What are the basal ganglia of the brain and what are they responsible for? Features of the basal ganglia
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).
- a complex and unique structure, all elements of which are connected by many neural connections. It consists of gray matter, a collection of nerve cell bodies, and white matter, which is responsible for transmitting impulses from one neuron to another. In addition to the cerebral cortex, which is represented by gray matter and is the center of our conscious thinking, there are many other subcortical structures. They are separate ganglia (nuclei) of gray matter in the thickness of white matter and ensure the normal functioning of the human nervous system. One of them is the basal ganglia, the anatomical structure and physiological role of which we will consider in this article.
Structure of the basal ganglia
In anatomy, the basal ganglia (nuclei) are usually called complexes of gray matter in the central white matter of the cerebral hemispheres. These neurological structures include:
- caudate nucleus;
- shell;
- substantia nigra;
- red kernels;
- pale globe;
- reticular formation.
The basal ganglia are located at the base of the hemispheres and have many thin long processes (axons), through which information is transmitted to other brain structures.
The cellular structure of these formations is different, and it is customary to divide them into stiatum (belongs to the extrapyramidal system) and pallidum (belongs to). Both stiatum and pallidum have numerous connections with the cerebral cortex, in particular the frontal and parietal lobes, as well as the thalamus. These subcortical structures create a powerful branched network of the extrapyramidal system, which controls many aspects of human life.
Functions of the basal ganglia
The basal ganglia have close connections with other brain structures and perform the following functions:
- regulate motor processes;
- responsible for the normal functioning of the autonomic nervous system;
- carry out the integration of processes of higher nervous activity.
The basal ganglia have been noted to be involved in activities such as:
- Complex motor programs involving fine motor skills, for example, hand movement when writing, drawing (if this anatomical structure is damaged, handwriting becomes rough, “uncertain”, difficult to read, as if a person had picked up a pen for the first time).
- Using scissors.
- Hammering nails.
- Playing basketball, football, volleyball (dribbling the ball, hitting the basket, hitting the ball with a baseball bat).
- Digging the ground with a shovel.
- Singing.
According to recent data, the basal ganglia are responsible for a certain type of movement:
- spontaneous rather than controlled;
- those that have been repeated many times before (memorized), and not new ones that require control;
- sequential or simultaneous rather than simple one-step.
Important! According to many neurologists, the basal ganglia are our subcortical autopilot, allowing us to perform automated actions without using up the reserves of the central nervous system. Thus, this part of the brain controls the execution of movements depending on the situation.
In normal life, they receive nerve impulses from the frontal lobe and are responsible for performing repetitive, goal-directed actions. In case of force majeure that changes the usual course of events, the basal ganglia are able to rebuild and switch to the optimal algorithm for the given situation.
Symptoms of basal ganglia dysfunction
The causes of damage to the basal ganglia are varied. It can be:
- degenerative brain lesions (Huntington's chorea);
- hereditary metabolic diseases (Wilson's disease);
- genetic pathology associated with disruption of enzyme systems;
- some endocrine diseases;
- chorea in rheumatism;
- poisoning with manganese, chlorpromazine;
There are two forms of pathology of the basal ganglia:
- Functional impairment. It occurs more often in childhood and is caused by genetic diseases. In adults, it is triggered by stroke or trauma. Insufficiency of the extrapyramidal system is the main cause of the development of Parkinson's disease in old age.
- Cysts, tumors. This pathology is characterized by serious neurological problems and requires timely treatment.
- With lesions of the basal ganglia, behavioral flexibility is impaired: a person has difficulty adapting to the difficulties that arise when performing the usual algorithm. It is difficult for him to adapt to performing more logical actions under these conditions.
In addition, the ability to learn is reduced, which occurs slowly, and the results remain minimal for a long time. Patients also often experience movement disorders: all movements become intermittent, as if twitching, tremors (trembling of the limbs) or involuntary actions (hyperkinesis) occur.
Diagnosis of damage to the basal ganglia is carried out on the basis of the clinical manifestations of the disease, as well as modern instrumental methods (CT, MRI of the brain).
Correction of neurological deficit
Therapy for the disease depends on the cause that caused it and is carried out by a neurologist. Generally, lifelong use is required. The ganglion does not recover on its own; treatment with folk remedies is also often ineffective.
Thus, for the proper functioning of the human nervous system, clear and coordinated work of all its components, even the most insignificant ones, is necessary. In this article, we looked at what the basal ganglia are, their structure, location and functions, as well as the causes and signs of damage to this anatomical structure of the brain. Timely detection of pathology will allow you to correct the neurological manifestations of the disease and completely eliminate unwanted symptoms.
