Meninges are the protective layer that covers the entire central nervous system. The meninges comes in three basic forms, the dura matter, the pia matter, and the arachnoid. While the entire central nercous system is protected by boney structures, namely the cranium and the spinal column, the meninges provide an additional layer of protective matter. It is simply a layer of connective tissue that serves various functions and areas of the central nervous system.



The dura mater is comprised of a dense connective tissue, suitable for connection with bone. Within the cranium, the dura mater is a double layered structure for additional protection. The outer layer, which is known as the periosteal layer, is constructed to slightly adjoin the cranium. Here, it constitutes the periosteum layer. The second layer is much thinner and considerably softer. Known as the meningeal layer, it adheres to the general contour of the brain but does not attach itself to the bone. The dura mater along the spinal column is single layered, and resembles the meninges of the cranium.

Throughout the dura mater of the cranium, nearly the entire layer is fused, with the exception of a few areas which the dura matter separates. These separations are to enable the dura mater to encase the dural sinuses, which are responsible for collecting venous blood and then in turn draining it into the jugular veins on the neck. In 4 distinct regions the dura mater of the cranium creates very noticeable partitions which not only segregate portion of the brain but also attach the brain to the inner surface of the skull.


Image: Meninges

The dura mater of the spine is really quite thick and encases the spinal cord in its protective sheath created by its tubular shape. Wrapping around the spinal cord, the dura matter travels the length of the spinal cord. The dural sheath and the vertebrates which create the vertebral canal are devoid of each other at this location. Rather, a potential cavity known as the epidural space fills this area. The epidural space creates a pad of protection for this area with its vascular loose fibers and the appropriate adipose tissue.


Of the 3 basic meninges, the arachnoid is known as the “middle” meninges. The membrane itself is rather delicate and is reminiscent of a fine fishnet. The arachnoid extends throughout the entire central nervous system yet ceases for the sulci or brain fissures. The arachnoid space can be located between the arachnoid matter and the pia mater and is filled with cerebrospinal fluid. Strands of tissue, which resemble a web, are able to maintain the space as well as connect the pia mater with the arachnoid mater.


The pia mater is the third and deepest of the three meninges. It is remarkably thin and slight but is able to maintain a tight bond to the convolutions of the brain and the irregularities of the spinal cord. The pia later is constructed of specialized modified connective tissue. In order to meet its responsibilities of providing support and assisting in nourishment to the cells of the brain and spinal cord in its general vicinity, the pia mater is extraordinarily vascular. In conjunction with the arachnoid, the pia mater also becomes intensely specialized to help create the roofs of the ventricles. Here, it contributes to the formation of the choroid plexus. It also assists in attaching the dura mater to the spinal cord via lateral extensions along the spine. These extensions are known as ligamentum denticulatum.
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