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Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.
When you think about muscles, you probably think about the muscles in your arms and legs that allow you to lift heavy objects and run really fast. Those muscles are called voluntary muscles because you choose to move them, but not all of the muscles in your body work that way. The muscles of your heart, organs and other internal structures are involuntary muscles because they are hard at work regardless of what you are doing; they even work while you sleep.
There are two types of involuntary muscles inside of you: cardiac muscle and smooth muscle. In this lesson, we will learn more about these types of muscles and how you depend on them to stay alive.
Did you ever watch a medical show on television where one of the patients went into cardiac arrest? If so, you probably know that means they were having a heart attack. Because the word 'cardiac' refers to things dealing with the heart, it is easy to see that cardiac muscle is the type of muscle that makes up your heart. This muscle is also known as the myocardium, which sounds like a big scientific word but is fairly easy to understand if you break it down. The prefix 'myo' refers to muscle, and the word 'cardium' is really close to cardiac, or heart, so the term 'myocardium' is literally the muscle of the heart.
The cardiac muscle has only one job, but it is a very important one; its job is to pump blood through the miles of blood vessels in your body. If the cardiac muscle stops, you stop. It's a good thing you don't have to consciously think about contracting your heart muscle. If you did, you would never be able to sleep!
Not only is cardiac muscle involuntary; I guess you could say it marches to its own beat. That's because your heart has its own electrical system that causes it to beat consistently, and the crazy thing about that is a heart will continue to beat even after it's removed from the body. All it needs is oxygen. If it has that, it will continue to beat!
One other thing to note about cardiac muscle is its appearance. If you were to put a slide containing a sliver of heart muscle under a microscope, you would notice that cardiac muscle is striated, which simply means it looks like it is striped. This fact is one of the differences between cardiac muscle and smooth muscle.
Smooth muscle is the type of muscle that makes up the walls of many internal organs and structures. You will find this type of muscle in your digestive tract, blood vessels and bladder. Unlike cardiac muscle, it is not striated; instead it looks like smooth sheets of muscle.
You might want to think of smooth muscle as the housekeeper of your body. If there is a job to do that is not under your conscious control and doesn't involve your heartbeat, then smooth muscle is likely taking care of it. For example, the smooth muscles in the walls of your stomach help mix foods with digestive juices. Smooth muscle in the walls of your blood vessels makes the vessels wider or narrower, depending on what your body needs, and it is smooth muscle that pushes urine out of your bladder when you visit the restroom.
As I said, these smooth muscles take care of chores all over your body. They even play a role in helping you see clearly and delivery of babies. Smooth muscles in your eyes are constantly adjusting to keep your world in focus, and smooth muscles make up the wall of the uterus, which is the organ inside a woman where a baby develops. When it's time for the baby to be born, the muscles of the uterus contract, pushing the baby into its new life.
Let's review.
Cardiac and smooth muscles are types of involuntary muscles, which means they work regardless of what you are doing and require no conscious thought to do their jobs.
Cardiac muscle, also known as the myocardium, is a type of muscle that makes up your heart. The cardiac muscle's job is to pump blood throughout your body. If you were to look at cardiac muscle under a microscope, you would notice that it's striated, which means it looks like it is striped. You don't see striations in smooth muscle.
Smooth muscle is a type of muscle that makes up the walls of many internal organs and structures. It does many of the housekeeping chores of your body, such as helping you to digest food, adjusting the flow of blood through your vessels, contracting your bladder, focusing your vision and contracting the uterus when a baby is being born.
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