WEBVTT

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Let's talk about muscles.

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And I've drawn the
human body on the right,

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kind of a figure of it.

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And I want to talk about the
three major types of muscles.

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And I thought it would
be helpful to have

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a picture, because then we
can actually draw on there

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and show where the different
types of muscles might be.

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So when I mention
muscles, the word

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I want you to start thinking
about in your head is movement.

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So think about all
the different types

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of movements that might
happen in your body.

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Just be really
creative and start

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thinking of all the
different movements.

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You might have, for example--
a really easy one would be,

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maybe, let's say
your leg is moving.

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I'm going to just draw on
our picture as we talk.

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But let's say your leg is moving
because you're playing soccer.

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And so you've got this
giant muscle in here,

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and this muscle is
attached to a bone.

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Right?

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There's a little bone here.

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I guess not so little, right?

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This as the largest
bone in the body.

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It's called the femur.

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And so this muscle is
attached to the femur.

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And this muscle is going to
be attached by way of tendon.

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It's going to have
tendons on both sides.

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And so this tendon is
attaching it to the bone

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and allowing it to
act on the bones.

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So this is an example
of skeletal muscle.

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Right?

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So this skeletal
muscle is going to be

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attached to a tendon and bone.

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Now, that brings
up the question--

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does every skeletal
muscle have to be

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attached to a tendon and bone?

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Well, the answer
is no, actually.

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There are some
muscles that really

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aren't attached
to tendons at all.

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In fact, right above
the muscle we just drew

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is a muscle called the
external oblique muscle.

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And don't worry so
much about the names.

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But the idea here is that
this muscle is actually not

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attached to a tendon.

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Well, in a sense, I guess, you
could think of it as a tendon,

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but it's like a flat tendon.

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Basically a giant kind of
sheet of fibrous tissue.

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And this fibrous tissue,
is it floating in midair?

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No.

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It's going to be connected
to fibrous tissue

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on the other side, because, of
course, your body is symmetric

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and so you've got fibrous
tissue on the other side.

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And you guessed it,
on the other side

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of that you've got
another external oblique.

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So you've got these muscles that
are kind of coming in to not

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really a tendon but
really a flat tendon,

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or something that looks
like a flat tendon,

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and we call that an aponeurosis.

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You might hear these words.

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I just want you to be
familiar with them.

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And now if someone asks
you, is every muscle

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in the body attached
to a tendon and bone?

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You can say no.

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Some are attached to a flat
tendon called an aponeurosis.

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The idea here is
that you can kind of

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start identifying
skeletal muscles.

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They're usually the muscles
that you can see on your body.

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Actually, I don't even
need to put quotes.

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That's the actual name for it.

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No need for quotes there.

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So you can identify skeletal
muscles pretty easily.

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But what about the other two?

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What about the cardiac
and smooth muscle?

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I mean, you might wonder,
does cardiac mean heart?

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And is that the only type
of cardiac muscle out there?

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And the answer is yes.

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This is your heart
muscle right here.

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And the only type of cardiac
muscle that we have in our body

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would be related to the heart.

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So in the heart, you can
find specialized cells that

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were so interesting
and different

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from skeletal and
smooth muscles,

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they got their own
name and category.

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These are the cardiac cells.

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And you can only find
them in the heart.

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I guess we're making a column of
where you can find these cells.

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So what about smooth muscle?

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Where can you find
smooth muscle?

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Well, for smooth muscle,
think about any hollow organ.

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Any organ that's got space on
the inside and blood vessels.

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Those are the two
major categories.

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Those aren't the only ones,
but those are the major ones.

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That'll get you about
95% of the way there.

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So blood vessels
and hollow organs

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are what you should think about.

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And hollow organs could be
anything from-- let's say,

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your stomach would
be a hollow organ.

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Let me just put
these examples here.

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Or your bowels would be a hollow
organ, anything like that.

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So I'm just going to
write stomach here just

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to jog your memory.

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Where there's basically some
empty cavity on the inside.

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Right?

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And then as for blood
vessels, just remember

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one of the largest blood
vessels, for example,

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is the aorta.

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And the aorta kind of comes
up and over like that.

