sliding filament theory

• 1. when an action potential reaches a muscle it stimulates a response
• 2. Calcium ions enter and bind to troponin, this causes a shape change in the protein and causes tropomyosin (which blocks binding sites on actin for the myosin head during relaxation) to move and uncover the binding sites.
• 3. Whilst ADP is attached to the myosin head the myosin heads bind to the actin to form a cross bridge
• 4. The angle created in the cross bridge creates tension, the actin filament is pulled and slides along the myosin. in doing so, the adp molecule is released
• 5. An ATP molecule binds to the myosin head and causes it to change shape slightly. as a result it detaches from the actin filament
• 6. within the sarcoplasm, there is the enzyme ATPase that is activated by calcium ions to hydrolyze the ATP into ADP and an inorganic phosphate ion- this releases the myosin head and enough energy for the myosin head to return to its original position
• 7. This entire process repeats continually while calcium ions remain high and therefore whilst the muscle remains stimulated by the nervous system