The innermost delicate membrane of the meninges that directly covers the surface of the brain and spinal cord is called what?

Introduction / Context:
The brain and spinal cord are extremely delicate organs that need protection from mechanical injury and infection. In addition to the skull and vertebral column, they are covered by three protective membranes collectively called meninges. Each meningeal layer has a specific position and structure. This question asks you to identify the innermost membrane that lies directly on the surface of the brain and spinal cord.

Given Data / Assumptions:

• The question refers to the innermost membrane covering the brain.
• Options include pleura, dura mater, pia mater, arachnoid membrane, and pericardium.
• We assume standard anatomical knowledge of meningeal layers.
• We focus on the layer that closely follows the contours of the brain and spinal cord.

Concept / Approach:
The three meningeal layers from outermost to innermost are dura mater, arachnoid mater, and pia mater. Dura mater is thick and tough, attached to the skull. Arachnoid mater is a web like middle layer. Pia mater is the innermost delicate membrane that adheres closely to the brain and spinal cord, following all their folds and grooves. The pleura is the membrane around the lungs, and the pericardium surrounds the heart, so they are unrelated to the central nervous system meninges. Therefore, the correct answer is pia mater.

Step-by-Step Solution:
Step 1: Recall the names of the three meninges: dura mater, arachnoid mater, and pia mater. Step 2: Understand their order: dura mater is outermost, arachnoid mater is in the middle, and pia mater is innermost. Step 3: Recognise that pia mater lies directly on the brain and spinal cord, closely following their surface. Step 4: Dura mater is tough and fibrous, providing strong outer protection, not the innermost membrane. Step 5: Arachnoid membrane is between dura and pia and contains the subarachnoid space with cerebrospinal fluid, but it does not directly adhere to the brain surface. Step 6: Pleura and pericardium are protective membranes of lungs and heart respectively, not parts of the meninges. Step 7: Therefore, the innermost membrane covering the brain is the pia mater.

Verification / Alternative check:
Anatomy textbooks consistently display cross sectional diagrams of the skull and brain, labelling the meninges in the order dura, arachnoid, and pia from outside to inside. They describe the pia mater as vascular and delicate, providing a supportive covering that accompanies the brain into all sulci and fissures. This description matches the innermost membrane requested in the question and confirms the answer.

Why Other Options Are Wrong:
Pleura: A double layered membrane surrounding the lungs, unrelated to brain coverings. Dura mater: The outermost tough meningeal layer, not the innermost. Arachnoid membrane: The middle meningeal layer, separated from pia by the subarachnoid space. Pericardium: A fibrous sac surrounding the heart, not part of the meninges.

Common Pitfalls:
Students sometimes confuse the order of the meningeal layers or mix up pia and dura because of similar sounding names. Others may not distinguish between meninges and other body membranes such as pleura. An easy memory aid is to think of the pia mater as the tender mother right on the brain, while dura mater is the tough mother on the outside.

Final Answer:
The correct answer is Pia mater.