The Cranial pia mater is anchored to the brain by the processes of astrocytes, which are glial cells responsible for many functions, including maintenance of the extracellular space. The cranial pia mater joins with the ependyma, which lines the cerebral ventricles to form choroid plexuses that produce cerebrospinal fluid. Together with the other meningeal layers, the function of the pia mater is to protect the central nervous system by containing the cerebrospinal fluid, which cushions the brain and spine.
The cranial pia mater covers the surface of the brain. This layer goes in between the cerebral gyri and cerebellar laminae, folding inward to create the tela chorioidea of the third ventricle and the choroid plexuses of the lateral and third ventricles. At the level of the cerebellum, the pia mater membrane is more fragile due to the length of blood vessels as well as decreased connection to the cerebral cortex.