PHYSIOLOGY
MUSCLE CONTRACTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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It transports sodium
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It transports calcium
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I takes the impulse (action potential) to the inside of the muscle cell.
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It relaxes the muscle cell
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Detailed explanation-1: -The T-tubules carry the action potential into the interior of the cell, which triggers the opening of calcium channels in the membrane of the adjacent SR, causing Ca++ to diffuse out of the SR and into the sarcoplasm.
Detailed explanation-2: -Transverse tubule T-tubules are invaginations of the plasma membrane, which are present exclusively in striated muscle. Their role is to maintain the SR calcium store under the tight control of membrane depolarization via the voltage sensor channel DHPR [2].
Detailed explanation-3: -With membranes that contain large concentrations of ion channels, transporters, and pumps, T-tubules permit rapid transmission of the action potential into the cell, and also play an important role in regulating cellular calcium concentration.
Detailed explanation-4: -An action potential moving through a T tubule triggers the release of Ca2+ from SER into the cytoplasm (Fig. 39.14). Ca2+ binding to troponin allows myosin to interact with the thin filament, initiating contraction. This signal transduction process is called excitation–contraction coupling.
Detailed explanation-5: -The action potential travels down the t-tubules and excites the sarcoplasmic reticulum which releases calcium. Calcium when bound to troponin causes conformational changes in the sarcomere. Consequently, the interaction of thick and thin filaments of the sarcomere leads to muscle contraction.