Contractile unit of muscle is part of myosfibril between

Options

A. X-line and I-band
B. Z-line and Z-line
C. Z- line and A-band
D. A-band and I- band

Answer

To solve the question regarding the contractile unit of muscle, follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Myofibrils**: Myofibrils are the basic rod-like units of a muscle cell. They are composed of repeating units called sarcomeres, which are responsible for muscle contraction.

2. **Identify the Components of a Sarcomere**: A sarcomere is defined as the segment of myofibril between two Z lines. It contains various bands, including the A band (which contains thick filaments) and I band (which contains thin filaments).

3. **Define the Contractile Unit**: The contractile unit of muscle is known as the sarcomere. It is the structural and functional unit of striated muscle tissue.

4. **Determine the Location of the Sarcomere**: Since the sarcomere is located between two Z lines, we can conclude that the contractile unit of muscle is part of the myofibril between the Z line and Z line.

5. **Evaluate the Options**:
- X line and I band: Incorrect.
- Z line and Z line: Correct (this is where the sarcomere is located).
- Z line and A band: Incorrect.
- A band and I band: Incorrect.

6. **Select the Correct Answer**: Based on the analysis, the correct answer is "Z line and Z line."

### Final Answer:
The contractile unit of muscle is part of myofibril between the Z line and Z line.

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