Vascular Layer of the Eyeball - Video Tutorials & Practice Problems
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1
concept
Vascular Layer
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6m
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As we continue learning about the different layers of the eye, we're now gonna talk about the vascular layer and remember the vascular layer is the middle layer of those three layers that make up the eyeball. And we said that it's also sometimes called the uvea. Now, I'm not gonna call it the UVEA, but you should be familiar with that term because it does come up sometimes. And we said the general role for this vascular layer is that it regulates light that enters the eye and it also supplies blood to the eye. Now, we're gonna break the vascular layer up into three parts and talk about them individually. But before we do that, let's just orient ourselves to our image here, we have this transverse section of the eyeball right here. This is a top down view of the eye and we're looking at the right eye and we can see that we've colored in these browns and oranges, the vascular layer in the front. Here in this brown, we have the iris as we move back, we have in this sort of reddish color here, the ciliary body and then all around the back here in this sort of orangish brown. We have the coro. So let's start by talking about the iris. The iris is that colored region around the pupil. So let me ask someone what color eyes do you have? You're asking them, what color is your iris? It's gonna be made of or comprised of muscles. And those muscles control the size of the iris and therefore control the size of the pupil. So if those muscles squeeze down the iris is gonna get bigger, the pupil will get smaller. If other muscles pull back, that iris is gonna get smaller, the pupil will get larger. It's also gonna be made of pigmented elastic fibers. So you have these muscles, but then you have these stretchy elastic fibers with pigment, a brown pigment that gives eyes its color wrapped around those muscles that can stretch back and forth as the muscles change size. And the job of those elastic fibers in the pigment is to block the light. The iris is there really controlling the total amount of light that gets into the eye. So you don't want it transparent, you wanna block light from going through it. Now, when we said when it changes size, what it's really changing is the size of the pupil and the pupil, you really just want to think of as a whole that pupil that black.in the middle of your eye, it's really just a hole so that light can get into the eye and we can change the size of the pupil to control how much light gets into the eye. Now, we're gonna talk about how all this works in a lot more detail coming up. But right now, we just sort of want to look at this and I want to take a second sort of even closer look to see how this is all put together. And so we're gonna look at this sort of super zoomed in image of an eye here. You can see that iris sort of changing shape a little bit. And I like this view here sort of an angle because you can really see how that pupil is just a hole in the middle of the iris, right? It's a hole, it's black because it's dark in there. And you can also see those elastic fibers really clearly. You can see how it really looks like they're just these fibers wrapped around those muscles. And as those muscles change size, the elastic fibers with the pigment in them, that color of your eye is gonna change size with it. All right. So let's move back to our page here. And next, we're gonna move back and we're gonna talk about the ciliary body again, that's that section here in this sort of orangish red. And we're gonna say the ciliary body is there to suspend the lens of your eye. And it also produces fluid, the eye, we're gonna break the ciliary body up into three individual parts. Though, first, we have the ciliary muscles and we have that labeled as a here and here. It's sort of a larger part of the ciliary body and the ciliary muscles are there to control the lenses shape and thereby to focus the light. So your lens is flexible and depending on how much those ciliary muscles are pulling on the lens, the lens will be rounder or flatter. Now, we'll talk about how that works and how that focus the light a lot more coming up. But for now, you just want to know that the ciliary muscles are responsible for changing that shape of the lens. Now, in B, we have labeled the C zone. So you can see here in B these are the ligaments that connect o sary muscles to the lens. And they're also sometimes just called the suspensa ligaments. So we're gonna say here they connect the lens two bacillary muscles. And you can remember that because Zono, that word Zono comes from the Latin, which means belt. So these are these sort of belts that are pulling on, tugging on that lens and helping to change its shape so that it can focus light. All right, the last part of the ciliary body that we want to talk about are these ciliary processes here. And you can see those in C and it's just sort of the back part here. You see how it's just a little bit bumpy those are those processes and those processes are what secrete fluid for the anterior or just the front part of the eye. OK. So the front part of your eye appear is filled with what we said is called aqueous humor. Again, we'll talk about that in more detail coming up. But that aqueous humor, that fluid is actually produced back here and it slowly flows forward through the pupil and then it's a uh sort of taken out and it leaves the eye sort of at the corners here. So it flows up through that way. That's where that fluid that fills the front of the eye is produced. All right, that takes us to our last section, that last section is going to be the coro and again, the cood is this orangish brown section that's going all the way around sort of inside the sclera between the sclera and the retina. And this is going to be a pigmented membrane. And so when you think of it being dark in your eye, it's probably because that whole back of the eye is a dark color. You have this cood this pigmented membrane and that is preventing reflection. You want light to come into your eye in this way, get focused by the lens and then end up on the retina, but not all the light is gonna be absorbed by the retina retina. Sun is gonna pass through the retina. You don't want that extra light reflecting off and bouncing all over the eye that's could really sort of mess up the image and the image processing that your retina does. So the coro absorbs that light and sort of just makes the whole thing dark. It's also gonna be rich in blood vessels and that's where that name the vascular layer comes from. So it's located between the retina and the sclera there. So those blood vessels are supplying a lot of blood some to the uh sclera. But really, it's supplying blood to the back half of the retina. The retina uses a lot of energy. It has a high, high need for oxygen because they're these uh you know, nervous cells and they use a lot of oxygen to do their job. So the back half of the retina gets that blood from the choroid. The front half of the retina actually has its own blood vessels that supply. OK. So that's the master layer. We're gonna go into the iris in more detail. Coming up later on, we'll talk about how the ciliary body works with a lens to focus light. I'm looking forward to it. I'll see you there.
