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.
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
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
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
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..