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  • Let's talk about muscles.

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

  • kind of a figure of it.

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

  • And I thought it would be helpful to have

  • a picture, because then we can actually draw on there

  • and show where the different types of muscles might be.

  • So when I mention muscles, the word

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

  • So think about all the different types

  • of movements that might happen in your body.

  • Just be really creative and start

  • thinking of all the different movements.

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

  • maybe, let's say your leg is moving.

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

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

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

  • and this muscle is attached to a bone.

  • Right?

  • There's a little bone here.

  • I guess not so little, right?

  • This as the largest bone in the body.

  • It's called the femur.

  • And so this muscle is attached to the femur.

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

  • It's going to have tendons on both sides.

  • And so this tendon is attaching it to the bone

  • and allowing it to act on the bones.

  • So this is an example of skeletal muscle.

  • Right?

  • So this skeletal muscle is going to be

  • attached to a tendon and bone.

  • Now, that brings up the question--

  • does every skeletal muscle have to be

  • attached to a tendon and bone?

  • Well, the answer is no, actually.

  • There are some muscles that really

  • aren't attached to tendons at all.

  • In fact, right above the muscle we just drew

  • is a muscle called the external oblique muscle.

  • And don't worry so much about the names.

  • But the idea here is that this muscle is actually not

  • attached to a tendon.

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

  • but it's like a flat tendon.

  • Basically a giant kind of sheet of fibrous tissue.

  • And this fibrous tissue, is it floating in midair?

  • No.

  • It's going to be connected to fibrous tissue

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

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

  • And you guessed it, on the other side

  • of that you've got another external oblique.

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

  • really a tendon but really a flat tendon,

  • or something that looks like a flat tendon,

  • and we call that an aponeurosis.

  • You might hear these words.

  • I just want you to be familiar with them.

  • And now if someone asks you, is every muscle

  • in the body attached to a tendon and bone?

  • You can say no.

  • Some are attached to a flat tendon called an aponeurosis.

  • The idea here is that you can kind of

  • start identifying skeletal muscles.

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

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

  • That's the actual name for it.

  • No need for quotes there.

  • So you can identify skeletal muscles pretty easily.

  • But what about the other two?

  • What about the cardiac and smooth muscle?

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

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

  • And the answer is yes.

  • This is your heart muscle right here.

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

  • would be related to the heart.

  • So in the heart, you can find specialized cells that

  • were so interesting and different

  • from skeletal and smooth muscles,

  • they got their own name and category.

  • These are the cardiac cells.

  • And you can only find them in the heart.

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

  • So what about smooth muscle?

  • Where can you find smooth muscle?

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

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

  • Those are the two major categories.

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

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

  • So blood vessels and hollow organs

  • are what you should think about.

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

  • your stomach would be a hollow organ.

  • Let me just put these examples here.

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

  • So I'm just going to write stomach here just

  • to jog your memory.

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

  • Right?

  • And then as for blood vessels, just remember

  • one of the largest blood vessels, for example,

  • is the aorta.

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

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

  • Right?

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

  • And blood is usually flowing through that space,

  • but at least it's hollow.

  • So it's really not that different conceptually

  • from the hollow organ.

  • And just like in the hollow organ,

  • the smooth muscle is in the walls of these things.

  • So think about where the smooth muscle would be.

  • It would be in the walls of the hollow organ

  • or in the walls of the blood vessel.

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

  • Right?

  • And thinking about movement, smooth muscle

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

  • Cardiac muscle is going to help your heart beat.

  • That's a pretty important movement.

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

  • Every time you give your friend a high five

  • or give your mom a hug, those are skeletal muscles

  • that are helping your body move around.

  • Right?

  • So let's move on.

  • Let's think about some other differences

  • between these categories.

  • Let's talk about now the movement control.

  • So who controls the movement?

  • Do you control it, or is it automatically done?

  • So smooth muscle is what I would consider automatic,

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

  • probably see that word more often.

  • Involuntary just means that your body is automatically

  • taking care of it.

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

  • Meaning, you don't have to actually think

  • about the next heartbeat.

  • It just happens automatically.

  • Right?

  • And skeletal muscle is the opposite-- there,

  • it's voluntary.

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

  • Or if I didn't want to go running,

  • then I wouldn't go running.

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

  • I can decide when to do those things.

  • Right?

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

  • Which ones are fast, and which ones are slow?

  • So up here, the smooth muscle is the slowest

  • and the skeletal muscle would be the fastest, which

  • is pretty cool because the voluntary stuff--

  • the stuff you control yourself-- is the fastest.

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

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

  • in between the two.

  • Somewhere in the middle.

  • So when your blood vessels get tinier

  • or they get big and vasodilate, all that stuff

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

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

  • That's all happening really, really quickly.

  • Thousands of little muscle movements

  • are happening really lightning quick.

  • And so those would be the fastest.

  • Now the final thing I'm going to draw

  • is what these things look like.

  • So how do they look?

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

  • actually look at each of these one by one

  • and figure out what they would look like.

  • So the smooth muscle actually looks like a little eye,

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

  • But I think of it as an eye.

  • One single eye.

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

  • are kind of tapered like that.

  • And so sometimes you'll see that these

  • are described as spindle shaped.

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

  • long ago when people thought about spindles more

  • than they do now.

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

  • Drew that right in the middle.

  • One nuclei.

  • And it's in the middle of the cell.

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

  • What about a cardiac cell?

  • Well, this cell is branched.

  • That's actually one of the most interesting hallmark

  • features of it.

  • Now, not every single cardiac cell is branched.

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

  • maybe like this.

  • But the fact that you can find branched ones

  • is what really makes these so easy to recognize.

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

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

  • but I'm going to focus on the branched one

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

  • And they also have nuclei.

  • Sometimes one, but sometimes two,

  • which is interesting because, you know,

  • usually you think, one cell, one nuclei.

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

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

  • these cardiac cells have more than one.

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

  • here-- branched and one or two nuclei.

  • Not always two, but they can have two.

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

  • And I'll show you what I mean by middle

  • when I draw the skeletal muscle.

  • I'll do that now.

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

  • It's got these little outpouchings

  • I'm trying to draw for you.

  • And you'll see in just a second what I'm drawing.

  • These are little spots on the edge, or on the periphery,

  • for nuclei.

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

  • but bunches of nuclei.

  • So these cells are actually working as a giant cell,

  • in a sense.

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

  • They're not branched.

  • So straight.

  • And they've got many nuclei.

  • This is actually really, really important,

  • and you can see how it would be easy to spot these guys, right?

  • Because they've got many nuclei, and the nuclei

  • themselves are in the periphery, kind of on the edges.

  • That's why I wanted to point out that the other two are

  • in the middle.

  • Now, kind of a final point is that if you

  • were to look at these under a microscope-- and actually,

  • this is something that was noticed a long time ago--

  • they would look something like this.

  • And this is called striated.

  • So they basically have these striations.

  • But notice that the smooth muscle cells don't have this.

  • It's really just the skeletal muscle and the cardiac muscle

  • that has these striations.

  • Sometimes you'll hear about striated muscle,

  • and they could be talking about either of the two.

  • Right?

  • They could be talking about cardiac or skeletal,

  • but you know that they're not talking

  • about the smooth muscle.

  • So this is striated.

  • And striated just refers to those stripes.

  • And that's what it looks like under a microscope.

  • And we'll talk about exactly why they're