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Trunk of the brain: functions and structures

Trunk of the brain: functions and structures

May 9, 2021

The encephalon is almost always associated with a kind of oval with a rough surface full of folds, but below this cerebral cortex there are a multitude of very important structures.

In fact, if we had to consider the importance of each part of the brain judging them according to how relevant they are to our survival, we would conclude that the most fundamental structure is one that neither has the folded form of the cortex nor is it shaped of oval. Se is about the brainstem, or brainstem, located in the lower part of the brain and in direct contact with the spinal cord.

What is the brainstem?

The brainstem, sometimes called brainstem, is a part of the brain with the shape of a cylinder or elongated cone and is located between the rest of the brain and the spinal cord . That means that the brainstem is aligned with the neuronal fibers that run through the spinal cord under the spinal column; Specifically, it passes in front of the cerebellum.

Therefore, it is the part of the brain that is in an anatomically lower position and close to the neck. In addition, most cranial nerves (or cranial nerves) leave the brainstem.

The brainstem is composed of both parts of white matter and some areas where gray matter predominates, which means that they travel through both connection areas and areas where the bodies of the neurons are concentrated forming control nuclei.

Functions of the brainstem

Although the brainstem is attached to the spinal cord and its shape can be confused with an extension of this, its main function it is not acting as a simple bridge between the brain and the nerves that run through the human body .

The brainstem is the part of the human brain that harbors the most primitive and ancestral functions, and appeared in our evolutionary line in species that did not resemble anything human beings. It's part of what, according to Paul MacLean's theory of 3 brains, It has been called "reptilian brain" , precisely because it has been associated with ancestral physiological processes (although MacLean's ideas are not considered valid, among other things, because they are based on a very simplified vision of the evolution of the human brain.

Thus, the brainstem is responsible for performing the most basic tasks of the nervous system for our survival, those where we can hardly influence voluntarily and that have been automated from millions of years of evolution just so that our misguided decisions or our distractions do not cost us our lives.

Maintaining vital signs

Among the functions in which the brainstem plays a fundamental role are the regulation and maintenance of the heart rate and the automatic control of breathing . That is why the stem of the brain is composed of vital centers that when damaged can cause immediate death.

Other functions of the brainstem somewhat less important but practically as primitive are the control of hiccups, sneezing and coughing, sucking, swallowing, vomiting and sensitivity to pain. It also has a very important role in the regulation of arousal levels . In particular, a network of neurons distributed in part by the brainstem called reticular formation intervenes both in the regulation of the circadian cycle (sleep-wakefulness) and in the maintenance of consciousness.

A bridge of communication with the spinal cord

In addition to all these functions, of course, the brainstem serves to communicate the cranial nerves and the spinal cord with the brain , thus being the communication route between the brain and the rest of the body both in the afferences and in the eferences. This is a more passive role than the previous ones, but equally essential for the survival of the brain and of the whole organism in general.

Parts of the brain stem

The brainstem is composed of three main structures: the mesencephalon, the brainstem bridge and the medulla .


The midbrain is the structure of the brainstem located in a higher position and, therefore, closer to structures located in the upper part, such as the thalamus. Like other parts of the brainstem, it intervenes in functions as primitive as the regulation of the sleep-wake cycle and body temperature, but also plays a role in reacting quickly to visual and auditory stimuli in a reflex manner, as well as in the control of certain movements.

The two basic components of the mesencephalon are structures called tectum Y tegmentum.

Trunk bridge

The trunk bridge , or pons, is located just below the mesencephalon and above the medulla oblongata. The cerebellum is on the posterior side (closest to the nape of the neck). This structure is the part of the trunk of the brain more bulky, and its front side is bent outward as if it were half an egg.

This part of the brain stem intervenes in the control of breathing, in the transition between the phases of sleep and in the regulation of the level of consciousness , among other basic survival processes.

Spinal bulb

The spinal bulb (or marrow oblong) is located in the lower part of the brainstem. Controls all types of automatic processes totally necessary for survival, such as cardiac control or the secretion of gastric substances . In addition, it is the part that communicates with the spinal cord directly.

Also, it is in this part of the brainstem where is the decussation of the pyramids , that is, the point at which the nerve fibers change from hemibody to go from right to left and vice versa (which explains that one half of the body is controlled by the opposite half of the brain).

If you want to know more about the medulla and its parts, this article may interest you: "Spinal bulb: anatomical structure and functions".

Introduction: Neuroanatomy Video Lab - Brain Dissections (May 2021).

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