Circulating within the meninges is a liquid called cerebrospinal fluid (CSF). This fluid cushions the brain and spinal cord to protect them from shocks that could lead to damage. CSF also acts as a transport system that delivers nutrients to different parts of the central nervous system and removes waste material.

There are three layers to the meninges:

Dura mater

The outermost membrane, this is the thickest of the three layers and has both an outer and inner layer. It is one of the few structures of the skull capable of feeling pain. The brain itself cannot.

Arachnoid mater 

Connected to the dura mater on the side closest to the CNS, this middle layer includes a webbing of fibers and collagen that are part of the suspension system that helps protect the brain and spinal cord from impact. They also form a gap between the arachnoid and the pia maters called the subarachnoid space. This is where the cerebrospinal fluid is found.

Pia mater

The final layer, the pia mater hugs the spinal cord and brain like a coat. It has blood vessels that deliver oxygen and nutrients to the spinal cord.

To check for problems of the CNS such as meningitis, a procedure called a lumbar puncture is performed. This involves withdrawing samples of CSF from the spine for testing.

The nerves of the peripheral nervous system connect the brain to the rest of the body, allowing communication and response to stimuli.

These nerves are named after the areas they service. The sciatic and femoral nerves, named for the hip and femur, respectively, are among those that serve the lower body. The ulnar nerve (related to the arm’s ulna bone) is one that serves part of the arm and hand.