| Front | Muscle contraction stages |
|---|---|
| Back | action potential from motor neurone stimulates muscle cell Depolarisation of sarcolemma occurs Depolarisation spreads across T-tubules into sarcoplasmic reticulum Sarcoplasmic reticulum releases stored calcium ions into sarcoplasm Calcium ions bind to a protein attached to tropomyosin causing the protein to change shape Tropomyosin pulled out of actin-myosin binding site Myosin head can bind Myosin head binds to actin filaments and actin-myosin cross bridge formed Calcium ions activates ATP hydrolase to provide energy need for muscle contraction energy released causes myosin head to bend which pulls actin filament along Another ATP molecule provides energy to break actin-myosin cross bridge Myosin head detaches from actin filament Myosin head reattaches to different binding site and new actin-myosin cross bridge forms and cylce repeated cycle continues as long as calcium ions are present |
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