Muscles are primarily made up of muscle cells, called fibers. Fibers are the parts of your muscles that contract and expand, such as how you move your legs while running. There are three types of muscles in the human body: skeletal, smooth and cardiac.
Identification
Skeletal muscle is the type that you usually think of when considering the structure of muscles. These are the muscles you use to move your legs, arms, abs and back. Cardiac muscle resembles skeletal muscle but is only in the heart. Smooth muscles are found in places such as your digestive tract, reproductive organs and hair and blood vessels.
Function
People use skeletal muscles to consciously move their bodies and other objects, and unconsciously to maintain posture. Skeletal muscles help blood flow and create heat to help you stay warm. Cardiac muscles enable your heart to beat. Smooth muscles transport food through your digestive tract and move egg cells through women's Fallopian tubes. Smooth muscles in women's uteruses are responsible for a woman's childbirth contractions. Cardiac and smooth muscles are involuntary, meaning you don't have conscious control over their function (unlike skeletal muscles, which you consciously activate to for walk around, for example).
Features
All three types of muscles have three primary features. Electrical elasticity is the muscle's ability to produce electrical signals that enable your muscles to contract. The second feature is extensibility, the muscle's ability to stretch without getting damaged. For example, a woman's uterus stretches a great deal during pregnancy without harming the smooth muscle. The smooth muscles of your stomach can also stretch quite a bit without bursting after you eat. Muscles are also elastic, which means they can return to their normal length after extending or contracting. Your heart wall, for example, returns to its normal size after it contracts during a heartbeat.
Considerations
When your skeletal muscle gets "bulked up" from regular exercise, such as resistance training, your muscle fibers get thicker, a process called hypertrophy. Testosterone triggers hypertrophy of your muscle fibers, which is why men usually have bigger skeletal muscles than women. Abusing anabolic steroids also causes hypertrophy to your skeletal muscle fibers, along with potentially dangerous and undesirable side effects.
Types
There are some differences between the three types of muscles. One major difference between striated (skeletal and cardiac) muscles and non-striated (smooth) muscles is that your non-striated muscles can stretch a larger amount than striated muscles without getting damaged. Skeletal and cardiac muscles contract more quickly, like the rapidity of your heartbeats, than smooth muscles.
References
- Principles of Anatomy and Physiology; Gerard Tortora and Bryan Derrickson; 2006
- Centers for Disease Control and Prevention: Physiologic Responses and Long-Term Adaptations to Exercise
