Cerebral cortex: its layers, areas and functions

This is the most visible and iconic part of the brain, being full of folds. How does it work?

As human beings, everything we feel, reason and perceive, as well as our ability to move and perform any activity, originates in our brain.

Throughout this article we will talk about the cerebral cortex, as well as its layers and the different structures that compose it. and the different structures that compose it and the functions that have each one of them.

What is the cerebral cortex?

The cerebral cortex refers to the outer layer of the brain. This layer is formed by thin film of nervous tissue that surrounds the surface of the cerebral hemispheres, being the primates who enjoy a much more developed cerebral cortex than the rest of animals.

Thanks to the correct functioning of the cerebral cortex, we humans have the ability to perceive what happens and surrounds us, as well as to imagine, think, have the capacity to make judgments and decisions and, finally, the ability to understand and produce language.

Although, as explained above, the cerebral cortex is a thin layer of neurons and neural connections, it is not homogeneous, since it is made up of six layers of cells, each of which has a different shape. is made up of six layers of cellsand each one of them has specific and concrete functions.

Types of brain cortex

If we base ourselves on both the structural and phylogenetic perspective of the cerebral cortex, three different classes of the cerebral cortex can be differentiated. These are as follows.

1. Archicortex

Evolutionarily speaking, it is the oldest part of the cerebral cortex. Formed by the hippocampus, the archicortex is in charge of those automatic responses and physiological mechanisms responsible for survival. automatic responses and physiological mechanisms responsible for survival..

2. Paleocortex

Phylogenetically, the paleocortex is midway between the more primary areas of the between the most primitive areas of the cerebral cortex and the most evolved ones.. This kind of cortex harbors the endings of the olfactory pathways, and the olfactory brain of humans is found here.

3. Isocortex or neocortex

This is the most recent area of the cortex, and is responsible for the processes of reasoning and abstract thinking. processes of reasoning and abstract thought.. These regions of the central nervous system receive input from a wide variety of structures, and integrate this information to give way to general concepts.

The layers of the cerebral cortex

As mentioned above, the cerebral cortex is made up of different layers of neural tissue known as gray matter. Each of these layers has a different functional specialization and has originated at a different time in human evolution.

This means that, throughout our evolution and development as human beings, these layers have been increasing in quantity, which has implied a powerful development of our cognitive and intellectual capacities. development of our cognitive and intellectual capacities compared to other animal species. compared to other animal species.

These layers are the following.

Molecular layer

The molecular layer is the outermost, and therefore the most recent in origin, of all the layers of the cerebral cortex.

Also known as the plexiform layerIt is essentially a synaptic layer formed by a thick network of neuronal fibers.

2. External granular layer

The second layer that makes up the cerebral cortex is the external granular layer. This is formed by a large number of small stellate cells. large number of small stellate and pyramidal cells..

The axons of this layer infiltrate the molecular layer entering into more submerged areas of the cerebral cortex, coupling with different areas of the cortex.

3. External pyramidal layer

The external pyramidal layer is named after the type of cells that compose it: pyramidal cells.. These cells direct their axons to other areas of the cortex and to other subcortical destinations in the form of projection, association and commissural fibers.

4. Inner granular layer

This layer consists essentially of a compact mass of stellate cells, most of which receive afferents from the area of the thalamus. These horizontally arranged fibers are known as Baillarger's outer band..

5. Inner pyramidal layer, or ganglionic layer

This fifth layer contains a large number of medium and large pyramidal cells, as well as stellate and Martinot cells. stellate and Martinotti cells. Its horizontally arranged filaments also form part of the internal Baillarger band.

6. Multiform or polymorphic layer

The last of these layers is formed by fusiform cells which derive information to the cortex, thalamus and striate nuclei. In addition, it also includes pyramidal cells of triangular or ovoid body.

Its areas and functions

In addition to the types of cortex and the layers that comprise it, the cerebral cortex can be divided according to its different functional areas. That is, according to the functions or tasks carried out in each of these areas.

Taking into account this classification, the cerebral cortex can be divided into sensory, motor or association areas.

Sensitive areas

The sensitive area receives sensory information from specific nuclei of the thalamus. This information is of a sensitive naturewhich means that it transports the information perceived by the different senses: sight, hearing, smell, touch, taste...

This same area can also be divided into two different sensory areas. The primary sensory area, which has direct connections with the peripheral sensory receptors; and the secondary sensory and association area, which receives sensory information from both the primary association area and the lower areas of the brain.

The purpose of the different areas of association, both primary and secondary, is to to create patterns of recognition and behavior by assimilating sensory information. These sensory areas of the cerebral cortex are:

• Primary somatosensory area..
• Primary visual area.
• Primary olfactory area.
• Primary auditory area.
• Primary gustatory area.

2. Motor area

The areas in charge of the cerebral mechanisms associated with body movement are located in the anterior portion of both hemispheres, that is, in the frontal lobe. The motor area is the origin of the descending motor tracts that depart from the cerebral cortex towards the motor neurons of the trunk and the spinal cord.

Within this region we find two essential areas for our functioning:

• Primary motor area.
• Broca's language area.

3. Association area

Finally, the association areas are those that make possible the existence of the most complex and abstract mental functions. more complex and abstract mental functions, such as memory and such as the mechanisms of memory and cognition, the mastery of emotions, the ability to reason, and the will. In addition, they also influence the development of personality and intelligence.

Bibliographic references:

• Horton, J.C.; Adams, D.L. (2005). The cortical column: a structure without a function. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 360(1456): pp. 837 - 862.
• Moerel M, De Martino F, Formisano E (2006). An anatomical and functional topography of human auditory cortical areas. Front. Neurosci. 8(225): 225.
• Noback, C.R.; Strominger N.L.; Demarest, R.J.; Ruggiero, D.A. (2005). The Human Nervous System: Structure and Function (Sixth ed.). Totowa, NJ: Humana Press. ISBN 1-59259-730-0.
• Zuluaga, J.A. (2001). Neurodesarrollo y estimulación. Madrid: Médica Panamericana.