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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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- 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.
The coordinator of the coordinated work of the body is the brain. It consists of different departments, each of which performs specific functions. A person’s ability to function directly depends on this system. One of its important parts is the basal ganglia of the brain.
Movement and certain types of higher nervous activity are the result of their work.
What are the basal ganglia
The concept “basal” translated from Latin means “relating to the base.” It was not given by chance.
Massive areas of gray matter are the subcortical nuclei of the brain. The peculiarity of the location is in depth. The basal ganglia, as they are also called, are one of the most “hidden” structures of the entire human body. The forebrain, in which they are observed, is located above the brainstem and between the frontal lobes.
These formations represent a pair, the parts of which are symmetrical with each other. The basal ganglia are deepened into the white matter of the telencephalon. Thanks to this arrangement, information is transferred from one department to another. Interaction with other parts of the nervous system is carried out using special processes.
Based on the topography of the brain section, the anatomical structure of the basal ganglia is as follows:
- The striatum, which includes the caudate nucleus of the brain.
- The fence is a thin plate of neurons. Separated from other structures by stripes of white matter.
- Amygdala. Located in the temporal lobes. It is called part of the limbic system, which receives the hormone dopamine, which provides control over mood and emotions. It is a collection of gray matter cells.
- Lenticular nucleus. Includes globus pallidus and putamen. Located in the frontal lobes.
Scientists have also developed a functional classification. This is a representation of the basal ganglia in the form of the nuclei of the diencephalon, midbrain, and striatum. Anatomy implies their combination into two large structures.
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The first is called striopallidal. It includes the caudate nucleus, white ball and putamen. The second is extrapyramidal. In addition to the basal ganglia, it includes the medulla oblongata, cerebellum, substantia nigra, and elements of the vestibular apparatus.
Functionality of the basal ganglia
The purpose of this structure depends on the interaction with adjacent areas, in particular with the cortical sections and sections of the trunk. And together with the pons, cerebellum and spinal cord, the basal ganglia work to coordinate and improve basic movements.
Their main task is to ensure the vital functions of the body, perform basic functions, and integrate processes in the nervous system.
The main ones are:
- The onset of the sleep period.
- Metabolism in the body.
- Reaction of blood vessels to changes in pressure.
- Ensuring the activity of protective and orienting reflexes.
- Vocabulary and speech.
- Stereotypical, frequently repeated movements.
- Maintaining the posture.
- Muscle relaxation and tension, fine and gross motor skills.
- Showing emotions.
- Facial expressions.
- Eating behavior.
Symptoms of basal ganglia dysfunction
A person’s general well-being directly depends on the condition of the basal ganglia. Causes of dysfunction: infections, genetic diseases, injuries, metabolic failure, developmental abnormalities. Often the symptoms remain unnoticeable for some time, and patients do not pay attention to the malaise.
Characteristic features:
- Lethargy, apathy, poor general health and mood.
- Tremor in the limbs.
- Decreased or increased muscle tone, limitation of movements.
- Poor facial expressions, inability to express emotions with the face.
- Stuttering, changes in pronunciation.
- Tremor in the limbs.
- Blurred consciousness.
- Problems with remembering.
- Loss of coordination in space.
- The emergence of unusual postures for a person that were previously uncomfortable for him.
This symptomatology gives an understanding of the importance of the basal ganglia for the body. Not all of their functions and methods of interaction with other brain systems have been established to date. Some are still a mystery to scientists.
Pathological conditions of the basal ganglia
Pathologies of this body system are manifested by a number of diseases. The degree of damage also varies. Human life directly depends on this.
- Functional deficiency. Occurs at an early age. It is often a consequence of genetic abnormalities corresponding to heredity. In adults, it leads to Parkinson's disease or subcortical paralysis.
- Neoplasms and cysts. Localization is varied. Causes: malnutrition of neurons, improper metabolism, atrophy of brain tissue. Pathological processes occur in utero: for example, the occurrence of cerebral palsy is associated with damage to the basal ganglia in the second and third trimesters of pregnancy. Difficult childbirth, infections, and injuries in the first year of a child’s life can provoke the growth of cysts. Attention deficit hyperactivity disorder is a consequence of multiple neoplasms in infants. In adulthood, pathology also occurs. A dangerous consequence is cerebral hemorrhage, which often ends in general paralysis or death. But there are asymptomatic cysts. In this case, no treatment is required, they need to be observed.
