(a) What is myelin sheath?
(b) How are neurons classified based on function?

Explanation

On the basis of functions the neurons are categorised as:
(a) Sensory or afferent neurons, which carry impulses from the sense organ to the central nervous system.
(b) Motor or efferent neuron, which carry impulses from the central nervous system to effector organ such as the muscle fibre and the gland.
(c ) Association neurons, which conduct impulses between sensory and motor neurons.