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Basal ganglia: structure, location and functions
The basal ganglia are a complex of subcortical neural ganglia located in the central white matter of the cerebral hemispheres. The basal ganglia provide regulation of motor and autonomic functions and participate in the implementation of integrative processes of higher nervous activity. The basal ganglia, like the cerebellum, represent another auxiliary motor system that usually does not function on its own, but in close connection with the cerebral cortex and the corticospinal motor control system. On each side of the brain, these ganglia consist of the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus. The anatomical connections between the basal ganglia and other brain elements that support motor control are complex. One of the main functions of the basal ganglia in motor control is its participation in regulating the execution of complex motor programs together with the corticospinal system, for example in the movement of writing letters. Other complex motor activities that require the basal ganglia include cutting with scissors, hammering nails, throwing a basketball through a hoop, dribbling a soccer ball, throwing a baseball, shoveling while digging, most vocalizations, controlled eye movements, and physical activity. any of our precise movements, most of the time performed unconsciously. The basal ganglia are part of the forebrain, located on the border between the frontal lobes and above the brain stem. The basal ganglia include the following components:
- globus pallidus - the most ancient formation of the striopallidal system
- neostriatum - it includes the striatum and putamen
— the fence is the newest formation.
Connections of the basal ganglia: 1. inside, between the basal ganglia. Due to them, the components of the basal ganglia closely interact and form a single striopallidal system 2. connection with the formations of the midbrain. They are bilateral in nature due to dopaminergic neurons. Due to these connections, the striopallidal system inhibits the activity of the red nuclei and substantia nigra, which regulate muscle tone 3. connection with the formations of the diencephalon, the thalamus and hypothalamus 4. with the limbic system 5. with the cerebral cortex.
Functions of the globus pallidus: - regulates muscle tone, participates in the regulation of motor activity - participates in emotional reactions due to its influence on facial muscles - participates in the integrative activity of internal organs, promotes the unification of the function of internal organs and the muscular system.
When the globus pallidus is irritated, there is a sharp decrease in muscle tone, slowing of movements, impaired coordination of movements, and the activity of the internal organs of the cardiovascular and digestive systems.
Functions of the striatum:
The striatum consists of larger neurons with long processes that extend beyond the striopallidal system. The striatum regulates muscle tone, reducing it; participates in the regulation of the work of internal organs; in the implementation of various behavioral reactions food-procuring behavior; participates in the formation of conditioned reflexes.
Functions of the fence: - participates in the regulation of muscle tone - participates in emotional reactions - participates in the formation of conditioned reflexes.
Date added: 2015-12-15 | Views: 953 | Copyright infringement
Basal gangliaAt 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. And also in the section “Basal ganglia” |
Chapter VIl. SUBCORTICAL GANGLIA, INTERNAL CAPSULE, SYMPTOMOCOMPLEXES OF THE LESION
VISUAL BURGERS
A continuation of the brain stem anteriorly are the visual tubercles located on the sides. III ventricle (see Fig. 2 and 55, III).
Optic thalamus(thalamus opticus - Fig. 55, 777) is a powerful accumulation of gray matter, in which a number of nuclear formations can be distinguished.
There is a division of the visual thalamus into the thalamus itself, hupothalamus, metathalamus and epithalamus.
Thalamus - the bulk of the visual thalamus - consists of the anterior, external, internal, ventral and posterior nuclei.
Hypothalamus has a number of nuclei located in the walls of the third ventricle and its funnel (infundibulum). The latter is very closely related to the pituitary gland both anatomically and functionally. This also includes the mamillary bodies (corpora mamillaria).
Metathalamus includes the external and internal geniculate bodies (corpora geniculata laterale et mediale).
Epithalamus includes the epiphysis, or pineal gland (glandula pinealis), and the posterior commissure (comissura posterior).
The visual thalamus is an important stage in the path of sensitivity. The following sensitive conductors approach it (from the opposite side).
Medial loop with its bulbo-thalamic fibers (touch, joint-muscular sense, vibration sense, etc.) and the spinothalamic pathway (pain and temperature sense).
2. Lemniscus trigemini - from the sensitive nucleus of the trigeminal nerve (sensitivity of the face) and fibers from the nuclei of the glossopharyngeal and vagus nerves (sensitivity of the pharynx, larynx, etc., as well as internal organs).
3. visual tracts, ending in the pulvinar of the visual thalamus and in the corpus geniculatum laterale (visual pathways).
4. Lateral loop ending in the corpus geniculatum mediale (auditory tract).
The olfactory pathways and fibers from the cerebellum (from the red nuclei) also end in the visual thalamus.
Thus, impulses of exteroceptive sensitivity flow to the visual thalamus, perceiving irritations from the outside (pain, temperature, touch, light, etc.), proprioceptive (articular-muscular feeling, sense of position and movement) and interoceptive (from internal organs).
Such a concentration of all types of sensitivity in the visual thalamus will become understandable if we take into account that at certain stages of the evolution of the nervous system, the visual thalamus was the main and final sensitive center, determining the general motor reactions of the body of a reflex order by transmitting irritation to the centrifugal motor apparatus.