- Cortical palsy– a definition that speaks about the consequences of changes in the activity of the globus pallidus and the striopallidal system. Characterized by stretching of the lips, involuntary twitching of the head, and twisting of the mouth. Convulsions and chaotic movements are noted.
Diagnosis of pathologies
The primary step in establishing the causes is an examination by a neurologist. His task is to analyze the medical history, assess the general condition and prescribe a series of examinations.
The most revealing diagnostic method is MRI. The procedure will accurately determine the location of the affected area.
Computed tomography, ultrasound, electroencephalography, study of the structure of blood vessels and blood supply to the brain will help in making an accurate diagnosis.
It is incorrect to talk about the prescription of a treatment regimen and prognosis before carrying out the above measures. Only after receiving the results and carefully studying them does the doctor give recommendations to the patient.
Consequences of basal ganglia pathologies
Basal ganglia and their functional connections
The basal ganglia, or subcortical ganglia, are located at the base of the cerebral hemispheres in the thickness of the white matter in the form of individual nuclei, or nodes. The basal nuclei include: the striatum, consisting of the caudate and lenticular nuclei; fence and amygdala (Atl., Fig. 25, p. 134).
Caudate nucleus located anterior to the thalamus. Its anterior thickened part is head- placed in front of the optic thalamus, in the lateral wall of the anterior horn of the lateral ventricle, behind it gradually narrows and turns into tail. The caudate nucleus covers the visual thalamus in front, above and on the sides.
Lenticular nucleus got its name for its resemblance to a lentil grain and is located lateral to the thalamus and caudate nucleus. The lower surface of the anterior part of the lentiform nucleus is adjacent to the anterior perforated substance and connects with the caudate nucleus, the medial part of the lentiform nucleus faces the internal capsule, located on the border of the thalamus and the head of the caudate nucleus. The lateral surface of the lenticular nucleus is convex and faces the base of the insular lobe of the cerebral hemispheres. On the frontal section of the brain, the lenticular nucleus has the shape of a triangle, the apex of which faces the medial side and the base faces the lateral side. The lenticular nucleus is divided by layers of white matter into a darker colored lateral part - shell and medial - pale ball, consisting of two segments: internal and external. Shell according to genetic, structural and functional characteristics, it is close to the caudate nucleus, and they belong to phylogenetically newer formations. The globus pallidus is an older formation.
Fence located in the white matter of the hemisphere, on the side of the shell, from which a thin layer of white matter is separated - outer capsule. The same thin layer of white matter separates the enclosure from the insular cortex.
Amygdala located in the white matter of the temporal lobe of the hemisphere, approximately 1.5-2.0 cm posterior to the temporal pole.
Functions The basal ganglia are determined primarily by their connections, which they have in fairly large quantities. For example, the caudate nucleus and putamen receive descending connections primarily from the extrapyramidal system. Fibers from neurons of the cortex, thalamus and substantia nigra terminate on them. Other cortical fields also send large numbers of axons to the caudate nucleus and putamen.
The main part of the axons of the caudate nucleus and putamen goes to the globus pallidus, from here to the thalamus, and only from it to the sensory fields. Consequently, there is a vicious circle of connections between these formations. The caudate nucleus and putamen also have functional connections with structures lying outside this circle: with the substantia nigra, the red nucleus.
The abundance of connections between the caudate nucleus and the putamen indicates participation in integrative processes, organization and regulation of movements, regulation of the work of internal organs.
The medial nuclei of the thalamus have direct connections with the caudate nucleus, as evidenced by the onset of the reaction 2-4 ms after stimulation of the thalamus.
In the interactions between the caudate nucleus and the globus pallidus, inhibitory influences prevail. When the caudate nucleus is stimulated, most of the neurons of the globus pallidus are inhibited, and a smaller part is excited.
The caudate nucleus and the substantia nigra have direct and feedback connections with each other. For example, stimulation of the substantia nigra leads to an increase, and destruction leads to a decrease in the amount of dopamine in the caudate nucleus. Thanks to dopamine, a disinhibitory mechanism of interaction between the caudate nucleus and the globus pallidus appears.
