Assertion:Myelinated nerve fibres are present in spinal and cranial nerves.
Reason:Myelinated nerves conduct impulses more radidly than unmyelinated nerves.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

To analyze the given question, we will break it down into its components: the assertion and the reason.

### Step 1: Understand the Assertion
The assertion states that "Myelinated nerve fibres are present in spinal and cranial nerves."
- Myelinated nerve fibers are indeed found in both spinal nerves and cranial nerves. These fibers are characterized by the presence of a myelin sheath, which is a fatty layer that insulates the axons of the neurons.

### Step 2: Understand the Reason
The reason states that "Myelinated nerves conduct impulses more rapidly than unmyelinated nerves."
- This statement is also true. Myelinated nerves conduct impulses faster due to the process of saltatory conduction, where the nerve impulse jumps from one node of Ranvier (gaps in the myelin sheath) to another, rather than traveling continuously along the entire length of the axon as in unmyelinated fibers.

### Step 3: Determine the Relationship
Now, we need to assess whether the reason provided is a correct explanation of the assertion.
- Since myelinated fibers are indeed present in spinal and cranial nerves, and they conduct impulses more rapidly than unmyelinated fibers, the reason explains why the assertion is true.

### Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both assertion and reason are true, and the reason is the correct explanation of the assertion.

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