NEURONS AND GLIA ARE PRODUCED IN THE “PROLIFERATIVE ZONE” (continued)
From ED 28 until ED 42 cell division is “symmetrical” and thus each round of cell division doubles the number of cells in the Proliferative Zone. Cells produced during this period are “progenitor” cells that will give rise to all of the neurons and glial cells that will eventually make up the brain and peripheral nervous system.
After day 42, “asymetrical”cell division begins. Some of the new cells stop dividing begin to migrate away from the proliferative zone and take their place in different regions of the brain. Initially the proportion of migrating cells is small, but the proportion changes systematically over time.