The glymphatic system is a system for waste clearance in the central nervous system of vertebrates. According to this model, cerebrospinal fluid flows into the paravascular space around cerebral arteries, combining with interstitial fluid and parenchymal solutes, and exiting down venous paravascular spaces. The pathway consists of a para-arterial influx route for CSF to enter the brain parenchyma, coupled to a clearance mechanism for the removal of interstitial fluid and extracellular solutes from the interstitial compartments of the brain and spinal cord. Exchange of solutes between CSF and ISF is driven primarily by arterial pulsation and regulated during sleep by the expansion and contraction of brain extracellular space. Clearance of soluble proteins, waste products, and excess extracellular fluid is accomplished through convective bulk flow of ISF, facilitated by astrocytic aquaporin 4 water channels.