Photoreceptors

by Jason Amores Sumpter
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These light signals are transducer in our photo receptors in the retina, and we actually have two types in the human eye rods and these other types called cones, that we'll get to in just a moment now, rods or photoreceptors that are capable of detecting lower levels of light. However, they're not capable of detecting color of light. So these air sort of like our black and white receptors. They're usually found around the outer edges of the retina and make up more of our peripheral vision. But that's not the case with all organisms. For example, cats tend to have lots of rods, uh, in their retinas, and not just on the outer edges, so that they can see better in the dark. Since you know they are are they tend to be nocturnal hunters. No reduction is the light sensitive receptor protein that's actually going thio. You know, do the photo transaction in rods, and it's composed of two components. Retinal an option. Retinol is a light absorbing molecule. It's actually a form of vitamin A. That's why just another reason it's important to take your vitamins an option is a light sensitive protein. Now what's going to happen is retinol will absorb light and this is going thio rearrange its structure and cause a confirmation. I'll change in option and basically it's going to act as a G protein receptor that will lead to the opening of sodium ion channels. And you can see a little model of that here. So if light and I'm just gonna use a sort of lightning bolt arrow if light strikes read option, it's going thio cause, uh, retinol to absorb it. And that's going to cause a change in the structure. And here, you see, they'll actually split in. The option will go and, you know, ultimately act as a g protein, too. Open this ion channel and you can see what a Rod looks like. Sort of big picture wise over here. Uh, you know, it's not your typical looking nerve cell. It has some weird structures. It does have, you know, a synaptic body and, you know, sell body with the nucleus. That's kind of normal looking. But, you know, then this stuff all up here is just bonkers. And the read option is going to actually be stored in this outer segment that has thes uh, in folded membranes all through here. That's what that pink line is thes in folded membranes, and that's going to contain the read option and have it ready to go when light strikes. Now cones are the photo receptors that we use for color vision. And unlike rods that can pick up low levels of light, these really function best in bright light. And they use different pigments to absorb different wavelengths of light. You can actually see a really nice chart right here that shows you the absorption of blue cones, green cones and red cones, three types of cones we have in our eyes. And, you know, maybe if you've ever seen a projector with the three different colored bulbs in it, you might have noticed that those are actually blue, green and red bulbs. Now you can also see Rod's absorption here kind of in the middle. In the middle of all these, however, I do want you to note that it's gonna be picking up light in, you know, a range that has a decent amount of energy. That's that's the only thing I want to convey their Now the phobia is a special part of the retina. It's a little pit in the back, sort of in the center of the retina, and it's gonna be packed with cones. And this is so that as light enters the eye, the center of our you know, our field of photo receptors is gonna have tons of these cones. And that's going to be the central point for light to be focused on. And so that's going to give us the clearest possible image. You know, when we translate all those signals in our brain and you can see a cone structure here. It's not, uh, terribly similar to A Rod's, but it has that same component of the outer segment with the in folded membrane that's going to contain the photo pigment, Uh or rather, the pigment used for photo reception. However, of course, its outer segment is shaped more like a cone, whereas the rods outer segment is shaped more like a rod. And scientists just aren't very creative when it comes to naming most of the time. So with that, let's go ahead and turn the page