Cerebellum. Cerebellar connections. Cerebellar peduncles. Ways. Symptoms of cerebellar damage. Functions and structure of the cerebellum of the brain What is the cerebellum of the brain responsible for?

Table of contents of the topic "Rhomboid brain. Medulla oblongata, myelencephalon, medulla oblongata. Hindbrain, metencephalon. Pons, pons. Cerebellum, cerebellum.":

White matter of the cerebellum in cross-section it looks like small plant leaves corresponding to each gyrus, covered on the periphery with the bark of the gray matter. As a result, the overall picture of white and gray matter on a section of the cerebellum resembles tree, arbor vitae cerebelli (tree of life; the name is given based on its appearance, since damage to the cerebellum is not an immediate threat to life). The white matter of the cerebellum is composed of various types of nerve fibers. Some of them connect the gyri and lobules, others go from the cortex to the internal nuclei of the cerebellum, and, finally, others connect the cerebellum with neighboring parts of the brain. These last fibers come as part of three pairs of cerebellar peduncles:

1. Lower legs, pedunculi cerebellares inferiores (to the medulla oblongata). In their composition they go to the cerebellum tractus spinocerebellaris posterior, fibrae arcuatae extenae- from the nuclei of the posterior cords of the medulla oblongata and fibrae olivocerebellares- from olive. The first two tracts end in the cortex of the vermis and hemispheres. In addition, there are fibers from the nuclei of the vestibular nerve, ending in nucleus fastigii. Thanks to all these fibers, the cerebellum receives impulses from the vestibular apparatus and the proprioceptive field, as a result of which it becomes the core of proprioceptive sensitivity, making automatic corrections to the motor activity of the rest of the brain. As part of the lower legs there are also descending pathways in the opposite direction, namely: from nucleus fastigii to the lateral vestibular nucleus (see below), and from it to anterior horns of the spinal cord, tractus vestibulospinalis. Through this pathway, the cerebellum influences the spinal cord.

2. Middle legs, pedunculi cerebellares medii (towards the bridge). They contain nerve fibers from the pontine nuclei to the cerebellar cortex. The pathways that arise in the pons nuclei to the cerebellar cortex, tractus pontocerebellares, are ongoing cortical-pontine tract, fibrae corticopontinae, ending in the cores of the bridge after the cross. These pathways connect the cerebral cortex with the cerebellar cortex, which explains the fact that the more developed the cerebral cortex, the more developed the pons and cerebellar hemispheres are, which is observed in humans.

3. Upper legs, pedunculi cerebellares superiores (to the roof of the midbrain). They consist of nerve fibers going in both directions: 1) to the cerebellum - tractus spinocerebelldris anterior and 2) from nucleus dentatus cerebellum to tegmentum of the midbrain - tractus cerebellotegmentalis, which after decussation ends in the red nucleus and thalamus. Along the first paths, impulses from the spinal cord go to the cerebellum, and along the second, it sends impulses to the extrapyramidal system, through which it itself influences the spinal cord.

Cerebellum- a section of the brain that belongs to the hindbrain itself, participating in the regulation of muscle tone, coordination of movements, maintaining posture, body balance in space, and also performing an adaptive-trophic function. It is located behind the pons.

The cerebellum is divided into a middle part - the vermis - and two hemispheres located on either side of it. The surface of the cerebellum is made up of gray matter called the cortex. Inside the cerebellum there is white matter, which is the processes of neurons. On the surface of the cerebellum there are many folds, or sheets, formed by the complex bends of its cortex.

Rice. 1. Intracentral connections of the cerebellum: A - cerebral cortex; b - visual thalamus; B - midbrain; G - cerebellum; D - spinal cord; E - skeletal muscles; 1 - corticospinal tract; 2 - reticular tract; 3 - spinocerebellar tracts

The cerebellum is connected to the brain stem through three pairs of peduncles (inferior, middle and superior). The lower legs connect it with the oblong and dorsal brain, the middle ones - with the pons, and the upper ones - with the midbrain and thalamus.

Main functions of the cerebellum- coordination of movements, normal distribution of muscle tone and regulation of autonomic functions. The cerebellum exerts its influence through the nuclear formations of the midbrain and medulla oblongata, as well as through motor neurons of the spinal cord.

In experiments on animals, it was found that when the cerebellum is removed, they develop profound motor disorders: atony - the disappearance or weakening of muscle tone and the inability to move for some time; asthenia - rapid fatigue due to continuous movement with the expenditure of a large amount of energy; astasia - loss of the ability to perform tetanic contractions.

In animals with these disorders, coordination of movements is impaired (shaky gait, awkward movements). After a certain time after removal of the cerebellum, all these symptoms weaken somewhat, but do not disappear completely even after several years. Functional impairments after removal of the cerebellum are compensated as a result of the formation of new conditioned reflex connections in the cerebral cortex.

The cerebellar cortex contains the auditory and visual areas.

The cerebellum is also involved in the control system of visceral functions. Its irritation causes several autonomic reflexes: increased blood pressure, dilated pupils, etc. When the cerebellum is damaged, disturbances in the functioning of the cardiovascular system, the secretory function of the gastrointestinal tract and other systems occur.

Structure of the cerebellum

Cerebellum located rostral to the tentorium cerebellum, caudal to the foramen magnum and occupies most of the posterior cranial fossa. Inferiorly and ventrally, it is separated by the cavity of the fourth ventricle from the pons.

Various approaches are used to divide the cerebellum into its structures. From a functional and phylogenetic point of view, it can be divided into three large divisions:

• vestibulocerebellum;
• spinocerebellum;
• cerebrocerebellum.

