Basal ganglia and their functional connections
The basal ganglia, or subcortical ganglia, are located at the base of the cerebral hemispheres in the thickness of the white matter in the form of individual nuclei, or nodes. The basal nuclei include: the striatum, consisting of the caudate and lenticular nuclei; fence and amygdala (Atl., Fig. 25, p. 134).
Caudate nucleus located anterior to the thalamus. Its anterior thickened part is head- placed in front of the optic thalamus, in the lateral wall of the anterior horn of the lateral ventricle, behind it gradually narrows and turns into tail. The caudate nucleus covers the visual thalamus in front, above and on the sides.
Lenticular nucleus got its name for its resemblance to a lentil grain and 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 connects with the caudate nucleus, the medial part of the lentiform nucleus faces the internal capsule, located on the border of the thalamus and the head of the caudate nucleus. The lateral surface of the lenticular nucleus is convex and faces the base of the insular lobe of the cerebral hemispheres. On the frontal section of the brain, the lenticular nucleus has the shape of a triangle, the apex of which faces the medial side and the base faces the lateral side. The lenticular nucleus is divided by layers of white matter into a darker colored lateral part - shell and medial - pale ball, consisting of two segments: internal and external. Shell according to genetic, structural and functional characteristics, it is close to the caudate nucleus, and they belong to phylogenetically newer formations. The globus pallidus is an older formation.
Fence located in the white matter of the hemisphere, on the side of the shell, from which a thin layer of white matter is separated - outer capsule. The same thin layer of white matter separates the enclosure from the insular cortex.
Amygdala located in the white matter of the temporal lobe of the hemisphere, approximately 1.5-2.0 cm posterior to the temporal pole.
Functions The basal ganglia are determined primarily by their connections, which they have in fairly large quantities. For example, the caudate nucleus and putamen receive descending connections primarily from the extrapyramidal system. Fibers from neurons of the cortex, thalamus and substantia nigra terminate on them. Other cortical fields 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, the red nucleus.
The abundance of connections between the caudate nucleus and the putamen indicates participation in integrative processes, organization and regulation of movements, regulation of the work of internal organs.
The medial nuclei of the thalamus have direct connections with the caudate nucleus, as evidenced by the onset of the reaction 2-4 ms after stimulation of the thalamus.
In the interactions between the caudate nucleus and the globus pallidus, inhibitory influences prevail. When the caudate nucleus is stimulated, most of the neurons of the globus pallidus are inhibited, and a smaller part is excited.
The caudate nucleus and the substantia nigra have direct and feedback connections with each other. For example, stimulation of the substantia nigra leads to an increase, and destruction leads to a decrease in the amount of dopamine in the caudate nucleus. Thanks to dopamine, a disinhibitory mechanism of interaction between the caudate nucleus and the globus pallidus appears.
The caudate nucleus and globus pallidus take part in such integrative processes as conditioned reflex activity and motor activity. Switching off the caudate nucleus is accompanied by the development of hyperkinesis such as involuntary facial reactions, tremor, athetosis, torsion spasm of chorea (twitching of the limbs, torso, as in an uncoordinated dance), motor hyperactivity in the form of aimless moving from place to place.
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.
Despite the functional similarity of the caudate nucleus and the putamen, there are a number of functions specific to it. Thus, the shell is characterized by participation in the organization of eating behavior. Irritation of the shell leads to changes in breathing and salivation.
The globus pallidus has connections with the thalamus, putamen, caudate nucleus, midbrain, hypothalamus, somatosensory system, etc., which indicates its participation in the organization of simple and complex forms of behavior.
Stimulation of the globus pallidus, unlike stimulation of the caudate nucleus, does not cause inhibition, but provokes an orienting reaction, movements of the limbs, and feeding behavior (sniffing, chewing, swallowing).
Damage to the globus pallidus causes people to have a mask-like appearance of the face, tremor of the head and limbs (and this tremor disappears at rest, during sleep and intensifies with movement), monotony of speech. In a person with globus pallidus dysfunction, the onset of movements is difficult, auxiliary movements of the arms when walking disappear, and a symptom of propulsion appears: long preparation for movement, then rapid movement and stopping.
The fence forms connections primarily with the cerebral cortex. 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 has been noted 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 disorders are observed.
The amygdala receives impulses from a variety of afferent systems, including the olfactory system, and is related to emotional reactions.
Thus, the basal ganglia 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. In addition, the basal ganglia are the connecting link between the associative and motor areas of the cerebral cortex.
Development of the basal ganglia. The basal ganglia develop more intensively than the visual thalamus. The globus pallidus (pallidum) myelinates before the striatum (striatum) and the cerebral cortex. It has been noted that myelination in the globus pallidus is almost completely completed by 8 months of fetal development.
