Sliding filament mechanism

• Stimulation of the muscle fibre at the neuromuscular junction reaching threshold triggers action potentials along the sarcolemma of the muscle fibre
• Depolarisation from the action potentials leads to the release of calcium ions from the sarcoplasmic reticulum into the myofibrils
• Calcium ions cause tropomyosin molecules to change shape, moving away from the myosin binding sites on the actin filament
• Myosin heads can now attach to their binding sites on actin, forming "actinomyosin cross-bridges"
• Heads of myosin change angle in a "power stroke", pulling the actin filament along and releasing ADP and Pi molecules
• ATP molecule binds to the myosin head, causing detachment from the actin filament
• Hydrolysis of ATP to ADP and Pi by ATP hydrolase in the myosin head provides energy for the myosin head to return to its normal position
• Heads of myosin re-attach to binding sites further along the actin filament, repeating the cycle