Muscle types

Muscles perform four important body functions. They maintain body posture, they stabilize the joints, they provide mobility, enabling us to move where we want, and they generate heat that the body requires. The body contains three types of muscle to perform these functions: skeletal muscle, cardiac muscle, and smooth muscle Smooth muscle is found in the walls of body organs, like the stomach and small intestines. It is also called involuntary muscle because it functions without conscious directions. If smooth muscle required conscious directions, we would have to focus our concentration on functions like digesting our food and passing it through the entire length of our small and large intestines. Another involuntary muscle group, cardiac muscle, is found only in the heart, where it makes up the heart wall. It has its own specialized electrical conduction system. What this microscopic view doesn’t show you is that all of the separate muscle fibers act in concert, so that the heart contracts and relaxes as if it were one enormous muscle. If cardiac muscle needed conscious instructions to contract and relax, we would have to think about every heartbeat. The third type of muscle is skeletal muscle, and it is the only type under voluntary control. Skeletal muscle attaches to and covers our bony skeleton. In this microscopic view, you can see that it has a series of dark and light stripes, or striations. Because of this, it is often called striated muscle. Regular workouts that include resistance training, such as weight lifting, can result in an increase in skeletal muscle size. It’s important to realize that skeletal muscles are under voluntary control. Otherwise, we would not be able to control the body’s movements.

Muscle types

Review Date: 5/10/2019

Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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