Medulla oblongata: structure and functions. Human medulla oblongata The medulla oblongata is responsible for the following functions

It is a part of the brain located between the spinal cord and.

Its structure differs from the structure of the spinal cord, but the medulla oblongata has a number of structures in common with the spinal cord. Thus, the ascending and descending cords of the same name pass through the medulla oblongata, connecting the spinal cord with the brain. A number of cranial nerve nuclei are located in the upper segments of the cervical spinal cord and in the caudal part of the medulla oblongata. At the same time, the medulla oblongata no longer has a segmental (repeatable) structure, its gray matter does not have a continuous central localization, but is presented in the form of separate nuclei. The central canal of the spinal cord, filled with cerebrospinal fluid, at the level of the medulla oblongata turns into the cavity of the fourth ventricle of the brain. On the ventral surface of the bottom of the fourth ventricle there is a rhomboid fossa, in the gray matter of which a number of vital nerve centers are localized (Fig. 1).

The medulla oblongata performs sensory, conductive, integrative, and motor functions, realized through the somatic and (or) autonomic systems, that are characteristic of the entire central nervous system. Motor functions can be performed by the medulla oblongata reflexively or it can participate in voluntary movements. In the implementation of some functions called vital (respiration, blood circulation), the medulla oblongata plays a key role.

Rice. 1. Topography of the location of the cranial nerve nuclei in the brain stem

The medulla oblongata contains the nerve centers of many reflexes: breathing, cardiovascular, sweating, digestion, sucking, blinking, muscle tone.

Regulation breathing carried out through, consisting of several groups located in different parts of the medulla oblongata. This center is located between the upper border of the pons and the lower part of the medulla oblongata.

Sucking movements occur when the lip receptors of a newborn animal are irritated. The reflex occurs when the sensory endings of the trigeminal nerve are stimulated, the excitation of which is switched in the medulla oblongata to the motor nuclei of the facial and hypoglossal nerves.

Chewing reflexively occurs in response to irritation of oral receptors that transmit impulses to the center of the medulla oblongata.

Swallowing - a complex reflex act in which the muscles of the oral cavity, pharynx and esophagus take part.

blinking refers to protective reflexes and is carried out when the cornea of ​​the eye and its conjunctiva are irritated.

Oculomotor reflexes promote complex eye movements in various directions.

Vomiting reflex occurs when the receptors of the pharynx and stomach are irritated, as well as when the vestibuloreceptors are irritated.

Sneeze reflex occurs when the receptors of the nasal mucosa and the endings of the trigeminal nerve are irritated.

Cough- a protective respiratory reflex that occurs when the mucous membrane of the trachea, larynx and bronchi is irritated.

The medulla oblongata is involved in the mechanisms through which the animal’s orientation in the environment is achieved. For regulation equilibrium in vertebrates the vestibular centers are responsible. The vestibular nuclei are of particular importance for the regulation of posture in animals, including birds. Reflexes that ensure the maintenance of body balance are carried out through the centers of the spinal cord and medulla oblongata. In the experiments of R. Magnus, it was found that if the brain is cut above the medulla oblongata, then when the animal’s head is thrown back, the thoracic limbs are pulled forward and the pelvic limbs are bent. When the head is lowered, the thoracic limbs bend and the pelvic limbs straighten.

Centers of the medulla oblongata

Among the numerous nerve centers of the medulla oblongata, vital centers are of particular importance, on the preservation of whose functions the life of the body depends. These include the centers of respiration and circulation.

Table. Main nuclei of the medulla oblongata and pons

The medulla oblongata contains the nuclei of five cranial pairs of nerves (VIII-XII). The nuclei are grouped in the caudal part of the medulla oblongata below the bottom of the fourth ventricle (see Fig. 1).

Core XII pair(hypoglossal nerve) is located in the area of ​​the lower part of the rhomboid fossa and the three upper segments of the spinal cord. It is represented mainly by somatic motor neurons, the axons of which innervate the muscles of the tongue. The neurons of the nucleus receive signals via afferent fibers from the sensory receptors of the muscle spindles of the tongue muscles. In its functional organization, the nucleus of the hypoglossal nerve is similar to the motor centers of the anterior horns of the spinal cord. The axons of the cholinergic motor neurons of the nucleus form fibers of the hypoglossal nerve, which follow directly to the neuromuscular synapses of the tongue muscles. They control the movements of the tongue during eating and processing food, as well as during speech.

Damage to the nuclei or the hypoglossal nerve itself causes paresis or paralysis of the tongue muscles on the side of the injury. This may be manifested by deterioration or absence of movement of half of the tongue on the side of the injury; atrophy, fasciculations (twitching) of the muscles of half the tongue on the side of the injury.

Core XI pair(accessory nerve) is represented by somatic motor cholinergic neurons located both in the medulla oblongata and in the anterior horns of the 5-6th upper cervical segments of the spinal cord. Their axons form neuromuscular synapses on the myocytes of the sternocleidomastoid and trapezius muscles. With the participation of this nucleus, reflex or voluntary contractions of the innervated muscles can be carried out, leading to tilting of the head, raising the shoulder girdle and displacement of the shoulder blades.

Core X pair(vagus nerve) - the nerve is mixed and is formed by afferent and efferent fibers.

One of the nuclei of the medulla oblongata, where afferent signals are received via the vagus fibers and fibers of the VII and IX cranial nerves, is the solitary nucleus. Neurons of the nuclei VII, IX and X of pairs of cranial nerves are included in the structure of the nucleus of the solitary tract. To the neurons of this nucleus, signals are carried through the afferent fibers of the vagus nerve mainly from the mechanoreceptors of the palate, pharynx, larynx, trachea, and esophagus. In addition, it receives signals from vascular chemoreceptors about the content of gases in the blood; mechanoreceptors of the heart and baroreceptors of blood vessels about the state of hemodynamics, receptors of the gastrointestinal tract about the state of digestion and other signals.

