- Produced by the four choroid plexuses:
- Located in the two lateral, third, and fourth ventricles
- Highly vascular invaginations of pia mater
- Covered by specialised ciliated ependymal cells
- Produced by a combination of:
- Filtration of plasma through the fenestrated capillaries
- Active transport of solutes
- Control of substances entering is regulated by the blood-CSF barrier (distinct from the BBB)