 Muscle cells. This is my brother, Rutler, jumping over the head of his bride on his wedding day. My brother's muscles are extraordinary. And we're going to look at the characteristics of the muscle cell that actually enable this incredible function. I mean, seriously, the thing that he was worried about this day was he didn't want his pants to rip. That's awesome. I'm glad that he was a little concerned about that. This is a visual of an actual, a full muscle organ. We're going to back up at some point in this lecture and remind ourselves of what a muscle organ is. But I want you to take a look at the level of organization that we're going to examine right now. And this right here is a muscle cell. Muscle cells are weird. They definitely are unlike anything else. So what I'm doing is I'm zooming in to a little section of muscle cell, and then I'm going to tell you, this is my image, so we can come back to that thing. I'm going to tell you some characteristics of muscle cells that are different than other cells. First of all, let's see. Muscle cells, skeletal muscle cells have multiple nuclei. Seriously, how cool is that? And that's actually because when they were baby muscle cells, they decided, dude, who wants to live in your own house by yourself? Let's all fuse together little baby cells and all live in the same house and they kept all their nuclei. Brilliant. Muscle cells can be extremely long, so it's kind of nice that they all decided to work together and make one cell. Muscle cells, skeletal muscle cells, have tons of mitochondria. Why? Mitochondria make your ATP, and so you need lots of them to function to have your muscle cell contract. You have an intuitive sense that, yeah, it takes energy to contract muscle cells, so we got to have mitochondria in order to fuel that process. And then this is another really interesting... Okay, those are characteristics that are like normal cell characteristics that are weird. You totally understood what I just said, didn't you? In addition to having some interesting characteristics, they also have unique names, so here are some names we're going to refer to. First of all, you're going to have the sarcolemma. That's the cell membrane. It has a phospholipid bilayer, plus some extra stuff that makes the sarcolemma, so it is a different structure than just our traditional cell membrane. That extra stuff plays a role in the neuromuscular junction, which is that place where the motor end plate, where the somatic motor neuron dumps the acetylcholine. So we have the sarcolemma. You have sarcoplasm, what do you think that is? That's just cytoplasm in a muscle cell. You also have the sarcoplasmic reticulum. Sarcoplasmic reticulum, what? Who's this related to? This is related to the smooth endoplasmic reticulum, and you're like, dude, I've got this, smooth endoplasmic reticulum, of course. That's the crazy folded cell membrane labyrinth that's smooth and not covered with ribosomes that's found inside most cells. And I'm telling you right now, the sarcoplasmic reticulum in the muscle cell is like crazy. I'm going to show it to you because it's a significantly weird thing. And then I'll tell you about some other characteristics. There's something very weird that isn't found in other cells. Nuclei are found in other cells. Myocondria are found in other cells. These things are all found in other cells. Okay, cool, they just have different names. But you have something called a myofibril, myofibril. And this is a package like a bundle, a bundle of contractile proteins. And this is, they're actually like cytoskeleton. That's a cytoskeleton. Of course it does. So myofibrils, and I'm going to show them to you. Okay, let's go back and look at our picture. This is one skeletal muscle cell. This is a myofibril. It contains these contractile proteins. And look at how there's little bundles of myofibrils all around, like all over inside the cell itself. You might think of it like, well I think of them like spaghetti noodles. And it's like having a package of spaghetti noodles. I could actually put, this makes me want to make this, I could take a balloon and fill it with spaghetti noodles. I do agree that I could totally still pour water in. And that's my sarcoplasm, that's the cytoplasm. And it's just going to surround those spaghetti noodles because there's going to be some space in there. Okay, here's some other interesting and weird things. The nuclei of skeletal muscle cells are squished to the outside because of all of these myofibrils. You can see my many mitochondria here. And guess what this is? These like net looking wrappers around. It's like they're wearing these cool dresses. Each myofibril is wearing a dress that has holes in it. That's the sarcoplasmic reticulum. And it has a very important function when it comes to muscle contraction and stimulating the muscle contraction. You also have these things, t-tubules. T-tubules are like places where cell membrane, it's like you take the cell, you take your balloon, and then you poke your finger through it. And the cell membrane invaginates where your finger goes and pokes down inside. And t-tubules are like these little holes, these little tunnels that are basically made up of the sarcolemma, the cell membrane itself, but they go down and they come very close and connected. Look, they're very close and connected with the sarcoplasmic reticulum. That's important too. What else? Hmm, okay. These guys are all going to come into play now. Are you curious about the myofibril? It totally should be. And we're going to break the myofibril down into its filaments that it's made out of. It's made of thick filaments and thin filaments. And they're organized in a certain way. And when you get a bundle of thick and thin filaments, that's a myofibril. So let's start by looking at the thick filaments.