The caudate nucleus and globus pallidus take part in such integrative processes as conditioned reflex activity and motor activity. Switching off the caudate nucleus is accompanied by the development of hyperkinesis such as involuntary facial reactions, tremor, athetosis, torsion spasm of chorea (twitching of the limbs, torso, as in an uncoordinated dance), motor hyperactivity in the form of aimless moving from place to place.
In case of damage to the caudate nucleus, significant disorders of higher nervous activity, difficulty in orientation in space, memory impairment, and slowed growth of the body are observed. After bilateral damage to the caudate nucleus, conditioned reflexes disappear for a long period of time, the development of new reflexes becomes difficult, general behavior is characterized by stagnation, inertia, and difficulty switching. When affecting the caudate nucleus, in addition to disorders of higher nervous activity, movement disorders are noted.
Despite the functional similarity of the caudate nucleus and the putamen, there are a number of functions specific to it. Thus, the shell is characterized by participation in the organization of eating behavior. Irritation of the shell leads to changes in breathing and salivation.
The globus pallidus has connections with the thalamus, putamen, caudate nucleus, midbrain, hypothalamus, somatosensory system, etc., which indicates its participation in the organization of simple and complex forms of behavior.
Stimulation of the globus pallidus, unlike stimulation of the caudate nucleus, does not cause inhibition, but provokes an orienting reaction, movements of the limbs, and feeding behavior (sniffing, chewing, swallowing).
Damage to the globus pallidus causes people to have a mask-like appearance of the face, tremor of the head and limbs (and this tremor disappears at rest, during sleep and intensifies with movement), monotony of speech. In a person with globus pallidus dysfunction, the onset of movements is difficult, auxiliary movements of the arms when walking disappear, and a symptom of propulsion appears: long preparation for movement, then rapid movement and stopping.
The fence forms connections primarily with the cerebral cortex. Stimulation of the fence causes an indicative reaction, turning the head in the direction of irritation, chewing, swallowing, and sometimes vomiting movements. Irritation from the fence inhibits the conditioned reflex to light and has little effect on the conditioned reflex to sound. Stimulation of the fence during eating inhibits the process of eating food. It has been noted that the thickness of the fence of the left hemisphere in humans is somewhat greater than that of the right; When the right hemisphere fence is damaged, speech disorders are observed.
The amygdala receives impulses from a variety of afferent systems, including the olfactory system, and is related to emotional reactions.
Thus, the basal ganglia are integrative centers for the organization of motor skills, emotions, and higher nervous activity, and each of these functions can be enhanced or inhibited by the activation of individual formations of the basal ganglia. In addition, the basal ganglia are the connecting link between the associative and motor areas of the cerebral cortex.
Development of the basal ganglia. The basal ganglia develop more intensively than the visual thalamus. The globus pallidus (pallidum) myelinates before the striatum (striatum) and the cerebral cortex. It has been noted that myelination in the globus pallidus is almost completely completed by 8 months of fetal development.
In the structures of the striatum, myelination begins in the fetus and ends only by 11 months of life. The caudate body doubles in size during the first two years of life, which is associated with the development of automatic motor acts in the child.
The motor activity of a newborn is largely associated with the globus pallidus, impulses from which cause uncoordinated movements of the head, torso and limbs.
In a newborn, the pallidum already has multiple connections with the optic thalamus, subtuberculous region and substantia nigra. The connection between the pallidum and the striatum develops later; some of the striopallidal fibers become myelinated in the first month of life, and the other part only by 5 months and later.
The pyramidal system in a newborn is not yet sufficiently developed, and impulses to the muscles are delivered from the subcortical ganglia through the extrapyramidal system. As a result, the child’s movements in the first months of life are characterized by generalization and undifferentiation.
It has been noted that acts such as crying are motorized by the globus pallidus. The development of the striatum is associated with the appearance of facial movements, and then the ability to sit and stand. Since the striatum has an inhibitory effect on the pallidum, a gradual separation of movements is created.
In order to sit, the child must be able to hold his head and back upright. This appears by the age of two months, and the child begins to raise his head while lying on his back by 2-3 months. Starts sitting at 6-8 months.
