Meninges

The meninges are three protective membranes that envelop the brain and spinal cord: dura mater, arachnoid mater, and pia mater. They provide mechanical protection, help contain cerebrospinal fluid (CSF), and contribute to the brain’s stable environment. In the skull, the dura mater has an outer periosteal layer and an inner meningeal layer that are usually fused but separate at dural folds such as the falx cerebri and tentorium cerebelli. Beneath the dura lies the arachnoid mater, and between it and the pia mater is the subarachnoid space, which contains CSF and cerebral vessels. The pia mater is the delicate inner membrane that closely adheres to the brain and spinal cord surfaces.

CSF circulates in the subarachnoid space, produced by the choroid plexuses, and is absorbed into venous blood through arachnoid granulations in the dural sinuses. The meninges receive blood supply mainly from meningeal arteries; sensory innervation of the dura is primarily via branches of the trigeminal nerve, explaining headaches when meninges are irritated.

Clinically, meninges are involved in meningitis, an inflammatory infection, and in subarachnoid hemorrhage, when blood enters the subarachnoid space. Lumbar puncture accesses CSF within the subarachnoid space to aid diagnosis.