2
example
Vascular Layer of the Eyeball Example 1
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3m
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Our folks. Our example tells us that the table below lists three parts of the vascular layer. Then I also know how does each component help regulate or control the light coming into the eye? And the three structures we're talking about here are the iris, the choroid and the ciliary body. Now, before we answer that, let's look at our diagram here. This is our transverse section or our top down view of this right eye and you can see that we have the vascular layer color coded here. So let's start with our first structure, the iris. So do you remember what the iris is and how it controls or regulates light coming into the eye? Now, the first thing I'm gonna do is I'm gonna find the iris on my diagram here. And that's that brown structure in the front. The iris is that circular colored part of the eye in the front. And what it's doing right? The iris is this circular structure that has a hole in the middle and that hole is the pupil and the pupil is the only way that light can get into the eye. So what the Irish does, I'm gonna say, is it controls the size of the people and thereby it controls the total amount of light entered in the eye. If that iris opens up, the pupil is bigger, more light gets in the iris closes down, the pupil is smaller, less light gets in. All right. Next up, we have the choroid. You remember the role of the coro in terms of regulating or controlling light in the eye. Well, in my diagram here, the cood is this part all the way around the back. It's between the sclera and the vascular layer. I'm sorry, between the sclera and the retina, it is the vascular layer. And so as light comes into the eye, right, light is gonna come in through the pupil, it's gonna go through the lens and then what you want is it to be absorbed by the retina so that you can see it but not all light will be absorbed by the retina. And what you don't want happening is light hitting the back of the eye and then bouncing off and hitting other parts of the retina. That's gonna create problems with your vision. What you want to have happen is light enter the eye, get picked up by the retina. But if it isn't picked up by the retina hit the coo and stop so that we we said that the chloride has pigmented cells in it and those pigmented cells are gonna absorb excess white right now. Remember the coid also has the role of having a lot of blood supply in it, right. So this is the vascular layer and that's really where most of that vascular vascularization is is in the cord and it is providing blood to the back half of the retina. So that's another really important job for the chid. But in terms of controlling light, it's there to absorb excess light in the eye. So light doesn't bounce around and reflect. All right. Finally, we have the ciliary body, remember the job of the ciliary body. Well, in our diagram here, the ciliary body bodies here in this sort of orangish red color. And importantly, we have the ciliary muscles here. And then we had these ciliary zones or the suspensa ligaments sometimes called and those are suspending the lens. So together those work to control the shape of the lens, the word of shape of the lens, right. So light is gonna come in and you want that light focused by the lens. So it creates a really clear image on the retina. The job of changing the shape of the lens so that it can focus is the sill body, the Cillian muscles and the ciliary zones. Now, we'll talk about how the lens works in more detail coming up right. Now, you just wanna understand that that ciliary body has that role. OK. So the vascular layer, remember vascular means blood supply. So it does provide blood to the eye. But you wanna also remember that it has this job of controlling and regulating the light. All right, with that there's practice problems to follow. See you there.
3
Problem
Problem
The aqueous humor is the fluid that fills the anterior portion of the eye between the lens and the cornea. This fluid is constantly regenerated and drains out through the scleral venous sinus. If the scleral venous sinus is blocked, aqueous humor can accumulate, putting pressure on the structures of the eye. Which structure of the vascular layer is responsible for producing the aqueous humor?
A
Iris.
B
Choroid.
C
Ciliary Body.
D
Ciliary Process.
4
Problem
Problem
Which structure(s) of the middle layer contains muscles?
A
Choroid & iris.
B
Choroid & ciliary body.
C
Iris only.
D
Iris & ciliary body.