With the advent and development of the cerebral cortex, the sensitive function becomes more complex and improved; the ability to finely analyze, differentiate and localize irritation appears. The main role in sensitive function passes to the cerebral cortex. However, the course of the sensory pathways remains the same; there is only a continuation of them from the visual thalamus to the cortex. The visual thalamus becomes basically just a transmission station on the path of impulses from the periphery to the cortex. Indeed, there are numerous thalamo-cortical pathways (tractus thalamo-corticales), those (mainly third) sensory neurons that have already been discussed in the chapter on sensitivity and which need only be briefly mentioned:
1) third neurons of cutaneous and deep sensitivity(pain, temperature, tactile, joint-muscular sense, etc.), starting from the ventrolateral part of the visual thalamus, passing through the internal capsule to the region of the posterior central gyrus and the parietal lobe (Fig. 55, VII);
2) visual pathways from primary visual centers (corpus geniculatum laterale - radiatio optica) or the Graciole bundle, in the fissurae calcarinae area of the occipital lobe (Fig.
55, VIII),
3) auditory pathways from the primary auditory centers (corpus geniculatum mediale) to the superior temporal gyrus and Heschl’s gyrus (Fig. 55, IX).
Rice. 55. Subcortical ganglia and internal capsule.
I - nucleus caudatus; II- nucleus lenticularis; III- thalamus opticus; IV - tractus cortico-bulbaris; V- tractus cortico-spinalis; VI- tractus oc-cipito-temporo-pontinus; VII - tractus ttialamo-corticalis: VIII - radiatio optica; IX- auditory pathways to the cortex; X- tractus fronto-pontinus.
In addition to the connections already mentioned, the visual thalamus has pathways connecting it with the strio-pallidal system. In the same way that the thalamus opticus is the highest sensitive center at certain stages of the development of the nervous system, the strio-pallidal system was the final motor apparatus, carrying out rather complex reflex activity.
Therefore, the connections between the visual thalamus and the named system are very intimate, and the entire apparatus as a whole can be called thalamo-strio-pallidal system with a perceptive link in the form of the thalamus opticus and a motor link in the form of the strio-pallidal apparatus (Fig. 56).
The connections between the thalamus and the cerebral cortex - in the direction of the thalamus - cortex have already been said. In addition, there is a powerful system of conductors in the opposite direction, from the cerebral cortex to the visual thalamus. These pathways originate from various parts of the cortex (tractus cortico-thalamici); the most massive of them is the one that begins from the frontal lobe.
Finally, it is worth mentioning the connections of the visual thalamus with the subthalamic region (hypothalamus), where the subcortical centers of autonomic-visceral innervation are concentrated.
The connections between the nuclear formations of the thalamic region are very numerous, complex, and have not yet been sufficiently studied in detail. Recently, mainly on the basis of electrophysiological studies, it has been proposed to divide the thalamo-cortical systems into specific(associated with certain projection areas of the cortex) and nonspecific, or diffuse. The latter begin from the medial group of nuclei of the visual thalamus (median center, intralaminar, reticular and other nuclei).
Some researchers (Penfield, Jasper) attribute to these “nonspecific nuclei” of the thalamus opticus, as well as the reticular formation of the brainstem, the function of the “substrate of consciousness” and the “highest level of integration” of nervous activity. In the concept of the “centroencephalic system,” the cortex is considered only as an intermediate stage on the path of sensory impulses flowing from the periphery to the “highest level of integration” in the interstitial and midbrain. Supporters of this hypothesis thus come into conflict with the history of the development of the nervous system, with numerous and obvious facts establishing that the most subtle analysis and complex synthesis (“integration”) of nervous activity are carried out by the cerebral cortex, which, of course, does not function in isolation , and in inextricable connection with the underlying subcortical, stem and segmental formations.
Rice. 56. Diagram of connections of the extrapyramidal system. Its centrifugal conductors.
N. s. nucleus caudatus; N. L. - nucleus lenticularis; gp. - globe pallidus; Pat. - putamen; Th. - thalamus; N. rub. - red core, Tr. r. sp. - rubrospinal fascicle; Tr. cort. th. - tractus cortico-thalamicus; Subst. nigra- substantia nigra; Tr. tecto-sp. - tractus tecto-spinalis; 3. cont. puch.
Basal ganglia
Posterior longitudinal fasciculus; I. Darksh. - Darkshevich nucleus.
Based on the above anatomical data, as well as existing clinical observations, the functional significance of the visual thalamus can be determined mainly by the following provisions. The optic thalamus is:
1) a transfer station for conducting all types of “general” sensitivity, visual, auditory and other irritations into the cortex;
2) an afferent link of the complex subcortical thalamo-strio-pallidal system, which carries out rather complex automated reflex acts;
3) through the visual thalamus, which is also a subcortical center for visceroreception, automatic regulation of internal ones is carried out due to connections with the hypothalamic region and the cerebral cortex. processes of the body and the activity of internal organs.