In the structures of the striatum, myelination begins in the fetus and ends only by 11 months of life. The caudate body doubles in size during the first two years of life, which is associated with the development of automatic motor acts in the child.
The motor activity of a newborn is largely associated with the globus pallidus, impulses from which cause uncoordinated movements of the head, torso and limbs.
In a newborn, the pallidum already has multiple connections with the optic thalamus, subtuberculous region and substantia nigra. The connection between the pallidum and the striatum develops later; some of the striopallidal fibers become myelinated in the first month of life, and the other part only by 5 months and later.
The pyramidal system in a newborn is not yet sufficiently developed, and impulses to the muscles are delivered from the subcortical ganglia through the extrapyramidal system. As a result, the child’s movements in the first months of life are characterized by generalization and undifferentiation.
It has been noted that acts such as crying are motorized by the globus pallidus. The development of the striatum is associated with the appearance of facial movements, and then the ability to sit and stand. Since the striatum has an inhibitory effect on the pallidum, a gradual separation of movements is created.
In order to sit, the child must be able to hold his head and back upright. This appears by the age of two months, and the child begins to raise his head while lying on his back by 2-3 months. Starts sitting at 6-8 months.
In the first months of life, the child has a negative support reaction: when trying to put him on his legs, he lifts them and pulls them towards his stomach. Then this reaction becomes positive: when you touch the support, the legs unbend. At 9 months the child can stand with support; at 10 months he can stand freely.
From 4-5 months of age, various voluntary movements develop quite quickly, but for a long time they are accompanied by a variety of additional movements.
The appearance of voluntary (such as grasping) and expressive movements (smiling, laughter) is associated with the development of the striatal system and motor centers of the cerebral cortex. The axons of their cells grow to the basal ganglia, and the activity of the latter begins to be regulated by the cortex. A child begins to laugh loudly at 8 months.
As all parts of the brain and the cerebral cortex grow and develop, the child’s movements become less generalized and more coordinated. Only by the end of the preschool period is a certain balance of cortical and subcortical motor mechanisms established.
Large hemispheres The brain is covered on top with a thin layer of gray matter - the cerebral cortex. There are two of them (right and left), they are connected to each other by a thick horizontal plate - corpus callosum, consisting of nerve fibers running transversely from one hemisphere to the other. Below the corpus callosum is vault, representing two arched white cords that are connected to each other by the middle part, and diverge in front and behind, forming the columns of the arch in front, behind the legs of the arch.
Each hemisphere has three surfaces: superolateral (most convex), medial (flat, facing the adjacent hemisphere) and lower, which has a complex relief corresponding to the internal base of the skull. Each hemisphere has the most prominent areas, called poles: frontal pole, occipital pole and temporal pole.
Throughout its entire length, the bark deepens, forming numerous furrows, which divide the surface of the hemispheres into convolutions and lobes. Each hemisphere has six lobes: frontal, parietal, temporal, occipital, marginal and insula. They are separated by the lateral, central, parieto-occipital, cingulate and collateral grooves (Atl., Fig. 22, p. 133).
Lateral sulcus begins at the base of the hemisphere with a significant depression, the bottom of which is covered with grooves and convolutions island. Then it moves to the superolateral surface of the hemisphere, heading back and slightly upward, separating the temporal lobe from the higher lobes: the frontal - in front and the parietal - in the back.
Central sulcus begins on the upper edge of the hemisphere, slightly behind its middle and goes forward downwards, most often not reaching the lateral (side) sulcus. The central sulcus separates the frontal lobe from the parietal lobe (Atl., Fig. 27, p. 135).
Parieto-occipital sulcus runs vertically along the medial surface of the hemisphere, separating the parietal lobe from the occipital lobe.
cingulate groove runs along the medial surface of the hemisphere parallel to the corpus callosum, separating the frontal and parietal lobes from the cingulate gyrus.
Collateral groove On the lower surface of the hemisphere, it separates the temporal lobe from the marginal and occipital lobes.
On the lower surface of the hemisphere, in its anterior part, is located olfactory sulcus, in which lies the olfactory bulb, which continues into the olfactory tract. At the back it bifurcates into lateral and medial stripes, forming an olfactory triangle, in the center of which lies the anterior perforated substance.
