Final answer:
Muscle contraction is achieved through the sliding filament model, where the thick myosin and thin actin filaments slide past each other, facilitated by myosin heads forming cross-bridges with actin, all powered by ATP.
Step-by-step explanation:
Sliding Filament Model of Contraction
The sliding filament model of muscle contraction explains how muscles contract through the interaction of thick (myosin) and thin (actin) filaments within the sarcomere, the basic unit of a muscle cell. When a muscle fiber is stimulated, the myosin heads attach to the actin to form cross-bridges. These myosin heads then pull on the actin filaments, causing the sarcomeres to shorten and the muscle to contract.
In terms of structure, a sarcomere is defined by the distance between two Z discs or Z lines. During contraction, the H zone and the I band shorten, but the A band remains the same length. This change is due to the sliding of the thin filaments past the thick filaments, towards the center of the sarcomere, increasing the zone of overlap.
ATP (Adenosine Triphosphate) is integral to this process, as it provides the energy required for the myosin heads to bind to actin, perform their power stroke, detach, and reset for another cycle. This continuous process of cross-bridge formation and breakdown, powered by ATP, leads to the contraction of the muscle fiber and, consequently, the muscle.