5
concept
Control of Light Entering the Eye
Video duration:
8m
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As we continue talking about the vascular layer of the eye, we now want to talk about control of light entering the eye in a lot more detail. And remember light enters through the pupil, but the pupil is just a hole that's in the center of the iris. So to understand how we control the light entering the eye, we need to understand how the iris works in more detail. Well, the iris is the color of your eye. So we're gonna start off by saying that that color of the iris just comes from the pigment melanin. And you'll remember from the integumentary system that melanin is a brown pigment. And it's the same thing that gives your skin, its color. People with very dark skin colors have a lot of melanin. People with very fair or pale skin have very little melanin in their skin, same thing in the eyes. We're gonna say that more pigment equals brown eyes. And as we look up here, we have this sort of scale of eye color here, we have five eyes laid out from a blue to a green to darker and darker browns. And as we go to the right on this scale, we see that it says high melanin, we're putting more and more melon in the eyes. We can see that the eyes go from sort of a light brown to darker and darker browns. And some people have very dark brown eyes because they just have a lot of melanin in their eyes. But you'll notice as we go to the left on the scale, it's not like skin color, it doesn't just get paler or a lighter brown. Eventually, it sort of looks kind of greenish or blue. So we're gonna say here that less pigment is gonna equal a green or blue color of the eyes. But importantly, we're still just talking about melanin. There's nothing blue or green in the irises of people have blue or green eyes. So I have fairly blue eyes. If you were to gouge out my eye, rip out my iris and lay it on the table, you would see it would look probably just kind of like this unpigmented pale beigeish tissue. The reason it looks blue in my eye is the same reason that the sky is blue, blue is a shorter wavelength light. So like all light, when the light passes through materials of different densities. In this case, the elastic tissue of the eye, it's going to refract or bend but shorter wavelengths refract or bend more than longer wavelengths. So that blue light hits the iris starts bending and more of the blue light bends and comes back out of the eye eye for people to see the eye looks blue. If I had more melon in my eye, that blue light would just get absorbed and my eyes with the brown, right? What we really want to talk about here though is how light gets past the iris though. And that's going through the pupil. So we're gonna say here that changing the size of the pupil changes the amount of light coming into the eye. And of course, we change the size of the pupil by changing the size of the iris. Now, before we get into the details here, I just wanna watch a video of this, a super close up vision uh video of the eye so that we can sort of think about how all this is working. So we're gonna see here someone whose eye or whose pupil is dilated. So the pupil is gonna be really big starting out and then that iris is gonna squeeze in and make the pupil smaller. So here we go, we have this big pupil and you can see that Iris squeezing in the elastic tissue with the, with the melanin in it, squeezing in with it, getting pulled along with it. Now, I'm gonna play this again for you one more time. And as we do, I want you to think about how the muscles in this iris must be working. How must those Iris be those muscles in the iris be arranged to squeeze in in this way. And then if we wanted to open up the pupil, how must those muscles be arranged and how would they work as well? All right. So now that we're thinking about that, let's look back at our page. So there's two basic actions that the iris can do. We can have constriction of the pupil. The iris can squeeze inwards or we can have dilation of the pupil. The iris can pull outwards and make that pupil bigger. We are, we're gonna talk about two muscles here and they're pretty easy to remember the names because they're just named after the action. So to constrict, the pupil, we have the pupillary constrictor muscle and to dilate the pupil, we have the pupillary dilator. So let's start with this pupillary constrictor muscle. We can see here, we have, well, we have two images of the iris here where we remove that elastic tissue off of the iris. And so now we're just looking at the muscles and we can see this pupillary constrictor in the middle here. This is this sort of circular shaped muscle and the circular muscle, well, like all circular muscles when it squeezes in, it squeezes in like a sphincter. So when it contracts it constricts in and makes the hole in the middle smaller. All right. So that is going to make that iris bigger, the pupil smaller. Now, in contrast on the outside of the iris here, we have these mu soul, this pupillary dilator muscle. It's almost, uh, arranged like spokes on a wheel. And we're gonna call this a radial shape sort of pulling outwards. And so to open up this Iris to dilate the pupil, these muscles are gonna pull outwards. Ok. So, now why would they do that in what cases would each, uh, different muscle contract? Well, the pupillary constrictor is gonna contract for bright lights. That makes sense. If it's really bright out, you wanna shut down that pupil. So you don't get too much light in the eye and damage the retina. It's also gonna do it though for close vision and why that is we'll talk about in more detail when we talk about focusing light on the retina using a lens for now though, just remember that for close vision, that's another thing that's gonna cause this iris to close down this pupillary constrictor muscle to contract. All right. Well, in contrast, the dilation of the pupil, the pupillary dilator, that's gonna happen for dim lights. And that makes sense. If it's