Which of the following is not a structure found inside a single sarcomere ?

Options

A. A band
B. Z line
C. M line
D. I band

Answer

To determine which structure is not found inside a single sarcomere, we need to analyze the components of a sarcomere. A sarcomere is the basic contractile unit of muscle tissue and is defined by specific structures.

### Step-by-Step Solution:

1. **Identify the Components of a Sarcomere**:
- A sarcomere includes several key structures: A-band, I-band, M-line, and Z-line.

2. **Understand Each Component**:
- **A-band**: This is known as the anisotropic band and contains thick filaments made of myosin. It is part of the sarcomere.
- **I-band**: This band is referred to as the isotropic band and contains thin filaments made of actin. It is also part of the sarcomere.
- **M-line**: This line is located in the center of the sarcomere and serves as an anchoring point for the thick filaments (myosin). It is part of the sarcomere.
- **Z-line**: This line marks the boundaries of a sarcomere. It is where the thin filaments (actin) are anchored.

3. **Determine Which Structure is Not Inside a Sarcomere**:
- The Z-line is not considered a part of the sarcomere itself; rather, it defines the limits of the sarcomere. The sarcomere is the region between two Z-lines.

4. **Conclusion**:
- Based on the definitions and locations of these structures, the correct answer to the question is **Z-line**. It is not a structure found inside a single sarcomere; instead, it marks the boundaries of the sarcomere.

### Final Answer:
**Z-line** is not a structure found inside a single sarcomere.

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