Meninges

The meninges are three membranes—dura mater, arachnoid mater, and pia mater—that surround the brain and spinal cord, protecting them and enclosing cerebrospinal fluid.

Dura mater: The tough outer meningeal layer surrounding the brain and spinal cord. Its thick, outer position gives the meninges much of their mechanical protection.
Dural venous sinuses: Endothelium-lined channels between layers of cranial dura mater that drain venous blood from the brain. They show how the outer meningeal layer also provides routes for cranial venous drainage.
Lumbar puncture: A procedure that inserts a needle into the lumbar subarachnoid space to sample cerebrospinal fluid or administer medication. The procedure passes between vertebrae to reach the fluid compartment bounded by the meninges.
Ventricular system: A connected system of cavities in the brain that produces and circulates cerebrospinal fluid. It circulates the same fluid as the subarachnoid space but lies inside the brain.
Arachnoid mater: The middle meningeal layer, separated from the pia by the cerebrospinal-fluid-filled subarachnoid space. Its web-like structure bounds the fluid-filled space beneath the dura.
Arachnoid granulation: An outgrowth of arachnoid mater that projects into a dural venous sinus and permits cerebrospinal-fluid drainage. These structures connect the subarachnoid fluid compartment to venous blood.
Epidural anesthesia: Regional anesthesia produced by delivering medication into the epidural space near spinal nerve roots. Its target space lies outside the dura, making meningeal boundaries clinically decisive.
Blood–brain barrier: A selective interface formed mainly by brain endothelial cells that regulates movement from blood into brain tissue. It controls exchange at brain capillaries, unlike the meninges’ enclosing and protective layers.
Pia mater: The delicate innermost meningeal layer that closely follows the brain and spinal cord surfaces. It completes the three-layer covering by adhering closely to nervous tissue.
Meningeal arteries: Arteries that supply the dura mater and other meningeal tissues. Their course through the dura helps explain how meningeal injury can cause bleeding.

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