Muscle cells form muscle tissue, which is important for moving the body. There are three types of muscle cells: skeletal muscles, cardiac muscles, and smooth muscles. Skeletal muscle tissue, like a tendon, attaches to bones and allows us to move as we please. Cardiac muscle cells form the muscles in the heart, which help the heart contract as it pumps blood. These muscles are involuntary, which means that they move without us telling them to do so. Smooth muscle is also involuntary. It is a type of muscle that forms the walls of many organs, including kidneys, intestines, blood vessels and lung airways.