Features of the basal nuclei. The role of the basal ganglia in providing motor functions

Basal ganglia (basal nuclei) - this is a striopallidar system, consisting of three pairs of large nuclei, immersed in the white matter of the telencephalon at the base of the cerebral hemispheres, and connecting the sensory and associative cortex zones with the motor cortex.

Structure

The phylogenetically ancient part of the basal ganglia is the pale ball, the later formation is the striatum, and the youngest part is the fence.

The pale ball consists of external and internal segments; striatum - from the caudate nucleus and the shell. The fence is located between the shell and the insular (insular) cortex. Functionally, the basal ganglia also include the subthalamic nuclei and the substantia nigra.

Functional connections of the basal ganglia

Excitatory afferent impulses enter mainly the striatum (in the caudate nucleus) mainly from three sources:

1) from all areas of the cortex directly and indirectly through the thalamus;

2) from nonspecific nuclei of the thalamus;

3) from black substance.

Among the efferent connections of the basal ganglia, three main outputs can be noted:

• from the striatum, inhibitory pathways go to the pale ball directly and with the participation of the subthalamic nucleus; from the pale ball begins the most important efferent path of the basal nuclei, going mainly to the motor ventral nuclei of the thalamus, from them the excitatory path goes to the motor cortex;
• part of the efferent fibers from the globus pallidus and the striatum go to the centers of the brain stem (the reticular formation, the red nucleus and further to the spinal cord), and also through the inferior olive to the cerebellum;
• from the striatum, inhibitory pathways go to the substantia nigra and, after switching, to the nuclei of the thalamus.

Therefore, the basal ganglia are intermediate. They connect the associative and, in part, the sensory cortex with the motor cortex. Therefore, in the structure of the basal nuclei, several parallel functional loops are distinguished, connecting them with the cerebral cortex.

Fig.1. Scheme of functional loops passing through the basal ganglia:

1 - skeletal motor loop; 2 - oculomotor loop; 3 - complex loop; DC, motor cortex; PMC, premotor cortex; SSC, somatosensory cortex; PFC, prefrontal association cortex; P8 - field of the eighth frontal cortex; P7 - field of the seventh parietal cortex; FAC, frontal association cortex; VLA, ventrolateral nucleus; MDN, mediodorsal nucleus; PVN, anterior ventral nucleus; BS - pale ball; CV is black matter.

The skeletal-motor loop connects the premotor, motor, and somatosensory areas of the cortex to the putamen. The impulse from it goes to the pale ball and the substantia nigra and then returns through the motor ventrolateral nucleus to the premotor cortex. It is believed that this loop serves to regulate such movement parameters as amplitude, strength, direction.

The oculomotor loop connects the areas of the cortex that control the direction of gaze to the caudate nucleus. From there, the impulse goes to the globus pallidus and the black substance, from which it is projected, respectively, to the associative mediodorsal and anterior relay ventral nuclei of the thalamus, and from them it returns to the frontal oculomotor field 8. This loop is involved in the regulation of spasmodic eye movements (sakkals).

The existence of complex loops is also assumed, along which impulses from the frontal associative zones of the cortex enter the caudate nucleus, the globus pallidus, and the substantia nigra. Then, through the mediodorsal and ventral anterior nuclei of the thalamus, it returns to the associative frontal cortex. It is believed that these loops are involved in the implementation of the higher psychophysiological functions of the brain: the control of motivations, prediction, and cognitive activity.

Functions

Functions of the striatum

Effect of the striatum on the globus pallidus. The influence is carried out mainly by the inhibitory mediator GABA. However, some of the globus pallidus neurons give mixed responses, and some only give EPSPs. That is, the striatum has a double effect on the pale ball: inhibitory and excitatory, with a predominance of inhibitory.

Influence of the striatum on the substantia nigra. There are bilateral connections between the substantia nigra and the striatum. The striatal neurons have an inhibitory effect on the neurons of the substantia nigra. In turn, substantia nigra neurons have a modulating effect on the background activity of striatal neurons. In addition to affecting the striatum, the substantia nigra has an inhibitory effect on the neurons of the thalamus.

Influence of the striatum on the thalamus. Irritation of the striatum causes the appearance of high-amplitude rhythms in the thalamus, characteristic of the non-REM sleep phase. The destruction of the striatum disrupts the sleep-wake cycle by reducing the duration of sleep.