The rostral part of the solitary nucleus, which is sometimes called the taste nucleus, receives signals from taste receptors along the fibers of the vagus nerve. The neurons of the solitary nucleus are the second neurons of the taste analyzer, which receives and transmits sensory information about taste qualities to the thalamus and further to the cortical region of the taste analyzer.

Neurons in the solitary nucleus send axons to the reciprocal (double) nucleus; the dorsal motor nucleus of the vagus nerve and the centers of the medulla oblongata that control blood circulation and respiration, and through the pontine nuclei to the amygdala and hypothalamus. The solitary nucleus contains peptides, enkephalin, substance P, somatostatin, cholecystokinin, neuropeptide Y, which are related to the control of eating behavior and autonomic functions. Damage to the solitary nucleus or solitary tract may be accompanied by eating disorders and breathing disorders.

The fibers of the vagus nerve include afferent fibers that conduct sensory signals to the spinal nucleus, the trigeminal nerve from the receptors of the external ear, formed by the sensory nerve cells of the superior ganglion of the vagus nerve.

The dorsal motor nucleus is part of the vagus nerve nucleus. (dorsalmotornucleus) and the ventral motor nucleus, known as the reciprocal (n. ambiguus). The dorsal (visceral) motor nucleus of the vagus nerve is represented by preganglionic parasympathetic cholinergic neurons, which send their axons laterally to the bundles of the X and IX cranial nerves. Preganglionic fibers end in cholinergic synapses on ganglionic parasympathetic cholinergic neurons, located mainly in the intramural ganglia of the internal organs of the thoracic and abdominal cavities. Neurons of the dorsal nucleus of the vagus nerve regulate the functioning of the heart, the tone of smooth myocytes and glands of the bronchi and abdominal organs. Their effects are realized through the control of acetylcholine release and stimulation of M-ChR cells of these effector organs. Neurons of the dorsal motor nucleus receive afferent inputs from neurons of the vestibular nuclei, and with strong excitation of the latter, a person may experience a change in heart rate, nausea, and vomiting.

Axons of neurons of the ventral motor (mutual) nucleus of the vagus nerve, together with fibers of the glossopharyngeal and accessory nerves, innervate the muscles of the larynx and pharynx. The reciprocal nucleus is involved in the reflexes of swallowing, coughing, sneezing, vomiting and regulating the pitch and timbre of the voice.

A change in the tone of neurons in the vagus nerve nucleus is accompanied by a change in the function of many organs and body systems controlled by the parasympathetic nervous system.

Nuclei of the IX pair (glossopharyngeal nerve) represented by neurons of the SNS and ANS.

The afferent somatic fibers of the IX nerve are axons of sensory neurons located in the superior ganglion of the vagus nerve. They transmit sensory signals from the tissues of the postauricular region to the nucleus of the spinal tract of the trigeminal nerve. Afferent visceral fibers of the nerve are represented by axons of receptor neurons for pain, touch, thermoreceptors of the posterior third of the tongue, tonsils and eustachian tube, and axons of neurons of the taste buds of the posterior third of the tongue, transmitting sensory signals to the solitary nucleus.

Efferent neurons and their fibers form two nuclei of the IX nerve: the reciprocal and the salivary. Mutual core represented by ANS motor neurons, the axons of which innervate the stylopharyngeal muscle (t. stylopharyngeus) larynx. Inferior salivary nucleus represented by preganglionic neurons of the parasympathetic nervous system, which send efferent impulses to postganglionic neurons of the ear ganglion, and the latter control the formation and secretion of saliva by the parotid gland.

Unilateral damage to the glossopharyngeal nerve or its nuclei may be accompanied by deviation of the velum palatine, loss of taste sensitivity in the posterior third of the tongue, impairment or loss of the pharyngeal reflex on the side of the injury, initiated by irritation of the posterior wall of the pharynx, tonsils or root of the tongue and manifested by contraction of the tongue muscle and laryngeal muscles. Because the glossopharyngeal nerve carries some of the sensory signals from the carotid sinus baroreceptors to the nucleus solitarius, damage to this nerve can lead to decreased or loss of the carotid sinus reflex on the injured side.

In the medulla oblongata, some of the functions of the vestibular apparatus are realized, which is due to the location under the bottom of the IV ventricle of the fourth vestibular nuclei - superior, inferior (siinal), medial and lateral. They are located partly in the medulla oblongata, partly at the level of the pons. The nuclei are represented by the second neurons of the vestibular analyzer, which receive signals from the vestibuloreceptors.

In the medulla oblongata, the transmission and analysis of sound signals entering the cochlear (ventral and dorsal nuclei) continues. The neurons of these nuclei receive sensory information from auditory receptor neurons located in the spiral ganglion of the cochlea.

In the medulla oblongata, the inferior cerebellar peduncles are formed, through which afferent fibers of the spinocerebellar tract, reticular formation, olives, and vestibular nuclei follow into the cerebellum.

The centers of the medulla oblongata, with the participation of which vital functions are performed, are the centers for the regulation of respiration and blood circulation. Damage or dysfunction of the inspiratory portion of the respiratory center can lead to rapid respiratory arrest and death. Damage to or dysfunction of the vasomotor center can lead to a rapid drop in blood pressure, slowing or stopping of blood flow, and death. The structure and functions of the vital centers of the medulla oblongata are discussed in more detail in the sections on the physiology of respiration and circulation.

Functions of the medulla oblongata

The medulla oblongata controls both simple and very complex processes that require fine coordination of the contraction and relaxation of many muscles (for example, swallowing, maintaining body posture). The medulla oblongata performs the functions: sensory, reflexive, conductive and integrative.

