Arachnoid mater
Encyclopedia
The arachnoid mater, literally from Latin "spider (web)-like mother", 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
.
The delicate, spiderweb-like (hence the name) arachnoid layer, attached to the inside of the dura, surrounds the brain and spinal cord but does not line the brain down into its sulci
(folds). Cerebrospinal fluid
flows under this membrane in the subarachnoid space, which is full of the delicate fibres of the arachnoid extending down to attach to the pia mater.
The portions covering the brain
and spinal cord
are called arachnoidea encephali and arachnoidea spinalis, respectively.
The arachnoid and pia mater are sometimes considered as a single structure, the leptomeninx, or the plural version, leptomeninges. (Lepto- from the root meaning thin in Greek). Similarly, the dura in this situation is called the pachymeninx.
international standard.
Meninges
The meninges is the system of membranes which envelopes the central nervous system. 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.-Dura...
, the membranes that cover the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. It is interposed between the two other meninges, the more superficial
Superficial
Superficial may refer to:*Superficial , an album by Heidi Montag*"Superficial" *The Superficial, a website devoted to celebrity gossip...
dura mater
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
and the deeper pia mater
Pia mater
Pia mater often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. The word finds its roots in Latin, meaning literally "tender mother." The other two meningeal membranes are the dura mater and the arachnoid mater....
, and is separated from the pia mater by the subarachnoid space
Subarachnoid space
In the central nervous system, the subarachnoid cavity is the interval between the arachnoid membrane and pia mater....
.
The delicate, spiderweb-like (hence the name) arachnoid layer, attached to the inside of the dura, surrounds the brain and spinal cord but does not line the brain down into its sulci
Sulcus (neuroanatomy)
In neuroanatomy, a sulcus is a depression or fissure in the surface of the brain.It surrounds the gyri, creating the characteristic appearance of the brain in humans and other large mammals....
(folds). Cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
flows under this membrane in the subarachnoid space, which is full of the delicate fibres of the arachnoid extending down to attach to the pia mater.
The portions covering the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
are called arachnoidea encephali and arachnoidea spinalis, respectively.
The arachnoid and pia mater are sometimes considered as a single structure, the leptomeninx, or the plural version, leptomeninges. (Lepto- from the root meaning thin in Greek). Similarly, the dura in this situation is called the pachymeninx.
Etymology
Arachnoid is from a Greek root, and means cobweb-like. The mater designation (meaning mother in Latin) is borrowed from the dura mater and Pia mater, which were Latin translations of Arabic terms. While mater does not technically belong with the arachnoid layer, it has nevertheless been adopted by it for uniformity with the other meninges, and arachnoid mater is currently the Terminologia AnatomicaTerminologia Anatomica
Terminologia Anatomica is the international standard on human anatomic terminology. It was developed by the Federative Committee on Anatomical Terminology and the International Federation of Associations of Anatomists and was released in 1998. It supersedes the previous standard, Nomina...
international standard.
See also
- Arachnoid cystArachnoid cystArachnoid cysts are cerebrospinal fluid covered by arachnoidal cells and collagen that may develop between the surface of the brain and the cranial base or on the arachnoid membrane, one of the three membranes that cover the brain and the spinal cord...
- Leptomeningeal collateral circulationLeptomeningeal collateral circulationThe term leptomeningeal refers to the two deep layers of the meninges — the pia mater and the arachnoid mater. The leptomeningeal collateral circulation is a network of blood vessels supplying the brain that follows a diffuse course over the superficial surface of the brain.-Leptomeningeal...