- - cranial a. mater [TA] that portion of the a. that lies within the cranial cavity and surrounds the brain and the cranial portion of the subarachnoid space. In several sites it is relatively widely separated from the pia mater, creating the cranial subarachnoid cisterns. SEE ALSO: a. mater. SYN: arachnoidea mater cranialis [TA], arachnoidea mater encephali, a. mater cranialis, a. mater encephali, a. of brain, cerebral part of a..- a. mater [TA] A delicate fibrous membrane forming the middle of the three coverings of the central nervous system. In life the a. (specifically the a. barrier cell layer) is tenuously attached to the externally adjacent dura mater (specifically the dural border cells) and there is no naturally occurring space at the dura-a. interface. Thus in a spinal puncture dura mater and a. are penetrated simultaneously as if a single layer. Separation of the a. mater from the dura mater (usually through the dural border cell layer) may result from traumatic or pathologic processes creating what is commonly, but incorrectly, called a subdural hematoma. The a. mater is named for the delicate, spider weblike filaments that extend from its deep surface, through the CSF of the subarachnoid space, to the pia mater. SEE ALSO: leptomeninx. SYN: arachnoidea mater, arachnoides [TA], a. membrane, a., parietal layer of leptomeninges.- spinal a. mater [TA] that portion of the a. that lies within the vertebral canal and surrounds the spinal cord and the vertebral portion of the subarachnoid space. It extends from the foramen magnum above to the S2 vertebral level. Since the spinal cord ends at the L2 vertebral level, a wide separation occurs between the a. and pia mater, the lumbar cistern, filled with cerebrospinal fluid in which the cauda equina is suspended. SYN: arachnoidea mater spinalis [TA], a. of spinal cord, arachnoidea spinalis, spinal part of a..
* * *arach·noid ə-'rak-.nȯid n a thin membrane of the brain and spinal cord that lies between the dura mater and the pia materarachnoid also arach·noi·dal ə-.rak-'nȯid-əl adj of or relating to the arachnoid <the \arachnoid membrane>
* * *n.the middle of the three membranes covering the brain and spinal cord (see meninges), which has a fine, almost cobweb-like, texture. Between it and the pia mater within lies the subarachnoid space, containing cerebrospinal fluid and large blood vessels; the membrane itself has no blood supply.
* * *arach·noid (ə-rakґnoid) 1. resembling a spider's web. 2. arachnoidea mater.
Medical dictionary. 2011.