During muscular contraction, which of the following events occur?
(i)H-zone disappears
(ii) A-band widens
(iii) I-band reduces in width
(iv) Width of A-is unaffected
(v) M-line and Z-line come closer

Options

A. (i), (iii), (iv) and (v)
B. (i), (ii) and (v)
C. (ii), (iv) and (v)
D. (i), (ii) and (iii)

Explanation

To answer the question regarding the events that occur during muscular contraction, we will analyze each statement provided:

1. **H-zone disappears**:
- During muscular contraction, the actin filaments slide over the myosin filaments. This sliding action causes the H-zone (the area where only myosin is present) to disappear as the actin filaments overlap with the myosin filaments.
- **Conclusion**: This statement is true.

2. **A-band widens**:
- The A-band, which contains both actin and myosin filaments, does not widen during contraction. Instead, it remains the same width because the length of the myosin filaments does not change.
- **Conclusion**: This statement is false.

3. **I-band reduces in width**:
- The I-band, which contains only actin filaments, does reduce in width during contraction as the actin filaments slide over the myosin filaments, causing the sarcomere to shorten.
- **Conclusion**: This statement is true.

4. **Width of A-band is unaffected**:
- As mentioned earlier, the A-band does not change in width during contraction. Thus, this statement is correct.
- **Conclusion**: This statement is true.

5. **M-line and Z-line come closer**:
- As the sarcomere contracts, the Z-lines (the boundaries of the sarcomere) move closer together, and consequently, the M-line (the middle of the sarcomere) also moves closer to the Z-lines.
- **Conclusion**: This statement is true.

### Final Evaluation:
Based on the analysis:
- True statements: (i) H-zone disappears, (iii) I-band reduces in width, (iv) Width of A-band is unaffected, (v) M-line and Z-line come closer.
- False statement: (ii) A-band widens.

### Correct Answer:
The correct events that occur during muscular contraction are (i), (iii), (iv), and (v).