Influence of the striatum on the motor cortex. The caudate nucleus of the striatum “brakes out” the degrees of freedom of movement that are unnecessary under given conditions, thus ensuring the formation of a clear motor-defensive reaction.

Stimulation of the striatum. Stimulation of the striatum in its various parts causes various reactions: turning the head and torso in the direction opposite to the irritation; delay in food production; suppression of pain.

The defeat of the striatum. The defeat of the caudate nucleus of the striatum leads to hyperkinesis (excessive movements) - chorea and athetosis.

Functions of the pale ball

From the striatum, the pale ball receives a predominantly inhibitory and partially excitatory influence. But it has a modulating effect on the motor cortex, cerebellum, red nucleus and reticular formation. The pale ball has an activating effect on the center of hunger and satiety. The destruction of the pale ball leads to weakness, drowsiness, emotional dullness.

The results of the activity of all basal ganglia:

• development together with the cerebellum of complex motor acts;
• control of motion parameters (strength, amplitude, speed and direction);
• regulation of the sleep-wake cycle;
• participation in the mechanism of formation of conditioned reflexes, complex forms of perception (for example, comprehension of the text);
• participation in the act of inhibition of aggressive reactions.

The basal ganglia include the following anatomical formations:

the striatum (striatum), consisting of the caudate nucleus and the shell; pale ball (pallidum), subdivided into internal and external sections; substantia nigra and subthalamic nucleus of Lewis.

BG functions:

1. Centers of complex unconditioned reflexes and instincts
2. Participation in the formation of conditioned reflexes
3. Coordination of muscle tone and voluntary movements. Control of amplitude, strength, direction of movements
4. Coordination of combined motor acts
5. Eye movement control (saccades).
6. Programming complex purposeful movements
7. Centers of inhibition of aggressive reactions
8. Higher mental functions (motivation, forecasting, cognitive activity). Complex forms of perception of external information (for example, text comprehension)
9. Involved in the mechanisms of sleep

Afferent connections of the basal ganglia.

Most of the afferent signals coming to the basal ganglia enter the striatum. These signals come almost exclusively from three sources:

- from all areas of the cerebral cortex;

- from the intralamellar nuclei of the thalamus;

- from the substantia nigra (along the dopaminergic pathway).

Efferent fibers from the striatum go to the globus pallidus and substantia nigra. From the latter, not only the dopaminergic pathway to the striatum begins, but also the pathways leading to the thalamus.

The most important of all the efferent tracts of the basal ganglia originates from the inner part of the globus pallidus, ending in the thalamus, as well as in the roof of the midbrain. Through the stem formations, with which the basal ganglia are connected, centrifugal impulses follow to the segmental motor apparatus and muscles along the descending conductors.

- from red nuclei - along the rubrospinal tract;

- from the nucleus of Darkshevich - along the posterior longitudinal bundle to the nuclei of 3, 4,6 nerves and through it to the nucleus of the vestibular nerve;

- from the nucleus of the vestibular nerve - along the vestibulospinal tract;

- from the quadrigemina - along the tectospinal tract;

- from the reticular formation - along the reticulospinal tract.

Thus, the basal ganglia play mainly the role of an intermediate link in the chain connecting the motor areas of the cortex with all other areas of it.

Symptoms of damage to the basal ganglia.

Damage to the basal ganglia is accompanied by a wide variety of movement disorders. Of all these disorders, Parkinson's syndrome is the most well-known.

Gait - cautious, with small steps, slow, reminiscent of an old man's gait. The initiation of the movement is broken: it is not possible to move forward immediately. But in the future, the patient cannot immediately stop: he still continues to be pulled forward.

facial expressions- extremely poor, her face takes on a frozen mask-like expression. A smile, a grimace of crying with emotions belatedly arise and just as slowly disappear.

normal pose- the back is bent, the head is tilted to the chest, the arms are bent at the elbows, at the wrists, the legs are at the knee joints (pose of the petitioner).

Speech- quiet, monotonous, deaf, without sufficient modulation and sonority.

akinesia- (hypokinesia) - great difficulties in the manifestation and motor initiation: difficulty in starting and completing the movement.

Muscle stiffness- a constant increase in muscle tone, independent of the position of the joints and movements. The patient, having taken a certain position, keeps it for a long time, even if it is not comfortable. "Freezes" in the accepted position - plastic or wax rigidity. With passive movements, the muscles relax not gradually, but intermittently, as if in steps.

