Architecture of a skeletal muscle
Skeletal muscle is a form of striated muscle tissue which is under the control of the somatic nervous system; that is to say, it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle. As their name suggests, most skeletal muscles are attached to bones by bundles of collagen fibers known as tendons.
Skeletal muscle is made up of individual components known as myocytes, or "muscle cells," sometimes colloquially called "muscle fibers." They are formed from the fusion of developmental myoblasts (a type of embryonic progenitor cell that gives rise to a muscle cell) in a process known as myogenesis. These long, cylindrical, multinucleated cells are also called myofibers.
The myofibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments repeated in units called a sarcomere, the primary functional group of the muscle fiber. The sarcomere is responsible for skeletal muscle's striated appearance and forms the machinery necessary for muscle contraction. The term muscle refers to multiple bundles of muscle fibers held together by connective tissue.