 Muscle tissue, there's actually only three types of muscle tissue, and its function is super straightforward, muscle tissue shortens. That's it. The tissue itself shortens. When tissue shortens, it can cause movement. Depending on the shape of the muscle structure, you can cause different kinds of movements. So you can imagine this massive bicep. If I shorten my bicep, I'm actually going to flex my forearm at my elbow joint, right? If I contract and shorten my triceps, I'm actually going to extend my forearm at that elbow joint. And that's because you actually, your muscle tissue only contracts. So if you want to relax a muscle or stretch it back out again, you have to have another muscle to actually do contraction to sort of counterbalance that. Because it shortens, it always causes movement of something. There are three kinds of muscle tissue. If there's a movement in your body, a muscle is somehow involved in that. The muscle tissue that I just demonstrated is skeletal muscle. Skeletal muscle is attached to bone most of the time, but actually not always. The orbicularis aurus is a circular muscle that surrounds your lips and makes it so you can make a kissing move. You got to do that every now and then with your orbicularis aurus. Sometimes when you make your kissing move, you also close your eyes and so you need your orbicularis oculi for that. Thank you, skeletal muscles. It's not the only movement. Skeletal muscles aren't the only things that are moving. Something else is moving. Aww, you have cardiac muscle. Cardiac muscle is only found in your heart and it's responsible. It's contracting and it's responsible for generating pressure to move your blood through your body. Thanks, heart. Everybody pat your heart right now. And then use your orbicularis aurus to kiss your fingers and put that on your heart. And then the last kind of muscle tissue is called smooth muscle. Smooth muscle is a involuntary muscle. It surrounds blood vessels and bronchi in your respiratory system and it causes changes in the diameter of those tubes. So when you see smooth muscle, it's actually there's smooth muscle in your digestive, surrounding your digestive tubing as well. And that actually allows for peristalsis, right? So movements are happening. Smooth muscle is helping us do that. That's it. That's muscle. I don't think there's anything else I need to tell you about it. It takes energy to make it happen. Super cool. We're spending an entire six lectures and labs on skeletal muscle and that's it. And then another three on cardiac muscle. So we're going to see these guys in a little bit more detail in the future. Let's do our last tissue type, nervous tissue.