 The glia limitans also plays an important role in regulating the movement of small molecules and cells into the brain parenchyma by working in concert with other components of the central nervous system (CNS) such as the blood–brain barrier (BBB).The perivascular feet of astrocytes form a close association with the basal lamina of the brain parenchyma to create the glia limitans.This membrane lies deep to the pia mater and the subpial space and surrounds the perivascular spaces (Virchow-Robin spaces).