There are more than 600 muscles in the human body, which collectively comprise about 40 percent of one’s bodyweight. The tissues that constitute these muscles are typically classified, however, as one of three basic types: striated, smooth, or cardiac. Named for its banded appearance under the microscope, striated muscle comprises the bulk of muscle tissue in the human body. Sometimes alternatively known as skeletal muscle, this tissue type is usually attached to the body’s skeleton via fibrous tendons and is under voluntary control. Contrariwise, smooth muscle, which consists of spindle-shaped fibers arranged in sheets along the walls of most hollow organs, and cardiac muscle, which is striated and found only in the heart, are controlled involuntarily by the autonomic nervous system.