<P> The ependyma is made up of ependymal cells called ependymocytes, a type of glial cell . These cells line the CSF - filled ventricles in the brain and the central canal of the spinal cord . These are nervous tissue cells with a ciliated simple columnar form much like that of some mucosal epithelial cells . </P> <P> The basal membranes of these cells are characterized by tentacle - like extensions that attach to astrocytes . </P> <P> Lining the CSF - filled ventricles, the ependymal cells play an important role in the production and regulation of CSF . Their apical surfaces are covered in a layer of cilia, which circulate CSF around the CNS . Their apical surfaces are also covered with microvilli, which absorb CSF . Within the ventricles of the brain, a population of modified ependymal cells and capillaries together known as the tela choroidea form a structure called the choroid plexus, which produces the CSF . </P> <P> Modified tight junctions between epithelial cells control fluid release . This release allows free exchange between CSF and nervous tissue of brain and spinal cord, which is why sampling of CSF (e.g. through a "spinal tap") provides a window to the CNS . </P>

Csf is formed by specialized ependymal cells and capillaries called