Which delicate inner membrane intimately covers the brain and spinal cord?

• A. Pia mater
• B. Arachnoid mater
• C. Dura mater
• D. Parietal pleura

Answer: (A)

Delicate membranes that enclose the CNS come in three layers, with the one that is intimately attached to the brain and spinal cord being the pia mater. This inner layer is very thin and follows every contour of the neural surface, dipping into sulci and wrapping around gyri as well as along the spinal cord. It is highly vascular and forms the immediate surface from which blood vessels enter the brain tissue, helping to accompany them as they penetrate deeper into the tissue.

Because the pia mater adheres so closely to neural tissue, it remains in direct contact with the brain and spinal cord, unlike the arachnoid mater, which is the middle, more loose membrane, or the dura mater, the tough outer covering. The space beneath the arachnoid and above the pia is the subarachnoid space, filled with cerebrospinal fluid. The parietal pleura is a membrane of the thoracic cavity and has no role in enclosing the CNS.

So the membrane described as the delicate inner layer that intimately covers the brain and spinal cord is the pia mater.