Meninges: anatomy, parts and functions in the brain.

A series of membranes that protect the brain and spinal cord and ensure their function.

The meninges are one of the most important parts that cover the central nervous system.. They envelop both the brain and the spinal cord, and fulfill several very important functions for the maintenance in good condition of these structures of the organism.

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

What are the meninges?

The first thing that jumps to the sight on having seen the meninges without special instruments of measurement is that they constitute something like a membrane that envelops the brain, acting as a sort of a layeracting as a kind of outer layer just below the bones of the skull. Because of this, it is common to think of them primarily as a protective element, providing shock absorption and reducing the likelihood of damage to the brain from elements introduced into the skull (breaking the bone).

It makes sense. Regardless of the high levels of sedentary lifestyles observed in the population, as a general rule we humans are constantly moving.

We walk, run, dance, jump, interact with the environment and with other individuals... all these actions can cause that under certain circumstances the organs that are part of our organism, including those of the nervous system, are at risk of being damaged, run the risk of being damaged..

That is why it is necessary the presence of protection systems that keep everything in place and block the arrival of possible injuries. Fortunately, our organism has different structures that allow us to protect our viscera, organs and internal structures. In the case of the nervous system and the brain, this is protected by the skull and the spinal column, together with other structures and elements such as the blood-brain barrier or, in this case, a series of membranes called meninges, a series of membranes known as the meninges..

Functions of this part of the human anatomy

Let us 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, the bony structure that protects the brain. However, However, if we pass through this bony protection we do not directly encounter the brain.However, if we pass through this bony protection we would not directly meet the brain, but we would find a series of membranes surrounding the nervous system. These membranes are called meninges, and they are very important for our survival, to the point that an infection in these membranes can put us in danger of death.

The meninges are a set of protective layers located between the located between the central nervous system and its bony protection.both at the level of the brain and the spinal cord. Specifically, a series of three membranes can be found located one below the other, receiving from the outermost to the innermost the name of dura mater, arachnoid and pia mater.. Through them circulate different fluids that contribute to keep the brain clean and nourished, being crossed and irrigated by different Blood vessels,

Although when we speak of the meninges we think mainly of the membranes that cover the brain, it is important to point out that these structures cover the entire central nervous system. the whole of the central nervous system and not only the encephalon.The three meninges also protect the spinal cord.

The three meninges

As we have indicated above, we understand as meninges a set of three membranes that internally protect the nervous system.

From the outermost to the innermost, they are as follows.

1. Dura mater

In addition to being the outermost meningeal membrane, the dura mater is the hardest, the dura mater is the hardest and most condensed of the three membranes and it is also the one that is closest to the exterior. Partly attached to the skull, this membrane protects the brain and provides structural support to the entire nervous system by dividing the cranial cavity into different cells.

The dura mater contains most of the large blood vessels of the brain.In addition to protecting them, it allows them to have a space through which they can be distributed and pass from one location to the next. Subsequently, these blood vessels will diversify into different subdivisions as they go deeper into the brain.

• To learn 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 the dura mater and the pia mater, the arachnoid is a meningeal layer that receives its name due to its morphological resemblance to a spider's web, i.e. its web-like configuration.i.e., its lattice-like 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 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 bloodstream 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 innermost, most flexible meninx in greater contact with the structures of the nervous system is the pia mater. is the pia mater. Numerous blood vessels supplying the structures of the nervous system can be found in this layer.

It is a thin membrane that remains attached to and infiltrates the cerebral fissures and convolutions. 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.

Spaces between the meninges

Although the meninges are located one behind the other, it is true that there may be some intermediate spaces between them through which cerebrospinal fluid flows. intermediate spaces through which the cerebrospinal fluid flows.. There are two intermediate spaces, one between the dura mater and the arachnoid called the subdural space and the other between the arachnoid and the 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 the following.

1. Subdural space

Located between the dura mater and the arachnoid, 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 in contact with the arachnoid and pia mater 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 cerebral cisterns from which the cerebrospinal fluid 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 mater is attached to the skull, this is not the case inside the spinal column: in the spinal cord there is a small gap between the bone and the cord. This gap is called the epidural space, It contains connective tissue and lipids that protect the spinal cord as we move or change our position. while we move or change position.

It is in this location where the epidural anesthesia is injected in women who are in the process of in women who are in the process of giving birth, blocking the transmission of nerve impulses between the medulla and the lower part of the body.

Functions of the meninges

The existence of the meninges is a great advantage for humans in maintaining the functioning of the nervous system. This is because these membranes perform a series of functions that allow the adaptation of the nervous system.These can be summarized as follows.

1. They protect the nervous system from physical injury and other damage.

The meningeal system as a whole is a barrier and buffering element that prevents or hinders blows, trauma or injury from causing 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 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 that prevents harmful chemical agents from entering the nervous system. In other words, the meninges offer a protection consisting of a physical and chemical barrier. However, this barrier can be penetrated by certain substances, so there are still vulnerabilities to be taken into account.

2. It 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 shocks or injuries, and can even be deformed quite easily. In addition, it needs 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 functioning and in maintaining intracranial pressure.

Other fluids, such as interstitial fluid, also circulate through this system, allowing the aqueous medium in which the nervous system is located to remain stable. In addition, the blood vessels that irrigate the brain pass through the meninges and are also protected by the meninges. In conclusion, the meninges 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 and by maintaining a fixed internal structure, as occurs in the intracranial cavity.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 lining that is in contact with all its nooks and crannies, and that does not let it "dance" inside our body.

In short, the meninges act as a girdle and give shape and unity to this part of the nervous system as a whole, allowing it to function normally.

4. Informs the organism 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 inform of internal problems, such as nociceptors. However, such an important set of organs as the brain should be very well protected, so that at the slightest sign that something is wrong, it can react quickly and move away from danger.

Therefore, although the brain does not have receptors for pain or any other sensation related to physical stimuli applied to it, fortunately this is not the case with the meninges, which do have receptors for tension, expansion, expansion, relaxation and relaxation. do have receptors for tension, expansion, pressure and pain. and therefore inform about what is happening 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.

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