- Glia limitans
The Glia limitans, or glial limiting membrane, is the outermost layer of proper
nervous tissue of thebrain andspinal cord , lying directly under thepia mater .tructure
It is composed of a dense multilayered meshwork of the processes of
astrocytes covered by an outerbasal lamina that makes intimate contact with cells of the pia mater. The astrocyte processes that cover the surface (end-feet) are firmly attached to the basal lamina byjunctional complexes resembling half punctate adhesions (related to hemidesmosomes, although smaller). [cite book |author= Peters, Alan |coauthors= Palay, Sanford L. and Henry deF. Webster |title= The Fine Structure of the Nervous System: Neurons and Their Supporting Cells. |edition= 3rd edition |year= 1991 |publisher= Oxford University Press |location= New York |isbn= 0-19-506571-9 |pages= pp. 288, 400-402] This organization persists as the surface invaginates around arteries and veins that enter the interior from thesubarachnoid space . The glial limiting membrane is physically separated from the larger penetrating vessels by the Virchow-Robin space, an extension of the subarachnoid space, down to the capillary level where its basal lamina becomes continuous with the capillary basal lamina. [cite book |author= Nolte, John |title= The Human Brain: An Introduction to Its Functional Anatomy |edition= 5th edition |year= 2002 |publisher=Mosby |location= St. Louis |isbn= 0-323-01320-1 |pages= p. 89]Function
The primary function of the glial limiting membrane is structural: it forms a firm, well-defined protective surface for the
central nervous system . Astrocyte end-feet continue to form a dense but discontinuous layer surrounding capillaries, and this capillary investment is generally considered to be an extension of the glial limiting membrane. The glia limitans does not form theblood-brain barrier , which is instead a function of tight junctions between endothelial cells that make up the capillary walls, and does not by itself present a barrier to the diffusion of water or low molecular weight solutes.References
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