Sensitive impulses received by the visual thalamus can acquire one or another emotional coloring here. According to M.I. Astvatsaturov, the visual thalamus is an organ of primitive affects and emotions, closely related to the feeling of pain; At the same time, reactions from visceral devices occur (redness, pallor, changes in pulse and respiration, etc.) and affective, expressive motor reactions of laughter and crying.
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Anatomy and physiology of the basal ganglia and limbic system.
The limbic system has the shape of a ring and is located on the border of the neocortex and the brain stem. In functional terms, the limbic system is understood as the unification of various structures of the telencephalon, diencephalon and midbrain, providing emotional and motivational components of behavior and the integration of visceral functions of the body. In the evolutionary aspect, the limbic system was formed in the process of complicating the forms of behavior of the organism, the transition from rigid, genetically programmed forms of behavior to plastic ones, based on learning and memory.
Structural and functional organization of the limbic system
In a narrower sense, the limbic system includes formations of the ancient cortex (olfactory bulb and tubercle), old cortex (hippocampus, dentate and cingulate gyri), subcortical nuclei (amygdala and septal nuclei). This complex is considered in relation to the hypothalamus and the reticular formation of the brainstem as a higher level of integration of autonomic functions.
Afferent inputs to the limbic system are made from various areas of the brain, through the hypothalamus from the RF trunk, olfactory receptors along the fibers of the olfactory nerve. The main source of excitation of the limbic system is the reticular formation of the brain stem.
Efferent outputs from the limbic system are carried out: 1) through the hypothalamus to the underlying autonomic and somatic centers of the brainstem and spinal cord, and 2) to the new cortex (mainly associative).
A characteristic property of the limbic system is the presence of pronounced circular neural connections. These connections make it possible to reverberate excitation, which is a mechanism for its prolongation, increasing the conductivity of synapses and memory formation. Reverberation of excitation creates conditions for maintaining a single functional state of closed circle structures and transferring this state to other brain structures. The most important cyclic formation of the limbic system is the Peipetz circle, going from the hippocampus through the fornix to the mamillary bodies, then to the anterior nuclei of the thalamus, then to the cingulate gyrus and through the parahippocampal gyrus back to the hippocampus. This circle plays a large role in the formation of emotions, learning and memory. Another limbic circuit runs from the amygdala through the stria terminalis to the mammillary bodies of the hypothalamus, then to the limbic region of the midbrain and back to the tonsils. This circle is important in the formation of aggressive-defensive, food and sexual reactions.
Functions of the limbic system
The most general function of the limbic system is that, receiving information about the external and internal environment of the body, after comparing and processing this information, it launches vegetative, somatic and behavioral reactions through efferent outputs, ensuring the body’s adaptation to the external environment and maintaining the internal environment at a certain level. level. This function is carried out through the activity of the hypothalamus. The adaptation mechanisms that are carried out by the limbic system are associated with the latter’s regulation of visceral functions.
The most important function of the limbic system is the formation of emotions. In turn, emotions are a subjective component of motivations - states that trigger and implement behavior aimed at satisfying emerging needs. Through the mechanism of emotions, the limbic system improves the body's adaptation to changing environmental conditions. The hypothalamus, amygdala and ventral frontal cortex are involved in this function. The hypothalamus is the structure responsible primarily for autonomic manifestations of emotions. When the amygdala is stimulated, a person experiences fear, anger, and rage. When tonsils are removed, uncertainty and anxiety arise. In addition, the amygdala is involved in the process of comparing competing emotions, identifying the dominant emotion, that is, in other words, the amygdala influences the choice of behavior.
9. Basal ganglia, their functions
The cingulate gyrus plays the role of the main integrator of various brain systems that form emotions, since it has extensive connections with both the neocortex and brainstem centers. The ventral frontal cortex also plays a significant role in emotion regulation. When it is defeated, emotional dullness sets in.
The function of memory formation and learning is associated primarily with the Peipetz circle. At the same time, the amygdala is of great importance in one-time learning, due to its property of inducing strong negative emotions, promoting the rapid and strong formation of a temporary connection. The hippocampus and its associated posterior frontal cortex are also responsible for memory and learning. These formations carry out the transition of short-term memory to long-term memory. Damage to the hippocampus leads to disruption of the assimilation of new information and the formation of intermediate and long-term memory.
