Which of the following statements is correct
for node of Ranvier of nerve ?

Options

A. Neurilemma is discontinuous
B. Myelein sheeth is discontinuous
C. Both neurilema and myelin sheath are discontinuous
D. covered by Myelin sheath

Answer

To determine which statement is correct regarding the node of Ranvier in a nerve, we need to analyze the structure and function of the node of Ranvier and its components.

### Step-by-Step Solution:

1. **Understanding the Structure of a Neuron**:
- A neuron consists of dendrites, a cell body, and an axon. The axon is a long, thread-like structure that transmits signals.

**Hint**: Remember the basic structure of a neuron, focusing on the axon and its coverings.

2. **Myelin Sheath**:
- The axon is covered by a protective layer known as the myelin sheath, which is formed by Schwann cells in the peripheral nervous system.

**Hint**: Identify the role of the myelin sheath in insulating the axon.

3. **Node of Ranvier**:
- The node of Ranvier is a gap in the myelin sheath where the axon is exposed. These nodes are crucial for the rapid conduction of nerve impulses through a process called saltatory conduction.

**Hint**: Focus on the significance of the nodes in speeding up nerve signal transmission.

4. **Discontinuity of Myelin Sheath**:
- At the nodes of Ranvier, the myelin sheath is indeed discontinuous. This means that there are gaps where the myelin is absent, allowing for ion exchange and rapid signal propagation.

**Hint**: Consider how the discontinuity of the myelin sheath affects nerve impulse transmission.

5. **Neurolemma**:
- The neurolemma, which is the outermost layer of the Schwann cell, is also present at the nodes of Ranvier. However, it is not discontinuous; it continues along the axon.

**Hint**: Differentiate between the myelin sheath and the neurolemma in terms of continuity.

6. **Evaluating the Statements**:
- The statement that the neurolemma is discontinuous is incorrect.
- The statement that the myelin sheath is discontinuous is correct.
- The statement that both neurolemma and myelin sheath are discontinuous is incorrect.
- The statement that they are covered by the myelin sheath is misleading as it suggests continuity where there is none.

### Conclusion:
The correct statement regarding the node of Ranvier is that **the myelin sheath is discontinuous at the node of Ranvier**.