Figure 3.

A schematic diagram of arachnoid barrier at the meninges. This diagram shows that NPs may exit the fenestrated blood vessels in the dura mater. It also shows that CSF in the subarachnoid space (SAS) enters the brain parenchyma via the paravascular space and interstitial fluid ISF exits the brain parenchyma along the BL and mixes with CSF in the SAS. The arachnoid barrier separates the dura mater from the SAS, and the pia mater separates brain parenchyma from the SAS. Glia limitans and astrocytes form a barrier between the pia mater and the brain parenchyma. The subpia mater is mainly composed of collagen fibers.