 Alright, a skeletal muscle organ is made up of many bundles of tissue. So let's look at what makes up this organ. First of all, you know that our skeletal muscle usually attaches to a bone. And you also hopefully are comfortable with the idea that the skeletal muscle attaches to the bone at a tendon. Does that work for you? In the tendon, we're going to talk in a second about what makes up the tendon itself. I'm going to give you a little hint by doing this kind of a cross-section of a skeletal muscle where this right here is the muscle organ or the muscle tissue. Now can you visualize how I could actually carry this out and make an entire muscle to have another bone that it attaches to? And we would have striations in this thing that would indicate fiber direction and then those fibers would shorten and that would shorten the muscle and bring the two bones together. Do you have a vision for where we are? Okay, look, we're going to do a cross-section in my crazy visual. This is the organ, the muscle organ. Each level of organization is covered with a connective tissue casing. And the muscle organ is covered in a connective tissue casing called epimysium. Epimysium. Epimysium surrounds the entire muscle organ. When we go in and look at our bodies, we can actually grab an entire muscle organ and the connective tissue that covers it, that's the epimysium. This is not on accident, it's on purpose that you notice that the epimysium is the same color as my tendon and that's because the epimysium is a structure that eventually becomes tendon. It's what actually connects to the bone organ itself. Now, the muscle organ is made of these structures called fascicles. So if you were to do a cross-section of a muscle organ, you would see these circular fascicles. And the fascicles, let's just name them fascicles, fascicles. The fascicles are surrounded by their own connective tissue, what? Covering. So each fascicle is surrounded by a connective tissue. It's not epi on the outside and it's not endo on the inside. So that gives you a hint to what we're looking at here. This is actually called perimysium. Perimysium surrounds each individual fascicle. If you go, we talked about in the last section how you could string beef or steak or meat that you eat. You can pull pieces of it and string it all up. You can make a pulled pork sandwich. All of those pulled pieces that you string out, those are all fascicles surrounded in perimysium. Perimysium actually keeps the fascicle together. The epimysium keeps the whole organ together. Now, if we were to take the fascicle out, like, dude, what is this fascicle that you speak of, Riggs? Look. Oh, a fascicle is a bundle of something. And are you ready to know what the bundle of it is? Okay, watch. Oh, look at my incredible, dang it. I would have used a different color. I did not use a different color. Some opportunities are just lost. This little thing that I pulled out, that there are a whole bunch of them that make up the fascicle, this is called a myofiber. Oh, myofiber, the plot thickens. A myofiber is a muscle cell. Man, I wish I would have made that a different color. It makes me mad. Myofibers. Okay, seriously, it's a cell. It's like a piece of spaghetti. That's how long it is. And it's filled with all sorts of other stuff. But this is my muscle cell. Now, cells have nuclei. This is my nucleus. And I'm putting, I'm showing you the nuclei, that one kind of bulged on out. And they have many nuclei. And I already told you that in the previous section. So we've got lots of nuclei in a single muscle fiber. And you know we got to be covered in something, doggies. What would you be covered in if you could cover? I mean, but of course. There's another connective tissue covering. Doggies, that's your endomyceum. How awesome is that? So you've got the muscle. The muscle is made up of bundle of fascicles. And the fascicle is actually a bundle of myofibers, or the cells themselves. Now we're not even close to being done. What? You would think we'd be done. Inside the muscle cell. Inside the myofiber. There's actually these like, whoa, holy, I don't know what to say, like it's just filled with these spaghetti noodle long protein fibers, bundles. So watch this. I'm going to have to make it like what, orange? Sure. What? Inside each one of my myofibers are these little protein bundles called myofibrils. True story. What is a myofibril? Are you ready for this? We don't have any more connective tissue going on. So myofibrils are bundles of myofilaments. Now, we have two flavors of myofilaments. We have thick and thin myofilaments. You can call them thick and thin filaments. That's fine. Calling them myofilaments lets you know where we're talking about. So let's do it one more time just for the fun of it. A skeletal organ is made up of bundles of muscle cells called fascicles. Muscle cells are made up of bundles of myofilaments called myofibrils. The functional unit of a skeletal muscle organ is inside the myofiber and it's a thing that we're going to see here in a second results from the organization of the thick and thin filaments inside my myofibrils. Now, if you're feeling like, holy crap, take a second, take a deep breath, go, study, make sure this organization of the muscle organ is comfortable to you because we're about to go into the myofibril and the myofilaments in a lot more detail. Before we do that, take a look at, I highly recommend going around and looking at many different illustrations. But if you can see this illustration here, here's my organ, my organ is made up of bundles, each bundle is made up of cells, each cell, here's a cell, here's a nucleus, each cell is made up of myofibrils. These are my myofibrils and each myofibril is made up of myofilaments. What true story. All right, let's look closer at the myofilaments and how they do what they're supposed to do and make sure you're comfortable with the organization before you do that. Okay, bye-bye.