Shell
Pale ball
In the thickness of the white matter of each cerebral hemisphere there are accumulations of gray matter, forming separately lying nuclei (Fig. 7). These nuclei lie closer to the base of the brain and are called basal (subcortical, central). These include: 1) striped the body, which in lower vertebrates constitutes the predominant mass of the hemispheres; 2) fence; 3) amygdala.
Let's consider the structure of the striatum (corpus striatum), which in sections of the brain looks like alternating stripes of gray and white matter. Most medially and in front is: a) caudate nucleus, located lateral and superior to the thalamus, being separated from it by the knee of the internal capsule. The nucleus has a head located in the frontal lobe, protruding into the anterior horn of the lateral ventricle and adjacent to the anterior perforated substance. The body of the caudate nucleus lies under the parietal lobe, limiting the central part of the lateral ventricle on the lateral side. The tail of the nucleus participates in the formation of the roof of the inferior horn of the lateral ventricle and reaches the amygdala, which lies in the anteromedial parts of the temporal lobe (posterior to the anterior perforated substance); b) lenticular the nucleus is located lateral to the caudate nucleus. Layer of white matter - inner capsule– separates the lenticular nucleus from the caudate nucleus and from the thalamus.
The lower surface of the anterior part of the lentiform nucleus is adjacent to the anterior perforated substance and is connected to the caudate nucleus. The medial part of the lenticular nucleus in a horizontal section of the brain narrows and is angled towards the knee of the internal capsule, located on the border of the thalamus and the head of the caudate nucleus. The convex lateral surface of the lenticular nucleus faces the base of the insular lobe of the cerebral hemisphere.
Fig.7. Frontal section of the brain at the level of the mastoid bodies.
1 – choroid plexus of the lateral ventricle (central part), 2 – thalamus, 3 – internal capsule, 4 – insular cortex, 5 – fence, 6 – amygdala, 7 – optic tract, 8 – mastoid body, 9 – globus pallidus, 10 – putamen, 11 – fornix, 12 – caudate nucleus, 13 – corpus callosum.
On the frontal section of the brain, the lenticular nucleus also has the shape of a triangle, the apex of which faces the medial side and the base faces the lateral side (Fig. 7). Two parallel vertical layers of white matter divide the lenticular nucleus into three parts. The darker one lies most laterally shell, more medial is " pale ball", consisting of two plates: medial and lateral. The caudate nucleus and putamen belong to phylogenetically newer formations, while the globus pallidus belongs to older ones. The nuclei of the striatum form the striopallidal system, which, in turn, belongs to the extrapyramidal system involved in the control of movements and regulation of muscle tone (Fig.).
Fig.8. Horizontal section of the brain. Basal ganglia.
1–cerebral cortex (cloak), 2–genu of the corpus callosum, 3–anterior horn of the lateral ventricle, 4–internal capsule, 5–external capsule, 6–fence, 7–outermost capsule, 8–putamen, 9–globus pallidus , 10–III ventricle, 11–posterior horn of the lateral ventricle, 12–optic tubercle, 13–cortical substance (bark) of the insula, 14–head
Slim vertically positioned fence, lying in the white matter of the hemisphere on the side of the shell, is separated from the shell by the outer capsule, and from the insular cortex by the outermost capsule.
Caudate nucleus and putamen receive descending connections primarily from the extrapyramidal cortex through the subcallosal fasciculus. Other areas of the cerebral cortex also send large numbers of axons to the caudate nucleus and putamen.
The main part of the axons of the caudate nucleus and putamen goes to the globus pallidus, from here to the thalamus, and only from it to the sensory fields. Consequently, there is a vicious circle of connections between these formations. The caudate nucleus and putamen also have functional connections with structures lying outside this circle: with the substantia nigra, red nucleus, Lewis body (subthalamic nucleus), vestibular nuclei, cerebellum, gamma cells of the spinal cord.
The abundance and nature of the connections between the caudate nucleus and the putamen indicate their participation in integrative processes, the organization and regulation of movements, and the regulation of the work of vegetative organs.
The medial nuclei of the thalamus have direct connections with the caudate nucleus, as evidenced by the reaction of its neurons, which occurs 2-4 ms after stimulation of the thalamus. The reaction of neurons in the caudate nucleus is caused by skin irritations, light and sound stimuli.
With a lack of dopamine in the caudate nucleus (for example, with dysfunction of the substantia nigra), the globus pallidus is disinhibited, activating the spinal-stem systems, which leads to motor disorders in the form of muscle rigidity.
The caudate nucleus and globus pallidus take part in such integrative processes as conditioned reflex activity and motor activity. This is detected by stimulation of the caudate nucleus, putamen and globus pallidus, destruction and by recording electrical activity.
Direct stimulation of some zones of the caudate nucleus causes the head to turn in the direction opposite to the stimulated hemisphere, and the animal begins to move in a circle, i.e. a so-called circulatory reaction occurs.
In humans, stimulation of the caudate nucleus during a neurosurgical operation disrupts speech contact with the patient: if the patient said something, he becomes silent, and after the irritation stops he does not remember that he was addressed. In cases of brain injury with irritation of the head of the caudate nucleus, patients experience retro-, antero-, retroanterograde amnesia.
Stimulation of the caudate nucleus can completely prevent the perception of painful, visual, auditory and other types of stimulation. Irritation of the ventral region of the caudate nucleus reduces, and the dorsal region increases salivation.
In case of damage to the caudate nucleus, significant disorders of higher nervous activity, difficulty in orientation in space, memory impairment, and slowed growth of the body are observed. After bilateral damage to the caudate nucleus, conditioned reflexes disappear for a long period of time, the development of new reflexes becomes difficult, general behavior is characterized by stagnation, inertia, and difficulty switching. When affecting the caudate nucleus, in addition to disorders of higher nervous activity, movement disorders are noted. Many authors note that in different animals, with bilateral damage to the striatum, an uncontrollable desire to move forward appears, and with unilateral damage, manege movements occur.
The shell is characterized by participation in the organization of eating behavior: food search, food orientation, food capture and digestion; a number of trophic disorders of the skin and internal organs occur when the function of the shell is impaired. Irritation of the shell leads to changes in breathing and salivation.
As mentioned earlier, irritation of the caudate nucleus inhibits the conditioned reflex at all stages of its implementation. At the same time, irritation of the caudate nucleus prevents the extinction of the conditioned reflex, i.e. development of inhibition; the animal ceases to perceive the new environment. Considering that stimulation of the caudate nucleus leads to inhibition of the conditioned reflex, one would expect that the destruction of the caudate nucleus causes facilitation of conditioned reflex activity. But it turned out that the destruction of the caudate nucleus also leads to inhibition of conditioned reflex activity. Apparently, the function of the caudate nucleus is not simply inhibitory, but lies in the correlation and integration of RAM processes. This is also confirmed by the fact that information from different sensory systems converges on the neurons of the caudate nucleus, since most of these neurons are polysensory.
Pale ball has predominantly large type 1 Golgi neurons. Connections between the globus pallidus and the thalamus, putamen, caudate nucleus, midbrain, hypothalamus, and somatosensory system indicate its participation in the organization of simple and complex forms of behavior.
Stimulation of the globus pallidus with the help of implanted electrodes causes contraction of the muscles of the limbs, activation or inhibition of gamma motor neurons of the spinal cord.
Stimulation of the globus pallidus, unlike stimulation of the caudate nucleus, does not cause inhibition, but provokes an orienting reaction, movements of the limbs, feeding behavior (sniffing, chewing, swallowing, etc.).
Damage to the globus pallidus causes in people hypomimia, mask-like appearance of the face, tremor of the head and limbs (and this tremor disappears at rest, during sleep and intensifies with movements), and monotony of speech. When the globus pallidus is damaged, myoclonus is observed - rapid twitching of the muscles of individual groups or individual muscles of the arms, back, and face.
In the first hours after damage to the globus pallidus in an acute experiment on animals, motor activity sharply decreased, movements were characterized by incoordination, the presence of incomplete incoordination, incomplete movements was noted, and when sitting there was a drooping posture. Having started moving, the animal could not stop for a long time. In a person with dysfunction of the globus pallidus, the onset of movements is difficult, auxiliary and reactive movements disappear when standing up, friendly movements of the arms when walking are disrupted, and a symptom of propulsion appears: long-term preparation for movement, then rapid movement and stopping. Such cycles are repeated many times in patients.
Fence contains polymorphic neurons of different types. It forms connections primarily with the cerebral cortex.
The deep localization and small size of the fence present certain difficulties for its physiological study. This nucleus is shaped like a narrow strip of gray matter located beneath the cerebral cortex deep in the white matter.
Stimulation of the fence causes an indicative reaction, turning the head in the direction of irritation, chewing, swallowing, and sometimes vomiting movements. Irritation from the fence inhibits the conditioned reflex to light and has little effect on the conditioned reflex to sound. Stimulation of the fence during eating inhibits the process of eating food.
It is known that the thickness of the fence of the left hemisphere in humans is somewhat greater than that of the right; when the right hemisphere fence is damaged, speech disorder is observed.
Thus, the basal ganglia of the brain are integrative centers for the organization of motor skills, emotions, and higher nervous activity, and each of these functions can be enhanced or inhibited by the activation of individual formations of the basal ganglia.
Amygdala lies in the white matter of the temporal lobe of the hemisphere, approximately 1.5–2 cm posterior to the temporal pole. Amygdala (corpus amygdoloideum), amygdala is a subcortical structure of the limbic system, located deep in the temporal lobe of the brain. The neurons of the amygdala are diverse in form, function and neurochemical processes in them. The functions of the amygdala are associated with the provision of defensive behavior, autonomic, motor, emotional reactions, and the motivation of conditioned reflex behavior.
The electrical activity of the tonsils is characterized by oscillations of different amplitudes and frequencies. Background rhythms can correlate with the rhythm of breathing and heart contractions.
The tonsils react with many of their nuclei to visual, auditory, interoceptive, olfactory, skin irritations, and all these irritations cause changes in the activity of any of the nuclei of the amygdala, i.e. The amygdala nuclei are multisensory. The reaction of the nucleus to external stimuli lasts, as a rule, up to 85 ms, i.e. significantly less than the reaction to similar stimulation of the neocortex.
Neurons have pronounced spontaneous activity, which can be enhanced or inhibited by sensory stimulation. Many neurons are multimodal and multisensory and fire synchronously with the theta rhythm.
Irritation of the nuclei of the amygdala creates a pronounced parasympathetic effect on the activity of the cardiovascular and respiratory systems, leads to a decrease (rarely to an increase) in blood pressure, a decrease in heart rate, disruption of the conduction of excitation through the conduction system of the heart, the occurrence of arrhythmia and extrasystole. In this case, vascular tone may not change.
The slowdown in the rhythm of heart contractions when affecting the tonsils has a long latent period and has a long-lasting effect
Irritation of the tonsil nuclei causes respiratory depression and sometimes a cough reaction.
