Editing Cerebrospinal fluid (section)

== Structure ==
===Circulation===
[[File:NPH MRI 272 GILD.gif|thumb|MRI showing pulsation of CSF]][[File:dist vent.png|thumb|Distribution of CSF|350x350px]]

In humans, there is about 125–150&nbsp;mL of CSF at any one time.<ref name="WRIGHT2012" /> This CSF circulates within the [[ventricular system]] of the brain. The ventricles are a series of cavities filled with CSF. The majority of CSF is produced from within the two [[lateral ventricles]]. From here, CSF passes through the [[Interventricular foramina (neuroanatomy)|interventricular foramina]] to the [[third ventricle]], then the [[cerebral aqueduct]] to the [[fourth ventricle]]. From the fourth ventricle, the fluid passes into the [[subarachnoid space]] through four openings{{snd}}the [[central canal]] of the spinal cord, the [[median aperture]], and the two [[lateral aperture]]s.<ref name="WRIGHT2012" /> CSF is present within the subarachnoid space, which covers the brain and spinal cord, and stretches below the end of the spinal cord to the [[sacrum]].<ref name="WRIGHT2012" /><ref name=GH2005/> There is a connection from the subarachnoid space to the [[bony labyrinth]] of the [[inner ear]] making the cerebrospinal fluid continuous with the [[perilymph]] in 93% of people.<ref name="SAKKA2011">{{cite journal | vauthors = Sakka L, Coll G, Chazal J | title = Anatomy and physiology of cerebrospinal fluid | journal = European Annals of Otorhinolaryngology, Head and Neck Diseases | volume = 128 | issue = 6 | pages = 309–16 | date = December 2011 | pmid = 22100360 | doi = 10.1016/j.anorl.2011.03.002 | doi-access = free }}</ref>

CSF moves in a single outward direction from the ventricles, but multidirectionally in the subarachnoid space.<ref name="Proulx2021">{{cite journal |last1=Proulx |first1=Steven T. |title=Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics |journal=Cellular and Molecular Life Sciences |date=March 2021 |volume=78 |issue=6 |pages=2429–2457 |doi=10.1007/s00018-020-03706-5|pmid=33427948 |pmc=8004496 }}</ref><ref name="SAKKA2011"/> The flow of cerebrospinal fluid is pulsatile, driven by the [[cardiac cycle]].<ref name="Mestre2018">{{cite journal |vauthors=Mestre H, Tithof J, Du T, Song W, Peng W, Sweeney AM, Olveda G, Thomas JH, Nedergaard M, Kelley DH |title=Flow of cerebrospinal fluid is driven by arterial pulsations and is reduced in hypertension |journal=Nat Commun |volume=9 |issue=1 |pages=4878 |date=November 2018 |pmid=30451853 |pmc=6242982 |doi=10.1038/s41467-018-07318-3 |bibcode=2018NatCo...9.4878M |url=}}</ref> The flow of CSF through perivascular spaces in the brain (surrounding the [[cerebral arteries]]) is obtained through the pumping movements of the walls of the arteries.<ref name="Mestre2018"/>

===Contents===
CSF is derived from [[blood plasma]] and is largely similar to it, except that CSF is nearly protein-free compared with plasma and has some different [[electrolyte]] levels. Due to the way it is produced, CSF has a lower [[chloride]] level than plasma, and a higher [[sodium]] level.<ref name=GH2005/><ref name=SALADIN2012 />

CSF contains approximately 0.59% plasma proteins, or approximately 15 to 40&nbsp;mg/dL, depending on sampling site.<ref name="pmid4456012">{{cite journal | vauthors = Felgenhauer K | title = Protein size and cerebrospinal fluid composition | journal = Klinische Wochenschrift | volume = 52 | issue = 24 | pages = 1158–64 | date = December 1974 | pmid = 4456012 | doi = 10.1007/BF01466734 | s2cid = 19776406 }}</ref> In general, globular proteins and albumin are in lower concentration in ventricular CSF compared to lumbar or cisternal fluid.<ref>{{cite journal | vauthors = Merril CR, Goldman D, Sedman SA, Ebert MH | title = Ultrasensitive stain for proteins in polyacrylamide gels shows regional variation in cerebrospinal fluid proteins | journal = Science | volume = 211 | issue = 4489 | pages = 1437–8 | date = March 1981 | pmid = 6162199 | doi = 10.1126/science.6162199 | bibcode = 1981Sci...211.1437M }}</ref> {{anchor|IgG index}} This continuous flow into the [[venous system]] dilutes the concentration of larger, lipid-insoluble molecules penetrating the brain and CSF.<ref name="pmid10027064">{{cite journal | vauthors = Saunders NR, Habgood MD, Dziegielewska KM | title = Barrier mechanisms in the brain, I. Adult brain | journal = Clinical and Experimental Pharmacology & Physiology | volume = 26 | issue = 1 | pages = 11–9 | date = January 1999 | pmid = 10027064 | doi = 10.1046/j.1440-1681.1999.02986.x | s2cid = 34773752 | doi-access =  }}</ref> CSF is normally free of [[red blood cell]]s and at most contains fewer than 5 [[white blood cell]]s per mm<sup>3</sup> (if the white [[cell counting|cell count]] is higher than this it constitutes [[pleocytosis]] and can indicate inflammation or infection).<ref>{{cite book| vauthors  = Jurado R, Walker HK |title=Clinical Methods: The History, Physical, and Laboratory Examinations|date=1990|publisher=Butterworths|isbn=978-0409900774|edition=3rd|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK398/|chapter=Cerebrospinal Fluid|pmid=21250239}}</ref>