Arrange the following events of muscle contraction in the sequence :
(i) Generate an action potential in the sarcolemma
(ii) Form a cross bridge
(iii) Release a neurotransmitter (Acetylcholine)
(iv) Release of calcium ions in sarcoplasm
(v) Pulls the attached actin filaments towards the centre of "A" band
(vi) Remove the masking of active sites for myosin
The correct option is :-

Options

A. `i-ii-iii-iv-v-vi`
B. iii-iv-i-ii-vi-v
C. iii-i-iv-ii-v-vi
D. iii-i-iv-vi-ii-v

Answer

To arrange the events of muscle contraction in the correct sequence, we can follow these steps:

1. **Release of neurotransmitter (Acetylcholine)**: The process begins at the neuromuscular junction where a nerve impulse triggers the release of acetylcholine, a neurotransmitter that facilitates communication between the nerve and muscle.

2. **Generate an action potential in the sarcolemma**: Once acetylcholine binds to its receptors on the muscle cell membrane (sarcolemma), it causes sodium channels to open, leading to depolarization and the generation of an action potential.

3. **Release of calcium ions in the sarcoplasm**: The action potential travels along the sarcolemma and down the T-tubules, which triggers the release of calcium ions from the sarcoplasmic reticulum into the sarcoplasm.

4. **Remove the masking of active sites for myosin**: The influx of calcium ions binds to troponin, causing a conformational change that moves tropomyosin away from the active sites on actin filaments, exposing them for interaction with myosin.

5. **Form a cross bridge**: With the active sites exposed, myosin heads can now bind to the actin filaments, forming cross bridges.

6. **Pulls the attached actin filaments towards the center of "A" band**: Finally, the myosin heads pivot and pull the actin filaments towards the center of the sarcomere (A band), resulting in muscle contraction.

Thus, the correct sequence of events is:
(iii) Release a neurotransmitter (Acetylcholine) → (i) Generate an action potential in the sarcolemma → (iv) Release of calcium ions in sarcoplasm → (vi) Remove the masking of active sites for myosin → (ii) Form a cross bridge → (v) Pulls the attached actin filaments towards the centre of "A" band.

### Final Sequence:
(iii) → (i) → (iv) → (vi) → (ii) → (v)

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