The role of red nuclei. The red nucleus of the midbrain is the center of the extrapyramidal system
107. Midbrain. Midbrain nuclei
Midbrain (mesencephalon) develops from the mesencephalon and is part of the brain stem. On the ventral side it is adjacent to the posterior surface of the mastoid bodies in front and the anterior edge of the bridge behind (Fig. 3.14, 3.15). On the dorsal surface, the anterior border of the midbrain is the level of the posterior commissure and the base of the pineal gland (epiphysis), and the posterior border is the anterior edge of the medullary velum. The midbrain includes the cerebral peduncles and the roof of the midbrain (Fig. 3.27; Atl.). The cavity of this part of the brain stem is brain aqueduct - a narrow canal that communicates below with the fourth ventricle, and above with the third (Fig. 3.27). In the midbrain there are subcortical visual and auditory centers and pathways that connect the cerebral cortex with other brain structures, as well as pathways that transit through the midbrain and its own pathways.
Four Hills, or roof of the midbrain (tectum mesencephali)(Fig. 3.27) is divided into superior and inferior colliculi by grooves perpendicular to each other. They are covered by the corpus callosum and the cerebral hemispheres. On the surface of the mounds there is a layer of white matter. Below it, in the superior colliculus, lie layers of gray matter, and in the lower colliculus, the gray matter forms nuclei. Some pathways end and begin from gray matter neurons. The right and left colliculi in each colliculus are connected by commissures. From each hillock extend laterally handles of mounds, which reach the geniculate bodies of the diencephalon.
Superior colliculus contains centers of orienting reflexes to visual stimuli. The fibers of the optic tract reach the lateral geniculate bodies, and then some of them along the handles of the upper mounds continues into the superior colliculi, the rest of the fibers go to the thalamus.
Inferior colliculus serves as the center of orienting reflexes to auditory stimuli. Handles extend forward and outward from the mounds, ending at the medial geniculate bodies. The mounds receive some of the fibers lateral loop the rest of its fibers go as part of the handles of the lower colliculi to the medial geniculate body.
Originates from the roof of the midbrain tectospinal tract. Its fibers after cross in the tegmentum of the midbrain they go to the motor nuclei of the brain and to the cells of the anterior horns of the spinal cord. The pathway carries efferent impulses in response to visual and auditory stimuli.
At the border of the midbrain and diencephalon lie preopercular(pretectal) kernels, having connections with the superior colliculus and parasympathetic nuclei of the oculomotor nerve. The function of these nuclei is the synchronous reaction of both pupils when the retina of one eye is illuminated.
Pedunculi cerebri occupy the anterior part of the midbrain and are located above the pons. Between them, the roots of the oculomotor nerve (III pair) appear on the surface. The legs consist of a base and a tegmentum, which are separated by highly pigmented cells of the substantia nigra (see Atl.).
IN base of the legs passes a pyramidal path consisting of corticospinal, traveling through the pons to the spinal cord, and corticonuclear, the fibers of which reach the neurons of the motor nuclei of the cranial nerves located in the area of the fourth ventricle and aqueduct, as well as cortical-pontine pathway, ending on the cells of the base of the bridge. Since the base of the peduncles consists of descending pathways from the cerebral cortex, this part of the midbrain is the same phylogenetically new formation as the base of the pons or pyramid of the medulla oblongata.
Black substance separates the base and tegmentum of the cerebral peduncles. Its cells contain the pigment melanin. This pigment exists only in humans and appears at the age of 3–4 years. The substantia nigra receives impulses from the cerebral cortex, striatum and cerebellum and transmits them to the neurons of the superior colliculus and brainstem nuclei, and then to the motor neurons of the spinal cord. The substantia nigra plays an essential role in the integration of all movements and in the regulation of the plastic tone of the muscular system. Disruption of the structure and function of these cells causes parkinsonism.
Leg cover continues the tegmentum of the pons and medulla oblongata and consists of phylogenetically ancient structures. Its upper surface serves as the bottom of the brain's aqueduct. The kernels are located in the tire bloc(IV) and oculomotor(III) nerves. These nuclei develop in embryogenesis from the main plate lying under the marginal sulcus, consist of motor neurons and are homologous to the anterior horns of the spinal cord. Lateral to the aqueduct, it extends along the entire midbrain nucleus of the mesencephalic tract trigeminal nerve. It receives proprioceptive sensitivity from the muscles of mastication and the muscles of the eyeball.
Underneath the gray matter surrounding the aqueduct, from neurons intermediate core the phylogenetically old path begins - medial longitudinal fasciculus. It contains fibers connecting the nuclei of the oculomotor, trochlear and abducens nerves. The bundle is also joined by fibers starting from the nucleus of the vestibular nerve (VIII) and carrying impulses to the nuclei of the III, IV, VI and XI cranial nerves, as well as descending ones to the motor neurons of the spinal cord. The bundle passes into the pons and medulla oblongata, where it lies under the bottom of the fourth ventricle near the midline, and then into the anterior column of the spinal cord. Thanks to such connections, when the balance apparatus is irritated, the eyes, head and limbs move.
In the region of the nuclei of the third pair of nerves lies the parasympathetic nucleus; it develops at the site of the border sulcus and consists of interneurons of the autonomic nervous system. In the upper part of the tegmentum of the midbrain there passes the dorsal longitudinal fasciculus, connecting the thalamus and hypothalamus with the nuclei of the brain stem.
At the level of the inferior colliculus it occurs cross fibers of the superior cerebellar peduncles. Most of them end up in massive cellular clusters lying in front - red nuclei (nucleus ruber), and the smaller part passes through the red nucleus and continues to the thalamus, forming dentate-thalamic tract.
Fibers from the cerebral hemispheres also end in the red nucleus. From its neurons there are ascending pathways, in particular to the thalamus. The main descending pathway of the red nuclei is rubrospinal (rednuclear-spinal cord). Its fibers, immediately upon exiting the nucleus, cross over and are directed along the tegmentum of the brain stem and the lateral cord of the spinal cord to the motor neurons of the anterior horns of the spinal cord. In lower mammals, this pathway transmits to them, and then to the muscles of the body, impulses switched in the red nucleus, mainly from the cerebellum. In higher mammals, the red nuclei function under the control of the cerebral cortex. They are an important part of the extrapyramidal system, which regulates muscle tone and has an inhibitory effect on the structures of the medulla oblongata.
The red nucleus consists of large cell and small cell parts. The large cell part is developed to a large extent in lower mammals, while the small cell part is developed in higher mammals and in humans. The progressive development of the small cell part proceeds in parallel with the development of the forebrain. This part of the nucleus is like an intermediate node between the cerebellum and the forebrain. The large cell part in humans is gradually reduced.
