What Are Muscles?

The muscles in the human body can be divided into three main
networks of specialized muscle tissues. These networks move our
bones, blood vessels, internal organs, and more, twenty-four hours a day.
Within the three systems, more than eight hundred muscles generate
movement and heat when they contract—or tighten—during use, or
relax when not in use.
The three main muscle systems are the skeletal muscle system,
the smooth muscle system, and the cardiac muscle system. The skeletal
muscle system holds our bones in place so that we remain upright. This
voluntary system responds when we tell our bodies to use muscles to do
things like clench a fist or run. The smooth muscle system lines many

• Different types of muscle fibers are responsible for many

voluntary and involuntary actions in the body.

The seemingly simple act of throwing something is actually a complex process that involves the muscles and other body systems, such as the nervous and skeletal systems. internal organs, such as the liver and kidneys. It helps to push substances, such as blood, food, and waste, through the body. The cardiac muscle system helps the heart pump blood throughout the body. We cannot tell the smooth or cardiac muscle systems what to do. These two involuntary systems work automatically. Muscles give us the power to smile, frown, speak, chew, jump, climb, throw a ball, type, digest the food we eat, read these words, and much more. With all these jobs, it is no wonder that muscles in the three muscle systems make up the highest percentage of body weight in an averagesized person. That is more than the weights of bones, fat, blood, orother tissues. When healthy muscles are well fed, exercised, and rested, they can literally make us jump for joy. The flexibility and support muscles provide make it possible for us to participate in life.

Muscles are found throughout the body and help to protect organs and other parts, all while

allowing us to move and balance