There are three types of muscles in the body. Each of them are found in specific areas and serve important roles in the proper functioning of many parts of your body. Skeletal muscle, which is almost entirely under your direct control, is known as striated muscle. The muscles that make up the heart are very specialized and are known as cardiac muscle. Lastly, many of your internal organs and arteries use a type of muscle known as smooth muscle to control their functions.
Striated muscle is the type you are likely most familiar with. It is the type of muscle tissue which makes up the muscles attached to your bones. You have direct control over the contraction and relaxation striated muscle. To demonstrate this, you simply need to move any part of your body such as a hand, finger, elbow, knee, or leg. Striated muscle is given its name because when it is examined under a microscope, it contains numerous lines throughout the tissue known as striations.
Skeletal muscle is attached to bones by tendons. There are two major categories of striated muscle, fast twitch and slow twitch. Fast twitch muscles are responsible for quick bursts of power, but fatigue quickly. On the other hand, slow twitch muscles do not provide as much instantaneous power, but are able to contract for long periods of time without fatiguing. Sprinters will rely more heavily on fast twitch muscles while marathon runners will rely on their slow twitch muscles.
Smooth muscle is found in various internal organs throughout your body. This type of muscle is not able to be controlled voluntarily. For example, it is found in the internal lining of the major arteries of your circulatory system. Have you ever tried to flex your aorta? Well, you can't. And that's because the muscular layer surrounding the aorta is made up of smooth muscle.
Smooth muscle is also found in the reproductive organs, lungs, gastrointestinal tract, and in certain parts of the eye. The term smooth muscle is a descriptive term given to this type of muscle as it does not contain the same types of stripes seen in striated and cardiac muscle. These stripes are only visible when a piece of muscle tissue is looked at under a microscope. Smooth muscle cells contain only one centrally located nucleus.
Cardiac muscle is specifically designed to function in the heart. In fact, given its name, it is understandable that it is only found in heart tissue. Cardiac muscle has several properties which distinguish it from striated and smooth muscle. It must be able to contract on arrhythmic basis continually without stopping throughout your lifetime. As such, it does not fatigue in the same way that striated and even smooth muscle does. There are specific cells on the heart which function to initiate the heart beat. Cardiac muscle is the only type of muscle that can initiate a contraction by itself.
Cardiac muscle is under involuntary control by your brain and those specialized cardiac cells. You cannot control your heart rate consciously. Of course doing things such as exercising can increase your heart rate, but that is merely a reaction of your body to be activity.