New Brain Layer Have Just Been Discovered by Scientists
New Brain Layer: The human brain is an absurdly complicated organ that guards its mysteries jealously. As imaging technology improves, previously unknown aspects of neurological anatomies, such as new types of nerve cells and nubs of tissue, continue to surface.
Danish and American scientists have distinguished a previously undisclosed layer of tissue that helps shield our grey and white matter. Though it’s only a few cells thick, this membrane appears to play a role in mediating the movement of small, dissolved substances between different regions of the brain. It appears to be the primary location for immune cells that specifically attack the brain, and it also plays a role in the brain’s waste-removal (glymphatic) system.
The Subarachnoid LYmphatic-like Membrane (New Brain Layer) was discovered by a team led by molecular biologist Kjeld Mallgaard of the University of Copenhagen (SLYM). While most of their studies on this structure have been conducted in mice, they have used two-photon microscopy and dissections to confirm the SLYM’s presence in the brain of an adult human.
The SLYM (New Brain Layer) is sandwiched between two other membranes that together provide a protective barrier for the brain. It creates two compartments for the fluid in our brains, bringing the total number of membranes that surround our brains to four. As far as we can tell, it forms a barrier for molecules larger than about 3 kilodaltons in our brain fluid, which is roughly the size of a very small protein.
Our brain and spinal cord are examples of “immune privileged” organs, along with the eyes and testicles, because they lack lymphatic (immune) vessels and thus are protected from immune attack. Therefore, the group hypothesizes that cerebrospinal fluid may take on some of the function of the immune system in the brain. This might be explicable due to the presence of the SLYM (New Brain Layer).
Neuroscientist Maiken Nedergaard from the University of Rochester says, “The discovery of a new anatomical structure that separates and assists control the flow of cerebrospinal fluid (CSF) in and around the brain gives us a much better understanding of the complex role that CSF plays not only in transferring and eliminating waste from the brain but also in helping its immune defenses.”
Myeloid cells, macrophages, and other immune cells were discovered by Mllgrd and colleagues to be stationed in the SLYM (New Brain Layer) and responsible for monitoring the brain. Changes in cell types in response to swelling and aging in mice indicate a potential role for this area in disease pathologies.
Similar molecular markers can be found between the SLYM and the mesothelial membrane that surrounds blood vessels and harbors immune cells in the rest of our organs. The SLYM (New Brain Layer) is hypothesized to be the mesothelium, the lining of the blood vessels in the subdural space between the brain and the skull. Furthermore, mesothelium acts as a lubricant between sliding organs.
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The brain is constantly being moved within the cranial cavity due to “physiological pulsations induced by the cardiovascular system, respiration, and positional changes of the head,” the authors write. It’s possible that SLYM (New Brain Layer), like other mesothelial membranes, lessens the amount of pressure exerted by the brain on the skull when the body is in motion.
Mollgard and colleagues postulate that tears in the SLYM (New Brain Layer) may account for some of the persistent symptoms of traumatic brain injury. If this barrier were compromised, immune cells from the skull could enter the brain unimpeded, even though they are not adapted to the specific environmental conditions found there. As such, this may account for the persistence of inflammation.
Changes in cerebrospinal fluid flow patterns after membrane rupture may account for persistent suppression of waste removal from the brain after injury. Because this protective buffer for the mind was only recently discovered, there is still a lot to figure out. Scientists are curious as to whether or not this tissue also plays a role in the central nervous system’s immunity and, by extension, in diseases like multiple sclerosis.
We conclude that SLYM (New Brain Layer) satisfies the characteristics of a mesothelium by covering blood vessels in the subarachnoid space and acting as an immune barrier to prevent the swap of small solute molecules between both the outer and inner subarachnoid space partitions.
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FAQ
What is the newest part of the brain?
Neocortex
The cerebral cortex has by far the most surface area and is the most noticeable part of the human brain. This is the part of the brain that has changed the most over time. It is also called the neocortex.