Muscle cells resemble nerve cells in their ability to conduct action potentials along their membrane surfaces. In addition, however, muscle cells have the ability to translate the electrical signal into a mechanical contraction , which enables the muscle cell to perform its work. There are three types of muscle cells: skeletal muscle , which moves the bones of the skeleton at the joints; cardiac muscle , whose contraction enables the heart to pump blood; and smooth muscle , which is located in the walls of blood vessels and contractile visceral organs. Skeletal and cardiac muscle cells have a banded appearance under a microscope, with alternating light and dark bands, and thus they are called striated muscles. They have similar (though not identical) contractile mechanisms. Smooth muscle, on the other hand, is not striated, and its physiology is considerably different from the other two types of muscle.