sarkómerum

The sarcomere is the basic functional unit of muscle tissue, responsible for generating force and enabling contraction. It is the repeating unit that makes up a myofibril, which in turn is a component of a muscle fiber. The sarcomere is characterized by its distinct structure, which includes the I-band, H-zone, and A-band.

The I-band, or isotropic band, is the light region at each end of the sarcomere. It contains the thin filaments of actin, which are composed of actin proteins and troponin-tropomyosin complexes. The H-zone, or homogenous zone, is the dark central region of the sarcomere that contains only thick filaments of myosin. The A-band, or anisotropic band, is the dark region that overlaps the I-band and the H-zone, containing both thick and thin filaments.

During muscle contraction, the thin filaments slide over the thick filaments, shortening the length of the sarcomere. This sliding is facilitated by the interaction between actin and myosin, which involves the binding and release of ATP, leading to the power stroke that pulls the thin filaments. The sarcomere's ability to shorten and return to its original length is crucial for muscle function, allowing for activities such as walking, running, and lifting objects.