Lateral to the red nucleus in the tegmentum is located medial loop. Between it and the gray matter surrounding the aqueduct lie nerve cells and fibers reticular formation(continuation of the reticular formation of the pons and medulla oblongata) and pass through ascending and descending pathways.
The midbrain develops in the process of evolution under the influence of visual afferentation. In lower vertebrates, which have almost no cerebral cortex, the midbrain is highly developed. It reaches significant sizes and, together with the basal ganglia, serves as a higher integrative center. However, only the superior colliculus is developed in it. In mammals, in connection with the development of hearing, in addition to the upper ones, the lower tubercles also develop. In higher mammals and, in particular, in humans, in connection with the development of the cerebral cortex, the higher centers of visual and auditory functions move into the cortex. In this case, the corresponding centers of the midbrain find themselves in a subordinate position.
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RED CORE RED CORE
(nucleus ruber), a structure of the midbrain of terrestrial vertebrates, located symmetrically in the thickness of the cerebral peduncles under the central gray matter. K. I. consists of a phylogenetically ancient (reptiles, birds) large cell part (neuron body diameter 50-90 µm), from which the descending rubrospinal tract begins, and a young (mammals) small cell part (diameter 20-40 µm), switching impulses from the nuclei cerebellum to thalamus. The number of small cell neurons increases in primates and humans. K. I. has projections to the motor nuclei of the spinal cord, which control the movement of the fore and hind limbs, and is under the control of the cerebral cortex. The cerebral cortex is an important intermediate authority for integrating the influences of the forebrain and cerebellum during the formation of the brain. commands to the neurons of the spinal cord.
.(Source: “Biological Encyclopedic Dictionary.” Editor-in-chief M. S. Gilyarov; Editorial Board: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected - M.: Sov. Encyclopedia, 1986.)
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Functions of the spinal cord. The spinal cord performs two functions - reflex and conduction. Spinal cord reflexes can be divided into motor(carried out by alpha motor neurons of the anterior horns), and vegetative(carried out by cells of the lateral horns). Motor elementary reflexes - flexion and extension, tendon, myotatic, rhythmic, tonic. The spinal cord contains the centers of the autonomic nervous system: vasomotor, sweating, respiratory, urinary, defecation, and reproductive centers.
The conductive function of the spinal cord is associated with the transmission of information flow from the periphery to the overlying parts of the nervous system and with the conduction of impulses coming from the brain to the spinal cord.
Brain functions. The brain is divided into five main sections: the medulla oblongata, hindbrain, midbrain, diencephalon, and forebrain.
Functions of the medulla oblongata. Performs two functions - reflex and conductive. The following reflexes occur through the medulla oblongata: 1) protective: coughing, sneezing, blinking, vomiting, lacrimation; 2) food: sucking, swallowing, secretion of juice from the digestive glands; 3) cardiovascular, regulating the activity of the heart and blood vessels; 4) in the medulla oblongata there is a respiratory center that provides ventilation to the lungs; 5) changes in posture are carried out due to static and statokinetic reflexes.
Conducting pathways pass through the medulla oblongata, connecting the cortex, diencephalon, midbrain, cerebellum and spinal cord with a bilateral connection.
Functions of the hindbrain. The hindbrain includes the pons and cerebellum. Functions bridge determined by the structures included in it. The ascending and descending pathways connecting the medulla oblongata and cerebellum with the cerebral hemispheres pass through the bridge. It conducts impulses from one hemisphere of the cerebellum to the other, coordinating muscle movements on both sides of the body; participates in the regulation of complex motor acts, muscle tone and body balance.
Cerebellum is a suprasegmental department of the central nervous system that does not have a direct connection with the executive organs. It takes part in the regulation of postural-tonic reactions and coordination of motor activity. After removal of the cerebellum, the animal experiences motor disturbances: body position reflexes, static reflexes and voluntary movements are impaired. With unilateral removal of the cerebellum, a disturbance in movements occurs on the side of the operation: muscle tone increases, the head and torso turn in the same direction, and therefore the animal moves in a circle. The cerebellum takes part in the regulation of autonomic functions: breathing, digestion, cardiovascular activity, thermoregulation.
Functions of the midbrain. The midbrain consists of the cerebral peduncles and quadrigeminal region. The main centers of the midbrain: the red nucleus and the substantia nigra. Red core The midbrain performs motor functions - regulates the tone of skeletal muscles. If a transverse incision is made in a cat between the medulla oblongata and the midbrain, then its muscle tone sharply increases, especially the extensors. An animal placed on outstretched paws like sticks can stand. This condition is called decerebrate rigidity.
Black substance The midbrain activates the forebrain, giving emotional coloring to some behavioral reactions. The function of the substantia nigra is associated with the implementation of chewing and swallowing reflexes.
Superior colliculus nuclei are the primary visual centers. They turn the eyes and head towards the stimulus (visual orienting reflex). Nuclei of the inferior colliculus are the primary auditory centers. They regulate orientation reflexes that occur in response to sound stimulation.
Functions of the diencephalon. The diencephalon consists of the thalamus, hypothalamus, epithalamus and metathalamus. Thalamus is a collector of almost all types of sensitivity (except olfactory). According to the functional significance, the nuclei of the thalamus are divided into specific, nonspecific and associative.
Specific nuclei of the thalamus The thalamus regulates tactile, temperature, pain and taste sensitivity, as well as auditory and visual sensations. Nonspecific nuclei of the thalamus have both activating and inhibitory effects on small areas of the cortex. Association nuclei of the thalamus transmit impulses from switching nuclei to associative zones of the cortex.
Hypothalamus is the highest subcortical center of the autonomic nervous system. Functionally, the nuclei of the hypothalamus are divided into anterior, middle and posterior groups of nuclei. Anterior nuclei The hypothalamus is the center of parasympathetic regulation; they also produce releasing factors that regulate the activity of the pituitary gland. Posterior cores regulate sympathetic influences. Nuclear stimulation middle group leads to a decrease in the influence of the sympathetic nervous system.
Epithalamus (epiphysis) regulates the processes of sleep and wakefulness. Metathalamus (geniculate bodies) participate in the regulation of vision and hearing.
Limbic system. The limbic system includes the cingulate gyrus, hippocampus, part of the nuclei of the thalamus and hypothalamus, the septum, etc. This system is involved in the regulation of autonomic functions, influences the cycle of sleep and wakefulness, ensures memory processes and plays an important role in the formation of emotions.
Reticular formation. This is a special system of nerve cells with densely intertwined processes. It is located throughout the medulla oblongata, hindbrain, midbrain and diencephalon and has an activating and inhibitory effect on neurons of different parts of the central nervous system.
Basal ganglia (nuclei). The basal nuclei include the striatum, consisting of the caudate and lenticular nuclei and the ordium. These nuclei coordinate movements, participate in the formation of conditioned reflexes and the implementation of complex unconditioned reflexes (defensive, food-procuring, etc.).
