Which of the following statements is true ?

Options

A. Saltatory conduction is seen in non-myelinated nerve fibres
B. Nissl's granules are found in muscle fibres
C. Non-myelinated nerve fibres do not possess
nodes of Ranvier
D. Non-myelinated nerve fibres are
com-pletely enclosed by myelin sheath

Answer

To determine which of the statements is true, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The first statement claims that "solitary conduction is seen in non-myelinated nerve fibers."
- **Analysis**: Solitary conduction, also known as saltatory conduction, occurs in myelinated nerve fibers where the action potential jumps from one node of Ranvier to another. Non-myelinated fibers do not exhibit this type of conduction.
- **Conclusion**: This statement is **false**.

2. **Evaluate the Second Statement**:
- The second statement claims that "Nissl granules are found in muscle fibers."
- **Analysis**: Nissl granules are actually found in the cell body (soma) of neurons and are composed of rough endoplasmic reticulum and ribosomes. They are not present in muscle fibers.
- **Conclusion**: This statement is **false**.

3. **Evaluate the Third Statement**:
- The third statement claims that "non-myelinated nerve fibers do not possess nodes of Ranvier."
- **Analysis**: Nodes of Ranvier are gaps in the myelin sheath of myelinated fibers. Non-myelinated fibers lack myelin sheaths altogether, and therefore, they do not have nodes of Ranvier.
- **Conclusion**: This statement is **true**.

4. **Evaluate the Fourth Statement**:
- The fourth statement claims that "non-myelinated nerve fibers are completely enclosed by myelinated sheath."
- **Analysis**: This is incorrect because non-myelinated fibers do not have a myelin sheath at all. Myelinated fibers are the ones that are enclosed by myelin.
- **Conclusion**: This statement is **false**.

### Final Conclusion:
After evaluating all the statements, the only true statement is the third one: "non-myelinated nerve fibers do not possess nodes of Ranvier."