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Skeletal muscles are voluntary muscles under the control of the somatic nervous system. Each individual fiber, and each muscle is surrounded by a type of connective blood oranges for sale layer of fascia. Muscle fibers are in turn composed of myofibrils.

Most muscles occur in bilaterally-placed pairs to serve both sides of the body. Muscles are often classed as groups of muscles that work together to carry out an action. Apart from the contractile part of a muscle consisting of its fibers, a muscle contains a non-contractile part of dense fibrous connective tissue that makes up the tendon at each end. The tendons attach the muscles to bones to give skeletal movement. The length of a muscle includes the tendons. Two types of sensory receptors found in muscles are muscle spindles, and Golgi tendon organs.

Muscle spindles are stretch receptors located in the muscle belly. Skeletal muscle cells are the individual contractile cells within a muscle, and are often termed as muscle fibers. A single muscle such as the biceps in a young adult male contains around 253,000 muscle fibers. Skeletal muscle fibers are the only muscle cells that are multinucleated with the nuclei often referred to as myonuclei.

This occurs during myogenesis with the fusion of myoblasts each contributing a nucleus. Many nuclei are needed by the skeletal muscle cell for the large amounts of proteins and enzymes needed to be produced for the cell’s normal functioning. A single muscle fiber can contain from hundreds to thousands of nuclei. A muscle fiber for example in the human biceps with a length of 10 cm can have as many as 3000 nuclei. A group of muscle stem cells known as myosatellite cells, also satellite cells are found between the basement membrane and the sarcolemma of muscle fibers.

These cells are normally quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair. Muscles attach to tendons in a complex interface region known as the musculotendinous junction also known as the myotendinous junction, an area specialised for the primary transmission of force. At the muscle-tendon interface, force is transmitted from the sarcomeres in the muscle cells to the tendon. Muscle architecture refers to the arrangement of muscle fibers relative to the axis of force generation, which runs from a muscle’s origin to its insertion. The fibers in pennate muscles run at an angle to the axis of force generation. This pennation angle reduces the effective force of any individual fiber, as it is effectively pulling off-axis.