Flex and extend, contract and relax! You may have heard these commands in an exercise or dance class. They’re also commands your muscles and muscle fibers receive constantly from your nervous system. The human body consists of over 650 muscles categorized into 3 types: smooth, skeletal, and cardiac muscle.

Skeletal muscles, also called striated, are the muscles over which you have conscious control. They are recognized by light and dark bands, or striations, and are the muscles that move the bones in the body. They can be developed through fitness and sports training.

Smooth muscles are controlled by the autonomic nervous system and are often referred to as involuntary muscles. They do not appear striated and move the body’s internal organs and secretory glands. Smooth muscle allows you to swallow, digest food, and circulate blood.

Cardiac muscle is found in the heart and looks similar to striated muscle but is involuntary. Cardiac muscle is responsible for the continual contraction/relaxation cycle that pumps blood throughout the body. For an average person, on an average day, the heart beats about 100,000 times. That’s a lot of responses to contract/relax commands!

Introduce or review the muscular system with the Muscular System infographic that visualizes the 3 types of muscle and diagrams the muscle contraction process.