In this particular concept a cell from the choroid plexus is shown. These epithelial cells produce the cerebrospinal fluid (CSF) that circulates through the central nervous system. The brush like structures on the top of the cell are called microvilli, and their function is to increase the area of secretion and reabsorption of substances, which enhances the circulation of CSF. Pathological conditions such as hydrocephalus, can arise from abnormalities in the function of these cells.