Myelencephalon: characteristics, functions and stages of development.

Let's see what this part of the nervous system of embryos looks like.

The myelencephalon is an embryonic vesicle, i.e. it is a part of the nervous system in formation.that is, it is a part of the nervous system in formation. Although it cannot be found in the adult brain as such, it is the precursor of a fundamental structure, since it fulfills several basic functions for our survival.

Below we will take a closer look at what the myelencephalon is, what it corresponds to in the postnatal brain, what stages of neurological development it goes through, and what functions are associated with the structure it eventually becomes.

What is the myelencephalon?

The myelencephalon is a secondary vesicle of the neural tube, that is, the embryonic nervous system in formation, which is located in the area of the rhomboencephalon..

Throughout embryonic development, this part of the brain extends to become the medulla oblongata, also known as the medulla oblongata, also known as the medulla oblongata, also known as the medulla oblongata, and forms part of the central canal. Despite its small size, the myelencephalon becomes a contributing part of several systems and functions.

The myelencephalon is also included in part of the fourth ventricle, specifically in the lower part of it. On the other hand, in its inner part we can find the reticular formation, a part of the brain involved in the regulation of several basic functions.

As with other structures formed from the hindbrain, the myelencephalon, and specifically its mature structure, the medulla oblongata, plays a very important role in the control of the most basic human impulses.The myelencephalon is the structure of the myelinating brain, such as alertness, attention, and the sleep-wake cycle, as well as being behind several reflexes that are fundamental for survival.

In many respects, the myelencephalon is a step structure between what will become the encephalon, i.e., the cerebrum and cerebellum, and the spinal cord. This can be seen from its functional organization and shape, which are very similar to those of the medulla.

Embryological development

As we have already mentioned, the myelencephalon is a secondary vesicle of the embryonic tube, halfway between the primary vesicles of the same tube and the more or less developed structures later during embryological development. That is to say, it is not a part of the adult brainHowever, a part of the adult brain is formed from this structure, namely the medulla oblongata.

There are two phases that can be highlighted in terms of its development

1. First phase: from neural tube to myelencephalon

When the fetus begins to form in the mother's womb, it presents a structure that will be the precursor of the nervous system: the neural tube. This tube will become more specialized as the weeks go by.The neural tube will become more specialized as the weeks go by, forming more complex neurological structures, such as the mature brain and nerves.

However, before the neural tube becomes the postnatal nervous system as we know it, it has to be segmented into different parts:

The first three parts are what are known as the primary vesicles, which form at about three weeks after conception: the forebrain, midbrain and hindbrain..

The primary vesicles then segment, forming the secondary vesicles. The forebrain segments into two parts, the telencephalon and the diencephalon, and the hindbrain divides into the metencephalon and the myelencephalon. This part of neurological development occurs in the fifth week.

2. Second phase: from myelencephalon to medulla

As we have already mentioned, the myelencephalon is a structure that could be situated halfway between the brain proper and the medulla. halfway between the brain proper and the spinal cord.. This develops into the medulla oblongata, which can be clearly differentiated from the rest of the brain and the spinal cord after the 20th week of gestation.

Parts and contents of the myelencephalon

Although the myelencephalon is an embryonic structure, its adult version, the medulla oblongata or medulla oblongata, can be found in the brain stem, can be found in the brain stem, serving as a connection between the spinal cord and the encephalon.being located at the point of Varolio. We can see that this structure is the apparent origin or contains part of the following components:

• The lower part of the fourth ventricle.
• The glossopharyngeal nerve (IX cranial nerve).
• The vagus nerve (X cranial nerve).
• The accessory nerve (XI cranial nerve).
• The hypoglossal nerve (XII cranial nerve).
• A portion of the vestibulocochlear nerve (VIII cranial nerve).

Functions

As a precursor of the medulla oblongata, we could consider the myelencephalon as part of the autonomic nervous system. part of the autonomic nervous system. The medulla oblongata is responsible for regulating a multitude of basic functions related to survival reflexes. In addition, it is also involved in more complex brain functions, such as attention, alertness or the sleep-wake cycle. These are explained in more detail below.

1. Respiration

The myelencephalon is involved in the regulation of the respiratory cycle.. The medulla oblongata constantly monitors the levels of acidification in the blood, preventing them from reaching levels that imply organic damage.

Once the medulla oblongata detects that this is occurring, it sends nerve signals to the intercostal muscle tissues, i.e. the muscles between the ribs, activating them for respiratory movements.

In this way these muscles can increase their rate of contractionThis allows more oxygen to enter the blood and the blood to reach the right pH levels so that the organism is not damaged.

2. Cardiovascular control

In addition to the respiratory function, the medulla oblongata is responsible for regulating several components of cardiac activity and, consequently, of the circulatory system.. Although it is not the only structure responsible for regulating the activity of the heart, it is one of the most important.

The medulla oblongata is responsible for exciting the sympathetic nervous system to increase the heart rate. This is especially important for those situations in which a greater physical effort is required, such as when we do sports or when we are in a threatening situation, to facilitate the activation of fight or flight responses.

But, in addition, it is responsible for producing the opposite effect, ie, to lower the heart rate by activating the parasympathetic nervous system.. As might be expected, this function will be necessary in opposite situations, such as relaxation or states of low alertness.

In addition to increasing and decreasing the heart rate, the medulla oblongata regulates Blood Pressure by vasodilation and vasoconstriction mechanisms.

3. Alertness and reflexes

Due to the function of the medulla oblongata on the sympathetic and parasympathetic systems, the development of the midbrain is of utmost importance for the regulation of all processes involved in attention, alertness and, as mentioned above, the sleep-wake cycle.

Finally, the adult structure of the midbrain is directly related to the realization of several reflexes and instincts that are fundamental for survival.which are produced automatically and unconsciously in the presence of various stimuli. Based on research, the medulla oblongata is known to be the main brain component behind partially involuntary behaviors, such as coughing, sneezing, the swallowing reflex, vomiting and gagging, or the maseterine reflex.

Bibliographic references:

• Carlson, N.R. (2014). Behavioral Physiology (11th Edition). Madrid: Pearson Educación.
• Kandel, E.R.; Schwartz, J.H. & Jessell, T.M.. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.