Resting tremor- trembling, which is observed at rest, is expressed in the distal extremities, sometimes in the lower jaw and is characterized by low amplitude, frequency and rhythm. The tremor disappears during purposeful movements and resumes after their completion (different from cerebellar tremor, which appears during movement and disappears at rest).

Parkinson's syndrome is associated with the destruction of the path (brake), going from the substantia nigra to the striatum. In the region of the striatum, the neurotransmitter dopamine is released from the fibers of this pathway. The manifestation of parkinsonism and, in particular, akinesia are successfully treated with the introduction of the precursor of dopamine - dopa. On the contrary, destruction of the globus pallidus and thalamus (ventrolateral nucleus), which interrupts the path to the motor cortex, leads to the suppression of involuntary movements, but does not relieve akinesia.

With damage to the caudate nucleus, athetosis develops - in the distal parts of the limbs, slow, worm-like, wriggling movements are observed at certain intervals, during which the limb assumes unnatural positions. Athetosis may be limited or widespread.

When the shell is damaged, chorea develops - it differs from athetosis in the speed of twitching and is observed in the proximal limbs and on the face. A rapid change in the localization of convulsions is characteristic, then the facial muscles twitch, then the muscles of the leg, simultaneously the eye muscles and the arm, etc. In severe cases, the patient becomes like a clown. Often there is grimacing, smacking, speech is upset. Movements become sweeping, redundant, dancing gait.

The human body is made up of a large number of organs and structures, the main ones being the brain and the heart. The heart is the engine of life, and the brain is the coordinator of all processes. In addition to knowledge about the main parts of the brain, you need to know about the basal ganglia.

The basal ganglia are responsible for movement and coordination

The basal nuclei (ganglia) are accumulations of gray matter that form groups of nuclei. This part of the brain is responsible for movement and coordination.

Functions that the ganglia provide

Motor activity is manifested due to the constant control of the pyramidal (cortico-spiral) tract. But he does not provide it completely. Some of the functions are taken over by the basal ganglia. Parkinson's disease or Wilson's disease is caused precisely by pathological disorders of subcortical accumulations of gray matter. The functions of the basal ganglia are considered vital, and their disorders are difficult to treat.

According to scientists, the main task of the work of the nuclei is not motor activity itself, but its control over the functioning, as well as the connection of muscle groups and the nervous system. There is a function of control over human movements. Characterizes this interaction of two systems, which includes the accumulation of subcortical substance. The striopallidar and limbic systems have their own functional features. The first tends to control muscle contraction, which together forms coordination. The second is subject to the work and organization of vegetative functions. Their failure leads not only to discoordination of a person, but also to a violation of the mental activity of the brain.

Malfunctions in the functioning of the nuclei lead to impaired brain function

Structural features

The basal nuclei of the brain have a complex structure. According to the anatomical structure, they include:

• striatum (striate body);
• amygdaloidium (almond-shaped body);
• fence.

The modern study of these accumulations has created a new, convenient division of the nuclei into an accumulation of black substance and a nucleus cover. But such a figurative structure does not give a complete picture of the anatomical connections and neurotransmitters, so it is the anatomical structure that should be considered. Thus, the concept of the striatum is characterized by the accumulation of white and gray matter. They are visible in a horizontal section of the cerebral hemispheres.

Basal ganglia is a complex term that includes concepts about the structure and functions of the striatum and amygdala. In addition, the striatum consists of the lenticular and caudate ganglion. Their location and connection has its own characteristics. The basal ganglia of the brain are separated by a neuronal capsule. The caudate ganglion is associated with the thalamus.

The caudate ganglion is associated with the thalamus

Features of the structure of the caudate ganglion

The second type of Golgi neurons is identical to the structure of the caudate nucleus. Neurons play an important role in the formation of accumulations of gray matter. This is noticeable by the similar features that unite them. The thinness of the axon and the shortening of the dendrites are identical. This core provides its main functions with its own connections with individual sections and departments of the brain:

• thalamus;
• pale ball;
• cerebellum;
• black substance;
• vestibule nuclei.

The versatility of the nuclei makes them one of the most important parts of the brain. The basal ganglia and their connections provide not only coordination of movements, but also autonomic functions. We must not forget that the ganglia are also responsible for integrative and cognitive abilities.