Sensory functions of the medulla oblongata

Sensory functions consist in the perception by neurons of the nuclei of the medulla oblongata of afferent signals coming to them from sensory receptors that respond to changes in the internal or external environments of the body. These receptors can be formed by sensoroepithelial cells (for example, taste, vestibular) or the nerve endings of sensory neurons (pain, temperature, mechanoreceptors). The bodies of sensory neurons are located in the peripheral nodes (for example, the spiral and vestibular - sensitive auditory and vestibular neurons; the inferior ganglion of the vagus nerve - sensitive taste neurons of the glossopharyngeal nerve) or directly in the medulla oblongata (for example, CO 2 and H 2 chemoreceptors).

In the medulla oblongata, the sensory signals of the respiratory system are analyzed - the gas composition of the blood, pH, the state of stretching of the lung tissue, based on the results of which not only breathing, but also the state of metabolism can be assessed. The main indicators of blood circulation are assessed - heart function, blood pressure; a number of signals from the digestive system - the taste of food, the nature of chewing, the functioning of the gastrointestinal tract. The result of the analysis of sensory signals is an assessment of their biological significance, which becomes the basis for the reflex regulation of the functions of a number of organs and body systems controlled by the centers of the medulla oblongata. For example, changes in the gas composition of blood and cerebrospinal fluid are one of the most important signals for the reflex regulation of pulmonary ventilation and blood circulation.

The centers of the medulla oblongata receive signals from receptors that respond to changes in the external environment of the body, for example, thermoreceptors, auditory, taste, tactile, and pain receptors.

Sensory signals from the centers of the medulla oblongata are carried along pathways to the overlying parts of the brain for their subsequent more refined analysis and identification. The results of this analysis are used to form emotional and behavioral reactions, some of the manifestations of which are realized with the participation of the medulla oblongata. For example, the accumulation of CO 2 in the blood and the decrease in O 2 is one of the reasons for the appearance of negative emotions, a feeling of suffocation and the formation of a behavioral reaction aimed at searching for fresher air.

Conducting function of the medulla oblongata

The conductor function is to conduct nerve impulses in the medulla oblongata itself, to neurons of other parts of the central nervous system and to effector cells. Afferent nerve impulses enter the medulla oblongata along the same fibers of the VIII-XII pairs of cranial nerves from sensory receptors of the muscles and skin of the face, mucous membranes of the respiratory tract and mouth, interoreceptors of the digestive and cardiovascular systems. These impulses are conducted to the nuclei of the cranial nerves, where they are analyzed and used to organize reflex responses. Efferent nerve impulses from the neurons of the nuclei can be carried out to other nuclei of the brainstem or other parts of the brain to carry out more complex CNS responses.

Sensitive (gracilis, sphenoid, spinocerebellar, spinothalamic) pathways pass through the medulla oblongata from the spinal cord to the thalamus, cerebellum and brainstem nuclei. The location of these pathways in the white matter of the medulla oblongata is similar to that in the spinal cord. In the dorsal part of the medulla oblongata there are thin and wedge-shaped nuclei, on the neurons of which the same bundles of afferent fibers coming from the receptors of muscles, joints and tactile receptors of the skin end with the formation of synapses.

In the lateral region of the white matter there are descending olivospinal, rubrospinal, and tectospinal motor tracts. From the neurons of the reticular formation the reticulospinal tract follows into the spinal cord, and from the vestibular nuclei the vestibulospinal tract follows. The corticospinal motor tract runs in the ventral part. Some of the fibers of the motor cortex neurons end on the motor neurons of the nuclei of the cranial nerves of the pons and medulla oblongata, which control contractions of the muscles of the face and tongue (corticobulbar tract). The fibers of the corticospinal tract at the level of the medulla oblongata are grouped into formations called pyramids. The majority (up to 80%) of these fibers at the level of the pyramids passes to the opposite side, forming a decussation. The rest (up to 20%) of uncrossed fibers passes to the opposite side already at the level of the spinal cord.

Integrative function of the medulla oblongata

Manifests itself in reactions that cannot be classified as simple reflexes. Its neurons are programmed with algorithms for some complex regulatory processes, which require the participation of centers of other parts of the nervous system and interaction with them for their implementation. For example, a compensatory change in the position of the eyes when the head oscillates during movement, realized on the basis of the interaction of the nuclei of the vestibular and oculomotor systems of the brain with the participation of the medial longitudinal fasciculus.

Some of the neurons in the reticular formation of the medulla oblongata are automatic, toning and coordinating the activity of the nerve centers of various parts of the central nervous system.

Reflex functions of the medulla oblongata

The most important reflex functions of the medulla oblongata include the regulation of muscle tone and posture, the implementation of a number of protective reflexes of the body, the organization and regulation of the vital functions of breathing and circulation, and the regulation of many visceral functions.

This function is performed by the medulla oblongata together with other structures of the brain stem.

From an examination of the course of the descending pathways through the medulla oblongata, it is clear that all of them, with the exception of the corticospinal tract, begin in the nuclei of the brain stem. These pathways are located mainly on y-motoneurons and interneurons of the spinal cord. Since the latter play an important role in coordinating the activity of motor neurons, through interneurons it is possible to control the state of synergistic, agonist and antagonist muscles, to exert reciprocal effects on these muscles, to involve not only individual muscles, but also their entire groups, which makes it possible to connect to simple movements are additional. Thus, through the influence of the motor centers of the brain stem on the activity of motor neurons of the spinal cord, it is possible to solve more complex problems than, for example, reflex regulation of the tone of individual muscles, which is realized at the level of the spinal cord. Among such motor tasks, which are solved with the participation of motor centers of the brain stem, the most important are the regulation of posture and maintaining body balance, implemented through the distribution of muscle tone in various muscle groups.

