The pia mater is the innermost layer of the three meninges that surround and protect the brain and spinal cord. The meninges are a set of three protective membranes that surround the brain and spinal cord, and they are composed of the dura mater, arachnoid mater, and pia mater.

The pia mater is a thin, delicate layer of connective tissue that adheres directly to the surface of the brain and spinal cord, following the contours of the gyri and sulci. It is highly vascularized and contains numerous blood vessels that supply the underlying nervous tissue with oxygen and nutrients. The pia mater also contains a network of fine collagen fibers and elastic fibers that help to support and protect the underlying nervous tissue.

The primary function of the pia mater is to provide a protective barrier between the delicate nervous tissue of the brain and spinal cord and the surrounding cerebrospinal fluid (CSF) and blood vessels. The pia mater also plays a role in the regulation of the flow of CSF and the exchange of nutrients and waste products between the nervous tissue and the surrounding fluid.

Diseases or injuries that affect the pia mater can have serious consequences for the function of the central nervous system. For example, inflammation of the pia mater (pia materitis) can lead to neurological symptoms such as headaches, seizures, and cognitive impairment. In addition, damage to the blood vessels in the pia mater can result in bleeding into the brain or spinal cord, which can cause stroke or other serious neurological complications.