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And it's kind of like a
hollow organ, as well.

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Right?

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I mean, there's a space on the
inside of that blood vessel.

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And blood is usually
flowing through that space,

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but at least it's hollow.

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So it's really not that
different conceptually

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from the hollow organ.

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And just like in
the hollow organ,

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the smooth muscle is in
the walls of these things.

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So think about where the
smooth muscle would be.

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It would be in the walls
of the hollow organ

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or in the walls of
the blood vessel.

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So that tells you where to find
these different muscle types.

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Right?

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And thinking about
movement, smooth muscle

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can help the stomach, for
example, move food forward.

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Cardiac muscle is going
to help your heart beat.

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That's a pretty
important movement.

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And skeletal muscle, I mean,
we use that every single day.

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Every time you give
your friend a high five

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or give your mom a hug,
those are skeletal muscles

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that are helping your
body move around.

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Right?

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So let's move on.

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Let's think about
some other differences

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between these categories.

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Let's talk about now
the movement control.

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So who controls the movement?

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Do you control it, or is
it automatically done?

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So smooth muscle is what I
would consider automatic,

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or I'm going to call it
involuntary because you'll

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probably see that
word more often.

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Involuntary just means that
your body is automatically

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taking care of it.

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And the same is true for your
cardiac muscle-- involuntary.

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Meaning, you don't
have to actually think

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about the next heartbeat.

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It just happens automatically.

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Right?

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And skeletal muscle is
the opposite-- there,

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it's voluntary.

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Meaning if I didn't want to get
up, then I would not get up.

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Or if I didn't
want to go running,

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then I wouldn't go running.

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All of those movements in my
body are under my control.

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I can decide when
to do those things.

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Right?

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Actually, maybe I'll draw little
arrows here-- what about speed?

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Which ones are fast,
and which ones are slow?

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So up here, the smooth
muscle is the slowest

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and the skeletal muscle
would be the fastest, which

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is pretty cool because
the voluntary stuff--

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the stuff you control
yourself-- is the fastest.

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And the stuff that's happening
automatically is pretty slow.

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And actually it's nice, because
cardiac muscle is somewhere

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in between the two.

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Somewhere in the middle.

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So when your blood
vessels get tinier

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or they get big and
vasodilate, all that stuff

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is happening on a pretty slow
time scale as compared to,

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let's say, I jump and
try to catch a ball.

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That's all happening
really, really quickly.

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Thousands of little
muscle movements

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are happening really
lightning quick.

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And so those would
be the fastest.

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Now the final thing
I'm going to draw

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is what these things look like.

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So how do they look?

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If you actually take a
look at these cells-- let's

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actually look at each
of these one by one

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and figure out what
they would look like.

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So the smooth muscle actually
looks like a little eye,

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or like an almond-- sometimes
it's described that way.

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But I think of it as an eye.

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One single eye.

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And you can see that
the edges, or the ends,

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are kind of tapered like that.

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And so sometimes
you'll see that these

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are described as spindle shaped.

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I think that's kind of a
holdover from a time period

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long ago when people
thought about spindles more

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than they do now.

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And the other thing,
it's got one nuclei.

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Drew that right in the middle.

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One nuclei.

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And it's in the
middle of the cell.

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So that's basically what a
smooth muscle cell looks like.

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What about a cardiac cell?

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Well, this cell is branched.

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That's actually one of the
most interesting hallmark

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features of it.

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Now, not every single
cardiac cell is branched.

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Some are actually just kind
of humdrum-looking, normal,

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maybe like this.

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But the fact that you
can find branched ones

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is what really makes these
so easy to recognize.

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If you look at a
whole bunch-- I'm

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going to erase this guy now
that you know he exists,

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but I'm going to focus
on the branched one

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because these are the ones that
make them very easy to spot.

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And they also have nuclei.

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Sometimes one,
but sometimes two,

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which is interesting
because, you know,

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usually you think,
one cell, one nuclei.

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But the reason I had to point
that out for the smooth muscle

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cell, that there's only
one, is that sometimes

00:08:54.570 --> 00:08:57.430
these cardiac cells
have more than one.

