noun, plural: skeletal muscles
The muscular system of the vertebrates is comprised of various muscles. There are three major types of muscles and these are the skeletal muscles, the smooth muscles, and the cardiac muscles. The skeletal muscle is the type of muscle that are known for their multinucleated (syncytial) feature, long cylindrical muscle fibers, transverse markings on the muscle fibers (as seen under the microscope), and being anchored to the bones (by tendons). The skeletal muscle is made up of bundles of muscle fibers. Each of these fibers contains a bundle of smaller myofibrils. Each myofibril consists of two myofilaments: the thin filaments and the thick filaments. The myofilaments are arranged in such a way that there appears a repeating pattern of light and dark bands. Each of the repeating units of light and dark bands is called sarcomere. The sarcomere is regarded as the fundamental machinery responsible for muscle contraction. The skeletal muscles are responsible for moving parts of the skeleton (such as in locomotion). These muscles are under the control of the somatic nervous system, the part of the peripheral nervous system associated with voluntary muscle contractions.
The skeletal muscle fibers can be classified according to their twitch capabilities, i.e. fast-twitch muscles and slow-twitch muscles. Fast-twitch muscles are skeletal muscle fibers having high myofibrillar ATPase activity, high glycolytic enzyme activities, and an intermediate glycogen content which produce a fast twitch. There are two types: (1) fast-fatigable fibers -- also called white fibers (with low myoglobin content, a small mitochondrial content, and fatigue rapidly due to their limited glycogen content and low capacity for oxidative metabolism) and (2) fast fatigue-resistant fibers -- also called red fibres (with large mitochondrial content and high myoglobin content relevant to their resistance to fatigue).
Slow-twitch muscles are skeletal muscle fibers having low 63b myofibrillar ATPase activity, low glycogen content, and high myoglobin content, high mitochondrial oxidative enzyme activities, and an intermediate mitochondrial content which produce a slow twitch and are fatigue-resistant.