The Ventricular Systemand CSF (CerebrospinalFluid)

The entire surface of central nervous system is bathed by a clear,colorless fluid called cerebrospinal fluid (CSF). The CSF is contained within a system of fluid-filled cavities called ventricles. The ventricles are shown in blue on thefollowing midsagittal section of the brain.

The Ventricles

CSF is produced mainly by a structurecalled the choroid plexus located in the lateral,third and fourth ventricles. CSF flows from the lateral ventricle to thethird ventricle through the interventricularforamen (also called the foramen of Monro). The third ventricleand fourth ventricle are connected to each other by the cerebral aqueduct (also called the Aqueduct of Sylvius). CSFthen flows into the subarachnoid space through the foramina of Luschka(there are two of these) and the foramen of Magendie (only one ofthese).

Absorption of the CSF into the blood stream takes place in the superiorsagittal sinus through strutures called arachnoid villi. When the CSF pressure is greater than the venous pressure, CSFwill flow into the blood stream. However, the arachnoid villi act as "oneway valves"...if the CSF pressure is less than the venous pressure, thearachnoid villi will NOT let blood pass into theventricular system.

Ok..so there is CSF flowingthrough the ventricles...what does the CSF do? The CSF has several functions including:

  1. Protection: the CSFprotects the brain from damage by "buffering" thebrain. In other words, the CSF acts to cushion a blow to the head andlessen the impact.
  2. Buoyancy: since thebrain is immersed in fluid, the net weight of thebrain is reduced from about 1,500 gm to about 50 gm. Therefore,pressure at the base of the brain is reduced.
  3. Excretion of wasteproducts: theone-way flow from the CSF to theblood takes potentially harmful metabolites, drugs and other substancesaway from the brain.
  4. Endocrine medium for thebrain:the CSF serves to transport hormonesto other areas of the brain. Hormones released into the CSF can becarried to remote sites of the brain where they may have some action.

Imageadapted from Biodidac

Under some pathological conditions, CSF builds up within the ventricles.This condition is called hydrocephalus.Hydrocephalus may result from:

  1. Overproduction of CSF
  2. An obstruction at some point within the ventricular system
  3. Problems with CSF absorption

To model how the CSF works, tryout this experiment with Mr.Egghead!

Some CSF facts:

  1. The total volume of CSF is 125-150 ml.
  2. Normal resting pressure of the CSF is between 150-180 mmH2O.
  3. Total production of CSF is about 400-500 ml/day (about .36 ml/min).

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For more on CSF and hydrocephalus,see:

  1. BrainVentricles: Our Internal Lake
  2. Formation,circulation and absorption of CSF
  3. TheHydrocephalus Foundation
  4. Hydrocephalus Fact Sheet from the Hydrocephalus Association
  5. AboutHydrocephalus from the Spina Bifida Association of Nova Scotia
  6. Hydrocephalus- from Beth Israel Hospital
  7. Hydrocephalusfrom Pediatric Neurosurgery
  8. Hydrocephalus general concepts

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