There are three general types of muscle. The first two are "striated", they contain sarcomeres; the third type is "smooth":
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2 Muscular Composition
Contraction and Relaxation
The three types of muscles have significant differences, but all use the movement of actin, against myosin, to produce contraction and relaxation. Contraction is stimulated by electrical impulses transmitted by the nerves, and by the motor nerves and motoneurons in particlular. Muscles and muscular activity account for a lot of the body's energy consumption.
Muscle is composed of muscle cells (sometimes known as "muscle fibers"). Within the cells are myofibrils; myofibrils contain sarcomere, which is composed of actin and myosin. Muscle cells are grouped together into bundles of fascicle; the bundles are then grouped together to form muscle.