Which one of the following statements regarding muscle contraction and relaxation is correct?

Question

Question

This question was previously asked in

UPSC CAPF Previous Year Paper 2(Held on: 12 Aug 2018)

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It involves movement of \(Xn^{++}\) ion
It involves \(Ca^{++}\)ion if blood
It involves release of \(Ca^{++}\) from sarcoplasmic reticulum (SR) and pumping \(Ca^{++}\) back in SR
It involves exchange of Na and K

Answer 1

The correct answer is option 3 i.e It involves release of \(Ca^{++}\) from sarcoplasmic reticulum (SR) and pumping \(Ca^{++}\) back in SR

Explanation:

Muscle contraction is the activation of tension- generating sites within muscle fibres.
The sequence of events in the contraction of muscle fibre is as follows: -
It begins with a signal- the neurotransmitter, Ach - from the motor neuron innervating that fibre.
The local membrane of the fibre will depolarize as positively charged Na+ ions enter, triggering an action potential that spreads to the rest of the membrane will depolarize, including the T-tubules.
This triggers the release of \(Ca^{++}\) ions from the sarcoplasmic reticulum.
These \(Ca^{++}\) ions initiate contraction, which is sustained by ATP.
As long as \(Ca^{++}\) ions remain in the sarcoplasm to bind to troponin, which keeps the actin-binding sites unshielded and as long as ATP is available to drive the cross bridge cycling and pulling of actin strands by myosin.
Muscle contraction usually ends when signalling from the neuron ends and after this \(Ca^{++}\) ion pumped back to the SR. Hence, correct answer is option 3.