Hemisphere lobes. Frontal lobe. In the anterior part of each hemisphere is the frontal lobe. It ends anteriorly with the frontal pole and is limited inferiorly by the lateral sulcus (Sylvian fissure) and posteriorly by the deep central sulcus. Anterior to the central sulcus, almost parallel to it, is located precentral sulcus. The superior and inferior frontal sulci extend forward from it. They divide the frontal lobe into convolutions. The frontal lobe has 4 convolutions: precentral, located between the central sulcus posteriorly and the precentral sulcus anteriorly; superior frontal(above the superior frontal sulcus); middle frontal(between the superior and inferior frontal sulci); inferior frontal(downward from the inferior frontal sulcus). The inferior frontal gyrus is divided into three parts: operculum (frontal operculum) - between the inferior precentral sulcus posteriorly, the inferior frontal sulcus superiorly, and the ascending branch of the lateral sulcus anteriorly; triangular part - between the ascending and anterior branches of the lateral sulcus and orbital - below the anterior branch of the lateral sulcus.
Parietal lobe located posterior to the central sulcus. The posterior border of this lobe is the parieto-occipital sulcus. Within the parietal lobe there is postcentral sulcus, which lies behind the central sulcus and is almost parallel to it. Between the central and postcentral sulci is located postcentral gyrus. It extends posteriorly from the postcentral sulcus intraparietal sulcus. It is parallel to the upper edge of the hemisphere. Above the intraparietal sulcus is the superior parietal lobule. Below this groove lies the inferior parietal lobule, within which there are two gyri: supramarginal and angular. The supramarginal gyrus covers the end of the lateral sulcus, and the angular gyrus covers the end of the superior temporal sulcus.
Temporal lobe occupies the inferolateral parts of the hemisphere and is separated from the frontal and parietal lobes by a deep lateral sulcus. On its superolateral surface there are three parallel grooves. Superior temporal sulcus lies directly under the lateral and limits superior temporal gyrus. The inferior temporal sulcus consists from separate segments, bounds from below middle temporal gyrus. The inferior temporal gyrus on the medial side is limited by the inferolateral edge of the hemisphere. Anteriorly, the temporal lobe curves into the temporal pole.
Occipital lobe located behind the parieto-occipital sulcus. Compared to other lobes, it is small in size. It has no permanent grooves on the superolateral surface. Its main calcarine groove is located horizontally on the medial surface and runs from the occipital pole to the parieto-occipital groove, with which it merges into one trunk. Between these grooves lies a triangular gyrus - wedge. The lower surface of the occipital lobe lies above the cerebellum (Atl., Fig. 27, p. 135). At the posterior end the lobe tapers into occipital pole.
Marginal lobe located on the medial and inferior surfaces of the hemisphere. It includes the cingulate and parahippocampal gyri. The cingulate gyrus is limited inferiorly groove of the corpus callosum, and above - cingulate groove, separating it from the frontal and parietal lobes . Parahippocampal gyrus limited from above hippocampal sulcus, which serves as a downward and forward continuation of the posterior end of the groove of the corpus callosum. Inferiorly, the gyrus is separated from the temporal lobe by the collateral sulcus.
White matter is located under the cerebral cortex, forming a continuous mass above the corpus callosum. Below, the white matter is interrupted by clusters of gray (basal ganglia) and is located between them in the form of layers or capsules (Atl., Fig. 25, p. 134).
The white matter consists of associative, commissural and projection fibers.
Association fibers connect different parts of the cortex of the same hemisphere. They are divided into short and long. Short fibers connect neighboring convolutions in the form of arcuate bundles. Long association fibers connect areas of the cortex that are more distant from each other. Long associative fibers include:
The superior longitudinal fasciculus connects the inferior frontal gyrus with the inferior parietal lobe, temporal and occipital lobes; it has the shape of an arc that goes around the island and stretches along the entire hemisphere;
The inferior longitudinal fasciculus connects the temporal lobe with the occipital lobe;
Fronto-occipital fascicle - connects the frontal lobe with the occipital and insula;
The cingulate bundle - connects the anterior perforated substance with the hippocampus and the uncus, located in the shape of an arc in the cingulate gyrus, bends around the corpus callosum from above;
Uncinate fasciculus - connects the lower part of the frontal lobe, the uncinate and the hippocampus.
Commissural fibers connect the cortex of the symmetrical parts of both hemispheres. They form so-called commissures or commissures. The largest cerebral commissure is corpus callosum, connecting the same areas of the neocortex of the right and left hemispheres. It is located deep in the longitudinal slit and is a flattened, elongated formation. The surface of the corpus callosum is covered with a thin layer of gray matter, which forms four longitudinal stripes. The fibers diverging from the corpus callosum form its radiance. It is divided into frontal, parietal, temporal and occipital parts.
For the phylogenetically ancient cortex, the commissural fiber systems are the anterior and posterior commissures. Anterior commissure connects the uncinates of the temporal lobes and parahippocampal gyri, as well as the gray matter of the olfactory triangles.
