Which of the following sarcomeres is lablled correctly ?

Options

A.
B.
C.
D.

Answer

To determine which sarcomere is labeled correctly, we need to understand the structure of a sarcomere and the components involved in muscle contraction.

### Step-by-Step Solution:

1. **Understand the Sarcomere Structure**:
- A sarcomere is the basic structural and functional unit of skeletal muscle. It consists of thick and thin filaments, primarily myosin (thick) and actin (thin).
- The sarcomere is bounded by Z lines (or Z discs), which anchor the actin filaments.

2. **Identify the Components**:
- **Myosin Filaments**: These are the thick filaments and appear darker under a microscope. They are also referred to as the A band (anisotropic band).
- **Actin Filaments**: These are the thin filaments and appear lighter. They are referred to as the I band (isotropic band).
- **Z Line**: This line bisects the I band and serves as an attachment point for actin filaments.

3. **Analyze the Options**:
- Look at each option provided and check the labeling of the components.
- Ensure that the myosin is labeled correctly as the A band and actin as the I band.
- Check if the Z line is labeled correctly, as it is crucial for identifying the boundaries of a sarcomere.

4. **Eliminate Incorrect Options**:
- If any option incorrectly labels myosin as actin or vice versa, eliminate those options.
- Also, if the Z line is labeled incorrectly, that option should be eliminated.

5. **Select the Correct Option**:
- After analyzing the options, the one that correctly labels myosin, actin, and the Z line is the correct answer.
- In this case, option A correctly identifies the Z line, myosin, and actin.

### Conclusion:
The correct answer is **Option A**, where all components of the sarcomere are labeled accurately.