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Current time:0:00Total duration:11:29

Video transcript

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'd be helpful to have a picture because then we can actually draw in 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 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 in 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 is 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 bone so this is an example of skeletal muscle right so this skeletal muscle is going to be attached attached to a tendon in 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's some muscles that don't that really aren't attached to tendons at all in fact right above the the muscle we just dhruv's 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 kind of floating in mid-air no it's 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 not really a tendon but really a flat tendon or something that looks like a flat tendon and we call that an aponeurosis so you might hear these words I just want you to kind of be familiar with them and now someone asks you you know is every muscle in the body attached to a tendon bone you can say no some are attached to a flat tendon called an aponeurosis so the idea here is that you can kind of start identifying skeletal muscles right there they're usually the muscles that you can see on your body right actually I don't even need to put quotes that's the actual name for it so no need for quotes there so you can identify skeletal muscles pretty easily but what about the other two I mean what about the cardiac and smooth muscle I mean you might you might wonder you know as cardiac does that mean heart and 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 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 so these are the cardiac cells and you can only find them in the heart so actually 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 kind of major categories those aren't the only ones but those are the major ones that'll 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 or 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 kind of jog your memory where there's basically some empty cavity on the inside right and then this for blood vessels just remember I mean one of the largest blood vessels for you 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 heartbeat I mean that's a pretty important movement and skeletal muscle I mean we use that every single day everytime 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 sohow who controls the movement right do you control it or is it automatically done so smooth muscle is what I would consider automatic or I'm going to call 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 right or if I didn't want to go running and I wouldn't go running all of those movements of my body are under my control I can decide when to do those things right and actually maybe I'll draw a 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 vaso dilate all that stuff is happening on a pretty slow timescale 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 were to 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 in fact or like an almond you know 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 spindle shaped and 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 right and 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 you know 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 right now 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 think oh well 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 and one so the the two features I'm going to just write out here branched and one or two nuclei so not always two but they can have two and then also located kind of in the middle of the cell and I'll show you what I 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 outpouching x' 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'd 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 and 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 and so 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 kind of refers to those stripes and that's what it looks like under microscope and we'll talk about exactly why they're striated and what that would imply about the cell in another video but I just want you to get it a kind of a rough lay of the land and then you can see there's actually some interesting stuff you have some similarities between the cardiac and the smooth muscle they're both involuntary you've got some similarities between the skeletal and the cardiac they're both striated and so you can see how all three are are somehow similar but also somehow different from one another
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