Projection fibers extend beyond the hemispheres as part of the projection pathways. They provide two-way communication between the cortex and the underlying parts of the central nervous system. Some of these fibers conduct excitation centripetally, towards the cortex, while others, on the contrary, centrifugally.
Projection fibers in the white matter of the hemisphere closer to the cortex form the so-called corona radiata and pass into internal capsule(Atl., Fig. 25, p. 134). In the internal capsule there are anterior and posterior legs and a knee. Descending projection pathways, passing through the capsule, connect various zones of the cortex with underlying structures. The anterior peduncle contains the frontopontine tract (part of the corticopontine tract) and the anterior thalamic radiance. In the knee there are fibers of the corticonuclear tract, and in the upper part of the posterior leg there are corticospinal, corticoronuclear, corticoreticular tracts, as well as fibers of the thalamic radiance. In the most distant part of the posterior peduncle there are corticotectal, temporopontine and thalamic radiant fibers, going to the occipital and temporal areas of the cortex in the visual and auditory areas. The parieto-occipital-pontine fascicle also runs here.
Descending projection pathways coming from the cortex are combined into pyramidal pathway consisting of the corticonuclear and corticospinal tracts.
Ascending projection pathways carry impulses to the cortex that arise from the sensory organs, as well as from the organs of movement. These projection pathways include: the lateral spinothalamic tract, the fibers of which, passing through the posterior leg of the internal capsule, forming the corona radiata, reach the cerebral cortex, its postcentral gyrus; the anterior spinothalamic tract, which carries impulses from the skin to the cerebral cortex into the postcentral gyrus; conductive path of proprioceptive sensitivity of the cortical direction, supplying impulses of the muscular-articular sense to the cerebral cortex in the postcentral gyrus.
A special place in the system of fibers of the cerebral hemispheres is occupied by vault. It is a curved cord, in which the body, legs, and pillars are distinguished. Body the fornix is located under the corpus callosum and fuses with it. In front, the body of the fornix passes into the columns of the fornix, which bend downward, and each of them passes into the mamillary body of the hypothalamus. Vault pillars located above the anterior parts of the thalamus. Between each column and the thalamus there is a gap - the interventricular foramen. In front of the pillars of the arch, merging with them, lies anterior commissure. Posteriorly, the body of the fornix continues into the paired crura of the fornix, which extend laterally downwards, separate from the corpus callosum and fuse with the hippocampus, forming its fimbria. The right and left hippocampi are connected to each other through commissioner of the arch located between the legs. Thus, with the help of the fornix, the temporal lobe of the hemisphere is connected to the mammillary bodies of the diencephalon. In addition, some of the fibers of the fornix are directed from the hippocampus to the thalamus, amygdala and ancient cortex.
The basal ganglia include a complex of neuronal nodes of the gray matter, which are located in the white matter of the cerebral hemispheres. These formations are called the striopolitan system. Refers to the caudate nucleus, putamen- together they form striatum. Pale ball in cross-section it consists of 2 segments - external and internal. The outer segment of the globus pallidus has a common origin with the striatum. The internal segment develops from the gray matter of the diencephalon. These formations have a close connection with the subthalamic nuclei of the diencephalon, with black substance the midbrain, which consists of two parts - the ventral part (reticular) and dorsal (compact).
Pars compacta neurons produce dopamine. And the reticular part of the substantia nigra in structure and function resembles the neurons of the inner segment of the globus pallidus.
The substantia nigra forms connections with the anterior ventral nucleus of the visual thalamus, the colliculus colliculi, the pontine nuclei, and bilateral connections with the striatum. These educations are received afferent signals and themselves form efferent pathways. Sensory pathways to the basal ganglia come from the cerebral cortex and the main afferent pathway begins from the motor and premotor cortex.
Cortical areas 2,4,6,8. These pathways go to the striatum and globus pallidus. There is a certain topography of the projection of the muscles of the dorsal part of the shell - the muscles of the legs, arms, and in the ventral part - the mouth and face. From the segments of the globus pallidus there are paths to the visual thalamus, the anterior ventral and ventrolateral nuclei, from which information will return to the cortex.
The pathways to the basal ganglia from the visual thalamus are of great importance. Provide sensory information. Influences from the cerebellum are also transmitted to the basal ganglia through the optic thalamus. There are also sensory pathways to the striatum from the substantia nigra . Efferent pathways are represented by connections of the striatum with the globus pallidus, with the substantia nigra, reticular formation of the brain stem; from the globus pallidus there are paths to the red nucleus, to the subthalamic nuclei, to the nuclei of the hypothalamus and visual thalamus. At the subcortical level there are complex circular interactions.
