to give a specific type of response. This is the response. I’m going to draw a graph over here that plots, as usual, the membrane potential versus time, and I’m going to draw one over here that does the same thing, time and membrane potential. We’re going to say that this is the center, this is when rods in the center of the receptive field are stimulated, and this is in the surround. We’re going to get 2 different responses. The response that I’m going to get here when there’s stimulation from the center is that we’re going to get an increase in the membrane potential, so it’s going to depolarize, and as we looked at with the ganglion cells before, we’re going to get a burst of nerve impulses in response to that stimulus. This is the on center response.
Now, if a rod gets stimulated in the surround of that ganglion cell’s receptive field, we’re going to get the exact opposite where we’re going to get a hyperpolarization, and then the membrane potential is going to come back up. In some cases, what we’re going to get here once this hyperpolarization happens and we get this rebound back to where the membrane potential was before, you’re going to get a burst of nerve impulses, but those nerve impulses are going to come after the stimulation. This is called a post-inhibitory rebound. So that’s basically saying it’s post-inhibition, so it’s after that inhibition happens, we’re going to get a rebound and some firing as soon as the stimulation stops.
Once again here, in the on center response, we get depolarization and a burst of nerve impulses in the ganglion cell. In the surround, we’re going to get an off surround response which is basically going to give us hyperpolarization, and then a post-inhibitory rebound. And you can see that those are 2 totally different responses, and the key ingredient here in that off surround response are these horizontal cells, because when they get stimulated by these bipolar cells, they are actually going to inhibit the ganglion cell that you see here. So this refers to the on center, off surround response of ganglion cells. This is a specific type of ganglion cells.
I just want to mention really quickly that we can also have off center, on surround ganglion cells, and if that were the case, we would get an off center response. In other words, if it’s stimulated in the center, we’d get this response over here with the post-inhibitory rebound, and if it’s stimulated in the surround of the ganglion cell’s receptive field, we’re going to get this burst of nerve impulses in response to the depolarization that happens.
That’s really all I want to talk about for this video. If you have any questions, as usual, go ahead and leave them in the comments section below, and I’d be happy to answer your questions. That’s it for now, and I’ll see you in the next video.