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The ventral layer of arachnoid membrane, on the other hand, is a direct anterior extension of this arachnoid envelope that the dorsal layer forms over the pineal region. [4] [clarification needed] The arachnoid mater in the rat is composed of approximately 10 layers of fibroblast cells. [5]
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.
The dura mater has several functions and layers. The dura mater is a membrane that envelops the arachnoid mater.It surrounds and supports the dural venous sinuses that reabsorbs cerebrospinal fluid and carries the cerebral venous return, back toward the heart.
The brain and spinal cord are covered by the meninges, the three protective membranes of the tough dura mater, the arachnoid mater and the pia mater. The cerebrospinal fluid (CSF) within the skull and spine provides further protection and also buoyancy, and is found in the subarachnoid space between the pia mater and the arachnoid mater.
Embryologically, the arachnoid trabeculae are the remnants of the common precursor that forms both the arachnoid and pial layers of the meninges. The initial development of the subarachnoid space occurs in two phases: [13] A mesenchymal layer "invades" between the embryonic epithelium and the developing neuroepithelium of the telencephalon.
The bases of denticulate ligaments arise in the pia mater and are firmly attached to the arachnoid mater and dura mater at the apex. [2] The denticulate ligaments extend across the subarachnoid space between anterior nerve roots and posterior nerve roots, piercing the intervening spinal arachnoid mater to reach the dura.
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]