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So the two features-- I'm
going to just write out

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here-- branched and
one or two nuclei.

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Not always two, but
they can have two.

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And they're also located kind
of in the middle of this cell.

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And I'll show you
what I mean by middle

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when I draw the skeletal muscle.

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I'll do that now.

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This is the skeletal muscle, and
it's got something like this.

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It's got these
little outpouchings

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I'm trying to draw for you.

00:09:29.820 --> 00:09:32.530
And you'll see in just a
second what I'm drawing.

00:09:32.530 --> 00:09:35.870
These are little spots on the
edge, or on the periphery,

00:09:35.870 --> 00:09:37.120
for nuclei.

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And notice that there's not
one nuclei, not two nuclei,

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but bunches of nuclei.

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So these cells are actually
working as a giant cell,

00:09:47.400 --> 00:09:47.900
in a sense.

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So these are actually, first
of all, they're straight.

00:09:50.580 --> 00:09:53.250
They're not branched.

00:09:53.250 --> 00:09:54.980
So straight.

00:09:54.980 --> 00:09:57.540
And they've got many nuclei.

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This is actually really,
really important,

00:09:59.350 --> 00:10:03.080
and you can see how it would be
easy to spot these guys, right?

00:10:03.080 --> 00:10:05.200
Because they've got many
nuclei, and the nuclei

00:10:05.200 --> 00:10:08.390
themselves are in the
periphery, kind of on the edges.

00:10:08.390 --> 00:10:10.880
That's why I wanted to point
out that the other two are

00:10:10.880 --> 00:10:12.500
in the middle.

00:10:12.500 --> 00:10:14.707
Now, kind of a final
point is that if you

00:10:14.707 --> 00:10:17.040
were to look at these under
a microscope-- and actually,

00:10:17.040 --> 00:10:20.100
this is something that was
noticed a long time ago--

00:10:20.100 --> 00:10:23.020
they would look
something like this.

00:10:23.020 --> 00:10:25.420
And this is called striated.

00:10:25.420 --> 00:10:28.420
So they basically
have these striations.

00:10:28.420 --> 00:10:31.660
But notice that the smooth
muscle cells don't have this.

00:10:31.660 --> 00:10:35.860
It's really just the skeletal
muscle and the cardiac muscle

00:10:35.860 --> 00:10:38.590
that has these striations.

00:10:38.590 --> 00:10:40.980
Sometimes you'll hear
about striated muscle,

00:10:40.980 --> 00:10:43.140
and they could be talking
about either of the two.

00:10:43.140 --> 00:10:43.640
Right?

00:10:43.640 --> 00:10:45.659
They could be talking
about cardiac or skeletal,

00:10:45.659 --> 00:10:47.200
but you know that
they're not talking

00:10:47.200 --> 00:10:49.340
about the smooth muscle.

00:10:49.340 --> 00:10:51.620
So this is striated.

00:10:51.620 --> 00:10:55.099
And striated just
refers to those stripes.

00:10:55.099 --> 00:10:57.140
And that's what it looks
like under a microscope.

00:10:57.140 --> 00:10:58.940
And we'll talk about
exactly why they're

00:10:58.940 --> 00:11:02.200
striated what that would
imply about the cell

00:11:02.200 --> 00:11:03.400
in another video.

00:11:03.400 --> 00:11:05.130
But I just want
you to get a kind

00:11:05.130 --> 00:11:07.210
of a rough lay of the land.

00:11:07.210 --> 00:11:09.264
And now you can see
there's actually

00:11:09.264 --> 00:11:10.430
some interesting stuff here.

00:11:10.430 --> 00:11:13.650
You have some similarities
between the cardiac

00:11:13.650 --> 00:11:14.680
and the smooth muscle.

00:11:14.680 --> 00:11:16.210
They're both involuntary.

00:11:16.210 --> 00:11:19.720
You've got some similarities
between the skeletal

00:11:19.720 --> 00:11:21.080
and the cardiac.

00:11:21.080 --> 00:11:22.680
They're both striated.

00:11:22.680 --> 00:11:26.480
And so you can see how all
three are somehow similar,

00:11:26.480 --> 00:11:29.460
but also somehow different
from one another.