okay so for this particular video we are going to be looking at the skeletal muscles so the first part of this video is just going to be looking at the structure of the skeletal muscles you know the important organal and such now skeletal muscles are just muscles attached to our bones examples of skeletal muscles that you might have heard of will be things like your biceps your triceps your quadriceps and so many other types of muscles as long as they attached to the Bone and you have control over it which means to say if I tell you okay move that part of your body and if you can voluntarily move it that usually is a skeletal muscle uh smooth muscles are usually muscles that you don't have control over like the muscles of your intestine your arteries or the muscles in your veins and cardiac muscles are obviously muscles in the heart we've talked about this in chapter 9 yeah in a chapter 9 in as so before we talk about skeletal muscles we kind of have to understand that skeletal muscles are referred to as tissues as well and the reason why they are called tissues is because they're made out of cells we know this all right here's where it becomes a little bit confusing typically when you draw out an animal cell just a normal animal cell in your body like a liver cell or a white blood cell for that matter most of the time the cell will have you know something referred to it s they would have like um a cell surface membrane cytoplasm and typically they have one nucleus and most cells in your body will have a limited length and width now I put the bracket over there for their limited length and width as 40 micromet that's kind of like the average in a way uh some cells in your body can be 7 micromet like your R blood cells you know some cells can be slightly larger some cells can be slightly smaller than 40 micromet you don't have to m this but what I'm just trying to tell you is most times in our body our cells have these features they have one cell surface membrane one nucleus one cytoplasm and a limited length and width now the reason why I bring this up is because skeletal muscle cells and if you notice I put the word I put the quotation mark cells um they don't really behave like cells now what do I mean by that is under normal circumstances one skeletal muscle cell can be extremely long they can be 2 to 3 cm long to convert that into micrometer a single cell a single skeletal muscle cell can be 20,000 to 30,000 micromet now you might be thinking hey wait a second doesn't that um defy the total surface area to volume ratio they are able to do so because they're quite flat okay and see typically cells are not supposed to be that long but a skeletal muscle cell is able to defy that now another very weird thing is within that one skeletal muscle cell it can have multiple nuclei and I don't mean just having two nuclei they can have up to thousands of nuclei within that one cell so that is why if you see in certain textbooks they may refer to the skeletal muscle cell as a citium now you don't have to memorize that word citium it's okay okay but you have to know that we do not usually refer to the skeletal muscle as a cell it's kind of weird to call it a cell so instead what we use is we just call it a skeletal muscle fiber just know that when we use the word skeletal muscle fiber it is at the same level as the cell now just like any other cells they must have a cell surface membrane they must also have a cytoplasm but because they don't you know behave like cells we give them different names the cell surface membrane of the skeletal muscle is referred to as something called as a sarola and the cytoplasm of the skeletal muscle is referred to as something called as the sarcoplasm now the word Sarco is derived from the Greek language which means flesh so do you have to know the term sarcoplasm and sarola yes um in the exam if they do ask you to label it you can call it cytoplasm and you can call it the cell surface membrane it is allowed but sometimes they may throw those words out at you in paper for they might use the word Sara and sarcoplasm so you need to know what they're referring to so what I'm going to do here is I'm going to be drawing out a bone okay because you know skeletal muscles are attached to the bones anyway and I'm going to draw a tendon you don't have to memorize what's the meaning of a tendon but just as a general knowledge a tendon is just a particular structure that attaches the skeletal muscles to your bones okay those of you who do sports or follow Sports uh related content you might know a lot about this uh especially when athletes have tendon related injuries you know that that's quite serious anyway moving on so then I'm just growing out the skeletal muscle and I'm going to cut the skeletal muscle so you can see the section within it as you can see over there now that's the section of the skelet muscle which is made up of a few bundles now you don't have to memorize that part but I'm just pulling out one of that bundle and those bundles are still visible with the under the naked eye but if we zoom into the bundle you'll see that those bundles have those tiny little dots and if I were to pull that tiny little dot out it's actually a line by the way it's like a single fiber that fiber is the one muscle fiber which is technically the cell that we talked about earlier okay that is why the muscle fiber or the muscle cell can be extremely long so what I'm going to do is from that muscle fiber I'm going to magnify that