The trunk of the brain

The trunk of the brain is the extension of the spinal cord in the rostral direction. The conditional boundary between them is the place where the first cervical roots and the cross of the pyramids exit. The trunk is divided into the posterior and middle brains. The first includes the medulla oblongata, the brain bridge and the cerebellum. Its continuation is the middle brain, consisting of quadruplets and cerebral legs and bordering on the intermediate brain (the thalamus, hypothalamus, subthalamus). Ontogenetically, the spinal cord and trunk develop from the medullary tube, while the remaining parts of the brain (cerebellum, forebrain) are the derivatives of these formations. The spinal cord and the brain stem are considered as the central tubular core of the brain, consisting of a relatively undifferentiated neuronal mass, to which specific neural groups join from the outer surface as appendages. If in the spinal cord the sensory and motor constellations constitute continuous half-columns in the form of anterior and posterior horns, then in the brain stem, these formations look like independent nuclei, in the topography of which traces of continuous columns of the spinal cord are traced. Thus, the dorsomedial series comprise the motor nuclei of XII, VI, IV, III pairs of cranial nerves, and the anterolateral column - gill motor nuclei (XI, X, VII, V). The V system of the nerve clearly corresponds to the dorsal horn of the spinal cord, while the real gill senseus (X, IX) is less clearly separated from the core. A special position is occupied by the VIII nerve: one part of its nuclei - the vestibular one - is part of the core of the brain, the auditory nuclei have a separate highly differentiated structure.

Thus, a part of the brainstem formations (namely, the nucleus of the cranial nerves) is the homolog of the anterior and posterior horns of the spinal cord and carries out segmentary innervation. The second composite specific part of the brainstem is the ascending classical afferent systems that carry information to the brain from extero-, proprio- and interoreceptors, as well as the pyramidal pathway to the spinal cord descending from the cerebral cortex. The latter provision should be accepted with a reservation, since the fibers from the cells of Betz (motor cortex) form a small part of the pyramidal tract. The latter includes both descending fibers from the autonomic apparatus of the brain, and fibers that carry the efferent function of the cortical-subcortical formations that organize the motor act. In addition, there are clearly differentiated formations in the brain stem: olives, a red core, a black substance that plays an important role in cortical-subcortical-stem-cerebellar systems regulating the maintenance of the posture and the organization of movements. The red nucleus is the beginning of the rubospinal pathway, which is described in animals and is absent, according to the latest data, in humans.

In addition to the three groups of formations (nuclei of the cranial nerves, classical afferent and efferent pathways and distinctly differentiated nuclear groups), the network of the brain stem includes a networked formation represented by a diffuse cluster of cells of different types and sizes separated by a multitude of differently directed fibers. The anatomy of the reticular formation of the brainstem has been described for a long time. In recent decades, the most serious studies have been carried out by J. Olscewski (1957), A. Brodal (1958), AL Leontovich (1968), and others.

Along with the ideas of the diffuseness of influences and the absence of regularities in morphological organization, a theory has developed on the existence of a morphofunctional structure of a networked formation. The most common cytoarchitectonic patterns consist of the identification in the medial regions of the reticular formation of the medulla oblongata and the brain bridge of large and even giant neurons, in the lateral sections of the same level, small and medium neurons are found; In the reticular formation of the midbrain there are mainly small neurons. In addition, J. 0I-scewski (1957) identified within the reticular formation 40 nuclei and sub-nuclei, the largest of which are the following:

1. lateral reticular nucleus, located lateral and downward from the lower olive;
2. the reticular nucleus of the Bekhterev bridge cover is dorsal to the bridge's own nuclei;
3. the paramedian reticular nucleus is near the midline, dorsal from the lower olive;
4. reticular giant cell nucleus - from the olive to the level of the nuclei of the VIII pair;
5. caudal reticular nucleus of the bridge;
6. the oral reticular nucleus of the bridge;
7. reticular small cell nucleus of the medulla oblongata;
8. the reticular central nucleus of the medulla oblongata.

