Muscle cells serve a remarkable variety of functions in your body, many of them occurring involuntarily. The specialized structure of the 3 types of muscle cells in the human body enables their functional purposes. Skeletal muscle cells are primarily specialized for voluntary movements, like dancing or snapping your fingers. Smooth muscle cells are structured to produce involuntary movement, such as propelling food through your digestive system. Cardiac muscle cells keep your heart beating and have features of both skeletal and smooth muscle cells.
Your muscle cells, also known as muscle fibers, have one principal function -- generating movement. Each muscle cell contains many long, stringlike proteins called myofilaments. When these proteins connect and slide past one another in a complex interaction, the muscle fiber contracts and generates movement. Muscle fibers primarily use the sugar glucose along with other chemicals in the cell to generate the energy needed to power each contraction.
Skeletal Muscle Cells
Skeletal muscles are attached to bones. Examples include the large muscles of your arms and legs, and the smaller muscles of your face. Skeletal muscle is also known as striated muscle due to a striped pattern visible under the microscope. This appearance results from a highly organized pattern of myofilaments in the muscle cells. Skeletal muscle cells power voluntary movements, stabilize your joints and enable you to maintain an upright posture. Skeletal muscle cells come in slow-twitch and fast-twitch varieties. Slow-twitch muscle cells are adapted for endurance activities and maintaining posture. Fast-twitch muscle fibers are adapted for rapid movements and activities that require maximum effort, such as jumping and lifting.
Smooth Muscle Cells
Smooth muscle cells perform automatic movements in the hollow organs of your body. For example, they move food through your digestive system, expel urine from your bladder and are responsible for contractions of the uterus when delivering a baby. Smooth muscle cells are also found inside blood vessels and around the pupil of the eye. Smooth muscle cells are much smaller than skeletal muscle cells and the myofilaments within them are less organized. Smooth muscle cells contract for a longer period of time and with less force than skeletal muscle cells.
Cardiac Muscle Cells
Heart, or cardiac, muscle cells have structural and functional characteristics of both skeletal and smooth muscle cells. Your heart muscle cells are highly coordinated to contract together with each heartbeat. A special electrical signaling system in your heart stimulates the coordinated contraction of the muscle cells. Like skeletal muscle cells, heart muscle cells have a highly organized internal structure. But they are much smaller than skeletal muscle fibers, like smooth muscle cells.
Reviewed by: Tina M. St. John, M.D.