The subventricular zone (SVZ) is one of two sources of adult-born neurons in the mammalian brain, the other being the subgranular zone (SGZ) of the hippocampus. In most adult mammals, the SVZ is a three-layered sheath that lies along the lateral wall of the lateral ventricle and consists of type A, B, and C cells. Type A rest along the ventricle wall and are neuronal precursor cells, Type B are adjacent astrocytes, and Type C are immature precursors to the Type A neuroblasts. The neuronal precursor cells travel along the rostral migratory stream ensheathed in a tube of Type B astrocytes, until they reach the olfactory bulb. There they integrate into the existing cellular network and mature into local interneurons. While the majority become adult-born granule cells, a subset become periglomerular cells. Interestingly, the human SVZ differs from other mammals' in several ways. It consists of four layers rather than three: ependymal cells (layer I), a hypo cellular gap (layer II), a ribbon of astrocytes (layer III), and a transitional zone (layer IV). The astrocytes are capable of differentiating into many kinds of tissue including new neurons. However, there is no evidence that the proliferating neurons travel along the rostral migratory stream in a chain to populate the olfactory bulb with new interneurons, as is the case for other mammals.

http://neurolex.org/wiki/Category:Subventricular_Zone