With artificial activation of the amygdala, reactions of sniffing, licking, chewing, swallowing, salivation, changes in the peristalsis of the small intestine appear, and the effects occur with a long latent period (up to 30-45 s after irritation). Stimulation of the tonsils against the background of active contractions of the stomach or intestines inhibits these contractions.
The various effects of irritation of the tonsils are due to their connection with the hypothalamus, which regulates the functioning of internal organs.
Damage to the amygdala in animals reduces the adequate preparation of the autonomic nervous system for the organization and implementation of behavioral reactions, leading to hypersexuality, the disappearance of fear, calmness, and inability to rage and aggression. Animals become gullible. For example, monkeys with a damaged amygdala calmly approach a viper that previously caused them horror and flight. Apparently, in case of damage to the tonsils, some innate unconditioned reflexes that implement the memory of danger disappear.
The white matter of the hemisphere includes the internal capsule and fibers, which have different directions. The following types of fibers should be distinguished: 1) fibers passing to the other hemisphere of the brain through its commissures (corpus callosum, anterior commissure, fornix commissure) and heading to the cortex and basal ganglia of the other side ( commissural fibers); 2) systems of fibers connecting areas of the cortex and subcortical centers within one half of the brain ( associative); 3) fibers going from the cerebral hemisphere to its underlying parts, to the spinal cord and in the opposite direction from these formations ( projection fibers).
The next section of the telencephalon is the corpus callosum, which is formed by commissural fibers connecting both hemispheres. The free upper surface of the corpus callosum, facing the longitudinal fissure of the cerebrum, is covered with a thin plate of gray matter. The middle part of the corpus callosum is its trunk– in front it bends downwards, forming knee corpus callosum, which, thinning, turns into beak, continuing downwards into terminal (border) plate. The thickened posterior part of the corpus callosum ends freely in the form of a ridge. The fibers of the corpus callosum form its radiance in each hemisphere of the cerebrum. The genu corpus callosum fibers connect the cortex of the frontal lobes of the right and left hemispheres. Brainstem fibers connect the gray matter of the parietal and temporal lobes. The roller contains fibers connecting the cortex of the occipital lobes. The areas of the frontal, parietal and occipital lobes of each hemisphere are separated from the corpus callosum by the groove of the same name.
Please note that under the corpus callosum there is a thin white plate - vault, consisting of two arched strands connected in its middle part by a transverse commissure of the arch (Fig.). The body of the vault, gradually moving away in the anterior part from the corpus callosum, arches forward and downward and continues into the column of the vault. The lower part of each column of the fornix first approaches the terminal plate, and then the columns of the fornix diverge laterally and are directed downward and posteriorly, ending in the mastoid bodies.
Between the crura of the fornix at the back and the terminal plate at the front there is a transverse anterior (white) commissure, which, along with the corpus callosum, connects both hemispheres of the cerebrum.
Posteriorly, the body of the fornix continues into the flat peduncle of the fornix, fused with the lower surface of the corpus callosum. The crus of the fornix gradually moves laterally and downwards, separates from the corpus callosum, becomes even more dense and on one side fuses with the hippocampus, forming the hippocampal fimbria. The free side of the fimbria, facing the cavity of the lower horn of the lateral ventricle, ends in the hook, connecting the temporal lobe of the telencephalon with the diencephalon.
The area bounded above and in front by the corpus callosum, below by its beak, terminal plate and anterior commissure, behind by the crus of the fornix, is occupied on each side by a sagittally located thin plate - the transparent septum. Between the plates of the transparent septum there is a narrow sagittal cavity of the same name containing a transparent liquid. The lamina pellucidum is the medial wall of the anterior horn of the lateral ventricle.
Let's look at the structure internal capsule(capsula internet) - a thick, angled plate of white matter, bounded on the lateral side by the lenticular nucleus, and on the medial side by the head of the caudate nucleus (in front) and the thalamus (back). The internal capsule is formed by projection fibers connecting the cerebral cortex with other parts of the central nervous system. The fibers of the ascending pathways, diverging in different directions to the cerebral cortex, form radiant crown. Downward, the fibers of the descending pathways of the internal capsule in the form of compact bundles are directed to the peduncle of the midbrain.
Fig.9. Fornix and hippocampus.
1 – corpus callosum, 2 – nucleus of the fornix, 3 – crus of the fornix, 4 – anterior commissure, 5 – column of the fornix, 6 – mastoid body, 7 – fimbria of the hippocampus, 8 – uncus, 9 – dentate gyrus, 10 – parahippocampal gyrus, 11 – hippocampal peduncle, 12 – hippocampus, 13 – lateral ventricle (opened), 14 – bird’s spur, 15 – fornix commissure.
Please note that the cavities of the cerebral hemispheres are lateral ventricles(I and II), located in the thickness of the white matter under the corpus callosum (Fig. 11). Each ventricle has four parts: anterior horn lies in the frontal lobe, the central part is in the parietal lobe, posterior horn- in the occipital lower horn- in the temporal lobe. The anterior horn of both ventricles is separated from the adjacent one by two plates of a transparent septum. The central part of the lateral ventricle bends from above around the thalamus, forms an arc and passes posteriorly into the posterior horn, downwards into the inferior horn. The medial wall of the inferior horn is hippocampus(a section of the ancient cortex), corresponding to a deep groove of the same name on the medial surface of the hemisphere. The fimbria stretches medially along the hippocampus, which is a continuation of the crus of the fornix (Fig.). On the medial wall of the posterior horn of the lateral ventricle of the brain there is a protrusion - hippocampus, corresponding to the calcarine groove on the medial surface of the hemisphere. The choroid plexus projects into the central part and lower horn of the lateral ventricle, which through the interventricular foramen connects with the choroid plexus of the third ventricle.
Fig. 10. Projection of the ventricles on the surface of the cerebrum.
1–frontal lobe, 2–central sulcus, 3–lateral ventricle, 4–occipital lobe, 5–posterior horn of the lateral ventricle, 6–IV ventricle, 7–brain aqueduct, 8–III ventricle, 9–central part of the lateral ventricle, 10 – inferior horn of the lateral ventricle, 11 – anterior horn of the lateral ventricle.
Fig. 11. Frontal section of the brain at the level of the central part of the lateral ventricles.
1–central part of the lateral ventricle, 2–choroid plexus of the lateral ventricle, 3–anterior villous artery, 4–internal cerebral vein, 5–fornix, 6–corpus callosum, 7–vascular base of the third ventricle, 8–choroid plexus of the third ventricle, 9 – III ventricle, 10 – thalamus, 11 – attached plate, 12 – thalamostriatal vein, 13 – caudate nucleus.
BASAL NUCLIA[Late Latin basalis referring to the base; synonym: central nodes, subcortical nuclei (nuclei subcorticales)] - accumulations of gray matter in the thickness of the cerebral hemispheres, involved in the correction of the program of complex motor acts and the formation of emotional and affective reactions.
The first information on the morphology of the basal ganglia is found in the works of Burdach (K. F. Burdach), 1819; I. P. Lebedeva, 1873; Anton, 1895; Kappers (S. A. Kappers), 1908, etc. A great contribution to the study of the basal ganglia was made by the anatomical and clinical-morphological studies of S. Vogt and O. Vogt (S. Vogt, O. Vogt), 1920; M. O. Gurevich, 1930; Foix and Nicolesco, 1925; E.K. Seppa, 1949; T. A. Leontovich, 1952, 1954; N. P. Bekhtereva, 1963; E.I. Kandelya, 1961; L. A. Kukueva, 1968, etc.
The basal ganglia, along with the cerebral cortex located on the surface of the hemispheres (cortex cerebri), make up the cellular substance of the telencephalon. Unlike the cortex, which has the structure of screen centers (characterized by certain cytoarchitectonic features: clear separation of layers, vertical orientation of most neurons, their differentiation in shape and size depending on their position in different layers), the basal ganglia have the structure of nuclear centers, where a similar structural there is no organization. Often these nuclei are called the subcortex. These include: the caudate nucleus (nucleus caudatus), the lentiform nucleus (nucleus lentiformis, s. nucleus lenticularis), the fence (claustrum) and the amygdala (corpus amygdaloideum). The basal nuclei also include the basal complex of nuclei, located between the anterior perforated substance (substantia perforata anterior) and the anterior part of the globus pallidus (globus pallidus), belonging to the septal region (see).
Comparative anatomy
Studies of the development of the basal ganglia in phylo and ontogenesis have shown that the caudate nucleus and the shell of the lentiform nucleus (putamen) develop from the ganglionic tubercle located on the lower wall of the lateral ventricle. They represent a single cell mass, which in higher vertebrates is separated by fibers of the anterior leg of the internal capsule (crus anterior capsulae internae). Due to the common origin and the connection between the head of the caudate nucleus and the anterior part of the putamen that remains throughout life by stripes of gray matter alternating with white bundles of fibers of the internal capsule, the caudate nucleus and putamen are combined under the name “striatum” (corpus striatum), or “striatum” ( striatum). Since the striatum is a phylogenetically later formation than the medially located part of the lenticular nucleus - the globus pallidus, consisting of external and internal segments, it is called “neostriatum”, and the globus pallidus is called “paleostriatum” (paleostriatum). Last in crust, time is separated into a special morphological unit called “pallidum” (pallidum).
Research by L.A. Kukuev (1968) shows that the external and internal segments of the globus pallidus have different origins. The external segment, like the shell, develops from the ganglionic tubercle of the telencephalon; the internal segment is from the diencephalon and is homologous to the entopeduncular nucleus of subprimates (located in their brain above the optic tract, that is, its topography is similar to the topography of the internal segment of the globus pallidus in the early stages of development of the human embryo). In the process of both phylogenetic and ontogenetic development, the internal segment moves towards the external one, as a result of which they come closer together.
The basal ganglia are represented differently in the brain of different classes of vertebrates. Thus, in fish and amphibians, the basal ganglia are represented only by the globus pallidus; the caudate nucleus and putamen appear for the first time in reptiles; they are especially well developed in birds. In mammals (carnivores and rodents), the globus pallidus is represented by a single formation; in humans, it consists of two segments separated by a layer of white matter. The size of the striatum decreases as the brain develops in phylogeny. Among mammals, in lower insectivores it makes up 8% of the size of the entire telencephalon, in tupaia and prosimians - 7%, and in monkeys - 6%.
In ontogenesis, the striatum can be differentiated at the beginning of the 2nd month of embryonic development. At the 3rd month of development, the head of the caudate nucleus protrudes into the cavity of the lateral ventricle. Lateral to the caudate nucleus, the putamen is formed, which is initially vaguely delimited from the rest of the hemisphere. The amygdala occupies a special position among the basal ganglia; in the early stages of embryonic development, it is separated from the striatum; cytological differentiation occurs in it later than in the globus pallidus, but somewhat earlier than in the striatum. Based on onto- and phylogenetic development, it also cannot be considered as an altered, thickened part of the cortex of the temporal lobe or as a result of its immersion inward and detachment. When studying the amygdala in a comparative anatomical aspect, a noticeable decrease in its size was revealed in mammals - from lower insectivores, where it, together with the paleocortex, makes up 31% of the entire size of the telencephalon, to humans, in whose brain the amygdala makes up only 4% of the telencephalon. the entire mass of the telencephalon. Studies of the development of the fence in onto- and phylogeny (I.N. Filimonov) showed that it cannot be considered a derivative of the cortical plate or associated in origin with the striatum. It represents an intermediate formation between these main cell masses of the telencephalon.
