The function of the cerebrospinal fluid space and its expansion.

In addition to its nutritive and protective effects, the basic function of the cerebrospinal fluid space resides in dynamic equilibration of pressure fluctuations caused by volume changes in three compartments contained within the rigid skull cavity: brain tissue, blood and cerebrospinal fluid. An increase in volume in one of them brings about a compliant withdrawal in volume in the other two. The degree of cerebrospinal fluid compliance can be expressed by means of the pressure/volume index which is directly proportional to this compliance. On the other hand an expansion of fluid space which forces the brain to withdraw its tissue, brings about the dilatation of brain ventricles. The degree of their dilatation depends on the effective pressure of cerebrospinal fluid which counteracts with the resistance of brain venous collectors. The blood in the venous network of the brain and cerebral extracellular fluid play a reversible role in cerebral mass restoration and reduction. These facts explain the reason why, from the physical point of view, the brain is considered to represent a viscous and elastic spongious matter. (Ref. 21.)