Cerebrospinal fluid (CSF):
- provides cushioning for the delicate neural structures and support for the brain since it literally floats in this fluid. Alone, the brain weighs about 1400 grams (3.1 lb.), but it weighs only 50 g (1.76 oz.) when supported by the cerebrospinal fluid.
- transports nutrients, chemical messengers, and waste products.
- is in constant chemical communication with the interstitial fluid of the CNS through the permeable ependymal lining except at the choroid plexus.
- is produced at the choroid plexus, a vascular network that extends into each of the four ventricles. It then circulates between the different ventricles, passes along the central canal, and enters the subarachnoid space. Once inside, it continues around the spinal cord and cauda equina and across the surfaces of the brain.
- is secreted at a rate of about 500 ml/day, and the volume at any given moment is approximately 150 ml, with the entire volume being replaced every eight hours.
- sometimes produces changes in its composition because it mingles freely with the interstitial fluid. Therefore, samples are taken via a lumbar puncture (spinal tap) to provide useful clinical information concerning CNS injury, infection, or disease.