Connections between the cerebral cortex, the thalamus opticus, the basal ganglia and again the cortex form two pathways: direct (facilitates the passage of impulses) and indirect (inhibitory)
Indirect path. Has an inhibitory effect. This inhibitory pathway goes from the striatum to the outer segment of the globus pallidus and the striatum inhibits the outer segment of the globus pallidus. The outer segment of the globus pallidus inhibits the body of Lewis, which normally has an exciting effect on the internal segment of the globus pallidus. In this chain there are two sequential braking.
In the direct path, the cerebral cortex exerts an inhibitory effect on the striatum on the inner segment of the globus pallidus, and disinhibition occurs.
Substantia nigra (produces dopamine) In the striatum there are 2 types of receptors D1 - excitatory, D2 - inhibitory. The striatum with the substantia nigra has two inhibitory pathways. The substantia nigra inhibits the striatum with dopamine, and the striatum inhibits the substantia nigra with GABA. High copper content in the substantia nigra, the blue spot of the brain stem. The emergence of the striopolitan system was necessary for the movement of the body in space - swimming, crawling, flying. This system forms a connection with the subcortical motor nuclei (red nucleus, tegmentum of the midbrain, nuclei of the reticular formation, vestibular nuclei) From these formations there are descending pathways to the spinal cord. All this together forms extrapyramidal system.
Motor activity is realized through the pyramidal system - descending pathways. Each hemisphere is connected to the opposite half of the body. In the spinal cord with alpha motor neurons. All our desires are realized through the pyramid system. It works with the cerebellum, the extrapyramidal system and builds several circuits - the cerebellar cortex, the cortex, the extrapyramidal system. The origin of thought arises in the cortex. In order to accomplish it, you need a movement plan. Which includes several components. They are connected into one image. For this you need programs. Rapid movement programs – in the cerebellum. Slow ones - in the basal ganglia. Cora selects the necessary programs. It creates a single general program that will be implemented through the spinal pathways. To throw the ball into the hoop, we need to take a certain position, distribute muscle tone - this is all on a subconscious level - the extrapyramidal system. When everything is ready, the movement itself will take place. The striopolitan system can provide stereotypical learned movements - walking, swimming, cycling, but only when they are learned. When performing a movement, the striopolitan system determines the scale of movements - the amplitude of movements. The scale is determined by the striopolitar system. Hypotonia - decreased tone with hyperkinesis - increased motor activity.
The coordinator of the coordinated work of the body is the brain. It consists of different departments, each of which performs specific functions. A person’s ability to function directly depends on this system. One of its important parts is the basal ganglia of the brain.
Movement and certain types of higher nervous activity are the result of their work.
What are the basal ganglia
The concept “basal” translated from Latin means “relating to the base.” It was not given by chance.
Massive areas of gray matter are the subcortical nuclei of the brain. The peculiarity of the location is in depth. The basal ganglia, as they are also called, are one of the most “hidden” structures of the entire human body. The forebrain, in which they are observed, is located above the brainstem and between the frontal lobes.
These formations represent a pair, the parts of which are symmetrical with each other. The basal ganglia are deepened into the white matter of the telencephalon. Thanks to this arrangement, information is transferred from one department to another. Interaction with other parts of the nervous system is carried out using special processes.
Based on the topography of the brain section, the anatomical structure of the basal ganglia is as follows:
- The striatum, which includes the caudate nucleus of the brain.
- The fence is a thin plate of neurons. Separated from other structures by stripes of white matter.
- Amygdala. Located in the temporal lobes. It is called part of the limbic system, which receives the hormone dopamine, which provides control over mood and emotions. It is a collection of gray matter cells.
- Lenticular nucleus. Includes globus pallidus and putamen. Located in the frontal lobes.
Scientists have also developed a functional classification. This is a representation of the basal ganglia in the form of the nuclei of the diencephalon, midbrain, and striatum. Anatomy implies their combination into two large structures.
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The first is called striopallidal. It includes the caudate nucleus, white ball and putamen. The second is extrapyramidal. In addition to the basal ganglia, it includes the medulla oblongata, cerebellum, substantia nigra, and elements of the vestibular apparatus.
Functionality of the basal ganglia
The purpose of this structure depends on the interaction with adjacent areas, in particular with the cortical sections and sections of the trunk. And together with the pons, cerebellum and spinal cord, the basal ganglia work to coordinate and improve basic movements.
Their main task is to ensure the vital functions of the body, perform basic functions, and integrate processes in the nervous system.
The main ones are:
- The onset of the sleep period.
- Metabolism in the body.
- Reaction of blood vessels to changes in pressure.
- Ensuring the activity of protective and orienting reflexes.
- Vocabulary and speech.
- Stereotypical, frequently repeated movements.
- Maintaining the posture.
