What protective membrane surrounds the brain and spinal cord?

The protective membrane surrounding the brain and spinal cord is the meninges.

The meninges are three connective-tissue layers: the tough outer dura mater, the web-like arachnoid mater, and the delicate pia mater, which closely follows the brain and spinal cord. Together, they cushion the central nervous system, provide physical and immune protection, and help contain cerebrospinal fluid, blood vessels, and nerves.

Cerebrospinal fluid occupies the subarachnoid space between the arachnoid and pia layers. This fluid helps absorb mechanical shock and supports the brain's buoyancy. The meninges also continue around the spinal cord, creating a protected channel within the vertebral column.

A common mix-up is choosing one of the three layers as the answer. Arachnoid mater, pia mater, and dura mater are each individual meninges; meninges is the collective name. Inflammation of these membranes is called meningitis, which may be caused by infections or other conditions.