Anatomy & Physiology

Anatomy & Physiology Study Guide

14.2 Spinal Meninges The vertebral column and its adjacent ligaments, tendons, and muscles protect the spinal cord from the rest of the body, and these structures also create a protection against bumps, shocks, and blows to the skin of the back. The gentle neural tissues must also be sheltered from damaging contacts with the surrounding bony walls of the vertebral canal. The spinal meninges are a series of specialized membranes surrounding the spinal cord, providing the necessary physical stability and shock absorption. The spinal meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The tough, fibrous dura mater is the layer that forms the outermost covering of the spinal cord. The dense collagen fibers of this layer orient along the longitudinal axis of the cord. The spinal dura mater does not have extensive, firm connections to the surrounding vertebrae. Longitudinal stability is provided by localized attachment sites at the ends of the vertebral canal and provide stability for the dura mater. Local anesthetics are often injected into the epidural space. Administered in this manner, the drug should affect only the spinal nerves in the immediate area of the injection. The result is an epidural block, which is a temporary sensory loss and motor paralysis, depending on the anesthetic selected. Epidural blocks in the inferior lumbar or sacral regions may be used to control pain during childbirth. Arachnoid mater is the middle meningeal layer. The inner surface of the dura mater and the outer surface of the arachnoid mater are enclosed by simple squamous epithelia. The arachnoid mater includes the arachnoid trabeculae, a gentle network of collagen and elastic fibers that spreads between the arachnoid membrane and the outer surface of the pia mater. The space between the two layers is called the subarachnoid space and is filled with cerebrospinal fluid (CSF) that acts as a shock absorber and a diffusion channel for dissolved gases, chemical messengers, nutrients, and waste products. The innermost meningeal layer is the pia mater. The pia mater consists of a meshwork of elastic and collagen fibers that is tightly connected to the underlying neural tissue. These connective- tissue fibers are extensively connected with those that cover the subarachnoid space, tightly binding the arachnoid to the pia mater.

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