An electrophysiological feature of the hippocampus is that in response to sensory stimulation, stimulation of the reticular formation and the posterior hypothalamus, synchronization of electrical activity in the form of a low-frequency θ rhythm develops in the hippocampus. In this case, in the neocortex, on the contrary, desynchronization occurs in the form of a high-frequency β-rhythm. The pacemaker of the θ rhythm is the medial nucleus of the septum. Another electrophysiological feature of the hippocampus is its unique ability, in response to stimulation, to respond with long-term post-tetanic potentiation and an increase in the amplitude of the postsynaptic potentials of its granule cells. Post-tetanic potentiation facilitates synaptic transmission and underlies the mechanism of memory formation. An ultrastructural manifestation of the participation of the hippocampus in memory formation is an increase in the number of spines on the dendrites of its pyramidal neurons, which ensures increased synaptic transmission of excitation and inhibition.
Basal ganglia
The basal ganglia are a set of three paired formations located in the telencephalon at the base of the cerebral hemispheres: the phylogenetically ancient part - the globus pallidus, the later formation - the striatum and the youngest part - the fence. The globus pallidus consists of outer and inner segments; striatum - from the caudate nucleus and putamen. The fence is located between the shell and the insular cortex. Functionally, the basal ganglia include the subthalamic nuclei and substantia nigra.
Functional connections of the basal ganglia
Exciting afferent impulses enter predominantly the striatum mainly from three sources: 1) from all areas of the cortex directly and through the thalamus; 2) from nonspecific nuclei of the thalamus; 3) from the substantia nigra.
Among the efferent connections of the basal ganglia, three main outputs can be noted:
· from the striatum, inhibitory pathways go to the globus pallidus directly and with the participation of the subthalamic nucleus; from the globus pallidus the most important efferent path of the basal ganglia begins, going mainly to the ventral motor nuclei of the thalamus, from them the excitatory path goes to the motor cortex;
· part of the efferent fibers from the globus pallidus and striatum goes to the centers of the brain stem (reticular formation, red nucleus and then to the spinal cord), as well as 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 an intermediate link. They connect the associative and, in part, sensory cortex with the motor cortex. Therefore, in the structure of the basal ganglia there are several parallel functioning functional loops that connect them with the cerebral cortex.
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Features of the basal ganglia
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Consequences of damage to the basal ganglia
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When the BG is damaged, movement disorders occur. In 1817, the British physician D. Parkinson described a picture of the disease that could be called shaking paralysis. It affects many older people. At the beginning of the twentieth century, it was found that in people suffering from Parkinson's disease, pigment disappears in the substantia nigra. Later it was established that the disease develops as a result of the progressive death of dopaminergic neurons of the substantia nigra, after which the balance between inhibitory and excitatory outputs from the striatum is disrupted. There are three main types of movement disorders in Parkinson's disease. Firstly, this is muscle rigidity or a significant increase in muscle tone, due to which it is difficult for a person to carry out any movement: it is difficult to rise from a chair, it is difficult to turn the head without simultaneously turning the entire torso. He is unable to relax the muscles in the arm or leg so that the doctor can bend or straighten the limb at the joint without encountering significant resistance. Secondly, there is a sharp restriction of accompanying movements or akinesia: hand movements disappear when walking, facial accompaniment of emotions disappears, and the voice becomes weak. Thirdly, a large-scale tremor appears at rest - trembling of the limbs, especially their distal parts; tremor of the head, jaw, tongue is possible.
Thus, it can be stated that the loss of dopamineergic neurons of the substantia nigra leads to severe damage to the entire motor system. Against the background of reduced activity of dopaminergic neurons, the activity of the cholinergic structures of the striatum increases relatively, which can explain most of the symptoms of Parkinson's disease.
The role of the basal ganglia in providing motor functions
The discovery of these circumstances of the disease in the 50s of the twentieth century marked a breakthrough in the field of neuropharmacology, since it led not only to the possibility of treating it, but made it clear that brain activity can be disrupted due to damage to a small group of neurons and depends on certain molecular processes.
To treat Parkinson's disease, they began to use a precursor for dopamine synthesis - L-DOPA (dioxyphenylalanine), which, unlike dopamine, is able to overcome the blood-brain barrier, i.e. penetrate the brain from the bloodstream. Later, neurotransmitters and their precursors, as well as substances that affect signal transmission in certain brain structures, began to be used to treat mental illnesses.
When neurons in the caudate nucleus and putamen that use GABA or acetylcholine as mediators are damaged, the balance between these mediators and dopamine changes, and a relative excess of dopamine occurs. This leads to the appearance of involuntary and unwanted movements for a person - hyperkinesis. One example of a hyperkinetic syndrome is chorea or St. Vitus's dance, in which violent movements appear, characterized by variety and disorder, they resemble voluntary movements, but are never combined into coordinated actions. Such movements occur both during rest and during voluntary motor acts.
Remember : BASAL GANGLIA :
The cerebellum and basal ganglia are classified as movement software structures. They contain genetically determined, congenital and acquired programs for the interaction of different muscle groups in the process of performing movements.
The highest level of regulation of motor activity is carried out by the cerebral cortex.
ROLE OF THE LARGE HEMISPHERES CORTEX
IN REGULATION OF TONE AND CONTROL OF MOVEMENTS.
