Meninges: anatomy, parts and functions in the brain

The meninges are one of the most important parts that cover the Central Nervous System. They involve both the brain and the spinal cord, and fulfill several very important functions for the maintenance of these structures in the body in good condition.

In this article we will see what the meninges are, what their parts are and what functions they fulfill.

• Related article: "Parts of the Nervous System: anatomical structures and functions"

What are the meninges?

The first thing that jumps 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 outer layer that is just below the bones of the skull. Due to this, it is usual to think that they are, above all, a protective element, which provides shock absorption and reduces the likelihood that elements inserted into the skull (breaking the bone) will damage the skull brain.

It makes sense that this is so. 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 provoke that under certain circumstances the organs that are part of our body, including those of the system highly strung, risk being harmed.

That is why it is necessary the presence of protection systems that keep everything in place and that block the arrival of possible injuries. Fortunately, our body has different structures that allow us to protect our viscera, organs and internal structures. In the case of the nervous system and brain, this is protected by the skull and 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

Imagine that we are on an operating table and we need to work our way to a part of the patient's brain. After crossing 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 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 mortal danger.

The meninges are a set of protective layers located between the central nervous system and its bone 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 the outermost to the 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 think fundamentally about the membranes that cover the brain, it is important to note that these structures 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 meninges as a set of three membranes that internally protect the nervous system.

From outermost to innermost, they are as follows.

1. Dura mater

In addition to being the outermost meninx, the dura mater is the hardest and most condensed of the three of which 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 a structural support for the entire nervous system by dividing the cranial cavity into different cells.

In the dura are most of the large blood vessels of the brain, since in addition to protecting them, it allows them to have a space through which to distribute themselves and move from one location to the next. Later, these blood vessels will diversify into different subdivisions as they go deeper into the brain.

• To know more about this layer of the meninges, you can visit this article: "Dura mater (brain): anatomy and functions"

2. Arachnoid

Located in an intermediate zone between dura mater and pia mater, the arachnoid is a meninx 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 and non-vascularized layer attached to the dura mater.

It is mainly through this meninx and the space between the arachnoid and pia mater where the cerebrospinal fluid circulates. In addition, it is in the arachnoid where the end of the life cycle of the cerebrospinal fluid, 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. Pia mater

The meninx more internal, flexible and in greater contact with the structures of the nervous system It is the pia mater. In this layer can be found numerous blood vessels that supply the structures of the nervous system.

It is a thin membrane that remains attached and infiltrates through the cerebral fissures and convolutions. In the part of the pia mater in contact with the cerebral ventricles we can find the plexuses choroids, structures in which the cerebrospinal fluid that supplies the system is synthesized and released highly strung.

Spaces between the meninges

Although the meninges are located one behind the other, the truth is that some interspaces through which cerebrospinal fluid flows. There are two intermediate spaces, one between the dura mater and arachnoid called the subdural space and the other between the arachnoid and pia mater, the subarachnoid. It should also be mentioned that in the spinal cord we can find one more space, the epidural space. These spaces are as follows.

1. Subdural space

Located between the dura and arachnoids, 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 by putting the arachnoid and pia mater in 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 cerebrospinal fluid is distributed to the rest of the brain.

3. Epidural space

While in the brain the outermost layer of the dura is attached to the skull, within the The same is not the case: in the spinal cord there is a small gap between bone and marrow. This separation is what is called the epidural space, finding in it connective tissue and lipids that protect the marrow while we move or change position.

It is at 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 injury and other damage

The meningeal system as a whole is a barrier and shock absorbing element that prevents or hinders blows, trauma or injuries cause serious or irreparable damage to the central nervous system, let's be talking about the skull or the spinal cord. We must bear 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 environment Exterior.

They also act as a filter that prevents harmful chemicals from entering the nervous system. In other words, the meninges offer protection that consists of a physical and at the same time chemical barrier. However, this barrier can be crossed by certain substances, so there are still vulnerabilities to be taken 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. Also, you need to be constantly nourished.

The meninges participate in the genesis and allow the circulation of cerebrospinal fluid, a key element in eliminating the waste generated by the continuous brain function and maintain intracranial pressure.

Other liquids, 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, I also feel protected by them. In conclusion, the meninges act 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 causing a fixed internal structure to be maintained, 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. For 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 girdle and give shape and unity to the whole of this part of the nervous system, which allows its normal functioning.

4. Inform the body of possible problems

Although the perception of stimuli and internal states of the organism is given thanks to the action of the nervous system, the Its own central nervous system does not itself have receptors that report internal problems, such as nociceptors. However, a set of organs as important as the brain should be very protected, so that at the slightest sign that something is 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 physical stimuli applied on it, fortunately this is not the case of the meninges, which Yes possess tension, expansion, pressure and pain receptors and therefore they report on what happens in that part of the internal environment.

Thus, it is thanks to them that it is possible to capture the existence of neurological problems (regardless of the fact that said problems cause other perceptual or behavioral problems), headaches being the product of alterations in these membranes.

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