Muscle cells belong to one of three types: skeletal, cardiac or smooth muscle, according to InnerBody. All muscles cells are essential in allowing movement of the body and its organs.
Skeletal muscle accounts for 40 percent of the human body's mass and is the most widely dispersed type of muscle in the body, says InnerBody. It makes up major muscles, such as the biceps brachii, and is also present in the eyes, throat and diaphragm. Skeletal muscle cells have multiple nuclei, are non-branching and appear striped under a microscope. The arrangement of heavier myosin and lighter actin proteins that allow skeletal muscle to contract cause the stripes. Skeletal muscle is also the only voluntary muscle, meaning that it is under conscious control of the brain.
Cardiac muscle cells make up the heart and are present nowhere else in the body, notes InnerBody. These muscle cells have a single nucleus and a branching structure, and they appear striped under a microscope. Special connections between cardiac muscle cells, called intercalated disks, prevent the cells from detaching during vigorous beating of the heart. Cardiac muscle cells act involuntarily but have pacemaker cells with the ability to set cardiac muscle rhythm without input from the rest of the nervous system.
Smooth muscle cells make up the muscle of the organs and blood vessels, states InnerBody. Smooth muscle cells have a single nucleus, are non-branching and do not appear striped under magnification. These muscle cells act involuntarily and account for processes such as stomach movement during digestion or uterine contractions during childbirth.