In the first months of life, the child has a negative support reaction: when trying to put him on his legs, he lifts them and pulls them towards his stomach. Then this reaction becomes positive: when you touch the support, the legs unbend. At 9 months the child can stand with support; at 10 months he can stand freely.
From 4-5 months of age, various voluntary movements develop quite quickly, but for a long time they are accompanied by a variety of additional movements.
The appearance of voluntary (such as grasping) and expressive movements (smiling, laughter) is associated with the development of the striatal system and motor centers of the cerebral cortex. The axons of their cells grow to the basal ganglia, and the activity of the latter begins to be regulated by the cortex. A child begins to laugh loudly at 8 months.
As all parts of the brain and the cerebral cortex grow and develop, the child’s movements become less generalized and more coordinated. Only by the end of the preschool period is a certain balance of cortical and subcortical motor mechanisms established.
Large hemispheres The brain is covered on top with a thin layer of gray matter - the cerebral cortex. There are two of them (right and left), they are connected to each other by a thick horizontal plate - corpus callosum, consisting of nerve fibers running transversely from one hemisphere to the other. Below the corpus callosum is vault, representing two arched white cords that are connected to each other by the middle part, and diverge in front and behind, forming the columns of the arch in front, behind the legs of the arch.
Each hemisphere has three surfaces: superolateral (most convex), medial (flat, facing the adjacent hemisphere) and lower, which has a complex relief corresponding to the internal base of the skull. Each hemisphere has the most prominent areas, called poles: frontal pole, occipital pole and temporal pole.
Throughout its entire length, the bark deepens, forming numerous furrows, which divide the surface of the hemispheres into convolutions and lobes. Each hemisphere has six lobes: frontal, parietal, temporal, occipital, marginal and insula. They are separated by the lateral, central, parieto-occipital, cingulate and collateral grooves (Atl., Fig. 22, p. 133).
Lateral sulcus begins at the base of the hemisphere with a significant depression, the bottom of which is covered with grooves and convolutions island. Then it moves to the superolateral surface of the hemisphere, heading back and slightly upward, separating the temporal lobe from the higher lobes: the frontal - in front and the parietal - in the back.
Central sulcus begins on the upper edge of the hemisphere, slightly behind its middle and goes forward downwards, most often not reaching the lateral (side) sulcus. The central sulcus separates the frontal lobe from the parietal lobe (Atl., Fig. 27, p. 135).
Parieto-occipital sulcus runs vertically along the medial surface of the hemisphere, separating the parietal lobe from the occipital lobe.
cingulate groove runs along the medial surface of the hemisphere parallel to the corpus callosum, separating the frontal and parietal lobes from the cingulate gyrus.
Collateral groove On the lower surface of the hemisphere, it separates the temporal lobe from the marginal and occipital lobes.
On the lower surface of the hemisphere, in its anterior part, is located olfactory sulcus, in which lies the olfactory bulb, which continues into the olfactory tract. At the back it bifurcates into lateral and medial stripes, forming an olfactory triangle, in the center of which lies the anterior perforated substance.
Hemisphere lobes. Frontal lobe. In the anterior part of each hemisphere is the frontal lobe. It ends anteriorly with the frontal pole and is limited inferiorly by the lateral sulcus (Sylvian fissure) and posteriorly by the deep central sulcus. Anterior to the central sulcus, almost parallel to it, is located precentral sulcus. The superior and inferior frontal sulci extend forward from it. They divide the frontal lobe into convolutions. The frontal lobe has 4 convolutions: precentral, located between the central sulcus posteriorly and the precentral sulcus anteriorly; superior frontal(above the superior frontal sulcus); middle frontal(between the superior and inferior frontal sulci); inferior frontal(downward from the inferior frontal sulcus). The inferior frontal gyrus is divided into three parts: operculum (frontal operculum) - between the inferior precentral sulcus posteriorly, the inferior frontal sulcus superiorly, and the ascending branch of the lateral sulcus anteriorly; triangular part - between the ascending and anterior branches of the lateral sulcus and orbital - below the anterior branch of the lateral sulcus.
