Source: Images and Video Created by Amanda Soderlind
Welcome to this lesson on Types of Skeletal Muscle. Today, we're going to discuss the two types of skeletal muscle, which are fast skeletal muscle, also known as white skeletal muscle, and slow, or red, skeletal muscle. So we're going to discuss examples of which types of muscle fall into each of these categories and what the difference between fast and slow, or white and red, skeletal muscles are. So let's start by discussing red skeletal muscles.
So red skeletal muscles, as I mentioned, are also known as slow skeletal muscles. So these are types of skeletal muscles that can contract slowly for long periods of time. So examples of red skeletal muscles are muscles that you use on a very regular basis, muscles that help you to maintain your posture, muscles that allow you to walk, so the muscles of your legs. These are muscles that we're using daily and we use for long periods of time. So these muscles need to be able to sustain activity for long periods of time.
So the muscles of your leg we'll use as an example. So these types of muscles have fibers that have more myoglobin and more capillaries in them to allow for the sustained activity that they require. So myoglobin is a protein that binds to oxygen, and it's found in the fibers of red muscle cells.
So this myoglobin that's found in these cells has a red color to it, so that's what gives muscles its red color is because of this myoglobin. So it's this protein that binds to oxygen. And it also has more capillaries running to it. So we have more blood running to these muscles, delivering oxygen and taking away carbon dioxide as these muscles work. So red muscles, muscles that can sustain activity for long periods of time.
White skeletal muscles, or fast muscles on the other hand, can contract quickly for short periods of time. So an example of this would be the muscles in your hand. The muscles in your hand can contract quickly, but they can't sustain activity for a very long period of time.
If you are writing, for example, you can only write so long before your hand really starts to cramp up. So the reason for this-- the reason that they have this white appearance to them, is because they have fewer capillaries running to them and less myoglobin. So remember, myoglobin is what gives red muscles that red appearance; but because white skeletal muscles don't have as much myoglobin, they have a white appearance.
They're not as red. And again, they have fewer capillaries running to them, which means less blood is supplied to them as well. So this is why they can only contract for short periods of time.
White skeletal muscles also have fewer mitochondria in them, which is another reason that they can only contract for short periods of time. There's more mitochondria in your red skeletal muscles, which provides those muscles with more ATP and more energy to sustain those contractions. So red skeletal muscles are able to contract for longer periods of time, whereas white skeletal muscles can only contract for shorter periods of time. So this lesson has been an overview on the two types of skeletal muscle, red and white.
Source: Images and Video Created by Amanda Soderlind
Welcome to this lesson today on muscle contractions, macro view. So we're going to be discussing the large scale view on how muscle contractions allow for the movement of our skeleton. So we're talking about how skeletal muscles interact with our skeleton in order to allow for movement. So our example that we're going to use today is going to be with our bicep and tricep.
So the bicep and tricep are arranged in a pair, and they are antagonistic to one another. So what this means is that the action of one muscle opposes the action of the other. So for example, when the bicep contracts, the tricep relaxes. And when the tricep contracts, the bicep relaxes. So they're antagonistic to one another.
And this is allowed for by something called reciprocal innervation. So reciprocal innervation acts on groups of muscles so that when one muscle contracts, no signals are sent to the opposing muscle, so it relaxes. So that's how when your bicep contracts, your triceps relaxes. Because when that bicep contracts, your nervous system is not sending any signals to your tricep, which allows for it to relax. So our muscles, our bones, our tendons, they're working together to act like a series of levers in order to allow for our skeleton to be able to move.
So we're going to take a look at our diagrams here to describe our following terms, origin and insertion. So origin is the end of a muscle that attaches to a stable bone, while insertion is the end of a muscle that attaches to a bone that moves. So like I said, our skeleton and our muscles and our tendons are working together like a series of levers. When a muscle contracts, it's allowing part of your skeleton to be able to move.
So our origin in this example, if we're using our bicep as an example, is going to be our scapula. So we have our bicep muscle here. We have the tendon, which is a dense connective tissue that attaches bone to muscle. That's attached to our scapula. So when your bicep contracts or relaxes, your scapula is not going to move. So that's our origin, our stable bone that's not moving when that muscle contracts or relaxes.
However, our forearm is what does move when our bicep contracts or relaxes. So that would be our insertion here. So when our bicep contracts or relaxes or when our tricep does that, it's allowing for our forearm to move up and down. So when the bicep contracts, the tricep relaxes, and our arm is going to move up.
Now, let's take a look at what happens when our tricep contracts. So in this case, if our tricep contracts, our bicep then relaxes and our arm moves down. So you can try this with your arm. If you relax or contract your bicep, you'll notice how it allows your forearm to move up or down. So as we said, these are antagonistic muscles. They work antagonistically where the action of one opposes the action of the other.
Another type of group of muscles are synergistic muscles, whereas instead of opposing reactions, you have these muscle groups that are working together to increase the force or to stabilize another muscle in the body. OK, so you can have synergistic groups of muscles or antagonistic groups of muscles. So this lesson has been a large scale overview on how muscle contractions allow for skeletal movement.