The given diagram shows an ultra-structure of striated muscle fibres. During muscle contraction, the function of structure X is to
Correct answer: D. Conduct impulses from the neuron down into the myofibril
- A. Provide ATP
- B. Release calcium ions
- C. Allow acetylcholine to bind with myofibril
- D. Conduct impulses from the neuron down into the myofibril
Explanation
The correct answer is that structure X conducts impulses from the neuron down into the myofibril. This process is facilitated by the T-tubules, which are extensions of the muscle cell membrane that penetrate into the center of skeletal and cardiac muscle cells. This conduction is crucial for triggering the release of calcium ions from the sarcoplasmic reticulum, ultimately leading to muscle contraction. The other options, such as providing ATP, releasing calcium ions, or allowing acetylcholine binding, are functions of other components within the muscle fibers.
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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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