What is "arachnoid"?

The arachnoid is a thin, transparent membrane that covers the brain and spinal cord, forming a protective barrier. It gets its name from its spiderweb-like appearance due to numerous fine fibers extending from its surface. The arachnoid helps regulate the flow of cerebrospinal fluid, which surrounds and nourishes the brain and spinal cord. It works in conjunction with the other meninges (dura mater and pia mater) to provide support and protection to the central nervous system.