 Okay, we're going to talk a little bit about muscle tissue. Muscle tissue is made of proteins, and the way that those proteins are arranged tells us a little bit about each type of muscle tissue and how it looks. You have three types of muscle tissue, skeletal, cardiac, and smooth, and skeletal and cardiac muscle have their proteins arranged in a way that they appear striated. Skeletal also means striped. Smooth muscle, as you might guess, has its proteins arranged in a way that it's smooth. Now skeletal muscle is the muscles that control your movement, your arms, your legs, and so those are controlled by your somatic nervous system. All muscles are controlled by the nervous system, and your somatic nervous system is voluntary. So you choose, for the most part, when you move those muscles. Cardiac muscle is found in the walls of your heart, and smooth muscle is found lining the walls of your blood vessels or in your stomach that helps your stomach muscles contract and shorten and digest your food. So both of these types of muscles are controlled by your autonomic nervous system, and you can think about the word auto, and that can tell you that these muscles are involuntary. So they automatically contract, which is good because if you had to think about making your heartbeat, you wouldn't be thinking for very long, and you want to be able to have your blood vessels constrict or dilate so that you can regulate your temperature, things like that, you don't want to have to think about those things. So cardiac and smooth muscles contract involuntarily, whereas your skeletal muscle you are controlling. So skeletal muscle cells are muscle fibers, and this is one of them. They're called muscle fibers or muscle cells, are striated, like we said, so you can see this striped appearance. They're also multi-nucleated. So that means they have more than one nucleus in one cell. So that's one way you can tell skeletal muscle, which is striated, from cardiac muscle, which is also striated. Now, cardiac muscle has another difference besides being only having a single nucleus. It's also branched. So one cardiac muscle cell is going to be branched, and that's another way that you can tell it from skeletal muscle. When you're looking at two striated muscle types, you can count the nuclei, you can look for branching. Smooth muscle, like we said, doesn't appear striated. The muscle cells have no stripes, and they also have only one nucleus. So that's your three types of muscle cells.