Like other neurons, α-MNs transmit signals as action potentials, rapid changes in electrical activity that propagate from the cell body to the end of the axon. To increase the speed at which action potentials travel, α-MN axons have large diameters and are heavily myelinated by both oligodendrocytes and Schwann cells. Oligodendrocytes myelinate the part of the α-MN axon that lies in the central nervous system (CNS), while Schwann cells myelinate the part that lies in the peripheral nervous system (PNS). The transition between the CNS and PNS occurs at the level of the pia mater, the innermost and most delicate layer of meningeal tissue surrounding components of the CNS.