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The arachnoid mater covering the brain is referred to as the arachnoidea encephali, and the portion covering the spinal cord as the arachnoidea spinalis. The arachnoid and pia mater are sometimes considered as a single structure, the leptomeninx, or the plural version, leptomeninges (lepto, from the Greek root meaning "thin" or "slender").
The middle element of the meninges is the arachnoid mater, or arachnoid membrane, so named because of its resemblance to a spider web. It cushions the central nervous system. This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, has an outer layer of tightly packed flat cells, forming the arachnoid barrier. [8]
The membrane in this area is much thicker than the cranial pia mater, due to the two-layer composition of the pia membrane. The outer layer, which is made up of mostly connective tissue, is responsible for this thickness. Between the two layers are spaces which exchange information with the subarachnoid cavity as well as blood vessels.
Arachnoid granulations (also arachnoid villi, and pacchionian granulations or bodies) are small outpouchings of the arachnoid mater and subarachnoid space into the dural venous sinuses of the brain. The granulations are thought to mediate the draining of cerebrospinal fluid (CSF) from the subarachnoid space into the venous system .
Its floor is formed by the arachnoid membrane extending between the temporal lobes of either side. [2] Anteriorly, it extends to the optic chiasm. [1] The cistern communicates superiorly with the chiasmatic cistern, and inferiorly with the pontine cistern. [3]
The dura covers the arachnoid mater and the pia mater the other two meninges in protecting the central nervous system. At major boundaries of brain regions such as the longitudinal fissure between the hemispheres, and the tentorium cerebelli between the posterior brain and the cerebellum the dura separates, folds and invaginates to make the ...
This results in fluid-filled cavities with random spacing and size. The mesenchymal material between these cavities is the origin of the arachnoid trabeculae. The upper and lower surfaces of the layer become the arachnoid and pia mater membranes, to which the trabecular structure remains attached.
Arachnoiditis is an inflammatory condition of the arachnoid mater or 'arachnoid', one of the membranes known as meninges that surround and protect the central nervous system. The outermost layer of the meninges is the dura mater (Latin for hard) and adheres to inner surface of the skull and vertebrae. [ 1 ]