The human brain 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 cannot 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 thanks to which we can carry out the most complex mental operations and have consciousness, that is, a sense of self. Precisely because of this, inside the brain there is a large number of structures working together at great speed, a fact that makes the functioning of the brain a mystery in many of its aspects even today.

To begin to understand what we know about this complex machinery, it is indispensable 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 can be by looking at the different formations that are formed inside the head of a human embryo. They are a total of three structures .

1.1. Rhombicephalus

It is the upper part of the spinal cord and throughout the development of the fetus will be transformed into the structures responsible for performing tasks indispensable for survival , such as controlling heart rate and breathing. It will end up transforming into the cerebellum, the trunk-brain bridge and the spinal cord, as we shall see.

1.2. Midbrain

In human embryos, it appears just above the rhombic brain, and will gradually transform into the medial part of the brain , which is also responsible for carrying out a large part of the basic survival functions but which also acts as a bridge between the other two structures.

1.3. Prosencephalon

Located at the far end of the spinal cord and on the side closest to the face of the embryo, the prosencephalon is the formation that will be transformed into the parts of the brain that have appeared most recently in our evolutionary line and that, therefore, 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 rhombo-cephalon gives way to are the diencephalon and the telencephalon.

2.The parts of the adult brain

Going into more detail, we can stop and look at the different components of the brain in fully developed human beings. It is in this set of organs that we find all those parts of the brain that define the way our mind works.

Here we will see, first, the parts of the brain that are generated from the prosencephalon, and then move on to the midbrain area and the rhombo-brain, in that order.

2.1. Telencephalon

The telencephalon is the part of the brain that is easiest to see with the naked eye, as it occupies most of the brain’s surface area. Its components are the cerebral cortex, the basal ganglia and the limbic system .

2.1.1. Cerebral cortex

The cerebral cortex is the part of the brain that is rough and full of folds . It covers the rest of the brain, and is the area in which the information necessary to carry out the most complex mental processes is integrated, since the information that reaches this region has already been partially processed by other structures of the brain. The cortex is divided into two brain 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 brain lobes , each of which is more involved in certain mental processes. These are the lobes of the brain:

  • Frontal lobe
  • Parietal lobe
  • Occipital lobe
  • Temporal lobe
  • Insula
  • You can read more about it in this article on brain lobes.

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 of the hemispheres. The basal ganglia are the globus pallidus, 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 make relatively complex and precise movements easily and almost automatically: writing, speaking, modifying our facial expressions voluntarily , etc. Therefore, they monitor in a semi-automatic way the way in which we perform chains of movements that we have already practiced many times before until we master them, and at the same time they allow us to learn them well, among other functions.

  • To read more about this set of brain structures, you can visit the article dedicated to the basal ganglia.

2.1.3. Limbic system

The limbic system is a set of encephalic structures whose boundaries are rather diffuse , as it mixes with many different parts of the brain. Its functions are related to the appearance and regulation of emotions and the bodily responses beyond the head that accompany them. That is why it is sometimes 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 function well independently , and therefore this distinction between rational and emotional zones is very artificial, especially considering that we are not as rational as it might seem.

If you are interested in knowing more about this part of the brain, you can access this article on the limbic system .

2.1.4. Hippocampus

The hippocampus is an elongated structure located on the inside of the temporal lobes, one of the oldest regions of the cerebral cortex, present in the oldest mammalian forms. Its function is related to the storage and retrieval of memories, learning and spatial navigation.

  • You can read more about this part of the brain in this article dedicated to the hippocampus.

2.1.5. Amygdala

The cerebral amygdala is a set of neurons that are grouped together on the inner side of the temporal lobe of each of the hemispheres. That is, like the hippocampus, it is one of those parts of the brain that are found in duplicate in every 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 brain structures that are most important when it comes to relating emotional states to situations we live in; that is why it plays a key role in the mental processes related to emotional memory and the learning linked to it, which are very important. At the end of the day, knowing with which emotions each type of stimulus or experience is paired with makes us adopt an attitude towards them and decide on some possible reactions and not others.

  • You can read more about the cerebral amygdala in this article.

2.2. Diencephalon

The diencephalon is the second major structure forming the prosencephalon, and is located just below the telencephalon , deep in the Central Nervous System. The parts of the brain that make up the diencephalon are basically the thalamus and hypothalamus.

