Human muscle system , the muscles of the human body that work the skeletal system , that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle-like the muscles of all vertebrates-is often divided into striated muscle or skeletal muscle , smooth muscle , and cardiac muscle. Smooth muscle is under involuntary control and is found in the walls of blood vessels and of structures such as the urinary bladder , the intestines , and the stomach. Cardiac muscle makes up the mass of the heart and is responsible for the rhythmic contractions of that vital pumping organ; it too is under involuntary control. With very few exceptions, the arrangement of smooth muscle and cardiac muscle in humans is identical to the arrangement found in other vertebrate animals.