“The human encephalon has been described as the most complex system in the known universe, and not without reason.”
It is composed of a network of glia, neurons and nerve pathways and is the most important part of the Central Nervous System, but its intricate structure and functioning does not mean that we can not make a classification of the main parts of the brain.
1. Main parts of the brain
In humans, the brain is the part of the Central Nervous System that is located at the end of the spinal cord, inside the skull. It is, in short, the organ through which we can perform the most complex mental operations and have consciousness, that is, sense of self. Precisely for that reason within the brain there are a lot of structures working together at a great speed, a fact that makes the functioning of the brain is, even today, a mystery in many aspects.
To begin to understand what we know about this complex machinery, it is essential to know the parts of the brain, that is, the way in which the structures that compose it can be classified. A good way to classify the different parts of the brain above can be by attending to the different formations that are formed within the head of a human embryo. They are a total of three structures.
It is the upper part of the spinal cord and throughout the development of the fetus will be transformed into structures responsible for performing essential tasks for survival, such as control of heart rate and breathing. It will end up transforming the cerebellum, the brainstem bridge and the medulla oblongata, as we will see.
In human embryos appears just above the rhombencephalon, and will be transformed into the medial part of the brain, which is also responsible for performing many of the basic functions of survival but also acts as a bridge between the other two structures.
Located at the far end of the spinal cord and on the side closest to the face of the embryo, the forebrain is the formation that will be transformed into the parts of the brain that have appeared more recently in our evolutionary line and that, therefore, they have to do with the use of language, planning and the search for creative solutions to new problems. As we will see, the two main structures that the development of the rombencephalon gives way to are the diencephalon and the telencephalon.
2. Parts of the adult brain
Going into more detail, we can stop to see the different components of the brain in fully developed humans. It is in this set of organs that we find all those parts of the brain that define the way of functioning of our mind.
Here we will see, in the first place, the parts of the brain that are generated from the forebrain, and then go to the mesencephalon area and the rhombencephalon, in that order.
The telencephalon is the part of the brain that is easier to see with the naked eye, since it occupies most of the surface of the brain. Its components are the cerebral cortex, the basal ganglia and the limbic system.
2.1.1. Cerebral cortex
The cerebral cortex (or cortex) is the part of the brain that is rough and full of folds. It covers the rest of the brain above, and it is the area in which the necessary information is integrated to carry out the most complex mental processes, since the information that arrives at this region has already been partially processed by other structures of the brain. The cortex is divided into two cerebral hemispheres that are almost symmetrical to the naked eye, although on a microscopic scale they are very different.
In addition, each hemisphere is composed of several lobes of the brain, each of which is more involved in certain mental processes. The lobes of the brain are these:
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
2.1.2. Basal ganglia
The second component of the telencephalon is the set formed by the basal ganglia. These are a group of structures located below the cerebral cortex and distributed symmetrically under each hemisphere. The basal ganglia are the pale globe, the putamen and the caudate nucleus, which are complemented by a region known as the substantia nigra.
The basal ganglia are the parts of the brain that allow us to perform relatively complex and precise movements easily and almost automatically: writing, speaking, changing our facial expressions voluntarily, etc. Therefore, they monitor in a semi-automatic way the way in which we carry out chains of movements that we have practiced before many times until we have mastered them, and at the same time they allow us to learn them well, among other functions.
2.1.3. Limbic system
The limbic system is a set of brain structures whose limits are quite diffuse, since it mixes with many different parts of the brain. Its functions are related to the appearance and regulation of emotions and bodily responses beyond the head that accompany them.
That is why sometimes it is considered “the emotional brain” as opposed to the “rational brain” that would correspond to the areas occupied by the cerebral cortex (and especially the frontal lobe).
However, neither the limbic system nor the cortex can work well independently, and therefore this distinction between rational and emotional areas is very artificial, and more so considering that we are not as rational as it might seem.
The hippocampus is an elongated structure located in the inner part of the temporal lobes, one of the oldest regions of the cerebral cortex, present in the forms of older mammals. Its function is related to the storage and recovery of memories, learning and spatial navigation.
