Explanation

Three key functions of myelin sheath are: (i)Protection of nerve fibre. (ii)Insulation of nerve fibre (iii)Increases the rate of transmission of nerve impulses. Key functions of nodes of Ranvier include: (i)Allowing nutrients and waste products to enter/leave the neuron. (ii)Allowing nerve impulses to move along the neuron through a process of de-polarization and re-polarization of the nerve membrane.