The caudate nucleus, with its connections with individual parts of the brain, forms a single closed neural network. And a disruption in the work of any of its sections can cause serious problems with the neuro-motor activity of a person.

Neurons are essential to the gray matter of the brain

Features of the structure of the lenticular nucleus

The basal ganglia are interconnected by neuronal capsules. The lenticular nucleus is located outside the caudate and has an external connection with it. This ganglion has an angle shape with a capsule located in the middle. The inner surface of the nucleus is connected to the cerebral hemispheres, and the outer surface forms a connection with the head of the caudate ganglion.

White matter is a septum that separates the lenticular nucleus into two main systems that differ in color. Those that have a dark tint are the shell. And those that are lighter - refer to the structure of the pale ball. Modern scientists working in the field of neurosurgery consider the lentiform ganglion to be part of the striopallidar system. Its functions are associated with the autonomic action of thermoregulation, as well as metabolic processes. The role of the nucleus significantly exceeds the hypothalamus in these functions.

Fence and amygdala

A fence is a thin layer of gray matter. It has its own characteristics associated with the structure and relationships with the shell and the "island":

• the fence is surrounded by a white substance;
• the fence is connected to the body and the shell by internal and external neural connections;
• the shell borders the amygdala.

Scientists believe that the amygdala performs several functions. In addition to the main ones related to the limbic system, it is a component of the department responsible for the sense of smell.

The connection is confirmed by the nerve fibers that connect the olfactory lobe with the perforated substance. Therefore, the amygdala and its work are an integral part of the organization and control of mental work. The psychological state of a person also suffers.

The amygdala performs primarily an olfactory function.

What problems does ganglion dysfunction lead to?

The resulting pathological failures and disorders in the basal ganglia quickly lead to a deterioration in the human condition. Not only his well-being suffers, but also the quality of mental activity. A person with disruptions in the work of this part of the brain can become disoriented, suffer from depression, etc. This is due to two types of pathologies - neoplasms and functional insufficiency.

Any neoplasms in the subcortical part of the nuclei are dangerous. Their appearance and development leads to disability and even death. Therefore, at the slightest symptoms of pathology, you should consult a doctor for the purpose of diagnosis and treatment. The fault of the formation of cysts or other neoplasms are:

• degeneration of nerve cells;
• attack by infectious agents;
• trauma;
• hemorrhage.

Functional insufficiency is diagnosed less frequently. This is due to the nature of the occurrence of such a pathology. It manifests itself more often in infants during the period of maturation of the nervous system. In adults, failure is characterized by previous strokes or trauma.

Studies show that functional failure of the nuclei in more than 50% of cases is the main cause of the onset of signs of Parkinson's disease in old age. Treatment of such a disease depends on the severity of the pathology itself and the timeliness of contacting specialists.

Features of diagnosis and treatment

At the slightest sign of a violation of the activity of the basal ganglia, you should contact a neurologist. The reason for this may be the following symptoms:

• violation of motor activity of muscles;
• tremor;
• frequent muscle spasms;
• uncontrolled limb movements;
• memory problems.

Diagnosis of diseases is carried out on the basis of a general examination. If necessary, the patient may be referred for a brain scan. This type of study can show dysfunctional zones not only in the basal ganglia, but also in other parts of the brain.

Treatment of dysfunctions of the basal ganglia is ineffective. Most often, therapy reduces symptoms. But in order for the result to be permanent, it should be treated for life. Any breaks can adversely affect the patient's well-being.

Basal ganglia, or subcortical nuclei, are closely interconnected brain structures located in the depths of the cerebral hemispheres between the frontal lobes and.

The basal ganglia are paired formations and consist of nuclei of gray matter separated by layers of white - fibers of the inner and outer capsules of the brain. IN composition of the basal ganglia includes: striatum, consisting of a tail nucleus and a shell, a pale ball and a fence. From a functional point of view, sometimes the concept of the basal ganglia also includes the subthalamic nucleus and the substantia nigra (Fig. 1). The large size of these nuclei and the similarity in structure in different species suggest that they make a great contribution to the organization of the brain of terrestrial vertebrates.

