PHYSIOLOGY
MUSCLE STRUCTURE FUNCTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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calcium ions are pumped back into the SR, moving the troponin-tropomyosin complex back over the actin binding sites
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sodium ions leave the muscle cell, preventing myosin from binding to actin
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ACh attaches to receptors in the sarcolemma, stopping sarcomere contraction
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calcium ions bind directly to the myosin heads, preventing them from attaching to the thin filaments
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Detailed explanation-1: -Calcium is pumped back up into the SR to lower calcium ion concentration in the sarcoplasm, to relax the muscle (turn off contraction).
Detailed explanation-2: -Muscle contraction usually stops when signaling from the motor neuron ends, which repolarizes the sarcolemma and T-tubules, and closes the calcium channels in the SR. Ca++ ions are then pumped back into the SR, which causes the tropomyosin to re-cover the binding sites on actin (Figure 10.3. 2).
Detailed explanation-3: -This phase is called the relaxation phase. During this phase calcium is actively transported back into the sarcoplasmic reticulum using ATP. The troponin moves back into position blocking the myosin binding site on the actin and the muscle passively lengthens.
Detailed explanation-4: -Powered by ATP, it pumps calcium ions back into the sarcoplasmic reticulum, reducing the calcium level around the actin and myosin filaments and allowing the muscle to relax. Calcium ions are also used for signaling inside other cells, and similar pumps are found in the cell membrane of most cells.