arachnoid mater

(noun)

The middle layer of the meninges. A membrane that protects the brain and spinal cord below the dura mater and above the subarachnoid space and the pia mater.

Related Terms

Examples of arachnoid mater in the following topics:

  • Body Cavity Membranes

    • In mammals, the meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater .
    • The dura mater is composed of dense fibrous tissue, and its inner surface is covered by flattened cells like those present on the surfaces of the pia mater and arachnoid mater.
    • The dura mater is a sac which envelops the arachnoid and has been modified to serve several functions.
    • The middle element of the meninges is the arachnoid mater, so named because of its spider web-like appearance.
    • The arachnoid mater is a thin, transparent membrane.

  • Meninges

    • In mammals, the meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater .
    • The dura mater is a sac that envelops the arachnoid and has been modified to serve several functions.
    • The arachnoid mater is a thin, transparent membrane.
    • The arachnoid and pia mater are sometimes together called the leptomeninges.
    • The arachnoid is attached to the dura mater, while the pia mater is attached to the central nervous system tissue.

  • Oculomotor (III) Nerve

    • On emerging from the brain, the nerve is invested with a sheath of pia mater and enclosed in a prolongation from the arachnoid mater.
    • It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process (gives attachment to the tectorium cerebella), passing between the free and attached borders of the tentorium cerebelli.

  • Overview of the Spinal Cord

    • The dura mater is the outermost layer, and it forms a tough protective coating.
    • The space between the dura mater and the surrounding bone of the vertebrae is called the epidural space.
    • The middle layer is called the arachnoid mater.
    • The pia mater is the innermost protective layer and is tightly associated with the surface of the spinal cord.
    • The space between the arachnoid and pia maters is called the subarachnoid space and is where the CSF is located.

  • Cerebrospinal Fluid and Its Circulation

    • The CSF occupies the space between the arachnoid mater (the middle layer of the brain cover, the meninges) and the pia mater (the layer of the meninges closest to the brain).
    • CSF is reabsorbed into venous sinus blood via arachnoid granulations.
    • Since the subarachnoid space around the brain and spinal cord can contain only 135 to 150 ml, large amounts are drained primarily into the blood through arachnoid granulations in the superior sagittal sinus.

  • Optic (II) Nerve

    • The optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in the peripheral nerves.

  • Ventricles

    • The CFS within the skull and spine is found between the pia mater and the arachnoid and provides further cushioning.
    • The fluid then flows around the superior sagittal sinus to be reabsorbed via the arachnoid villi into the venous system.

  • Veins of the Head and Neck

    • Dural sinuses are composed of dural mater lined with endothelium, making them distinct from both arteries, veins and capillaries.

  • Epidural Anesthesia

    • The needle for the epidural is injected between vertebra into the space outside the dura mater of the spinal cord.

  • Abducens (VI) Nerve

    • It runs upward between the pons and the clivus, and then pierces the dura mater to run between the dura and the skull.