Vestibulocerebellam (Archicerebellum) is the most ancient part of the cerebellum, represented in humans by the flocculonodular lobe and part of the vermis, associated primarily with the vestibular system. The department is connected by reciprocal connections with the vestibular and reticular nuclei of the brain stem, which is the basis for its participation in the control of body balance, as well as the coordination of eye and head movements. This is realized through the regulation and distribution of the tone of the axial muscles of the body by the vestibular part of the cerebellum. Damage to the vetibulocerebellum may be accompanied by impaired coordination of muscle contraction, the development of an ataxic (drunk) gait, as well as ocular nystagmus.

Spinocerebellum (paleocerebellum) is represented by the anterior and small part of the posterior lobe of the cerebellum. It is connected by spinocerebellar tracts to the spinal cord, from where it receives somatotopically organized information from the spinal cord. Using the received signals, the spinocerebellum takes part in the regulation of muscle tone and control of movements mainly of the muscles of the limbs and axial muscles of the body. Its damage is accompanied by impaired coordination of movements, similar to those that develop after damage to the neocerebellum.

Neocerebellum (Cerebrocerebellum) is represented by the posterior lobe of the cerebellar hemisphere and is the largest part of the human cerebellum. The neurons of this part of the cerebellum receive signals along the axons of neurons in many fields. Therefore, neocerebellum is also called cerebrocerebellum. It modulates signals received from the motor cortex and is involved in the planning and regulation of limb movements. Each side of the neocerebellum modulates signals coming from the motor areas of the cerebral cortex of the opposite side. Since this contralateral side of the cortex controls the movements of the ipsilateral limb, the neocerebellum regulates the motor activity of the muscles on the same side of the body.

The cerebellar cortex consists of three layers: outer, middle and inner and is represented by five types of cells. The outer layer is made up of basket and stellate neurons, the middle layer is made up of Purkinje cells, and the inner layer is made up of granular and Golgi cells. With the exception of Purkinje cells, all other cells form with their processes neural networks and connections within the cerebellum. Through the axons of Purkinje cells, the cerebellar cortex is connected to the deep cerebellar nuclei and other areas of the brain. Purkinje cells have an extremely highly branched dendritic tree.

Afferent connections of the cerebellum

The cerebellar neurons receive signals via afferent fibers from various parts of the central nervous system, but their main flow comes from the spinal cord, vestibular system and cerebral cortex. The richness of the afferent connections of the cerebellum is confirmed by the ratio of afferent and efferent fibers of the cerebellum, which is 40: 1. Along the spinocerebellar pathways, mainly through the lower cerebellar peduncles, it receives information from proprioceptors about the state of activity of the spinal cord motor neurons, the state of the muscles, the tension of the tendons, and the position of the joints. Afferent signals entering the cerebellum from the vestibular apparatus and the vestibular nuclei of the brain stem bring information about the position of the body and its parts in space (body posture) and the state of balance. Corticocerebellar descending pathways are interrupted on the neurons of the pontine nuclei (cortico-pontocerebellar pathway), the red nucleus and inferior olive (corticolivocerebellar pathway), the reticular nuclei (corticoreticulocerebellar pathway) and the hypothalamic nuclei and, after their processing, proceed to the neurons of the cerebellum. Through these pathways, information about the planning, initiation and execution of movements enters the cerebellum.

Afferent signals enter the cerebellum through two types of fibers - mossy and climbing (climbing, liana-like). Mossy fibers originate in various areas of the brain, while climbing fibers originate from the inferior olivary nucleus. Mossy fibers exocytic acetylcholine diverge widely and end on the dendrites of granule cells of the cerebellar cortex. Afferent pathways formed by climbing fibers are characterized by low divergence. The synapses they form on Purkinje cells use the excitatory neurotransmitter aspartate.

The axons of granule cells travel to Purkinje cells and interneurons and exert an excitatory effect on them through the release of aspartate. Ultimately, excitation of Purkinje cells is achieved through neural connections of mossy fibers (granule cells) and through climbing fibers. These cells have an excitatory effect on neurons of the cerebellar cortex, while interneurons have an inhibitory effect through the release of GABA (Golgi neurons and basket cells) and taurine (stellate cells).

All types of neurons in the cerebellar cortex are characterized by a high frequency of neural activity during mowing. In this case, the frequency of Purkinje cell discharges changes in response to the receipt of sensory signals through afferent fibers or from proprioceptors when the activity of spinal cord motor neurons changes. Purkinje cells are efferent neurons of the cerebellar cortex that release GABA, so their effect on neurons of other brain structures is inhibitory. Most Purkinje cells send axons to the neurons of the deep (dentate, corrugated, spherical, tent) nuclei of the cerebellum, and some to the neurons of the lateral vestibular nuclei.

The arrival of excitatory signals to the neurons of the deep nuclei through the collats of mossy and climbing fibers maintains constant tonic activity in them, which is modulated by the inhibitory influences of Purkinje cells.

Table. Functional connections of the cerebellar cortex.

Efferent pathways of the cerebellum

They are divided into intracerebellar and extracerebellar. Intracerebellar pathways are represented by axons of Purkinje cells that follow the neurons of the deep nuclei. The bulk of extracerebellar efferent connections are represented by axons of neurons in the deep cerebellar nuclei, emerging as part of the nerve fibers of the cerebellar peduncles and ending with synapses on neurons of the reticular nuclei, red nucleus, inferior olives, thalamus and hypothalamus. Through neurons of the stem and thalamic nuclei, the cerebellum can influence the activity of neurons in the motor areas of the cerebral cortex, forming the descending pathways of the medial system: corticospinal, corticorubral, corticorsticular, etc. In addition, the cerebellum is connected by efferent pathways with neurons of the parietal and temporal association areas of the cerebral cortex brain

Thus, the cerebellum and the cerebral cortex are connected by numerous neural pathways. Through these pathways, the cerebellum receives information from the cortex, in particular, copies of motor programs for upcoming movements, and mainly through the dentate-thalamic pathways influences motor commands sent by the cerebral cortex to the stem motor centers and to the spinal cord.

