"T tubule is formed as part of Triad system in man" This T tubule represents

Options

A. Invaginated plasma membrane at Z-line
B. Invaginated sarcoplasmic reticulum at A - I Junction
C. Invaginated plasma membrane at A-I junction
D. Invaginated sarcoplasmic reticulum at Z-line

Answer

To answer the question "T tubule is formed as part of Triad system in man. This T tubule represents," we will analyze the options provided and determine which one correctly describes the T tubule's representation in the triad system.

### Step-by-Step Solution:

1. **Understanding the Triad System**:
- The triad system in muscle cells consists of a T tubule and two terminal cisternae of the sarcoplasmic reticulum. The T tubule is an extension of the muscle cell's plasma membrane that penetrates into the cell.

2. **Identifying the Components**:
- The T tubule is specifically an invagination of the plasma membrane. It plays a crucial role in transmitting action potentials into the muscle fiber, facilitating muscle contraction.

3. **Evaluating the Options**:
- **Option 1**: Invaginated plasma membrane at the Z-line.
- This is incorrect because the T tubules are not located at the Z-line; they are situated at the A-I junction.
- **Option 2**: Invaginated sarcoplasmic reticulum at the A-I junction.
- This is incorrect as the T tubule is not part of the sarcoplasmic reticulum; it is part of the plasma membrane.
- **Option 3**: Invaginated plasma membrane at the A-I junction.
- This is correct. The T tubule is indeed an invagination of the plasma membrane located at the A-I junction.
- **Option 4**: Invaginated sarcoplasmic reticulum at the Z-line.
- This is incorrect because it misidentifies the location and structure of the T tubule.

4. **Conclusion**:
- Based on the evaluation of the options, the correct answer is **Option 3: Invaginated plasma membrane at the A-I junction**.

### Final Answer:
The T tubule represents the invaginated plasma membrane at the A-I junction.

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