Final answer:
The CNS is protected by three layers of meninges: the tough dura mater as the outermost layer, the web-like arachnoid mater in the middle, and the delicate pia mater directly in contact with the CNS.
Step-by-step explanation:
Protective Coverings of the Brain and Spinal Cord
The central nervous system (CNS) is shielded by three layers of protective tissues known as the meninges. The outermost layer, the dura mater, is the thickest and acts as a durable shield. Its name translates to "tough mother" in Latin, indicating its primary function to protect the brain and spinal cord. The dura mater also houses vein-like structures that allow blood to travel from the brain back to the heart.
The arachnoid mater is the middle layer of the meninges. It is named for its spider-web-like trabeculae that extend from this layer down to the next. The arachnoid mater encapsulates the CNS in a sac-like structure and interacts with the dural sinuses through arachnoid granulations where cerebrospinal fluid (CSF) is filtered back into the bloodstream.
The innermost layer is the pia mater, referred to as "soft mother", which tenderly envelops the CNS. It conforms closely to the brain's and spinal cord's surface, much like plastic wrap, extending into the convolutions, and contains the blood vessels that nourish the CNS. The space between the arachnoid and pia maters is called the subarachnoid space and is filled with CSF. This fluid acts as a protective cushion, shock absorber, and serves to circulate chemicals throughout the brain and spinal cord.