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Meninges
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"Meninx" redirects here. For the Tunisian island formerly known as "Meninx", see Djerba.
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Meninges
The meninges: dura mater, arachnoid mater and pia mater
Details
Artery
middle meningeal artery, meningeal branches of the ascending pharyngeal artery, accessory meningeal artery, branch of anterior ethmoidal artery, meningeal branches of vertebral artery
Nerve
middle meningeal nerve, nervus spinosus
Identifiers
Latin
Meninges
MeSH
A08.186.566
Dorlands
/Elsevier
12523818
TA
A14.1.01.001
FMA
231572
Anatomical terminology
[edit on Wikidata]
The meninges (/məˈnɪndʒiːz/,[1][2] singular: meninx (/ˈmiːnɪŋks/ or /ˈmɛnɪŋks/[3]), from Ancient Greek: μῆνιγξ mēninx "membrane",[4] adjectival: meningeal /məˈnɪndʒəl/) 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.
Contents
[hide]
1 Structure
1.1 Dura mater
1.2 Arachnoid mater
1.3 Pia mater
1.4 Leptomeninges
1.5 Spaces
2 Clinical significance
3 Other animals
4 Additional images
5 References
Structure[edit]
Dura mater[edit]
Main article: Dura mater
The dura mater (Latin: tough mother) (also rarely called meninx fibrosa or pachymeninx) is a thick, durable membrane, closest to the skull and vertebrae. The dura mater, the outermost part, is a loosely arranged, fibroelastic layer of cells, characterized by multiple interdigitating cell processes, no extracellular collagen, and significant extracellular spaces. The middle region is a mostly fibrous portion. It consists of two layers: the endosteal layer, which lies closest to the calvaria (skullcap), 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 that envelops the arachnoid mater and surrounds and supports the large dural sinuses carrying blood from the brain toward the heart.
The dura has four areas of infolding:
Falx cerebri, the largest, sickle-shaped; separates the cerebral hemispheres. Starts from the frontal crest of frontal bone and the crista galli running to the internal occipital protuberance.
Tentorium cerebelli, the second largest, crescent-shaped; separates the occipital lobes from cerebellum. The falx cerebri attaches to it giving a tentlike appearance.
Falx cerebelli, vertical infolding; lies inferior to the tentorium cerebelli, separating the cerebellar hemispheres.
Diaphragma sellae, smallest infolding; covers the pituitary gland and sella turcica.
Arachnoid mater[edit]
Main article: Arachnoid mater
The middle element of the meninges is the arachnoid mater, so named because of its spider web-like appearance. It cushions the central nervous system. This thin, transparent membrane is composed of fibrous tissue and, like the pia mater, is covered by flat cells also thought to be impermeable to fluid.
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 is composed of an outermost portion (arachnoid barrier cell layer) with tightly packed cells and no extracellular collagen; that is why it is considered to represent an effective morphological and physiological meningeal barrier between the cerebrospinal fluid and 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.
Pia mater[edit]
Main article: Pia mater
The pia mater (Latin: tender mother[5]) is a very delicate membrane. It is the meningeal envelope that firmly adheres to the surface of the brain and spinal cord, following all of the brain's contours (the 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.
Leptomeninges[edit]
The arachnoid and pia mater together are sometimes called the leptomeninges,[6] literally "thin meninges" (Greek: λεπτός leptos - thin). Acute meningococcal meningitis can lead to an exudate within the leptomeninges along the surface of the brain.[7] 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.[clarification needed][citation needed]
Spaces[edit]
Main article: Subarachnoid space
The subarachnoid space is the space that normally exists between the arachnoid and the pia mater, which is filled with cerebrospinal fluid.
The dura mater is attached to the skull, whereas in the spinal cord, the dura mater is separated from the bone (vertebrae) by a space called the epidural space, which contain 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.
Clinical significance[edit]
There are three types of hemorrhage involving the meninges:[8]
A subarachnoid hemorrhage is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma.[9]
A subdural hematoma is a hematoma (collection of blood) located in a separation of the arachnoid from the dura mater. The small veins that connect the dura mater and the arachnoid are torn, usually during an accident, and blood leaks into this area.
