The subarachnoid space is a fluid-filled area located between the arachnoid mater and the pia mater, two of the three protective membranes surrounding the brain and spinal cord. This space contains cerebrospinal fluid (CSF), which cushions the brain and spinal cord, providing protection from injury and helping to maintain stable pressure within the central nervous system. In addition to CSF, the subarachnoid space also contains blood vessels that supply the brain. It plays a crucial role in the circulation of CSF, allowing it to flow freely around the brain and spinal cord, facilitating nutrient transport and waste removal.