MYELNCEPHALON: FUNCTIONS, DEVELOPMENT, DAMAGE - NEUROPSYCHOLOGY - 2025

The myelencephalon is a secondary vesicle of the neural tube, located in the area of ​​the rhomboencephalon. This part of the brain continues until it becomes the medulla oblongata, as well as being part of the central canal. Despite being small in size, this area of ​​the brain contributes several systems and functions.

In addition to being part of the brain structures that we have already seen, the myelencephalon is also partly included in the fourth ventricle, specifically in its lower part. On the other hand, inside we can find the reticular formation, a component of the brain that intervenes in the regulation of several basic functions.

Main subdivisions of the brain of a vertebrate embryo. I, Nrets / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)

The myelencephalon, like the rhombencephalon and most nearby structures, plays a very important role in controlling some of our most basic impulses. For example, it is known to be related to alertness, attention, the sleep-wake cycle, and various instincts and reflexes that have to do with survival.

Source: ruf.rice.edu

In many respects, the myelencephalon is a passing structure between the brain proper and the spinal cord. This can be seen in the functional organization and the shape it presents, both very similar to those of the medulla.

Development

From the neural tube to the myelencephalon

When the fetus is formed inside the womb, it presents an organ known as the neural tube that will later specialize and form most of the brain structures. In one of these specializations it divides to form the hindbrain, inside which we find the rhomboencephalon.

This division between the hind, middle, and forebrain occurs 28 days after conception, so it occurs extremely early. After this moment, the resulting structures continue to divide, and at 5 weeks of embryo development it is possible to differentiate the myelncephalon and other similar components of the brain.

From the myelencephalon to the marrow

As we have already seen, in many ways the myelencephalon acts as a kind of intermediate structure between the brain proper and the spinal cord. The end of this structure becomes the medulla oblongata, and the differentiation between the two can be seen as early as the 20th week of gestation.

Parts and content of the myelencephalon

Together, the myelencephalon and medulla oblongata act as a single structure in the adult brain. Among its components are the following:

- A portion of the fourth ventricle, specifically the lower one.

- The glossopharyngeal nerve (CN IX).

- The vagus nerve (CN X).

- The accessory nerve (CN XI).

- The hypoglossal nerve (CN XII).

- A portion of the vestibulocochlear nerve (CN VIII).

Medulla oblongata or medulla oblongata

The medulla oblongata or medulla oblongata is a part of the brain stem that serves as a connection between the spinal cord and the brain itself. It is the adult version of the myelencephalon and is formed from the rhombencephalon. It is located between the Varolio bridge and the spinal cord.

Features

The medulla oblongata and the myelencephalon are part of the autonomic nervous system, and as such are responsible for regulating a multitude of basic functions related to survival reflexes. In addition, they also play an important role in the development of more complex brain functions, such as attention, alertness or the sleep-wake cycle.

Next we will see some of the most important functions of this brain component.

Breathing

The myelencephalon fulfills one of its most important functions in regulating the respiratory cycle. This brain structure is responsible for constantly monitoring acidification levels in the blood, to prevent them from reaching levels that can be dangerous for the body.

Once the myelencephalon detects that this is happening, its next function is to send an electrical signal to the intercostal muscle tissues through their neural connections.

In this way, the muscles in this area can increase their rate of contraction, in such a way that more oxygen enters the blood and it returns to the appropriate levels for survival.

Cardiovascular control

On the other hand, the myelencephalon is responsible for regulating various components of the activity of the heart and circulatory system. Although it is not the only brain element that participates in the process of pumping blood, it is one of the most important.

On the one hand, the myelencephalon and the medulla oblongata are primarily responsible for exciting the sympathetic nervous system to increase the rate at which the heartbeat occurs. This occurs in situations that require greater physical effort, such as in the presence of imminent danger.

In addition to this, both brain structures are also responsible for the opposite effect: the decrease in heart rate by activating the parasympathetic nervous system. This phenomenon occurs in the opposite situations, and is the main responsible for the state of relaxation and low alertness.

As if this were not enough, the myelencephalon and the medulla oblongata are also the main responsible for regulating blood pressure, using mechanisms such as vasodilation and vasoconstriction for them.

Attention and alert

Due to its control over the two components of the autonomic nervous system, the midbrain has great importance in the regulation of all those processes that have to do with attention, alertness, and even the sleep-wake cycle.

Reflexes

Lastly, the midbrain and the medulla oblongata are directly related to the presence of various reflexes and instincts necessary for survival, which are produced completely unconsciously in certain situations.

Thus, for example, it is known that this cerebral component is the main responsible for phenomena as varied as coughing, sneezing, the swallowing reflex, vomiting, nausea or the masseter reflex. All of them are related in some way to survival, although their relationship with it is not clear in all cases.

Damage to the midbrain

We have already stated that the midbrain and the medulla oblongata fulfill fundamental functions in the regulation of basic processes of the human body, such as respiration or blood circulation. Because of this, any damage to this part of the brain is often fatal, often immediately.

References

1. "Myelencephalon" in: Science Direct. Retrieved on: April 11, 2020 from Science Direct: sciencedirect.com.
2. "Myelencephalon" in: Merriam - Webster Dictionary. Retrieved on: April 11, 2020 from Merriam - Webster Dictionary: merriam-webster.com.
3. "Hindbrain" in: Wikipedia. Retrieved on: April 11, 2020 from Wikipedia: en.wikipedia.org.
4. "Myelencephalon" in: Dictionary. Retrieved on: April 11, 2020 from Dictionary: dictionary.com.
5. "Myelencephalon" in: Wikipedia. Retrieved on: April 11, 2020 from Wikipedia: en.wikipedia.org.