National League for Nursing (NLN) Science Practice Exam 2025 – The Comprehensive All-in-One Prep Guide for Success!

The sliding filament theory is the fundamental mechanism that explains muscle contraction at the cellular level. According to this theory, muscle fibers contain two main types of protein filaments: actin (thin filaments) and myosin (thick filaments). When a muscle is stimulated to contract, the myosin heads bind to specific sites on the actin filaments, forming a cross-bridge. This interaction prompts a change in the shape of the myosin and causes the actin filaments to slide past the myosin filaments. As this sliding occurs, the muscle fibers shorten, resulting in overall muscle contraction.

This contraction process is further regulated by the presence of calcium ions. When a muscle cell is stimulated, calcium is released from the sarcoplasmic reticulum into the cytoplasm of the muscle cell. The increase in calcium concentration allows the binding sites on the actin filaments to become accessible to myosin heads, which is crucial for the sliding mechanism to occur.

While neurotransmitters facilitate communication between neurons and muscle cells, and electrical impulses are essential for initiating contraction, the sliding filament theory specifically describes the physical process that results in muscle shortening and tension generation. Therefore, understanding the sliding filament theory is essential for comprehending muscle contraction on