Eyes part 3

All right so right on the inside of the choroid you have a layer of cells that actually do the work of transducing Light into action potentials And this layer is called the retina it starts right here behind the ciliary body and it sits in just inside of the choroid And it wraps all the way to the back. You’ll notice that there’s a little tube that exits the eye This is where the retina connects with the optic nerve and the optic nerve kind of leaves the eyeball Right down here all right You’ll also notice that the dark sclera here was actually white but in this illustration is dark It leaves as well. This is actually continuous with the dura mater the outermost layer of the meninges that covers the brain All right, so this retina is really important consists Photoreceptors that have this job of transducing light into action potentials these Photoreceptors come in two different varieties the first type are called rods Alright and these rods are much more numerous than the other type of photoreceptor all right these guys are twenty times more Numerous and these rods lie within this retina, and what these rods do is that they encode? Dim Light and or they can and can encode dim light all right in grayscale So they do not encode color these guys are 20 times more numerous than the other type of photoreceptor and they’re really great at encoding dim Light in Greyscale Alright, the other type of photoreceptor called photoreceptors are called cones These are much less numerous than rods, but these guys are can encode color In fact we have three different types of cones. We have Combs’s encode red light Blue light and green light so just like your computer R G B and when color stimulate multiple types of cones at the same time so if you have Multiple types of cones that are stimulated at the same time that will allow you to see obviously colors other than red green and blue Okay Let’s see the whole color spectrum all right, it’s just like kind of Combining which type of cone you stimulate only problem the cones are is that they just require a lot more light to Be stimulated and so they don’t do nearly as well And dem light this makes sense if if the lights are very dim you’ll notice that it’s nearly impossible to see colors But you can still make out the shapes of the objects that might be around you all right umm How these guys are kind of set up is is quite interesting so if I were to just zoom in on a little part of The retina right here and kind of redraw it down here what you would see is you have I’ll redraw this This is the back of the choroid Okay Inside this retina you’ll find that These little rods Are gonna kind of look like that you’ll have your nuclei right there and they’ll have like oval shaped cells that lie right beside the core right there’s a very thin layer of the Of the retina it’s called a pigmented layer of the ripa it lies right behind these Rod cells and the pigmented layer of the retina which is right there, we’ll just call that pigmented you See that pigmented layer That just can say it contains Basically some macrophages that work really well in the renewal process Of all of these different cells, they help kind of renew These cells when necessary so you have all these rods that kind of line right there. You’ll have much more rods thancones All right, you’ll have these rods and cones And what they are all connected to they’re actually all connected to a Bipolar neuron Right here That lies right beside all of these cells and Then that bipolar neuron is attached to an afferent nerve or neuron That leaves the retina in this direction And then leaves the eye so if we were to follow these afferent nerves they would start here and come here And they would exit out the eye Right here in this little tube. Well this little tube is called the blind spot so right there. It’s called the blind Spot and that’s called the blind spot because there’s no photoreceptors in this little area, and you literally can’t encoded any information in in that region of the eye You don’t notice this because your brain does a really great job of kind of filling in what it thinks should be there And so you don’t really notice that there’s a blind spot, and then in the eye all right Now one more thing about the the retina here is that there’s this location right at the back of the eye? And we’ll draw it like right here, and it’s like a little bulge It’s like a little bulge in the retina. That’s right behind the cornea this guy is called the fovea centralis And this fovea centralis contains a very high density of rots and this is actually the only part of your visual field That that’s in focus Most of our visual field is not in focus when we’re when we’re looking around if you The only really part of your vision, that’s in focus is

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