Question

During skeletal muscle contractions following events can occur:
I. I-band shortens
II. A-band shortens
III. H-zone shortens
IV. Sarcomere contract
V. ATP changes to ADP and Pi
Choose the option with incorrect events.

• A. Only I
• B. Only III
• C. IV and V
• D. Only II

Answer 1

The correct option is D Only II

I-band consists of only thin filaments. A-band consists of both the thin and thick filaments. H-zone is the band of thick filament only. For skeletal muscle contraction following events occur:

1. The nerve impulse is transmitted to the sarcolemma and it causes release of calcium ions from sarcoplasmic reticulum.

2. These calcium bind to the troponin and tropomyosin rotates.

3. Then, the myosin binds to the tropomyosin.

4. ATP is hydrolysed to detach the myosin from the tropomyosin and muscle can be relaxed.

The shortening of I-band and H-zone causes the contraction of sarcomere.

A-band does not change.

Hence, the correct answer is 'only II'