MEDULLA OBLONGATA: FUNCTION, ANATOMY, PYRAMIDS, DISEASES - NEUROPSYCHOLOGY - 2024

The medulla oblongata, brainstem or midbrain, is a specific region of the brain. Specifically, a segment of the brainstem is formed that is located between the brainstem bridge and the spinal cord.

It has a truncating cone shape at the lower vertex and is approximately three centimeters long. It is one of the most internal parts of the brain and its functions mainly include the transmission of impulses from the spinal cord to the brain.

Medulla oblongata in yellow

In this sense, the medulla oblongata constitutes a basic region to be able to communicate the brain with the spinal cord and the rest of the body regions. Likewise, this neuronal structure controls cardiac, respiratory, gastrointestinal and vasoconstrictor functions.

Location

The situation and location of this structure allows us to understand a large part of the operation and activities carried out by the bulb. This is located between the spinal cord and brain, specifically, between the spinal cord and the bridge of the brainstem.

The medulla oblongata is connected to the spinal cord through a decussation of the pyramids, also known as decussation of Misticheli.

The boundary between both structures (between the medulla oblongata and the spinal cord) is clear and is easily observed on the anterior and lateral faces. However, on the back face the division becomes less clear and it is difficult to delimit the beginning of one structure and the end of the other.

Medulla oblongata in red

For its macroscopic description, the medulla oblongata can be divided, in a general way, into an anterior face and an anterior median sulcus.

The anterior face contains a longitudinal groove in its midline. For its part, the anterior median sulcus contains the bulboprotuberancial sulcus, which is located through a depression known as the foramen caecum or blind hole.

On both sides of this groove there are two reliefs (the pyramids), which represent the pyramidal route. The reliefs that exchange nerve fibers with the spinal cord crossing the midline form the region known as decussation of the pyramids.

Functions of the medulla oblongata

As is clear from its own anatomy, the main function of the medulla oblongata is to connect the brain with the spinal cord. In this sense, despite being a small structure, this brain region is essential to carry out activities related to nerve transmission.

The medulla oblongata is a neurovegetative nerve center, which is why it plays a vital role in the automatic functioning of the organs. Thus, the activity of this brain region is responsible for carrying out such important actions as:

1. Regulates the heart rate of the body and control its cardiovascular function.
2. Regulates blood pressure.
3. Regulates and controls visceral functions.
4. Regulates the respiratory system.
5. Participate in the swallowing processes.
6. Regulates the secretion of digestive juices.
7. It controls vomiting, coughing, and sneezing, as well as the action of the muscles that are required to perform such actions.

Structure: parts

Structure of the medulla oblongata.

The medulla oblongata has a median anterior fissure on the anterior surface that connects with the spinal cord. At the intersection between both structures, a series of pyramids is formed that form the corticospinal tract of the pyramidal pathway.

In the lateral region of the medulla oblongata there are the pyramids and to their side the anterolateral sulcus, where the hypoglossal nerve (XII cranial nerve) is observed. Behind this are the glossopharyngeal (IX cranial nerve), vagus (X cranial nerve) and accessory (XI cranial nerve) nerves.

In the bulbopontine sulcus of the medulla oblongata, the abductor nerve (VI cranial nerve) is also observed. On its side is the cranial or facial nerve and the vestibuloclear nerve.

Finally, on the posterior aspect of the medulla oblongata there is a medial posterior sulcus in the continuation midline. This region is subdivided by a small paramedian sulcus in the cord of Goll and by a cueniform fascicle.

Thus, the medulla oblongata is one of the most subcortical, that is, the deepest, regions of the brain. This is full of nerve endings and nerves that modulate different activities of the brain.

Anatomy

Source: daviddarling.info

In the anatomical study of the medulla oblongata, it is usually divided into three different thirds. A lower, a medium and a higher.

The lower region of the medulla oblongata is characterized by pyramidal decussation. The medial part has the sensory decussation and the upper part contains the bulbar olives.

Likewise, in general, in the anatomy of this brain region two different organizations are detected: the external organization and the internal organization.

- External anatomy

The medulla oblongata is a structure located in the lower region of the brain stem. In fact, a lower portion of this brain structure results, which includes regions other than the medulla oblongata.

On the other hand, it should be noted that the medulla oblongata is the last region of the brainstem and, therefore, of the brain itself. For this reason, it stands out for its limit with the spinal cord.

The transition between the spinal cord and the medulla oblongata is gradual in its external appearance. That is, a precise macroscopic limit is not observed.

However, at the theoretical level, it is defined that the medulla oblongata is extended by the lower part with the spinal cord to a certain point. Specifically, this point refers to the region immediately superior to the exit of the roots of the first spinal nerve.

In other words, the elements that make it possible to differentiate the spinal cord from the medulla oblongata do not reside so much in the anatomy of both regions but in the observation of the last nerve referring to the spinal cord.

On the other hand, both regions present a series of differences in their eternal appearance due to the development of the fourth ventricle. This structure also serves to determine that the posterior structures are located posterolaterally.

a) Anterior face

A deep cleft is seen on the anterior surface of the bulb, known as the median anterior fissure. This brain element turns out to be the continuation of the structure of the same name in the spinal cord.

That is, there is an anterior median fissure referring to the medulla oblongata and an anterior median fissure referring to the spinal cord that are directly interconnected.

On each side of this structure are pyramids, brain regions that are bulging columns of white matter and contain bundles of motor fibers.