Parietal lobe located posterior to the central sulcus. The posterior border of this lobe is the parieto-occipital sulcus. Within the parietal lobe there is postcentral sulcus, which lies behind the central sulcus and is almost parallel to it. Between the central and postcentral sulci is located postcentral gyrus. It extends posteriorly from the postcentral sulcus intraparietal sulcus. It is parallel to the upper edge of the hemisphere. Above the intraparietal sulcus is the superior parietal lobule. Below this groove lies the inferior parietal lobule, within which there are two gyri: supramarginal and angular. The supramarginal gyrus covers the end of the lateral sulcus, and the angular gyrus covers the end of the superior temporal sulcus.
Temporal lobe occupies the inferolateral parts of the hemisphere and is separated from the frontal and parietal lobes by a deep lateral sulcus. On its superolateral surface there are three parallel grooves. Superior temporal sulcus lies directly under the lateral and limits superior temporal gyrus. The inferior temporal sulcus consists from separate segments, bounds from below middle temporal gyrus. The inferior temporal gyrus on the medial side is limited by the inferolateral edge of the hemisphere. Anteriorly, the temporal lobe curves into the temporal pole.
Occipital lobe located behind the parieto-occipital sulcus. Compared to other lobes, it is small in size. It has no permanent grooves on the superolateral surface. Its main calcarine groove is located horizontally on the medial surface and runs from the occipital pole to the parieto-occipital groove, with which it merges into one trunk. Between these grooves lies a triangular gyrus - wedge. The lower surface of the occipital lobe lies above the cerebellum (Atl., Fig. 27, p. 135). At the posterior end the lobe tapers into occipital pole.
Marginal lobe located on the medial and inferior surfaces of the hemisphere. It includes the cingulate and parahippocampal gyri. The cingulate gyrus is limited inferiorly groove of the corpus callosum, and above - cingulate groove, separating it from the frontal and parietal lobes . Parahippocampal gyrus limited from above hippocampal sulcus, which serves as a downward and forward continuation of the posterior end of the groove of the corpus callosum. Inferiorly, the gyrus is separated from the temporal lobe by the collateral sulcus.
White matter is located under the cerebral cortex, forming a continuous mass above the corpus callosum. Below, the white matter is interrupted by clusters of gray (basal ganglia) and is located between them in the form of layers or capsules (Atl., Fig. 25, p. 134).
The white matter consists of associative, commissural and projection fibers.
Association fibers connect different parts of the cortex of the same hemisphere. They are divided into short and long. Short fibers connect neighboring convolutions in the form of arcuate bundles. Long association fibers connect areas of the cortex that are more distant from each other. Long associative fibers include:
The superior longitudinal fasciculus connects the inferior frontal gyrus with the inferior parietal lobe, temporal and occipital lobes; it has the shape of an arc that goes around the island and stretches along the entire hemisphere;
The inferior longitudinal fasciculus connects the temporal lobe with the occipital lobe;
Fronto-occipital fascicle - connects the frontal lobe with the occipital and insula;
The cingulate bundle - connects the anterior perforated substance with the hippocampus and the uncus, located in the shape of an arc in the cingulate gyrus, bends around the corpus callosum from above;
Uncinate fasciculus - connects the lower part of the frontal lobe, the uncinate and the hippocampus.
Commissural fibers connect the cortex of the symmetrical parts of both hemispheres. They form so-called commissures or commissures. The largest cerebral commissure is corpus callosum, connecting the same areas of the neocortex of the right and left hemispheres. It is located deep in the longitudinal slit and is a flattened, elongated formation. The surface of the corpus callosum is covered with a thin layer of gray matter, which forms four longitudinal stripes. The fibers diverging from the corpus callosum form its radiance. It is divided into frontal, parietal, temporal and occipital parts.
For the phylogenetically ancient cortex, the commissural fiber systems are the anterior and posterior commissures. Anterior commissure connects the uncinates of the temporal lobes and parahippocampal gyri, as well as the gray matter of the olfactory triangles.
Projection fibers extend beyond the hemispheres as part of the projection pathways. They provide two-way communication between the cortex and the underlying parts of the central nervous system. Some of these fibers conduct excitation centripetally, towards the cortex, while others, on the contrary, centrifugally.
