Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson on skeletal muscles. Today we're going to be discussing the structure and function of skeletal muscles.
Skeletal muscles are type of muscle that interacts with your skeleton in order to allow for movement. Skeletal muscles are the most common type of muscle in the body. You have three different types of muscle within your body, but skeletal muscles are the most common type.
We're going to take a look at this diagram down here as we discuss the structure of skeletal muscles. Let's take a look at this word right here. Origin. Origin is the end of a muscle that attaches to a stable bone. We're going to use our biceps and triceps, for example, which are muscles found in your upper arm. If we're talking about the origin of this muscle, it's the end of the muscle that attaches to a stable bone. That, in this case, would be the scapula. I have that labeled up here.
So if you think of your bicep, when it contracts or relaxes, which part of your arm is allowed to move. Is it going to be up here, or down here? Is it going to be your forearm or your scapula? Well, when you contract or relax your bicep, you know that your forearm is allowed to move. Therefore, our origin would be up here, because this bone is not going to be moving when the biceps contracts or relaxes. It's attached to the stable bone that is not going to move.
Our insertion, then, is the end of the muscle that attaches to a bone that will move. So when you contract or relax your bicep, as we said, your forearm is what's actually going to move. So are our insertion would be down here on our forearm.
Tendons are what connect muscle to bone, or to other muscles. In red here, I have the actual muscle, but the blue is actually our tendons. Tendons work to connect the muscle to bones. They work to stabilize joints, and they're made of a dense connective tissue. So that's what's actually connecting our muscle to our bone at the origin and insertion.
Some skeletal muscles are arranged in groups or pairs. So the bicep and triceps are an example of muscles that are arranged in groups or pairs. If you were to do more research about that, you would learn how they work antagonistically of each other in that way. And that'll be another lesson later to discuss that.
So moving on. We're going to talk a little bit more about the structure of skeletal muscles, more on a micro-level here. We're going to still pretend that this is our biceps muscle. We're going to keep that as our example. This here would be the outer sheath. It's the outer covering of our biceps muscle. And then here we have a cross section of what it might look like close up, if we were to cut that. Within that, we have bundles of fibers.
You'll notice we have all of these bundles of fibers that are contained within this sheath. If we were to take one of those bundles, within that bundle we have fibers. You'll notice how this is a bundle of a whole bunch of fibers, and then we're pulling out and looking at just one fiber right here. And within those fibers we have something called myofibrils.
So skeletal muscle is made up of all these bundles of fibers. Fibers contain myofibrils, and myofibrils contain units that allow for muscle contractions. So they contain something called a sarcomere, and the sarcomere is the basic unit of muscle contraction.
This lesson has been an overview on the structure and function of skeletal muscles.
