Action potential travels deep into the fibre through T-tubules in sacroplasm. Tubules are in contact with endoplasmic rectilum of the muscle (sacroplasmic rectilum) which actively transports calicum ions from cytoplasm of that muscle.
Action potential opens the calcuim ion channels on the endoplasmic rectilum and calcium ions flood into the muscle sytoplasm (down a concentration gradient). Calcium ions cause the tropomyosin molecules that were blocking the binding sites on actin filaments to pull away.ADP molecule attached to myosin heads means thet are now in a state to find bind to the actin filament and form a crossbridge
Once attached to actin filament, myosin heads change their angle, pulling the actin filament along with it and releasing a molecule of ADP
An ATP molecule attaches to each myosin head, causing it to become detached from actin filament. Calcium ions activate ATPase, which hydrolyses ATP to ADP. This provides energy got myosin head to return to original position
Myosin head then reattaches itself further along the actin filament ad the cycle is repeated as long as there is nervous stimulation of the muscle
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