At full muscle contraction the Z-lines attached to thin filaments are almost touching

Options

A. A-band
B. I-band
C. Actin fibres
D. H-zone.

Answer

To answer the question "At full muscle contraction, the Z-lines attached to thin filaments are almost touching," we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Sarcomere Structure**:
- A sarcomere is the basic structural unit of striated muscle tissue. It is defined as the segment between two Z-lines (Z-discs).
- Each sarcomere contains thick filaments (myosin) and thin filaments (actin).

2. **Identifying Bands in Sarcomere**:
- The sarcomere consists of alternating dark (A bands) and light (I bands) regions.
- The A band contains the thick filaments and some overlapping thin filaments.
- The I band contains only thin filaments and is lighter in appearance.

3. **Understanding the H Zone**:
- The H zone is the central part of the A band where there are only thick filaments and no thin filaments.
- During muscle contraction, the H zone becomes narrower as the thin filaments slide over the thick filaments.

4. **Muscle Contraction Mechanism**:
- Muscle contraction occurs through the sliding filament theory, where thin filaments slide over thick filaments.
- As the thin filaments slide towards the center of the sarcomere, the Z-lines are pulled closer together.

5. **Full Muscle Contraction**:
- At full contraction, the Z-lines are drawn closer to the thick filaments, resulting in the Z-lines almost touching the A band.
- This means that the distance between the Z-lines decreases significantly during contraction.

6. **Conclusion**:
- Therefore, at full muscle contraction, the Z-lines attached to thin filaments are almost touching, confirming that the correct answer is related to the A band.

### Final Answer:
At full muscle contraction, the Z-lines attached to thin filaments are almost touching the A band.

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