Meninges: Anatomy, Parts And Functions In The Brain
The meninges are one of the most important parts that cover the Central Nervous System They surround both the brain and the spinal cord, and fulfill several very important functions for the maintenance of these body structures in good condition.
In this article we will see what the meninges are, what their parts are and what functions they perform.
The first thing that stands out when viewing the meninges without special measuring instruments is that They constitute something like a membrane that surrounds the brain, acting as a kind of external layer that is just below the bones of the skull. Due to this, it is common to think that they are, above all, a protective element, which absorbs blows and reduces the probability that elements introduced into the skull (breaking the bone) cause damage to the brain.
It makes sense that it is like that. Regardless of the high levels of sedentary lifestyle observed in the population, as a general rule human beings are constantly moving.
We walk, run, dance, jump, interact with the environment and with other individuals… all these actions can cause the organs that are part of our body, including those of the nervous system, to, under certain circumstances, run the risk of being damaged
That is why it is necessary to have protection systems that keep everything in its place and block the arrival of possible injuries. Fortunately, our body has different structures that protect our viscera, organs and internal structures. In the case of the nervous system and the brain, it is protected by the skull and the spinal column, along with other structures and elements such as the blood-brain barrier or, in the case at hand, a series of membranes called meninges
The functions of this part of the human anatomy
Let’s imagine that we are on an operating table and we need to make our way to a part of the patient’s brain. After passing through a layer of skin and muscle, we would reach the skull, a bone structure that protects the brain. However, If we go through this bone protection we do not find ourselves directly with the brain, but rather we would find a series of membranes that surround the nervous system. These membranes are called meninges, and they are very important for our survival, to the point where an infection in them can put us in danger of death.
The meninges are a set of protective layers located between the central nervous system and its bony protection, both at the level of the brain and the spinal cord. Specifically, you can find a series of three membranes located one below the other, receiving from outermost to innermost the name of dura mater, arachnoid mater and pia mater Different fluids circulate through them that help keep the brain clean and nourished, being crossed and irrigated by different blood vessels,
Although when we talk about the meninges we mainly think of the membranes that cover the brain, it is important to note that these structures They cover the entire central nervous system and not just the brain also protecting the spinal cord.
The three meninges
As we have indicated previously, we understand the meninges to be a set of three membranes that internally protect the nervous system.
From most external to most internal, they are as follows.
1. Dura mater
In addition to being the outermost meninge, The dura mater is the hardest and most condensed of the three that we have, and it is also the one that is closest to the outside. Partially attached to the skull, this membrane protects the brain and acts as structural support for the entire nervous system by dividing the cranial cavity into different cells.
Most of the large blood vessels of the brain are located in the dura mater, since in addition to protecting them, it allows them to have a space through which to spread out and move from one location to the next. Subsequently, these blood vessels will diversify into different subdivisions as they go deeper into the brain.
2. Arachnoids
Located in an intermediate area between the dura mater and pia mater, the arachnoid is a meninge that receives its name due to its morphological similarity to a spider’s web, that is, its grid configuration. It is the most delicate of the three meninges, a transparent, non-vascularized layer attached to the dura mater.
It is mainly through this meninge and the space between the arachnoid and pia mater that the cerebrospinal fluid circulates. Furthermore, it is in the arachnoid where the end of the life cycle of the cerebrospinal fluid occurs, which is returned to the blood flow through the villi or structures known as arachnoid granulations in contact with the large veins that run through the dura mater.
3. Piamadre
The most internal, flexible meninge and in greater contact with the structures of the nervous system It is the pia mater. In this layer you can find numerous blood vessels that supply the structures of the nervous system.
It is a thin membrane that remains attached and infiltrates the brain fissures and gyri. In the part of the pia mater in contact with the cerebral ventricles we can find the choroid plexuses, structures in which the cerebrospinal fluid that irrigates the nervous system is synthesized and released.