Cerebellar functions and consequences of their impairment

Main functions of the cerebellum:

• Regulation of posture and muscle tone
• Correction of slow, purposeful movements and their coordination with postural maintenance reflexes
• Correct execution of fast, purposeful movements following commands from the cerebral cortex within the structure of the general movement program
• Participation in the regulation of autonomic functions

The cerebellum develops from the sensory structures of the rhomboid fossa region, receives numerous sensory signals from various parts and uses them to implement one of its most important functions - participation in the organization and control of the execution of movements. There is a certain similarity between the position of the cerebellum and the basal ganglia in the formations of the central nervous system that organize and control movements. Both of these CNS structures are involved in the control of movements, but do not initiate them, and are embedded in the central neural pathways connecting the motor areas of the cortex with other motor centers of the brain.

The cerebellum plays a particularly important role in assessing and comparing signals from the speed of eye movements in the orbit, movements of the head and body coming to it from the retina, proprioceptors of the ocular muscles, the vestibular analyzer and proprioceptors of the skeletal muscles during combined movements of the eyes, head and torso. It is likely that such combined signal processing is carried out by neurons of the worm, in which the selective activity of Purkinje cells on the nature, direction, and speed of movement is recorded. The cerebellum plays an exceptional role in calculating the speed and amplitude of upcoming movements when preparing their motor programs, as well as in controlling the accuracy of the execution of movement parameters that were incorporated in these programs.

Characteristics of cerebellar dysfunctions

Triad Luciani: atony, asthenia, astasia.

Dysarthria- disorder of the organization of speech motor skills.

Adiadochokinesis- slowing down reactions when changing from one type of movement to the exact opposite.

Dystonia - involuntary increase or decrease in muscle tone.

Charcot's triad: nystagmus, inertial tremor, scanned speech.

Ataxia- impaired coordination of movements.

Dysmetria- a disorder of uniformity of movement, expressed in excessive or insufficient movement.

The motor functions of the cerebellum can be judged by the nature of their impairment that occurs after damage to the cerebellum. The main manifestation of these disorders is the classic triad of symptoms - asthenia, ataxia and atony. The occurrence of the latter is a consequence of a violation of the main function of the cerebellum - control and coordination of the motor activity of motor centers located at different levels of the central nervous system. Normally, our movements are always coordinated; various muscles participate in their implementation, contracting or relaxing with the necessary force at the required time. A high degree of coordination of muscle contraction determines our ability, for example, to pronounce words in a certain sequence with the required volume and rhythm when speaking. Another example is swallowing, which involves many muscles contracting in a strict sequence. If the cerebellum is damaged, such coordination is disrupted - movements become uncertain, jerky, and jerky.

Ataxia

One of the manifestations of impaired coordination of movements is the development ataxia- unnatural, unsteady gait with widely spaced legs, abducted balancing arms, with the help of which the patient maintains body balance. The movements are of an uncertain nature, accompanied by excessive jerking throws from side to side. The patient cannot stand or walk on his toes or heels.

Dysarthria

Smoothness of movements is lost, and with bilateral damage to the cerebellar cortex, dysarthria, manifested by slow, slurred, inarticulate speech.

Adiadochokinesis

The nature of movement disorders depends on the location of damage to the cerebellar structures. Thus, impaired coordination of movements with damage to the cerebellar hemispheres is manifested by disturbances in speed, amplitude, strength, and timeliness of the beginning and end of the movement. The smoothness of the movement performed is ensured not only by a smooth increase and subsequent decrease in the force of contraction of the synergist muscles, but also by a commensurate smooth decrease in the tension of the antagonist muscles. Violations of such coordination in diseases of the neocerebellum are manifested by asynergy, uneven movements, and decreased muscle tone. A delay in the initiation of contractions of individual muscle groups can manifest as ataxia and becomes especially noticeable when performing movements that are opposite in direction (pronation and supination of the forearms) with increasing speed. The delay in movements of one of the arms (or other actions) arising due to a delay in the initiation of contractions is called adiadochokinesis.

Dysmetria

A delay in stopping an already initiated contraction of one of the antagonistic muscle groups leads to dysmetria and the inability to perform precise actions.

Intention tremor

Continuously receiving sensory information from the proprioceptors of the motor apparatus at rest and during movements, as well as information from the cerebral cortex, the cerebellum uses it to regulate, through feedback channels, the force and temporal characteristics of movements initiated and controlled by the cerebral cortex. Violation of this function of the cerebellum when it is damaged leads to tremor. A characteristic feature of tremor of cerebellar origin is its intensification at the final stage of movement - intention tremor. This distinguishes it from tremor that occurs when the basal ganglia are damaged, which manifests itself more often at rest and weakens when performing movements.

The neocerebellum is involved in motor learning, planning and control of the execution of voluntary movements. This is confirmed by observations that changes in neural activity in the deep cerebellar nuclei occur simultaneously with those in pyramidal neurons of the motor cortex even before the onset of movements. The vestibulocerebellum and spinocerebellum influence motor functions through neurons in the vestibular and reticular nuclei of the brainstem.

