(CSF) The entire surface of central nervous system is bathed by a cerebrospinal fluid, a clear, colorless fluid. The CSF is contained within a system of fluid-filled cavities called ventricles. The Cerebral Spinal fluid has several functions: 1. Protection: the CSF protects the brain from damage by "buffering" the brain. 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, CSF reduces pressure at the base of the brain. 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.