View source for Medicine:Meninges

{{short description|Three membranes that envelop the brain and spinal cord}}
{{Infobox anatomy
| Name        = Meninges
| Latin       = Meninges
| Greek       =
| Image2       = Meninges-en.svg
| Caption2     = The meninges: dura mater, arachnoid mater and pia mater
| Width       =
| Image       = 3D Medical Illustration Meninges Details.jpg
| Caption     = Image depicting meninges around the brain
| Precursor   =
| System      =
| Artery      = middle meningeal artery, meningeal branches of the ascending pharyngeal artery, accessory meningeal artery, branch of anterior ethmoidal artery, meningeal branches of vertebral artery
| Vein        =
| Nerve       = middle meningeal nerve, nervus spinosus
| Lymph       =
}}

In [[Biology:Anatomy|anatomy]], the '''meninges''' ({{IPAc-en|m|ə|ˈ|n|ɪ|n|dʒ|iː|z}},<ref>{{Cite web |title=meninges |url=https://www.oxfordlearnersdictionaries.com/definition/english/meninges |website=Oxford Learner's Dictionaries}}</ref><ref>{{cite dictionary|url=https://www.merriam-webster.com/dictionary/meninges|title=Definition of meninges|dictionary=Merriam-Webster Online Dictionary|access-date=28 July 2012}}</ref> {{singular}}: '''meninx''' ({{IPAc-en|ˈ|m|iː|n|ɪ|ŋ|k|s}} or {{IPAc-en|ˈ|m|ɛ|n|ɪ|ŋ|k|s}}<ref>{{cite dictionary|url=https://www.merriam-webster.com/dictionary/meninx|title=Definition of meninx|dictionary=Merriam-Webster Online Dictionary|access-date=28 July 2012}}</ref>), {{ety|grc|''μῆνιγξ'' (mēninx)|membrane}}<ref>{{LSJ|mh{{=}}nigc|μῆνιγξ|ref}}</ref>) are the three [[Chemistry:Membrane|membrane]]s that envelop the [[Biology:Brain|brain]] and [[Biology:Spinal cord|spinal cord]]. In [[Biology:Mammal|mammal]]s, the meninges are the [[Medicine:Dura mater|dura mater]], the arachnoid mater, and the pia mater. [[Biology:Cerebrospinal fluid|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 [[Biology:Central nervous system|central nervous system]].<ref>{{cite web |last1=Castillero Mimenza |first1=Oscar |title=Meninges: anatomía, partes y funciones en el cerebro |date=January 2017 |url=https://psicologiaymente.com/neurociencias/meninges}}</ref>

==Structure==

===Dura mater===
{{Main|Medicine:Dura mater}}
The dura mater ({{lang-la|tough mother}}),<ref>{{cite dictionary|url=https://www.merriam-webster.com/dictionary/dura+mater|title=Definition of dura mater|dictionary=Merriam-Webster Online Dictionary|access-date=22 June 2022}}</ref>{{Efn|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,{{cn|date=October 2020}} 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 skull, and the inner meningeal layer, which lies closer to the brain.<ref name="scalp">{{cite web|title=Scalp Anatomy: Structure, Nerve Supply, Arterial Supply|url=https://emedicine.medscape.com/article/834808-overview|date=20 June 2017}}</ref> 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 [[Biology:Cerebral hemisphere|cerebral hemisphere]]s. 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 [[Biology:Occipital lobe|occipital lobe]]s from [[Biology:Cerebellum|cerebellum]]. The falx cerebri attaches to it giving a tentlike appearance.
* Falx cerebelli, vertical infolding; lies inferior to the tentorium cerebelli, separating the [[Biology:Cerebellar hemisphere|cerebellar hemisphere]]s.
* Diaphragma sellae, smallest infolding; covers the [[Medicine:Pituitary gland|pituitary gland]] and sella turcica.
[[File:Brain layers.jpg|thumb|Diagram of brain layers]]