Postural reflexes are used to maintain a certain body posture and are realized through the regulation of muscle contractions through the reticulospinal and vestibulospinal pathways. This regulation is based on the implementation of postural reflexes, which are under the control of higher cortical levels of the central nervous system.

Righting reflexes contribute to the restoration of disturbed positions of the head and body. These reflexes involve the vestibular apparatus and stretch receptors in the neck muscles and mechanoreceptors in the skin and other body tissues. In this case, the restoration of the body’s balance, for example when slipping, occurs so quickly that only a few moments after the postural reflex occurs, we realize what happened and what movements we performed.

The most important receptors, the signals from which are used to carry out postural reflexes, are: vestibuloreceptors; proprioceptors of the joints between the upper cervical vertebrae; vision. In the implementation of these reflexes, not only the motor centers of the brain stem, but also motor neurons of many segments of the spinal cord (executors) and the cortex (control) are normally involved. Among the postural reflexes, labyrinthine and cervical reflexes are distinguished.

Labyrinth reflexes ensure, first of all, maintaining a constant position of the head. They can be tonic or phasic. Tonic - maintain a posture in a given position for a long time by controlling the distribution of tone in various muscle groups, phasic - maintain a posture mainly in case of imbalance, controlling rapid, transient changes in muscle tension.

Neck reflexes are responsible mainly for changes in muscle tension in the limbs that occur when the position of the head relative to the body changes. The receptors whose signals are necessary for the implementation of these reflexes are the proprioceptors of the motor apparatus of the neck. These are muscle spindles, mechanoreceptors of the joints of the cervical vertebrae. Cervical reflexes disappear after dissection of the dorsal roots of the upper tricervical segments of the spinal cord. The centers of these reflexes are located in the medulla oblongata. They are formed mainly by motor neurons, which with their axons form the reticulospinal and vestibulospinal tracts.

Maintaining a posture is most effectively achieved with the joint functioning of the cervical and labyrinthine reflexes. This achieves not only maintaining the position of the head relative to the body, but also the position of the head in space and, on this basis, the vertical position of the body. Labyrinthine vestibuloreceptors can only inform about the position of the head in space, while receptors in the neck inform about the position of the head relative to the body. Reflexes from the labyrinths and from the neck receptors can be reciprocal relative to each other.

The reaction speed during the implementation of labyrinthine reflexes can be assessed in fact. Already approximately 75 ms after the onset of the fall, coordinated muscle contraction begins. Even before landing, a reflexive motor program is launched aimed at restoring body position.

In keeping the body in balance, the connection between the motor centers of the brain stem and the structures of the visual system and, in particular, the tectospinal tract, is of great importance. The nature of the labyrinthine reflexes depends on whether the eyes are open or closed. The exact ways in which vision influences postural reflexes are still unknown, but it is obvious that they enter the vestibulospinal pathway.

Tonic postural reflexes occur when turning the head or acting on the neck muscles. Reflexes originate from the vestibular apparatus receptors and the stretch receptors of the neck muscles. The visual system contributes to the implementation of postural tonic reflexes.

Angular acceleration of the head activates the sensory epithelium of the semicircular canals and causes reflexive movements of the eyes, neck and limbs, which are directed in the opposite direction relative to the direction of body movement. For example, if the head turns to the left, then the eyes will reflexively turn the same angle to the right. The resulting reflex will help maintain the stability of the visual field. The movements of both eyes are friendly and turn in the same direction and at the same angle. When the head rotation exceeds the maximum eye rotation angle, the eyes quickly return to the left and find a new visual object. If the head continues to turn to the left, this will be accompanied by a slow turn of the eyes to the right, followed by a rapid return of the eyes to the left. These alternating slow and fast eye movements are called nystagmus.

Stimuli that cause the head to rotate to the left will also lead to increased tone and contraction of the extensor (anti-gravity) muscles on the left, resulting in increased resistance to any tendency to fall to the left during head rotation.

Tonic neck reflexes are a type of postural reflexes. They are initiated by stimulation of muscle spindle receptors in the neck muscles, which contain the largest concentration of muscle spindles of any muscle in the body. Topical neck reflexes are the opposite of those that occur when vestibular receptors are stimulated. In their pure form, they appear in the absence of vestibular reflexes when the head is in a normal position.

Sneeze reflex manifested by forced exhalation of air through the nose and mouth in response to mechanical or chemical irritation of the receptors of the nasal mucosa. There are nasal and respiratory phases of the reflex. The nasal phase begins when the sensory fibers of the olfactory and ethmoidal nerves are affected. Afferent signals from the receptors of the nasal mucosa are transmitted along the afferent fibers of the ethmoidal, olfactory and (or) trigeminal nerve to the neurons of the nucleus of this nerve in the spinal cord, the solitary nucleus and the neurons of the reticular formation, the totality of which constitutes the concept of the sneezing center. Efferent signals are transmitted along the petrosal and pterygopalatine nerves to the epithelium and blood vessels of the nasal mucosa and cause an increase in their secretion when the receptors of the nasal mucosa are irritated.

The respiratory phase of the sneezing reflex is initiated at the moment when, when afferent signals enter the nucleus of the sneezing center, they become sufficient to excite a critical number of inspiratory and expiratory neurons of the center. Efferent nerve impulses sent by these neurons arrive at the neurons of the vagus nerve nucleus, neurons of the inspiratory and then expiratory sections of the respiratory center, and from the latter to the motor neurons of the anterior horns of the spinal cord, innervating the diaphragmatic, intercostal and auxiliary respiratory muscles.

