As human beings, everything we feel, reason and perceive, as well as our ability to move and perform any activity, has an origin 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 functions that each one of them has.

What is the cerebral cortex?

The cerebral cortex refers to the outer layer of the brain. This layer is made up of a thin film of nerve tissue that surrounds the surface of the cerebral hemispheres. Primates have a much more developed cerebral cortex than other animals.

Thanks to the correct functioning of the cerebral cortex, we humans have the capacity to perceive what happens to us and our surroundings, as well as to imagine, think, have the capacity for judgment and decision and, finally, the capacity 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, as it is made up of six layers of cells , each with specific and concrete functions.

Types of brain cortex

Based on both the structural and phylogenetic perspectives of the cerebral cortex, three different classes of the cortex can be distinguished. These are as follows.

1. Arquicorteza

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

2. Paleocortex

Phylogenetically, the paleo-cortex is halfway between the most primary areas of the cerebral cortex and the most evolved ones . This kind of cortex houses the endings of the olfactory pathways, and here we find the olfactory brain of people.

3. Isocortex or neocortex

It is the most recent area of the crust, and the one in charge of the processes of reasoning and abstract thinking .

The layers of the cerebral cortex

As mentioned above, the cerebral cortex is made up of different layers of neural tissue known as grey 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 in comparison with other animal species.

These layers are as follows.

1. Molecular layer

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

Also known as the plexiform layer , it is essentially a synaptic layer formed by a thick network of neural fibers.

2. External granular layer

The second layer that makes up the cerebral cortex is the outer granular layer. It is made up of a large number of small star-shaped and pyramidal cells .

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

3. External pyramidal layer

The outer pyramidal layer is named after the type of cells that make it up: pyramidal cells . These cells direct their axons towards other areas of the cortex and towards other subcortical destinations in the form of projection, association and commissural fibres.

4. Internal granular layer

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

5. Inner pyramid layer, or ganglion layer

This fifth layer involves a large number of medium and large pyramidal cells, as well as starred and Martinotti cells . Its horizontally arranged filaments also form part of the inner 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 striated nuclei. In addition, it also includes pyramidal cells with a triangular or ovoid body

Its areas and functions

In addition to the types of cortex and the layers that form 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 sensitive, motor or association areas.

1. Sensitive areas

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

This same area can also be divided into two different sensitive areas. The primary sensory area, which has direct connections to 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 aim of the different association zones, both primary and secondary, is to create patterns of recognition and behaviour by assimilating sensory information. These sensory areas of the cerebral cortex are

  • Primary somatosensitive area .
  • Primary visual area.
  • Primary olfactory area.
  • Primary hearing area .
  • Primary taste area.

2. Motor area

The areas responsible for the brain mechanisms associated with body movement are located in the anterior portion of both hemispheres, i.e. in the frontal lobe. In the motor area there are the descending motor treatments that start 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 operation:

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

3. Association area

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