Question

All the following events (except one) occur once the muscle contraction is initiated by the motor signals from CNS. Choose the exception
1) Z-line comes closer to M-line
2) Width of A-band increases
3) Width of I-band reduces
4) Width of H-zone reduces
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Answer 1

Answer:

Option 2

During muscle contraction the length of A BAND does not affected

Answer 2

The muscle contraction is initiated by the motor signals from CNS (2) Width of A-band increase

Explanation:

1.The A band is the region of a striated muscle sarcomere that contains myosin thick filaments. In fact, the A band is the entire length of the thick filament of the sarcomere. Its length is approximately 1 μm. The center of the A band is located at the center of the sarcomere (M line).

2.The dark band of the muscle sarcomere that corresponds to the thick myosin (protein) filaments.

3.The A band is situated on either side of the H zone of a muscle sarcomere, that is the area where contraction and relaxation of the muscle occurs, where sarcomeres overlap during muscle movements.