Stimulation of muscles in response to irritation of the nasal mucosa causes a deep breath, closing the entrance to the larynx and then forced exhalation through the mouth and nose and removal of mucus and irritants.

The sneezing center is localized in the medulla oblongata at the ventromedial border of the descending tract and the nucleus (spinal nucleus) of the trigeminal nerve and includes neurons of the adjacent reticular formation and the solitary nucleus.

Disorders of the sneezing reflex can manifest as its excess or suppression. The latter occurs in mental illness and tumor diseases with the spread of the process to the sneezing center.

Vomit- this is a reflex removal of the contents of the stomach and, in severe cases, the intestines into the external environment through the esophagus and oral cavity, carried out with the participation of a complex neuro-reflex chain. The central link of this chain is the set of neurons that make up the vomiting center, localized in the dorsolatsral reticular formation of the medulla oblongata. The vomiting center includes a chemoreceptor trigger zone in the area of ​​the caudal part of the bottom of the fourth ventricle, in which the blood-brain barrier is absent or weakened.

The activity of neurons in the vomiting center depends on the influx of signals to it from sensory receptors in the periphery or on signals coming from other structures of the nervous system. Directly to the neurons of the vomiting center, afferent signals from taste receptors and from the wall of the pharynx arrive through the fibers of the VII, IX and X cranial nerves; from the gastrointestinal tract - along the fibers of the vagus and splanchnic nerves. In addition, the activity of the neurons of the vomiting center is determined by the receipt of signals from the cerebellum, vestibular nuclei, salivary nucleus, sensory nuclei of the trigeminal nerve, vasomotor and respiratory centers. Centrally acting substances that cause vomiting when introduced into the body usually do not have a direct effect on the activity of neurons in the vomiting center. They stimulate the activity of neurons in the chemoreceptor zone of the bottom of the fourth ventricle, and the latter stimulate the activity of neurons in the vomiting center.

The neurons of the vomiting center are connected via efferent pathways to the motor nuclei that control the contraction of the muscles involved in the implementation of the vomiting reflex.

Efferent signals from the neurons of the vomiting center go directly to the neurons of the nuclei of the trigeminal nerve, the dorsal motor nucleus of the vagus nerve, and the neurons of the respiratory center; directly or through the dorsolateral tegmentum of the bridge - to the neurons of the nuclei of the facial, hypoglossal nerves of the reciprocal nucleus, and motor neurons of the anterior horns of the spinal cord.

Thus, vomiting can be initiated by the action of drugs, toxins or specific emetics of central action through their influence on the neurons of the chemoreceptor zone and the influx of afferent signals from taste receptors and interoreceptors of the gastrointestinal tract, receptors of the vestibular apparatus, as well as from various parts of the brain.

Swallowing consists of three phases: oral, pharyngolaryngeal and esophageal. During the oral phase of swallowing, a bolus of food formed from crushed food moistened with saliva is pushed to the entrance to the pharynx. To do this, it is necessary to initiate contraction of the tongue muscles to push food, pulling up the soft palate and closing the entrance to the nasopharynx, contracting the muscles of the larynx, lowering the epiglottis and closing the entrance to the larynx. During the pharyngeal-laryngeal phase of swallowing, the bolus of food must be pushed into the esophagus and prevent food from entering the larynx. The latter is achieved not only by keeping the entrance to the larynx closed, but also by inhibiting inhalation. The esophageal phase is provided by a wave of contraction and relaxation in the upper parts of the esophagus of striated muscle, and in the lower parts - smooth muscles and ends with the pushing of the food bolus into the stomach.

From a brief description of the sequence of mechanical events of a single swallowing cycle, it is clear that its successful implementation can only be achieved with precisely coordinated contraction and relaxation of many muscles of the oral cavity, pharynx, larynx, esophagus and the coordination of the processes of swallowing and breathing. This coordination is achieved by a set of neurons that form the swallowing center of the medulla oblongata.

The swallowing center is represented in the medulla oblongata by two regions: dorsal - a solitary nucleus and neurons scattered around it; ventral - the reciprocal nucleus and neurons scattered around it. The state of activity of neurons in these areas depends on the afferent influx of sensory signals from the receptors of the oral cavity (root of the tongue, oropharyngeal region) arriving along the fibers of the glossopharyngeal and vagus nerves. The neurons of the swallowing center also receive efferent signals from the prefrontal cortex, limbic system, hypothalamus, midbrain, and pons along pathways descending to the center. These signals allow you to control the implementation of the oral phase of swallowing, which is controlled by consciousness. The pharyngeal-laryngeal and esophageal phases are reflex and are carried out automatically as a continuation of the oral phase.

The participation of the centers of the medulla oblongata in the organization and regulation of the vital functions of respiration and blood circulation, the regulation of other visceral functions is discussed in topics devoted to the physiology of respiration, blood circulation, digestion and thermoregulation.

Being an integral part of the brainstem, located on the border of the spinal cord and the pons, the medulla oblongata is a cluster of vital centers of the body. This anatomical formation includes elevations in the form of rollers, which are called pyramids.

This name didn't just appear out of nowhere. The shape of the pyramids is perfect, a symbol of eternity. The pyramids are no more than 3 cm long, but our life is concentrated in these anatomical formations. On the sides of the pyramids there are olive trees, and also outward the rear pillars.

This is a concentration of pathways - sensitive from the periphery to the cerebral cortex, motor from the center to the arms, legs, and internal organs.

The pathways of the pyramids include motor portions of nerves that partially intersect.

The crossed fibers are called the lateral pyramidal tract. The remaining fibers in the form of the anterior path do not lie on their side for long. At the level of the upper cervical segments of the spinal cord, these motor neurons also extend to the contralateral side. This explains the occurrence of motor disorders on the other side of the pathological focus.