The cerebellum does not have direct efferent connections with the spinal cord, but under its control, realized through the motor nuclei of the brain stem, is the activity of the γ-motor neurons of the spinal cord. In this way, the cerebellum controls the sensitivity of muscle spindle receptors to decreased muscle tone and stretching. When the cerebellum is damaged, its tonic effect on γ-motor neurons weakens, which is accompanied by a decrease in the sensitivity of proprioceptors to a decrease in muscle tone and to impaired coactivation of γ- and a-motor neurons during contraction. Ultimately, this leads to decreased muscle tone at rest (hypotonia), as well as impaired smoothness and precision of movements.

Dystonia and asthenia

At the same time, another variant of tone changes develops in some muscles, when, when the interaction of y- and a-motoneurons is disrupted, the tone of the latter becomes high at rest. This is accompanied by the development of a-rigidity in individual muscles and uneven distribution of tone. This combination of hypotension in some muscles with hypertension in others is called dystonia. It is obvious that the patient's dystonia and lack of coordination make his movements uneconomical and highly energy-consuming. For this reason, patients develop asthenia- rapid fatigue and decreased muscle strength.

One of the common manifestations of insufficiency of coordination function when a number of parts of the cerebellum are damaged is an imbalance of the body and gait. In particular, if the flocculus, nodule and anterior lobe of the cerebellum are damaged, imbalance and posture disorders, dystonia, impaired coordination of semi-automatic movements and gait instability, and spontaneous ocular nystagmus may develop.

Ataxia and dysmetria

If the connections of the cerebellar hemispheres with the motor areas of the cerebral cortex are damaged, the execution of voluntary movements may be disrupted - they develop ataxia And dysmetria. In this case, the patient loses the ability to complete the started movement on time. At the final stage of the movement, tremor, uncertainty, and additional movements arise, with the help of which the patient seeks to correct the inaccuracy of the movement being performed. These changes are characteristic of dysfunctions of the cerebellum and help differentiate them from movement disorders due to damage to the basal ganglia, when patients have difficulty initiating movements and muscle tremors when bending over. To identify dysmetria, the subject is asked to perform a knee-heel or finger-to-toe test. In the latter case, a person with eyes closed should slowly bring the previously abducted hand and touch the tip of the nose with the index finger. If the cerebellum is damaged, the smooth movement of the hand is lost and its trajectory may be zigzag. At the final stage of the movement, additional vibrations and the finger may miss the target.

Asynergia, dysdiadochokinesia and dysarthria

Damage to the cerebellum may be accompanied by the development asynergy, characterized by the disintegration of complex movements; dysdiadochokinesia, manifested by difficulty or inability to perform synchronized actions with both hands. The degree of dysdiadochokinesia increases with increasing frequency of performing similar movements. Often, as a result of impaired coordination of the muscles of the speech-motor apparatus (respiratory muscles, muscles of the larynx), patients develop speech ataxia or dysarthria.

Dysfunction of the cerebellum can also be manifested by difficulties or inability to perform movements with a given rhythm and disruption of fast, ballistic movements.

From the given examples of movement disorders after damage to the cerebellum, it follows that it performs or is directly involved in the performance of a number of motor functions. Among them are maintaining muscle tone and posture, participation in maintaining body balance in space, programming upcoming movements and their implementation (participation in muscle selection, control of the duration and force of contraction of the muscles performing the movement), participation in the organization and coordination of complex movements (coordination of function motor centers that control movement). The cerebellum plays an important role in motor learning processes.

At the same time, it is known that the cerebellum develops from the sensory structures of the rhomboid fossa region and, as already mentioned, is connected by numerous afferent connections with many structures of the central nervous system. Recent data obtained by functional magnetic resonance imaging, positron emission tomography and clinical observations have given reason to believe that the motor function of the cerebellum is not its only function. The cerebellum is actively involved in the continuous monitoring and analysis of sensory, cognitive and motor information, in preliminary calculations of the likelihood of certain events occurring, associative and anticipatory learning, thereby freeing up the higher parts of the brain and cortex for higher-order functions and, in particular, consciousness.

One of the important functions of Purkinje cells VI-VII lobules of the cerebellum is participation in the implementation of the processes of the latent phase of orientation and visuospatial attention. The cerebellum prepares the brain's internal systems for upcoming events by supporting a wide range of brain systems involved in motor and non-motor functions (involving the prediction, orientation and attention systems). An increase in neural activity in the posterior areas of the cerebellum is recorded in healthy subjects during their visual selection of targets when solving problems that require attention without a motor component, when solving problems under conditions of attentional bias, and solving spatial or temporal problems.

Confirmation of the possibility of the cerebellum performing the listed functions is provided by clinical observations of the consequences that develop in humans after suffering from cerebellar diseases. It turned out that with cerebellar diseases, along with movement disorders, the hidden orientation of visual-spatial attention slows down. A healthy person, when solving problems that require spatial attention, orients their attention approximately 100 ms after presentation of the task. Patients with cerebellar damage show clear signs of attention orientation only after 800-1200 ms; their ability to quickly switch attention is impaired. Attention deficits become especially pronounced after damage to the cerebellar vermis. Damage to the cerebellum is accompanied by a decrease in cognitive functions and impaired social and cognitive development of the child.

Table of contents of the topic "Rhomboid brain. Medulla oblongata, myelencephalon, medulla oblongata. Hindbrain, metencephalon. Pons, pons. Cerebellum, cerebellum.":

Cerebellum, cerebellum, is a derivative of the hindbrain, which developed in connection with gravity receptors. Therefore, it is directly related to the coordination of movements and is an organ of the body’s adaptation to overcoming the basic properties of body mass - gravity and inertia.