- Muscle relaxation and tension, fine and gross motor skills.
- Showing emotions.
- Facial expressions.
- Eating behavior.
Symptoms of basal ganglia dysfunction
A person’s general well-being directly depends on the condition of the basal ganglia. Causes of dysfunction: infections, genetic diseases, injuries, metabolic failure, developmental abnormalities. Often the symptoms remain unnoticeable for some time, and patients do not pay attention to the malaise.
Characteristic features:
- Lethargy, apathy, poor general health and mood.
- Tremor in the limbs.
- Decreased or increased muscle tone, limitation of movements.
- Poor facial expressions, inability to express emotions with the face.
- Stuttering, changes in pronunciation.
- Tremor in the limbs.
- Blurred consciousness.
- Problems with remembering.
- Loss of coordination in space.
- The emergence of unusual postures for a person that were previously uncomfortable for him.
This symptomatology gives an understanding of the importance of the basal ganglia for the body. Not all of their functions and methods of interaction with other brain systems have been established to date. Some are still a mystery to scientists.
Pathological conditions of the basal ganglia
Pathologies of this body system are manifested by a number of diseases. The degree of damage also varies. Human life directly depends on this.
- Functional deficiency. Occurs at an early age. It is often a consequence of genetic abnormalities corresponding to heredity. In adults, it leads to Parkinson's disease or subcortical paralysis.
- Neoplasms and cysts. Localization is varied. Causes: malnutrition of neurons, improper metabolism, atrophy of brain tissue. Pathological processes occur in utero: for example, the occurrence of cerebral palsy is associated with damage to the basal ganglia in the second and third trimesters of pregnancy. Difficult childbirth, infections, and injuries in the first year of a child’s life can provoke the growth of cysts. Attention deficit hyperactivity disorder is a consequence of multiple neoplasms in infants. In adulthood, pathology also occurs. A dangerous consequence is cerebral hemorrhage, which often ends in general paralysis or death. But there are asymptomatic cysts. In this case, no treatment is required, they need to be observed.
- Cortical palsy– a definition that speaks about the consequences of changes in the activity of the globus pallidus and the striopallidal system. Characterized by stretching of the lips, involuntary twitching of the head, and twisting of the mouth. Convulsions and chaotic movements are noted.
Diagnosis of pathologies
The primary step in establishing the causes is an examination by a neurologist. His task is to analyze the medical history, assess the general condition and prescribe a series of examinations.
The most revealing diagnostic method is MRI. The procedure will accurately determine the location of the affected area.
Computed tomography, ultrasound, electroencephalography, study of the structure of blood vessels and blood supply to the brain will help in making an accurate diagnosis.
It is incorrect to talk about the prescription of a treatment regimen and prognosis before carrying out the above measures. Only after receiving the results and carefully studying them does the doctor give recommendations to the patient.
Consequences of basal ganglia pathologies
Basal ganglia.
Accumulation of gray matter in the thickness of the cerebral hemispheres.
Function:
1) correction of the program of a complex motor act;
2) formation of emotional and affective reactions;
3) assessment.
The basal ganglia have the structure of nuclear centers.
Synonyms:
Subcortical ganglia;
Basal ganglia;
Strio-pollidar system.
Anatomically to the basal ganglia relate:
Caudate nucleus;
Lenticular nucleus;
amygdala nucleus.
The head of the caudate nucleus and the anterior part of the putamen of the lentiform nucleus form the striatum.
The medially located part of the lentiform nucleus is called the globus pallidus. It represents an independent unit ( pallidum).
Connections of the basal nucleus.
Afferent:
1) from the thalamus;
2) from the hypothalamus;
3) from the tegmentum of the midbrain;
4) from the substantia nigra, afferent pathways end on the cells of the striatum.
5) from the striatum to the globus pallidus.
The globus pallidus receives an afferent signal:
1) directly from the bark;
2) from the cortex through the thalamus;
3) from the striatum;
4 from the central gray matter of the diencephalon;
5) from the roof and tegmentum of the midbrain;
6) from the substantia nigra.
Efferent fibers:
1) from the globus pallidus to the thalamus;
2) the caudate nucleus and putamen send signals to the thalamus through the globus pallidus;
3) hypothalamus;
4) substantia nigra;
5) red core;
6) to the nucleus of the inferior olive;
7) quadrigeminal.
There is no exact information about the connections between the fence and the amygdala nuclei.
Physiology of the basal ganglia.
The wide connections of the BN determine the complexity of the functional significance of the BN in various neurophysiological and psychophysiological processes.
The participation of BYA has been established:
1) in complex motor acts;
2) vegetative functions;
3) unconditioned reflexes (sexual, food, defensive);
4) sensory processes;
5) conditioned reflexes;
6) emotions.
