H' zone is

Options

A. Outer part of A band with overlapping thick and thin filaments
B. A part of I band with overlapping thick and thin filaments
C. Central part of A band with only thick filaments
D. Central part of I band with only thin filaments

Answer

### Step-by-Step Solution:

1. **Understanding Sarcomere Structure**: The sarcomere is the basic functional unit of striated muscle tissue. It is composed of thick and thin filaments that slide past each other to produce muscle contraction.

2. **Identifying Filaments**: In a sarcomere, the thick filaments are primarily made of myosin, while the thin filaments are primarily made of actin.

3. **Defining the Bands**:
- **I Band**: This is the region that contains only thin filaments (actin).
- **A Band**: This region contains both thick (myosin) and thin (actin) filaments. The A band is where the thick and thin filaments overlap.
- **H Zone**: This is the central part of the A band where only thick filaments (myosin) are present, without any overlapping thin filaments.

4. **Identifying the Z Line**: The Z line is the boundary between adjacent sarcomeres and is located at the center of the I band.

5. **Conclusion**: The H zone is specifically defined as the central part of the A band where only thick filaments (myosin) are present.

6. **Correct Answer**: The H zone is the central part of the A band with only thick filament.