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 will analyze the options provided in the question. A sarcomere is the basic contractile unit of muscle fibers and has specific structures within it.

### Step-by-Step Solution:

1. **Understand the Sarcomere Structure**:
- A sarcomere is defined as the segment between two Z lines. It contains various structures that play a role in muscle contraction.

2. **Analyze the Options**:
- **Option 1: A band**: The A band is the region where thick filaments (myosin) and thin filaments (actin) overlap. This structure is indeed part of the sarcomere.
- **Option 2: Z line**: The Z line marks the boundaries of a sarcomere. However, it is not found within the sarcomere itself; it is the line that defines the start and end of the sarcomere.
- **Option 3: M line**: The M line is located in the center of the sarcomere and holds the thick filaments together. Therefore, it is included within the sarcomere.
- **Option 4: I band**: The I band consists of thin filaments and is also part of the sarcomere. It is the area that appears lighter and is found on either side of the A band.

3. **Identify the Correct Answer**:
- Based on the analysis, the Z line is not a structure found inside a single sarcomere; it is the boundary that defines the sarcomere.

### Conclusion:
The structure that is not found inside a single sarcomere is **Option 2: Z line**.

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