Skeletal muscle

Skeletal muscle

Skeletal muscle fibres are multinucleated cells, with the nuclei situated immediately beneath the sarcolemma (cell membrane). An individual fibre may be up to 35cm long. A mature skeletal muscle fibre is composed of a large number parallel running myofibrils. The myofibrils in turns consist of overlapping parallel-arranged thin actin filaments and thick myosin filaments. The filaments are anchored to specific accessory proteins. The functional unit of the fibril is the sarcomere, which is situated between two Z-lines.

A thin layer of connective tissue, the endomysium, surrounds each muscle fibre. Several muscle fibres are bundled together as a fasciculus (Pl fasciculi). The connective tissue layer surrounding the fasciculi is known as the perimysium. An individual muscle is a number of fasciculi enclosed by the epimysium, a thick dense connective tissue capsule. The connective tissue framework is continuous with that of the tendons and muscle attachments to direct the muscle forces to the bone, skin, etc.

Muscles are highly vascular with the blood vessels running in the various connective tissue layers. The different fibre types may histologically visualized by the use of histochemical techniques.  Skeletal muscle contraction is regulated by intracellular calcium stored in the T-tubule system.