The muscular system is one of the body's organ systems and consists of three types of muscles: skeletal, smooth, and cardiac. The body's muscles allow for movement, posture and circulation of blood. In vertebrates such as humans, the muscular system is controlled by the nervous system, although the cardiac muscles are completely autonomous.
Skeletal muscles are the soft tissue that most people think of when they consider their body's muscles. It is a soft tissue that is anchored to the bone by tendons and allows for the body's movements. Skeletal muscles are striated, meaning that they contain bundles of sarcomeres, the basic unit of a muscle. There are about 639 skeletal muscles in the human body.
Smooth muscles are the involuntary muscles located within the body's organs and operate without conscious control. Smooth muscles are located in the esophagus, stomach, intestines, uterus, urethra, bladder, bronchi, blood vessels and the arrector pili in the skin, which are connected to hair follicles and when contracted form "goose bumps."
Cardiac muscles, which are found only in the heart, are involuntary muscles like smooth muscles but structurally resemble skeletal muscles in that they also are comprised of sarcomeres. However, heart muscle fibers are connected laterally and are controlled by the sinus node, a tissue located in the right atrium.