Nearly half of a human's body weight comes from muscle mass. By weight, that makes the muscular system the largest of the body's systems. It is comprised of more than 650 muscles working together. Human muscles come in three types: skeletal, cardiac and smooth. Each one performs different functions within your body.
What the Muscular System Does
Without muscles, your body wouldn't move. You wouldn't be able to breathe, walk, excrete waste or even have a beating heart without muscles. Though people usually are familiar with the functions of skeletal muscles, most of the body's muscles are not under a person's control.
Muscles produce heat from their movements, which helps to maintain your body temperature. They also pump lymph, the fluid that surrounds cells, throughout your body. Finally, the muscular system helps us maintain our posture.
Skeletal muscles are called voluntary muscles because they can be controlled consciously to help you move. These muscles are connected to the bones with tendons. When your muscles contract, they actually shorten and pull two bones closer together. Flexor muscles cause a joint to bend, while extensor muscles cause the joint to straighten. Ligaments are tissues that hold the bones together so they don't separate when the muscles force them to move.
Smooth muscles, or involuntary muscles, are not controlled consciously. They are controlled by the autonomic nervous system, and found and in around your circulatory, lymph and intestinal systems. Smooth muscles are not attached to bones, move slowly and can stay contracted for long periods of time. They help push food through your digestive system, and constrict and dilate blood vessels.
Cardiac muscle is the muscle tissue found in the heart. This muscle tissue allows the heart to push blood into the arteries.
How the Muscles Work
The brain sends signals through the nervous system to motor neurons on muscles telling them to contract. Nerve impulses then cause the muscle cells to contract, which can make a heart beat or an arm bend.