Describe how schwann cells form the myelin sheath and the neurilemma.

Schwann cells or neurilemma cells are the cells which form the myelin sheath around neuronal axons in the peripheral nervous system (PNS) only.

Neurilemma is the collective term used for cytoplasm and nuclei present around the myelin sheath which helps in the regeneration process of nerves.

A Schwann cell surrounds the axon, invaginate it and the plasmalemma of the Schwann cells joins and from a double membrane structure called mesaxon. This mesaxon starts wrapping the axon in spiral fashion and cytoplasm start condensing into the compact myelin sheath.