 Hey everybody, Dr. O here. In this video we're going to talk about muscle organization and how that impacts its function. So the muscle organization, the type of muscle or pattern you're seeing will affect the power, the range of motion, the speed of muscle movement in different muscles. So muscles are all going to be organized in these bundles of muscle fibers called fascicles and how they're arranged is actually how we classify muscles. So there are four patterns of fascicle organization that you can see right here. We'll go through each of them. Convergent, pennate, and circular. So let's start with the most common type. So most skeletal muscles are going to be called parallel muscles. All the fibers in the fascicle, they run parallel to the long axis of the muscle. So the example here, let's see, where we have the biceps brachii as an example of a parallel muscle and so is the sartorius there in the corner. So parallel muscles, they're nice because you get a lot of movement. When a parallel muscle contracts, the muscle moves about 30% of its length. It shortens about 30% of its length as it kind of thickens there in the middle. So you get a lot of movement from a parallel muscle. But as we'll see, it's not the strongest muscle type that we have. But tension in parallel muscle, how much weight you can move with a parallel muscle is going to depend on its cross-sectional area. So obviously if a muscle is bigger, it's generally going to be more powerful. One square inch of cross-sectional muscle will develop about 50 pounds of tension. So if somebody's bicep is twice as big as yours, it can generally generate a lot more force and move a lot more weight, same with all the muscle types. But especially with these parallel muscles. So that's your parallel muscles and the key example is going to be the biceps brachii there, but also you do see the sartorius. Then we have convergent muscles. So these are muscles where they start real broad and all the muscle fibers come from different directions to converge on an attachment site. Either a tendon and aponeurosis, which is like a flat sheet-like tendon, or a rave, which is a thin band of collagen, you don't hear about those very much. So convergent fibers have muscle fibers that aren't running in parallel, like parallel muscles, they're coming from different directions and they're converging on their attachment. Reason that's so important, and the textbook example here is the pectoralis major, is you'll see that there are pectoralis major fibers that run down, straight across, and up. So these type of muscles, or convergent muscles, are going to allow for all sorts of different types of movements. And this is why some muscles, you have to treat them like they're more than one muscle. So the pectoralis major talking about it as one muscle is totally fine. But if you're a strength training athlete, or if you're a powerlifter or a bodybuilder, you don't treat the pectoralis major as one muscle. You do things to strengthen the upper pec, the middle pec, and the lower pec, or upper and lower, especially the upper and lower pectoralis major, you treat them separately. Because the fibers run in different directions, different movements will strengthen different parts of convergent muscles, if you're trying to strengthen them. But it also allows the pectoralis major to do a whole lot more, because you've got muscle fibers running in different directions. All right, so those are convergent muscles, pectoralis major being the key example there. Then we have your pennate muscles. So pennate muscles, I always kind of think of like the, I don't know what you call it, the thing at the end of an arrow that where the feather on the end of an arrow. So pennate muscles, they form an angle with the tendon. So these, you're not going to get near as much range of motion from a pennate muscle as you will a parallel muscle. But because of their arrangement, you can cram more muscle fibers, more myofibril specifically, into a square inch. So they're going to develop more tension. So for parallel muscles, think more range of motion, more movement. Convergent muscles, they can allow for movements in multiple different directions because fibers are coming from different directions. But pennate muscles are going to be really powerful. They're going to be able to develop the most tension. So you'll see that pennate muscles can be further broken down into unipennate, bipennate, and multi-penate. So let's see, unipennate would be the excensurgitorum there. All the muscle fibers are on one side of the tendon. That's a unipennate muscle. Bipennate muscles, the example there would be the rectus femoris on the bottom, you're going to have muscle fibers on both sides of the tendon. And then multi-penate muscles, that's going to be your deltoid there. The tendons are actually going to branch within the muscle. So there's actually large tendons that are inside that delta that you cannot see. So that would be a multi-penate muscle. So remember the advantage of the pennate muscles would be the amount of force they can generate, the amount of tension they can generate. Then the last group is the circular muscles. See at the top there, the obicularis oris. These are also called sphincters. So they open and close and guard, and it's just to the body. So the obicularis oris can compress the lips, or obicularis oculi closes the eyes. So those are skeletal muscle sphincters. Most of our sphincters are going to be smooth muscle and involuntary, like the smooth muscles, the sphincters that allow stuff to move from the stomach into your small intestine, that kind of thing. All right, so those are the four different ways that we classify muscles based on fascicle organization and arrangement. I hope this helps. Have a wonderful day. Be blessed.