The nerves that are insulated by a sheath or myelin are called myelinated nerve fibres and the nerves which lack such sheath are called non-myelinated nerve fibres. 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 whereas due to absence of myelin sheath in non- myelinated nerve fibre so there is more chances of loss of impulse during conduction. Myelinated nerve fibre has nodes of Ranvier which is always constant in number whereas non-myelinated nerve fibre do not have node of Ranvier.