FIGURE 22-17 Three types of glial cells. (a) A single oligodendrocyte in the central nervous system can myelinate segments of multiple axons. Astrocytes interact with neurons but do not form myelin. (b) Each Schwann cell insulates a section of a single peripheral nervous system axon. See B. Stevens, 2003, Curr. Biol. 13:R469, and D. L. Sherman and P. Brophy, 2005, Nature Rev. Neurosci. 6:683–690.

[Photos: Varsha Shukla and Douglas Fields from NIH.]