Medulla oblongata: structure and functions

The medulla oblongata or medulla oblongata It is a subcortical structure that is located in the lower part of the brain stem. Its nervous connections carry out basic bodily functions that guarantee our survival, such as: regulating heart rate, maintaining respiratory function, carrying out digestion, coordinating body movements, among others.

A vitally important structure

The medulla oblongata is so relevant that without it we would be risking our survival. Despite its small size, three centimeters long and two centimeters wide, we cannot underestimate it.

A work carried out by researchers from the University of Amsterdam indicates that the medulla oblongata It is like a station for all the important information that enters and leaves the brainTherefore, the study of this brain component is essential to better understand how we function and how we can address various health conditions.

Likewise, recent research published in NeuroImagen found that its size is a significant indicator to predict the survival of people with amyotrophic lateral sclerosis (ALS).

Thus, It is one of the most significant brain structures, whose injury could imply severe conditions. That said, let’s see how it is formed and what its main functions are.

External structure of the medulla oblongata

The medulla oblongata is the most caudal structure of the brainstem. Its shape is similar to that of an inverted cone and connects the brain with the spinal cord.

The ventral and dorsal surfaces of the medulla oblongata have unique protuberances and fissures., which are made up of different nuclei and associated tracts. At this point, it should be noted that the nuclei are groupings of the cell bodies of neurons; while tracts are groupings of axons, generally myelinated, that connect the nuclei of different parts of the central nervous system.

Having clarified this aspect, below we show the characteristics of each surface and the parts that make it up.

ventral surface

On the ventral or anterior surface of the medulla oblongata are:

Anterior middle fissure: It is a continuation of the anterior middle fissure of the spinal cord.bulbar pyramids: They are found on the floor of the bulb and on either side of the anterior median fissure. They highlight the bundles of nerve fibers that connect the bulb with the cortex and the spine.pyramidal decussation: Below the base of the bulbar pyramids, the anterior middle fissure is interrupted by the fascicles of the corticospinal tract that decussate (change sides) crossing the fissure and forming the pyramidal decussation in the midline.anterolateral sulcus and posterolateral sulcus: located on each half of the ventral surface of the medulla oblongata. They serve as output pathways for some cranial nerves, such as the hypoglossal, glossopharyngeal, and vagus.Olive: This is an oval structure that is located between the grooves, just to the side and behind each bulbar pyramid. The nuclei that make up the olive regulate voluntary muscle movements.

Dorsal surface

For its part, on the posterior surface of the medulla oblongata there are the following structures:

Middorsal groove: located in the midline of the bulb, which is continuous with its equivalent in the spinal cord.Vertical prominences: located on each side of the median dorsal sulcus and run parallel to it. These are formed by the gracile fasciculuswhich contains a nucleus that forms a visible eminence on the dorsal surface of the bulb, called the gracile tubercle.cuneiform fasciculus: lateral to each gracile fasciculus is another vertical prominence formed by the cuneiform fasciculus, composed of the cuneiform nucleus.Trigeminal tubercle: This is another prominence located on each side of the cuneiform nucleus. It is made up of the spinal nucleus of the trigeminal nerve.

Internal structure of the medulla oblongata

If we make a cross section of the medulla oblongata, we can identify three parts, ranging from the most ventral to the most dorsal:

Base: contains the pyramidal decussation of the corticospinal tract.Tegmentum or shell: houses the inferior olivary nuclei, as well as cranial nerves IX to XII.Ceiling: It is composed of the inferior medullary velum, which is the posteroinferior portion of the fourth ventricle.

It is worth mentioning that the nuclei (gray matter or matter) are found, for the most part, in the dorsal portion of the medulla oblongata, while the tracts (white matter) are located in the ventral part.

Nuclei of the medulla oblongata

The nuclei that make up the medulla oblongata are involved in various vital functions of the body. These are:

Hypoglossal nucleus

It is a motor nucleus that gives rise to the hypoglossal nerve (IX nerve) and innervates all intrinsic and extrinsic muscles of the tongue, except the palatoglossus.

Subhypoglossal (or Roller) nucleus

It is located adjacent to the hypoglossal nucleus and is part of complex circuits that involve eye movements.

Medial vestibular nucleus (or Schwalbe’s)

It belongs to the vestibular system and includes the caudal portion of the pons and the rostral portion of the medulla oblongata. It is in charge of receive information from the semicircular canals of the inner ear and then projects them through fibers that join the medial longitudinal fasciculus.

cuneiform nucleus

Receives sensory information about light touch, proprioception, and vibration of the ipsilateral upper extremity, carried by the cuneiform fasciculus.

trigeminal nucleus

It is a sensory nucleus of the face, which is responsible for receive information from touch, vibration, pain and temperature. It is worth mentioning that this is an area where neuronal cell bodies accumulate to process information at a very basic level. Other more advanced brain structures assume responsibility for continuing to process the information emitted by this nucleus.

