The meninges

These are the ‘envelopes’ that wrap round your brain and spinal cord. Their main function is to protect the central nervous system. The meninges consist of three layers or membranes with fluid flowing between them.

• The dura mater is the thick outermost layer. It is attached to the skull and surrounds and supports blood vessels.
• The arachnoid is the middle layer. It is pressed close to the dura mater although it is not actually attached to it. It has a spider's web-like appearance with projections that loosely attach it to the inner (pia) membrane. This makes it able to cushion the brain.
• The pia mater is the innermost layer and is attached to the surface of the brain. It follows the brains contours deep into the cracks (sulci).

In between the arachnoid and pia membranes, there is a potential space called the subarachnoid space. This space contains a fluid called cerebral spinal fluid (CSF). Together with the meninges, the CSF helps to cushion the brain and to prevent friction against the skull. Learn more about the CSF.