Stem cells are characterized by their capability to differentiate into multiple cell types via exogenous stimuli from their environment. Neural stem cells (NSCs) are multipotent stem cells that are capable of self-renewing and differentiating into the three main central nervous system (CNS) lineages: neurons, astrocytes, and oligodendrocytes. Neural stem cells undergo proliferative symmetric and asymmetric divisions to replenish themselves and to produce intermediate neural progenitors (INPs), NSCs are stimulated to begin differentiation via exogenous cues from the microenvironment, or stem cell niche. This capability of the NSCs to replace lost or damaged neural cells is called neurogenesis. Some neural cells are migrated from the SVZ along the rostral migratory stream which contains a marrow-like structure with ependymal cells and astrocytes when stimulated. Thus, a balance of symmetric and asymmetric neural stem cell divisions regulates the number of neural stem cells, intermediate neural progenitors and produced neurons, and is critical for defining the adult brain.