1.9. Smooth, Skeletal, and Cardiac Muscles http://www.ck12.org
Types of Muscles
Themuscular systemconsists of all the muscles in the body. This is the body system that allows us to move. You
also depend on many muscles to keep you alive. Your heart, which is mostly muscle, pumps blood around your
body.
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 can control some muscle movements. However, certain muscle movements happen without you thinking about
them. Muscles that are under your conscious control are calledvoluntary muscles. Muscles that are not under your
conscious control are calledinvoluntary muscles.
Muscle tissue is one of the four types of tissue found in animals. There are three different types of muscle in the
body (Figure1.18):
1.Skeletal muscleis made up of voluntary muscles, usually attached to the skeleton. Skeletal muscles move the
body. They can also contract involuntarily by reflexes. For example, you can choose to move your arm, but
your arm would move automatically if you were to burn your finger on a stove top.
2.Smooth muscleis composed of involuntary muscles found within the walls of organs and structures such
as the esophagus, stomach, intestines, and blood vessels. These muscles push materials like food or blood
through organs. Unlike skeletal muscle, smooth muscle can never be under your control.
3.Cardiac muscleis also an involuntary muscle, found only in the heart. The cardiac muscle fibers all contract
together, generating enough force to push blood throughout the body.FIGURE 1.18
There are three types of muscles in the
body: cardiac, skeletal, and smooth.Vocabulary
- cardiac muscle: Involuntary muscle found only in the walls of the heart.
- contraction: Shortening of muscle fibers.
- involuntary muscle: Muscle that is not under your conscious control.
- muscle fiber: Long, thin cell that has the ability to contract, or shorten.
- muscular system: Consists of all the muscles in the body, especially the ones that help you move.