Anatomy
Caudate nucleus has a pear shape; its anterior part is thickened and is called the head of the caudate nucleus (caput nuclei caudati). It is located in the anterior part of the hemisphere and protrudes into the anterior horn of the lateral ventricle (cornu anterius ventriculi lateralis), forming its wall below and laterally. Posterior to the head, the caudate nucleus narrows and this section is called the body of the caudate nucleus (corpus nuclei caudati). The body of the caudate nucleus limits the central part of the lateral ventricle (pars centralis ventriculi lateralis) on the lateral side and describes a semicircle above the optic thalamus and the lentiform nucleus. The thinned posterior section of the caudate nucleus, forming part of the roof of the lower horn of the lateral ventricle (cornu inferius ventriculi lateralis), forms the tail of the caudate nucleus (cauda nuclei caudati). The lateral surface of the caudate nucleus is adjacent to the internal capsule (capsula interna), its medial edge is adjacent to the stria terminalis.
Lenticular nucleus has the shape of a wedge, the base of which is directed laterally, and the apex is directed medially and downward, adjacent to the subtubercular region. It lies laterally and slightly lower (ventral) from the caudate nucleus and thalamus optica, from which it is separated by the internal capsule. Anteriorly and ventrally, the lentiform nucleus is connected to the head of the caudate nucleus by thin strips of gray matter. Its lateral surface is somewhat convex and is located vertically, bordering the external capsule (capsula externa), which is a thin white brain plate, limited laterally by gray matter - the fence (claustrum). The ventral surface of the lenticular nucleus lies horizontally and in its middle part is connected to the cortex in the region of the anterior perforated substance. Two thin brain plates, medial and lateral (laminae medullares medialis et lateralis), divide it into three parts: the outer part, darker colored, is called the putamen, the other two are more faintly colored external and internal segments of the globus pallidus. The fence is a narrow plate of gray matter, which is located lateral to the lenticular nucleus and is separated from it by the outer capsule. The enclosure is separated from the insular cortex by a layer of white matter that forms the outer capsule (capsula extrema).
Amygdala- this is a complex of nuclei located in the area of the uncus of the parahippocampal gyrus (uncus gyri parahippocampalis), well differentiated and differing from each other cytologically and cytoarchitectonically (see Amygdaloid region).
Histology
The caudate nucleus and putamen are similar in histological structure. The gray matter of these nuclei consists of two types of cellular elements: small and large cells. Small cells, up to 15-20 microns in size, with short dendrites and thin axons, have delicate granulation and a large nucleus with a nucleolus. Large cells, up to 50 microns in size, are mostly triangular and polygonal, their nucleus is often located eccentrically, the protoplasm contains chromatin grains and in the vicinity of the nucleus there is a large amount of yellow lipoid pigment. These cells are normally surrounded by satellites. The ratio of large to small cells in the caudate nucleus and putamen averages 1:20. Both small and large cells have long axons that can be traced to other deep brain structures.
Rice. 1. Diagram of the main connections of the extrapyramidal system (according to S. and O. Vogt): 7 -cortex prefrontalis; 2 - tractus frontothalamicus; 3 - nucleus caudatus; 4 - thalamus; 5 -nucleus medialis thalami; 6 and 25 - nucleus ventralis thalami; 7 -nucleus campi Forell (BNA); 8 - nucleus subthalamicus; 9 -decussatio Foreli (BNA); 10 - nucleus ruber; 11 - substantia nigra; 12 - comissura post.; 13 - nucleus Darkschewitschi; 14 - nucleus interstitialis; 15 - pedunculi cerebelli superiores (tractus cerebellotegmentalls); 16 - cerebellum; 17 - nucleus dentatus; 18 - pedunculi cerebelli medii; 19 - nucleus vestibularis sup.; 20 - canalis semicirculatis; 21 - nucleus vestibularis lat.; 22 - fasciculus longitudinalis medius; 23 - fasciculus rubrospinalis; 24 - crus cerebri; 26 - globus pallidus; 27 - putamen; 28 - area gigantopyramidalis; 29 - capsule interna.
Certain relationships between cellular elements and fibers allowed Vogt (O. Vogt) to point out the similarity of the structure of the striatum with the cortex. In the caudate nucleus, under the ependyma, there is a zone poor in fibers; the outer part of this zone is poor in ganglion cells, the inner part is richer in them. Deeper is a layer of tangential fibers containing a small number of ganglion cells. Based on this, Vogt developed a diagram of the structural and functional organization of the striatum (color Fig. 1): striopetal fibers end on small cells, closely connected with each other and with large cells, from which striofugal fibers begin. In small cells the fibrils are not differentiated, in large cells they are distributed in bundles. There are few myelin fibers in the striatum; most of them arise in the striatum itself and serve to connect to the pallidum; between the bundles of myelinated fibers there is a dense network of unmyelinated ones. A rich network of neuroglia surrounds nerve cells and nerve fibers. The pallidum contains only very large cells of various shapes - pyramidal, spindle-shaped, multipolar with long dendrites (colored Fig. 2 and 3). There are many chromatophilic clumps in the protoplasm. The surface of the cells is covered with loop-shaped terminal bodies - the ends of unmyelinated fibers surrounding the cells and myelin fibers. There are many more myelin fibers than gray matter; this explains the pale color of the kernel.
The blood supply to the basal ganglia is carried out mainly from the middle cerebral artery (a. cerebri media), with branches going to the striatum (rr. striati). The branches of the anterior cerebral artery (a. cerebri anterior) also take part in the blood supply to the basal ganglia. All basal ganglia, especially the striatum, are very rich in capillaries; the distribution of capillaries in the striatum resembles that in the cortex; with lesions of the cerebral vessels, areas of softening especially often appear in the striatum.
Connections of the basal ganglia
The striatum receives afferent fibers from the optic thalamus, from the nuclei of the hypothalamus surrounding the third ventricle, from the midbrain tegmentum (tegmentum mesencepnali) and from the black substance (substantia nigra). These fibers end near the small cells of the striatum, from which the axons mainly go to the large cells, and from these latter fibers go to the pallidum as part of the strio-pallidal bundle (fasciculus striopallidalis). The fibers of the caudate nucleus cross the internal capsule, enter the putamen, and then, penetrating the medulla, penetrate the pallidum. From the shell, from its large cells, fibers also enter the pallidum through the medulla. The latter is the main place where fibers from the caudate nucleus and putamen are sent. Some authors do not deny the possibility of the existence of long fibers running directly from the shell to the trunk, without interruption in the pallidum. Afferent fibers going to the pallidum consist of fibers coming: 1) directly from the cortex; 2) from the cortex through the visual thalamus; 3) from the striatum; 4) from the central gray matter (substantia grisea centralis) of the diencephalon; 5) from the roof (tectum) and tegmentum (tegmentum) of the midbrain; 6) from the black substance.
Efferent fibers of the basal ganglia arise from the globus pallidus. The main bundle emerging from it is the lenticular loop (ansa lenticularis); its fibers begin in the caudate nucleus and take part in the formation of the medullary plates (laminae medullares). The loop is interrupted in the globus pallidus. Fibers emerging from the globus pallidus cross the internal capsule; at the border with the cerebral peduncles in the hypothalamus, they scatter in a fan-shaped manner and end in the anterior and lateral nuclei of the visual thalamus, in the hypothalamus, substantia nigra, subthalamic nucleus (nucleus subthalamicus) and red nucleus (nucleus ruber). Part of the fibers goes as part of the anterior decussation of the tire (decussatio tegmentalis anterior) to the opposite side, where it ends in the formations of the same name. Another bundle emerging from the globus pallidus is the lenticular bundle (fasciculus lenticularis). This bundle is located under the zona incerta and includes fibers going to the subtubercular nucleus (around which they form a bag), to the optic tubercle, red nucleus, nucleus of the inferior olive (nucleus olivaris), reticular substance (formatio reticularis), quadrigeminal, periventricular nuclei. Some of the fibers pass through the front cross of the tire to the opposite side and end in the same formations. The paths connecting the striatum with the funnel area (infundibulum) and located above the zona incerta are described. From the red nucleus, the quadrigeminal, peripheral extrapyramidal fibers (tractus rubrospinalis, tractus tectospinalis) begin. There is no exact data yet on the connection between the fence and the amygdala. In the literature, there are indications of a connection in animals between the fence and fibers from the external bursa, originating from the piriform region, its connection with the amygdala of the opposite region and the ventral region of the diencephalon. It was also established that the fence is connected to the cortex of the island. Connections of the amygdala - see Amygdala region.
Physiology of the basal ganglia
Rice. The main afferent and efferent connections (indicated by arrows) of the basal ganglia with other brain systems (I, II, IV - according to Bucy; III - according to Glies): I - connections from the motor and premotor zones (fields 4, 4S, 6,8, 24 ) cerebral cortex to the caudate nucleus and putamen; II - connections of the basal nuclei with the nuclei of the visual thalamus; III - connections between individual basal ganglia and between the basal ganglia and the motor and premotor areas of the cortex; IV - connections of the basal ganglia with the substantia nigra and the red nucleus. S. N. (C - according to Glies) - nuci, caudatus; V. A. (Nva - according to Glies) - nuci, ventralis ant. thalami; V. L. - nuci, lateralis thalami; V. P. - nuci, ventralis post, thalami; S. M. - nuci, medialis thalami; R. N. - nuci, ruber; S. N. - substantia nigra; C. e. - corpus callosum; F - fornix; Na-nuci. ant. thalami; Tr. o.- tractus opticus; P - putamen; Pi - globus pallidus (inner segment); Pe - globus pallidus (external segment); Ca - comissura ant.; Th - thalamus; G. P. - globus pallidus; H.- hypothalamus; S. S. - sulcus centralis.
At lower stages of evolution (in fish, reptiles, birds), the basal ganglia are the highest centers for coordinating complex behavior. In humans and higher animals (primates), complex integrative activity is carried out by the cerebral cortex, but the role of the basal ganglia does not decrease, but only changes (E.K. Sepp, 1959).
