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.

Answer

B

Explanation

Myelinated nerve fibres are present in spinal and cranial nerves, Myelinated nerve fibres are enclosed by schwann cells that form myelin sheath around the axon. The conduction of imulses is faster in myelinated nerve fibre (or medullated nerve fibre) because when an impulse travels along a medullate medullated nerve fibre, it does not proceed uniformly along the length of the axis cylinder,but jumps form one node of Ranvier to the next. This is called the slatatroy conduction of impluses. This way the conduction is faster in myelinated nerve fibre.