Meninges

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Meninges
Meninges-en.svg
The meninges: dura mater, arachnoid and pia mater
LatinMeninges
Gray'ssubject #193 872
Arterymiddle meningeal artery, meningeal branches of the ascending pharyngeal artery, accessory meningeal artery, branch of anterior ethmoidal artery, meningeal branches of vertebral artery
Nervemiddle meningeal nerve, nervus spinosus
MeSHMeninges
 
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Meninges
Meninges-en.svg
The meninges: dura mater, arachnoid and pia mater
LatinMeninges
Gray'ssubject #193 872
Arterymiddle meningeal artery, meningeal branches of the ascending pharyngeal artery, accessory meningeal artery, branch of anterior ethmoidal artery, meningeal branches of vertebral artery
Nervemiddle meningeal nerve, nervus spinosus
MeSHMeninges

The meninges (/məˈnɪnz/,[1][2] singular: meninx (/ˈmnɪŋks/ or /ˈmɛnɪŋks/[3]), from Ancient Greek: μῆνιγξ mēninx “membrane”,[4] adjectival: meningeal /məˈnɪnəl/) are the membranes that envelop the central nervous system. In mammals, the meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.

Anatomy[edit]

Dura mater[edit]

The dura mater [Latin: 'tough mother'] (also rarely called meninx fibrosa or pachymeninx) is a thick, durable membrane, closest to the skull. It consists of two layers: the periosteal layer, which lies closest to the calvaria (skull)—and the inner meningeal layer, which lies closer to the brain. It contains larger blood vessels that split into the capillaries 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 mater. The dura mater is a sac which envelops the arachnoid mater and surrounds and supports the large venous channels (dural sinuses) carrying blood from the brain toward the heart.

The dura has four areas of infolding:

Arachnoid mater[edit]

The middle element of the meninges is the arachnoid mater, so named because of its spider web-like appearance. It provides a cushioning effect for the central nervous system. The arachnoid mater is 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 together, are sometimes called the leptomeninges.

Pia mater[edit]

The pia mater [Latin: 'soft mother'] is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord, following the brain's minor 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.

Spaces[edit]

The subarachnoid space is the space that normally exists between the arachnoid and the pia mater, which is filled with cerebrospinal fluid.

Normally, the dura mater is attached to the skull, or to the bones of the vertebral canal in the spinal cord. 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.

Pathology[edit]

There are three types of hemorrhage involving the meninges:[5]

Other medical conditions that affect the meninges include meningitis (usually from 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 other animals[edit]

In fish, there is a single membrane (the primitive meninx). In amphibians, reptiles and birds, the meninges include a thick outer dura mater and a thick inner secondary meninx. Mammals retain the dura mater, and the secondary meninx divides into the arachnoid and pia mater.[6]

Additional images[edit]

References[edit]

  1. ^ OED 2nd edition, 1989.
  2. ^ Entry "meninges" in Merriam-Webster Online Dictionary, retrieved 2012-07-28.
  3. ^ Entry "meninx" in Merriam-Webster Online Dictionary, retrieved 2012-07-28.
  4. ^ μήνιγξ, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus.
  5. ^ Orlando Regional Healthcare, Education and Development. 2004. "Overview of Adult Traumatic Brain Injuries." Retrieved on January 16, 2008.
  6. ^ Kardong, Kenneth V. (1995). Vertebrates: Comparative Anatomy, Function, Evolution. Dubuque, Iowa: Wm. C. Brown Publishers. pp. 539. ISBN 0069219917