PHYSIOLOGY
GENERAL PHYSIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Which of the following steps occurs last in this series?
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Calcium enters the neuron and attaches to synaptic vesicles that carry acetylcholine
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sodium enters and an action potential occurs across the sarcolemma
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calcium attaches to troponin and causes a change in the shape of the tropomyosin
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the myosin head binding sites are exposed
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Explanation:
Detailed explanation-1: -To enable a muscle contraction, tropomyosin must change conformation, uncovering the myosin-binding site on an actin molecule and allowing cross-bridge formation. This can only happen in the presence of calcium, which is kept at extremely low concentrations in the sarcoplasm.
Detailed explanation-2: -Once the myosin forms a cross-bridge with actin, the Pi disassociates and the myosin undergoes the power stroke, reaching a lower energy state when the sarcomere shortens. ATP must bind to myosin to break the cross-bridge and enable the myosin to rebind to actin at the next muscle contraction.
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