Meninx

Meninx is the singular term for one of the protective membranes that enclose the brain and spinal cord. In common usage, the collective term meninges refers to the entire set of membranes. The meninx and its partners create a protective covering that helps cushion the central nervous system and maintain the environment needed for neural function. The meninges also participate in the circulation and drainage of cerebrospinal fluid.

The outermost layer is the dura mater, a tough, fibrous membrane. In the cranial cavity it consists of two layers, the periosteal layer connected to the skull and the innermost meningeal layer. The two layers can separate to form dural reflections such as the falx cerebri and tentorium cerebelli. In the spinal canal only the meningeal layer remains, and a potential epidural space lies between the dura and surrounding bone.

Beneath the dura is the arachnoid mater, a delicate, spiderweb-like membrane. It does not follow the sulci of the brain as closely as the pia does. The subarachnoid space lies between the arachnoid and the pia mater and contains cerebrospinal fluid, which cushions the CNS. Arachnoid granulations protrude into the venous sinuses to help drain CSF into the bloodstream.

The innermost layer is the pia mater, a thin membrane that tightly adheres to the brain and spinal cord, following every contour and feeding the CNS with small vessels.

Clinical relevance includes meningitis (inflammation of the meninges), subdural or subarachnoid hemorrhage, and meningiomas (tumors arising from the arachnoid layer). Embryology and pathology highlight the meninges’ essential protective and supportive roles.