As we talked about the structure of the retina, as we said that there were 2 types of photoreceptor cells, our rods and our cones. Here we want to figure out what the difference between those two things are. Now we're going to talk about rods and cones a fair amount going forward and really sort of dive into how they work. Here, we just sort of want to look in sort of grand schemes, what's the difference between these two things. So we're just going to start out saying that there are 2 types of photoreceptors in the retina, and they are going to be named for their shape. And so we can look over here at our image, and this is sort of just pulled out from that image that we had before of the retina. We can see here we have the axons and then the ganglion cells. We have the bipolar cells, and then this is what we're really talking about here, the rods and the cones. And just remember, light is coming in this way to the eye. So you can see in orange here, these are the rods, and you can see that they are sort of long and skinny, but sort of the same thickness the entire way through. Where in contrast, our cone, here in red, has a sort of pointed cone-shaped end on it. So that's where those names come from. Alright. What's actually different between them and how they function, though?

Well, rods and cones, the first difference and probably the key difference that people are aware of is their ability to see color. Rods can only see in grayscale. Rods are going to be really good at sensing the brightness of things, but they cannot distinguish different colors. So if you're using only rod vision, your vision is in black and white. Now, in contrast, cones. Cones provide color vision. Now, we normally think of seeing the world in color, so when you think of color vision, you're really thinking of your cone vision. Alright. Well, I like to see in color, so why do I have rods? Well, a key difference here that makes rods very useful is that rods have really high sensitivity. And by that, they mean that they work in very low light. Now in contrast, cones have low sensitivity. They require relatively bright light to sense anything. Now in today's world, we don't experience our raw vision nearly as much as probably our ancestors did because, well, it's bright everywhere. If it's dark in a room, I just turn on a light and make it bright, and heck, everything's in color. But if you've ever spent some time in a dark place or walking around at night, you'll know that you can actually see things pretty well even in very dim light, but you can't see color very well in that dim light. If you're walking around at night again, you can see well, but you can't see color that's because you're really experiencing your rod vision. The light is low enough that those rods are being stimulated, but the cones are not. And in fact, in bright light, your rods largely shut down. So your rods during the daytime in bright light really aren't doing much at all. Really, you're pretty much only using your cones when it's bright up. Alright. Our next difference is going to be acuity. And by acuity, we just mean how fine or how detailed is that image that they can see? Well, this comes down to the fact that rods have this many to 1 ganglion relationship. So by that we mean, as we look over here, we have 3 different rods, and they're all sort of funneling up and connected to the same ganglion cell up here. In reality, there's going to be dozens of rod cells that connect to every ganglion cell. So that means that when this ganglion cell is stimulated and it sends an action potential down its axon, down the optic nerve to the brain, the brain will know where in the retina it came from, but it can't map it back down to the individual cell. It just knows that this ganglion cell was stimulated. It doesn't know which rod that it connects to actually did the stimulation. So this means that rods see with low acuity. They sort of see in low definition. You can sort of think of it as kind of like a big pixel size, because all of these rods are funneling in. It's sort of covering a decently large area of the retina, at least relatively large area of the retina connected to a single ganglion cell. So that's sort of like a big pixel you're seeing with. Now one of the reasons it does that is that helps with that sensitivity. Now a single rod might not be stimulated enough to set off this action potential in a ganglion cell, but if many rods are stimulated just a little bit, that might be enough to get this ganglion cell over that threshold and send a signal 1 to 1 ganglion relationship, and that allows us to see with our cones in very high acuity. So we look over here, we have this cone right here, and we can see this, like every cone, connects to a single bipolar cell, which connects to a single ganglion cell, which then sends the signal to the brain, and the brain can map that back to the single cell that was stimulated, the exact place in the retina. That means that with your cone vision, you can see in really high definition. Alright. Location. These are not distributed equally in the retina. In fact, the rods are going to be concentrated in the periphery. So your peripheral vision, the sides of your vision, is largely rod vision. You do have cones out there, but that's where most of the rods are. That means that in your peripheral vision, well, you have low acuity. Right? It's tough to see detail in your peripheral vision, but you do have high sensitivity, and this kind of makes sense. You want to see things that are moving or flying at you or, I don't know, a tiger jumping out of the bushes out of your peripheral vision. Your rods will be able to see that, but th