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Current time:0:00Total duration:10:28

Video transcript

in this video we're going to talk about the structure of the eye and we're going to do that by drawing a cross sectional diagram of the eyeball the first thing we're going to draw is the white part of the eye which is known as the sclera so I'm just drawing that in and I'm labeling sclera and the sclera is a thick fibrous tissue that basically forms the substance of the eyeball so the white part of the eye is the sclera and it serves to protect the eye and it also serves as an attachment point for muscles so that you can move your eyeball around when you're looking at different things so this white part is the sclera the next thing we're going to look at so let's imagine that this is the front of the eyeball and this is the back of the eyeball so when you're looking at somebody you're looking at them this way so the first thing you look at is something known as the cornea so the cornea is actually transparent so you can't see it but it basically serves to protect the front of the eye and it also serves to bend light just a little bit so let me label this cornea so the cornea is actually protected it's really sensitive to has to be protected by a thin layer of cells so it's a thin layer of epithelial cells and it is known as the conjunct t-bot so this thin layer of epithelial cells protects the cornea from friction so when you rub your eyeball you don't scratch your cornea and that's because you're actually it's actually protected by the conduct key but also helps moisturize the cornea and protects it from dust and debris so that the cornea is protected so when you're looking at somebody in when you're looking at someone's eye you look at the cornea and the next thing you actually look at you can't even see is the aqueous food or so inside the cornea imagine over here is basically it's a chamber and it's filled with a fluid and that fluid is known as the aqueous aqueous kina so the aqueous humor is basically just water and salt and in form it fills in this terior Chamber VI so human each chamber it uses water suits the water chamber the anterior chamber of the eye so the next thing that you would see so let's imagine a light ray comes in as I mentioned the cornea kind of bends the light ray just a little bit the next thing this light ray would hit would be the lens so the lens is back here so by convex lens which means that it's actually just it's curved on both ends and so when the light ray hits the lens it bends a little bit more so it'll bend a little bit more and the lens actually can change shape so can either get thinner or thicker depending on whether an object is nearby or far away and so the thing that actually makes the lens thinner or thicker is known as the ciliary body and the ciliary body is composed of a few things the first are these ligaments that are connected to the lens and they're known as dispensary suspensory ligaments and these suspensory ligaments are connected to the lens and they're also connected to these ciliary muscles so ciliary muscle it's on both sides of the lens and the ciliary muscle nough suspensory ligaments I change the shape of the lens and they form this bigger structure known as the ciliary body which also secretes this aqueous humor over here so the cornea bends the light and the lens bends it a little bit further and what's interesting is when you dive underwater you everything becomes really blurry and the reason is when light is emitted so let's just draw the Sun over here happy Sun so when the Sun emits a light ray it actually comes in and it's passing the air normally and when it hits the cornea gets bent to certain about but when you're underwater the air is replaced by water and so the light ray actually gets bent a slightly different amount so let's say this is how much we get back if there was air outside and this is how much it gets that one there's water and so that's why everything's a little bit blurry because the light rays are converging where they should be so when you wear goggles when you're under water so let's imagine that you're wearing goggles underwater what the goggles serve to do is they add a little layer of air in front of the cornea so that when the light hits the cornea it bends the correct amount instead of bending this abnormal amount which normally would if there's water right outside here so the next thing that we want to look at is something known as the iris and so the iris is actually the part of the eye that is colored so if somebody has blue eyes or if they have green eyes that's because the iris is pigmented differently so the iris is actually two different muscles that contract and expand and when they can track and expand the size of the hole right here it actually gets bigger and smaller and so this is let me just label the iris and this hole is known as the people label that so I know there are a lot of words but just bear with me they should all make sense after we've drawn the entire diagram so the pupil is this just a term for the hole that is controlled by this the size of the hole is controlled by the iris and so the whether the if it's really dark outside you want the hole to be really big that's so that you can get the maximum amount of light rays entering the back of the eye when it's really bright outside you want the iris to contract so that the pupil constricts and there's less light entering the eye so that you can actually focus in on what you're looking at um so the light weight hits the lens and gets bent and now it's passing through something known as the vitreous treatment so the vitreous humor kind of makes up this posterior chamber the eye services from here to here is the anterior chamber and from here to the back of the eyes the posterior chamber of the eye and the posterior chamber has discomposed to the vitreous humour so humor means chamber and vitreous is a jelly-like substance within the posterior chamber so it's employees of water and some salt and some protein and their main protein is albumin this part of the and this part of the iron so the vitreous humor helps to spend the lens in place and it also provides some structure for the so that the eye doesn't just collapse in on itself so it's also transparent so the light is able to display right through so once the light ray comes to the towards the back of the eye it will hit the structure known as the red man so the renter kind of coats the entire back of the eyeball towards the entire back of the eyeball and so the Rena is composed of a bunch of different cells known as photoreceptors that actually take this light ray and convert convert it into a neural impulse that the brain can understand and so the retina is tinted red it's a reddish in color and that's why when I you take a photo of someone at night and the flash goes off and what happens is the flash goes off and the light ray enters the back of the eye and actually bounces off of the retina and gets picked up by the camera so it causes something known as the red-eye effect and some cameras actually have a something that reduces the redeye a redeye reduction feature and so what happens there is you have two flashes that go up the first flash simply serves to constrict the iris so that the people actually get smaller and then the second flash goes off and when the second flash goes off to actually take the photo that people is a lot smaller so there's less light actually getting reflected off of the retina so it reduces the red-eye effect so the retina sends fibers through the back of the eye so that the fibers can actually go to the brain and these fibers form something known as the optic nerve so this is the optic nerve and when you label this retina so the retina sends fibers through the optic nerve which goes to the brain and then you're able to make sense of what you're looking at so the next thing that we want to talk about the next structure is just inside of the retina and it see just like this it's a membrane known as the choroid and the corn is basically a network of blood vessels that nourishes the retinal cells and nourishes other cells within the eye so there's little kind of blood vessels that come off of the Korowai that nourish all the cells on in the retina and other parts of the eye and so the cord is also pigmented lack so that's why when you look at somebody's eye if you look you the people it's actually really dark it's black and that's because you're looking at the coid which is actually pigmented black and in other species like cats there's they don't have thickness so the cords actually shine in what that serves to do is it gives them better night vision so you can imagine a light ray coming in turn off to the side over here and in humans if that slight Ray wasn't absorbed by the retina it would be absorbed by the quarry because corn is black and black absorbs light but in cats it's shiny so the light ray would actually reflect off the choroid and hit the retina again and be absorbed by the retina so it gets two chances to absorb the light ray and actually enhances night vision and other and as a cat for example so the cord is this network of blood vessels and it's pigments is black and I just wanted to point out one more feature of the retina there's a little dimple over here and this dimple is filled with cones and these cones actually allow you to see in really rich detail or rich amount of detail when you're looking at something that's known as the fovea and the fovea is actually in the very center of a broader region known as the macula so the macula is just a anatomical name for a particular region of the eye and the very center of the macula is the fovea which is rich in cones and lets you see in really high levels of detail these are all the structures of the eye