Biology 2020 Lab 2 The Eye Models

Hello anatomists! Michele Glass here and today our 
video is all about the eye. So we're going to do   a series of videos or one video with the models 
and then I'll do a second video with diagrams.   So to get started on this particular eye 
model you can see, we're looking at left eye,   and we can get our orientation because 
we have the lacrimal gland on the top lateral side of the eye. And then we have what's 
called the lacrimal sac on the medial side.   Okay. And so the lacrimal gland and the 
lacrimal sac are part of the lacrimal   apparatus. That's going to help 
us when we look at the muscles   that are on the eyeball itself. So right 
here is the lacrimal gland so this is the   top of the eye and this muscle remember from 
A&P I is the superior rectus, straight muscle.

And then remember that lacrimal sac is medial 
so that would make this the medial rectus,   inferior rectus at the bottom, and then lateral 
rectus here. So we have four rectus muscles,   remember rectus is talking about straight muscles, 
and then we have two oblique muscles and oblique   is like a curve. Right? So when we're looking 
at the top of our model we'll see on the top we   have a superior oblique, and then when we look at 
the bottom we have an inferior oblique. Okay. Now   notice the inferior oblique is pointing towards 
that lacrimal sac. Which remember is medial.   Right? Your tears drain down into your nose. 
Right? When you cry you blow your nose a lot.   So lacrimal sac is medial. So if we look at 
this model here, we can see superior rectus,   and we can see inferior rectus, and because the 
inferior oblique is curving around that tells us   that this (let me double check myself, I'm right) 
this is medial rectus, and then this would be   lateral rectus. Now these external muscles 
of the eyeball are letting us look up   and down and to the left and to the right.

And 
when you're super annoyed, just rolling those   eyes baby, So we work those muscles hard when 
we're teenagers – maybe you didn't but I did.   All right, now those external muscles are attached 
to this white tissue of the eyeball which is   called the sclera. The sclera is part of the 
outer layer of the eyeball, which we call a tunic,   and that outer layer that outer tunic is called 
the fibrous tunic. It includes not just the sclera   but also what we call the cornea. So the cornea 
you can see on this model is only shown on half,   but the cornea is going to be this transparent 
part of the fibrous tunic that's going to be   on the front of the eyeball. So it needs to 
be transparent so that the light can enter   or penetrate.

So with this model I can take 
the top portion of the fibrous tunic off,   and when I do that I'm able to really see 
into what's called the vascular tunic. So   when we're looking at our eyeball you could 
think of it as like a three layered onion.   So the outer layer, remember, fibrous tunic,   the middle layer is the vascular tunic and it's 
named vascular because this is where we see   all of the blood vessels penetrating 
and servicing the tissue of the eyeball.   Okay so this bulk of this vascular tunic 
that we see here is called the choroid.   When we're looking at the front, the iris which 
is the colored part of the eye. It is a muscle   that actually controls the diameter of the pupil. 
And so the iris and the choroid are part this is   easier if I do this) are part of that vascular 
tunic.

Now take a look the iris (I'm going to   open it up take out its guts there) the iris 
controls the opening, the diameter of the pupil.  Pupil is just a hole, people. So this is like 
a structure that we're naming that's like   not a structure because it's a hole. I 
always think that's super interesting. As I put it back together, we'll see that the 
pupil allows the light to penetrate to the   lens. So also part of the vascular tunic is 
the structure called the lens which we can see   is this piece right here.

The lens is going 
to be important actually focusing the light   onto your photoreceptor cells, and it's going 
to be like held in place by some ligaments and   those ligaments are controlled by a muscle and so 
we'll see those structures better on our diagrams. This whole space, let me put it back together 
a minute, this whole space once you're inside   the cornea, and you're in this space here in 
front of the iris, and then you're in this space   all the way to the lens there, is going to be 
called the anterior cavity. And we'll do some more   labeling on our diagrams to help with that, but 
that anterior cavity is full of a fluid and that   fluid is called aqueous humor. So the humor 
here is like an old-fashioned word for liquid,   aqueous it means like watery. So we have 
an aqueous humor fluid which is going to   help support and nourish the tissue here 
that's located in the anterior cavity.   When I pop off this part of the model, 
when I dissect, I showed you the lens here,   the area behind the lens to the back 
of the eyeball is called the posterior   cavity and is full of a fluid which is represented 
here.

And this fluid is called vitreous humor.   Now the way I remember this, is vitreous kind of 
sounds like the word viscous. And the word viscous   means like thick. So like maple syrup, corn syrup 
probably even better example, or honey maybe even   better example because it tastes super delicious. 
Honey is very viscous. So vitreous humor is going   to be actually almost like holding its shape it's 
so solid. So that's helping to hold the whole   shape and support the shape of the eyeball itself. 
And that's filling up the posterior cavity. When we take a look then inside the model here, what we can 
see is in all of this tissue here   this is called the retina. The retina is part of 
our neural tunic. So this is actually where the   photoreceptors are located.

These are sensory 
receptor cells and they're synapsing onto our   sensory neurons which will make up our optic 
nerve cranial nerve number II. So the neural   tunic is so named because this is where we start 
to see the sensation of vision being detected,   not processed really, but detected. Okay 
now notice you have like this curly red line   that's going to be called the ora serrata. 
And that's going to be this division between   our choroid and our neuron – excuse me – our 
retina. Right neural tunic is the big name for   this layer. All right when we look at the retina 
we're going to see a very special place. You see   it's kind of like highlighted in pink. This is 
called the fovea centralis. This is where you have   your highest concentration of cone cells. Cone 
cells are our photoreceptors that detect color,   and they give us like our best vision. So 
the reason we like things to be in color   is because we can see it really clear when it's in 
color.

So when we're looking directly at something   that wavelength of light should get focused 
directly on our highest center, our most accurate   vision center, which is the fovea centralis. We 
already mentioned here the optic nerve cranial   nerve number II, and if you notice you have 
kind of like this circular area where that nerve   is going to actually come out of the eyeball and 
into the brain. That area is going to be called   the optic disk and this is actually a place where 
we have a blind spot. So we're not actually able   to detect if a wavelength of light lands in 
that particular area, like we don't see that,   but we have two eyes and so our visual spectrums 
overlap. So this is not something that we   notice in our everyday life and our brain 
really fills in a lot of gaps for us.

So even a person maybe with one eye their brain 
is helping to fill in some of those gaps   although clearly that individual is going to have   compromised vision. Let me double check my list 
and see if we've covered all of our structures.   All right y'all it looks like that's all we 
can detect on our models. So stay tuned for   the next video with our diagrams. Alright 
take care of yourself and each other..

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