Clear, colorless fluid that fills the neural tube and later circulates through the four ventricles of the brain, within which it is secreted and then propelled by ependymal cells that line the walls of the ventricles. The fluid is absorbed into the bloodstream and re-circulated. It contains some white blood cells and supplies nutrients to the brain. Another function is to act as shock absorber for the brain. Its total volume is about 150 millilitres and it is replaced every three to four hours in the adult human. In all then, between 400 and 600 millilitres are produced each day. If it is not kept within normal limits, and the fluid accumulates in the ventricles, it can give rise to hydrocephalus.
See Central nervous system (CNS), Cochlea, Ependymal cell, Hydrocephalus (or hydrocephaly), Limbic cortices, Meninges, Neural tube, Pia mater, Proliferative ventricular zone, Ventricle