The role of actin and myosin in muscle contraction is crucial for movement. Actin is a thin filament, while myosin is a thick filament that interacts with actin to produce contraction through a process called the sliding filament model. When a muscle receives a nerve signal, myosin heads bind to actin filaments, forming cross-bridges. As ATP is hydrolyzed, myosin pulls the actin filaments closer together, shortening the muscle fiber. This coordinated action of actin and myosin contributes to muscle relaxation and contraction, enabling various physical activities and functionalities in organisms.