Muscle Contraction: Sliding Filament Model

• A contracting muscle shortens, but the filaments that bring about contraction stay the same length.
• The filaments in a sarcomere slide past each other, similar to the segments of a telescoping support pole, to bring about contraction.
• The sliding-filament model explains muscle contraction, where thin and thick filaments ratchet past each other powered by myosin molecules.
• Myosin molecules have a long "tail" region that binds to the tails of other myosin molecules, forming the thick filament, and a globular "head" region that binds ATP.
• The hydrolysis of bound ATP converts myosin to a high-energy form that binds to actin, forming a cross-bridge between the myosin and the thin filament.
• The myosin head returns to its low-energy form as it pulls the thin filament toward the center of the sarcomere, contributing to muscle contraction.
• Muscle contraction requires repeated cycles of binding and release of myosin heads to actin filaments.
• During each cycle, the myosin head is freed from a cross-bridge, cleaves the newly bound ATP, and binds again to actin, repeating the process.

Understand the mechanism of muscle contraction through the sliding filament model, where thin and thick filaments slide past each other, powered by myosin molecules. Learn how this process explains the apparent paradox of muscle contraction. Quiz yourself on the details of muscle physiology and the myosin molecule's role in contraction.