Layer I The innermost layer (Layer I) contains a single layer (monolayer) of ependymal cells lining the ventricular cavity; these cells possess apical cilia and several basal expansions that may stand in either parallel or perpendicular to the ventricular surface. These expansions may interact intimately with the astrocytic processes that are interconnected with the hypocellular layer (Layer II). Layer II The secondary layer (Layer II) provides for a hypocellular gap abutting the former and has been shown to contain a network of functionally correlated Glial Fibrillary Acid Protein (GFAP)-positive astrocytic processes that are linked to junctional complexes, yet lack cell bodies except for the rare neuronal somata. While the function of this layer is yet unknown in humans, it has been hypothesized that the astrocytic and ependymal interconnections of Layer I and II may act to regulate neuronal functions, establish metabolic homeostasis, and/or control neuronal stem cell proliferation and differentiation during development. Potentially, such characteristics of the layer may act as a remainder of early developmental life or pathway for cellular migration given similarity to a homologous layer in bovine<unk>  shown to have migratory cells common only to higher order mammals. Layer III The third layer (Layer III) forms a ribbon of astrocyte cell bodies that are believed to maintain a subpopulation of astrocytes able to proliferate in vivo and form multipotent neurospheres with self-renewal abilities in vitro. While some oligodendrocytes and ependymal cells have been found within the ribbon, they not only serve an unknown function, they are uncommon by comparison to the population of astrocytes that reside in the layer. The astrocytes present in Layer III can be divided into three populations through electron microscopy, with no unique functions yet recognizable; the first type is a small astrocyte of long, horizontal, tangential projections mostly found in Layer II; the second type is found between Layers II and III as well as within the astrocyte ribbon, characterized by its large size and many organelles; the third type is typically found in the lateral ventricles just above the hippocampus and is similar in size to the second type but contains few organelles. Layer IV The fourth and final layer (Layer IV) serves as a transition<unk>  between Layer III with its ribbon of astrocytes and the brain parenchyma. It is identified by a high presence of myelin in the region. Cell types Four cell types are described in the<unk> : 1. Ciliated Ependymal Cells (Type E): are positioned facing the lumen of the ventricle, and function to circulate the cerebrospinal fluid. 2. Proliferating Neuroblasts (Type A): express PSA-NCAM (NCAM1), Tuj1 (TUBB3), and Hu, and migrate in line order to the Olfactory Bulb 3. Slow Proliferating Cells (Type B): express Nestin and GFAP, and function to ensheathe migrating Type A Neuroblasts 4. Actively Proliferating Cells or Transit Amplifying Progenitors (Type C): express Nestin, and form clusters interspaced among chains throughout region
Subventricular zone
Proisocortex
Watershed area 
Periventricular nucleus
Fusiform body area
Postcentral sulcus
Periaqueductal gray
Cortical minicolumn