===Arachnoid mater===
[[File: 1316 Meningeal LayersN.jpg|thumb|upright=1.6|Diagram of section of top of brain showing the meninges and subarachnoid space]]
The middle element of the meninges is the arachnoid mater, or arachnoid membrane, so named because of its resemblance to a [[Biology:Spider web|spider web]]. It cushions the [[Biology:Central nervous system|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'''.<ref name="Abbott">{{cite journal |last1=Abbott |first1=NJ |last2=Patabendige |first2=AA |last3=Dolman |first3=DE |last4=Yusof |first4=SR |last5=Begley |first5=DJ |title=Structure and function of the blood-brain barrier. |journal=Neurobiology of Disease |date=January 2010 |volume=37 |issue=1 |pages=13–25 |doi=10.1016/j.nbd.2009.07.030 |pmid=19664713|s2cid=14753395 }}</ref>

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.
===Pia mater===
The pia mater ({{lang-la|tender mother|links=no}})<ref name="merriam-webster.com_pia_mater">{{cite dictionary|url=https://www.merriam-webster.com/dictionary/pia+mater|title=Definition of pia mater|dictionary=Merriam-Webster Online Dictionary|access-date=27 November 2015}}</ref> 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 ([[Biology:Gyrus|gyri]] and [[Biology:Sulcus (neuroanatomy)|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.

=== Subarachnoidal lymphatic-like membrane ===
{{Excerpt|subarachnoidal lymphatic-like membrane}}
===Leptomeninges===
The arachnoid and pia mater are sometimes together called the ''leptomeninges'',<ref>{{cite web|title=leptomeninges |url=https://en.oxforddictionaries.com/definition/leptomeninges|archive-url=https://web.archive.org/web/20161104012057/https://en.oxforddictionaries.com/definition/leptomeninges|url-status=dead|archive-date=November 4, 2016|website=Oxford Dictionaries {{!}} English}}</ref> literally "thin meninges" ({{lang-el|λεπτός}} "leptos"—"thin"). Acute meningococcal meningitis can lead to an [[Biology:Exudate|exudate]] within the  leptomeninges along the surface of the brain.<ref>{{Cite book |last=Kumar |first=Vinay |year=2015 |title=Robbins and Cotran Pathologic Mechanisms of Disease |location=Philadelphia |publisher=Elsevier Saunders |edition=9th |page=1273 |oclc=892583347 |quote=In acute meningitis, an exudate is evident within the leptomeninges over the surface of the brain (Fig. 28-21).}}</ref> 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.<ref>{{cite journal |last1=Yamashima |first1=Tetsumori |last2=Sakuda |first2=Kazushige |last3=Tohma |first3=Yasuo |last4=Yamashita |first4=Junkoh |last5=Oda |first5=Hiroshi |last6=Irikura |first6=Daisuke |last7=Eguchi |first7=Naomi |last8=Beuckmann |first8=Carsten T. |last9=Kanaoka |first9=Yoshihide |last10=Urade |first10=Yoshihiro |last11=Hayaishi |first11=Osamu |title=Prostaglandin D Synthase (β-Trace) in Human Arachnoid and Meningioma Cells: Roles as a Cell Marker or in Cerebrospinal Fluid Absorption, Tumorigenesis, and Calcification Process |url= |journal=Journal of Neuroscience |pages=2376–2382 |language=en |date=1 April 1997 |volume=17 |issue=7 |doi=10.1523/JNEUROSCI.17-07-02376.1997|pmid=9065498 |pmc=6573504 |s2cid=15404074 }}</ref>

===Subarachnoid space===
[[File: Gray770-en.svg|thumb|Diagram of section of spinal cord showing the meninges and spaces. Subarachnoid space coloured blue]]
The '''subarachnoid space''' is the space that normally exists between the arachnoid and the pia mater. It is filled with [[Biology:Cerebrospinal fluid|cerebrospinal fluid]] and continues down the [[Biology:Spinal cord|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 [[Biology:Vertebra|vertebra]]e by a space called the [[Biology:Epidural space|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 [[Biology:Glia limitans|glia limitans]].

