Upon arrival of nerve impulse, which of the following allows calcium ions to enter the cytosol?
Correct answer: C. Sarcoplasmic reticulum
- A. Sarcolemma
- B. Sarcomere
- C. Sarcoplasmic reticulum
- D. Myofilaments
Explanation
When an impulse reaches a muscle fibre, the sarcoplasmic reticulum releases its stored calcium ions into the cytosol, and the calcium binds troponin to start contraction. The sarcolemma carries the impulse into the T tubules but does not store calcium, and sarcomeres and myofilaments are the contractile units that respond to it.
This question appeared on the UHS MDCAT 2026 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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More Muscle Contraction questions
Muscle fatigue results due to deficiency of _ and excess accumulation of _.
According to the sliding filament hypothesis, the release of_ from the sarcoplasmic reticulum causes the reorientation of certain components in the thin filament, permitting them to bind with extension from the thick myosin filaments:
The sarcomere is the region of a myofibril between two successive:
When the muscle is at rest, _____ is disposed in such a way that it covers the sites on the _____ chain where the head of _____ becomes attached.
During muscle relaxation, the calcium ions are: