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So now we have to think about what happens within the sarcomere during muscle contraction, or rather, what
happens to bring about contraction.
Firstly we've got the nerve impulse coming down through to the neuromuscular junction to the muscle cell.
This triggers a release of calcium ions from the sarcoplasmic reticulum, which then diffuse through to the
Next we need to think about the structures within the sarcomere...so we've got two main protein components:
actin and myosin.…read more

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When the impulse stops, Calcium ions are actively pumped out of the sarcoplasm. This means the calcium
ions aren't around to bind to the troponin on the actin filament, so the tropomyosin covers up the myosin binding
sites. This all leads to the relaxation of the muscle because the actin returns to its original position.
When there is no ATP present, the myosin can't be detached from the actin, so the crossbridges remain
intact. This means the muscles stay in one position.…read more


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