part so what I'm doing is I'm magnifying it and I'm zooming in to see what's inside there first and foremost the muscle fiber contains sarola which is the cell surface membrane and they also have the sarcoplasm which is the cytoplasm and I've highlighted that in blue and I also told you earlier about a few minutes ago the muscle fiber is weird in the sense that within that one structure it can actually have multiple nuclei so as you can see here I'm just drawing out three nuclei and I'm drawing out a few mitochondria because obviously your muscles need mitochondria because they need to generate ATP for your muscles to contract now the other thing that I'm also going to draw out over here is I want you to see these very weird elongated structures that um a way just a way to describe them I guess is like a they are like these strips or this uh they are like this tube like structure and they are made out of areas where it's dark and light all right so you can see like a darker region which I've colored in like a you know darker orange color and of course the lighter region which I've covered colored in a uh lighter orange color I guess uh I think that's orange yeah that is orange looks beige but looks orange too anyway yeah this this is always going to be a common recurving theme in this channel are those the actual colors what are those colors exactly you know am I I don't at least I don't think I'm color blind but I don't know anyway so um now I want you to understand now you don't have to go into the detail of this structure yet but that thing that thing uh the muscle within the muscle they actually have a few of these structures not just one tube like that I'm throwing out three of that tube like structure and those things are called the myofibril I will talk about the myofibril in the next video cu the myofibril is one of the most important parts anyway so they have a special video dedicated just for them now if we were to just zoom in on the cell surface membrane or the S Colma we notice that certain parts of the cell surface membrane will fold inwards but not completely they just fold inwards slightly and I'm just drawing in where they I'm just going in no this is not cyto nesis okay but yeah the cell surface membrane folds inwards and every part where it falls inwards are referred to as something called T tubules or transverse tubules yeah stay with me this is only the starting it's only going to get worse okay least let's be honest with ourselves right so um yeah the in t tubules are just the infoldings of the subma they they are made out of cell membrane by the way and the T tubules are connected to these weird structures which I'm drawing in green and those structures are referred to as something called sarcoplasmic reticulum not endoplasmic reticulum endoplasmic I mean technically it does look like an endoplasmic reticulum but because it's inside the muscle fiber we give it a different name we call it the sarcoplasmic reticulum and unlike the smooth ER and the rough ER they also have a slightly different function we will talk about the function later so this is a general alized structure of the muscle fiber you can see the CMA sarcoplasm the mitochondria nucleus those you understand the new structures that you have to know are the T tubules sarcoplasmic reticulum and the myofibril okay now some students are still like look I still don't understand that t tub can you elaborate on that further so what I'm going to do is I'm just going to take out the muscle uh fiber here and I'm going to delete out all the other structures because I just want to focus on the Alma T tubule and also the SOP plasmic reticulum only okay so I've deleted the my myofibrils and such so what I'm doing here is I'm drawing out the phospholipid B layer we just zooming in and that is the cell surface membrane or the sarola right and the C Lima where it folds inwards that structure forms the T tubul that's what it means by infolding that's all it is and of course the t tubule is also connected to the sarcoplasmic reticulum all those are membranes and of course the blue color Parts where I'm highlighting uh the parts where I'm highlighting in blue are the sarcoplasm now there are a few important points that I want you to know all right the first important thing I want you to know is the Suma is connected to the T tubu which is connected to the sarcoplasmic reticulum through a network of membranes this will the reason why this is important to understand now is because when we study the contraction of the muscles this part part is going to be repeated again the second important thing I also want you to know is within the sarcoplasmic reticulum in the sister which is the container the the the space within the uh reticulum it contains calcium ions and along the membrane of the SOP plasmic reticulum those purple color bits that you can see there those are calcium ion channels so the cop plasmic reticulum contains calcium ions within the sister and it also contains calcium ion channels on its membrane now again you might be thinking why is this important I know that I'm info dumping info dumping just basically means I'm just basically Force feeding you with a lot of information but just like I do with most of my videos everything will be connected together I promise okay so just understand the structure of the skeletal muscle cell or the skeletal muscle fiber however you want to call it this is just the generalized structure that we just have to know first all right