The main functions of the basal ganglia:

• Participation in the formation and storage of programs of congenital and acquired motor reactions and coordination of these reactions (main)
• Regulation of muscle tone
• Regulation of vegetative functions (trophic processes, carbohydrate metabolism, salivation and lacrimation, respiration, etc.)
• Regulation of the body's sensitivity to the perception of stimuli (somatic, auditory, visual, etc.)
• GNI regulation (emotional reactions, memory, speed of development of new conditioned reflexes, speed of switching from one form of activity to another)

Rice. 1. The most important afferent and efferent connections of the basal ganglia: 1 paraventricular nucleus; 2 ventrolateral nucleus; 3 median nuclei of the thalamus; SN - subthalamic nucleus; 4 - corticospinal tract; 5 - cortico-bridge tract; 6 - efferent path from the pale ball to the midbrain

It has long been known from clinical observations that one of the consequences of diseases of the basal ganglia is impaired muscle tone and movement. On this basis, one could assume that the basal ganglia must be connected with the motor centers of the brain stem and spinal cord. Modern research methods have shown that the axons of their neurons do not follow in a downward direction to the motor nuclei of the trunk and spinal cord, and damage to the ganglia is not accompanied by muscle paresis, as is the case with damage to other descending motor pathways. Most of the efferent fibers of the basal ganglia follow in an ascending direction to the motor and other areas of the cerebral cortex.

Afferent connections

The structure of the basal ganglia, to the neurons of which most of the afferent signals are received, is striatum. Its neurons receive signals from the cerebral cortex, thalamic nuclei, cell groups of the substantia nigra of the diencephalon containing dopamine, and from raphe nucleus neurons containing serotonin. At the same time, the striatal shell neurons receive signals mainly from the primary somatosensory and primary motor cortex, and the caudate nucleus neurons (already pre-integrated polysensory signals) from the neurons of the associative areas of the cerebral cortex. An analysis of the afferent connections of the basal nuclei with other brain structures suggests that from them the ganglia receive not only information related to movements, but also information that can reflect the state of general brain activity and be associated with its higher, cognitive functions and emotions.

The received signals are subjected to complex processing in the basal ganglia, in which its various structures are involved, interconnected by numerous internal connections and containing various types of neurons. Among these neurons, the majority are GABAergic striatal neurons, which send axons to neurons in the globus pallidus and substantia nigra. These neurons also produce dynorphin and enkephalin. A large share in the transmission and processing of signals within the basal ganglia is occupied by its excitatory cholinergic interneurons with widely branching dendrites. The axons of the substantia nigra neurons, which secrete dopamine, converge to these neurons.

Efferent connections in the basal ganglia are used to send signals processed in the ganglia to other brain structures. The neurons that form the main efferent pathways of the basal ganglia are located mainly in the outer and inner segments of the globus pallidus and in the substantia nigra, receiving afferent signals mainly from the striatum. Part of the efferent fibers of the globus pallidus follows the intralaminar nuclei of the thalamus and from there to the striatum, forming a subcortical neural network. Most of the axons of the efferent neurons of the internal segment of the globus pallidum follow through the internal capsule to the neurons of the ventral nuclei of the thalamus, and from them to the prefrontal and additional motor cortex of the cerebral hemispheres. Through connections with motor areas of the cerebral cortex, the basal ganglia influence the control of movements carried out by the cortex through the corticospinal and other descending motor pathways.

The caudate nucleus receives afferent signals from the associative areas of the cerebral cortex and, having processed them, sends efferent signals mainly to the prefrontal cortex. It is assumed that these connections are the basis for the participation of the basal ganglia in solving problems related to the preparation and execution of movements. So, if the caudate nucleus is damaged in monkeys, the ability to perform movements that require information from the spatial memory apparatus (for example, accounting for where an object is located) is impaired.

The basal ganglia are connected by efferent connections with the reticular formation of the diencephalon, through which they participate in the control of walking, as well as with neurons of the superior colliculi, through which they can control eye and head movements.

