Meningar

The meninges are the protective membranes surrounding the brain and spinal cord. They consist of three layers: the dura mater (outer), the arachnoid mater (middle), and the pia mater (inner). Together they enclose the subarachnoid space, which contains cerebrospinal fluid (CSF) and major blood vessels.

The dura mater is a tough, fibrous outer membrane. In the skull there are two dural layers, the endosteal layer lining the bone and the meningeal layer forming folds that partition spaces within the brain, such as the falx cerebri and tentorium cerebelli. The dura also contains dural venous sinuses that drain blood from the brain and orbit.

The arachnoid mater is a thin, avascular membrane beneath the dura. It forms a web-like network, and the subarachnoid space beneath it contains CSF and cerebral vessels. Arachnoid trabeculae connect to the pia mater, helping to suspend the brain within the CSF.

The pia mater is the delicate innermost layer that closely follows the contours of the brain and spinal cord, extending into the sulci. It is highly vascular and contributes to the brain’s microcirculation.

Clinically relevant spaces include the subdural space, a potential space between dura and arachnoid, and the subarachnoid space, which contains CSF. Inflammation of the meninges is meningitis, which can be bacterial, viral, or fungal. Symptoms typically include fever, headache, and neck stiffness; diagnosis relies on clinical assessment, imaging, and CSF analysis.

A related term is meningioma, a usually slow-growing tumor that arises from the meningeal layers, most often the dura. The meninges play roles in CSF homeostasis, immune defense, and protection of neural tissue.