The Ventricular System and CSF
(Cerebrospinal Fluid)
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 the following midsagittal section of the brain.

The Ventricles

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

Absorption of the CSF into the blood stream takes place in the superior sagittal sinus through structures called arachnoid villi . When the CSF pressure is greater than the venous pressure, CSF will flow into the blood stream. However, the arachnoid villi act as "one way valves"...if the CSF pressure is less than the venous pressure, the arachnoid villi will NOT let blood pass into the ventricular system. there is CSF flowing through the ventricles...what does the CSF do? The CSF has several functions including:

  1. Protection: the CSF protects the brain from damage by "buffering" the brain. In other words, the CSF acts to cushion a blow to the head and lessen the impact.
  2. Buoyancy: because the brain is immersed in fluid, the net weight of the brain is reduced from about 1,400 gm to about 50 gm. Therefore, pressure at the base of the brain is reduced.
  3. Excretion of waste products: the one-way flow from the CSF to the blood takes potentially harmful metabolites, drugs and other substances away from the brain.
  4. Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.

Image adapted 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

Some CSF facts:

  1. The total volume of CSF is 125-150 ml.
  2. Normal resting pressure of the CSF is between 150-180 mm H2O.
  3. Total production of CSF is about 400-500 ml/day (about .36 ml/min).