Functions of the cerebral cortex. The cerebral hemispheres consist of white matter, covered on the outside with gray (cortex), the thickness of which in various parts of the cerebral hemispheres is 1.3-5 mm. The number of neurons in the cortex reaches 10-14 billion. In the cerebral cortex, the neuron bodies form six layers: 1st molecular; 2nd outer granular; 3rd outer pyramidal; 4th internal granular; 5th internal pyramidal; 6th multimorph. Areas of the cortex that are similar in structure, topography, and timing of differentiation in ontogenesis are called cytoarchitectonic fields. K. Brodman identified 52 cytoarchitectonic (cellular) fields in the cortex.
Localization of functions in the cortex. The cerebral cortex has the following areas: sensitive (sensory), motor (motor) and associative
Sensory areas of the cortex. Afferent impulses from all receptors (except olfactory) enter the cortex through the thalamus. The central projections of somatic and visceral sensitivity are separated into primary and secondary somatosensory zones. Primary somatosensory area located in the postcentral gyrus (fields 1,2,3). It receives impulses from receptors in the skin and motor system . Secondary somatosensory area located more ventrally in the area of the lateral (Sylvian) fissure. There is a projection of the body surface here, but less clear than in the primary somatosensory area.
Visual cortex located in the occipital region of the cortex on both sides of the calcarine sulcus (fields 17,18,19). Auditory cortex located in the temporal region (fields 41,42). Olfactory cortex located at the base of the brain, in the region of the parahippocampal gyrus (field 11). Taste analyzer projection localized in the lower part of the postcentral gyrus (field 43). Speech areas of the cortex. Areas 44 and 45 (Broca's center) and area 22 (Wernicke's center), located in the left hemisphere of the brain of right-handed people, are associated with speech function in the cerebral cortex.
Motor cortex localized in the precentral gyrus (fields 4, 6). Electrical stimulation of the upper part of the gyrus causes movement of the muscles of the legs and torso, the middle part of the arms, and the lower part of the facial muscles. The area that controls the movements of the hand, tongue, and facial muscles is especially large.
Association cortical areas occupy 1/3 of its entire area and communicate between different areas of the cortex, integrating all impulses entering the cortex into integral acts of learning (reading, speaking, writing), logical thinking, memory and, finally, conscious reflection of reality.
Bioelectrical activity of the cortex. Fluctuations in the electrical potentials of the cortex were first recorded by V.V. Pravdich-Neminsky in 1913. The curve reflecting the electrical activity of cortical neurons is called an electroencephalogram (EEG). To record EEG, multichannel electroencephalographs are used, and when placing electrodes, the international “10-20” scheme is used.
The following EEG rhythms are distinguished: alpha rhythm with a frequency of 8-13 Hz and an amplitude of 50 μV; beta rhythm with a frequency of 14-30 Hz and an amplitude of 25 μV; theta rhythm with a frequency of 4-8 Hz and an amplitude of 100-150 μV; delta rhythm with a frequency of 0.5-4 Hz and an amplitude of 250-300 μV.
In clinical practice, EEG allows one to assess the functional state of the brain.
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The midbrain includes the quadrigeminal peduncle and cerebral peduncles (Fig. 28). The main centers of the midbrain: the red nucleus, the substantia nigra, the nuclei of the oculomotor and trochlear nerves.
The midbrain is a subcortical regulator of muscle tone, the center of visual and auditory orientation reflexes, as well as some complex motor reflex acts (swallowing and chewing).
The influence of the midbrain on the tone of skeletal muscles is carried out through the red nucleus. Impulses from the cerebral cortex, subcortical nuclei and cerebellum, as well as from the reticular formation of the brainstem, converge to it. Switching off the red nucleus leads to a sharp increase in the tone of skeletal muscles (decerebrate rigidity).
The substantia nigra of the midbrain activates the forebrain, giving emotional coloring to some behavioral reactions. Dopamine plays an important role in transmitting these effects. The function of the substantia nigra is associated with the implementation of chewing and swallowing reflexes.
With the joint participation of the midbrain and medulla oblongata, innate tonic reflexes are realized: postures (body positions), straightening, lifting reflexes and reflex movements of the eyeballs during body rotation (nystagmus). The midbrain provides regulation of motor orientation reflexes. The anterior tubercles of the quadrigeminal are the primary visual centers: they rotate the eyes and head towards the stimulus (visual orienting reflex).
Fig.28. Anterior surface of the brainstem, inferior surface of the cerebellum:
1 - optic nerve; 2 - island; 3 - pituitary gland; 4 - optic chiasm; 5 - funnel; 6 - gray tubercle; 7 - mastoid body; 8 - fossa between the cerebral peduncles; 9 - cerebral peduncles; 10 - semilunar node; 11 - small root of the trigeminal nerve; 12 - large root of the trigeminal nerve; 13 - abducens nerve; 14 - glossopharyngeal nerve; 15 - choroid plexus of the IV ventricle; 16 - vagus nerve; 17 - accessory nerve; 18 - first cervical nerve; 19 - intersection of pyramids; 20 - pyramid; 21 - hypoglossal nerve; 22 - auditory nerve; 23 - intermediate nerve; 24 - facial nerve; 25 - trigeminal nerve; 26 - pons; 27 - trochlear nerve; 28 - external geniculate body; 29 - oculomotor nerve; 30 - visual path; 31-32 - anterior perforated substance; 33 - external olfactory stripe; 34 - olfactory triangle; 35 - olfactory tract; 36 - olfactory bulb
The posterior tubercles of the quadrigeminal are the reflex centers of auditory orientation reflexes. When auditory receptors are irritated, the head becomes alert and turns towards the sound source.
Functions of the midbrain briefly
Almost every part of the human brain is irreplaceable. Together, these parts create one incredibly streamlined system. It is hardly worth expecting that in the near future any technology will be able to even replicate the functions of the brain. Unfortunately, only a very small percentage of the human brain has been studied today. However, quite a lot is known about the functions of the brain and its parts such as the midbrain.
Briefly, the functions of the midbrain can be reduced to the following types: sensory, movement, conduction function, reflexes.
The midbrain is necessary for a person for the normal functioning of some reflexes, for example, rectifying and adjusting ones. Thanks to such reflexes, a person can stand and walk. In addition, the midbrain coordinates muscle tone and regulates it.
Structure and functions of the midbrain
Therefore, normal functioning of the midbrain is a necessary condition for proper coordination of movements. The next important function of the midbrain is associated with vegetative processes. These processes include: chewing, swallowing, breathing, blood pressure.
