A Skeletal Coverings

(1) Brain. The bones of the cranium form a spherical case around the brain. The cranial cavity is the space inclosed by the bones of the cranium.

(2) Spinal cord. The vertebrae, with the vertebral foramina, form a cylindrical case around the spinal cord. The overall skeletal structure is the vertebral column (spine). The vertebral (spinal) canal is the space inclosed by the foramina of the vertebrae.

b. Meninges (Fibrous Membranes). The brain and spinal cord have three different membranes surrounding them called meninges (figure 11-7). These coverings provide protection.

Figure 11-7. A schematic diagram of the meninges, as seen in side view of the CNS.

(1) Dura mater. The dura mater is a tough outer covering for the CNS. Beneath the dura mater is the subdural space, which contains a thin film of fluid.

(2) Arachnoid mater. To the inner side of the dura mater and subdural space is a fine membranous layer called the arachnoid mater. It has fine spiderweb-type threads which extend inward through the subarachnoid space to the pia mater. The subarachnoid space is filled with cerebrospinal fluid (CSF).

ARACHNOID = spider-like

(3) Pia mater. The pia mater is a delicate membrane applied directly to the surface of the brain and the spinal cord. It carries a network of blood vessels to supply the nervous tissues of the CNS.

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