The role of BN in complex motor acts is that they determine myotatic reflexes, optimal redistribution of muscle tone due to modulating influences on the underlying structures of the central nervous system involved in the regulation of movements.
Methods for studying BU:
1) irritation– electrical and chemo stimulation;
2) destruction;
3) electrophysiological method
4) dynamics analysis
5)
6) with implanted electrodes.
Destruction striatum → disinhibition of the globus pallidus and midbrain structures (substantia nigra, RF trunk), which is accompanied by a change in muscle tone and the appearance hyperkinesis.
When the globus pallidus is destroyed or its pathology is observed, muscle hypertonicity, rigidity, and hyperkinesis are observed. However, hyperkinesis is not associated with a loss of function of the BU alone, but with a concomitant dysfunction of the thalamus and midbrain, which regulate muscle tone.
Effects BYA.
At stimulation shown:
1) ease of perception of motor and bioelectrical manifestations of epileptiform reactions of the tonic type;
2) the inhibitory effect of the caudate nucleus and putamen on the globus pallidus;
3) stimulation of the caudate nucleus and putamen → disorientation, chaotic motor activity. Connected with the transfer function of BN impulses from the RF to the cortex.
Vegetative functions. Autonomic components of behavioral reactions.
Emotional reactions:
Facial reactions;
Increased physical activity;
The inhibitory effect of irritation of the caudate nucleus on intelligence.
Studies of the influence of the caudate nucleus on conditioned reflex activity and purposeful movements indicate both inhibition and the facilitating nature of these influences.
Forebrain, basal ganglia and cortex.
Physiology of the basal ganglia.
These are paired nuclei located between the frontal lobes and the diencephalon.
Structures:
1. striatum (tail and shell);
2. globus pallidus;
3. substantia nigra;
4. subthalamic nucleus.
BG connections. Afferent.
Most of the afferent fibers enter the striatum from:
1. all areas of the PD cortex;
2. from the nuclei of the thalamus;
3. from the cerebellum;
4. from the substantia nigra along dopaminergic pathways.
Efferent connections.
1. from the striatum to the globus pallidus;
2. to the substantia nigra;
3. from the internal part of the globus pallidus → thalamus (and to a lesser extent to the roof of the midbrain) → motor area of the cortex;
4. to the hypothalamus from the globus pallidus;
5. to the red nucleus and RF → rubrospinal tract, reticulospinal tract.
BG function.
1. Organization of motor programs. This role is determined by the connection with the cortex and other parts of the central nervous system.
2. Correction of individual motor reactions. This is due to the fact that the subcortical ganglia are part of the extrapyramidal system, which provides correction of motor activity due to connections between the BG and the motor nuclei. And the motor nuclei, in turn, are connected with the nuclei of the cranial nerve and the spinal cord.
3. Provide conditioned reflexes.
Methods for studying BU:
1) irritation– electrical and chemo stimulation;
2) destruction;
3) electrophysiological method(registration of EEG and evoked potentials);
4) dynamics analysis conditioned reflex activity against the background of stimulation or switching off of the BU;
5) analysis of clinical and neurological syndromes;
6) psychophysiological studies with implanted electrodes.
Irritation effects.
Striped body.
1. Motor reactions: slow (worm-like) movements of the head and limbs appear.
2. Behavioral reactions:
a) inhibition of orientation reflexes;
b) inhibition of volitional movements;
c) inhibition of the motor activity of emotions during food acquisition.
Pale ball.
1. Motor reactions:
contraction of facial, masticatory muscles, contraction of muscles of the limbs, changing the frequency of tremor (if any).
2. Behavioral reactions:
the motor components of food-procuring behavior are enhanced.
They are a modulator of the hypothalamus.
Effects of destruction of nuclei and connections between BG structures.
Between the substantia nigra and the striatum is Parkinson's syndrome - shaking palsy.
Symptoms:
1. hand trembling with a frequency of 4 - 7 Hz (tremor);
2. mask-like face – waxy rigidity;
3. absence or sharp decrease in gestures;
4. careful gait in small steps;
Neurological studies indicate akinesia, i.e. patients experience great difficulty before starting or completing movements. Parkinsonism is treated with the drug L-dopa, but it must be taken for life, since parkinsonism is associated with a violation of the release of the neurotransmitter dopamine by the substantia nigra.
Effects of nuclear damage.
Striped body.
1. Athetosis - continuous rhythmic movements of the limbs.
2. Chorea – strong, incorrect movements, involving almost all the muscles.
These conditions are associated with the loss of the inhibitory influence of the striatum on the globus pallidus.
