Lihassammenta

Lihassammenta, in human anatomy, refers to a muscle fascicle, a bundle of skeletal muscle fibers that functions as a structural and functional unit within a skeletal muscle. The term is Finnish for this concept, and it is surrounded by a connective tissue sheath called the perimysium. Each fascicle contains numerous muscle fibers, which are long, multinucleated cells rich in myofibrils.

The organization of a muscle includes three connective tissue layers. The epimysium surrounds the entire muscle, the perimysium encloses each fascicle, and the endomysium wraps individual muscle fibers within a fascicle. Blood vessels and nerves run through the perimysial network, supplying fibers with oxygen and coordinating contraction via motor neurons.

Fascicles determine how a muscle converts neural signals into mechanical force. The orientation and distribution of fascicles within a muscle influence contraction direction, shortening, speed, and force production. Within a fascicle, fibers may be arranged parallel or in pennate patterns, affecting overall muscle mechanics. Variation among fascicles, including fiber type composition (for example, type I and type II fibers), contributes to a muscle’s endurance and strength characteristics.

Developmentally, fascicles form as muscle tissue develops from mesodermal progenitors and differentiates into distinct fiber types and connective tissues. Clinically, fascicles can be involved in conditions such as muscular disuse atrophy or neuropathies that alter neural input to specific fascicles, leading to weakness or fatigue in targeted muscle regions. See also: skeletal muscle, perimysium, endomysium, epimysium.