Cerebellar development During the process of phylogenesis, 3 main stages passed, corresponding to changes in the animal’s modes of movement.

Cerebellum first appears in the class of cyclostomes, in lampreys, in the form of a transverse plate. In lower vertebrates (fish) there are paired ear-shaped parts (archicerebellum) And unpaired body (paleocerebellum), corresponding to the worm; in reptiles and birds the body is highly developed, and the ear-shaped parts turn into rudimentary ones. Cerebellar hemispheres arise only in mammals (neocerebellum). In humans, due to upright walking with the help of one pair of limbs (legs) and the improvement of grasping movements of the hand during labor processes, the cerebellar hemispheres achieve the greatest development, so that the cerebellum in humans is more developed than in all animals, which constitutes a specific human feature of its structure.

Cerebellum is located under the occipital lobes of the cerebral hemispheres, dorsal to the pons and medulla oblongata, and lies in the posterior cranial fossa. It has voluminous side parts, or hemispheres, hemispheria cerebelli, and the middle narrow part located between them - worm.

At the anterior margin of the cerebellum is the anterior notch, which encloses the adjacent portion of the brain stem. At the posterior margin there is a narrower posterior notch that separates the hemispheres from each other.

Surface of the cerebellum covered with a layer of gray matter that makes up the cerebellar cortex, and forms narrow convolutions - leaves of the cerebellum, folia cerebelli, separated from each other furrows, fissurae cerebelli. Among them the deepest fissura horizontalis cerebelli runs along the posterior margin of the cerebellum, separating upper surface of the hemispheres, facies superior, from lower, facies inferior. With the help of horizontal and other large grooves, the entire surface of the cerebellum is divided into row of lobules, lobuli cerebelli. Among them, it is necessary to highlight the most isolated small lobe - shred, flocculus, lying on the lower surface of each hemisphere at the middle cerebellar peduncle, as well as the part of the vermis associated with the flocculus - nodulus, nodule. Flocculus connected to nodulus through a thin strip - legs of flocculi, pedunculus flocculi, which medially passes into the thin semilunar plate - inferior medullary velum, velum medullare inferius.

This article describes in detail the structure and functions of the cerebellum, one of the most important parts of the brain. Despite its relatively small size, it controls the performance of a large number of tasks, and dysfunction of this organ has a greater impact on a person’s quality of life.

So, the cerebellum is responsible for performing purposeful movements, their speed, coordinating the body in space and maintaining muscle tone. Recent research in the field of neurophysiology indicates that it, along with the cerebral cortex, is involved in memory and thought processes.

The cerebellum of the brain is relatively small in size (about 150 g in an adult), but contains about 50% of the neurons of the entire central nervous system. Inside the cranium, it is geographically located in the posterior fossa, between the temporal lobes. Despite the connection with the cerebral hemispheres, it is controlled at the subconscious level.

The cerebellum has an optimal location in the brain, and at the same time connects with other parts of the central nervous system, which control the functioning of the entire body. For example, the inner layer of the cerebellar cortex is connected with the medulla oblongata through the lower pair of legs, and with the midbrain through the upper ones.

The cerebellum is the functional extension of the telencephalon-spinal cord axis and is located under the posterior part of the cerebral hemispheres, and in front of it is the brain stem and pons. This location of the cerebellum is due to its main purpose: it is responsible for coordinating purposeful movements and controlling the quality of their execution.

The lobes of the cerebellum also affect the functioning of the internal organs of a person - for example, with a defect in the floculonodular zone, there is a violation of the tone of the muscles running along the spine.

Structure and functions of the cerebellum

It is known that at human birth this section noticeably lags behind in development and size compared to the cerebral hemispheres. But already during the first year of life it begins to increase rapidly, reaching a lower weight limit of 120 g by the age of 6. Its development can be tracked by the intensity of the child’s mastery of his body: for example, in the first three months of life, the child cannot coordinate movements, while the body is in constant tone.

In the period from 5 to 11, this organ rapidly enlarges, when learning to sit and walk upright begins, and already at 6 years old the child has relatively good command of fine motor skills of the fingers. The final development of this organ occurs at the age of 16.

The cerebellum is not part of the human brainstem, but is an appendage of it. This part of the central nervous system is involved in almost all physiological tasks of the body. Therefore, the quality of performance of its functions depends on the physical state of the cerebellum.

To understand what role this part plays in the brain, you first need to study its structure in detail. There are currently 2 descriptions of this organ.

The first option reflects the internal structure of the cerebellum. It includes a description of the anatomical features of the constituent structures. According to him, the main function of the cerebellum of the human brain is performed with the help of the cortex of this organ.

Anatomy of the human cerebellum

Structurally, this section resembles: it consists of 2 hemispheres connected by an unpaired part - the vermis. Like the telencephalon, the cerebellum is covered on the outside with cortex or gray matter, which is dotted with grooves similar to the convolutions of the cerebral cortex.

Also, the gray matter in the body of the cerebellum forms nuclei, through which impulses are exchanged with other structures and the cerebral cortex, through pathways that run through the cerebellar peduncles.

The cerebellar cortex has a complex structure and contains 3 layers represented by 5 types of neurons.

