Muscular System

Muscular System


This lesson will introduce the structure and function of the bodies muscular system including the three types of muscle.

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The Human Muscular System

Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson on the muscular system. In this lesson, we are going to be discussing the three main types of muscle found in the human body. But before that, I just want to give a brief overview on the muscular system itself.

The muscular system is one of our 11 body systems that consists of muscles. And these muscles, in our muscular system, allow for movement, production of body heat, flow of blood and other substances. The three main types of muscle found in our body are skeletal muscle, smooth muscle, and cardiac muscle.

Judging by the names of these three types of muscle, you might be able to have a guess at what the purpose and where these muscles are found in our body. And muscles can be either voluntary or involuntary.

Voluntary muscles are a type of muscle that you have control over. So if you were to flex and extend your arm, you have control over your bicep and your triceps that allow for that movement. Involuntary muscles are muscles that you do not have control over. Think of the muscles in your digestive tract that push food through your small and large intestine. You don't have control over those muscles, so they would be involuntary muscles.

Let's take a look at the structure of the three main types of muscle I mentioned prior, which are skeletal, smooth, and cardiac muscle. We're going to start here with cardiac muscle. Cardiac muscle is the type of muscle that is found in our heart. And cardiac muscle is a type of striated muscle. What this means is that it has a striped appearance.

This is the structure that is found in the heart. And this is just a diagram of what it might look like close up. You'll notice the little stripes that go through it, it gives it the striated appearance, because of the way that the cells are composed. Cardiac muscle can contract without stimulation from the nervous system. So this is a really cool part of cardiac muscle, is that it doesn't need any signals from the nervous system in order to be able to contract.

And the cells in cardiac muscle contract kind of as a single unit. They're not actually contracting as one single unit. But a contraction moves through these cells so quickly that it's as if these cells are contracting as a single unit. And cardiac muscle is a type of involuntary muscle.

So remember, involuntary muscle is muscle that you do not have control over. So you have no control over how your heart muscle contracts. It just does it on its own.

The next type of muscle we're going to take a look at here is skeletal muscle. Skeletal muscle is-- basically, the majority of muscles in your body are skeletal muscles. And skeletal muscles work in conjunction with your skeletal system. They help to stabilize the joints, they allow for movement of our body, and they allow for us to produce body heat.

As I said, they're interacting with your skeleton in order to allow for movement. The example here I have is the bicep muscle. It's working with your skeleton in order for your skeleton to be able to move in the way that you want. Skeletal muscles are long thin cells-- I'm sorry-- referred to as fibers.

You'll notice this is an example of what a bundle of muscle cells might look like. Muscle cells are made up of more than one nucleus. The structure of the fibers gives them their stripe look. These fibers are arranged into bundles, and then, those bundles are arranged in a way that looks like they have this stripe look, which we call striated muscle. Similar to cardiac muscle, skeletal muscle is also striated.

And skeletal muscle is a type of voluntary muscle. You have control over these muscles. You have control over extending or flexing your bicep, for example. So they are muscles that you can control how they move.

And then, our last type of muscle is smooth muscle. Smooth muscle, basically, composes the walls of hollow organs and tubes. For example, our blood vessels, digestive tract, they're made of smooth muscle. The inside of those tubes is composed of smooth muscle.

Smooth muscle is not striated. It doesn't have this striped appearance, like cardiac and skeletal muscle. Instead, it actually looks smooth, which gives it its name, smooth muscle. That one's an easy one to remember, hopefully.

The cells of smooth muscle are also generally a little bit smaller. And rather than organized into bundles, they're organized into sheets. Smooth muscle is another type of involuntary muscle.

OK. So here, for example, I have a picture of a blood vessel. And the inside of that blood vessel, then, would be lined with smooth muscle, which helps to contract and push blood through the blood vessel. Again, that's something that you don't have control over. It just kind of happens on its own with input from your nervous system.

This lesson has been an overview on the muscular system and the three main types of muscle found in your body.

  • Muscular system

    ​One of the eleven organ systems of the human body; contains three different types of histologically different forms of muscle (smooth, cardiac, skeletal) that are found in different areas of the body but all share the same primary function and movement.

  • Skeletal muscle


  • Cardiac muscle

    ​A form of muscle that contains short, branched, striated single nucleated cells; cardiac muscle is only located in the heart and is used to pump blood throughout the cardiovascular system.

  • Smooth muscle

    ​A form of muscle that contains short, tube-like (fusiform) single nucleated cells; smooth muscle range from having many layers to a single layer of cells; smooth muscle is found in the walls of hollow organs.

  • Voluntary muscle

    Muscle that we have conscious control of; skeletal muscle is the only one of the three.

  • Involuntary muscle

    Muscle that we have no conscious control of; cardiac and smooth muscle are in this category.