The membrane bisecting the I band of myofibril

Options

A. Z membrane
B. M membrane
C. H membrane
D. T membrane

Answer

### Step-by-Step Solution:

1. **Understanding Myofibrils**: Myofibrils are the basic structural units of muscle fibers. They are composed of long, thread-like structures that facilitate muscle contraction.

2. **Identifying the Components**: Myofibrils consist of two main types of filaments:
- **Actin Filaments**: These are the thin filaments, also referred to as the I-band.
- **Myosin Filaments**: These are the thick filaments.

3. **Recognizing the I-band**: The I-band is the region of the myofibril that contains only actin filaments. It appears lighter under a microscope compared to the A-band, which contains both actin and myosin.

4. **Locating the Membrane**: The membrane that bisects or divides the I-band is known as the **Z-line** or **Z-disc**. This structure serves as an anchor point for the actin filaments.

5. **Differentiating Other Membranes**:
- **M-line**: This line bisects the A-band and is associated with myosin filaments.
- **H-zone**: This is the region within the A-band where only myosin is present, without any overlapping actin.
- **Titin**: This is a large protein that helps stabilize the position of myosin filaments and is associated with the Z-line.

6. **Conclusion**: The membrane that bisects the I-band of the myofibril is called the **Z-line**.

### Final Answer:
The membrane bisecting the I band of myofibril is known as the **Z-line**.

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