"Third floor" or the level of movement regulation is the cerebral cortex, which organizes the formation of movement programs and their implementation. The plan for future movement, arising in the associative zones of the cortex, enters the motor cortex. Neurons of the motor cortex organize purposeful movement with the participation of the BG, cerebellum, red nucleus, vestibular nucleus of Deiters, reticular formation, as well as - with the participation of the pyramidal system, directly affecting the alpha motor neurons of the spinal cord.
Cortical control of movements is possible only with the simultaneous participation of all motor levels.
A motor command transmitted from the cerebral cortex exerts its influence through lower motor levels, each of which contributes to the final motor response. Without normal activity of the underlying motor centers, cortical motor control would be imperfect.
Much is now known about the functions of the motor cortex. It is considered as a central structure that controls the most subtle and precise voluntary movements. It is in the motor cortex that the final and specific version of motor control of movements is built. The motor cortex uses two motor control principles: control through sensory feedback loops and control through programming mechanisms. This is achieved by the fact that signals from the muscular system, from the sensorimotor, visual and other parts of the cortex, which are used for motor control and movement correction, converge to it.
Afferent impulses to the motor areas of the cortex arrive through the motor nuclei of the thalamus. Through them, the cortex is connected with the associative and sensory zones of the cortex itself, with the subcortical basal ganglia and the cerebellum.
The motor area of the cortex regulates movements using efferent connections of three types: a) directly to the motor neurons of the spinal cord through the pyramidal tract, b) indirectly through communication with underlying motor centers, c) even more indirect regulation of movements is carried out by influencing the transmission and processing of information in sensory nuclei of the brain stem and thalamus.
As already mentioned, complex motor activity, subtle coordinated actions determine the motor areas of the cortex, from which two important pathways are sent to the brainstem and spinal cord: corticospinal and corticobulbar, which are sometimes combined under the name pyramidal tract. The corticospinal tract, which controls the muscles of the trunk and limbs, ends either directly on the motor neurons or on the interonerons of the spinal cord. The corticobulbar tract controls the motor nuclei of the cranial nerves that control facial muscles and eye movements.
The pyramidal tract is the largest descending motor pathway; it is formed by approximately one million axons, more than half of which belong to neurons called Betz cells or giant pyramidal cells. They are located in layer V of the primary motor cortex in the area of the precentral gyrus. It is from them that the corticospinal tract or the so-called pyramidal system originates. Through interneurons or by direct contact, the fibers of the pyramidal tract form excitatory synapses on flexor motor neurons and inhibitory synapses on extensor motor neurons in the corresponding segments of the spinal cord. Descending to the motor neurons of the spinal cord, the fibers of the pyramidal tract give off numerous collaterals to other centers: the red nucleus, pontine nuclei, reticular formation of the brain stem, as well as to the thalamus. These structures are connected to the cerebellum. Thanks to the connections of the motor cortex with motor subcortical centers and the cerebellum, it is involved in ensuring the accuracy of all purposeful movements - both voluntary and involuntary.
The pyramidal tract is partially decussated, so a stroke or other damage to the right motor area causes paralysis of the left side of the body, and vice versa
You can still find, along with the term pyramidal system, another one: extrapyramidal pathway or extrapyramidal system. This term has been used to designate other motor pathways running from the cortex to the motor centers. In modern physiological literature, the terms extrapyramidal pathway and extrapyramidal system are not used.
Neurons in the motor cortex, as well as in sensory areas, are organized into vertical columns. The cortical motor (also called motor) column is a small ensemble of motor neurons that control a group of interconnected muscles. It is now believed that their important function is not simply to activate certain muscles, but to ensure a certain position of the joint. In a somewhat general form, we can say that the cortex encodes our movements not by orders to contract individual muscles, but by commands that ensure a certain position of the joints. The same muscle group can be represented in different columns and can be involved in different movements
The pyramidal system is the basis of the most complex form of motor activity - voluntary, purposeful movements. The cerebral cortex is the substrate for learning new types of movements (for example, sports, industrial, etc.). The cortex stores the movement programs formed throughout life,
The leading role in the construction of new motor programs belongs to the anterior sections of the CBP (premotor, prefrontal cortex). A diagram of the interaction of associative, sensory and motor areas of the cortex during the planning and organization of movements is presented in Figure 14.
Figure 14. Scheme of interaction of associative, sensory and motor areas during planning and organization of movements
The prefrontal associative cortex of the frontal lobes begins to plan upcoming actions based on information coming primarily from the posterior parietal areas, with which it is connected by many neural pathways. The output activity of the prefrontal association cortex is addressed to the premotor or secondary motor areas, which create a specific plan for upcoming actions and directly prepare the motor systems for movement. Secondary motor areas include the premotor cortex and the supplementary motor area (supplementary motor area). The output activity of the secondary motor cortex is directed to the primary motor cortex and to subcortical structures. The premotor area controls the muscles of the trunk and proximal limbs. These muscles are especially important in the initial phase of straightening the body or moving the arm towards the intended goal. In contrast, the accessory motor area is involved in creating a model of the motor program, and also programs the sequence of movements that are performed bilaterally (for example, when it is necessary to act with both limbs).
