Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Musculoskeletal System
Muscular System
Structure and Functions of Skeletal Muscles

Skeletal Muscles form the active component of The Musculoskeletal System. They are composed of striated Muscle fibers. Attached to the BONES OF THE Skeleton, these muscles contract (shorten) to move the bony levers. Muscles maintain the posture and position of the body and its parts in space, propel the skeletal levers during walking, running, and other movements, perform chewing, swallowing, and breathing actions, participate in speech articulation and facial expressions, and generate heat.

The Human Body contains about 600 muscles, the majority of which are paired. In adults, Skeletal Muscle mass accounts for 30–40% of total body weight. In newborns and children, muscles make up 20–25% of body weight. In elderly and advanced age, muscle mass drops to 20–30%.

Each Muscle consists of A large number of muscle fibers. Every fiber is enveloped in a thin sheath—the endomysium—formed by a small amount of Connective Tissue fibers. Bundles of muscle fibers are surrounded by loose Fibrous connective tissue known as the internal perimysium, which separates the muscle fascicles from one another. Externally, the muscle is also covered by a thin connective tissue sheath—the external perimysium—which closely fuses with the internal perimysium and with connective tissue fibers penetrating into the muscle. The connective tissue fibers surrounding the muscle fibers and their bundles extend beyond the muscle to form the tendon.

Each muscle is richly supplied with Blood Vessels that deliver nutrients and oxygen to the muscle fibers while removing Metabolic waste products. Glycogen serves as the primary energy source for muscle fibers. Its breakdown produces adenosine triphosphate (ATP), which drives Muscle contraction. The nerves entering the muscle contain both sensory and motor fibers.

Skeletal muscles exhibit properties such as excitability, conductivity, and contractility. Under METABOLISM/18.html">The Influence of nerve impulses, muscles become excited and enter an active operational state. The excitation rapidly propagates (is conducted) from the nerve endings (effectors) to the contractile structures—the muscle fibers. As a result, the muscle contracts, shortens, and sets the skeletal levers in motion.

Muscles comprise a contractile portion (the belly), built from striated muscle fibers, and tendinous ends (tendons) that attach to the skeletal bones. In some muscles, tendons blend into the Skin (facial expression muscles), attach to the Eyeball, or connect to neighboring muscles (in the Perineum). Tendons are formed of dense regular fibrous connective tissue and exhibit high tensile strength. Muscles located in the limbs typically feature narrow, long tendons. Many ribbon-like muscles have broad tendons known as aponeuroses.