Editing Arachnoid granulation (section)

==Function==
The arachnoid granulations are notably thought to be involved in resorption of [[cerebrospinal fluid]], however, their function is not entirely understood.<ref name="Standring-2020" />

=== 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>

=== Subarachnoid systolic overpressure dampening ===
A suggested alternative or additional function of the granulation may be the dispersal of the overpressure wave formed within the subarachnoid space by the pulsation of arteries during systole. As the venous sinuses are enclosed in rigid dural structures, they represent a non-distensible compartment into which subarachnoid pressure increases may be dispersed.<ref name="Standring-2020" />