Sliding filament theory

Excitation-Contraction Coupling (Step 1)

muscles contract in response to electrical stimulation; nerve impulse reaches axon terminal, releases ACh, then binds to ACh receptors on sarcolemma at NMJ

Action potential on T-Tubule (Step 2)

ACh attaches to sarcolemma, muscle fibers are positively charged; generates action potential into T tubule

Calcium release (Step 3)

as action potential travels along T-tubules, calcium is released from sarcoplasmic reticulum

Troponin binding (Step 4)

calcium binds to troponin and actin filaments; signals tropomyosin to move out of myosin binding sites on actin

Powerstroke (Step 5)

Myosin heads with ADP molecule and phosphate group bind to myosin binding sites on actin; myosin head rotates toward center of sarcomere, then myosin releases ADP and phosphate; the thin actin slides past thick filament, creating power stroke

Actin-myosin detachment (step 6)

actin-myosin cross-bridge remains intact until ATP molecule binds to myosin head