Assertion : Mylein sheath insulates the nerve fibre and prevents its depolarisation. Reason : Nerve impulses are conducted more rapidly in non - myelinated nerve fibres than in myelinated ones.

Step-by-step solution

In non-myelinated nerve fibres, the ionic changes are repeated over the membrane all along the length of the fibre. So, the action potential flows all along the membrane over the entire length of the fibre. But in myelinated fibres, the ionic changes and the consequent depolarisation can take place only at the nodes of Ranvier free from myelin sheath, because the myelin sheath between the nodes insulates the fibre and prevents its depolarisation. So, the action potential in effect jumps from one node to the next.Th