CSF and meningeal functions

The functions of the CSF are mechanical and metabolic. By equilibrating with brain extracellular fluid unwanted metabolites (urea, choline, dopamine and serotonin metabolites, creatinine, and K+) are transported into the blood, either through arachnoid villi or choroid plexuses. There are three mechanical effects that are protective:

- As the subarachnoid space is a fluid-filled compartment in which the brain floats, the effective weight of the brain is decreased from about 1350 g to about 50 g.

- Adjustments to the CSF and meninges avoid changes in intracranial pressure due to alterations in the cerebral blood flow. Whenever blood flow increases, the CSF is squeezed from ventricles into the subarachnoid space around the spinal cord. Here the dura mater is more elastic and stretches to accommodate the increase in volume. The Longer term increases in intracranial pressure can be offset by a increase in CSF flow into the venous sinuses via the arachnoid villi.

- The meninges (specially the dura) support the brain and the CSF decreases the force with which the brain impacts the inside of the cranium whenever the head moves.