During muscle relaxation, the calcium ions are:
Correct answer: B. Transported back from the sarcoplasm into the sarcoplasmic reticulum
- A. Released from the sarcoplasmic reticulum into the sarcoplasm
- B. Transported back from the sarcoplasm into the sarcoplasmic reticulum
- C. Further released from the sarcoplasmic reticulum into the sarcoplasm
- D. Remain constant without any movement
Explanation
During muscle relaxation, calcium ions are actively transported back from the sarcoplasm into the sarcoplasmic reticulum, which decreases their concentration in the sarcoplasm. This process allows the muscle fibers to relax as the removal of calcium ions leads to the detachment of the myosin heads from the actin filaments. Option B is correct because it accurately describes this process. The other options incorrectly describe the movement or state of calcium ions during muscle relaxation.
This question appeared on the ETEA MDCAT 2019 paper, which you can sit online with every answer explained.
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About Muscle Contraction
Muscle contraction is explained by the sliding filament model, in which myosin heads pull actin filaments within sarcomeres using ATP. The topic covers calcium, troponin, tropomyosin, the neuromuscular junction and relaxation, with attention to how filament length stays almost constant while the sarcomere shortens.
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Contraction can be sustained for a long period of time by:
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