What mechanism is applied when skeletal muscle contracts?

The sliding-filament mechanism is the correct description of how skeletal muscle contracts. In this process, the actin and myosin filaments within the muscle fibers slide past one another, leading to contraction. When a muscle is stimulated by a nerve impulse, the myosin heads attach to specific binding sites on the actin filaments, forming cross-bridges. The myosin heads then pivot, pulling the actin filaments towards the center of the sarcomere, which is the basic contractile unit of muscle fibers. This action shortens the muscle, generating force and movement.

The sliding-filament mechanism is crucial for muscle contraction, as it simplifies the understanding of how muscles can produce force and change length during various types of contraction—whether that's lifting a weight or performing athletic movements. Other options relate to different aspects of muscle function or regulation. For example, the cross-bridge cycle specifically refers to the series of events during the contraction process when the myosin heads bind, pivot, and release from actin; it is part of the broader sliding-filament mechanism. Meanwhile, the muscle spindle reflex pertains to the sensory mechanism that helps maintain muscle tone and protect muscles from injury, and motor unit recruitment involves the activation of additional motor units to increase