sarcomerek

A sarcomere is the basic contractile unit of striated muscle tissue. It is the smallest functional unit of a muscle fiber and is responsible for muscle contraction. Sarcomeres are organized in a repeating pattern along the length of muscle fibers, creating the characteristic striped appearance of skeletal and cardiac muscle. Each sarcomere is defined by the region between two Z-lines, which are thin, dense structures that anchor the ends of the filaments.

Within a sarcomere, several types of protein filaments are arranged in a precise manner. The thick filaments, primarily composed of the protein myosin, are located in the center of the sarcomere, forming the A-band. Thin filaments, composed mainly of actin, are attached to the Z-lines and extend towards the center of the sarcomere, overlapping with the thick filaments. The region where only thin filaments are present is called the I-band. The area where thick and thin filaments overlap is the zone of overlap. The central portion of the A-band, where only thick filaments are present, is known as the H-zone.

Muscle contraction, or the sliding filament theory, occurs when myosin heads bind to actin filaments and pull them towards the center of the sarcomere. This sliding action shortens the sarcomere, and consequently, the entire muscle fiber. ATP provides the energy for this process, and calcium ions play a crucial role in regulating the interaction between actin and myosin. The coordinated contraction of millions of sarcomeres results in the macroscopic movement of limbs and organs.