Pia mater ( or ), often referred to as simply the pia, is the delicate innermost layer of the
meninges, the membranes surrounding the
brain and
spinal cord.
Pia mater is medieval Latin meaning "tender mother". The other two meningeal membranes are the
dura mater and the
arachnoid mater. Pia mater is a thin
fibrous tissue that is impermeable to fluid. This allows the pia mater to enclose
cerebrospinal fluid. By containing this fluid the pia mater works with the other meningeal layers to protect and cushion the brain. The pia mater allows blood vessels to pass through and nourish the brain. The
perivascular space created between blood vessels and pia mater functions as a
lymphatic system for the brain. When the pia mater becomes irritated and inflamed the result is
meningitis.