Only higher mammals have pyramids, since they are necessary for upright walking and higher nervous activity. Thanks to the presence of pyramids, a person carries out commands that he hears, conscious thinking appears, and the ability to combine a set of small movements into combined motor skills.

Medulla, medulla oblongdta ( myelencephalon ), located between the hindbrain and the spinal cord.

Anatomy and topography of the medulla oblongata.

The upper border on the ventral surface of the brain runs along the lower edge of the pons; on the dorsal surface it corresponds to the medullary stripes of the fourth ventricle. The boundary between the medulla oblongata and the spinal cord corresponds to the level of the foramen magnum.

In the medulla oblongata there are ventral, dorsal and two lateral surfaces, which are separated by grooves.

Fissures of the medulla oblongata

are a continuation of the grooves of the spinal cord and have the same names: anterior median fissure,fissura mediana ventrdlls; posterior median sulcus,sulcus mednus dorsalis; anterolateral groove,sulcus ventrolaterdlis; posterolateral groove,sulcus dorsolaterdlis.

On the ventral surface medulla oblongata are located pyramids,pyramides.

In the lower part of the medulla oblongata, the bundles of fibers that make up the pyramids enter the lateral cords of the spinal cord. This fiber transition is called pyramid crossing,decussatioRUrAmidum. The decussation also serves as the anatomical boundary between the medulla oblongata and the spinal cord. On the side of each pyramid of the medulla oblongata there is olive,Oliva. In this groove, the roots of the hypoglossal nerve (XII pair) emerge from the medulla oblongata.

On the dorsal surface the thin and wedge-shaped bundles of the posterior cords of the spinal cord end.

Thin Bun

, fasciculus grdcilis, forms tubercle of the thin nucleus,tuberculum grdcile.

Wedge-shaped bundle

, fasciculus cuneatus, forms tubercle of the sphenoid nucleus,tuber­ culum cunnedtum.

Dorsal to the olive from the posterolateral sulcus of the medulla oblongata - retroolive furrow,sulcus retro— olivdris, the roots of the glossopharyngeal, vagus and accessory nerves (IX, X and XI pairs) emerge.

The dorsal part of the lateral funiculus is joined by fibers arising from the sphenoid and tender nuclei. Together they form the inferior cerebellar peduncle. The surface of the medulla oblongata, bounded below and laterally by the inferior cerebellar peduncles, participates in the formation of the rhomboid fossa, which is the bottom of the fourth ventricle.

In the inferolateral regions there are right and left lower olive kernels,nuclei olivares cauddles.

Slightly above the lower olive nuclei is located reticular formation,formdtio reticuldris. Between the lower olive cores there is an interolive layer, represented by internal arcuate fibers,fiber arcuatae internae, - shoots. These fibers form medial loop,lemniscus medialis. The fibers of the medial lemniscus belong to the proprioceptive pathway of the cortical direction and form in the medulla oblongata crossing of the medial loops,decussdtio lem— niscorum medidllum. Somewhat more ventral are the fibers of the anterior spinocerebellar and red nuclear spinal tracts. Above the intersection of the medial loops is the posterior longitudinal fasciculus, fasciculus longitudinalis dorsdlis.

Position of nuclei and pathways in the medulla oblongata.

The medulla oblongata contains nuclei IX, X, XI and XII pairs of cranial nerves.

The ventral sections of the medulla oblongata are represented by descending motor pyramidal fibers. Dorsolaterally, ascending pathways pass through the medulla oblongata, connecting the spinal cord with the cerebral hemispheres, brain stem and cerebellum.

Brain in all people it is considered the most important organ of the central nervous system (CNS). It is completely formed from cells, nerve endings and their processes. It is also divided into several sections, which include the cerebellum, midbrain, forebrain, pons, medulla oblongata and others.

And although medicine has made great progress, scientists and doctors continue to study this organ, since the secrets of its structure and functions have not yet been fully revealed.

Interesting fact: people of different sexes have different brain masses. In men it weighs 1345-1400 grams, and in women 1235-1275 grams. At the same time, scientists have proven that mental abilities do not depend on the mass of the brain. On average, the human brain in adulthood makes up 2% of the total body weight of a person.

Medulla oblongata

Division of the medulla oblongata(lat. Myelencephalon, Medulla oblongata) is one of the most important links that make up the structure of the brain. This section is represented by a continuation of the spinal cord in the form of its thickening, and also connects the brain to the spinal cord.

Oblong section looks very much like an onion. Below the medulla oblongata is the spinal cord, and above it is the pons. It turns out that this section connects the cerebellar part and the brain bridge with the help of special processes (legs).

U children in the first month of their life, this section is larger in size compared to other sections. Around the age of seven and a half, nerve fibers begin to become covered with a myelin sheath. This gives them additional protection.

Structure and structure of the oblongata section

In adults, the length of the oblongata is approximately 2.5-3.1 centimeters, which is where it got its name.

Its structure is very similar to the spinal cord and consists of gray and white brain matter:

1. Gray part located in the center of the brain and forms nuclei (clumps).
2. White part is located above and envelops the gray matter. It consists of fibers (long and short).

Nuclei oblongata part of the brain They are different, but they perform one function and connect it with other departments.

Types of kernels:

• olive-like kernels;
• Burdach and Gaulle kernels;
• nuclei of nerve endings and cells.

These kernels include:

• sublingual;
• accessory vagus;
• glossopharyngeal and descending nuclei of the ternary nerves.

Paths (descending and ascending) connect the main brain with the spinal cord, as well as with some parts. For example, with the reticular pharmacy, striopalidal system, cerebral cortex, limbic system and upper parts of the brain.

The medulla oblongata acts as a conductor for some reflex functions of the body.

