Myelencephalon: characteristics, functions and stages of development

The myelencephalon is an embryonic vesicleIn other words, it is part of the developing nervous system. Although it cannot be found in the adult brain as such, it is the precursor of a fundamental structure, as it performs several basic functions for our survival.

Below, we’ll take a closer look at what the myelencephalon is, what the postnatal brain is like, what stages of neurodevelopment it goes through, and what functions are associated with the structure it ultimately becomes.

    What is the myelencephalon

    The myelencephalon is a secondary vesicle of the neural tube, i.e. the developing embryonic nervous system, located in the rhomboencephalon area.

    Throughout embryonic development, this part of the brain extends into the medulla oblongata, also known as the medulla oblongata, in addition to being part of the central canal. Despite its small size, the myelencephalon becomes a part that contributes to various systems and functions.

    The myelencephalon is also included in a part of the ventricular chamber, more precisely in the lower part of it. On the other hand, in the internal part we can find the reticular formation, a part of the brain that participates in the regulation of several basic functions.

    As happens with other structures formed from the hindbrain, the myelencephalon and, concretely, its matured structure, the medulla oblongata, plays a very important role in controlling even the most basic human impulses, How to be alert, attentive and cycle of sleep and awakening, in addition to being behind various reflexes essential to survival.

    In many ways, the myelencephalon is a bridging structure between what will be the brain, that is, the brain and cerebellum, and the spinal cord. This is seen in the basis of the functional organization and the form it presents, very similar to those of the spinal cord.

    Embryonic development

    As we have mentioned, the myelencephalon is a secondary vesicle of the embryonic tube, midway between the primary vesicles of the same tube and the more or less developed structures later in embryonic development. In other words, that is to say it is not part of the adult brainBut part of the adult brain is formed from this structure, specifically being the medulla oblongata.

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

    1. First phase: from neural tube to myelencephalon

    When the fetus begins to form in the mother’s womb, it has a structure that will be the precursor to the nervous system: the neural tube. This tube will specialize over the weeks, 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 needs to be segmented into different parts:

    The first three parts are called primary vesicles, which form roughly three weeks after conception: forebrain, midbrain and hindbrain.

    The primary vesicles are then segmented to form the secondary vesicles. The forebrain is segmented into two parts, the telencephalon and the diencephalon, and the hindbrain is divided into the metencephalon and myelencephalon. This part of neurodevelopment occurs during the fifth week.

      2. Second phase: from the myelencephalon to the spinal cord

      As we have seen, the myelencephalon is a structure that could be localized halfway between the brain itself and the spinal cord. This develops until it becomes the medulla oblongata, which is clearly distinguishable from the rest of the brain and the spinal cord from the 20th week of gestation.

      Parts and contents of the myelencephalon

      Although the myelencephalon is an embryonic structure, its adult version, the medulla oblong or medulla oblongata, it can be found in the brainstem, serving as a connection between the spinal cord and the brain, Being located at the tip of Varolio. It can be seen that this structure is originally apparent or contains some of the following components:

      • The lower part of the ventricular chamber.
      • The glossopharyngeal nerve (cranial pair IX).
      • The vagus nerve (cranial pair X).
      • The accessory nerve (XI cranial pair).
      • The hypoglossal nerve (cranial pair XII).
      • Part of the vestibulocochlear nerve (cranial pair VIII)

      functions

      As a precursor of the medulla oblongata, we could consider the myelencephalon it is 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 and wake cycle. We explain them in more detail below.

      1. Breathing

      The myelencephalon is linked to the regulation of the respiratory cycle. The medulla oblongata constantly monitors blood acidification levels, preventing them from reaching levels that involve organ damage.

      Once the medulla oblongata senses that this is happening, it sends nerve signals to the intercostal muscle tissues, that is, the muscles between the ribs, activating them to perform respiratory movements.

      This way these muscles can increase their rate of contraction, Getting more oxygen into the blood and it acquires the proper pH levels so that no harm is done to the body.

      2. Cardiovascular control

      In addition to respiratory function, the medulla oblongata it is responsible for the regulation of various components of cardiac activity and, therefore, of the circulatory system. While this is not the only structure responsible for regulating cardiac activity, it is one of the most important.

      The medulla oblongata is responsible for stimulating the sympathetic nervous system to increase the rate of the heartbeat. This is especially important in situations where greater physical exertion is required, such as when playing sports or facing a threatening situation, to facilitate the activation of fight-or-flight responses.

      But in addition, it is responsible for producing the opposite effect, that is to say decrease heart rate by activating the parasympathetic nervous system. As expected, this feature will be needed in opposite situations, such as relaxation or low alert states.

      In addition to increasing and decreasing the heart rate, the medulla oblongata regulates blood pressure through vasodilation and vasoconstriction mechanisms.

      3. State of alert and reflexes

      Due to the function of the medulla oblongata on the sympathetic and parasympathetic systems, the development of the midbrain is of the utmost importance for the regulation of all processes related to attention, alertness and, as we have seen above. above, to the cycle of sleep and wakefulness. .

      Finally, the adult structure of the midbrain it is directly linked to the realization of various reflexes and instincts fundamental to survival, Which occur, automatically and unconsciously, in the presence of various stimuli. According to research, the medulla oblongata is known to be the main brain component behind partially involuntary behaviors, such as coughing, sneezing, swallowing reflex, vomiting and nausea, or masseter reflex.

      Bibliographical references:

      • Carlson, NR (2014). Behavioral physiology (11th edition). Madrid: Pearson Education.
      • Kandel, ER; Schwartz, JH and Jessell, TM (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Inter-American. Madrid.

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