The secondary motor cortex occupies a dominant position over the primary motor cortex in the hierarchy of motor centers: in the secondary cortex, movements are planned, and the primary cortex carries out this plan.
The primary motor cortex provides simple movements. It is located in the anterior central convolutions of the brain. Studies in monkeys have shown that the anterior central gyrus has unevenly distributed areas that control different muscles of the body. In these zones, the muscles of the body are represented somatotopically, that is, each muscle has its own section of the region (motor homunculus) (Fig. 15).
Figure 15. Somatotopic organization of the primary motor cortex - motor homunculus
As shown in the figure, the largest place is occupied by the representation of the muscles of the face, tongue, hands, fingers - that is, those parts of the body that bear the greatest functional load and can perform the most complex, subtle and precise movements, and at the same time are relatively poorly represented muscles of the trunk and legs.
The motor cortex controls movement using information coming both through sensory pathways from other parts of the cortex and from motor programs generated in the central nervous system, which are updated in the basal ganglia and cerebellum and reach the motor cortex through the thalamus and prefrontal cortex.
It is believed that the BG and the cerebellum already contain a mechanism that can update the motor programs stored in them. However, to activate the entire mechanism, it is necessary that these structures receive a signal that would serve as the initial impetus for the process. Apparently, there is a general biochemical mechanism for updating motor programs as a result of increased activity of dopaminergic and noradrenergic systems in the brain.
According to the hypothesis put forward by P. Roberts, the actualization of motor programs occurs due to the activation of command neurons. There are two types of command neurons. Some of them only launch one or another motor program, but do not participate in its further implementation. These neurons are called trigger neurons. Another type of command neurons is called gate neurons. They maintain or modify motor programs only when in a state of constant arousal. Such neurons typically control postural or rhythmic movements. The command neurons themselves can be controlled and inhibited from above. Removing inhibition from command neurons increases their excitability and thereby frees up “preprogrammed” circuits for the activities for which they are intended.
In conclusion, it should be noted that the motor areas of the cerebral cortex serve as the last link in which an idea formed in associative and other zones (and not just in the motor zone) is transformed into a movement program. The main task of the motor cortex is to select the group of muscles responsible for performing movements in any joint, and not to directly regulate the strength and speed of their contraction. This task is performed by the underlying centers down to the motor neurons of the spinal cord. In the process of developing and implementing a movement program, the motor area of the cortex receives information from the brainstem and cerebellum, which send corrective signals to it.
Remember :
CORTEX OF THE LARGE HEMISPHERES :
Note that the pyramidal, rubrospinal and reticulospinal tracts activate predominantly flexor, and the vestibulospinal tracts predominantly activate extensor motor neurons of the spinal cord. The fact is that flexor motor reactions are the main working motor reactions of the body and require more subtle and precise activation and coordination. Therefore, in the process of evolution, most descending pathways specialized in activating flexor motor neurons.
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See Ganglion, Brain. Large psychological dictionary. M.: Prime EUROZNAK. Ed. B.G. Meshcheryakova, acad. V.P. Zinchenko. 2003 ... Great psychological encyclopedia
BASAL GANGLIA- [cm. basal] the same as the basal ganglia, subcortical ganglia (see Basal ganglia) ...
Basal ganglia- (basal Greek ganglion - tubercle, tumor) - subcortical nuclei, including the caudate nucleus, putamen and globus pallidus. They are part of the extrapyramidal system, responsible for the regulation of movements. Damage to the basal ganglia and their connections with the cortex,... ... Encyclopedic Dictionary of Psychology and Pedagogy
BASAL GANGLIA- Three large subcortical nuclei, including the caudate nucleus, putamen and globus pallidus. These structures and some associated structures of the midbrain and hypothalamus constitute the extrapyramidal system and are directly responsible for the regulation... ... Explanatory dictionary of psychology
- (nuclei basalis), subcortical nuclei, basal ganglia, accumulations of gray matter in the thickness of the white matter of the cerebral hemispheres of vertebrates, involved in motor coordination. activity and formation of emotions. reactions. B. i. together with… … Biological encyclopedic dictionary
Several large accumulations of gray matter located in the thickness of the white matter of the cerebrum (see figure). They include the caudate (caudate) and lenticular nuclei (they form the striatum (corpus striatum)), and... ... Medical terms
BASAL GANGLIA, BASAL NUCLEI- (basal ganglia) several large accumulations of gray matter located in the thickness of the white matter of the cerebrum (see figure). They include the caudate (caudate) and lenticular nuclei (they form the striatum (corpus... Explanatory dictionary of medicine
BASAL GANGLIA- [from Greek. ganglion tubercle, node, subcutaneous tumor and basis] subcortical accumulations of nerve cells taking part in various reflex acts (see also Ganglion (in 1) meaning), Subcortical nuclei) ... Psychomotorics: dictionary-reference book
- (n. basales, PNA; synonym: basal ganglia outdated, subcortical I.) I. located at the base of the cerebral hemispheres; to Ya. b. include the caudate and lenticular ego, the fence and the amygdala... Large medical dictionary
A set of structures in the body of animals and humans, uniting the activities of all organs and systems and ensuring the functioning of the body as a whole in its constant interaction with the external environment. N. s. perceives... ... Great Soviet Encyclopedia
Basal ganglia (basal ganglia) is a striopallidal 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 zones of the cortex with the motor cortex.