Dorsal nucleus of the vagus

It is a visceral motor nucleus that innervates the smooth muscles of the digestive tract, lungs, and other organs of the abdomen and thorax. Therefore, it is closely linked to digestion and its functions include the control and production of gastric flows.

Ambiguous nucleus

It is a motor nucleus that provides nerve fibers for the glossopharyngeal, vagus, and accessory nerves. These, They participate in the processes of swallowing and digestion, controlling the muscles of the pharynx and larynx.

Nucleus of the solitary tract

He is in charge of control of visceral sensitivity and cardiorespiratory function. Furthermore, the facial-lateral part participates in taste perception.

Raphe nuclei

The numerous nuclei of the raphe belong to the reticular formation of the medulla oblongata. These are the main source of the neurotransmitter serotonin and also They are involved in the regulation of mood, pain, wakefulness and thermoregulation.

Olivary nuclei

Made up of: the dorsal accessory olivary nucleus, the inferior olivary nucleus, and the medial accessory olivary nucleus. They connect with the cerebellum to help with motor coordination.

Lateral reticular nucleus

It receives and integrates impulses from a variety of sources, which it transmits to the ipsilateral half of the cerebellum. Through this connection, the lateral reticular nucleus helps the cerebellum with planning and motor coordination.

Tracts of the medulla oblongata

The white matter of the bulb is composed of motor and sensory tracts, these being:

pyramidal tract

It is the main motor tract of the medulla oblongata. This travels from the cerebral cortex to the spinal cord, where it synapses with the lower neuron bodies; which also innervate the skeletal muscles of the body.

medial lemniscus

It connects with the fibers of the cuneiform and gracile nuclei, which transmit somatosensory information from the body. Therefore, it passes through the thalamus and ends within the primary somatosensory cortex.

inferior cerebellar peduncle

It is a mass of white matter that contains the tracts that connect the spinal cord to the brain stem and cerebellum. These tracts They carry proprioceptive somatosensory fibers, as well as nerve impulses from the cerebellum that regulate posture and balance of the body.

Spinal tract of the trigeminal nerve

It is located beneath the inferior cerebellar peduncle and transmits sensory information from the face to the spinal nucleus of the trigeminal nerve.

Spinocerebellar tract

It is located anterior to the lateral lenticular nucleus and sends proprioceptive information from the skeletal muscle to the cerebellum.

spinothalamic tract

It passes medial and ventral to the spinocerebellar tract. Sends information about pain and temperature from the contralateral part of the body to the thalamus. Passing through it, the fibers of this tract continue towards the primary somatosensory cortex.

Irrigation

The surface of the medulla oblongata is supplied by the branches of the vertebral and basilar arteries, which are: the anterior and posterior spinal arteries, and the posterior inferior cerebellar arteries. These blood branches also enter along with the roots of the glossopharyngeal, vagus, accessory, and hypoglossal nerves.

Functions of the medulla oblongata

As we see, The medulla oblongata is involved in various functions, which are vital for the body. In fact, the destruction of this structure or the interruption of its functioning results in death.

Among its main functions we find:

Control of autonomous functions

The medulla oblongata is responsible for controlling the involuntary functions of the viscera and maintaining homeostasis. For example:

Cardiovascular system: maintains blood pressure and vasoconstriction; and regulates heart rate.Breathing: regulates and maintains respiratory function.Digestion: manages the involuntary muscles that are involved in this process. It also controls the secretion of digestive juices and participates in swallowing processes.

In addition, it manages other involuntary actions such as coughing, vomiting and sneezing.

Sensory control

It is also responsible for the transfer of sensory information between the peripheral system and the central nervous system. To do this, it connects the two systems and sends information to the thalamus that is then communicated to the rest of the brain.

Problems associated with the medulla oblongata

In the medulla there are some cranial nerves (IX, X, XI, XII), whose damage causes problems in the regions and functions they control. These are:

Glossopharyngeal or cranial nerve IX: collects gustatory information and sensory information from the pharynx. It facilitates swallowing by coordinating various neck muscles. In addition, it transmits signals to the salivary gland.Vagus nerve or cranial nerve innervates the pharynx, esophagus, trachea, bronchi, heart, stomach and liver. Therefore, it regulates our autonomous system.Accessory nerve or cranial nerve XI: It is responsible for cephalogyro movement; therefore it intervenes in movements of the head, neck and shoulders.Hypoglossal nerve…