Asked in Premeth past paper pool — BiologyModerate

In the muscle fibre, transverse tubules (T-tubules) are formed by the invagination ofsarcolemma. The function of these T-tubules is to

Correct answer: B. Conduct nerve impulse into the cell

  • A. Unblock the binding sites of actin
  • B. Conduct nerve impulse into the cell
  • C. Synthesise glycogen in the sarcoplasm
  • D. Store calcium ions in the sarcoplasmic reticulum

Explanation

The correct answer is that T-tubules conduct nerve impulses into the muscle cell. This is crucial for initiating the process of muscle contraction. When a nerve impulse reaches the muscle fiber, it travels along the sarcolemma and down the T-tubules, leading to the release of calcium ions from the sarcoplasmic reticulum, which then interact with the muscle proteins to induce contraction. The other options are incorrect because they refer to functions not associated with T-tubules: actin binding site unblocking is related to calcium-troponin interaction, glycogen synthesis happens in the sarcoplasm independent of T-tubules, and calcium storage is a role of the sarcoplasmic reticulum.

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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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