Neurons and glial cells are the two main classes of cells present in brain. There are four classes of glial cells in the brain that differ by their origin, morphology, and function: microglia, oligodendrocytes, NG2 (nerve/glia antigen 2) cells, and astrocytes. Microglial cells, which are derived from the mesoderm, represent approximately 10% of glia and are the resident immune cells of the central nervous system (CNS). Three subclasses compose the macroglia and are derived from the ectoderm. As an overview one can consider that: (1) the oligodendrocytes are mainly involved in the myelination of axons, (2) the NG2 cells comprise oligodendrocyte precursor cells but they are also multipotential cells, although this issue is still debated, and (3) finally, astrocytes are the predominant glial cells in the brain that establish active interactions with neurons and the vascular system. With the exception of NG2 cells, all glial cells are characterized by the expression of gap junction proteins (connexins) with specific features and properties. In addition, a number of neuropathological disorders involve changes in Cx expression and channel function.WIREs Membr Transp Signal 2013, 2:133–142. doi: 10.1002/wmts.87
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