Diagram of the CSF "Circulation". This diagram summarizes fluid and cellular movements across the different barriers of the brain compartments (blood, interstitial fluid, Virchow Robin space, cerebrospinal fluid space comprising the cerebral ventricles, basal cisterns and cortical subarachnoid space). Aquaporins and other transporters control the fluid exchange at the glial, endothelial, and choroid plexus barrier. At the glial, endothelial, and pial barrier bi-directional flow may generate either a net in- or outflux, providing fluid exchange rates, which surpass the net CSF production rate by far. The choroid plexus is the only direct connection between the blood and the CSF compartment. Major portions of brain water are drained into the cervical lymphatics from the VRS (including its capillary section) via intramural arterial pathways (asterisks) and from the CSF space (via perineural subarachnoid space of cranial nerves). The capillary and venular endothelium may contribute to brain water absorption. Blood borne inflammatory cells may enter the brain via VRS venules or via CP. Fluid movements at the barriers are driven by osmotic and hydrostatic gradients or by active transporter processes. Fluid movements into and out of the VRS depend on respiratory and cardiac pressure pulsations.