00:01
Let's continue our discussion
of the special senses anatomy
by focusing on vision.
00:08
Vision is a bit complicated.
00:10
So we'll start with the
anatomy of the eye itself.
00:14
Externally, we can see a
lot of structures pretty easily,
including the eyebrow
that sits superior to the eye,
the upper eyelid, the other
word for eyelid being palpebra.
00:26
We have the lower eyelid.
00:29
And the junction between the two
called the commissure.
00:33
So we have one laterally,
and we have one medially.
00:39
And then the surface of
the eyeball itself
is covered in a very special type of
epithelium called the conjunctiva.
00:47
You may have heard that if you've
heard of the term conjunctivitis,
which is inflammation, usually
due to infection of the conjunctiva.
00:56
Then the round portion
that usually has
some type of eye color
to it is the iris.
01:04
And it's surrounds this
circular black area,
which is the pupil.
01:09
And it's actually not a
structure you can touch.
01:12
It's actually the space
in the center of the iris.
01:16
And it's just the space that
sits right under the cornea here.
01:20
If we sort of look
through the skin a little bit,
we can also see components of
what's called the lacrimal system.
01:26
Lacrimal refers to tears.
01:29
So when you hear that term,
you think something about
the tear ducts or
the drainage of tears.
01:35
There's actually a lacrimal gland
that sits in the upper outer
or superior lateral
aspect of the eye
in the area surrounding
the eye called the orbit.
01:47
And it transmits tear fluid
through the lacrimal duct
to reach the surface of the eye.
01:55
And it will sweep across the eye
towards the medial surface,
where it will coalesce add a little
opening called the lacrimal punctum,
and travel through tiny canals,
either the superior inferior
lacrimal canaliculus
Canaliculus just means tiny canal.
02:14
And then there's also this
lacrimal sac
just to the medial and inferior
aspect of the eye collecting tears,
and will eventually
drain through something
called the nasolacrimal duct.
02:26
And that tells you
where it's heading.
02:28
So naso tells you it's heading
towards the nose.
02:32
And if you've ever noticed,
when you've cried a lot,
that sometimes you get
a runny nose, this is why
because the tears are going
from lateral to medial
and draining out through
the nasal cavity.
02:45
Now we'll move on and talk
about what moves the eyeball itself.
02:50
These are muscles
sitting outside of the eye
and therefore they're called
extrinsic eye muscles.
02:58
We have one sitting superiorly
called the superior rectus.
03:03
And wherever you see rectus,
that means straight.
03:05
So that means there going to be some
muscles that affect the eye
that aren't running
in a straight line.
03:12
We have a corresponding
inferior rectus
along the inferior surface
of the eyeball,
a lateral rectus,
and a medial rectus.
03:22
But we also have a
superior oblique muscle.
03:26
And that is just
what it sounds like.
03:28
It's another muscle superiorly.
03:30
But it runs at an oblique angle
as opposed to the superior rectus
which is more straightforward.
03:36
Similarly, there's
an inferior oblique,
which again has more
of a diagonal orientation.
03:44
So eye movement.
03:46
It's actually a little bit more
complicated than you might think.
03:49
So we're just going to focus
on one eye for the moment.
03:52
So when the eye looks laterally,
that will be called abduction.
03:58
Abduction again means
away from the midline,
just like if you were to
abduct at the shoulder,
you're moving your upper limb
away from the midline.
04:08
That would go under the control of
the lateral rectus.
04:11
Because if you think a muscle
running along the lateral surface
of the eye were to contract,
what would the effect
be on the eyeball?
Will be pulled laterally
so that would be abduction.
04:24
Conversely, contraction
of the medial rectus
will pull the eye
more medially
and that would be
towards the midline.
04:31
So that would be adduction.
04:35
Moving the eye upward
in a more superior direction
would be called elevation.
04:41
Moving it downward
will be depression.
04:44
But because we have
this superior rectus
and inferior rectus,
and the oblique muscles,
it's not as straightforward
as abduction and adduction.
04:55
The inferior oblique because
of the way it's obliquely oriented
when it contracts is
going to move the eye,
and sort of a combination
of abduction and elevation.
05:08
Similarly, the superior oblique
because of its oblique orientation
is going to make the eye
look down and out,
or abduct and depress.
05:19
The inferior rectus
on the other hand,
because it's running
in a straight direction,
but actually the orbits
at an angle,
is actually going to depress the eye
but in a more medial orientation.
05:31
Similarly, superior
rectus will elevate it
but in a more medial orientation
than the inferior oblique.