The correct sequence of events during relaxation of muscle is `:-`
(i) Inactivation of the actin
(ii) `Ca^(++)` returend to SR
(iii) Cross bridges are boken

Options

A. (i),(ii),(iii)
B. (ii),(i),(iii)
C. (ii),(iii),(i)
D. (iii),(ii),(i)

Answer

To determine the correct sequence of events during the relaxation of a muscle, we need to analyze the process step by step.

### Step-by-Step Solution:

1. **Stimulation of the Nerve Stops**: The process of muscle contraction begins with a nerve impulse. When this stimulation ceases, it triggers the relaxation process.

2. **Calcium Ions Return to the Sarcoplasmic Reticulum (SR)**: After the nerve stimulation stops, calcium ions (Ca²⁺) are actively transported back into the sarcoplasmic reticulum. This is a crucial step as it decreases the calcium ion concentration in the sarcoplasm.

3. **Decrease in Calcium Ion Concentration**: As calcium ions are pumped back into the SR, the concentration of calcium in the sarcoplasm decreases. This reduction is vital for muscle relaxation.

4. **Removal of Calcium Ions from Troponin C**: Calcium ions bind to troponin C during contraction. When the calcium concentration decreases, these ions detach from troponin C, leading to a conformational change.

5. **Cessation of Cross Bridge Cycling**: With calcium ions removed from troponin C, the interaction between actin and myosin is inhibited, stopping the cross-bridge cycling.

6. **Relaxation of the Muscle Fiber**: Finally, the muscle fibers return to their relaxed state as the actin and myosin filaments disengage.

### Correct Sequence of Events:
Based on the above steps, the correct sequence of events during muscle relaxation is:
1. Calcium ions returned to the SR (ii)
2. Cross bridges are broken (iii)
3. Inactivation of the actin (i)

### Final Answer:
The correct sequence is:
(ii) Ca²⁺ returned to SR → (iii) Cross bridges are broken → (i) Inactivation of the actin.

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