Scientists Discover a “New” Fourth (Meningeal) Membrane Surrounding the Brain
Stop the presses, at least the ones for medical, physiology, and neuroscience textbooks! It looks like Science has done it again. It’s discovered something our bodies have but we didn’t know it!
How Life Works (Not Just How It Looks)
As New Scientist reports, the newly discovered layer of the meninges is called the subarachnoid lymphatic-like membrane (SLYM). With a width of only a few cells, the SLYM is now considered to be the fourth layer of the meninges, the connective tissue surrounding the brain that gives it support and protection.
The first layer of the meninges is the thick and tough dura mater which is attached to the inner surface of the skull. The second layer is the fibrous web-like arachnoid mater that sits just below and lines the dura mater separated from it by the subdural space. The third meningeal layer is the thin and very delicate pia mater which covers and is in direct contact with the brain tissue.
Between the arachnoid and pia maters is the subarachnoid space, which is filled with a clear, colorless liquid called the cerebrospinal fluid (CSF). Except for having a lot less protein, the chemical content of CSF is similar to plasma and is constantly being produced and recycled so there are about four to five ounces present in the brain. Propelled mostly by the pulsation of the heart, CSF circulates through the ventricular system within the brain and over its surface.
The SLYM is located within the subarachnoid space separating the CSF within it into inner and outer compartments. The SLYM is so delicate that the standard technique for removing the brain at autopsy causes it to disintegrate and so up until now has been unnoticed. Nuclear scanning of the brains of mice recently allowed for the detection of the SLYM and by changing post-mortem procedures, it has now become microscopically detectable in humans.
A Puzzle for Scientists
Due to the brain’s unique structure, for many years scientists have been puzzled by how it manages certain important physiological functions. The meninges, CSF, and the fluid between the brain cells, the interstitial fluid (ISF), have also been thought to play a role in these functions.
First, in contrast to most of the body, the brain seems to lack a normal lymphatic system to help manage the control of excess fluid and toxic chemicals while providing access for immune cells. Scientists have wondered how the brain compensates for this apparent lack. In the last decade the discovery of the glymphatics (drainage microtubules next to the arterioles in the subarachnoid space) and lymphatic vessels associated with the meninges seems to have at least partially answered this question. Now, it would seem that the SLYM is involved in this function too.
Second, in contrast to most of the body, which only has to deal with the ISF, the brain has two fluid compartments, the ISF and the CSF in the subarachnoid space. Scientists have always wondered if, or to what degree, the fluid in the ISF and CSF communicate. Studies in the last several years show that there is significant communication between the ISF and CSF through the glympathics, other pathways, and now it would seem the SLYM as well.
Third, in contrast to most of the body, the structure of the brain’s capillaries results in it having unique blood-brain and blood-CSF barriers which affects which molecules can pass through. Further analysis shows that the SLYM, which separates the CSF in the inner subarachnoid space from the CSF in the outer subarachnoid space, only allows very small molecules to pass through, thereby excluding most proteins. This means that the SLYM seems to act as yet another barrier within the brain that has to be taken into account when considering neurological function.
So far scientists think that the SLYM seems to be involved in the management of fluid along with various chemicals and molecules within the brain and the prevention of the build-up of toxic metabolic waste products. In addition, the SLYM seems to provide access to immune cells to protect the brain from microbes and toxins.
A better understanding of the microscopic and molecular structure of the SLYM and how it works to keep the brain healthy and functioning properly will afford medical science the ability to better understand brain malfunction and help in the development of more effective treatments.
It is thought that malfunction of the SLYM may be linked to many neurological conditions like Alzheimer’s disease, multiple sclerosis, and delayed healing after traumatic brain injury.
The Question of Causation
One has to wonder from where the SLYM came? After all, it’s been present and working in the brains of all humans since they came into being. But we didn’t even know about it until recently. The answer on offer to the question of causation is likely to be the standard narrative gloss that the SLYM “evolved.”
But such a simplistic knee-jerk response, especially when so little is known about the molecular and microscopic structure of the SLYM and its function within the brain, seems a tad premature. To say this would mean that, a priori, before Science knows anything about how any component of life works, and what it would have taken to build it from the ground up, one must assume to know how it was caused — evolution. This sounds more like ideology than anything else.
That being said, when considering the SLYM (and any other component of life) let’s see how my recent book, co-authored with Steve Laufmann, Your Designed Body, can help you to determine for yourself which of the only two possible explanatory options for causation (materialism or intelligent design) is more likely at work.
In the book we explain that the body consists of trillions of cells working together and that there are four basic types of tissues: epithelial, nerve, muscle, and connective tissue. Connective tissue consists of cells that secrete, and are embedded within, a clear, colorless, gel-like material (ground substance) and the supportive protein fibers crisscrossing within it.
The ground substance and the different types of protein fibers within it make up what is called the extracellular matrix (ECM). Different types of connective tissue, made up of various types of ECMs, provide the different tissues and organs of the body with the specific structural and chemical support they need to live and function properly.
As noted above, the meninges are specialized layers of connective tissue which surround and protect the brain. The dura mater is “thick and tough,” the arachnoid mater is “fibrous and web-like,” and the pia mater is “very thin and delicate.” Scientists are still working on categorizing the qualities of the SLYM.
Like types of connective tissues, each meningeal layer has a different ECM that affords it the ability to perform its specific functions. Our book delves into many of the different types of functions performed by the different tissues and organs of the body. Some of these as they apply to the meninges include protection, waste recycling, and fluid dynamics.
Only Two Possibilities
When it comes to causation, there are only two classes of causal forces; those are material causes and intelligent causes. In addition, one of the main causal hurdles that would have applied for the SLYM (and the other three layers of the meninges) is that there must have been a body plan somewhere to designate how to make, and where to place, each of them.
In other words, there must be information in the body that instructs it about how to make the right types of cells, secreting the right types of ECM, resulting in the four different types of meningeal membranes each with the right specifications, while placing each of them in the right order and position around the brain to provide it with the right amount of support and protection. But from where could this information have come?
Your Designed Body analyzes the causal factors of neo-Darwinism and concludes that neo-Darwinism lacks any power to generate non-trivial innovations, tends to select for death, and is counterintuitive. The increase in understanding of the true complexities of living systems over the last few decades has steadily eroded the plausibility of Darwin’s causal explanations.
As famed Brazilian chemist Marcos Eberlin wrote in his book Foresight, “If Nobel-caliber intelligence was required to figure out how this existing engineering marvel works, what was required to invent it in the first place?” With so many systems in the body, that is indeed the question.
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