Contractile proteins are specialized proteins that enable muscle contraction and movement in living organisms. The two main types of contractile proteins are actin and myosin. These proteins work together in muscle fibers to facilitate the sliding filament mechanism, which is essential for muscle contraction. When a muscle receives a signal from the nervous system, myosin heads attach to actin filaments and pull them closer together. This interaction shortens the muscle fiber, resulting in contraction. The process requires energy in the form of ATP (adenosine triphosphate) to continue, allowing muscles to perform various functions, from simple movements to complex actions.