Although you have more than 600 muscles in your body, there are only three types of muscle: smooth, cardiac and skeletal. Each muscle helps to keep you in motion, your heart beating or signal a natural response in your body, such as the ability to keep your eyes focused.
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Smooth muscles are also known as involuntary muscles, meaning a person cannot physically will them to move. Instead, smooth muscles are controlled by involuntary responses in the brain and body. One example of smooth muscle is the digestive system, where muscles in the esophagus contract to move food down to the stomach and tighten when you have an illness that causes you to vomit. Other examples of smooth muscle include the uterus, the bladder and the muscle behind the eyes that keeps your eyes focused. In terms of appearance, smooth muscles are long, thin-shaped cells attached to bones in the body. Smooth muscles are also found in the blood vessels, helping blood to move around the body.
Cardiac muscle is also known as myocardium. Similar to smooth muscle, cardiac muscle is an involuntary muscle. These muscles are thickened because they must contract frequently to move blood in and out of the heart. Cardiac muscle cells are quadrangular in terms of shape, and the muscles have striations resembling stripes or lines running through them.
Skeletal muscles are the voluntary muscles that allow you to control the movements of your body. Skeletal muscles also are striated and comprise the musculoskeletal system. These muscles are attached to your bones via tendons, which are cords of tissue. In order to move, your skeletal muscles, tendons and bones all must work together. Skeletal muscles come in different shapes and sizes, as evidenced by a weightlifter's large muscles. Other skeletal muscles in the body you may not be as aware of include those in the neck or face. Even your tongue contains skeletal muscles. Major skeletal muscles in the body include the deltoids (shoulders); pectorals (chest); abdominals (stomach); quadriceps (thighs); and gluteal muscles (buttocks). Skeletal muscles often work in pairs, such as the biceps, which bend the arms, which work with the triceps, which straighten the arms.