The meninges are one of the most important parts that give coverage to the Central Nervous System . They envelop both the brain and the spinal cord, and fulfil 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, what their parts are and what functions they perform.

What are meninges?

Regardless of the high levels of sedentariness in the population, as a rule we humans are moving around all the time.

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, run the risk of being damaged .

That is why it is necessary to have protective 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, it is protected by the skull and the spine, together with other structures and elements such as the blood-brain barrier or, in the case in question, a series of membranes known as the meninges .

The functions of this part of the human anatomy

Let’s imagine we’re on an operating table and 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, if we go through this bone protection we do not directly meet the brain , but we would find a series of membranes that surround the nervous system. These membranes are called the meninges, and are very important for our survival, to the extent that 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 bone protection , both at the level of the brain and the spinal cord. Specifically, there is a series of three membranes located one underneath the other, receiving the name of dura mater, arachnoid and pia mater from the most external to the most internal. Different fluids circulate through them that contribute to keeping 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 whole of the central nervous system and not just the brain , also protecting the spinal cord.

The three meninges

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

From more external to more internal, they are the following.

1. Duramadre

In addition to being the outermost meninx, the dura mater is the hardest and most condensed of the three available, and is also the one closest to the outside. Partly attached to the skull, this membrane protects the brain and acts as a structural support for the whole nervous system by dividing the cranial cavity into different cells.

In the dura mater 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 they can be distributed and pass 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: "Duramadre (brain): anatomy and functions"

2. Arachnoids

Located in an intermediate zone between the dura mater and the pia mater, the arachnoid is a meninx that receives its name due to its morphological similarity to the web of a spider , 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 that the cerebrospinal fluid circulates. In addition, 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. Mother Earth

The innermost, most flexible meninx, in greatest contact with the structures of the nervous system 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 stuck and infiltrates through the brain’s clefts 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 after the other, the truth is that some intermediate spaces can be found between them 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 by bringing arachnoids 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 arachnoids and pia mater widens, forming large cerebral 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 is not true within the spine: in the spinal cord there is a small gap between the bone and the cord. This separation is called the epidural space, and contains connective tissue and lipids that protect the spinal cord 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 marrow and the lower body.

Functions of the meninges

The existence of the meninges is a great advantage for the human being 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 summarised as follows.

1. Protect the nervous system from physical injury and other damage

The meningeal system as a whole is a barrier and a cushioning element that prevents or makes it difficult for blows, trauma or injury to cause serious or irreparable damage to the central nervous system, 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 external environment.

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 both a physical and a 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 should be borne in mind that the brain is a delicate body, very vulnerable to blows or injuries, and can even be deformed with some ease. 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 function and maintaining the intracranial pressure .

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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 irrigate the brain pass through the meninges, and I feel protected by these as well. 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 making it maintain 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 be kept 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 this part of the nervous system as a whole, allowing it to function normally.

4. Informs the body of possible problems

Despite the fact that 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 any receptors that report internal problems, such as nociceptors. However, such an important set of organs as the brain should be highly 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 the physical stimuli applied to it, fortunately this is not the case with the meninges, which do possess receptors for tension, expansion, pressure and pain and therefore 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 perceptive or behavioural problems), with headaches being the product of alterations in these membranes.

Bibliographic references:

  • Barton, R.A.; Harvey, P.H. (2000). Mosaic evolution of brain structure in mammals. Nature. 405 (6790): 1055–1058.
  • Kandel, E.R.; Schwartz, J.H.; Jessell, T.M. (2001). Principles of Neuroscience. Madrid: McGraw Hill.
  • Kumar, V. (2015). Robbins and Cotran Pathologic Mechanisms of Disease. Philadelphia: Elsevier Saunders.
  • Martínez, F.; Mañana, G.; Panuncio, A. and Laza, S. (2008). Anatomo-clinical review of the meninges and intracranial spaces with special reference to chronic subdural hematoma. Mexican Journal of Neuroscience: 9 (1): 17-60.
  • Ratey, J. J. (2003). Brain: instruction manual. Madrid: Mondadori.
  • Simmons P.J., Young, D. (1999). Nerve cells and animal behaviour. Cambridge University Press.
  • Tortora, J.G. (2002). Principles of anatomy and physiology. 9th edition. Mexico City, Oxford, USA, pp. 418-420.