4 Meningeal Coverings of the Brain and Spinal Cord
There Are Three Meningeal Layers: The Dura Mater, Arachnoid, and Pia Mater
The dura mater, or dura, is a thick connective tissue membrane that also serves as the periosteum of the inside of the skull (Fig. 4-1). The arachnoid and the pia mater (or pia) are much thinner collagenous membranes. The arachnoid is attached to the inside of the dura and the pia is attached to the outer surface of the CNS. Hence the only space normally present between or around the cranial meninges is subarachnoid space (not counting the venous sinuses found within the dura). The arrangement of spinal meninges is slightly different, as described later in this chapter.
The Dura Mater Provides Mechanical Strength
The thickness and abundant collagen of the dura make it the mechanical link that connects the skull to the delicate strands of arachnoid (arachnoid trabeculae) that suspend the CNS in its bath of cerebrospinal fluid (CSF). This combination of partial flotation of the CNS in subarachnoid CSF, together with mechanical suspension by the skull-dura-arachnoid-arachnoid trabeculae-pia-CNS connections (see Fig. 4-3), stabilizes the fragile CNS during routine head movements.