Based on the foregoing, it is clear that in general, the midbrain is responsible for the body’s response to various stimuli. Further, in addition to the already mentioned reflexes, the midbrain also ensures the restoration of balance and posture when its normal position has been disturbed.
Thus, it is clear that the midbrain is responsible for a number of functions and reflexes in the human body: movements as a reaction to stimuli, binocular vision, pupil response to light (accommodation), simultaneous rotation of the eyes and head, processing of primary information coming from the senses , muscle tone.
All this means that the importance of the midbrain is difficult to overestimate.
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Gray matter of the telencephalon.
The gray matter of the telencephalon is represented by two formations: the basal (subcortical) nuclei, which are earlier structures, and the cerebral cortex, a later and more advanced structure of the brain.
Basal ganglia lie in the form of separate formations in the thickness of the white matter, closer to the base of the brain (Fig. 27). Due to their position, they received their name basal (subcortical, central) nuclei, nuclei basales. There are four nuclei in each hemisphere: the caudate, lenticular, fence and amygdala.
The caudate nucleus, nucleus caudatus, is localized most medially and anterior to the thalamus. It has an expanded anterior part - the head, caput nuclei caudati, which is located in the frontal lobe and below is adjacent to the anterior perforated substance, in contact with the lentiform nucleus. Posteriorly, the head narrows and passes into the body, corpus nuclei caudati, which is located in the parietal lobe and is adjacent to the thalamus, separated from it by the terminal strip. The body passes into the thinnest part - the tail, cauda nuclei caudati, which passes into the temporal lobe and reaches the amygdala.
The lentiform nucleus, nucleus lentiformis, is located lateral to the caudate nucleus and thalamus. It has the shape of a triangle, with the base facing laterally. Thin layers of white matter, located sagittally, divide it into three parts. The lateral part is called the shell, putamen, and is dark in color. The other two parts are lighter in color, located medially and are called the medial and lateral medullary plates, laminae medullares medialis et lateralis, which are collectively called the globus pallidus, globus pallidus. The plates also have another name - the medial and lateral globus pallidus, globus pallidus medialis et lateralis.
The caudate and lentiform nuclei are combined under the common name striatum, corpus striatum. The caudate nucleus and putamen are newer formations - neostriatum (striatum), and the globus pallidus is an older formation - paleostriatum (pallidum). These names formed the basis of the term striopallidar system.
The fence, claustrum, is located lateral to the shell. This core has the appearance of a thin plate and is separated from the shell by a layer of white matter - the outer capsule, capsula externa.
The amygdala, corpus amygdaloideum, is located in the temporal lobe 1.5–2 cm posterior to its pole.
All basal ganglia belong to the subcortical motor centers. They have a wide connection with the thalamus and hypothalamus, with the substantia nigra and the red nucleus, and through them with the telencephalon cortex and motor neurons of the anterior columns of the spinal cord.
Their function is to maintain the tone of skeletal muscles, the implementation of involuntary movements by these muscles and the automatism of a number of functions based on voluntary movements, but transferred to an automatic mode of execution, for example, walking, speaking, stereotypical movements.
Cerebral cortex (cloak), cortex cerebri (pallium), It is represented by a layer of gray matter 1.5–5 mm thick, located outside along the entire surface of the telencephalon hemispheres.
The cortex consists of six layers of nerve cells. The distribution of these cells is referred to as “cytoarchitecture.” The largest cells (layer of large pyramidal cells, or Betz cells) are concentrated in the fifth layer - the inner pyramidal plate. Between the cells there are many nerve fibers. The peculiarity of their distribution in the cortex is defined by the term “myeloarchitecture”.
Based on the structural features of individual areas of the cortex, cytoarchitectonic maps were created, in which, according to various authors, from 52 to 150 fields or more are distinguished. Within these fields there are centers that regulate certain functions in the human body.
Functions of the midbrain
Localization of the cortical nuclei of the analyzers on the superolateral surface of the left hemisphere of the brain: 1 – nucleus of the cutaneous analyzer; 2 – core of stereognosis; 3 – motor analyzer core; 4 – praxia core; 5 – nucleus of combined rotation of the head and eyes; 6 – core of the auditory analyzer; 7 – nucleus of the vestibular analyzer; A – core of the motor analyzer of oral speech; B – core of the auditory analyzer of oral speech; B – core of the motor analyzer of written speech; G – core of the visual analyzer of written speech
Rice. 29. Localization of the cortical nuclei of the analyzers on the medial and lower surfaces of the right hemisphere of the brain: 1 – nucleus of the analyzers of smell and taste; 2 – core of the motor analyzer; 3 – vision analyzer core
Localization of functions in the cerebral cortex. I.P. Pavlov considered the cerebral cortex as a huge perceptive surface (450,000 mm 2), as a collection of cortical ends of analyzers. The analyzer consists of three parts: 1) peripheral or receptor, 2) conductive and 3) central or cortical. The cortical part (end of the analyzer) has a core and periphery. Identical neurons belonging to only one specific analyzer are concentrated in the nucleus. Its location is clearly defined. It is where the highest analysis and synthesis of information coming from receptors takes place.
The periphery of the cortical end of the analyzer does not have clear boundaries; the cell density decreases compared to the nucleus. The peripheries of the analyzers overlap each other and are represented by neurons of the cortical representations of adjacent nuclei. They carry out simple, elementary analysis and synthesis of information.
Ultimately, at the cortical end of the analyzer, based on the analysis and synthesis of incoming information, responses are developed that regulate all types of human activity. In the clinical aspect, the cortical ends of the analyzers (their nuclei) are considered in relation to the lobes of the telencephalon hemispheres, their gyri and sulci. The cortical ends of almost all analyzers are located symmetrically in both hemispheres.
1. The cortical nucleus of general sensitivity, or the skin analyzer (tactile, pain, temperature sensitivity), is located in the postcentral gyrus (Fig. 28). The skin surface of the human body in this gyrus is projected upside down and its area is directly proportional to the functional significance of a particular skin area of the body (Fig. 30, A). Therefore, most of the gyral cortex is associated with receptors of the upper limb (especially the skin of the thumb) and the scalp (especially the skin of the lips).
The cortical nucleus of the sense of stereognosis (recognition of objects by touch) is located in the superior parietal lobe of the hemispheres.
3. The cortical nucleus of the motor analyzer, i.e., the nucleus of proprioceptive stimuli emanating from the structures of the musculoskeletal system, is localized in the precentral gyrus and pericentral lobule. Receptor fields, like those of the skin analyzer, are projected upside down in direct proportion to the functional significance of a particular structure of the musculoskeletal system. The lower limb is projected in the upper part of the gyrus, the trunk and upper limb are projected in the middle, and the neck and head are projected in the lower part. The human figure (Fig. 30, B) is projected into this gyrus with a huge face and mouth, a hand and especially a thumb, a small body and a very small leg.
Rice. 30. Diagram of sensitive (A) and motor (B) homunculi: 1 – gyrus postcentralis; 2 – gyrus precentralis; 3 – ventriculus lateralis
4. The cortical nucleus of purposeful complex combined movements (praxia nucleus, from praxis - practice) is located in the inferior parietal lobule within the gyrus supramarginalis. The function of this nucleus is due to its large associative connections. Its defeat does not lead to paralysis, but excludes the possibility of performing practical (labor, professional) movements.
5. The cortical nucleus of the combined rotation of the head and eyes in the opposite direction is located in the posterior part of the middle frontal gyrus, which is part of the premotor zone.
The cortical nucleus of the olfactory analyzer is located in the uncus et
7. Cortical nucleus of the hippocampus taste analyzer (Fig. 29)
8. The cortical nucleus of the visual analyzer is located on the medial surface of the occipital lobe of the cerebral hemispheres along the edges of the sulcus calcarinus, within the cuneus, gyrus occipitotemporalis medialis seu lingualis (Fig. 27). In each hemisphere, within the nucleus, receptors are projected from the lateral half of the retina of the given side and the medial half of the retina of the opposite side.
9. The cortical nucleus of the auditory analyzer is located in the middle section of the superior temporal gyrus (Heschl’s gyrus), facing the insula. The nucleus receives nerve impulses from the receptors of the hearing organs on the left and right sides.
10. The cortical nucleus of the statokinetic (vestibular) analyzer is located in the middle parts of the lower and middle temporal gyri.
11. Cortical nuclei of speech analyzers. In humans, these nuclei were formed in connection with the development of the second signaling system (oral and written speech) based on associative connections with the cortical nuclei of vision and hearing (Fig. 28).
a) The nucleus of the motor analyzer of oral speech (speech articulation), Broca's center (P. Broca), is located in the posterior part of the inferior frontal gyrus in the pars triangularis. Damage to this nucleus results in loss of the ability to pronounce words, although the ability to pronounce sounds and sing is preserved. This phenomenon is called motor aphasia.
b) The nucleus of the auditory analyzer of oral speech, Wernicke's center (K. Wernicke), is located in the posterior part of the superior temporal gyrus, in the depth of the lateral sulcus in close proximity to the nucleus of the auditory analyzer. Damage to the nucleus leads to the disappearance of the ability to understand spoken speech and control the pronunciation of words, word deafness or sensory aphasia occurs. However, the auditory perception of sounds remains.
c) The cortical nucleus of the motor analyzer of written speech is located in the posterior part of the middle frontal gyrus, which is adjacent to that part of the cortex of the precentral gyrus, from where the work of the muscles of the hand, in particular the hand, is regulated, ensuring the writing of letters and other signs.
Damage to this nucleus leads to agraphia - the inability to perform the precise and subtle movements necessary to write letters, numbers and words.
d) The cortical nucleus of the visual analyzer of written speech is localized in the angular gyrus of the inferior parietal lobule, in the gyrus angularis, in close proximity to the nucleus of the visual analyzer. If this nucleus is damaged, a person’s ability to perceive written text, i.e., to read, disappears. This phenomenon is called alexia.
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Human midbrain
Midbrain is an ancient part of the brain included in its trunk. It includes the ancient visual center. The midbrain is located below the cerebral cortex and above the hindbrain, being, as it were, in the very center of the brain. Caudally, the midbrain is adjacent to the hindbrain, and rostrally to the diencephalon. In the ventral part of the midbrain there are the so-called cerebral peduncles, most of which are occupied by the pyramidal tracts. In the midbrain, between the legs, there is an interpeduncular fossa, from which the third oculomotor nerve originates. Deep in the interpeduncular fossa there is a posterior perforated substance.
The midbrain includes: roof of the midbrain(tectum), inferior colliculus(inferior colliculus), colliculus(superior colliculi), brain peduncles(cerebral peduncle), midbrain tegmentum(midbrain tegmentum), black matter(substantia nigra), cerebral peduncle(crus cerebri). It should be noted that there is no visible border with the diencephalon.
The midbrain is part of the brain stem. The substantia nigra of the midbrain is closely connected with the musculoskeletal system of the basal ganglia pathways. The substantia nigra and ventral tegmentum produce dopamine, which plays an important role in motivation and arousal. The midbrain transmits visual and auditory information.
Four Hills
The midbrain quadrigeminal consists of two pairs of inferior and superior colliculi. The upper pairs are visual, and the lower pairs are auditory. at the same time, the upper pairs of mounds are somewhat larger than the lower pairs. These hillocks are connected to structures of the diencephalon called the geniculate bodies. In this case, the upper colliculi are connected with the lateral ones, and the lower colliculi with the medial ones. The trochlear nerve emerges from the posterior surface of the midbrain. Four solid lobes help cross several optic fibers at right angles. The auditory nuclei are located inside the inferior colliculus.
Brain legs
The cerebral peduncles are paired structures that are located on the ventral side of the cerebral aqueduct. They transfer the tegmentum to the dorsal side. The middle part of the brain contains the substantia nigra, which is a type of nucleus basalis. The substantia nigra is the only part of the brain that contains melanin. Between the legs is the interpeduncular fossa.
The structure of the midbrain, its functions and features
which is filled with cerebrospinal fluid, is like a flush tank. The oculomotor nerve emerges between the crura, and the trochlear nerve prominently wraps around the outer sides of the crura.
The oculomotor nerve (parasympathetically) is responsible for the constriction of the pupil and some eye movements.
Structure of the midbrain in sections
With a horizontal section of the midbrain at the level of the superior colliculus, the red nucleus, the nuclei of the oculomotor nerve and the associated Edinger-Westphal nuclei, the medullary peduncles, and the substantia nigra are observed.
With a horizontal section of the midbrain at the level of the inferior colliculus, the substantia nigra is also observed, the nuclei of the trochlear nerve and the cross of the superior cerebellar peduncles are also clearly visible.
In both cases, there is a cerebral aqueduct connecting the third and fourth ventricles and the periaqueductal gray matter.
Midbrain Development
During embryonic development, the midbrain is formed from the second vesicle. It remains indivisible during further development, unlike the other two vesicles of the forebrain and hindbrain. Division into other areas of the brain does not occur during the development of the nervous system, unlike the forebrain, which is divided into the telencephalon and diencephalon.
During embryonic development, the midbrain undergoes continuous development of nerve cells, which are gradually compressed by the cerebral aqueduct. In some cases (with impaired development), partial or complete blockage of the cerebral aqueduct may occur, which leads to congenital hydrocephalus.
Midbrain comprises:
Bugrov quadrigeminal,
red core,
substantia nigra,
Seam cores.
Red core– provides the tone of skeletal muscles, redistribution of tone when changing posture. Just stretching is a powerful activity of the brain and spinal cord, for which the red nucleus is responsible. The red core ensures the normal tone of our muscles. If the red nucleus is destroyed, decerebrate rigidity occurs, with a sharp increase in the tone of the flexors in some animals and the extensors in others. And with absolute destruction, both tones increase at once, and it all depends on which muscles are stronger.
Black substance– How is excitation from one neuron transmitted to another neuron? Excitation occurs - this is a bioelectric process. It reaches the end of the axon, where a chemical substance is released - a transmitter. Each cell has its own mediator. A transmitter is produced in the substantia nigra in nerve cells dopamine. When the substantia nigra is destroyed, Parkinson's disease occurs (the fingers and head constantly tremble, or there is stiffness as a result of a constant signal being sent to the muscles) because there is not enough dopamine in the brain. The substantia nigra provides subtle instrumental movements of the fingers and influences all motor functions. The substantia nigra exerts an inhibitory effect on the motor cortex through the stripolidal system. If it is disrupted, it is impossible to perform delicate operations and Parkinson's disease occurs (stiffness, tremors).
Above are the anterior tubercles of the quadrigeminal, and below are the posterior tubercles of the quadrigeminal. We look with our eyes, but we see with the occipital cortex of the cerebral hemispheres, where the visual field is located, where the image is formed. A nerve leaves the eye, passes through a number of subcortical formations, reaches the visual cortex, there is no visual cortex, and we will not see anything. Anterior tubercles of the quadrigeminal- This is the primary visual area. With their participation, an indicative reaction to a visual signal occurs. The indicative reaction is the “reaction what is it?” If the anterior tubercles of the quadrigeminal are destroyed, vision will be preserved, but there will be no quick reaction to the visual signal.
Posterior tubercles of the quadrigeminal This is the primary auditory zone. With its participation, an indicative reaction to the sound signal occurs. If the posterior tubercles of the quadrigeminal are destroyed, hearing will be preserved but there will be no indicative reaction.
Seam cores– this is the source of another mediator serotonin. This structure and this mediator takes part in the process of falling asleep. If the suture nuclei are destroyed, the animal is in a constant state of wakefulness and quickly dies. In addition, serotonin takes part in positive reinforcement learning (this is when a rat is given cheese). Serotonin provides character traits such as unforgivingness, goodwill; aggressive people have a lack of serotonin in the brain.
12) The thalamus is a collector of afferent impulses. Specific and nonspecific nuclei of the thalamus. The thalamus is the center of pain sensitivity.
Thalamus- visual thalamus. He was the first to discover his relationship to visual impulses. It is a collector of afferent impulses, those that come from receptors. The thalamus receives signals from all receptors except the olfactory ones. The thalamus receives information from the cortex, the cerebellum, and the basal ganglia. At the level of the thalamus, these signals are processed, only the most important information for a person at a given moment is selected, which then enters the cortex. The thalamus consists of several dozen nuclei. The nuclei of the thalamus are divided into two groups: specific and nonspecific. Through specific nuclei of the thalamus, signals arrive strictly to certain areas of the cortex, for example, visual to the occipital lobe, auditory to the temporal lobe. And through nonspecific nuclei, information diffuses to the entire cortex in order to increase its excitability in order to more clearly perceive specific information. They prepare the BP cortex for the perception of specific information. The highest center of pain sensitivity is the thalamus. The thalamus is the highest center of pain sensitivity. Pain is formed necessarily with the participation of the thalamus, and when some nuclei of the thalamus are destroyed, pain sensitivity is completely lost; when other nuclei are destroyed, barely bearable pain occurs (for example, phantom pain is formed - pain in a missing limb).
13) Hypothalamic-pituitary system. The hypothalamus is the center of regulation of the endocrine system and motivation.
The hypothalamus and pituitary gland form a single hypothalamic-pituitary system.
Hypothalamus. The pituitary stalk departs from the hypothalamus, on which it hangs pituitary- main endocrine gland. The pituitary gland regulates the functioning of other endocrine glands. The hypoplamus is connected to the pituitary gland by nerve pathways and blood vessels. The hypothalamus regulates the work of the pituitary gland, and through it the work of other endocrine glands. The pituitary gland is divided into adenohypophysis(glandular) and neurohypophysis. In the hypothalamus (this is not an endocrine gland, it is a part of the brain) there are neurosecretory cells in which hormones are secreted. This is a nerve cell; it can be excited, it can be inhibited, and at the same time hormones are secreted in it. An axon extends from it. And if these are hormones, they are released into the blood, and then go to the decision organs, i.e. to the organ whose work it regulates. Two hormones:
- vasopressin – promotes the conservation of water in the body, it affects the kidneys, and with its deficiency, dehydration occurs;
- oxytocin – produced here, but in other cells, ensures contraction of the uterus during childbirth.
Hormones are secreted in the hypothalamus and released by the pituitary gland. Thus, the hypothalamus is connected to the pituitary gland via nerve pathways. On the other hand: nothing is produced in the neurohypophysis; hormones come here, but the adenohypophysis has its own glandular cells, where a number of important hormones are produced:
- ganadotropic hormone – regulates the functioning of the sex glands;
- thyroid-stimulating hormone – regulates the functioning of the thyroid gland;
- adrenocorticotropic – regulates the functioning of the adrenal cortex;
- somatotropic hormone, or growth hormone, – ensures the growth of bone tissue and the development of muscle tissue;
- melanotropic hormone – is responsible for pigmentation in fish and amphibians, in humans it affects the retina.
All hormones are synthesized from a precursor called proopiomellanocortin. A large molecule is synthesized, which is broken down by enzymes, and other hormones, smaller in number of amino acids, are released from it. Neuroendocrinology.
The hypothalamus contains neurosecretory cells. They produce hormones:
1) ADH (antidiuretic hormone regulates the amount of urine excreted)
2) oxytocin (provides contraction of the uterus during childbirth).
3) statins
4) liberins
5) thyroid-stimulating hormone affects the production of thyroid hormones (thyroxine, triiodothyronine)
Thyroliberin -> thyroid-stimulating hormone -> thyroxine -> triiodothyronine.
