The pia mater, the innermost membrane covering the central nervous system, protects delicate nerve tissue, supplies blood to the brain, and produces and circulates spinal fluid. It also connects different parts of the central nervous system to one another and provides support to the spinal cord.
Blood vessels travel through the pia mater to provide blood to the brain. The spaces between the vessels and the pia mater serve a similar function as the lymphatic system in the rest of the body, allowing waste material to circulate out. The pia mater also contains projections that connect it to the dura mater, which is the highest membrane of the spinal cord. This creates a continuous sheath surrounding the entire brain and spinal cord.