In the early stages of postnatal ontogenesis, the main motor function of the newborn - involuntary chaotic movements - is carried out mainly due to the pallidum. With the development of the striatum in later stages of postnatal ontogenesis, emotional manifestations (smile) are noted and statokinetic and tonic functions become more complicated (the child holds the head, performs friendly movements). When considering the physiological role of the basal ganglia, it is necessary to proceed from the characteristics of the connections of these nuclei with other parts of the brain (E. P. Kononova, 1959; I. N. Filimonov, 1959; O. Zager, 1962). The basal ganglia are characterized by a wealth of afferent and efferent connections with the motor areas of the cerebral cortex (Fig., /), with the nuclei of the thalamus opticus (Fig., II), between the basal ganglia (Fig., III), with the nuclei of the midbrain (Fig., IV), as well as with the hypothalamus, formations of the limbic system and the cerebellum. It is important for understanding the physiology of the basal ganglia to take into account the feedback connections coming from them to the cerebral cortex. Such a wide range of connections determines the complexity of the functional significance of the basal ganglia (united in the strio-pallidal system) in various neurophysiological and psychophysiological processes (V. A. Cherkes, 1963; E. Yu. Rivina, 1968; N. P. Bekhtereva, 1971). The participation of the basal ganglia in the following neurophysiological functions has been established: a) complex motor acts; b) vegetative functions; c) unconditioned reflexes; d) sensory processes; e) conditioned reflex mechanisms; f) psychophysiological processes (emotions). The role of the basal ganglia in the implementation of complex motor acts is that they determine myostatic reactions, optimal redistribution of muscle tone (due to modulating influences on the underlying structures of the central nervous system that determine the regulation of movements).
Thus, the study of the function of the pallidum, carried out under conditions of chronic experience, made it possible to establish its important role in the course of complex unconditioned reflexes of various biological orientations - sexual, food, defensive, etc.
The method of direct electrical stimulation of the pallidum shows the ease of reproducing the motor and bioelectrical manifestations of epileptiform reactions of the tonic type. Among the most important functions of the caudate nucleus and putamen, their inhibitory effect on the pallidum should be noted [Tilney and Riley (F. Tilney, H. A. Riley), 1921; Peips (J. W. Papez), 1942; A. M. Grinshtein, 1946, etc.]. The effects of turning off the neostriatum (striatum) are reflected in the functional activity of the pallidal and midbrain centers (substantia nigra, reticular formation of the brainstem). Their disinhibition occurs, which is accompanied by a change in muscle tone and the appearance of hyperkinesis (see). Numerous studies of the influence of the caudate nucleus on conditioned reflex activity and on purposeful movements indicate both the inhibitory and facilitatory nature of these influences, which led to the conclusion that there are two ascending activating systems: neostriatal and reticular; neostriatal influences the cerebral cortex both directly and indirectly, through the nuclei of the visual thalamus. Phenomena of convergence of sound, visual, and proprioceptive impulses were discovered in the basal ganglia. Apparently, the basal ganglia are the transmitting authority for impulses from the reticular formation to the cerebral cortex. This explains the phenomena of disorientation and chaotic motor activity against the background of stimulation of the caudate nucleus and putamen. The striatum is important in the regulation of the autonomic components of complex behavioral reactions. Irritation of the neostriatum is accompanied by emotionally expressive reactions (facial reactions, increased motor activity). When treating patients in neurosurgical clinics, carried out with the help of long-term implanted electrodes, the inhibitory effect of stimulation of the caudate nucleus on the performance of intellectual, speech activity, and memory was shown (N. P. Bekhtereva, 1971, etc.). The basal ganglia are of great importance in the mechanism of development of hyperkinesis. When the pallidum is destroyed or its pathology manifests itself as muscle hypertension, rigidity, and hyperkinesis. However, it has been established that the development of hyperkinesis is the result of a loss of function not of a separate basal ganglia, but is associated with dysfunction of the ventromedial nuclei of the thalamus opticus and midbrain centers that regulate tone (V. A. Cherkes, 1963; N. P. Bekhtereva, 1965, 1971).
Data from neurophysiological and clinical neurological studies of the functions of the basal ganglia allow us to conclude that their physiological significance must be considered in connection with other brain systems. Hartmann and Monakow (N. Hartmann, K. Monakow, 1960) showed that during a complex motor act, the basal nuclei are united by a continuous stream of impulses that spread through certain neural circles: a) thalamus - striatum - visual thalamus; b) visual thalamus - cerebral cortex - striatum - globus pallidus - visual thalamus.
The functional relationships between the basal ganglia are not yet fully understood. Electrophysiological studies have shown that striatal control of the globus pallidus is not solely inhibitory. In acute experiments on cats, a facilitative effect of the caudate nucleus on the neural activity of the globus pallidus was also revealed, as evidenced by an increase in the action potentials of individual elements of the globus pallidus under the influence of irritation of the head of the caudate nucleus.
The study of evoked potentials in the basal ganglia showed the possibility of convergence of excitations from different sensory channels on the same neuron [Segundo and Machne (I. P. Segundo, X. Machne), 1956; Albe-Fessard et al., 1960], and, in their opinion, somatotopic localization is not represented in any of the neuronal groups of the basal ganglia.
The large proportion of afferent morpho-functional connections suggests that the physiological role of the basal ganglia is not limited to the motor sphere. Considering the great importance of feedback connections and the close interaction of the basal ganglia with other brain systems, we can come to the conclusion that the role of the basal ganglia is to compare various afferent influences to perform the final motor task. Based on P.K. Anokhin’s concept of the functional system (1968), we can assume that the basal ganglia are involved in the formation of afferent synthesis, in correcting the program of a complex motor act and in assessing the results of the action. In addition, the functional state of the basal ganglia is reflected in other brain functions, especially in the formation of emotional and affective reactions.
Bibliography Anokhin P.K. Biology and neurophysiology of the conditioned reflex, M., 1968, bibliogr.; Beritov I. S. Nervous mechanisms of behavior of higher vertebrates, M., 1961, bibliogr.; Bekhtereva N. P. Neurophysiological aspects of human mental activity, L., 1971, bibliogr.; Belyaev F. P. Subcortical mechanisms of complex motor reflexes, D., 1965, bibliogr.; Granit R. Electrophysiological study of reception, trans. from English, M., 1957, bibliogr.; K o g and N A. B. Electrophysiological study of the central mechanisms of some complex reflexes, M., 1949, bibliogr.; Rozhansky N. A. Essays on the physiology of the nervous system, JI., 1957, bibliogr.; Sepp E.K. History of the development of the nervous system of vertebrates. M., 1959, bibliogr.; Suvorov N. F. Central mechanisms of vascular disorders, JI., 1967, bibliogr.; Filimonov I. N. Phylogenesis and ontogenesis of the nervous system, Multivolume. Guide to neurol., ed. N. I. Grashchenkova, vol. 1, book. 1, p. 9, M., 1959; Cherkes V. A. Essays on the physiology of the basal ganglia of the brain, Kyiv, 1963, bibliogr.; A 1 b e-Fessard D., Oswaldo-Cruz E. a. Rocha-M iranda S. Activity 6voqu6es dans le noyau caude du chat en rSponse h des types divers d’aff6rences, Electroenceph. clin. Neurophysiol., v. 12, p. 405, 1960; B u s R. S. The basal ganglia, the thalamus and hypothalamus, in the book: Physiol, basis med. pract., ed. by S. H. Best, p. 144, Baltimore, 1966, bibliogr.; Clara M. Das Nervensystem des Menschen, Lpz., 1959, Bibliogr.; The diseases of the basal ganglia, ed. by T. J. Putnam a. o., Baltimore, 1942, bibliogr.
N. N. Bogolepov, E. P. Kononova; F. P. Vedyaev (physics).
The basal ganglia are accumulations of gray matter in the form of nuclei or nodes located in each of the hemispheres in the thickness of the white matter, lateral and somewhat inferior to the lateral ventricles, closer to the base of the brain.
Clusters of gray matter, due to their position, are called basal ganglia, nuclei basales. Their second name is subcortical nodes, noduli subcorticales.
These in each hemisphere include: striatum, which includes the caudate and lentiform nuclei; fence And amygdala(complex).
The striatum, corpus striatum, got its name due to the fact that on horizontal and frontal sections of the brain it looks like alternating stripes of gray and white matter. The striatum consists of the caudate and lenticular nuclei, which are connected to each other by thin bridges of gray matter.
Caudate nucleus, nucleus caudatus, is located anterior to the thalamus, from which it is separated (visible on a horizontal section) by a strip of white matter - the knee of the internal capsule, and anterior and medial from the lenticular nucleus, from which it is separated by the anterior leg of the internal capsule. The anterior part of the nucleus is thickened and forms the head, caput, which forms the lateral wall of the anterior horn of the lateral ventricle. Located in the frontal lobe, the head of the caudate nucleus is adjacent to the anterior perforated substance below. At this point, the head of the caudate nucleus connects with the lentiform nucleus. Tapering posteriorly and upward, the head continues into a thinner body, the corpus, which lies in the bottom of the central part of the lateral ventricle and, as it were, spreads across the thalamus, separated from it by a terminal strip of white matter. The posterior section of the caudate nucleus - the tail, cauda, gradually thins, bends downward and anteriorly and participates in the formation of the upper wall of the lower horn of the lateral ventricle and reaches the amygdala, which lies in the thickness of the temporal pole (posterior to the anterior perforated substance).
Lenticular nucleus, nucleus lentiformis, which received its name for its resemblance to a lentil grain, is located anterior and lateral to the thalamus, and posterior and lateral to the caudate nucleus. The lenticular nucleus is separated from the thalamus by the posterior limb of the internal capsule. The lentiform nucleus is separated from the caudate nucleus by the anterior limb of the internal capsule. The lower surface of the anterior section of the lentiform nucleus is adjacent to the anterior perforated substance and connects here with the head of the caudate nucleus. On horizontal and frontal sections of the brain, the lenticular nucleus has the shape of a triangle with a rounded base. Its apex is directed medially to the knee of the internal capsule, located on the border of the thalamus and the head of the caudate nucleus, and its base is directed towards the base of the insular lobe of the brain.
Two parallel vertical layers of white matter, located almost in the sagittal plane, divide the lenticular nucleus into three parts. The shell, putamen, which has a darker color, lies most laterally. Medial to the putamen there are two light brain plates, which are called the “globus pallidus”, globus pallidus.
The medial plate is called the medial globus pallidus, globus pallidus medialis, the lateral plate is called the lateral globus pallidus, globus pallidus lateralis.
The caudate nucleus and shell belong to phylogenetically newer formations - neostriatum. The globus pallidus is an older formation – paleostriatum.
The fence, claustrum, is located in the white matter, between the putamen and the cortex of the insula. The fence has the appearance of a thin vertical plate of gray matter up to 2 mm thick. It is separated from the shell by a layer of white matter - the outer capsule, capsula externa, and from the insular cortex - by the same layer, called the “outermost capsule”, capsula extrema.
The amygdala, corpus amygdaloideum, is located in the white matter of the inferomedial part of the temporal lobe, approximately 1.5–2 cm posterior to the temporal pole, behind the anterior perforated substance. The amygdala is divided into a basal-lateral part, pars basolateralis, and a corticomedial part, pars corticomedialis. In the last part, the anterior amygdala area, area amygdaloidea anterior, is also distinguished.
The basal nuclei of the hemispheres include the striatum, consisting of the caudate and lenticular nuclei; fence and amygdala.
