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The meninges (singular meninx) is the system of membrane
Mesothelium

The mesothelium is a membrane that forms the lining of several body cavities: the pleura , peritoneum and pericardium . Mesothelial tissue also surrounds the male internal reproductive organs and covers the internal reproductive organs of women ....
s which envelops the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
. The meninges consist of three layers: the dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
, the arachnoid mater
Arachnoid mater

The arachnoid mater is one of the three meninges, the membranes that cover the brain and spinal cord. It is interposed between the two other meninges, the more superficial dura mater and the deeper pia mater, and is separated from the pia mater by the subarachnoid space....
, and the pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
. The primary function of the meninges and of the cerebrospinal fluid
Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain....
 is to protect the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
.

Pia mater The pia or pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
 is a very delicate membrane. It is the meningeal envelope which firmly adheres to the surface of the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
 and spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
.






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Encyclopedia


The meninges (singular meninx) is the system of membrane
Mesothelium

The mesothelium is a membrane that forms the lining of several body cavities: the pleura , peritoneum and pericardium . Mesothelial tissue also surrounds the male internal reproductive organs and covers the internal reproductive organs of women ....
s which envelops the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
. The meninges consist of three layers: the dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
, the arachnoid mater
Arachnoid mater

The arachnoid mater is one of the three meninges, the membranes that cover the brain and spinal cord. It is interposed between the two other meninges, the more superficial dura mater and the deeper pia mater, and is separated from the pia mater by the subarachnoid space....
, and the pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
. The primary function of the meninges and of the cerebrospinal fluid
Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain....
 is to protect the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
.

Anatomy


Pia mater

The pia or pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
 is a very delicate membrane. It is the meningeal envelope which firmly adheres to the surface of the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
 and spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
. As such it follows all the minor contours of the brain
Brain

The brain is the center of the nervous system in all vertebrate, and most invertebrate, animals. Some primitive animals such as cnidarian and echinoderm have a decentralized nervous system without a brain, while sponges lack any nervous system at all....
 (gyri
Gyrus

A gyrus is a ridge on the Cerebral cortex. It is generally surrounded by one or more sulcus ....
 and sulci
Sulcus (anatomy)

A sulcus is a depression or fissure in the surface of an organ, especially the brain....
). 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 which travel to the brain and spinal cord, and its capillaries are responsible for nourishing the brain.

Arachnoid membrane

The middle element of the meninges is the arachnoid membrane, so named because of its spider web
Spider web

File:Garden orbweaver with prey.jpgA spider web, spiderweb, spider's web or cobweb is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets....
-like appearance. It provides a cushioning effect for the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
. The arachnoid mater
Arachnoid mater

The arachnoid mater is one of the three meninges, the membranes that cover the brain and spinal cord. It is interposed between the two other meninges, the more superficial dura mater and the deeper pia mater, and is separated from the pia mater by the subarachnoid space....
 exists as a thin, transparent membrane. It is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid. The arachnoid does not follow the convolutions of the surface of the brain and so looks like a loosely fitting sac. In the region of the brain, particularly, 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 and pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
 are sometimes together called the leptomeninges.

Dura mater

The dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
 (also rarely called meninx fibrosa, or pachymeninx) is a thick, durable membrane, closest to the skull
Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
. It consists of two layers, the periosteal layer, closest to the calvaria and the inner meningeal layer. It contains larger blood vessels which split into the capilliaries in the pia mater. It 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. The dura mater is a sac which envelops the arachnoid and has been modified to serve several functions. The dura mater surrounds and supports the large venous channels (dural sinuses) carrying blood from the brain toward the heart.

Spaces

The subarachnoid space
Subarachnoid space

In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater.It is occupied by a spongy tissue consisting of trabecul? and intercommunicating channels in which the cerebrospinal fluid is contained....
 is the space which normally exists between the arachnoid and the pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
, which is filled with cerebrospinal fluid
Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain....
.

Normally, the dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
 is attached to the skull
Skull

The skull is a bone structure found in the head of many animals. The skull supports the structures of the face and protects the head against injury....
, or to the bones of the vertebral canal in the spinal cord
Spinal cord

The spinal cord is a long, thin, tubular bundle of neuron and glia that extends from the brain. The brain and spinal cord together make up the central nervous system....
. The arachnoid is attached to the dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
, and the pia mater
Pia mater

The pia mater is the delicate innermost layer of the meninges?the membranes surrounding the brain and spinal cord.The thin, mesh-like pia mater closely envelops the entire surface of the brain, running down into the fissures of the cortex....
 is attached to the central nervous system tissue. When the dura mater
Dura mater

The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
 and the arachnoid separate through injury or illness, the space between them is the subdural space
Subdural space

The subdural space is an artificial space created by the separation of the arachnoid mater from the dura mater as the result of trauma, pathologic process, or the absence of cerebrospinal fluid as seen in a cadaver....
.

Pathology

There are three types of hemorrhage involving the meninges:
  • A subarachnoid hemorrhage
    Subarachnoid hemorrhage

    A subarachnoid hemorrhage is bleeding into the subarachnoid space?the area between the arachnoid and the pia mater surrounding the brain. This may occur spontaneously, usually from a ruptured cerebral aneurysm, or may result from head injury....
     is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma.
  • A subdural hematoma
    Subdural hematoma

    A subdural hematoma is a form of traumatic brain injury in which blood gathers within the inner meningeal layer of the dura mater . Unlike in epidural hematomas, which are usually caused by tears in artery, subdural bleeding usually results from tears in veins that cross the subdural space....
     is a hematoma
    Hematoma

    A hematoma, or haematoma, is a collection of blood outside the blood vessels, generally the result of hemorrhage, or more specifically, internal bleeding....
     (collection of blood) located in a separation of the arachnoid from the dura mater
    Dura mater

    The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
    . The small veins which connect the dura mater
    Dura mater

    The dura mater , or pachymeninx, is the tough and inflexible outermost of the three layers of the meninges surrounding the brain and spinal cord....
     and the arachnoid are torn, usually during an accident, and blood can leak into this area.
  • An epidural hematoma
    Epidural hematoma

    Epidural or extradural hematoma is a type of traumatic brain injury in which a buildup of blood occurs between the dura mater and the skull....
     similarly may arise after an accident or spontaneously.


Other medical conditions which affect the meninges include meningitis
Meningitis

Meningitis is a medical condition caused by inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges....
 (usually from fungal, bacterial, or viral
Virus

A virus is a Optical microscope#Limitations of light microscopes infectious agent that is unable to grow or reproduce outside a host cell . Viruses infect all cellular life....
 infection
Infection

An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host resources to multiply ....
) and meningioma
Meningioma

Meningiomas are the most common primary tumor of the central nervous system, arising from the arachnoid "cap" cells of the arachnoid villi in the meninges....
s arising from the meninges or from tumor
Tumor

A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells . Tumor is not synonymous with cancer. A tumor can be Benign neoplasm, Carcinoma in situ or malignant, whereas cancer is by definition malignant....
s formed elsewhere in the body which metastasize
Metastasis

Metastasis , or Metastatic disease, sometimes abbreviated mets, is the spread of a disease from one Organ or part to another non-adjacent organ or part....
 to the meninges.

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