Check Your Understanding
- What is muscle tissue?
- What is the function of the muscular system?
Introduction
Themuscular systemis the body system that allows us to move. You depend on many
muscles to keep you alive. Your heart, which is mostly muscle, pumps blood around your
body. Muscles are always moving in your body. Certain muscle movements happen without
you thinking about them, while you can control other muscle movements. In this lesson you
will learn about the different types of muscles in your body and how your muscular system
works with the other body systems to keep you alive and healthy. You will also learn how
and why regular physical activity is important for good health.
Types of Muscles
Each muscle in the body is made up of cells called muscle fibers. Muscle fibersare long,
thin cells that can do something that other cells cannot do—they are able to get shorter.
Shortening of muscle fibers is calledcontraction. Nearly all movement in the body is the
result of muscle contraction.
You are aware of and can control certain muscle movements. Other muscle movements you
are not aware of and cannot control. Muscles that you can control are calledvoluntary
muscles. Muscles that you cannot control are calledinvoluntary muscles. There are three
different types of muscles in the body (Figure16.22):skeletal, smooth, andcardiacmuscle.
Skeletal muscle is voluntary muscle. Smooth muscle and cardiac muscle are involuntary
muscles.
- Skeletal muscleis usually attached to the skeleton. Skeletal muscles move the body.
They usually contract voluntarily, but they can contract involuntarily by reflexes. For
example, you can choose to move your arms, but your arm would move automatically
if you were to burn your finger on a stove top. - Smooth muscleis found within the walls of organs and structures such as the esoph-
agus, stomach, intestines, and blood vessels. Unlike skeletal muscle, smooth muscle is
involuntary muscle which means it not under your control. - Cardiac muscle is also an involuntary muscle but is a specialized kind of muscle
found only in the heart.