These include:

• vascular;
• cardiac;
• digestive;
• vestibular;
• skeletal;
• protective.

It also contains some regulatory centers.

These include:

• management of respiratory functions;
• regulation of saliva secretion;
• regulation of vasomotor functions.

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Functions of the oblongata

This part of the brain performs very important tasks that are necessary for the proper functioning of all systems and functions of the body.

However, doctors consider the most important functions to be reflexive and conductive:

1. Reflex function. It is responsible for the body’s protective reactions that prevent the entry of germs and other pathogens and microorganisms. Reflex functions include lacrimation, coughing, sneezing and others. These functions also help the body remove harmful substances from the body.
2. Conductor function. It is activated and acts through ascending and descending pathways that transmit signals to systems and organs about a threat. With its help, the body can prepare for “defense.” The cortex, diencephalon, midbrain, cerebellum and spinal cord are connected through two-way communication thanks to the conductive pathways.

Doctors also highlight the associative or sensory function:

• It provides facial sensitivity.
• Responsible for taste buds and vestibular stimuli.

This function is activated impulses, which come from external stimuli to the medulla oblongata. There they are processed and move to the subcortical zone. After signal processing, chewing, swallowing or sucking reflexes occur.

If damage to the medulla oblongata occurs, this will provoke improper functioning of the muscles of the face, neck and head, and possibly paralysis of the entire body.

Surfaces of the oblong section

The medulla oblongata has several surfaces.

These include:

• ventral (front) surface;
• dorsal (posterior) surface;
• two side surfaces.

All surfaces connected between themselves, and between their pyramids there is a middle gap of medium depth. It is part of the median fissure, which is located in the spinal cord.

Ventral surface

Ventral surface consists of two lateral convex pyramid-shaped parts, which are narrowed downward. They are formed by pyramidal tracts. In the median fissure, the fibers of the pyramidal parts intersect with the approach to the adjacent part and enter the cable fibers of the spinal cord.

The places where crossover occurs are edge medulla oblongata at the junction with the spinal cord. Olives are located near the pyramids. These are small elevations that are separated from the pyramidal surface by an anterolateral groove. The roots of the sublingual nerve endings and the nerves themselves extend from this groove.

Dorsal surface

Dorsal surface doctors call the posterior surface of the medulla oblongata. On the sides of the groove are the posterior funiculi, which are bounded on both sides by the posterolateral grooves. Each of the cords is divided by the posterior intermediate groove into two bundles: thin and wedge-shaped.

The main task of the beam is impulse transmission from the lower body. The bundles in the upper part of the oblong section expand and transform into thin tubercles, in which the nuclei of the bundles are located.

The main task wedge-shaped bundles The conduction and transmission of impulses from the joints, bones and muscles of the upper and lower extremities is considered. The expansion of each bundle allows the formation of additional wedge-shaped tubercles.

Posterolateral groove serves as a kind of outlet for the roots of the glossopharyngeal, accessory and vagus nerves.

Between the dorsal and ventral surfaces are located side surfaces. They also have lateral grooves that originate in the spinal cord and enter the medulla oblongata.

The medulla oblongata of the brain of the head organizes the smooth and coordinated functioning of the entire brain. The centers of nerve cells and endings, as well as pathways, allow information to quickly reach the required part of the brain and send a signal at the neuron level.

Cores, which are located on the surfaces of the medulla oblongata, allow incoming impulses to be converted into information that can be transmitted further.

Medulla oblongata (myelencephalon, bulbus) , - a derivative of the rhombencephalon, which at the stage of five vesicles is divided into the hindbrain, metencephalon , and medulla oblongata, myelencephalon.

Topography of the medulla oblongata.

Being part of the brain stem, it is a continuation of the spinal cord in the form of its thickening.

The medulla oblongata has cone shape , somewhat compressed in the posterior sections and rounded in the anterior ones. Its narrow end is directed down to the spinal cord, the upper, widened, to the pons and cerebellum.

The border between the medulla oblongata and the spinal cord is considered to be the exit point of the superior radicular filament of the first cervical nerve or the lower level of the decussation of the pyramids. The medulla oblongata is separated from the pons by a well-defined transverse bulbar-pontine groove on the anterior surface, from which the abducens nerve emerges onto the surface of the brain.

The longitudinal size of the medulla oblongata is 3.0-3.2 cm, the transverse size is on average up to 1.5 cm, and the anteroposterior size is up to 1 cm.

Medulla oblongata, bridge, pons, and cerebral peduncles, pedunculi cerebri;

front view.

The anterior (ventral) surface of the medulla oblongata is located on the slope and occupies its lower portion to the foramen magnum. The anterior median fissure passes through it, fissura mediana ventralis (anterior), which is a continuation of the spinal cord fissure of the same name.

At the level of the exit of the radicular filaments of the first pair of cervical nerves, the anterior median fissure is somewhat interrupted and becomes less deep due to the decussation of the pyramids formed here (motor decussation), decussatio pyramidum(decussatio motoria).

In the upper parts of the anterior surface of the medulla oblongata, on each side of the anterior median fissure there is a cone-shaped ridge - a pyramid (of the medulla oblongata), pyramidis (medullae oblongatae).

On transverse sections of the medulla oblongata, it can be determined that each pyramid is a complex of bundles (they are visible if the edges of the anterior median fissure are stretched to the sides), which partially intersect each other. Next, the fibers pass into the system of the lateral cord of the spinal cord, where they follow lateral corticospinal (pyramidal) tract. The remaining, smaller part of the bundles, without entering the decussation, follows in the system of the anterior cord of the spinal cord as anterior corticospinal (pyramidal) tract. These paths are combined into a single pyramidal path.