The reticular formation of the midbrain is less differentiated, the functional organization of which is refined as the study of the chodynological regularities. Efferent projections are clearly divided into two groups: projecting and not projecting onto the cerebellum. Three of the nuclei described above send their neurons to the cerebellum, while neurons have no other projections and are naturally associated with certain parts of the cerebellum. Thus, the lateral reticular nucleus sends fibers through the rope bodies to the homolateral sections of the cerebellum and hemisphere, the paramedian reticular nucleus - mainly homolaterally in the worm and the nucleus of the cerebellum, the reticular nucleus of the bridge cover - in the worm and hemisphere. In addition, the paramedian reticular nucleus transmits impulses mainly from the cerebral cortex, and the lateral nucleus - from the spinal cord.

Among the systems not projecting onto the cerebellum, the descending and ascending projections are distinguished. The main descending path is the reticulospinal, descending into the spinal cord along the anterior (ventral bundle) and lateral (medial and lateral bundles) columns of the spinal cord. Reticulospinal pathway originates from the bridge nuclei (the fibers go ipsilateral in the ventral columns) and the medulla oblongata (the fibers go in the lateral column to both halves of the spinal cord). In addition to the above-mentioned fibers, the tectospinal, vestibulo-spinal and rubrospinal (in animals) pathways are part of the reticulospinal pathway.

The ascending reticular pathways begin in the medial sections of the bridge of the brain and the medulla oblongata and in the central bundle of the tire reach the thalamus ( centrum medianum, reticular and intralaminar nuclei), hypothalamus, preoptic and septum. The fibers from the neurons of the midbrain go mainly to the hypothalamus, and from the more caudal divisions to the thalamus and subtalamus.

The afferent connections of the reticular formation are determined by the interaction with the cerebellum, spinal cord and brain regions lying higher. Cerebellar-reticular pathways start from the cerebellar nuclei and terminate on the neurons of the reticular formation, from where they are mainly directed to the red nucleus and thalamus.

Spinal cord pathways originate at all levels of the spinal cord, go in the lateral columns of it and terminate in the reticular formation of the medulla oblongata and the bridge of the brain. In the reticular formation, collaterals also terminate, departing from all sensory classical pathways.

Descending ways to the reticular formation are formed from fibers coming from the frontotemporal temporal cortex with the pyramidal tract; from the hypothalamus (periventricular system to the middle - longitudinal posterior fasciculus - and oblong brain); from the mastoid-cover bundle from the mamillary bodies to the reticular formation of the brainstem; from the tectoreticular path (straight and intersecting) - from the upper to the lower.

In close interaction with the reticular formation of the brainstem, a complex of vestibular nuclei is located, isolated from the neurons that make up its structure. The largest is the pre-door lateral core (the core of Deiters). The pre-upper upper nucleus (the Bechterew nucleus), the medial and lower vestibular nuclei are also differentiated clearly. The data of education have characteristic hodological links, allowing to understand their functional purpose. The efferent pathways from the vestibular lateral nucleus are directed to the spinal cord (homolateral vestibulospinal tract with somatotypic organization) and other vestibular nuclei. Paths from the pre-door lateral nuclei to the cerebellum were not detected. The upper vestibular nucleus is projected in the oral direction and follows in the medial longitudinal bundle to the nuclei of the oculomotor nerves. The medial and inferior vestibular nuclei are less specific, and their neurons direct their axons in the oral and caudal directions, ensuring the implementation of integrative processes.

The reticular formation of the brainstem can be regarded as one of the most important integrative devices of the brain. It has an independent meaning and at the same time is part of a wider integrating brain system. Some authors therefore include in the reticular formation the caudal sections of the hypothalamus, the reticular formation of the hypothalamus, the reticular nuclei of the hypothalamus.

Actually integrative functions of the reticular formation K. Lissak (1960) subdivides as follows:

1. sleep and wakefulness control;
2. phase and tonic muscular control;
3. decoding of information signals of the environment by modifying reception and carrying out pulses arriving through various channels.

In the brain stem there are also formations occupying an intermediate position between the so-called specific and nonspecific systems. These include congestion of neurons, which are designated as respiratory and vasomotor center. There is no doubt that these vital entities have a complex organization. The respiratory center has sections regulating the inhalation (inspiratory) and exhalation (expiratory) separately, and inside the vascular center there were described the populations of neurons determining the slowing or acceleration of the heart rate, the decrease or rise in blood pressure. In recent years, the homeostasis of arterial pressure has been studied in detail. Impulses from the baroreceptors located in the heart, carotid sinus, aortic arch and in other large vessels are transferred to the stem formations - the nucleus of the solitary tract and the paramedian nuclei of the reticular formation. From these structures, efferent influences go to the nuclei of the X nerve and to the vegetative nuclei of the spinal cord. The destruction of the nucleus of the solitary tract leads to an increase in blood pressure. We designate these formations as semi-specific. The same nuclei of the solitary tract participate in the regulation of sleep and wakefulness, and their irritation, in addition to circulatory or respiratory effects, is manifested by a change in the EEG and muscle tone, ie, forms a certain pattern of holistic forms of activity.