The blood vessel enters the hypothalamus, where it branches into capillaries, then the capillaries gather and this vessel passes through the pituitary stalk, branches again in the glandular cells, leaves the pituitary gland and carries with it all these hormones, which each go with the blood to its own gland. Why is this “wonderful vascular network” needed? There are nerve cells in the hypothalamus that end on the blood vessels of this wonderful vascular network. These cells produce statins And liberins - This neurohormones. Statins inhibit the production of hormones in the pituitary gland, and liberins it is strengthened. If there is an excess of growth hormone, gigantism occurs, this can be stopped with the help of samatostatin. On the contrary: the dwarf is injected with samatoliberin. And apparently there are neurohormones for any hormone, but they are not yet discovered. For example, the thyroid gland produces thyroxine, and in order to regulate its production, the pituitary gland produces thyroid-stimulating hormone, but in order to control thyroid-stimulating hormone, thyreostatin has not been found, but thyroliberin is used perfectly. Although these are hormones, they are produced in nerve cells, so in addition to their endocrine effects, they have a wide range of extraendocrine functions. Thyroid hormone is called panactivin, because it improves mood, improves performance, normalizes blood pressure, and accelerates healing in case of spinal cord injuries; it is the only thing that cannot be used for disorders of the thyroid gland.
The functions associated with neurosecretory cells and cells that produce neurofebtides were previously discussed.
The hypothalamus produces statins and liberins, which are included in the body's stress response. If the body is affected by some harmful factor, then the body must somehow respond - this is the stress reaction of the body. It cannot occur without the participation of statins and liberins, which are produced in the hypothalamus. The hypothalamus necessarily takes part in the response to stress.
The following functions of the hypothalamus are:
It contains nerve cells that are sensitive to steroid hormones, i.e. sex hormones, both female and male sex hormones. This sensitivity ensures formation of a female or male type. The hypothalamus creates the conditions for motivating behavior according to the male or female type.
A very important function is thermoregulation; the hypothalamus contains cells that are sensitive to blood temperature. Body temperature can change depending on the environment. Blood flows through all structures of the brain, but thermoreceptive cells, which detect the slightest changes in temperature, are found only in the hypothalamus. The hypothalamus turns on and organizes two responses of the body: heat production or heat transfer.
Food motivation. Why does a person feel hungry?
The signaling system is the level of glucose in the blood, it should be constant ~120 milligrams% - s.
There is a mechanism of self-regulation: if our blood glucose level decreases, liver glycogen begins to break down. On the other hand, glycogen reserves are not enough. The hypothalamus contains glucoreceptive cells, i.e. cells that record the level of glucose in the blood. Glucoreceptive cells form hunger centers in the hypothalamus. When blood glucose levels drop, these blood glucose-sensing cells become excited and a feeling of hunger occurs. At the level of the hypothalamus, only food motivation arises - a feeling of hunger; to search for food, the cerebral cortex must be involved, with its participation a true food reaction arises.
The satiety center is also located in the hypothalamus, it inhibits the feeling of hunger, which protects us from overeating. When the saturation center is destroyed, overeating occurs and, as a result, bulimia.
The hypothalamus also contains the thirst center - osmoreceptive cells (osmatic pressure depends on the concentration of salts in the blood). Osmoreceptive cells record the level of salts in the blood. When salts in the blood increase, osmoreceptive cells are excited, and drinking motivation (reaction) occurs.
The hypothalamus is the highest control center of the autonomic nervous system.
The anterior sections of the hypothalamus mainly regulate the parasympathetic nervous system, the posterior sections mainly regulate the sympathetic nervous system.
The hypothalamus provides only motivation and goal-directed behavior to the cerebral cortex.
14) Neuron – structural features and functions. Differences between neurons and other cells. Glia, blood-brain barrier, cerebrospinal fluid.
I Firstly, as we have already noted, in their diversity. Any nerve cell consists of a body - soma and processes. Neurons are different:
1. by size (from 20 nm to 100 nm) and shape of the soma
2. by the number and degree of branching of short processes.
3. according to the structure, length and branching of axon endings (laterals)
4. by the number of spines
II Neurons also differ in functions:
A) perceivers information from the external environment,
b) transmitting information to the periphery,
V) processing and transmitting information within the central nervous system,
G) exciting,
d) brake.
III Differ in chemical composition: various proteins, lipids, enzymes are synthesized and, most importantly, - mediators .
WHY, WHAT FEATURES IS THIS ASSOCIATED WITH?
Such diversity is determined high activity of the genetic apparatus neurons. During neuronal induction, under the influence of neuronal growth factor, NEW GENES are turned on in the cells of the ectoderm of the embryo, which are characteristic only of neurons. These genes provide the following features of neurons ( the most important properties):
A) The ability to perceive, process, store and reproduce information
B) DEEP SPECIALIZATION:
0. Synthesis of specific RNA;
1. No reduplication DNA.
2. The proportion of genes capable of transcriptions, make up in neurons 18-20%, and in some cells – up to 40% (in other cells - 2-6%)
3. The ability to synthesize specific proteins (up to 100 in one cell)
4. Unique lipid composition
B) Privilege of nutrition => Dependence on level oxygen and glucose in blood.
Not a single tissue in the body is in such a dramatic dependence on the level of oxygen in the blood: 5-6 minutes of stopping breathing and the most important structures of the brain die, and first of all the cerebral cortex. A decrease in glucose levels below 0.11% or 80 mg% - hypoglycemia may occur and then coma.
On the other hand, the brain is fenced off from the blood flow by the BBB. It does not allow anything into the cells that could harm them. But, unfortunately, not all of them - many low-molecular toxic substances pass through the BBB. And pharmacologists always have a task: does this drug pass through the BBB? In some cases this is necessary, if we are talking about brain diseases, in others it is indifferent to the patient if the drug does not damage nerve cells, and in others it should be avoided. (NANOPARTICLES, ONCOLOGY).
The sympathetic nervous system is excited and stimulates the adrenal medulla - the production of adrenaline; in the pancreas - glucagon - breaks down glycogen in the kidneys to glucose; glucocarticoids produced in the adrenal cortex - provides gluconeogenesis - the formation of glucose from ...)
And yet, with all the diversity of neurons, they can be divided into three groups: afferent, efferent and intercalary (intermediate).
15) Afferent neurons, their functions and structure. Receptors: structure, functions, formation of an afferent volley.
On its ventral surface there are two massive bundles of nerve fibers - the cerebral peduncles, through which signals are carried from the cortex to the underlying brain structures.
Rice. 1. The most important structural formations of the midbrain (cross section)
The midbrain contains various structural formations: quadrigeminal, red nucleus, substantia nigra and nuclei of the oculomotor and trochlear nerves. Each formation plays a specific role and contributes to the regulation of a number of adaptive reactions. All ascending pathways pass through the midbrain, transmitting impulses to the thalamus, cerebral hemispheres and cerebellum, and descending pathways, transmitting impulses to the medulla oblongata and spinal cord. The neurons of the midbrain receive impulses through the spinal cord and medulla oblongata from the muscles, visual and auditory receptors along the afferent nerves.
