1. An action potential arrives at neuromuscular junction .
2. Calcium ions enter into the synaptic knob triggering the release of neurotransmitters
(acetylcholine) from synaptic vesicles .
3. Acetylcholine diffuses across synapic cleft & depolarise the post-synaptic cell membrane
( sarcolemma ) of muscle cells .
4. When threshold level exceed , an action potential is generated .
5. The action potential propagate along sarcolemma .
6. A wave of depolarisation spreads to the T tubules and to
sarcoplasmic reticulum .
7. This causes the voltage-gated calcium channels open and
calcium ions release from sarcoplasmic reticulum into
sarcoplasm .
8. Ca2+ ions acts as trigger for muscle contraction .
9. Ca2+ions bind to troponin molecules on thin actin filament .
10. Troponin changes shape and position .
11. This causes the thin tropomyosin filament moves away to one
side .
12. Thus, exposes the myosin binding sites on actin filament .
13. Myosin molecules in thick myosin filament has a head
containing ATPase which catalyses hydrolysis of ATP.
14. Myosin head ( ADP + phosphate ) now has a high energy
configuration .
15. Myosin head binds to the exposed site on actin molecules .
16. An actomyosin cross-bridge form .
17. ADP + phosphate now release from myosin head .
18. Myosin head returns to low-energy configuration .
19. Myosin head bends .
20. Propelling the actin filamentto slide past the myosin filament .
21. "Power stroke" occurs.
22. New ATP molecule binds to myosin head .
23. Myosin head detach from actin filament . ( in low-energy
configuration )