The amygdala is a set of neurons that are grouped on the inner side of the temporal lobe of each of the hemispheres. That is to say, that just like what happens with the hippocampus, it is one of those parts of the brain that are found in duplicate in each human brain, with one in each half (left and right) of the brain.
The cerebral amygdala is part of the limbic system, and is one of the cerebral structures that have more importance when it comes to relating emotional states with situations that we live; that is why it plays a key role in the mental processes related to emotional memory and the learning related to it, which are very important. At the end of the day, knowing which emotions are matched to each type of stimulus or experience makes us adopt an attitude towards them and we opt for possible reactions and not others.
The diencephalon is the second great structure that forms the forebrain, and is located just below the telencephalon, in the depths of the Central Nervous System. The parts of the brain that make up the diencephalon are basically the thalamus and the hypothalamus.
It is the largest part of the diencephalon, and is the nucleus in which all the information that reaches us through the senses is integrated for the first time (with the exception of smell, which reaches the brain directly through the olfactory bulb of each hemisphere). cerebral). The thalamus sends this information to higher areas of the brain, so that it continues to process the information that has begun to be synthesized in it, and is also able to make it possible for the Autonomous Nervous System to react quickly to stimuli that may mean the presence of a danger.
The hypothalamus is located just below the thalamus, and is mainly responsible for making the whole organism is constantly in a state of homeostasis, that is, in balance in all senses: body temperature, levels of hormones in blood, rhythm of the breathing, etc.
In addition, thanks to its ability to cause different glands in the body to secrete hormones, it induces us to more or less high levels of stress and general activation depending on what is happening in other parts of the brain. It is also the structure responsible for the appearance of the state of thirst and hunger.
2.3. Brain stem
The brainstem, or brainstem, is the part of the brain that is most directly connected to the spinal cord, and is also responsible for performing the basic tasks of maintaining vital functions such as involuntary breathing or heart rhythm. It is formed by the parts that evolve from the mesencephalon and the rhombencephalon. Its parts are the following.
The mesencephalon is the part of the brainstem that is just below the diencephalon. It is responsible for communicating the brainstem with the superior structures and vice versa, and also intervenes in the maintenance of automatic processes that allow us to survive. It is divided into the tectum and the tegmentum.
This structure is also known as a Varolium bridge or brainstem bridge. It is located just below the mesencephalon.
2.3.3. Spinal bulb
It is the lower part of the brainstem, and its functions are very similar to those of the other two structures of this part of the brain. In addition, it is the link between the brain and the spinal cord. In the medulla, there is a part known as the decussation of the pyramids, which is where the bundles of nerve fibers of the two hemiframes (the left and right halves of the human body) intersect to pass from one side to the other; This explains why the right hemisphere is responsible for processing information from the left hand while the left hemisphere handles the other, for example.
Next to the medulla oblongata and the protuberance, the cerebellum is the third major structure that evolves from the hindbrain. In addition, the cerebellum and the protuberance are part of a region called metencephalon.
The cerebellum is one of the parts of the brain with a higher concentration of neurons and among its many functions the most studied is the regulation and monitoring of complex movements that require some coordination. It also has a role in maintaining balance when standing and walking.
Other structures of the nervous system related
The different parts of the brain not only work in coordination with each other, but also require the participation of other neuroendorin system surgeons.
These structures and systems, which do not belong in themselves to the brain, are the cerebral nerves (or cranial nerves) and the Autonomic Nervous System (ANS).
The cranial nerves are bundles of axons that leave different points of the lower brain area and go to other parts of the body without going through the spinal cord. Examples of cranial nerves are the trigeminal nerve, the vagus nerve or the olfactory nerve; all of them are of great importance, and in the case of the trigeminal, its incorrect functioning can generate a lot of pain.
Autonomic nervous system
The Autonomic Nervous System is a network of axons, ganglia and organs that regulates the functions that keep us alive, such as digestion, involuntary breathing or heartbeat.
That is why these functions can not be controlled voluntarily; they are too important, and they are fully automated. This network of neurons interacts especially with the parts of the brain that are lower (those of the brain stem), and is divided into sympathetic system, parasympathetic system and enteric system.