Anterior tubercles of the quadrigeminal are the primary visual centers, and they receive information from visual receptors. With the participation of the anterior tubercles, visual orientation and guard reflexes are carried out by moving the eyes and turning the head in the direction of the action of visual stimuli. The neurons of the posterior tubercles of the quadrigeminal form the primary auditory centers and, upon receiving excitation from auditory receptors, ensure the implementation of auditory orientation and guard reflexes (the animal's ears tense, it becomes alert and turns its head towards a new sound). The nuclei of the posterior colliculus provide a guard adaptive reaction to a new sound stimulus: redistribution of muscle tone, increased flexor tone, increased heart rate and respiration, increased blood pressure, i.e. the animal is preparing to defend, run, attack.
Black substance receives information from muscle receptors and tactile receptors. It is associated with the striatum and globus pallidus. Neurons of the substantia nigra are involved in the formation of an action program that ensures the coordination of complex acts of chewing, swallowing, as well as muscle tone and motor reactions.
Red core receives impulses from muscle receptors, from the cerebral cortex, subcortical nuclei and cerebellum. It has a regulatory effect on motor neurons of the spinal cord through the Deiters nucleus and the rubrospinal tract. The neurons of the red nucleus have numerous connections with the reticular formation of the brain stem and together with it regulate muscle tone. The red nucleus has an inhibitory effect on the extensor muscles and an activating effect on the flexor muscles.
Elimination of the connection between the red nucleus and the reticular formation of the upper part of the medulla oblongata causes a sharp increase in the tone of the extensor muscles. This phenomenon is called decerebrate rigidity.
|
Name |
Functions of the midbrain |
|
Nuclei of the roof of the superior and inferior colliculi |
Subcortical centers of vision and hearing, from which the tectospinal tract originates, through which indicative auditory and visual reflexes are carried out |
|
Nucleus of the longitudinal medial fasciculus |
Participates in ensuring a combined rotation of the head and eyes to the action of unexpected visual stimuli, as well as in case of irritation of the vestibular apparatus |
|
Nuclei of III and IV pairs of cranial nerves |
They participate in a combination of eye movements due to the innervation of the external muscles of the eye, and the fibers of the autonomic nuclei, after switching in the ciliary ganglion, innervate the muscle that constricts the pupil and the muscle of the ciliary body |
|
Red kernels |
They are the central link of the extrapyramidal system, since the paths from the cerebellum (tr. cerebellotegmenlalis) and basal nuclei (tr. pallidorubralis) end on them, and the rubrospinal path begins from these nuclei |
|
Black substance |
It has a connection with the striatum and cortex, is involved in complex coordination of movements, regulation of muscle tone and posture, as well as in coordinating the acts of chewing and swallowing, and is part of the extrapyramidal system |
|
Nuclei of the reticular formation |
Activating and inhibitory influences on the nuclei of the spinal cord and various areas of the cerebral cortex |
|
Gray central periaqueductal substance |
Part of the antinociceptive system |
The structures of the midbrain are directly involved in the integration of heterogeneous signals necessary for the coordination of movements. With the direct participation of the red nucleus, the substantia nigra of the midbrain, the neural network of the brain stem movement generator and, in particular, the eye movement generator is formed.
Based on the analysis of signals entering the stem structures from proprioceptors, vestibular, auditory, visual, tactile, pain and other sensory systems, a flow of efferent motor commands is formed in the stem movement generator, sent to the spinal cord along the descending pathways: rubrospinal, retculospinal, vestibulospinal, tectospinal. In accordance with the commands developed in the brain stem, it becomes possible to carry out not just contractions of individual muscles or muscle groups, but the formation of a certain body posture, maintaining body balance in various poses, making reflexive and adaptive movements when carrying out various types of body movement in space (Fig. 2 ).
Rice. 2. The location of some nuclei in the brain stem and hypothalamus (R. Schmidt, G. Thews, 1985): 1 - paraventricular; 2 - dorsomedial: 3 - preoptic; 4 - supraoptical; 5 - rear
The structures of the brainstem movement generator can be activated by voluntary commands that come from the motor areas of the cerebral cortex. Their activity can be enhanced or inhibited by signals from sensory systems and the cerebellum. These signals can modify already executed motor programs so that their execution changes in accordance with new requirements. For example, adapting posture to purposeful movements (as well as organizing such movements) is possible only with the participation of the motor centers of the cerebral cortex.
The red nucleus plays an important role in the integrative processes of the midbrain and its stem. Its neurons are directly involved in the regulation, distribution of skeletal muscle tone and movements, ensuring the maintenance of normal body position in space and the adoption of a posture that creates readiness to perform certain actions. These influences of the red nucleus on the spinal cord are realized through the rubrospinal tract, the fibers of which end on the interneurons of the spinal cord and have an excitatory effect on the a- and y-motoneurons of the flexors and inhibit the majority of the oto neurons of the extensor muscles.
The role of the red nucleus in the distribution of muscle tone and maintaining body posture is well demonstrated in experimental conditions on animals. When the brainstem is cut (decerebration) at the level of the midbrain below the red nucleus, a condition called decerebrate rigidity. The animal's limbs become straightened and tense, the head and tail are thrown back to the back. This body position occurs as a result of an imbalance between the tone of the antagonist muscles in the direction of a sharp predominance of the tone of the extensor muscles. After transection, the inhibitory effect of the red nucleus and cerebral cortex on the extensor muscles is eliminated, and the excitatory effect of the reticular and vestibular (Dagers) nuclei on them remains unchanged.
Decerebrate rigidity occurs immediately after transection of the brainstem below the level of the red nucleus. The y-loop is of utmost importance in the origin of rigidity. Rigidity disappears after cutting the dorsal roots and stopping the flow of afferent nerve impulses to the spinal cord neurons from the muscle spindles.
The vestibular system is related to the origin of rigidity. Destruction of the lateral vestibular nucleus eliminates or reduces the tone of the extensors.
In the implementation of the integrative functions of the brain stem structures, the substantia nigra plays an important role, which is involved in the regulation of muscle tone, posture and movements. It is involved in the integration of signals necessary to coordinate the work of many muscles involved in the acts of chewing and swallowing, and influences the formation of respiratory movements.
Through the substantia nigra, motor processes initiated by the brainstem movement generator are influenced by the basal ganglia. There are bilateral connections between the substantia nigra and the basal ganglia. There is a bundle of fibers that conducts nerve impulses from the striatum to the substantia nigra, and a path that conducts impulses in the opposite direction.
The substantia nigra also sends signals to the nuclei of the thalamus, and then these signal flows reach the cortex along the axons of the thalamic neurons. Thus, the substantia nigra is involved in closing one of the neural circuits through which signals circulate between the cortex and subcortical formations.
The functioning of the red nucleus, substantia nigra and other structures of the brain stem movement generator is controlled by the cerebral cortex. Its influence is carried out both through direct connections with many nuclei of the stem, and indirectly through the cerebellum, which sends bundles of efferent fibers to the red nucleus and other stem nuclei.