3. Hypotonicity and hyperkinesis .
Pale ball. 1.Hypertonicity and hyperkinesis. (stiffness of movements, poor facial expressions, plastic tone).
At the base of the cerebral hemispheres (the lower wall of the lateral ventricles) are located the nuclei of gray matter - the basal ganglia. They make up approximately 3% of the volume of the hemispheres. All basal ganglia are functionally combined into two systems. The first group of nuclei is a striopallidal system (Fig. 41, 42, 43). These include: the caudate nucleus (nucleus caudatus), putamen (putamen) and globus pallidus (globus pallidus). The putamen and caudate nucleus have a layered structure, and therefore their common name is the striatum (corpus striatum). The globus pallidus has no layering and appears lighter than the striatum. The putamen and the globus pallidus are united into a lentiform nucleus (nucleus lentiformis). The shell forms the outer layer of the lenticular nucleus, and the globus pallidus forms its inner parts. The globus pallidus, in turn, consists of an outer
and internal segments.
Anatomically, the caudate nucleus is closely related to the lateral ventricle. Its anterior and medially expanded part, the head of the caudate nucleus, forms the lateral wall of the anterior horn of the ventricle, the body of the nucleus forms the lower wall of the central part of the ventricle, and the thin tail forms the upper wall of the lower horn. Following the shape of the lateral ventricle, the caudate nucleus encloses the lentiform nucleus in an arc (Fig. 42, 1; 43, 1/). The caudate and lenticular nuclei are separated from each other by a layer of white matter - part of the internal capsule (capsula interna). Another part of the internal capsule separates the lenticular nucleus from the underlying thalamus (Fig. 43,
4).
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(on the right - below the level of the bottom of the lateral ventricle; on the left - above the bottom of the lateral ventricle; the fourth ventricle of the brain is opened from above):
1 - head of the caudate nucleus; 2 - shell; 3 - cerebral insula cortex; 4 - globus pallidus; 5 - fence; 6
Thus, the structure of the bottom of the lateral ventricle (which is a striopallidal system) can be schematically imagined as follows: the wall of the ventricle itself is formed by a layered caudate nucleus, then below there is a layer of white matter -
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Rice. 42. Topography of the basal nuclei of the telencephalon and stem structures (type
front left):
1 - caudate nucleus; 2 - shell; 3 - tonsil; 4 - substantia nigra; 5 - frontal cortex; 6 - hypothalamus; 7 - thalamus 
Rice. 43. Topography of the basal nuclei of the telencephalon and stem structures (type
left back):
1 - caudate nucleus; 2 - shell; 3 - globus pallidus; 4 - internal capsule; 5 - subthalamic nucleus; 6
- substantia nigra; 7 - thalamus; 8 - subcortical nuclei of the cerebellum; 9 - cerebellum; 10 - spinal cord; eleven
the internal capsule, below it is a layered shell, even lower is the globus pallidus and again a layer of the internal capsule, lying on the nuclear structure of the diencephalon - the thalamus.
The striopallidal system receives afferent fibers from the nonspecific medial thalamic nuclei, the frontal parts of the cerebral cortex, the cerebellar cortex and the substantia nigra of the midbrain. The bulk of the efferent fibers of the striatum converge in radial bundles to the globus pallidus. Thus, the globus pallidus is the output structure of the striopallidal system. Efferent fibers of the globus pallidus go to the anterior nuclei of the thalamus, which are connected to the frontal and parietal cortex of the cerebral hemispheres. Some of the efferent fibers that do not switch in the nucleus of the globus pallidus go to the substantia nigra and the red nucleus of the midbrain. The striopallidum (Fig. 41; 42), together with its pathways, is part of the extrapyramidal system, which has a tonic effect on motor activity. This motor control system is called extrapyramidal because it switches on its way to the spinal cord, bypassing the pyramids of the medulla oblongata. The striopallidal system is the highest center of involuntary and automated movements, reduces muscle tone, and inhibits movements carried out by the motor cortex. Lateral to the striopallidal system of the basal ganglia there is a thin plate of gray matter - the claustrum. It is bounded on all sides by white matter fibers
- external capsule (capsula externa).
At the end of the lower horn of the lateral ventricle in the white matter of the temporal lobe of the cerebral hemispheres there is a dense group of nuclei - the amygdala (amigdalae) (Fig. 42, 3). And finally, within the transparent septum lies the nucleus of the septum (nucleus septipellucidi) (see Fig. 37, 21). In addition to the listed basal nuclei, the limbic system includes: the cingulate cortex of the limbic lobe of the cerebral hemispheres, the hippocampus, the mamillary nuclei of the hypothalamus, the anterior nuclei of the thalamus, and the structures of the olfactory brain.