View source for Subarachnoid space

{{Infobox Anatomy |
  Name         = Subarachnoid space |
  Latin        = spatium subarachnoideum, cavum subarachnoideale |
  GraySubject  = 193 |
  GrayPage     = 876 |
  Image        = Gray769.png |
  Caption      = Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc. ("Subarachnoid cavity" visible at left.) |
  Image2       = Gray770.png |
  Caption2     = Diagrammatic transverse section of the medulla spinalis and its membranes. (Subarachnoid cavity labeled center.) |
  System       = |
  MeshName     = Subarachnoid+Space |
  MeshNumber   = A08.186.566.166.686 |
  DorlandsPre  = s_16 |
  DorlandsSuf  = 12746651  |
}}

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==Overview==
In the brain, the '''subarachnoid cavity''' ('''subarachnoid space''') is the interval between the [[arachnoid mater]] and [[pia mater]]. 

It is occupied by a spongy tissue consisting of [[trabeculæ]] (delicate connective tissue filaments that extend from the arachnoid mater and blend into the pia mater) and intercommunicating channels in which the [[cerebrospinal fluid]] is contained. 

This cavity is small on the surface of the hemispheres of the [[brain]]. On the summit of each [[gyrus]] the pia mater and the arachnoid are in close contact, but in the [[Sulcus (anatomy)|sulci]] between the gyri, triangular spaces are left, in which the subarachnoid trabecular tissue is found. Whilst the pia mater closely follows the surface of the brain and dips into the sulci, the arachnoid bridges across them from gyrus to gyrus. 

At certain parts of the base of the brain, the arachnoid is separated from the pia mater by wide intervals, which communicate freely with each other and are named subarachnoid cisternæ; in these the subarachnoid tissue is less abundant. The subarachnoid space is the location of the interface between the vascular tissue and the [[cerebrospinal fluid]] and is active in the [[blood brain barrier]].

The arachnoid mater continues down the [[spinal cord]] too, and the subarachnoid layer with it. It serves a similar function in the spinal cord as it does in the brain. 

==See also==
[[Subarachnoid hemorrhage]]

==External links==
* [http://instruct.uwo.ca/anatomy/530/SagSin.gif Diagram at uwo.ca]
* {{eMedicineDictionary|Subarachnoid+space}}

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{{Meninges}}
{{Spinal cord}}

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