Neurons and macroglia have a common origin in the neural tube of the early vertebrate embryo (see Figure 43.14). The neural tube contains rapidly dividing neuronal stem cells. Initially the divisions of these neural stem cells are symmetrical—all of the progeny are stem cells. Eventually, however, the cell divisions become asymmetrical, with one daughter cell remaining a stem cell and the other daughter cell becoming either a neural progenitor cell or a macroglial progenitor cell—a neuroblast or a gliablast. These progenitor cells produce the neurons and glia that together form the various structures of the nervous system.