not very bright, you need to open up the pupil, let more light into the eye. And also for distant vision again, why for distant vision we'll talk about when we talk about focusing light on the retina using the lens for now, just know that it happens when you're looking at something far away, that pupil is gonna be bigger. Ok. Control of the pupil is by the autonomic nervous system. This is something that you have no conscious control of. So for innovation, we want to think about which division of the autonomic nervous system is controlling it for the construction. That's going to be the pera sympathetic, the vision of the autonomic nervous system. And remember, parasympathetic uh division of the autonomic nervous system, we sometimes think of as our rest and digest nervous system. So when I think about it that way, I sort of think, well, if I want to rest and digest, I kind of wanna just shut things down, I wanna reduce the total amount of sensory information coming into my body. So I'm just gonna kind of turn those headlights down and just, you know, block stuff out. Now, in contrast, the pupillary dilators are gonna be controlled by the sympathetic division of the automatic autonomic nervous system. Remember the sympathetic division that is like your fight or flight response. So again, I think of it this way if I, you know, and like fight or flight, I'm scared, I need to fight something. I want as much sensory information coming into my body as possible. So I open up that pupil, I let a lot of light in so I can see everything super clearly, all right, associated with that, we can think of what emotional states is gonna con uh uh lead to constriction or dilation. So, uh that uh pupillary constrictor muscle is gonna contract in states of boredom. Right. Shut things down, rest and digest, but also things like an unpleasant sight. And I think of that again, like if I don't wanna see something, I can kind of shut things down a little bit and reduce the total amount of information coming in. In contrast, these dilators, you wanna open up the pupil. Well, for things like fear, desire, problem solving all these states where you really want a lot of censoring information coming in so that you can really process everything that's going on. All right. So with that, we're done talking about the vascular, but like always we have an example, practice problems to follow. Give him a try.
6
example
Vascular Layer of the Eyeball Example 2
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2m
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All right folks, our example asked us to imagine that you are waking up from a nap in a dark room with heavy curtains drawn. Sounds lovely. You walk to the window and open the curtains, letting direct sunlight flood the room describe how the muscles of the iris would respond to the two light environments described. All right. So our two light environments here, we have the darkened room and the room is sunlight. And for each one, we wanna know which muscle is contracted, which one is relaxed and then the size of the pupil. All right, I'm gonna start with the size of the pupil because figuring out the size of the pupil is gonna tell me everything else. And I think that part should be pretty easy to figure out. So you wake up in a dark room, you open your eyes, it's dark. You need to let a lot of light into the eye to be able to see things. Well, that pupil is gonna be nice and big, it's gonna open up. So I'm gonna say that the pupil here will be large, letting a lot of light into the eye. Now you walk over, over, you open the curtains, bright light hits your face. You're looking at the sun, uh, you wanna turn down those headlights, you wanna shut that pupil down? So here the pupil is going to be small in a room with a lot of sunlight. All right. So what is the muscle that contracts to get your pupil to be large? Remember, we had two muscles that we're talking about here, the pupillary dilator and the pupillary constrictor and those names just kind of tell you what they do. Right. So, first off, we know it's a pupillary muscle. So, pupillary, well, to get a large pupil, you want to dilate the eye, that means to make something bigger, that make that hole in the iris bigger. So pupillary dilator, remember those were those muscles arranged in sort of this radial fashion and they're gonna pull out on the eye or on the iris making that pupil larger. So therefore, our relaxed muscle will have to be our pupillary instructor, right? And that's that circular muscle that squeezes down like a sphincter to close the eye or to close the iris. And so if you want a large pupil, that one needs to relax, so it can be pulled back. All right, in the room with sunlight. Well, it's just gonna be the opposite, right. So the pupillary constrictor that round circular muscle is gonna squeeze down to make the pupil smaller and the muscle that needs to relax is going to be the pupillary dilator. And when that relaxes that pary constrictor can squeeze down, you're gonna get a small pupil blocking light entering the eye. Ok. We got more practice problems on this coming up. See you there.
7
Problem
Problem
Which of the following would increase the total amount of light coming into the eye?
A
Activation of the parasympathetic nervous system.
B
Looking at something close to the face.
C
Resting.
D
Feelings of rage.
8
Problem
Problem
True or False: if false, choose the answer that corrects the statement.
Pupils enlarge when the pupillary dilators contract after receiving stimuli from the parasympathetic nervous system.
A
True.
B
False; pupils enlarge when the pupillary dilators contract after receiving stimuli from the sympathetic nervous system.
C
False; pupils enlarge when the pupillary constrictors contract after receiving stimuli from the parasympathetic nervous system.
D
False; pupils enlarge when the pupillary constrictors contract after receiving stimuli from the sympathetic nervous system.
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