Taking into account the afferent and efferent connections of the basal ganglia with the cortex and other brain structures, several neural networks or loops are distinguished that pass through the ganglia or end inside them. motor loop It is formed by neurons of the primary motor, primary sensorimotor and supplementary motor cortex, whose axons follow the neurons of the putamen and then through the globus pallidus and thalamus reach the neurons of the supplementary motor cortex. Oculomotor loop formed by neurons of motor fields 8, 6 and sensory field 7, the axons of which follow to the caudate nucleus and further to the neurons of the frontal eye field 8. Prefrontal loops formed by neurons of the prefrontal cortex, the axons of which follow the neurons of the caudate nucleus, black body, pale ball and ventral nuclei of the thalamus and then reach the neurons of the prefrontal cortex. Kamchataya loop formed by neurons of the circular gyrus, orbitofrontal cortex, some areas of the temporal cortex, closely related to the structures of the limbic system. The axons of these neurons follow the neurons of the ventral striatum, globus pallidus, mediodorsal thalamus, and further to the neurons of those areas of the cortex in which the loop began. As can be seen, each loop is formed by multiple corticostriate connections, which, after passing through the basal ganglia, follow through a limited area of ​​the thalamus to a specific single area of ​​the cortex.

The areas of the cortex that send signals to one or another loop are functionally connected with each other.

Functions of the basal ganglia

The neural loops of the basal ganglia are the morphological basis of their main functions. Among them is the participation of the basal ganglia in the preparation and implementation of movements. Features of the participation of the basal ganglia in the performance of this function follow from observations of the nature of movement disorders in diseases of the ganglia. It is assumed that the basal ganglia play an important role in the planning, programming and execution of complex movements initiated by the cerebral cortex.

With their participation, the abstract idea of ​​movement turns into a motor program of complex voluntary actions. Their example can be such actions as the simultaneous implementation of several movements in separate joints. Indeed, when recording the bioelectrical activity of the neurons of the basal ganglia during the execution of voluntary movements, there is an increase in the neurons of the subthalamic nuclei, the fence, the inner segment of the pale ball and the reticular part of the black body.

An increase in the activity of neurons in the basal ganglia is initiated by an influx of excitatory signals to striatal neurons from the cerebral cortex, mediated by the release of glutamate. These same neurons receive a stream of signals from the substantia nigra, which has an inhibitory effect on striatal neurons (through the release of GABA) and helps to focus the influence of cortical neurons on certain groups of striatal neurons. At the same time, its neurons receive afferent signals from the thalamus with information about the state of activity of other areas of the brain related to the organization of movements.

The striatal neurons integrate all these flows of information and transmit it to the neurons of the globus pallidum and the reticular part of the substantia nigra, and further, but by efferent pathways, these signals are transmitted through the thalamus to the motor areas of the cerebral cortex, in which the preparation and initiation of the upcoming movement is carried out. It is assumed that the basal ganglia, even at the stage of movement preparation, select the type of movement necessary to achieve the goal, the selection of muscle groups necessary for its effective implementation. Probably, the basal ganglia are involved in the processes of motor learning by repeating movements, and their role is to choose the optimal ways to implement complex movements to achieve the desired result. With the participation of the basal ganglia, the elimination of redundancy of movements is achieved.

Another of the motor functions of the basal ganglia is participation in the implementation of automatic movements or motor skills. When the basal ganglia are damaged, the person performs them at a slower pace, less automated, with less precision. Bilateral destruction or damage of the fence and the pale ball in a person is accompanied by the occurrence of obsessive-compulsory motor behavior and the appearance of elementary stereotyped movements. Bilateral damage or removal of the globus pallidus leads to a decrease in motor activity and hypokinesia, while unilateral damage to this nucleus either does not affect or has little effect on motor functions.

Damage to the basal ganglia

Pathology in the region of the basal ganglia in humans is accompanied by the appearance of involuntary and impaired voluntary movements, as well as a violation of the distribution of muscle tone and posture. Involuntary movements usually appear during quiet wakefulness and disappear during sleep. There are two large groups of movement disorders: with dominance hypokinesia- bradykinesia, akinesia and rigidity, which are most pronounced in parkinsonism; with the dominance of hyperkinesia, which is most characteristic of Huntington's chorea.

Hyperkinetic motor disorders may appear rest tremor- involuntary rhythmic contractions of the muscles of the distal and proximal parts of the limbs, head and other parts of the body. In other cases, they may appear chorea- sudden, fast, violent movements of the muscles of the trunk, limbs, face (grimaces), appearing as a result of degeneration of the neurons of the caudate nucleus, bluish spot and other structures. In the caudate nucleus, a decrease in the level of neurotransmitters - GABA, acetylcholine and neuromodulators - enkephalin, substance P, dynorphin and cholecystokinin was found. One of the manifestations of chorea is athetosis- slow, prolonged writhing movements of the distal parts of the limbs, due to a violation of the function of the fence.

