All right, so ends of muscles. The most obvious is generating movement of things. But our postural muscles are also the reason why we aren't puddles along with our bones. Why we're not puddles of flesh on the floor, or even with bones without postural muscles or muscle tone. People who have spinal cord injuries that are paraplegic or quadriplegic have what's referred to as flaccid paralysis. If you've ever seen someone who had a stroke that just affected one side of the brain in the motor area, and their faces and everything look asymmetrical, and it's because they've lost muscle tone on that side of their face. It's not just that they can't... Well, it is that they can't move it, but we're not aware of that. Unless it's not there. Our joints, our articulations, right, where you have bone-doying to bone with ligaments are stabilized because muscles cross from one bone to the next. And then we have a certain level of protection for internal organs and padding on bones from muscle. And then the one I put at the top, which is its muscles roll in maintaining constant body temperature. Muscle is really metabolically active, it's second only to the brain in terms of the amount of ATP that's used and recharged per unit time. And anytime you have... Well, any chemical reaction will generate a little bit of heat. And when you have hydrolysis reactions or any kind of decomposition reaction, you generate... And you lose a significant amount of energy as heat. So if you're a warm-blooded organism like we are, then you've figured out a way of capturing some of that heat and using it to keep your chemistry moving. So we talked about the different types of muscle tissue and that the cells are called muscle fiber. Smooth muscle, right? As I said, you find it in the walls of hollow internal organs, including blood vessels, other than the heart. The innervation is from the autonomic nervous system, which kind of makes sense. And you can see this sort of fuser form cells. In this picture, we're looking at a cross-section through an artery. So you have adipose tissue out here. And then the smooth muscle cells are organized lengthwise around the loom in of the artery. You can see there's a little plasma there. There's red blood cells. And then this darker thing is... Or darker red band is elastic connected tissue. So you can kind of see what I mean about how... They just kind of look like cells, particularly when you compare them to cardiac and skeletal muscle. So in this diagram, you've got the intercalated discs. The other thing that's really characteristic of all muscle, but cardiac and skeletal muscle in particular, the presence of lots of mitochondria. And again, that's related to how much ATP generation is required. So if we look at cardiac muscle through a light microscope, which is on the left here, you can see the branched nature of the cells, single nucleus, the intercalated discs, which is where the black arrows are pointing. And at this magnification, and with the way this staining was done, you can't really see the striations, which is why I added the electron micrograph image on the right. So the intercalated disc is the dark area. And then you can see the striations, the red are mitochondria. And then skeletal muscle. You can kind of see why I said this is the simplest one to identify under the microscope, because the striations are really clear. The cells are really long and tubular. They just look like rods in longitudinal section. And you have multiple nuclei that are on the edges of the cell. So this is more up close and personal. You can see the nuclei along the outer edge and the banding patterns. And this is here, there's some sort of connective tissue, it looks like. All muscles are electrically excitable, meaning they can generate action potentials, they can shorten. And that's how they produce force. You can't actually move anything by lengthening your muscle cell. You can only, they can only pull. And they're also elastic by which we mean that you can get back to the cell springs back into its longer state after contractions over. So we talked about muscle being an organ. So it's got multiple tissue types associated with it. And for folks who are listening to this later, hopefully you recognize how closely the power points near what's in the concept checks. So skeletal muscles are attached to bone. Tendon is what attaches them. What is referred to as the origin is where the tendon attaches to the bone that's stationary. The insertion is the tendon that attaches to the bone that's being moved. So in this image, we're looking at the biceps brachy, which everybody calls just the bicep, but word to the wise call it the biceps brachy, because there is also a biceps muscle and in the back of your thigh. So if you just say biceps, you could mean biceps brachy or biceps femoris. Bicep, bi for two, step for head, and it's in the brachium of the upper arm. So you have two heads, two origins and a single insertion. Now, we don't really talk about it a lot in this class, but you're probably aware that muscles act in usually act antagonistic or synergistic pairs. So an antagonistic pair would be the biceps and the triceps. So when you contract the bicep, the tricep has to be relaxed in order for the bone to move. Synergistic muscles are where the muscles work together, as opposed to in opposite ways. Muscles are named, they're actually a sort of a method to the madness of naming muscles, although when you're first learning muscles, it may not seem like this. So use this to kind of guide you, cells are named by location. So we've got the bicep brachy or the bicep femoris, which is either in the break heel or the femoral region. They're also named by size, right? The gluteus maximus, for example, the number of origins. So again, the biceps, brachy or biceps femoris, the shape, the deltoid muscle, if you take it off of the body and let it flat, has a triangular shape and delta is a Greek letter that is written as triangle. There's also a muscle called the trapezoid, or sorry, trapezius, which has a trapezoid or diamond shape. Some muscles are named after the origin and insertion. So the brachio radialis, which goes from the humerus and the brachium to the radius and the anti-brakeum by action. So some muscles are extensors, some are flexors. So we have extensor digitorum that allows us to extend our fingers and the flexor digitorum, flexor, carpean extensor, carpean. And then we also name muscles based on how the muscle fibers run. So some of them run at an angle. Those are like the abdominal obliques. Some of them run straight up and down, perpendicular to the ground like the abdominis, or the rectus abdominis, rectus means upright. Oh, the other location when I wanted to mention are the intercostal muscles. So costal is another word for the rib area. The costal cartilage attaches the ribs to the sternum. So the intercostal muscles, both external and internal, are the muscles between the ribs and actually are if you eat meat and you're eating spare ribs, you're eating intercostal muscles.