ABSTRACT
The choroid epithelial cells (EC) of the brain form the blood-cerebrospinal fluid barrier (BCB), which is responsible by active and passive transport mechanisms for producing the major part of the cerebrospinal fluid (CSF). The BCB closely regulates the exchange of molecules between blood and CSF. The CSF is somewhat more acidic than blood and contains significantly less protein compared to serum. The CSF flows via the ventricles down to the spinal canal but also upward over the cortex. In this way, the CSF covers the entire brain, reaching into the sulci and depths of the cortex and thus acts as a mechanical cushion. The extracellular environment of neurons and neuroglia is in a steady state with the CSF, and this phenomenon is considered to be an important factor in maintaining homeostasis in the central nervous system.