As a result of unilateral (with hemorrhage) or bilateral damage to the subthalamic nuclei, ballism, manifested by sudden, violent, large amplitude and intensity, thrashing, rapid movements on the opposite (hemiballism) or both sides of the body. Diseases in the striatal region can lead to the development dystonia, which is manifested by violent, slow, repetitive, twisting movements of the muscles of the arm, neck, or torso. An example of local dystonia is an involuntary contraction of the muscles of the forearm and hand during writing - writing spasm. Diseases in the basal ganglia can lead to the development of tics, characterized by sudden, short-term violent movements of the muscles of various parts of the body.

Violation of muscle tone in diseases of the basal ganglia is manifested by muscle rigidity. If it is present, an attempt to change the position in the joints is accompanied by a movement in the patient, reminiscent of that of a gear wheel. The resistance exerted by the muscles occurs at certain intervals. In other cases, waxy rigidity may develop, in which resistance is maintained throughout the entire range of motion in the joint.

Hypokinetic motor disorders are manifested by a delay or inability to start a movement (akinesia), slowness in the execution of movements and their completion (bradykinesia).

Disturbances in motor functions in diseases of the basal ganglia can be of a mixed nature, resembling muscle paresis or, conversely, their spasticity. At the same time, movement disorders can develop from the inability to start movement to the inability to suppress involuntary movements.

Along with severe, disabling movement disorders, another diagnostic feature of parkinsonism is an expressionless face, often referred to as parkinsonian mask. One of its signs is the insufficiency or impossibility of spontaneous gaze shift. The patient's gaze may remain fixed, but he may move it on command in the direction of the visual object. These facts suggest that the basal ganglia are involved in the control of gaze shift and visual attention using a complex oculomotor neural network.

One of the possible mechanisms for the development of motor and, in particular, oculomotor disorders in case of damage to the basal ganglia may be a violation of signal transmission in neural networks due to an imbalance in the neuromedium. In healthy people, the activity of striatal neurons is under a balanced influence of afferent inhibitory (dopamine, GAM K) signals from the substantia nigra and excitatory (glutamate) signals from the sensorimotor cortex. One of the mechanisms for maintaining this balance is its regulation by signals from the globus pallidus. Disbalance in the direction of the predominance of inhibitory influences limits the possibility of reaching sensory information in the motor areas of the cerebral cortex and leads to a decrease in motor activity (hypokinesia), which is observed in parkinsonism. Loss of inhibitory dopamine neurons by the basal ganglia (during diseases or with age) can lead to an easier flow of sensory information into the motor system and an increase in its activity, as is observed in Huntington's chorea.

One of the evidence that the neurotransmitter balance is important in the implementation of the motor functions of the basal ganglia, and its violation is accompanied by motor failure, is the clinically confirmed fact that improvement in motor functions in parkinsonism is achieved by taking L-dopa, a precursor of dopamine synthesis, which penetrates into brain through the blood-brain barrier. In the brain, under the influence of the enzyme dopamine carboxylase, it is converted into dopamine, which contributes to the elimination of dopamine deficiency. The treatment of parkinsonism with L-dopa is currently the most effective method, the use of which has made it possible not only to alleviate the condition of patients, but also to increase their life expectancy.

Methods of surgical correction of motor and other disorders in patients by means of stereotaxic destruction of the globus pallidus or the ventrolateral nucleus of the thalamus have been developed and applied. After this operation, it is possible to eliminate the rigidity and tremor of the muscles on the opposite side, but akinesia and postural disturbance are not eliminated. Currently, the operation of implanting permanent electrodes into the thalamus is also used, through which its chronic electrical stimulation is carried out.

Transplantation of dopamine-producing cells into the brain and transplantation of brain cells of one of their adrenal glands into the region of the ventricular surface of the brain of patients with one of their adrenal glands were carried out, after which, in some cases, an improvement in the condition of patients was achieved. It is assumed that the transplanted cells could become for some time a source of dopamine production or growth factors that contributed to the restoration of the function of the affected neurons. In other cases, embryonic basal ganglia tissue has been implanted into the brain, with better results. Transplantation treatments have not yet become widespread and their effectiveness continues to be studied.

The functions of other neural networks in the basal ganglia remain poorly understood. Based on clinical observations and experimental data, it is assumed that the basal ganglia are involved in changing the state of muscle activity and posture during the transition from sleep to wakefulness.