Topography of the basal ganglia
Striatum
corpus stridtum, got its name due to the fact that on horizontal and frontal sections of the brain it looks like alternating stripes of gray and white matter.
Most medially and anteriorly located caudate nucleus,nucleus caudatus. forms head,cdput, which forms the lateral wall of the anterior horn of the lateral ventricle. The head of the caudate nucleus below is adjacent to the anterior perforated substance.
At this point the head of the caudate nucleus connects to lenticular nucleus. Next, the head continues into a thinner body,corpus, which lies in the area of the bottom of the central part of the lateral ventricle. Posterior part of the caudate nucleus - tail,cduda, participates in the formation of the upper wall of the lower horn of the lateral ventricle.
Lenticular nucleus
nucleus lentiformis, Named for its resemblance to a lentil grain, it is located lateral to the thalamus and caudate nucleus. The lower surface of the anterior part of the lentiform nucleus is adjacent to the anterior perforated substance and is connected to the caudate nucleus. The medial part of the lentiform nucleus is angled towards the genu of the internal capsule, located on the border of the thalamus and the head of the caudate nucleus.
The lateral surface of the lenticular nucleus faces the base of the insular lobe of the cerebral hemisphere. Two layers of white matter divide the lenticular nucleus into three parts: shell,putamen; brain plates- medial And lateral,laminae medullares medialis et lateralis, which are collectively called “globus pallidus”, globe pdllidus.
The medial plate is called medial globus pallidus,globe pdllidus medialis, lateral - lateral globus pallidus,globe pdllidus lateralis. The caudate nucleus and shell belong to phylogenetically newer formations - neostridtum (stridtum). The globus pallidus is an older formation - paleostridtum (pdllidum).
Fence,cldustrum, located in the white matter of the hemisphere, on the side of the putamen, between the latter and the cortex of the insular lobe. It is separated from the shell by a layer of white matter - outer capsule,cdpsula exlerna.
Amygdala
corpus amygdaloideum, located in the white matter of the temporal lobe of the hemisphere, posterior to the temporal pole.
The white matter of the cerebral hemispheres is represented by various systems of nerve fibers, among which are: 1) associative; 2) commissural and 3) projection.
They are considered as pathways of the brain (and spinal cord).
Association nerve fibers which emerge from the cerebral cortex (extracortical), are located within one hemisphere, connecting various functional centers.
Commissural nerve fibers pass through the commissures of the brain (corpus callosum, anterior commissure).
Projection nerve fibers going from the cerebral hemisphere to its underlying sections (intermediate, middle, etc.) and to the spinal cord, as well as following in the opposite direction from these formations, constitute the internal capsule and its corona radiata, corona radiata.
Inner capsule
capsule interna , - This is a thick, angled plate of white matter.
On the lateral side it is limited by the lenticular nucleus, and on the medial side by the head of the caudate nucleus (in front) and the thalamus (back). The internal capsule is divided into three sections.
Between the caudate and lentiform nuclei there is anterior limb of the internal capsule,crus anterius cdpsulae internae, between the thalamus and the lenticular nucleus - posterior limb of the internal capsule,crus pos— terius cdpsulae internae. The junction of these two sections at an angle open laterally is knee of the internal capsule,genu cdpsulae interpae.
The internal capsule contains all the projection fibers that connect the cerebral cortex with other parts of the central nervous system. Fibers are located in the knee of the internal capsule corticonuclear pathway. In the anterior section of the posterior leg there are corticospinal fibers.
Posterior to the listed pathways in the posterior leg are located thalamocortical (thalamoparietal) fibers. This pathway contains fibers of conductors of all types of general sensitivity (pain, temperature, touch and pressure, proprioceptive). Even more posterior to this tract in the central sections of the posterior leg is temporo-parietal-occipital-pontine fasciculus. The anterior limb of the internal capsule contains frontopontine
The basal ganglia provide motor functions that are different from those controlled by the pyramidal (corticospinal) tract. The term extrapyramidal emphasizes this distinction and refers to a number of diseases in which the basal ganglia are affected. Familial diseases include Parkinson's disease, Huntington's chorea and Wilson's disease. This paragraph discusses the issue of the basal ganglia and describes objective and subjective signs of disturbances in their activity.
Anatomical connections and neurotransmitters of the basal ganglia. The basal ganglia are paired subcortical accumulations of gray matter, forming separate groups of nuclei. The main ones are the caudate nucleus and putamen (together forming the striatum), the medial and lateral plates of the globus pallidus, the subthalamic nucleus and the substantia nigra (Fig. 15.2). The striatum receives afferent input from many sources, including the cerebral cortex, thalamus nuclei, brainstem raphe nuclei, and substantia nigra. Cortical neurons associated with the striatum release glutamic acid, which has an excitatory effect. Neurons of the raphe nuclei associated with the striatum synthesize and release serotonin. (5-GT). Neurons of the substantia nigra pars compacta synthesize and release dopamine, which acts on striatal neurons as an inhibitory transmitter. The transmitters released by the thalamic conductors have not been defined. The striatum contains 2 types of cells: local bypass neurons, the axons of which do not extend beyond the nuclei, and the remaining neurons, the axons of which go to the globus pallidus and the substantia nigra. Local bypass neurons synthesize and release acetylcholine, gamma-aminobutyric acid (GABA), and neuropeptides such as somatostatin and vasoactive intestinal polypeptide. Neurons of the striatum that have an inhibitory effect on the substantia nigra pars reticularis release GABA, while those that excite the substantia nigra release substance P (Fig. 15.3). Striatal projections to the globus pallidus secrete GABA, enkephalins and substance P.
Rice. 15.2. Simplified schematic diagram of the main neuronal connections between the basal ganglia, thalamus optic and cerebral cortex.
Projections from the medial segment of the pallidum form the main efferent pathway from the basal ganglia. CC - compact part, RF - reticular part, YSL - midline nuclei, PV - anteroventral, VL - ventrolateral.
Rice. 15.3. Schematic diagram of the stimulating and inhibitory effects of neuroregulators secreted by neurons of the basal ganglia pathways. The striatal region (outlined by the dashed line) indicates neurons with efferent projection systems. Other striatal transmitters are found in intrinsic neurons. The + sign means excitatory nossynaptic influence. The -- sign means inhibitory influence. YSL - midline nuclei. GABA-?-amnobutyric acid; TSH is a thyroid-stimulating hormone. PV/VL - non-medioventral and ventrolateral.
Axons emerging from the medial segment of the globus pallidus form the main efferent projection of the basal ganglia. There are a significant number of projections passing through or adjacent to the internal capsule (the lemniscus and lenticular fasciculus passing through Forel's areas) to the anterior and lateral ventral nuclei of the thalamus, as well as to the intralamellar nuclei of the thalamus, including the paracentral nucleus. The mediators of this pathway are unknown. Other efferent projections of the basal ganglia include direct dopaminergic connections between the substantia nigra and the limbic region and the frontal cortex of the cerebral hemispheres; the reticular part of the substantia nigra also sends projections to the nuclei of the thalamus and to the superior colliculus.
Modern morphological studies have revealed the distribution of ascending fibers from the thalamus in the cerebral cortex. Ventral thalamic neurons project to the premotor and motor cortex; The medial nuclei of the thalamus project primarily to the prefrontal cortex. The supplementary motor cortex receives many projections from the basal ganglia, including the dopaminergic projection from the substantia nigra, while the primary motor cortex and premotor area receive many projections from the cerebellum. Thus, there is a series of parallel loops connecting specific formations of the basal ganglia with the cerebral cortex. Although the precise mechanism by which various signals are translated into coordinated goal-directed action remains unknown, it is clear that the significant influence of the basal ganglia and cerebellum on the motor cortex is largely due to the influence of the thalamus nuclei. The main projections of the cerebellum, passing through the superior cerebellar peduncle, end together with fibers coming from the globus pallidus in the ventral anterior and ventrolateral nuclei of the thalamus opticum. In this part of the thalamus, a wide loop is formed, consisting of ascending fibers from the basal ganglia and cerebellum to the motor cortex. Despite the obvious significance of these formations, stereotactic destruction of the ventral parts of the thalamus can lead to the disappearance of manifestations of familial essential tremor, as well as rigidity and tremor in Parkinson's disease, without causing functional disorders. Ascending thalamocortical fibers pass through the internal capsule and white matter, so that when lesions occur in this area, both the pyramidal and extrapyramidal systems can be simultaneously involved in the pathological process.
The axons of some cortical neurons form an internal capsule (corticospinal and corticobulbar tracts); they also project into the striatum. A complete loop is formed - from the cerebral cortex to the striatum, then to the globus pallidus, to the thalamus and again to the cerebral cortex. Axons emerging from the paracentral nucleus of the thalamus give projections back to the striatum, thus completing the loop of subcortical nuclei - from the striatum to the globus pallidus, then to the paracentral nucleus and again to the striatum. There is another loop of basal ganglia between the striatum and the substantia nigra. Dopaminergic neurons of the substantia nigra pars compacta project to the striatum, and individual striatal neurons secreting GABA and substance P send projections to the substantia nigra pars reticularis. There is a reciprocal connection between the reticular and compact parts of the substantia nigra; the reticular part sends projections to the ventral part of the thalamus optica, the superior colliculus, and also to the reticular formation of the brainstem. The subthalamic nucleus receives projections from the formations of the neocortex and from the lateral segment of the globus pallidus; neurons within the subthalamic nucleus form reciprocal connections with the lateral segment of the globus pallidus and also send axons to the medial segment of the globus pallidus and the reticular part of the substantia nigra. The neurochemical agents involved in these processes remain unknown, although the involvement of GABA has been identified.
Physiology of the basal ganglia. Recordings of the activity of neurons in the globus pallidus and substantia nigra in a state of wakefulness, performed in primates, confirmed that the main function of the basal ganglia is to support motor activity. These cells are involved at the very beginning of the movement process, as their activity increases before movement becomes visible and detectable by EMG. Increased activity of the basal ganglia was associated primarily with movement of the contralateral limb. Most neurons increase their activity during slow (smooth) movements, while others increase in activity during fast (ballistic) movements. In the medial segment of the globus pallidus and the reticular part of the substantia nigra there is a somatotopic distribution for the upper and lower limbs and face. These observations made it possible to explain the existence of limited dyskinesias. Focal dystonia and tardive dyskinesia can occur with local disturbances of biochemical processes in the globus pallidus and substantia nigra, affecting only those areas in which the hand or face is represented.
Although the basal ganglia are motor in function, it is impossible to establish a special type of movement mediated by the activity of these nuclei. Hypotheses about the functions of the basal ganglia in humans are based on the obtained correlations between clinical manifestations and the localization of lesions in patients with disorders of the extrapyramidal system. The basal ganglia are a cluster of nuclei around the globus pallidus, through which impulses are sent to the thalamus optic and further to the cerebral cortex (see Fig. 15.2). The neurons of each accessory nucleus produce excitatory and inhibitory impulses, and the sum of these influences on the main pathway from the basal ganglia to the thalamus optic and the cerebral cortex, with a certain influence from the cerebellum, determines the smoothness of movements expressed through the corticospinal and other descending cortical pathways. If one or more accessory nuclei is damaged, the amount of impulses entering the globus pallidus changes and movement disorders may occur. The most striking of them is hemiballismus; a lesion of the subthalamic nucleus apparently removes the inhibitory effect of the substantia nigra and globus pallidus, which leads to the appearance of violent involuntary sharp rotational movements of the arm and leg on the side opposite to the lesion. Thus, damage to the caudate nucleus often leads to chorea, and the opposite phenomenon, akinesia, in typical cases develops with the degeneration of cells of the substantia nigra that produce dopamine, freeing the intact caudate nucleus from inhibitory influences. Lesions of the globus pallidus often lead to the development of torsion dystonia and impaired postural reflexes.
Basic principles of neuropharmacology of the basal ganglia. In mammals, the transfer of information from one nerve cell to another usually involves one or more chemical agents released by the first neuron into a special receptor site of the second neuron, thus changing its biochemical and physical properties. These chemical agents are called neuroregulators. There are 3 classes of neuroregulators: neurotransmitters, neuromodulators and neurohormonal substances. Neurotransmitters such as catecholamines, GABA, and acetylcholine are the best known and clinically significant class of neuroregulators. They produce short-latency transient postsynaptic effects (eg, depolarization) close to their site of release. Neuromodulators, such as endorphins, somatostatin and substance P, also act in the excretory zone, but do not usually cause depolarization. Neuromodulators appear to be able to enhance or weaken the effects of classical neurotransmitters. Many neurons containing classical neurotransmitters also accumulate neuromodulatory peptides. For example, substance P is found in brainstem raphe neurons that synthesize 5-HT, and vasoactive intestinal peptide, together with acetylcholine, is found in many cortical cholinergic neurons. Neurohormonal substances, such as vasopressin and angiotensin II, differ from other neuroregulators in that they are released into the bloodstream and transported to distant receptors. Their effects initially develop more slowly and have a longer duration of action. The differences between different classes of neuroregulators are not absolute. Dopamine, for example, acts as a neurotransmitter in the caudate nucleus, but its mechanism of action in the hypothalamus is a neurohormone.
The neurotransmitters of the basal ganglia are the most well studied. They are also more susceptible to the effects of medications. Neurotransmitters are synthesized in the presynaptic terminals of neurons, and some, such as catecholamines and acetylcholine, accumulate in vesicles. When an electrical impulse arrives, neurotransmitters are released from the presynaptic ending into the synaptic cleft, spread in it and connect with special areas of the receptors of the postsynaptic cell, initiating a number of biochemical and biophysical changes; the sum of all postsynaptic excitatory and inhibitory influences determines the probability that a discharge will occur. Biogenic amines dopamine, norepinephrine and 5-HT are inactivated by reuptake by presynaptic terminals. Acetylcholine is inactivated by intrasynaptic hydrolysis. In addition, the presynaptic terminals contain receptor sites called autoreceptors, irritation of which usually leads to a decrease in the synthesis and release of the transmitter. The affinity of the autoreceptor for its neurotransmitter is often much higher than that of the postsynaptic receptor. Drugs that excite dopamine autoreceptors should reduce dopaminergic transmission and may be effective in treating hyperkinesias such as Huntington's chorea and tardive dyskinesia. According to the nature of the response to the effects of various pharmacological agents. receptors are divided into groups. There are at least two populations of dopamine receptors. For example, stimulation of the D1 region activates adenylate cyclase, while stimulation of the D2 region does not have such an effect. The ergot alkaloid bromocriptine, used in the treatment of Parkinson's disease, activates D2 receptors and blocks D1 receptors. Most antipsychotics block D2 receptors.
Clinical manifestations of damage to the basal ganglia. Akinesia. If we divide extrapyramidal diseases into primary dysfunctions (a negative sign due to damage to connections) and secondary effects associated with the release of neuroregulators (a positive sign due to increased activity), then akinesia is a pronounced negative sign or deficiency syndrome. Akinesia is the inability of the patient to actively initiate movement and perform normal voluntary movements easily and quickly. The manifestation of a lesser degree of severity is defined by the terms bradykinesia and hypokinesia. Unlike paralysis, which is a negative sign due to damage to the corticospinal tract, in the case of akinesia, muscle strength is preserved, although there is a delay in achieving maximum strength. Akinesia should also be distinguished from apraxia, in which the demand to perform a certain action never reaches the motor centers that control the desired movement. Akinesia causes the greatest inconvenience to people suffering from Parkinson's disease. They experience severe immobility and a sharp decrease in activity; they can sit for quite a long time practically without moving, without changing their body position, and spend twice as much time compared to healthy people on everyday activities such as eating, dressing and washing. Restricted movement is manifested by the loss of automatic cooperative movements, such as blinking and freely swinging the arms when walking. As a result of akinesia, the well-known symptoms of Parkinson's disease, such as hypomimia, hypophonia, micrographia, and difficulty rising from a chair and walking, appear to develop. Although the pathophysiological details remain unknown, the clinical manifestations of akinesia support the hypothesis that the basal ganglia significantly influence the initial stages of movement and the automatic execution of acquired motor skills.
Neuropharmacological data suggest that akinesia itself is the result of dopamine deficiency.
Rigidity. Muscle tone is the level of muscle resistance during passive movement of a relaxed limb. Rigidity is characterized by a prolonged stay of the muscles in a contracted state, as well as constant resistance to passive movements. In extrapyramidal diseases, rigidity at first glance may resemble spasticity that occurs with lesions of the corticospinal tract, since in both cases there is an increase in muscle tone. Differential diagnosis can be made based on some clinical features of these conditions already during examination of the patient. One of the differences between rigidity and spasticity is the distribution pattern of increased muscle tone. Although stiffness develops in both flexor and extensor muscles, it is more pronounced in those muscles that help flex the torso. Stiffness in large muscle groups is easy to identify, but it also occurs in small muscles of the face, tongue, and throat. In contrast to rigidity, spasticity usually results in increased tone in the extensor muscles of the lower extremities and in the flexor muscles of the upper extremities. In the differential diagnosis of these conditions, a qualitative study of hypertonicity is also used. With rigidity, resistance to passive movements remains constant, which gives reason to call it “plastic” or “lead tube” type. In cases of spasticity, a free gap may be observed, after which a “jackknife” phenomenon occurs; muscles do not contract until they are stretched to a significant extent, and later, when stretched, muscle tone decreases rapidly. Deep tendon reflexes do not change with rigidity and become more active with spasticity. Increased activity of the muscle stretch reflex arc leads to spasticity due to central changes, without increasing the sensitivity of the muscle spindle. Spasticity disappears when the dorsal roots of the spinal cord are cut. Rigidity is less associated with increased activity of the arc of segmental reflexes and more dependent on increased frequency of alpha motor neuron discharges. A special form of rigidity is the cogwheel sign, which is especially characteristic of Parkinson's disease. When a muscle with increased tone is passively stretched, its resistance may be expressed in a rhythmic twitching, as if it were controlled by a ratchet.
Chorea. Chorea, a disease whose name is derived from the Greek word meaning dance, refers to common arrhythmic hyperkinesis of a fast, impetuous, restless type. Choreic movements are characterized by extreme disorder and variety. As a rule, they are long-lasting, can be simple or complex, and involve any part of the body. In complexity, they can resemble voluntary movements, but they are never combined into a coordinated action until the patient includes them in a purposeful movement in order to make them less noticeable. The absence of paralysis makes normal purposeful movements possible, but they are often too fast, unstable and deformed under the influence of choreic hyperkinesis. Chorea may be generalized or limited to one half of the body. Generalized chorea is the leading symptom of Huntington's disease and rheumatic chorea (Sydenham's disease), causing hyperkinesis of the muscles of the face, trunk and limbs. In addition, chorea often occurs in patients with parkinsonism in case of overdose of levodopa. Another well-known choreiform disease, tardive dyskinesia, develops against the background of long-term use of antipsychotics. The muscles of the cheeks, tongue and jaws are usually affected by choreic movements in this disease, although in severe cases the muscles of the trunk and limbs may be involved. Sydenham's chorea is treated with sedatives such as phenobarbital and benzodiazepines. Antipsychotics are commonly used to suppress chorea in Huntington's disease. Drugs that enhance cholinergic conduction, such as phosphatidylcholine and physostigmine, are used in approximately 30% of patients with tardive dyskinesia.
A special form of paroxysmal chorea, sometimes accompanied by athetosis and dystonic manifestations, occurs in sporadic cases or is inherited in an autosomal dominant manner. It first appears in childhood or adolescence and continues throughout life. Patients experience paroxysms that last for several minutes or hours. One of the varieties of chorea is kinesogenic, that is, it occurs during sudden, purposeful movements. Factors that provoke chorea, especially in those individuals who were diagnosed with Sydenham's disease in childhood, may be hypernatremia, alcohol consumption and diphenin intake. In some cases, seizures can be prevented with anticonvulsant medications, including phenobarbital and clonazepam, and sometimes levodopa.
Athetosis. The name comes from a Greek word meaning unstable or changeable. Athetosis is characterized by the inability to hold the muscles of the fingers, toes, tongue, and other muscle groups in one position. Long-lasting, smooth involuntary movements occur, most pronounced in the fingers and forearms. These movements consist of extension, pronation, flexion and supination of the hand with alternating flexion and extension of the fingers. Athetotic movements are slower than choreiform ones, but there are conditions called choreoathetosis in which it can be difficult to distinguish between these two types of hyperkinesis. Generalized athetosis can be seen in children with static encephalopathy (cerebral palsy). In addition, it can develop in the case of Wilson's disease, torsion dystonia and cerebral hypoxia. Unilateral posthemiplegic athetosis is observed more often in children who have had a stroke. In patients with athetosis that developed against the background of cerebral palsy or cerebral hypoxia, other movement disorders are noted that arise as a result of concomitant damage to the corticospinal tract. Patients are often unable to perform individual independent movements with the tongue, lips and hands; attempts to make these movements lead to contraction of all the muscles of the limb or some other part of the body. All types of athetosis cause rigidity of varying degrees of severity, which, apparently, causes the slowness of movements in athetosis, in contrast to chorea. Treatment of athetosis is usually unsuccessful, although some patients experience improvement when taking drugs used to treat choreic and dystonic hyperkinesis.
Dystonia. Dystonia is an increase in muscle tone, leading to the formation of fixed pathological postures. In some patients with dystonia, postures and gestures may change, becoming awkward and pretentious, due to uneven strong contractions of the muscles of the trunk and limbs. Spasms that occur with dystonia resemble athetosis, but are slower and more often affect the muscles of the trunk than the limbs. The phenomena of dystonia intensify with purposeful movements, excitement and emotional overstrain; they decrease with relaxation and, like most extrapyramidal hyperkinesis, completely disappear during sleep. Primary torsion dystonia, previously called deforming muscular dystonia, is often inherited in an autosomal recessive manner in Ashkenazi Jews and in an autosomal dominant manner in individuals of other nationalities. Sporadic cases have also been described. Signs of dystonia usually appear in the first two decades of life, although later onsets of the disease have also been described. Generalized torsion spasms can occur in children suffering from bilirubin encephalopathy or as a result of cerebral hypoxia.
The term dystonia is also used in another meaning - to describe any fixed posture that occurs as a result of damage to the motor system. For example, dystonic phenomena that occur with a stroke (bent arm and extended leg) are often called hemiplegic dystonia, and in parkinsonism - flexor dystonia. In contrast to such persistent dystonic phenomena, some drugs, such as antipsychotics and levodopa, can provoke the development of temporary dystonic spasms that disappear after stopping the drug.
Secondary, or local, dystonia is more common than torsion dystonia; these include diseases such as spasmodic torticollis, writer's cramp, blepharospasm, spastic dystonia and Meige's syndrome. In general, with local dystonia, the symptoms usually remain limited, stable and do not spread to other parts of the body. Local dystonias often develop in middle-aged and older people, usually spontaneously, without a hereditary predisposition factor or previous diseases provoking them. The most famous type of local dystonia is spastic torticollis. With this disease, constant or prolonged tension occurs in the sternocleidomastoid, trapezius and other muscles of the neck, usually more pronounced on one side, leading to a forced turn or tilt of the head. The patient cannot overcome this violent posture, which distinguishes the disease from a habitual spasm or tic. Dystonic phenomena are most pronounced when sitting, standing and walking; Touching the chin or jaw can often help relieve muscle tension. Women aged 40 years get sick 2 times more often than men.
Torsion dystonia is classified as an extrapyramidal disease even in the absence of pathological changes in the basal ganglia or other parts of the brain. Difficulties in selecting medications are aggravated by insufficient knowledge about changes in neurotransmitters in the case of this disease. Treatment of secondary dystonic syndromes also does not bring noticeable improvement. In some cases, sedatives such as benzodiazepines, as well as large doses of cholinergic drugs, have a positive effect. Sometimes a positive effect occurs with the help of levodopa. Improvement is sometimes noted with treatment using bioelectrical control; psychiatric treatment is not beneficial. In severe spastic torticollis, most patients benefit from surgical denervation of the affected muscles (from C1 to C3 on both sides, C4 on one side). Blepharospasm is treated with botulinum toxin injections into the muscles surrounding the eyeball. The toxin causes a temporary blockade of neuromuscular transmission. Treatment must be repeated every 3 months.
Myoclonus. This term is used to describe short-term violent random muscle contractions. Myoclonus can develop spontaneously at rest, in response to stimulation, or during targeted movements. Myoclonus may occur in a single motor unit and resemble fasciculations, or simultaneously involve groups of muscles, resulting in changes in the position of the limb or deformation of targeted movements. Myoclonus results from a variety of generalized metabolic and neurological disorders collectively called myoclonus. Posthypoxic intentional myoclonus is a special myoclonic syndrome that develops as a complication of temporary anoxia of the brain, for example, during short-term cardiac arrest. Mental activity is usually not affected; Cerebellar symptoms occur due to myoclonus, involving the muscles of the limbs and face, and voluntary movements and voice are distorted. Action myoclonus distorts all movements and greatly impairs the ability to eat, talk, write, and even walk. These phenomena may occur with lipid storage disease, encephalitis, Creutzfeldt-Jakob disease, or metabolic encephalopathies arising from respiratory, chronic renal, hepatic failure or electrolyte imbalance. For the treatment of postanoxic intentional and idiopathic myoclonus, 5-hydroxytryptophan, a precursor of 5-HT, is used (Fig. 15.4); Baclofen, clonazepam and valproic acid are used as alternative treatments.
Asterixis. Asterixis (“fluttering” tremor) is called rapid irregular movements that occur as a result of short-term interruptions of background tonic muscle contractions. To some extent, asterixis can be considered negative myoclonus. Asterixis can be observed in any striated muscle during its contraction, but it is usually clinically presented as a short-term drop in postural tone with recovery upon voluntary extension of the limb with backward flexion at the wrist or ankle joint. Asterixis is characterized by periods of silence from 50 to 200 ms during continuous study of the activity of all muscle groups of one limb using EMG (Fig. 15.5). This causes the wrist or shin to drop down before muscle activity resumes and the limb returns to its original position. Bilateral asterixis is often observed in metabolic encephalopathies, and in the case of liver failure it has the original name “liver clap.” Asterixis can be caused by certain medications, including all anticonvulsants and the radiographic contrast agent Metrizamide. Unilateral asterixis can develop after brain lesions in the area of the blood supply of the anterior and posterior cerebral arteries, as well as due to small focal lesions of the brain, covering formations that are destroyed during stereotactic cryotomy of the ventrolateral nucleus of the thalamus.
Rice. 15.4. Electromyograms of the muscles of the left arm in a patient with posthypoxic nonintentional myoclonus before (a) and during (b) treatment with 5-hydroxytryptophan.
In both cases the hand was in a horizontal position. The first four curves show the EMG signal from the wrist extensor, wrist flexor, biceps and triceps muscles. The lower two curves are recordings from two accelerometers located at right angles to each other on the arm. Horizontal calibration is 1 s, and - prolonged high-amplitude jerky twitches during voluntary movements on the EMG are represented by arrhythmic discharges of bioelectrical activity, interspersed with irregular periods of silence. The initial positive and subsequent negative changes occurred synchronously in the antagonist muscles; b - only mild irregular tremor is observed, the EMG has become more uniform (from J. N. Crowdon et al., Neurology, 1976, 26, 1135).
Hemiballism. Hemiballism is called hyperkinesis, characterized by violent throwing movements in the upper limb on the side opposite to the lesion (usually of vascular origin) in the region of the subthalamic nucleus. A rotational component may occur during movements of the shoulder and hip, flexion or extension movements in the hand or foot. Hyperkinesis persists during wakefulness, but usually disappears during sleep. Muscle strength and tone may be slightly reduced on the affected side, precise movements are difficult, but there are no signs of paralysis. Experimental data and clinical observations indicate that the subthalamic nucleus appears to have a controlling influence on the globus pallidus. When the subthalamic nucleus is damaged, this restraining influence is eliminated, leading to hemiballismus. The biochemical consequences of these disturbances remain unclear, but indirect evidence suggests that increased dopaminergic tone occurs in other structures of the basal ganglia. The use of antipsychotics to block dopamine receptors, as a rule, leads to a decrease in the manifestations of hemiballismus. If there is no effect from conservative treatment, surgical treatment is possible. Stereotactic destruction of the homolateral globus pallidus, thalamic fasciculus, or ventrolateral nucleus of the thalamus can lead to the disappearance of hemiballismus and normalization of motor activity. Although recovery may be complete, some patients experience varying degrees of hemichorea involving the muscles of the hand and foot.
Rice. 15.5. Asterixis recorded from the outstretched left arm of a patient with encephalopathy caused by taking metrizamide.
The top four curves were obtained from the same muscles as in Fig. 15.4. The last curve was obtained from an accelerometer located on the dorsum of the hand. Calibration 1 s. The recording of a continuous voluntary EMG waveform was interrupted in the region of the arrow by a short involuntary period of silence in all four muscles. After a period of silence, a change in posture followed with a convulsive return, which was recorded by the accelerometer.
Tremor. This is a fairly common symptom, characterized by rhythmic vibrations of a certain part of the body relative to a fixed point. As a rule, tremor occurs in the muscles of the distal limbs, head, tongue or jaw, and in rare cases - the trunk. There are several types of tremor, and each has its own clinical and pathophysiological characteristics and methods of treatment. Often, several types of tremor can be observed simultaneously in the same patient, and each requires individual treatment. In a general medical institution, most patients with suspected tremor are actually dealing with asterixis that has arisen against the background of some kind of metabolic encephalopathy. Different types of tremor can be divided into separate clinical variants according to their location, amplitude and influence on goal-directed movements.
Tremor at rest is a large-scale trembling with an average frequency of 4-5 muscle contractions per second. Typically, tremor occurs in one or both upper extremities, sometimes in the jaw and tongue; is a common symptom of Parkinson's disease. This type of tremor is characterized by the fact that it occurs during postural (tonic) contraction of the muscles of the trunk, pelvic and shoulder girdle at rest; volitional movements temporarily weaken it (Fig. 15.6). With complete relaxation of the proximal muscles, the tremor usually disappears, but since patients rarely achieve this state, the tremor persists constantly. Sometimes it changes over time and can spread from one muscle group to another as the disease progresses. Some people with Parkinson's disease do not have tremor, in others it is very weak and limited to the muscles of the distal parts; in some patients with Parkinson's disease and in people with Wilson's disease (hepatolenticular degeneration), more pronounced disorders are often observed that also involve the muscles of the proximal parts. In many cases, plastic type rigidity of varying degrees of severity occurs. Although this type of tremor brings certain inconvenience, it does not significantly interfere with the performance of purposeful movements: often a patient with tremor can easily bring a glass of water to his mouth and drink it without spilling a drop. Handwriting becomes small and illegible (micrographia), the gait is mincing. Parkinson's syndrome is characterized by resting tremors, slowness of movement, rigidity, flexion postures without true paralysis, and unsteadiness. Parkinson's disease is often combined with tremor that occurs during severe anxiety caused by a large crowd of people (one of the types of enhanced physiological tremor - see below), or with hereditary essential tremor. Both concomitant conditions are aggravated by an increase in the level of catecholamines in the blood and are reduced by taking drugs that block beta-adrenergic receptors, such as anaprilin.
Rice. 15.6. Tremor at rest in a patient with parkinsonism. The upper two EMG curves were taken from the extensors and flexors of the left hand, the lower curve was taken with an accelerometer located on the left hand. Horizontal calibration 1 s. Resting tremor occurs as a result of alternating contractions of antagonist muscles with a frequency of approximately 5 Hz. The arrow indicates the change in EMG after the patient bent the hand back and the tremor at rest disappeared.
The exact pathological and morphological picture of changes in resting tremor is not known. Parkinson's disease causes visible lesions primarily in the substantia nigra. Wilson's disease, in which tremor is combined with cerebellar ataxia, causes diffuse lesions. In older people, tremors at rest may not be accompanied by rigidity, slowness of movements, hunched posture and immobility of facial muscles. Unlike patients with parkinsonism, people with similar manifestations have preserved mobility; there is no effect from taking antiparkinsonian drugs. It is impossible to accurately predict in any given case whether tremor is the initial manifestation of Parkinson's disease. Patients with unsteadiness when walking and tremors at rest in the proximal limbs (rubal tremor) as a symptom of cerebellar disorders can be distinguished from patients with parkinsonism by the presence of ataxia and dysmetria.
Intention tremor develops with active movement of the limbs or when holding them in a certain position, for example, in an extended position. The amplitude of the tremor may increase slightly with more subtle movements, but never reaches the level observed in the case of cerebellar ataxia/dysmetria. Intention tremor easily disappears when the limbs are relaxed. In some cases, Intention tremor is a sharp increase in normal physiological tremor that can occur in some situations in healthy people. Similar tremor can also occur in patients with essential tremor and Parkinson's disease. This process involves the arm in an extended position, the head, lips and tongue. In general, this tremor is a consequence of a hyperadrenergic state, and sometimes has an iatrogenic origin (Table 15.2).
When α2-adrenergic receptors are activated in muscles, their mechanical properties are disrupted, which leads to the occurrence of intention tremor. These disorders manifest themselves in damage to the afferent formations of the muscle spindle, which leads to disruption of the muscle stretch reflex arc and contributes to an increase in the amplitude of physiological tremor. These types of tremor do not occur in patients with a violation of the functional integrity of the muscle stretch reflex arc. Drugs that block α2-adrenergic receptors reduce increased physiological tremor. Intention tremor occurs in many medical, neurological and psychiatric diseases, so it is more difficult to interpret than resting tremor.
Table 15.2. Conditions in which physiological tremor increases
Conditions accompanied by increased adrenergic activity:
Anxiety
Taking bronchodilators and other beta mimetics
Excited state
Hypoglycemia
Hyperthyroidism
Pheochromocytoma
Peripheral intermediates of levodopa metabolism.
Excitement before performing in public
Conditions that may be accompanied by increased adrenergic activity:
Taking amphetamines
Taking antidepressants
Withdrawal syndrome (alcohol, drugs)
Xanthines in tea and coffee
Conditions of unknown etiology:
Treatment with corticosteroids
Increased fatigue
Treatment with lithium drugs
There is also another type of intention tremor, slower, usually as a monosymptom, occurring either in sporadic cases or in several members of the same family. It is called essential hereditary tremor (Fig. 15.7) and can appear in early childhood, but more often develops later in life and is observed throughout life. Tremor brings certain inconvenience, as it seems that the patient is in an excited state. A peculiar feature of this tremor is that it disappears after taking two or three sips of an alcoholic drink, but after the cessation of the effect of alcohol it becomes more pronounced. Essential tremor is reduced when taking hexamidine and β-blockers that affect the activity of the central nervous system, such as anaprilin.
Rice. 15.7. Action tremor in a patient with essential tremor. The recording was made from the muscles of the right arm during backward bending of the hand; Otherwise, the records are similar to those in Fig. 15.4. Calibration 500 ms. It should be noted that during action tremor, discharges of bioelectrical activity on the EMG with a frequency of approximately 8 Hz occurred synchronously in the antagonist muscles.
The term intention tremor is somewhat inaccurate: pathological movements are certainly not intentional, intentional, and the changes would be more correctly called tremor ataxia. With true tremors, as a rule, the muscles of the distal parts of the limbs suffer; the trembling is more rhythmic, usually in one plane. Cerebellar ataxia, which causes minute-to-minute changes in the direction of pathological movements, manifests itself with precise, targeted movements. Ataxia does not manifest itself in stationary limbs even during the first stage of voluntary movement, however, as movements continue and greater precision is needed (for example, when touching an object, a patient’s nose, or a doctor’s finger), jerky, rhythmic twitching occurs, making it difficult to move the limb forward, with fluctuations in sides. They continue until the action is completed. Such dysmetria can create significant interference for the patient in performing differentiated actions. Sometimes the head is involved (in the case of a staggering gait). This movement disorder undoubtedly indicates damage to the cerebellar system and its connections. If the lesion is significant, every movement, even raising a limb, leads to such changes that the patient loses his balance. A similar condition is sometimes noted in multiple sclerosis, Wilson's disease, as well as vascular, traumatic and other lesions of the midbrain tegmentum and subthalamic region, but not the cerebellum.
Habitual spasms and tics. Many people have habitual hyperkinesis throughout their lives. Well-known examples include sniffing, coughing, protruding the chin, and the habit of fiddling with the collar. They are called habitual spasms. People who perform these actions recognize that the movements are purposeful, but they are forced to do them in order to overcome feelings of tension. Habitual spasms may decrease over time or with the patient’s willpower, but when attention is distracted, they resume again. In some cases, they become so ingrained that a person does not notice and cannot control them. Habitual spasms are especially common in children aged 5 to 10 years.
Tics are characterized by stereotypical, unintentional, irregular movements. The best known and most severe form is Gilles de la Tourette syndrome, a neuropsychiatric disease with movement and behavior disorders. As a rule, the first symptoms of this disease appear in the first twenty years of life; men get sick 4 times more often than women. Movement disorders include multiple short-term muscle spasms, known as tics, in the face, neck and shoulders. Vocal tics often occur, and the patient makes grunting and barking sounds. Changes in behavior manifest themselves in the form of coprolalia (swearing and repetition of other obscene expressions) and repetition of words and phrases heard from others (echolalia). The origin of Gilles de la Tourette syndrome is unknown. The pathophysiological mechanisms also remain unclear. Treatment with antipsychotics reduces the severity and frequency of tics in 75-90% of patients, depending on the severity of the disease. Clonidine, a drug from the group of adrenergic agonists, is also used to treat Gilles de la Tourette syndrome.
Examination and differential diagnosis for extrapyramidal syndromes. In a broad sense, all extrapyramidal disorders must be considered from the point of view of primary deficiency (negative symptoms) and emerging new manifestations (changes in body position and hyperkinesis). Positive symptoms arise due to the release of the immobile formations of the nervous system responsible for movements from the inhibitory effect, and the resulting disturbance in their balance. The doctor must accurately describe the observed movement disorders; one should not limit oneself to the name of the symptom and fit it into a ready-made category. If the doctor knows the typical manifestations of the disease, he will easily identify the full symptoms of extrapyramidal diseases. It must be remembered that Parkinson's disease is characterized by slowness of movements, weak facial expressions, tremors at rest and rigidity. It is also easy to identify typical changes in posture in the generalized form of dystonia or spasmodic torticollis. In the case of athetosis, as a rule, instability of postures, continuous movements of the fingers and hands, tension are observed, with chorea with characteristic rapid complex hyperkinesis, with myoclonus with impulsive jerking movements leading to a change in the position of the limb or torso. With extrapyramidal syndromes, purposeful movements are most often impaired.
Particular diagnostic difficulties arise, as in the case of many other diseases, in early or latent forms of the disease. Parkinson's disease often goes undetected until tremors appear. Unbalance and the appearance of a shuffling gait (walking in small steps) in older people are often mistakenly attributed to loss of confidence and fear of falling. Patients may complain of nervousness and restlessness and describe difficulty moving and soreness in various parts of the body. If there are no symptoms of paralysis and reflexes are not changed, these complaints can be regarded as rheumatic or even psychogenic in nature. Parkinson's disease may begin with hemiplegic manifestations, and for this reason vascular thrombosis or a brain tumor may be misdiagnosed. In this case, diagnosis can be facilitated by identifying hypomimia, moderate rigidity, insufficient amplitude of arm swing when walking, or disturbances in other combined actions. Wilson's disease should be excluded in every case of atypical extrapyramidal disorders. Moderate or early chorea is often confused with increased excitability. Examination of the patient at rest and during active movements is crucial. However, in some cases it is impossible to distinguish a simple restless state from the early manifestations of chorea, especially in children, and there are no laboratory tests to make an accurate diagnosis. Noting the initial changes in postures during dystonia, the doctor may mistakenly assume that the patient has hysteria, and only later, when the changes in postures become stable, can a correct diagnosis be made.
Movement disorders often occur in combination with other disorders. Extrapyramidal syndromes usually accompany lesions of the corticospinal tract and cerebellar systems. For example, with progressive supranuclear palsy, olivopontocerebellar degeneration and Shy-Drager syndrome, many signs of Parkinson's disease are observed, as well as impaired voluntary movements of the eyeballs, ataxia, apraxia, postural hypotension or spasticity with a bilateral Babinski sign. Wilson's disease is characterized by resting tremor, rigidity, slowness of movement, and flexion dystonia in the trunk muscles, while athetosis, dystonia, and intention tremor occur rarely. Mental and emotional disturbances may also occur. Gellervorden-Spatz disease can cause generalized rigidity and flexion dystonia, and in rare cases choreoathetosis can occur. In some forms of Huntington's disease, especially if the disease began in adolescence, rigidity gives way to choreoathetosis. With spastic bilateral paralysis, children may develop a combination of pyramidal and extrapyramidal disorders. Some of the degenerative diseases that cause damage to both the corticospinal tract and the nuclei are described in Chapter. 350.
Morphological studies of the basal ganglia, as well as data from studies of the content of neurotransmitters, make it possible to evaluate lesions of the basal ganglia and monitor the treatment of such diseases. This is best illustrated by Huntington's and Parkinson's diseases. In Parkinson's disease, the content of defamine in the striatum is reduced due to the death of neurons in the substantia nigra and degeneration of their axonal projections to the striatum. As a result of a decrease in dopamine levels, striatal neurons that synthesize acetylcholine are freed from inhibitory influence. This results in a predominance of cholinergic nerve transmission over dopaminergic transmission, which explains most of the symptoms of Parkinson's disease. Identification of such an imbalance serves as the basis for rational drug treatment. Drugs that enhance dopaminergic transmission, such as levodopa and bromocriptine, are likely to restore balance between the cholinergic and dopaminergic systems. These drugs, prescribed in combination with anticholinergic drugs, are currently the mainstay of treatment for Parkinson's disease. The use of excessive doses of levodopa and bromocriptine leads to the occurrence of various hyperkinesis due to overstimulation of dopamine receptors in the striatum. The most common of these is craniofacial choreoathetosis; generalized choreoathetosis, tics in the face and neck, dystonic changes in posture, and myoclonic jerks may also develop. On the other hand, the prescription of drugs that block dopamine receptors (for example, neurolentics) or cause depletion of accumulated dopamine [Tetrabenazine or reserpine] can lead to the occurrence of parkinsonism syndrome in apparently healthy people,
Huntington's chorea is in many respects the clinical and pharmacological opposite of Parkinson's disease. In Huntington's disease, characterized by personality changes and dementia, gait disturbance and chorea, neurons in the caudate nucleus and putamen die, leading to depletion of GABA and acetylcholine while dopamine remains unchanged. Chorea is thought to result from a relative excess of dopamine compared to other neurotransmitters in the striatum; Drugs that block dopamine receptors, such as antipsychotics, generally have a beneficial effect on chorea, while levodopa increases it. Likewise, physostigmine, which enhances cholinergic transmission, may reduce symptoms of chorea, whereas anticholinergic drugs increase them.
These examples from clinical pharmacology also demonstrate the delicate balance between stimulatory and inhibitory processes in the basal ganglia. In all patients, the various clinical manifestations noted during treatment are due to changes in the neurochemical environment, while morphological damage remains unchanged. These examples illustrate the possibilities of drug treatment of lesions of the basal ganglia and give reason to be optimistic about the prospects for treating patients with extrapyramidal movement disorders.
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