An epidural hematoma may arise after an accident or spontaneously.
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.
Other animals[edit]
In fish, there is a single membrane known as the primitive meninx. In other vertebrates – amphibians, reptiles and birds, the meninges include a thick outer dura mater and a thick inner secondary meninx. In the early 1900s, Giuseppe Sterzi an Italian anatomist carried out comparative studies on the meninges from the lancelet to man. Contrary to previous reports the spinal meninges were seen to be very simple, both in the adult lower vertebrates and in the early developmental stages of the more advanced vertebrates. From the mesenchyme surrounding the neural tube only a single leaflet forms the primitive meninx. In the following phylogenetic and ontogenetic stages, the latter divides into an internal leaflet: the secondary meninx, and into an external one: the dura mater. Finally, in higher vertebrates, even the secondary meninx divides into the arachnoid and the pia. In the same animals, Sterzi demonstrated that, while in the spinal medulla the dura keeps its identity, in the skull it fuses with the periosteum. He also demonstrated the continuity of all meninges with the envelopes of nerves and with the filum terminale.
Mammals (as higher vertebrates) retain the dura mater, and the secondary meninx divides into the arachnoid and pia mater.[10]
Additional images[edit]
Diagrammatic representation of a section across the top of the skull
Diagrammatic section of scalp.
References[edit]
Jump up ^ OED 2nd edition, 1989.
Jump up ^ Entry "meninges" in Merriam-Webster Online Dictionary, retrieved 2012-07-28.
Jump up ^ Entry "meninx" in Merriam-Webster Online Dictionary, retrieved 2012-07-28.
Jump up ^ μῆνιγξ. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
Jump up ^ Entry "pia mater" in Merriam-Webster Online Dictionary, retrieved 2015-11-27.
Jump up ^ "leptomeninges - definition of leptomeninges in English | Oxford Dictionaries". Oxford Dictionaries | English.
Jump up ^ Kumar, Vinay (2015). Robbins and Cotran Pathologic Mechanisms of Disease. Philadelphia: Elsevier Saunders. p. 1273. In acute meningitis, an exudate is evident within the leptomeninges over the surface of the brain (Fig. 28-21).
Jump up ^ "Overview of Adult Traumatic Brain Injuries" (PDF). Orlando Regional Healthcare, Education and Development. 2004. Archived from the original (PDF) on February 27, 2008.
Jump up ^ van Gijn J, Kerr RS, Rinkel GJ (2007). "Subarachnoid haemorrhage". Lancet. 369 (9558): 306–18. PMID 17258671. doi:10.1016/S0140-6736(07)60153-6.
Jump up ^ Kardong, Kenneth V. (1995). Vertebrates: Comparative Anatomy, Funuction, Evolution. Dubuque, Iowa: Wm. C. Brown Publishers. p. 539. ISBN 0-697-21991-7.
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Nervous system
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Spinal cord
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Rhombencephalon
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Pons
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Midbrain
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[show]
v
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Meninges of the brain and spinal cord
Layers
Dura mater
Falx cerebri
Tentorium cerebelli
Falx cerebelli
Diaphragma sellae
Trigeminal cave
Arachnoid mater
Arachnoid granulation
Arachnoid trabeculae
Subarachnoid cisterns:
Cisterna magna
Pontine cistern
Interpeduncular cistern
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Pia mater
Denticulate ligaments
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Filum terminale
Leptomeninges
Spaces
Epidural space
Subdural space
Subarachnoid space
Cerebrospinal fluid
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t
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The spinal cord
General features
Cervical enlargement
Lumbar enlargement
Conus medullaris
Filum terminale
Cauda equina
Meninges
Grey matter
Posterior grey column
Marginal nucleus
Substantia gelatinosa of Rolando
Nucleus proprius
Spinal lamina V
Spinal lamina VI
Lateral grey column
Intermediolateral nucleus
Posterior thoracic nucleus
Anterior grey column
Interneuron
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Onuf's nucleus
Gamma motor neuron
Other
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Central gelatinous substance
Gray commissure
Central canal
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Gracile
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Lateral:
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dorsal
ventral
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anterior
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External features
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