Cerebrospinal Fluid

Environmental control for the nervous system

Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the subarachnoid space and ventricular system around the brain and spinal cord. CSF’s primary purpose is to protect the brain and spinal cord from mechanical shock. In a normal adult, it is present in only modest amounts (100 – 150 mL), although its importance to the nervous system and body goes beyond its shock-absorbing role.

Roles of CSF

• Buoyancy – As the brain is "floating" in CSF, its net weight in the skull is reduced from about 1.5 kg to only 25–50 grams; net weight reduction is necessary to avoid the brain’s vascular efficiency being compromised and the organ being injured by its own weight.
• Regulating intracranial pressure – CSF can retain its protective properties while being kept at a reduced volume around the brain that exerts a lower pressure inside the skull; blood flow is facilitated and brain ischemia (restricted blood supply) is prevented.
• Waste removal – Similar to the way blood removes metabolic byproducts and toxins from the bloodstream, CSF clears waste compounds from in and around the brain as part of the glymphatic system.
• Homeostasis – The brain and nervous system are highly sensitive to even slight imbalances in chemical distribution among its cells, and CSF facilitates this distribution; also assists diffusion of compounds from neuroendocrine cells that secrete hormones and other carefully regulated factors.

Production, reabsorption and turnover

Most CSF is continuously produced (at a rate of up to 500 mL/day) by a vascular network called the choroid plexus, and is continuously reabsorbed into venous sinuses, lymphatic vessels and possibly other drainage locations under current scientific investigation. The body’s entire volume of CSF is replaced at a rate of three to four times per day.