The basal ganglia are involved in shaping the mood, motivations and emotions of a person, especially those associated with the execution of movements aimed at satisfying vital needs (eating, drinking) or obtaining moral and emotional pleasure (reward).

Most patients with dysfunction of the basal ganglia show symptoms of psychomotor changes. In particular, with parkinsonism, a state of depression (depressed mood, pessimism, increased vulnerability, sadness), anxiety, apathy, psychosis, and a decrease in cognitive and mental abilities can develop. This indicates the important role of the basal ganglia in the implementation of higher mental functions in humans.

Basal ganglia, like the cerebellum, represent another auxiliary motor system that usually functions not on its own, but in close connection with the cerebral cortex and the corticospinal motor control system. Indeed, most of the input signals to the basal ganglia come from the cerebral cortex, and almost all of the output from these ganglia returns back to the cortex.

The figure shows the anatomical connections basal ganglia with other brain structures. On each side of the brain, these ganglia are composed of the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus. They are located mainly lateral to and around the thalamus, occupying most of the inner regions of both cerebral hemispheres. It is also seen that almost all the motor and sensory nerve fibers connecting the cerebral cortex and the spinal cord pass through the space lying between the main structures of the basal ganglia, the caudate nucleus and the putamen. This space is called the internal capsule of the brain. Important to this discussion is the close relationship between the basal ganglia and the corticospinal motor control system.

Nerve circuit of the basal ganglia. The anatomical connections between the basal ganglia and other elements of the brain that provide motor control are complex. On the left, the motor cortex, thalamus, and the associated brainstem and cerebellar circuit are shown. On the right is the main outline of the basal ganglia system, showing the most important interconnections within the ganglia themselves and the extensive pathways in and out that connect other regions of the brain and the basal ganglia.
In the following sections, we will focus on two main contours: the shell contour and the caudate nucleus contour.

Physiology and function of the basal ganglia

One of the main functions of the basal ganglia in motor control is their participation in the regulation of the implementation of complex motor programs together with the corticospinal system, for example, in movement when writing letters. With severe damage to the basal ganglia, the cortical motor control system can no longer provide these movements. Instead, the person's handwriting becomes rough, as if they are learning to write for the first time.

To others complex motor acts that require basal ganglia involvement include cutting with scissors, driving nails with a hammer, throwing a basketball through a hoop, dribbling a football, throwing a ball in a baseball, digging with a shovel, most vocalization processes, controlled eye movements, and almost any of our precise movements. , in most cases performed unconsciously.

Nerve pathways of the shell contour. The figure shows the main pathways through the basal ganglia involved in the performance of acquired forms of motor activity. These pathways mainly originate in the premotor cortex and in the somatosensory areas of the sensory cortex. Then they pass into the putamen (mainly bypassing the caudate nucleus), from here to the inside of the pale ball, then to the anterior ventral and ventrolateral nuclei of the thalamus and, finally, return to the primary motor cortex of the cerebrum and to the areas of the premotor cortex and accessory cortex, closely related to the primary motor cortex. Thus, the main inputs to the shell circuit come from the areas of the brain adjacent to the primary motor cortex, but not from the primary cortex itself.

But exits from this circuit go mainly to the primary motor cortex or to areas of the premotor and supplementary motor cortex closely related to it. In close connection with this primary shell circuit, auxiliary circuits function, extending from the shell through the outer part of the pale ball, subthalamus and substantia nigra, finally returning to the motor cortex through the thalamus.

Movement disorders with damage to the contour of the shell: athetosis, hemiballismus and chorea. How is the shell contour involved in ensuring the implementation of complex motor acts? The answer is not clear. However, when part of the circuit is affected or blocked, some movements are significantly impaired. For example, lesions of the globus pallidus usually lead to spontaneous and often continuous undulating movements of the hand, arm, neck, or face. Such movements are called athetosis.

Subthalamic nucleus lesion often leads to the appearance of sweeping movements of the entire limb. This condition is called hemiballismus. Multiple small lesions in the shell lead to rapid twitches in the hands, face, and other parts of the body, which is called chorea.

Black matter lesions lead to a widespread and extremely severe disease with characteristic rigidity, akinesia and tremor. This disease is known as Parkinson's disease and will be discussed in detail below.

Educational video lesson - basal ganglia, pathways of the inner capsule of the brain

You can download this video and view it from another video hosting on the page: