In the PNS, one Schwann cell forms a single myelin sheath (Figure 1A). By contrast, in the CNS, the oligodendrocyte sends cell processes to myelinate multiple segments on many axons (Figure 2).

The axon is surrounded by multilamellar structure of myelin. (E) Myelinated nerve fiber reproduced in vitro by coculture of rat dorsal root ganglion neurons and Schwann cells. Myelin segments are ...