==Clinical significance==
Injuries involving the meninges, can result in a hemorrhage and two types of hematoma.<ref>{{cite web |publisher=Orlando Regional Healthcare, Education and Development |year=2004 |url=http://www.orlandoregional.org/pdf%20folder/overview%20adult%20brain%20injury.pdf |title=Overview of Adult Traumatic Brain Injuries |archive-url=https://web.archive.org/web/20080227162001/http://www.orlandoregional.org/pdf%20folder/overview%20adult%20brain%20injury.pdf |archive-date=February 27, 2008}}</ref>
* A [[Medicine:Subarachnoid hemorrhage|subarachnoid hemorrhage]] is acute bleeding under the arachnoid; it may occur spontaneously or as a result of trauma.<ref>{{cite journal |vauthors=van Gijn J, Kerr RS, Rinkel GJ |title=Subarachnoid haemorrhage |journal=Lancet |volume=369 |issue=9558 |pages=306–18 |year=2007 |pmid=17258671 |doi=10.1016/S0140-6736(07)60153-6|s2cid=29126514 }}</ref>
* A [[Medicine:Subdural hematoma|subdural hematoma]] is a hematoma (collection of blood) located in a separation of the arachnoid from the dura mater. The [[Medicine:Bridging vein|bridging vein]]s that connect the dura mater and the arachnoid are torn, usually during an accident, and blood leaks into this area.
* An [[Medicine:Epidural hematoma|epidural hematoma]], bleeding between the dura mater and the [[Biology:Skull|skull]], may arise after an accident or spontaneously.

Other medical conditions that affect the meninges include [[Medicine:Meningitis|meningitis]] (usually from a fungal, bacterial, or [[Biology:Virus|viral]] [[Medicine:Infection|infection]]) and [[Medicine:Meningioma|meningioma]]s that arise from the meninges, or from meningeal carcinomatoses (tumors) that form elsewhere in the body and [[Medicine:Metastasis|metastasize]] to the meninges.

==Other animals==
In [[Biology:Fish|fish]], there is a single membrane known as the primitive meninx.<ref name="Ostrander">{{cite book |last1=Ostrander |first1=Gary |title=The Laboratory Fish |url=https://books.google.com/books?id=Hp4YSFiSD0IC&q=fish+meninges&pg=PT135 |publisher=Elsevier |language=en |date=12 September 2000|isbn=9780125296502 }}</ref> [[Biology:Amphibian|Amphibian]]s and [[Biology:Reptile|reptile]]s have two meninges, and [[Biology:Bird|bird]]s and mammals have three.<ref name="Ostrander"/> In the early 1900s, Giuseppe Sterzi, an Italian anatomist, carried out comparative studies on the meninges from the [[Biology:Lancelet|lancelet]] to the human. 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 [[Biology:Neural tube|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 [[Biology:Periosteum|periosteum]]. He also demonstrated the continuity of all meninges with the envelopes of nerves and with the filum terminale.

[[Biology:Mammal|Mammal]]s (as higher vertebrates) retain the dura mater, and the secondary meninx divides into the arachnoid and pia mater.<ref>{{cite book |last=Kardong |first=Kenneth V. |year=1995 |title=Vertebrates: Comparative Anatomy, Function, Evolution |location=Dubuque, Iowa |publisher=Wm. C. Brown Publishers. |page=539 |isbn=0-697-21991-7}}</ref>

==Additional images==
<gallery>
File:Acta Eruditorum - IV fisiologia, 1703 – BEIC 13363829.jpg|Illustration of the work by Antonio Pacchioni ''Disquisitio anatomicae de durae meningis ...'' published in ''Acta Eruditorum'', 1703
</gallery>

==See also==
* Cranial cavity

==Notes==
{{Notelist}}

==References==
{{Reflist|2}}

== External links ==

{{Nervous system}}

[[Category:Human head and neck]]

{{Sourceattribution|Meninges}}