CVS Practice Test 2025 - Free CVS Practice Questions and Study Guide

Muscle contraction is primarily driven by the interaction between actin and myosin filaments, which slide past each other in a process often referred to as the "sliding filament theory." When a muscle fiber is stimulated by a nerve impulse, calcium ions are released from the sarcoplasmic reticulum. These calcium ions bind to troponin, causing a conformational change that shifts tropomyosin away from actin's binding sites, allowing myosin heads to attach to actin. As the myosin heads pivot, they pull the actin filaments inward, leading to muscle contraction.

This mechanism of actin filaments sliding past myosin filaments is central to how muscle fibers shorten during contraction, enabling movement. Understanding this process is crucial for comprehending muscle physiology and the underlying mechanisms of contraction. Other processes, such as calcium influx, do play important roles in initiating contraction, but it is the physical sliding of actin over myosin that is the definitive action causing the shortening of the muscle fibers.