Structure
The phylogenetically ancient part of the basal ganglia is the globus pallidus, the later formation is the striatum, and the youngest part is the cervix.
The globus pallidus consists of outer and inner segments; striatum - from the caudate nucleus and putamen. The fence is located between the putamen and the insular cortex. Functionally, the basal ganglia also include the subthalamic nuclei and substantia nigra.
Functional connections of the basal ganglia
Exciting afferent impulses enter predominantly the striatum (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 the substantia nigra.
Among the efferent connections of the basal ganglia, three main outputs can be noted:
- from the striatum, inhibitory pathways go to the globus pallidus directly and with the participation of the subthalamic nucleus; from the globus pallidus the most important efferent path of the basal ganglia begins, going mainly to the ventral motor nuclei of the thalamus, from them the excitatory path goes to the motor cortex;
- part of the efferent fibers from the globus pallidus and striatum goes to the centers of the brain stem (reticular formation, red nucleus and then to the spinal cord), as well as 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 an intermediate link. They connect the associative and, in part, sensory cortex with the motor cortex. Therefore, in the structure of the basal ganglia there are several parallel functioning functional loops that connect them with the cerebral cortex.
Fig.1. Diagram 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; VLN – ventrolateral nucleus; MDN – mediodorsal nucleus; PVN – anterior ventral nucleus; BS – globus pallidus; SN – black substance.
The skeletal-motor loop connects the premotor, motor, and somatosensory cortices to the putamen. The impulse from it goes to the globus pallidus and substantia nigra and then through the motor ventrolateral nucleus returns to the premotor area of the 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 gaze direction with the caudate nucleus. From there, the impulse goes to the globus pallidus and substantia nigra, from which it is projected, respectively, into the associative mediodorsal and anterior relay ventral nuclei of the thalamus, and from them returns to the frontal oculomotor field 8. This loop is involved in the regulation of saccadic eye movements (saccal).
It is also assumed that there are complex loops through which impulses from the frontal association zones of the cortex enter the caudate nucleus, globus pallidus and 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 higher psychophysiological functions of the brain: control of motivation, forecasting, cognitive activity.
Functions
Functions of the striatum
Influence of the striatum on the globus pallidus. The influence is carried out primarily by the inhibitory neurotransmitter GABA. However, some neurons of the globus pallidus give mixed responses, and some only EPSPs. That is, the striatum has a dual effect on the globus pallidus: inhibitory and excitatory, with a predominance of inhibitory action.
Influence of the striatum on the substantia nigra. There are bilateral connections between the substantia nigra and the striatum. Neurons of the striatum have an inhibitory effect on neurons of the substantia nigra. In turn, neurons of the substantia nigra have a modulating effect on the background activity of neurons in the striatum. In addition to influencing 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 slow-wave sleep phase. Destruction of the striatum disrupts the sleep-wake cycle by reducing sleep duration.
Influence of the striatum on the motor cortex. The caudate nucleus of the striatum “inhibits” degrees of freedom of movement that are unnecessary under given conditions, thereby ensuring the formation of a clear motor-defensive reaction.
Stimulation of the striatum. Stimulation of the striatum in its various parts causes different reactions: turning the head and torso in the direction opposite to the stimulation; delay in food-producing activity; suppression of the sensation of pain.
Damage to the striatum. Damage to the caudate nucleus of the striatum leads to hyperkinesis (excessive movements) - chorea and athetosis.
Functions of the globus pallidus
From the striatum, the globus pallidus receives predominantly inhibitory and partially excitatory influence. But it has a modulating effect on the motor cortex, cerebellum, red nucleus and reticular formation. The globus pallidus has an activating effect on the center of hunger and satiety. Destruction of the globus pallidus leads to adynamia, drowsiness, and emotional dullness.
Results of the activity of all basal ganglia:
- development, together with the cerebellum, of complex motor acts;
- control of movement parameters (force, 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 a text);
- participation in the act of inhibiting aggressive reactions.
