17.25: Cranial and Spinal Meninges
The cranial and spinal meninges are complex protective structures surrounding the central nervous system (CNS), consisting of the brain and spinal cord. These meninges consist of the dura mater, the arachnoid mater, and the pia mater. They protect the CNS, provide structural support, and aid in circulating cerebrospinal fluid (CSF).
Cranial Meninges
These meningeal layers cover the cranium. The dura mater is the outermost layer of cranial meninges. It is a thick and durable membrane of dense collagen fibers divided into two layers — the periosteal layer, which attaches to the skull's inner surface, and the meningeal layer. The dura mater also forms dural venous sinuses responsible for draining blood from the brain.
The arachnoid mater is the middle layer. It is a delicate membrane present beneath the dura mater. The subdural space, which contains a small amount of serous fluid, separates the arachnoid mater from the dura mater. The arachnoid mater also has thin strands called trabeculae that connect to the pia mater.
The innermost layer is the pia mater. It is a thin and highly vascularized membrane closely adhering to the surface of the spinal cord and brain. The pia mater contributes to the formation of the blood-brain barrier.
Spinal Meninges
The spinal dura mater is the outermost layer of the spinal meninges. It consists of dense collagen fibers. The dura mater consists of only one layer, known as the meningeal layer. It is separated from the vertebrae by the epidural space, which houses fat and blood vessels.
Beneath the dura mater is the spinal arachnoid mater. The delicate middle layer is separated from the dura mater by the serous fluid-filled subdural space. The subarachnoid space, a CSF-filled space, separates the arachnoid mater from the pia mater.
The spinal pia mater is a thin, vascularized membrane closely adhering to the spinal cord's surface. It extends as a filament called the filum terminale that anchors the spinal cord to the coccyx.
