Which of the following statements is correct regarding a myelinated nerve fibre?(i) Myelin sheath is always associated with an axon.(ii) It allows rapid conduction of nerve impulses.(iii) It allows slow conduction of nerve impulses.(iv) It has nodes of Ranvier.

Myelinated nerve fibre has myelin sheath wrapped around the axon.The lipid reach sheath acts as an insulator and transmits impulses much faster than the unmyelinated fibres. Saltatory conduction is observed. Nodes of Ranvier are the gaps in myelin-sheath, which occur along a myelinated axon where the axolemma is exposed to the extracellular space.