Although the meninges are located one behind the other, the truth is that some intermediate spaces through which cerebrospinal fluid flows There are two intermediate spaces, one between the dura mater and arachnoid mater called the subdural space and the other between the arachnoid mater and pia mater, the subarachnoid space. It should also be mentioned that in the spinal cord we can find one more space, the epidural space. These spaces are the following.
1. Subdural space
Located between the dura mater and the arachnoid mater, the subdural space is a very slight separation between these meninges through which interstitial fluid circulates, which bathes and nourishes the cells of the different structures.
2. Subarachnoid space
Below the arachnoid itself and bringing the arachnoid and pia mater into contact we can find the subarachnoid space, through which the cerebrospinal fluid flows. In some areas of the subarachnoid space the separation between arachnoid and pia mater widens, forming large brain cisterns from which the cerebrospinal fluid is distributed to the rest of the brain.
3. Epidural space
While in the brain the outermost layer of the dura mater is attached to the skull, the same does not happen within the vertebral column: in the spinal cord there is a small separation between the bone and the marrow. This separation is called the epidural space. finding connective tissue and lipids that protect the marrow while we move or change position.
It is in this location that epidural anesthesia is injected in women who are in the process of giving birth, blocking the transmission of nerve impulses between the spinal cord and the lower part of the body.
Functions of the meninges
The existence of the meninges is a great advantage for humans when it comes to maintaining the functioning of the nervous system. This is because these membranes perform a series of functions that allow adaptation which can be summarized in the following.
1. They protect the nervous system from physical injuries and other damage
The meningeal system as a whole is a barrier and cushioning element that prevents or makes it difficult for blows, trauma or injuries to cause serious or irreparable damage to the central nervous system, whether we are talking about the skull or the spinal cord. We must keep in mind that these structures are essential for our survival and at the same time they are relatively delicate, so they need to have several layers of protection that separate them from the outside environment.
They also act as a filter which prevents harmful chemical agents from entering the nervous system. That is, the meninges offer protection that consists of a physical and chemical barrier. However, this barrier can be crossed by certain substances, so there are still vulnerabilities to take into account.
2. Allows the brain environment to remain healthy and stable
It must be taken into account that the brain is a delicate body, very vulnerable to blows or injuries, and that it can even be deformed with some ease. Additionally, it needs to be constantly nourished.
The meninges participate in the genesis and allow the circulation of cerebrospinal fluid, a key element when it comes to eliminating waste generated by the continuous functioning of the brain and maintain intracranial pressure
Other fluids, such as the interstitial, also circulate through this system, allowing the aqueous medium in which the nervous system is located to be stable. In addition, the blood vessels that supply the brain pass through the meninges and are also protected by them. In conclusion, the meninges They act by facilitating the survival and nutrition of the nervous system
3. Keeps the nervous system in place
The presence of the meninges prevents the nervous system from moving too much, fixing the structures that are part of it to a more or less stable situation and maintaining a fixed internal structure, as occurs in the intracranial cavity and its division into cells. This is important, because the consistency of most parts of the nervous system is almost gelatinous and therefore does not have to stay in place. To do this, it needs a coating that is in contact with all its corners, and that does not let it “dance” inside our body.
In short, the meninges act as a belt and give shape and unity to this part of the nervous system as a whole, which allows its normal functioning.
4. Inform the organization of possible problems
Although the perception of stimuli and internal states of the organism occurs thanks to the action of the nervous system, the central nervous system itself does not have receptors that report internal problems, such as nociceptors. However, a set of organs as important as the brain should be highly protected, so that at the slightest sign that something is going wrong, you can react quickly and get away from danger.
Therefore, although the brain does not have receptors for pain or any other sensation related to the physical stimuli applied to it, fortunately this is not the case of the meninges, which do. They have receptors for tension, expansion, pressure and pain and therefore they inform about what happens in that part of the internal environment.
Thus, it is thanks to them that it is possible to detect the existence of neurological problems (regardless of whether these problems cause other perceptual or behavioral problems), headaches being the product of alterations in these membranes.