Outside the pyramid there is an oblong-rounded elevation - olive, oliva. It protrudes on the anterior surface of the lateral funiculus; behind it is limited by the retroolive groove, sulcus retroolivaris.

Medulla oblongata
oblongata; top view and several
front.

The olive is separated from the pyramid by an anterolateral groove, sulcus ventrolateralis (anterolateralis), which is a continuation of the spinal cord groove of the same name.

The transition of this groove from the spinal cord to the medulla oblongata is smoothed out by transversely running external arcuate fibers, fibrae arcuatae externae, which, located at the lower edge of the olive, are directed towards the pyramid.

There are anterior and posterior external arcuate fibers, fibrae arcuatae externae ventrales (anteriores) et dorsales (posteriores).

Anterior outer arcuate fibers are processes of cells of arcuate nuclei, nuclei arcuati, - accumulations of gray matter adjacent to the anterior and medial surfaces of the pyramid. These fibers emerge on the surface of the medulla oblongata in the region of the anterior median fissure, bend around the pyramid and olive, and follow as part of the inferior cerebellar peduncle to the cerebellar nuclei.

Posterior external arcuate fibers formed by processes of cells of the additional wedge-shaped nucleus, nucleus cuneatus accessorius, and are directed to the cerebellum as part of the inferior cerebellar peduncle of its side. The accessory cuneate nucleus is located dorsolateral to the cuneate nucleus, nucleus cuneatus. From the depths of the anterolateral groove, 6 to 10 roots of the hypoglossal nerve emerge to the surface of the medulla oblongata.

On transverse sections made through the olives, in addition to nerve fibers, accumulations of gray matter can also be distinguished. The largest of the clusters is horseshoe-shaped, with a folded surface - this is olive cloak, amiculum olivare, and the core itself is the lower olive core, nucleus olivaria caudalis, which contains the gate of the lower olive core, hilum nuclei olivaris caudalis (inferioris), for the olivocerebellar pathway.

Other nuclei are smaller: one lies medially - the medial accessory olivary nucleus, nucleus olivaris accessorius medialis, the other posteriorly is the posterior accessory olivary nucleus, nucleus olivaris accessorius dorsalis (posterior).

On the dorsal (posterior) surface of the medulla oblongata is the posterior median sulcus, sulcus medianus dorsalis (posterior). Heading upward, it reaches the thin brain plate - valves, obex. The latter, stretched between the tubercles of the thin nucleus, is part of the roof of the IV ventricle in the region of the posterior angle of the rhomboid fossa. Under the valve, the cavity of the central canal of the spinal cord passes into the cavity of the fourth ventricle.

Diamond-shaped fossa, fossa rhomboidea; top and back view.

There are two grooves running outward from the posterior median sulcus: one closer to the median sulcus - intermediate groove, the other more laterally is the posterolateral groove, sulcus dorsolateralis (posterolateralis). From the depths of the latter, 4-5 roots of the glossopharyngeal nerve, 12-16 roots of the vagus nerve and 3-6 cranial roots of the accessory nerve emerge to the surface of the medulla oblongata.

The posterior median and posterolateral grooves limit the posterior funiculus, funiculus posterior, which is a continuation of the spinal cord cord of the same name. The intermediate groove divides the posterior funiculus into two bundles. One bundle lies between it and the posterior median sulcus - this is a thin bundle fasciculus gracilis, passing at the top into a thickening - a tubercle of the thin nucleus, tuberculum gracile. The second fascicle is located between the intermediate and posterolateral sulci - this is the wedge-shaped fascicle, fasciculus cuneatus, passing at the top into a less pronounced tubercle of the sphenoid nucleus, tuberculum cuneatum. Each tubercle without sharp boundaries passes into the inferior cerebellar peduncle.

In both tubercles there are accumulations of gray matter: in the tubercle of the thin nucleus there is a thin nucleus, nucleus gracilis, in the tubercle of the sphenoid nucleus - the sphenoid nucleus, nucleus cuneatus. The fibers of the corresponding bundles of the posterior cord end on the cells of these nuclei.

On the dorsal surface of the medulla oblongata, between the sphenoid culcus and the roots of the accessory nerve, there is a variable elevation - the trigeminal tubercle, tuberculum trigeminale. It is formed by the caudal portion of the spinal tract nucleus of the trigeminal nerve.

Immediately at the upper end of the posterolateral sulcus, above the roots of the glossopharyngeal nerve, as a continuation of the posterior and lateral cords, there is a semicircular thickening - the inferior cerebellar peduncle. Each inferior cerebellar peduncle, right and left, includes fibers of the conduction systems, which form its lateral, larger, and medial, smaller parts.

On transverse sections of the medulla oblongata, dorsal to the pyramids, between the olivary nuclei, lie the fibers that make up the ascending tracts connecting the spinal cord to the brain. reticular formation, formatio reticularis, The medulla oblongata is represented by numerous clusters of neurons and complexly intertwined fibers. It is located predominantly in the dorsomedial part of the medulla oblongata and, without a distinct boundary, passes into the reticular formation of the pons. The nuclei of the VIII-XII pairs of cranial nerves are located in the same zone.

The reticular formation of the medulla oblongata also includes a number of cell accumulations localized near the nucleus of the hypoglossal nerve and the nucleus of the solitary tract: the posterior paramedian nucleus, nucleus paramedianus dorsalis (posterior); intercalary nucleus nucleus intercalatus, nucleus of the parasolitary tract, nucleus parasolitaris; commissural nucleus nucleus comissuralis.

The central core of the substance of the medulla oblongata, formed by clusters of reticular cells and their processes, is designated as the suture of the medulla oblongata, raphe medullae oblongatae.

Groups of cells of the reticular formation located paramedianly are designated as raphe nuclei, nuclei raphae.