1. Outer or molecular layer. Consists of basket and stellate neurons. With their help, the impulses sent by the pyriform Purkinje cells are inhibited.
2. Ganglion layer. Contains piriform neurons or Purkinje cells. Due to their large size, these particles are arranged in one row, and their branched processes penetrate the molecular layer. The axons of these neurons connect the cortex with the cerebellar nuclei.
3. Granular or granular layer. It has a complex structure and consists of granular, large stellate and spindle-shaped horizontal neurons. In this case, granular cells transmit impulses to pyriform cells, stellate cells, with the help of long axons, connect all parts of the cerebellar cortex, and fusiform cells combine the granular layer with the molecular one and go into the white matter.

The structure of the cerebellar cortex is determined by its main function: it processes incoming information and transmits it to the nuclei and other parts of the brain.

The leaves of the cerebellum are located on the entire surface and are outlined by grooves of different depths. The deepest of them divide the cerebellum into 3 main lobes:

1. Cerebrocerebellum;
2. Paleocerebellum;
3. The flocculo-nodular zone or archicerebellum.

With the help of 3 pairs of legs, the cerebellar system communicates with the corresponding part of the brain. Thus, the middle pair of cerebellar peduncles unites it with the pons, the upper ones with the midbrain, and the lower one with the medulla oblongata.

Inside the legs there are pathways that consist of long fibers of neurons. Depending on the direction of the signal, they are of 2 types:

1. Afferent or sensory fibers - receive incoming information;
2. Efferent or motor fibers transmit impulses between the cerebellum and parts of the brain.

Interneuronal connections are also represented by afferent mossy and climbing fibers. They start from the pons, vestibular nuclei and spinal cord, and through the cerebellar cortex are directed to the nuclei. The first (bryophytes) form intracerebellar connections, and the climbing ones connect parts of the brain and cerebellar structures.

Efferent fibers of the cortex are fibrous processes of Purkinje cells, which form the 2nd layer of the cerebellar cortex. With their help, the gray matter contacts the nuclei of the brain through the upper and lower legs. In addition, information is exchanged between cores through them.

The cerebellar nuclei are located in the white matter and consist of gray matter cells. Inside they are located closer to the center and the worm. The human cerebellum includes the following nuclei:

• toothed;
• corky;
• spherical;
• tent core.

The first three are in the lobes, and only the core of the tent is located in the worm.

The body of this section is represented by white matter, consisting of long processes of Purkinje cells and axons of afferent pathways, through which signals are sent through the cortex to other structures of this section.

The cerebellar vermis is formed by white nerve fibers. It connects the 2 hemispheres together and is responsible for maintaining posture in space and muscle tone.

Thus, the main work is performed by the gray matter of the nuclei and the cerebellar cortex, and the remaining components are engaged in the transmission of information generated as a result of the activity of the main parts.

The second method reflects the external neurophysiological structure of the cerebellum.

Thus, visually we can distinguish 3 main lobes, each of which was formed in the process of evolution.

Archicerebellum or vestibulocerebellum. The most ancient structure of the cerebellum. In humans, it is represented by the lower part of the worm containing the nucleus of the tent and the flocculonodular lobe, which consists of a nodule and a shred. It is separated from the rest by a deep prepyramidal groove.

The vestibulocerebellum forms a connection with the reticular formations of the medulla oblongata and the vestibular nuclei, which are located above the bottom of the fourth ventricle. Under its control is the vestibular apparatus, with the help of which it controls the coordination of eye and head movements, and the balance of the body in space. Damage to this lobe leads to problems with the muscles running along the spine, as a result a “drunken gait” develops, and the person loses control over the apples of the eyes.

Paleocerebellum or Spinocerebellum. Consists of the second half of the worm, the periclocular lobule, round and corky nuclei. This part is separated from the remaining lobes by the main groove. The spinocerebellar tract connects the cerebellum with the spinal cord. The paleocerebellum is involved in regulating muscle tone and controls the movement of the limbs with the help of muscles running along the spine. When this lobe is damaged, a person experiences disorientation in space.

Cerebrocerebellum or neocerebellum. This is the youngest and largest part of the cerebellum, consisting of the posterior lobe of the hemispheres and the dentate nucleus. This section is present only in mammals, but is most developed in humans, since with its help the verticalization of the body in space is controlled. The dentate nucleus sends an impulse to the cortex, then the signal is transmitted to the motor section of the cerebral cortex and returns back to the cerebellum. This is how preparation occurs for the purposeful movement of a person’s limbs, with each half controlling the actions on its part.

The main functions of the cerebellum are to coordinate movements, and it also controls their speed and direction, maintains muscle tone and body balance in space, and participates in the regulation of the autonomic system.

Each of the departments is in charge of implementing one of the tasks, but the main activity is carried out using the ganglion layer of the cerebellar cortex or, in other words, Purkinje cells. It is on their fibers that penetrate the cerebellum that the quality and speed of transmitted information depends. An interesting fact is that this organ is capable of learning, since a person, repeating the same movement, subsequently masters it perfectly, performing it “automatically”.

The influence of the cerebellum on the functioning of other body systems

Through the cerebellar pathways, this part of the brain communicates with other parts of the central nervous system. Thus, it exercises control over the coordination of movements and regulates muscle tone, and also reflexively monitors the execution of vital processes: heartbeat, breathing and digestion. That is why this small department received its second name - “small brain”, since a person’s life depends on the quality of performing these tasks. Moreover, the activity of the cerebellum is not regulated by consciousness, but is controlled by the cerebral cortex.

For example, in a stressful situation or during a long run, the heart rate increases and breathing becomes deepest. The occurrence of this behavior of the body is the work of the cerebellum - this is how the flow of blood rich in oxygen and nutrients increases to the muscle tissues, and metabolic processes are also accelerated.

The afferent pathways of the cerebellum transmit information along neuronal fibers from parts of the brain to the nuclei and cells of this organ. These pathways form a dense network, and their proportional ratio with efferent ones is 40:1. Through these connections, data is exchanged between the structures of the central nervous system.

