The sliding filament mechanism involves several key steps:
1. Calcium Ion Release: When a muscle fiber is stimulated by a nerve impulse, calcium ions are released from the sarcoplasmic reticulum. 2. Troponin and Tropomyosin Movement: Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the myosin-binding sites on actin. 3. Cross-Bridge Formation: Myosin heads attach to the exposed binding sites on actin, forming cross-bridges. 4. Power Stroke: The myosin heads pivot, pulling the actin filaments toward the center of the sarcomere. This action shortens the sarcomere and generates muscle contraction. 5. ATP Binding and Cross-Bridge Detachment: ATP binds to the myosin heads, causing them to detach from actin. The hydrolysis of ATP re-cocks the myosin heads, readying them for another cycle of attachment and power stroke.