The motor fibers from the pyramids descend into the spinal cord and form the corticospinal tracts in this region.

If one continues to observe the posterior area of ​​this structure of the medulla oblongata, a decussation of the pyramids is observed. At this site, most of the corticosepinal fibers cross to the opposite side to form the lateral corticospinal tract.

b) Rear face

On the posterior aspect of the medulla oblongata there is an oval area called the olive. Below this are the inferior cerebellar peduncles that form the floor of the lateral recess of the fourth ventricle.

Hypoglossal nerve roots emerge in the longitudinal groove between the pyramid (anterior face) and the olive (posterior face).

This cranial nerve is formed by the motor roots of the nerves of the occipital segments, so its roots continue in series with the anterior roots of the spinal nerves of the cervical segments.

Finally, in the lower part of the bulb there are two gracilis tubercles, which indicate the position of the gracilis nucleus. On the side of each tuber is the tuber cuneatus, a less obvious prominence that determines the position of the underlying cuneatus nucleus.

- External anatomy

The internal structure of the medulla oblongata is not as uniform as that of the spinal cord. For this reason, the sections of the bulb reflect important modifications in the spatial arrangement of the gray matter and the white matter.

The appearance and expansion of the fourth ventricle of the brain during the embryological development of the rhombencephalon, motivates a notable alteration of the external anatomy of the medulla oblongata.

In this sense, the medulla oblongata plates are located laterally and the basal plates medially with respect to the limiting sulcus.

Medulla oblongata pyramids

The most important regions of the medulla oblongata are undoubtedly the pyramids that form in its most prominent area to the spinal cord. In fact, it is these structures that allow both regions to be connected and, therefore, to produce the connection between brain and body.

Specifically, there are two pyramids in the medulla oblongata, which are located anteriorly and separate through the median anterior fissure.

Each of the pyramids contains corticospinal fibers that travel to the spinal cord. Likewise, they also have some corticonuclear fibers that are distributed through the different motor nuclei of the cranial nerves of the bulb.

The other elements contained in the pyramids of the medulla oblongata are:

1. Inferior cerebral peduncles: they are located in the posterolareal region, on the other side of the fourth ventricle.
2. Posterior spinocerebellar tract: it is located near the peduncles and joins them.
3. Anterior spinocerebellar tract: it is superficially between the inferior olive complex and the spinal trigeminal nucleus.
4. Medial lemniscus: it is a long and fine structure that is found on each side of the medial line of the medulla oblongata.
5. Medial longitudinal fasciculus: it is the region that is located next to each medial lemniscus. It contains a high number of ascending and descending fibers, and is a vital structure for the coordination of eye movements and the regulation of changes in the position of the head.

Pyramidal decusation

The pyramidal decussation is another of the key structures of the medulla oblongata. These refer to the pyramids that are located just on the line that separates the bulb from the spinal cord.

In this region are a large number of fibers that connect the medulla oblongata with the spinal cord. Of all of them, the majority (90%) cross the midline in a posterolateral direction and constitute the lateral corticospinal tract.

The decussation of the pyramids and therefore of their motor fibers, causes the disconnection of the gray matter from the anterior region. Likewise, in the posterior region, they have the fasciculus gracilis, which turns out to be an extension of the central gray matter.

Finally, in the posterolateral area of ​​the bulb is the nucleus of the trigeminal nerve that contains the fibers that make up the spinal tract.

Fourth ventricle

The fourth ventricle of the brain is a triangular cavity that is located between the medulla oblongata, pons, and midbrain.

In its lower part, it is connected to the spinal cord through the aqueduct of Silvio. By its upper part, and by its lateral and medial openings, it is connected with the subarachnoid space.

Fluids circulate through all the ventricular circuits, so the ventricular system is anatomically connected until it reaches the spinal cord.

Related diseases

Based on the activities and functions performed by the medulla oblongata, alterations in this brain region can lead to the appearance of certain symptoms and diseases.

In turn, there are various health problems that can affect the bulb's operation in a decisive way. Both congenital diseases and degenerative, tumor and vascular pathologies can damage the medulla oblongata. The main ones are:

1. Multisystemic atrophy: it is a neurodegenerative pathology of unknown cause that produces significant atrophy in the cerebellum.
2. Amyotrophic lateral sclerosis: it is a disease that damages the corticospinal fibers. It is the most prevalent pathology of the medulla oblongata.
3. Multiple sclerosis: this also common disease produces a notable decrease in the mobility of the individual and damages different brain regions, including the medulla oblongata.
4. Behcet's disease: this rare pathology causes ulcers of various kinds and lesions of the nodular class.
5. Medulla oblongata cancer: It is a serious disease that causes vision problems, vomiting, weakness and lethargy.

References

1. Carlson, NR (2014). Physiology of Behavior (11 Edition). Madrid: Pearson Education.
2. Del Abril, A; Caminero, AA.; Ambrosio, E.; García, C.; de Blas MR; de Pablo, J. (2009) Foundations of Psychobiology. Madrid. Sanz and Torres.
3. Madrid: Editorial Médica Panamericana.
4. Rosenzweig, Breedlove i Watson (2005). Psychobiology. An introduction to behavioral, cognitive, and clinical neuroscience. Barcelona: Ariel.
5. Nolte, J. (2009) The human brain in photographs and diagrams (3rd Ed.). Barcelona: Elsevier.
6. Nolte, J. (2010). Essentials of the human brain. Philadelphia, PA: Mosby / Elsevier.