Projection fibers in the white matter of the hemisphere closer to the cortex form the so-called corona radiata and pass into internal capsule(Atl., Fig. 25, p. 134). In the internal capsule there are anterior and posterior legs and a knee. Descending projection pathways, passing through the capsule, connect various zones of the cortex with underlying structures. The anterior peduncle contains the frontopontine tract (part of the corticopontine tract) and the anterior thalamic radiance. In the knee there are fibers of the corticonuclear tract, and in the upper part of the posterior leg there are corticospinal, corticoronuclear, corticoreticular tracts, as well as fibers of the thalamic radiance. In the most distant part of the posterior peduncle there are corticotectal, temporopontine and thalamic radiant fibers, going to the occipital and temporal areas of the cortex in the visual and auditory areas. The parieto-occipital-pontine fascicle also runs here.
Descending projection pathways coming from the cortex are combined into pyramidal pathway consisting of the corticonuclear and corticospinal tracts.
Ascending projection pathways carry impulses to the cortex that arise from the sensory organs, as well as from the organs of movement. These projection pathways include: the lateral spinothalamic tract, the fibers of which, passing through the posterior leg of the internal capsule, forming the corona radiata, reach the cerebral cortex, its postcentral gyrus; the anterior spinothalamic tract, which carries impulses from the skin to the cerebral cortex into the postcentral gyrus; conductive path of proprioceptive sensitivity of the cortical direction, supplying impulses of the muscular-articular sense to the cerebral cortex in the postcentral gyrus.
A special place in the system of fibers of the cerebral hemispheres is occupied by vault. It is a curved cord, in which the body, legs, and pillars are distinguished. Body the fornix is located under the corpus callosum and fuses with it. In front, the body of the fornix passes into the columns of the fornix, which bend downward, and each of them passes into the mamillary body of the hypothalamus. Vault pillars located above the anterior parts of the thalamus. Between each column and the thalamus there is a gap - the interventricular foramen. In front of the pillars of the arch, merging with them, lies anterior commissure. Posteriorly, the body of the fornix continues into the paired crura of the fornix, which extend laterally downwards, separate from the corpus callosum and fuse with the hippocampus, forming its fimbria. The right and left hippocampi are connected to each other through commissioner of the arch located between the legs. Thus, with the help of the fornix, the temporal lobe of the hemisphere is connected to the mammillary bodies of the diencephalon. In addition, some of the fibers of the fornix are directed from the hippocampus to the thalamus, amygdala and ancient cortex.
Performing the function of an information transmitter. Even in the embryo, the basal ganglia develop from the ganglion tubercle, then forming into mature brain structures that perform strictly specific functions in the nervous system.
The basal ganglia are located at the base of the brain, lateral to the thalamus. Anatomically highly specific nuclei are part of the forebrain, which is located on the border of the frontal lobes and the brainstem. Often under the term " subcortex“Experts mean precisely the set of basal ganglia of the brain.
Anatomists distinguish three concentrations of gray matter:
- Striatum. This structure means a set of two not entirely differentiated parts:
- Caudate nucleus brain. It has a thickened head, forming in front one of the walls of the lateral ventricle of the brain. The thin tail of the nucleus is adjacent to the bottom of the lateral ventricle. The caudate nucleus also borders the thalamus.
- Lenticular nucleus. This structure runs parallel to the previous accumulation of gray matter and, closer to the end, merges with it, forming the striatum. The lenticular nucleus consists of two white layers, each of which has its own name (globus pallidus, shell).
Corpus striatum received its name due to the alternating arrangement of white stripes on its gray matter. Recently, the lenticular nucleus has lost its functional meaning, and it is called exclusively in a topographical sense. The lenticular nucleus, as a functional compilation, is called the striopallidal system.
- Fence or claustrum is a small thin gray plate located near the shell of the striatum.
- Amygdala. This core is located under the shell. This structure also applies. The amygdala usually means several separate functional formations, but they were combined due to their close location. This area of the brain has multiple connections with other brain structures, in particular with the hypothalamus, thalamus and cranial nerves.
The concentration of white matter is:
- Internal capsule - white matter between the thalamus and the lentiform nucleus
- Outer capsule - white substance between the lentil and the fence
- The outermost capsule is the white substance between the enclosure and the insula.
