Myelinated/Medullated neuron: The neuron whose axon is covered by myelin sheath (myelin means white) is called myelinated neuron. The conduction of nerve impulse is faster in this neuron than non-myelinated neuron due to presence of myelin sheath over the axon. Myelin sheath avoids the loss of impulse during conduction.
Non-myelinated/non-Medullated neuron: The neuron whose axon is not covered by myelin sheath is called non-myelinated neuron. The conduction of nerve impulse in this neuron is slow than myelinated neuron due to absence of myelin sheath so there is more chances of loss of impulse during conduction.