What is statement correct about Z lines?

Options

A. Part between two H-lines
B. Part between two A- band
C. Part between two I-band
D. Part between two M-lines

Explanation

To determine the correct statement about Z lines, let's analyze the options step by step:

1. **Understanding Z Lines**: Z lines, also known as Z discs, are structural components of the sarcomere, which is the basic unit of muscle contraction in striated muscles.

2. **Analyzing the Options**:
- **Option 1: Part between two H-lines**: The H-zone is the region within the A-band where there are only thick filaments (myosin). There is no H-line; hence, this option is incorrect.
- **Option 2: Part between two A-bands**: The A-band is the region that contains both thick and thin filaments. Z lines do not lie between A-bands; thus, this option is also incorrect.
- **Option 3: Part between two I-bands**: The I-band is the region that contains only thin filaments (actin) and is bisected by the Z line. This means Z lines are indeed located at the boundary of two I-bands, making this option correct.
- **Option 4: Part between two M-lines**: The M-line is the center of the sarcomere where thick filaments are anchored. Z lines do not lie between M-lines; therefore, this option is incorrect.

3. **Conclusion**: The correct statement about Z lines is that they are part between two I-bands.

### Final Answer:
The correct statement about Z lines is: **They are part between two I-bands.**