The internal capsule is divided into 3 parts and contains the following pathways:
Front leg:
- Frontothalamic tract - connection between the frontal cortex and the mediadersal nucleus of the thalamus
- Frontopontine tract - connection between the frontal cortex and the pons
- Corticonuclear tract - connection between the nuclei of the motor cortex and the nuclei of the motor cranial nerves
Rear leg:
- Corticospinal tract - conducts motor impulses from the cerebral cortex to the nuclei of the motor horns of the spinal cord
- Thalamo-parietal fibers - Axons of thalamic neurons are connected to the postcentral gyrus
- Temporo-parieto-occipital-pontine fasciculus - connects the pontine nuclei with the lobes of the brain
- Auditory radiance
- Visual radiance
Functions of the basal ganglia
The basal ganglia provide the entire range of functions for maintaining the basic functioning of the body, be it metabolic processes or basic vital functions. Like any regulatory center in the brain, the set of functions is determined by the number of its connections with neighboring structures. The striopallidal system has many such connections with the cortical regions and areas of the brainstem. The system also has efferent And afferent ways. The functions of the basal ganglia include:
- control of the motor sphere: maintaining an innate or learned posture, ensuring stereotypical movements, response patterns, regulation of muscle tone in certain poses and situations, fine motor skills and integration of small motor movements (calligraphic writing);
- speech, vocabulary;
- the onset of sleep;
- vascular reactions to changes in pressure, metabolism;
- thermoregulation: heat transfer and heat generation.
- In addition, the basal ganglia provide the activity of protective and orientation reflexes.
Symptoms of basal ganglia dysfunction
When the basal ganglia are damaged or dysfunctional, symptoms associated with impaired coordination and precision of movements occur. Such phenomena are called the collective concept “ dyskinesia", which, in turn, is divided into two subtypes of pathologies: hyperkinetic and hypokinetic disorders. Symptoms of basal ganglia dysfunction include:
- akinesia;
- impoverishment of movements;
- voluntary movements;
- slow movements;
- increase and decrease in muscle tone;
- muscle tremor in a state of relative rest;
- desynchronization of movements, lack of coordination between them;
- poor facial expressions, scanned language;
- erratic and arrhythmic movements of small muscles of the hand or fingers, the entire limb or part of the whole body;
- pathological postures unusual for the patient.
Most manifestations of the pathological functioning of the basal ganglia are based on disturbances in the normal functioning of the neurotransmitter systems of the brain, in particular the dopaminergic modulating system of the brain. In addition, however, the causes of symptoms are previous infections, mechanical brain injuries or congenital pathologies.
Pathological states of nuclei
The most common pathologies of the basal ganglia are:
Cortical palsy. This pathology is formed as a result of damage to the globus pallidus and the striopallidal system as a whole. Paralysis is accompanied by tonic spasms of the legs or arms, torso, and head. A patient with cortical paralysis makes chaotic slow movements with a small scope, stretches out his lips and moves his head. A grimace appears on his face, he twists his mouth.
Parkinson's disease. This pathology is manifested by muscle rigidity, impoverishment of motor activity, tremor and instability of body position. Modern medicine, unfortunately, has no alternatives other than symptomatic therapy. Drugs only relieve the symptoms of the disease without eliminating its cause.
Getington's disease– genetically determined pathology of the basal ganglia. In addition to the physical manifestations of the disease (chaotic movements, involuntary muscle contractions, lack of coordination, spasmodic eye movements), patients also suffer from mental disorders. As the pathology progresses, patients undergo qualitative personality changes, their mental abilities are weakened, and the ability to think abstractly is lost. At the end of the pathology, as a rule, doctors are presented with a depressed, panicky, selfish and aggressive patient with weakened cognitive abilities.
Diagnosis and prognosis of pathology
In addition to neurologists, diagnostics is carried out by doctors from other offices (functional diagnostics). The main methods for identifying diseases of the basal ganglia are:
- analysis of the patient’s life, his anamnesis;
- objective external neurological examination and physical examination;
- magnetic resonance and computed tomography;
- study of the structure of blood vessels and the state of blood circulation in the brain;
- visual methods for studying brain structures;
- electroencephalography;
Prognostic data depends on many factors, such as gender, age, general constitution of the patient, the moment of the disease and the moment of diagnosis, his genetic predispositions, the course and effectiveness of treatment, the pathology itself and its destructive properties. According to statistics, 50% of diseases of the basal ganglia have an unfavorable prognosis. The remaining half of cases have a chance for adaptation, rehabilitation and normal life in society.