The middle crura transmit afferent information from the cerebral cortex.

The fronto-pontine-cerebellar tract starts from the frontal gyrus of the cerebral cortex, crosses the pons and goes to the opposite peduncle and stops in the Purkinje cells.

The temporopontine-cerebellar pathway begins in the temporal lobes of the brain, then follows the same trajectory as the first type of connection.

The occipital-pontine-cerebellar tract transmits visual data from the occipital cortex of the cerebral hemispheres.
The lower legs serve as a conductor of afferent connections coming from the spinal and diencephalon.

The posterior spinocerebellar tract connects the spinal cord to the cerebellum. Transmits impulses from tendon and joint cells to the cortex of this organ.

The olivocerebellar tract consists of climbing fibers and begins in the inferior olive of the medulla oblongata and ends with Purkinje cells. In this case, the lower nucleus receives data from the cerebral cortex from the remotor areas that plan movement.

The vestibulocerebellar tract originates from the superior vestibular nucleus and transmits information through the legs to the archicerebellum. Then it switches to the processes of Purkinje cells and reaches the nucleus located in the tent.

The reticulocerebellar tract connects the reticular zone of the brain stem and reaches the cortex of the vermis.
The efferent connections of the cerebellum transmit information from the cortex of this organ to the parts of the brain, and they pass only through the upper pair of legs.

The dentate red tract starts from the dentate nucleus and ends at the red nuclei of the midbrain. It is involved in the coordination of movements and provides tone to the back muscles when changing posture. It is the control center for the limbs.

The cerebellothalamic pathway is directed to the vertebral thalamic nuclei. Through them, a connection is formed between the cerebellar cortex and the part of the cerebral cortex responsible for motor movements.

Cerebellar-reticular tract - connects the cerebellum with the reticular nuclei of the brain stem, which control breathing, the cardiovascular system and provide the body's protective reflexes: sneezing, coughing, chewing, swallowing and sucking.

The cerebellovestibular tract consists of long fibers of Purkinje cells and follows from the tent nucleus to the nuclei of the vestibular apparatus. Directly through this pathway, the cerebellum maintains body balance and regulates muscle tone while maintaining posture.

In addition, an afferent connection runs through the upper pair of legs, connecting the spinal processes of neurons through the diencephalon and pons, and then through the cerebellar cortex with the dentate nucleus, which is located in the cerebrocerebellum.

Thus, this department serves as the main clarifying subcortical apparatus of the central nervous system (CNS).

Symptoms of cerebellar damage

Failure in the functioning of this organ can be determined by minor changes in motor activity or the inability to hold a posture in one position. Thus, the patient may not have a reflex to point his leg in the direction of falling, but a small push is enough for him to fall.

In medicine, this phenomenon is called static ataxia, and its cause lies in the damage of the worm. In this state, the patient tries to spread his legs as wide as possible to maintain balance. To test this reflex, the doctor asks the sick person to stand up and bring their legs together, then close their eyes and stretch their arms forward.

If the cerebellar vermis is truly damaged, then the body usually tilts backward; if the hemispheres are damaged, then the sick person leans towards the affected lobe. If the condition is severe, the patient will not be able to stand up, and difficulties will arise in maintaining a sitting posture.

With extensive damage to the hemispheres, the appearance of dynamic or kinetic ataxia is noted. In this case, the patient loses the ability to accurately carry out movements. Diagnosis of such disorders consists of performing certain exercises or tests under the supervision of a doctor.

With eyes closed, the patient is asked to stand up straight, then stretch his arms straight out in front of him and touch the tip of his nose. If one of the lobes is damaged, the index finger deviates towards it.

It is proposed to rotate your hands simultaneously and in one direction with your eyes closed; if one of the hemispheres is disrupted, the hand on its side will lag behind.

In the supine position, you need to lift one of your legs and then lower the heel of that leg onto the knee of the other. If everything went well, the doctor suggests lowering the heel further down the bone. If the leg begins to slip, this indicates the development of pathology.

Another simple way to test the functions of this organ is to be able to hold a full vessel of water without spilling a drop.

The patient has a deterioration in speech: rhythm appears, sentences lose meaning, and words are stressed incorrectly. Tremors in the limbs and changes in handwriting are also observed.

If the disturbances affect the cerebellar nuclei, then the patient experiences convulsive contractions of the muscles of the limbs, inertial trembling in the fingers when completing a movement, the movement of the eyeballs cannot be controlled, rhythmic speech appears and muscle tone decreases.

The cerebellar peduncles transfer received information from parts of the brain to the cortex and nuclei, and back through efferent communication they give a command to perform a certain task, therefore, when this structure is damaged, different symptoms are observed. For example, if the upper pair of crura and the dentate nucleus are damaged, choreic hyperkinesis develops, which is characterized by rapid chaotic movements of the facial muscles, reminiscent of a grimace, the autonomic functions of the cerebellum cease to be performed - breathing becomes erratic, cardiac arrhythmia and surges in blood pressure may be observed.

A number of diseases, both congenital and acquired, are also characterized by atrophy of the structures of this organ. For example, in Marie-Foy-Alajouanine disease, Purkinje neurons, the granular layer of the cerebellar cortex, and part of the vermis are damaged. In this case, the following symptoms are noted: gait disturbance, decreased tone in the lower extremities. There may be little or no hand shaking. Such changes are most often characteristic of middle-aged and elderly people.

