When skeletal muscle contraction occurs :

Options

A. the H and I bands gets smaller
B. the Z lines moves closer together
C. the width of A bands remain constant
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Skeletal Muscle Contraction**:
- Skeletal muscle contraction occurs when the muscle fibers shorten, leading to movement. This process is facilitated by the interaction between actin (thin filaments) and myosin (thick filaments) within the myofibrils.

2. **Identifying Sarcomere Structure**:
- The sarcomere is the basic unit of muscle contraction. It consists of various bands and lines:
- **Z Line**: The boundary between adjacent sarcomeres.
- **I Band**: The region containing only thin filaments (actin).
- **A Band**: The region containing both thick (myosin) and thin (actin) filaments.
- **H Band**: The central region of the A band where there are only thick filaments.

3. **Observing Changes During Contraction**:
- When a skeletal muscle contracts:
- The **I Band** becomes smaller as the actin filaments slide over the myosin filaments.
- The **H Band** also becomes smaller as the overlap between actin and myosin increases.
- The **Z Lines** move closer together as the sarcomere shortens.

4. **Determining the Width of the A Band**:
- The width of the **A Band** remains constant during contraction. This is because the length of the myosin filaments does not change; only their position relative to the actin filaments changes.

5. **Conclusion**:
- The correct answer to the question regarding the changes that occur during skeletal muscle contraction is that the I Band and H Band get smaller, the Z Lines move closer together, and the width of the A Band remains the same.

**Final Answer**:
- The correct option is that during skeletal muscle contraction, the I Band and H Band get smaller, the Z Lines move closer together, and the width of the A Band remains the same.

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