Muscle

Muscle is the body contractile tissue which moves the skeleton and makes it possible for the heart to pump blood. It is composed of muscle cells called fibers whose main property is elasticity. Muscle fibers are bound together by perimysium into bundles called fascicles which are grouped together to form muscle. The muscle is enclosed in a sheath of epimysium. Each fiber is made up of myofibrils, which contain sarcomeres. Sarcomeres are composed of actin and myosin. Individual fibers are surrounded by endomysium.

There are three types of muscle: skeletal, cardiac, and smooth. Skeletal muscle is anchored to bone by tendons; its contraction effects skeletal locomotion and keeps posture. Cardiac muscle is the heart muscle, which is involuntary; it contracts to pump blood throughout the body. Smooth muscle is the involuntary muscle found within the walls of organs and structures such as the liver, kidney, esophagus, stomach, blood vessels, uterus, etc.