Editing Arachnoid granulation (section)

=== Cerebrospinal fluid resorption ===
The arachnoid granulations act as one-way [[valve]]s. Normally the [[pressure]] of the CSF is higher than that of the [[venous system]], so CSF flows through the granulations into the blood. If the pressure is reversed for some reason, fluid will not pass back into the subarachnoid space.<ref name="Spierer2023">{{cite journal |last1=Spierer |first1=R |title=The debated neuroanatomy of the fourth ventricle. |journal=Journal of Anatomy |date=October 2023 |volume=243 |issue=4 |pages=555–563 |doi=10.1111/joa.13885 |pmid=37170923|pmc=10485575 }}</ref> The reason for this is not known. It has been suggested that the [[endothelial cell]]s of the venous sinus create [[vacuole]]s of CSF, which move through the cell and out into the blood.<ref>{{Cite journal |last1=McKnight |first1=Colin D. |last2=Rouleau |first2=Renee M. |last3=Donahue |first3=Manus J. |last4=Claassen |first4=Daniel O. |date=2020-10-19 |title=The Regulation of Cerebral Spinal Fluid Flow and Its Relevance to the Glymphatic System |url=https://doi.org/10.1007/s11910-020-01077-9 |journal=Current Neurology and Neuroscience Reports |language=en |volume=20 |issue=12 |pages=58 |doi=10.1007/s11910-020-01077-9 |issn=1534-6293 |pmc=7864223 |pmid=33074399}}</ref>

The importance of arachnoid granulations for the drainage of CSF is controversial.<ref name="Norwood-2019" /> The granulations are sparse during early life, possibly underscoring the importance of alternate mechanisms of drainage.<ref name="Standring-2020" /> A large portion (perhaps the majority) of CSF may in fact drain through lymphatics associated with extracranial segments of cranial nerves - especially through axons of CN I (olfactory nerve) through their extension through the [[cribriform plate]].<ref name="Norwood-2019">{{cite journal |last1=Norwood |first1=Jordan N |last2=Zhang |first2=Qingguang |last3=Card |first3=David |last4=Craine |first4=Amanda |last5=Ryan |first5=Timothy M |last6=Drew |first6=Patrick J |title=Anatomical basis and physiological role of cerebrospinal fluid transport through the murine cribriform plate |journal=eLife |date=7 May 2019 |volume=8 |pages=e44278 |doi=10.7554/eLife.44278 |pmid=31063132 |pmc=6524970 |doi-access=free }}</ref>