Figure 2.

Comparison of central and peripheral myelination. (a) Each oligodendrocyte in the CNS can extend cytoplasmic projections to form multiple, multi-layered myelin sheaths (pink) around different axons, whereas each SC in the PNS completely wraps around a single axon by laying down multiple layers of cell membrane, of which the innermost layers constitute the myelin sheath (purple). (b) There is typically one oligodendrocyte between two nodes of Ranvier, which is not covered by plasma membrane to allow action potentials to jump from node to node. (c) Compared to oligodendrocytes, SC myelinated axons possess thicker myelin sheaths. SCs also have an enlarged non-axonal domain due to the extra presence of the cytoplasm and nuclei, which is covered by the outermost layer, called the neurilemma.