Muscle Fiber Composition: Actin, Myosin & Troponin Explained

Myofilaments are made up of three types of proteins: actin, myosin, and troponin.

- Actin filaments are the thin filaments. Each actin monomer has a binding site for myosin, and when myosin binds to actin, the muscle fiber contracts.

- Myosin filaments are the thick filaments. Each myosin molecule has two heads, each of which can bind to an actin monomer. When a myosin head binds to an actin monomer, it pulls the actin filament toward the center of the sarcomere, causing the muscle fiber to contract.

- Troponin is a regulatory protein that controls the interaction between actin and myosin. Troponin binds to actin and prevents myosin from binding to it. When a nerve impulse reaches the muscle fiber, calcium ions are released into the sarcoplasm, which causes troponin to change shape and release actin. This allows myosin to bind to actin and the muscle fiber to contract.