The medullary sheath begins shortly after the fibre emerges from the cell body and ends just before terminal arborisation. It is continuous around the fibres in the CNS but in the fibres of the peripheral nerves it is absent at certain points known as the nodes of Ranvier. The part of the nerve fibre between two successive nodes is termed as internode. The neruilemma consists of tubular sheath or schwann’s cells placed end to end. A single sheath cell with a single large, flat nucleus covers an internode. HL7 training focuses on these.

Neurons can be classified according to the number of processes