2.2.1. Thalamus

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 in each brain hemisphere). The thalamus sends this information to higher areas of the brain, so that the information that has begun to be synthesized in it can continue to be processed there, and it is also capable of making it possible for the Autonomous Nervous System to react quickly to stimuli that may signify the presence of danger.

  • To read more about this part of the brain you can read this article about the thalamus

2.2.2. Hypothalamus

The hypothalamus is located just below the thalamus, and is mainly responsible for ensuring that the whole organism is constantly in a state of homeostasis , that is, in balance in all senses: body temperature, levels of hormones in the blood, rhythm of breathing, etc.

In addition, thanks to its ability to make different glands in the body secrete hormones, it induces us to more or less high states 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.

  • You can read more about the hypothalamus in this article

2.3. Brain stem

The brain stem is the part of the brain that is most directly connected to the spinal cord , and it also performs the basic tasks of maintaining vital functions such as involuntary breathing or heart rate. It is made up of the parts that evolve from the midbrain and the hindbrain. Its parts are as follows.

2.3.1. Midbrain

The midbrain is the part of the brain stem that lies just below the diencephalon . It is in charge of communicating the brain stem with the upper 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.

2.3.2. Protuberance

This structure is also known as the Varolio bridge or truncated-brain bridge . It is located just below the midbrain.

2.3.3. Spinal cord

It is the lower part of the brain stem , and its functions are very similar to those of the other two structures in this part of the brain. It is also the link between the brain and the spinal cord. In the spinal cord is a part known as the decustation of the pyramids , which is where the bundles of nerve fibers from the two hemicamps (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 one is responsible for the other, for example.

  • If you are interested in reading more about the brain stem, you can read this article

2.4. Cerebellum

Along with the spinal bulb and the protrusion, the cerebellum is the third large structure that evolves from the rhomboid . In addition, the cerebellum and the protrusion are part of a region called the metencephalon.

The cerebellum is one of the parts of the brain with the highest concentration of neurons and among its many functions the most studied is the regulation and monitoring of complex movements that require a certain amount of coordination. It also has a role in maintaining balance when standing and walking.

  • If you are interested in knowing more about the cerebellum, you can visit this article

Other related nervous system structures

The different parts of the brain not only work in coordination with each other , but they also need the participation of other ciruits of the neuroendorine system.

These structures and systems, which do not belong to the brain itself, are the brain nerves (or cranial nerves) and the Autonomous Nervous System (ANS).

Cranial Pairs

Cranial pairs are bundles of axons that come from different points in the lower brain and go to other parts of the body without passing through the spinal cord . This is what distinguishes them from the rest of the nerves, which do not come out of the different parts of the brain but from various parts of the spinal cord.

Examples of the cranial pairs 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, their incorrect functioning can generate a lot of pain.

You can read more about these brain nerves in this article.

Autonomous Nervous System

The Autonomous Nervous System is a network of axons, ganglia and organs that is responsible for regulating the functions that keep us alive , such as digestion, involuntary breathing or heartbeat. This is why these functions cannot be controlled voluntarily; they are too important, and are totally automated.

This network of neurons interacts especially with the lower parts of the brain (those in the brainstem), and is divided into the sympathetic, parasympathetic and enteric systems.

Through these communication channels, parts of the body are controlled that, because they are at the base of the survival of the tissues and cells that make up the body, cannot depend on voluntary decisions or care management. This means that in addition to being automated processes, even if a person wants to, they cannot be intervened on or stopped, since this could lead to immediate death. You can read more about it in this article.

Other related articles:

  • Neuron Types: Characteristics and Functions
  • What are neuron axons?

Bibliographic references:

  • Bradford, H.F. (1988). Fundamentals of Neurochemistry. Labor.
  • Hammond. (2001). Cellular and Molecular Neurobiology (with CD-ROM). Academic Press.
  • Kalat, J.W. (2004). Biological Psychology. Thomsomparaninfo.
  • Morgado, I. (coordinator) (2005). Psychobiology: From genes to cognition and behavior. Ariel Neuroscience.
  • Zuluaga, J. A. (2001). Neurodevelopment and stimulation. Madrid: Médica Panamericana.