At rest, when mucsle is relaxed, thin filaments interdigitate with thick filaments only

Options

A. Outside A band
B. Outside H band
C. Inside A band
D. Inside M line

Answer

To solve the question regarding the interdigitation of thin and thick filaments in a relaxed muscle, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Muscle Structure**:
- Muscles are made of myofibrils, which are the structural units of muscle fibers. These myofibrils consist of two types of protein filaments: thick filaments (myosin) and thin filaments (actin).

2. **Identifying Bands**:
- The thick filaments are dark and are found in the A band, while the thin filaments are lighter and are found in the I band. The H zone is the area within the A band where only thick filaments are present, and the M line is the center of the sarcomere where thick filaments are anchored.

3. **Relaxed Muscle Condition**:
- When the muscle is relaxed, the thin filaments (actin) interdigitate with the thick filaments (myosin) primarily in the A band. However, the interdigitation occurs outside the H zone, where only thick filaments are present.

4. **Evaluating Options**:
- **Option 1: Outside A band** - Incorrect, as this area does not contain thick filaments.
- **Option 2: Outside H band** - Correct, as this is where the thin filaments interdigitate with thick filaments.
- **Option 3: Inside A band** - Incorrect, as the thick filaments do not interdigitate with thin filaments in this area.
- **Option 4: Inside M line** - Incorrect, as this area does not have interdigitation.

5. **Conclusion**:
- The correct answer is that the thin filaments interdigitate with thick filaments only **outside the H band**.

### Final Answer:
The correct option is **outside H band**.

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