Which of the following layers directly contacts the brain and spinal cord?

The pia mater is the innermost layer of the three meninges that surround the brain and spinal cord. This layer is delicate and thin, directly adhering to the surface of the brain and spinal cord tissues. Its close contact allows it to provide essential support and protection for these critical components of the central nervous system. The pia mater also contains many blood vessels that supply nutrients to the nervous tissue, further highlighting its importance in maintaining the health and functionality of the brain and spinal cord.

In contrast, the arachnoid membrane and dura mater are the middle and outer layers, respectively, which do not have the same level of contact with the brain and spinal cord as the pia mater does. The arachnoid membrane lies above the pia mater and contains the subarachnoid space filled with cerebrospinal fluid, which acts as a cushion. The dura mater is the toughest outer layer that provides the most substantial protective barrier, but it is not in direct contact with the nervous tissue. The cerebrum, being a part of the brain itself, is not a layer but rather a structure that the pia mater directly interacts with.

Therefore, the pia mater is the correct answer as the layer that directly contacts the brain and spinal cord.