Figure 1. Overview of the circulation of CSF and ISF through the glymphatic pathway.

The bulk flow of CSF into brain specifically within the perivascular spaces of penetrating arteries drives interstitial metabolic waste products toward perivenous spaces, and ultimately from the cranium via several post-glymphatic clearance sites, including arachnoid granulations, meningeal lymphatic vessels, and along cranial and spinal nerve roots. AQP4 water channels densely expressed within astrocyte end-foot processes circumscribing both arteries and veins act to reduce the resistance to CSF movement from periarterial spaces into the interstitium, and from the interstitium into perivenous spaces. Reproduced with permission from (77).