Describe how the schwann cells form the myelin sheath

The myelin sheath, lipoprotein structure deposited around axons selected in inner nodules, interrupted periodically by Ranvier nodules, allows saltatory, rapid and effective conduction in the nervous system of vertebrates. The cells that construct myelin are the oligodendrocyte in the nervous central nervous system (CNS) and the Schwann cells in the peripheral nervous system. An oligonucleotide myelinates one or more axons, while the Schwann always forms a single myelin internodule. The process of myelination begins when a cell-sheath projection involves the axon and a loose spiral shape around it. Over time the formed layers are compacted by the expulsion of the cytoplasm and the formation of a lamellar structure with thick electrodes bands - derived from the apposition of the cytoplasmic phases of the membranes - and fewer electrodes - derived of the external phases of the membranes.