The descending influences of the reticular formation are realized through the reticulospinal path, which facilitates or inhibits the segmental apparatus of the spinal cord. The inhibiting field corresponds to the giant cell reticular nucleus, with the exception of its rostral part, and to the reticular nucleus of the medulla oblongata. The facilitating zones are less clearly localized, they capture a large zone - part of the giant cell nucleus, the core of the bridge; facilitating influences from the midbrain level are realized through polysynaptic connections. The descending influences of the reticular formation affect a- and y-motoneurons, which affect the muscle spindles and the intercalary neurons.

It is shown that most fibers of the reticulospinal tract terminate not below the thoracic segments and only vestibulospinal fibers can be traced to the sacral segments. The reticulospinal path also regulates the activity of the cardiovascular system and respiration.

Undoubtedly, the central integration of somatic and vegetative activity is one of the basic needs of the body. A certain stage of integration is carried out by the reticular formation of the trunk. It is important to note that somatic and vegetative influences go through the reticulospinal path and that the fields that increase motoneuron activity, arterial pressure and respiratory rate increase are very close. The opposite somatovegetative reactions are also related to each other. Thus, irritation of the carotid sinus leads to inhibition of respiration, cardiovascular activity and postural reflexes.

Important ascending streams of the reticular formation receiving abundant collaterals from classical afferent pathways, trigeminal and other sensitive cranial nerves. At the first stages of studying the physiology of the reticular formation, it was assumed that the stimuli of any modality cause a nonspecific activation flow directed toward the cerebral cortex. These ideas were shaken by the work of PK Anokhin (1968), which revealed the specific nature of this impulse, depending on various biological forms of activity. At the present time, the participation of the reticular formation in the decoding of information signals of the environment and the regulation of diffuse, to a certain extent, specific fluxes of ascending activity became evident. Data were obtained on the specific connections of the brainstem and forebrain to the organization of situational specific behavior. Connections with forebrain structures are the basis for sensory integration processes, elementary learning processes, memory functions.

Obviously, for the implementation of holistic forms of activity, the integration of ascending and descending flows, the unity of the psychic, somatic and vegetative components of holistic acts is necessary. There are a sufficient number of facts that indicate the correlation of descending and ascending influences. It was found that EEG wake-up reactions correlate with vegetative shifts-pulse rate and pupil size. Irritation of the reticular formation simultaneously with the EEG reaction of awakening caused an increase in the activity of muscle fibers. This relationship is explained by anatomical and functional features of the organization of the reticular formation. Among them there are a large number of interrelations between different levels of the reticular formation, carried out with the help of neurons with short axons, neurons with dichotomous division, axons having ascending and descending projections rostral and caudal. In addition, a general pattern has been revealed, according to which neurons with a rostral projection are located more caudally than neurons that make downdrafts, while they exchange many collaterals. It was also discovered that the cortical-reticular fibers terminate in the caudal sections of the reticular formation, from which the reticulospinal path originates; spinal-reticular pathways end in zones where ascending fibers arise to the thalamus and subthalamus; Oral departments receiving impulses from the hypothalamus, in turn, direct to it their projections. These facts indicate a vast correlation of descending and ascending influences and an anatomical and physiological basis for the implementation of this integration.

The reticular formation, being an important integrative center, in its turn represents only a part of more global integrative systems, including limbic and neocortical structures, in cooperation with which the organization of expedient behavior aimed at adapting to the changing conditions of the external and internal environment is carried out.

Rhinencephalic formations, septum, thalamus, hypothalamus, reticular formation are separate links of the functional system of the brain, which provides integrative functions. It should be emphasized that these structures are not limited to brain devices involved in the organization of holistic forms of activity. It is also important to note that when entering into one functional system built on a vertical principle, individual links have not lost specific features.

