CSF is formed by

The choroid plexus is a plexus of cells that produces the cerebrospinal fluid in the ventricles of the brain. The CSF occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain, as well as the central canal of the spinal cord. CSF serves several purposes: Buoyancy Protection Chemical stability Clearing waste Ref: guyton and hall textbook of medical physiology 12 edition page number: 813,814,815