(ORDO NEWS) — It has long been known that three membranes surround the brain and spinal cord. Recently, however, neurophysiologists have found another one.
This membrane is involved in the filtration of cerebrospinal fluid and serves as a “depot” for the accumulation of immune cells, and its damage can lead to the development of diseases of the central nervous system.
The central nervous system is surrounded by three shells : hard, arachnoid and soft.
These membranes provide protection, control the movement of substances between the cerebrospinal fluid and the rest of the body, and are involved in cleaning the central nervous system from the waste products of cells.
The three meningeal (meningeal) membranes are well known from anatomy, but the discovery of the fourth, the existence of which no one had previously suspected, became all the more unexpected.
The discovery was made by scientists from the UK and Denmark led by Professor Kjeld Møllgård of the University of Copenhagen.
They named the new membrane SLYM, short for Subarachnoidal LYmphatic-like Membrane.
As can be seen from this, SLYM lies beneath the arachnoid (arachnoid) membrane, separating it from the underlying pia mater.
The main studies were carried out on mice, although scientists have confirmed the presence of this membrane in humans.
SLYM is a mesothelial membrane like shells that surround many internal organs, protecting them and serving as reservoirs of immune cells. It turned out to be extremely thin – no more than a few cells in thickness – and very dense.
This allows even small molecules to be filtered, separating the “clean” cerebrospinal fluid, which directly bathes the brain, from the external, “dirty” one.
Thus, it acts as part of the glymphatic systemresponsible for cleaning the central nervous system from excess waste products.
The scientists also demonstrated the involvement of SLYM in protecting the brain from infections.
The CNS has its own population of immune cells, and a dense membrane prevents them from mixing with populations that work in other parts of the body.
Some of the lymphocytes are located directly in this shell, continuously monitoring the composition of the cerebrospinal fluid.
At the same time, with aging, as well as with increased inflammatory processes, the number of such cells in SLYM increases.
All this points to the important role that the fourth shell of the brain plays in the development of some diseases of the central nervous system.
Its damage leads to disruption of the glymphatic system and the accumulation of toxic substances in the brain.
It also allows lymphocytes from the rest of the body to enter the cerebrospinal fluid uncontrollably, causing damage to local cells.
Similar processes can accompany various infections, multiple sclerosis, Alzheimer’s disease, and the like.
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