An important role in ensuring the coordinated activity of these formations is played by the medial fascicle of the forebrain that connects the anterior, intermediate and middle brain. The main links, united by the ascending and descending fibers of the bundle, are the septum, tonsil, hypothalamus, reticular nuclei of the midbrain. The medial fascicle of the forebrain provides circulation of impulses within the limbic-reticular system.

The role of the new cortex in vegetative regulation is also evident. There are numerous experimental data on the stimulation of the cortex: thus, vegetative responses arise (it should be emphasized only that there is no strict specificity of the effects obtained). When stimulated by the wandering, celiac or pelvic nerve in the various zones of the cortex of the large hemispheres, the evoked potentials are recorded. Efferent vegetative influences are realized through fibers that are part of pyramidal and extrapyramidal pathways, where their specific gravity is great. With the participation of the cortex, the vegetative maintenance of such forms of activity as speech, singing is carried out. It is shown that, with the intention to perform a certain movement in humans, the improvement of the circulation of muscles participating in this act outstrips this movement.

Thus, the limbic-reticular complex, the features of which distinguish it from segmental autonomic apparatuses, are the leading link participating in supra-segmental vegetative regulation:

1. the irritation of these structures does not entail a strictly specific vegetative reaction and usually causes combined psychic, somatic and vegetative changes;
2. their destruction does not entail certain regular violations, except when specialized centers are being struck;
3. there are no specific anatomical and functional features characteristic for segmental vegetative apparatuses.

All this leads to an important conclusion about the absence of sympathetic and parasympathetic divisions at the investigated level. We support the point of view of the largest modern vegetologists who consider it expedient to divide the ngsegmental systems into ergotrophic and trophotropic systems, using the biological approach and the different role of these systems in the organization of behavior. The ergotropic system contributes to adaptation to the changing conditions of the external environment (hunger, cold), provides physical and mental activity, the course of catabolic processes. Trophotropic system causes anabolic processes and endophysical reactions, provides nutritional functions, helps maintain homeostatic balance.

The ergotropic system determines mental activity, motor readiness, vegetative mobilization. The degree of this complex reaction depends on the importance, significance of the novelty of the situation with which the organism met. At the same time, the devices of the segmental sympathetic system are widely used. The optimal blood circulation of working muscles is ensured, blood pressure rises, minute volume increases, coronary and pulmonary arteries expand, spleen and other blood vessels are reduced. In the kidneys there is a powerful vasoconstriction. Expanding bronchi, increasing pulmonary ventilation and gas exchange in the alveoli. The peristalsis of the digestive tract and the secretion of digestive juices are suppressed. The liver mobilizes glycogen resources. Defecation and urination are inhibited. Thermoregulation systems protect the body from overheating. The ability of the striated musculature increases. The pupil is enlarged, the excitability of the receptors increases, the attention becomes more acute. The ergotropic alteration has the first neural phase, which is enhanced by the secondary humoral phase, which depends on the level of circulating epinephrine.

The trophotropic system is associated with a rest period, with the digestive system, with some stages of sleep ("slow" sleep) and mobilizes, in its activation, mainly the vagoinsular apparatus. There is a slowing of the heart rate, a decrease in the strength of the systole, an increase in diastole, a decrease in blood pressure; breathing is calm, somewhat slower, bronchi slightly narrowed; increased intestinal peristalsis and secretion of digestive juices; the action of the excretory organs is intensified: braking of the motor somatic system is observed.

Inside the limbic-reticular complex, zones are distinguished, with the stimulation of which it is possible to obtain predominantly ergotropic or trophotropic effects.

Often, the principal difference between sympathetic and parasympathetic effect, on the one hand, and ergotropic and trophotropic, on the other, is not clearly detected. The first concept is anatomical and functional, the second is functional-biological. The first apparatuses are connected exclusively with the segmental vegetative system, and their damage has certain manifestations; the latter do not have a clear structural base, their defeat is not strictly deterministic and manifests itself in a number of areas - the psychic, the motor, and the vegetative. Nassegmental systems use certain vegetative systems to organize proper behavior - predominantly, but not exclusively, one of them. The activity of the ergotropic and trophotropic systems is organized synergistically, and one can note only the predominance of one of them, which in physiological conditions is precisely correlated with the concrete situation.