Editing Human brain (section)

===Cerebrospinal fluid===
[[Image:Blausen 0216 CerebrospinalSystem.png|thumb|[[Cerebrospinal fluid]] circulates in spaces around and within the brain]]
{{Main|Cerebrospinal fluid}}
Cerebrospinal fluid is a clear, colourless [[transcellular fluid]] that circulates around the brain in the [[subarachnoid space]], in the [[ventricular system]], and in the [[central canal]] of the spinal cord. It also fills some gaps in the subarachnoid space, known as [[subarachnoid cisterns]].{{sfn|Gray's Anatomy|2008|pp=242–244}} The four ventricles, two [[lateral ventricle|lateral]], a [[third ventricle|third]], and a [[fourth ventricle]], all contain a [[choroid plexus]] that produces cerebrospinal fluid.{{sfn|Purves|2012|p=742}} The third ventricle lies in the midline and [[Interventricular foramina (neuroanatomy)|is connected]] to the lateral ventricles.{{sfn|Gray's Anatomy|2008|pp=242–244}} A single [[duct (anatomy)|duct]], the [[cerebral aqueduct]] between the pons and the cerebellum, connects the third ventricle to the fourth ventricle.{{sfn|Gray's Anatomy|2008|p=243}} Three separate openings, the [[Medial aperture|middle]] and two [[lateral aperture]]s, drain the cerebrospinal fluid from the fourth ventricle to the [[cisterna magna]], one of the major cisterns. From here, cerebrospinal fluid circulates around the brain and spinal cord in the subarachnoid space, between the arachnoid mater and pia mater.{{sfn|Gray's Anatomy|2008|pp=242–244}}
At any one time, there is about 150mL of cerebrospinal fluid – most within the subarachnoid space. It is constantly being regenerated and absorbed, and is replaced about once every 5–6 hours.{{sfn|Gray's Anatomy|2008|pp=242–244}}

A [[glymphatic system]] has been described as the lymphatic drainage system of the brain.<ref name="Yankova2021">{{cite journal |last1=Yankova |first1=Galina |last2=Bogomyakova |first2=Olga |last3=Tulupov |first3=Andrey |title=The glymphatic system and meningeal lymphatics of the brain: new understanding of brain clearance |journal=Reviews in the Neurosciences |date=1 November 2021 |volume=32 |issue=7 |pages=693–705 |doi=10.1515/revneuro-2020-0106|pmid=33618444 }}</ref><ref name="Glymphatic system and brain waste clearance 2017 review" /> The brain-wide glymphatic pathway includes drainage routes from the cerebrospinal fluid, and from the [[meningeal lymphatic vessels]] that are associated with the [[dural sinuses]], and run alongside the cerebral blood vessels.<ref name="D-O">{{cite journal|last1=Dissing-Olesen|first1=L.|last2=Hong|first2=S. |last3=Stevens|first3=B. |title=New brain lymphatic vessels drain old concepts |journal=eBioMedicine |date=August 2015|volume=2|issue=8|pages=776–7|doi=10.1016/j.ebiom.2015.08.019|pmid=26425672|pmc=4563157}}</ref><ref name="Sun">{{cite journal |last1=Sun |first1=BL |last2=Wang |first2=LH |last3=Yang |first3=T |last4=Sun |first4=JY |last5=Mao |first5=LL |last6=Yang |first6=MF |last7=Yuan |first7=H |last8=Colvin |first8=RA |last9=Yang |first9=XY |title=Lymphatic drainage system of the brain: A novel target for intervention of neurological diseases. |journal=Progress in Neurobiology |date=April 2018 |volume=163–164 |pages=118–143 |doi=10.1016/j.pneurobio.2017.08.007 |pmid=28903061|s2cid=6290040 }}</ref> The pathway drains [[interstitial fluid]] from the tissue of the brain.<ref name="Sun"/>