Мидың және жұлынның қабықшалары

Three membranes that envelop the brain and spinal cord

In anatomy, the meninges (/m//ə/'/n//ɪ//n//dʒ//iː//z/, : meninx ('/m//iː//n//ɪ//ŋ//k//s/ or '/m//ɛ//n//ɪ//ŋ//k//s/), ) are the three membranes that envelop the brain and spinal cord. In mammals, the meninges are the dura mater, the arachnoid mater, and the pia mater. Cerebrospinal fluid is located in the subarachnoid space between the arachnoid mater and the pia mater. The primary function of the meninges is to protect the central nervous system.

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. The shape of the arachnoid does not follow the convolutions of the surface of the brain and so looks like a loosely fitting sac. In particular, in the region of the brain a large number of fine filaments called arachnoid trabeculae pass from the arachnoid through the subarachnoid space to blend with the tissue of the pia mater. The arachnoid barrier has no extracellular collagen and is considered to represent an effective morphological and physiological meningeal barrier between the cerebrospinal fluid in the subarachnoid space and the blood circulation in the dura. The arachnoid barrier layer is characterized by a distinct continuous basal lamina on its inner surface toward the innermost collagenous portion of the arachnoid reticular layer.

The pia mater (tender mother) is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surfaces of the brain and spinal cord, following all of the brain's contours (gyri and sulci). It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels to the brain and spinal cord, and its capillaries nourish the brain.

The arachnoid and pia mater are sometimes together called the leptomeninges, literally "thin meninges" (λεπτός "leptos"—"thin"). Acute meningococcal meningitis can lead to an exudate within the leptomeninges along the surface of the brain. Because the arachnoid is connected to the pia by cob web like strands, it is structurally continuous with the pia, hence the name pia arachnoid or leptomeninges. They are responsible for the production of beta trace protein (prostaglandin D2 synthase), a major cerebrospinal fluid protein.

The subarachnoid space is the space that normally exists between the arachnoid and the pia mater. It is filled with cerebrospinal fluid and continues down the spinal cord. Spaces are formed from openings at different points along the subarachnoid space; these
are the subarachnoid cisterns, which are filled with cerebrospinal fluid. The dura mater is attached to the skull, whereas in the spinal cord, the dura mater is separated from the vertebrae by a space called the epidural space, which contains fat and blood vessels. The arachnoid is attached to the dura mater, while the pia mater is attached to the central nervous system tissue. When the dura mater and the arachnoid separate through injury or illness, the space between them is the subdural space. There is a subpial space underneath the pia mater that separates it from the glia limitans.

Injuries involving the meninges, can result in a hemorrhage and two types of hematoma. A subarachnoid hemorrhage is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma. A subdural hematoma is a hematoma (collection of blood) located in a separation of the arachnoid from the dura mater. The bridging veins that connect the dura mater and the arachnoid are torn, usually during an accident, and blood leaks into this area. An epidural hematoma, bleeding between the dura mater and the skull, may arise after an accident or spontaneously. Other medical conditions that affect the meninges include meningitis (usually from a fungal, bacterial, or viral infection) and meningiomas that arise from the meninges, or from meningeal carcinomatoses (tumors) that form elsewhere in the body and metastasize to the meninges.

In fish, there is a single membrane known as the primitive meninx. Amphibians and reptiles have two meninges, and birds and mammals have three.