With such a congenital disease as Chiari disease, a low location of the cerebellar tonsils is noted. Depending on the type of disease, the manifestation of clinical signs may differ, but most often there is pain in the neck and its muscles, nausea and vomiting occurs, independent of food intake. With different degrees of prolapse, the following symptoms may also appear: speech dysfunction, noise in the head, frequent dizziness, impaired breathing and muscle tone in the limbs, numbness of the arms and legs, changes in blood pressure.

Consequences of defeats

In a healthy person, all movements are clearly coordinated, and the muscles with which they are produced contract and relax in the required sequence and with the appropriate strength. This can be observed when performing unconditioned reflexes such as breathing or swallowing. For example, when swallowing food or water, the muscles contract in a strict sequence, and a malfunction in their work can lead to the reflux of what is swallowed into the respiratory tract.

Damage to the structures causes dysfunction of the cerebellum. The symptoms are expressed in the following signs of the disorder - the patient develops asthenia, ataxia and atony. These disorders arise due to the destruction of the motor centers of movements responsible for performing basic tasks.

Types and symptoms of lesions

Asthenia is expressed in rapid muscle fatigue and a decrease in the strength of their contractions.

Ataxia is manifested by an uncertain, shaky gait, while the patient places his legs wide apart and has his arms in different directions to balance the body position in space. At the same time, the steps become unnatural and jerky; as a result, the sick person cannot rise on his toes or fall only on his heels.

Atony is the lack of normal tone of the muscles of the skeleton and internal organs. It manifests itself, for example, in digestion or blood pressure disorders.

These three symptoms occur first and are the so-called Luciani triad.

Dysarthria . This condition is characterized by a loss of plasticity in the movements produced. Also, when all areas of the cerebellar cortex are damaged, slow, inarticulate monotonous speech is observed.

Dysmetria is characterized by a delay in muscle contractions at the end of a movement and manifests itself in the difficulty of performing precise actions.

Adiadochokinesis. Symptoms of the lesion depend on the location of the damaged area. For example, when the hemispheres are damaged, the speed, amplitude, and strength of movements change, and the motor reaction to external stimuli is also delayed. When the neocerebellum is damaged, there is a decrease in muscle tone, while movements become jerky, the patient loses the ability to synchronously act with both limbs - one of them will lag behind.

Inertial tremor appears when the cerebellum is unable to process signals received from its own cortex and the cerebral cortex, while trembling of the limbs is noted at the end of the completed action. This behavior is a hallmark of disorders in the structure of this organ.

The neocerebellum is involved in motor learning, planning and control of movements. This feature is explained by changes in the activity of neurons in the nuclei located in its thickness. This activity occurs synchronously with the motor cortex, even before movement begins. The vestibulocerebellum and spinocerebellum are also involved in motor functions through the vestibular and reculatory nuclei located in the brainstem.

The efferent pathways of the cerebellum are located in the superior peduncles, so they do not connect it directly with the spinal cord, and the interaction between these sections is carried out using the motor nuclei of the brain stem. In this way, the cerebellum can control and make changes to the trajectory or force of movement of the limb muscles. Therefore, when the legs are damaged, the connection between the neurons of the nuclei weakens, which leads to a decrease in the sensitivity of the receptors responsible for muscle tone. Thus, there is a violation of plasticity and accuracy of movements.

Dystonia and asthenia. Sometimes, different tone is observed in the motor muscles, while there is a disturbance in the sense of balance in space, the patient is not able to coordinate the movements of the limbs. The process of standing or moving forward expends a large amount of energy, so as a result, asthenia or rapid muscle fatigue and a decrease in the strength of their contraction develop.

Most often, this condition is characterized by a change in gait and body balance, in particular, when the flocculo-nodular zone is damaged, dystonia is noted, the inability to maintain a certain position in space, the apples of the eyes make spontaneous, uncontrolled movements.

Ataxia and dysmetria. When the efferent connection of the upper legs with the motor areas of the cerebral cortex is damaged, ataxia and dysmetria develop. At the same time, a person is not able to complete an action that has been started correctly, since trembling and uncertainty develop at the end. Such a violation can be detected with a finger-nose and knee-heel test - the patient, trying to complete the movement he has started, performs additional actions.

As a result of damage to the structures and connections of the cerebellum, there may be a breakdown of complex movements (asynergia), the inability to synchronize the actions of both hands (dysdiadochokinesia), and also as a result of improper functioning of the muscles responsible for the patient’s speech, the development of speech ataxia or dysarthria is noted.

With all these deviations, the role of the cerebellum in the regulation of motor activity is clearly visible, since when this organ is damaged, there is a violation of any motor activity of the body, be it maintaining a posture or participating in programming a planned action. The dependence of the work of the cerebellum on its physiological state is clearly visible in the diagnosis of certain diseases.

For example, agenesis of the cerebellar vermis leads to impaired motor function; symptoms become noticeable in the first days of a child’s life and are manifested in the inability to maintain even breathing, hold the head level and make coordinated muscle movements.

An ascitoma, or tumor, can be located in any part of the brain, but in children it most often forms in the area of ​​the cerebellar vermis. It is a pathology and develops due to improper division of specific ascites cells that protect neurons from negative effects. Depending on the degree of malignancy, it can be piloid, fibrillary, anaplastic, or develop into glioblastoma. The first 2 occur in childhood, and the latter in adulthood and old age. A distinctive feature of this disease in the first stages is a violation of orientation in space and coordination of movements.

Diagnosis of problems

Some congenital pathologies, such as aplasia of the cerebellar vermis, are most often diagnosed during an ultrasound examination of the fetus during pregnancy. Unfortunately, such children are most often born with a large number of neurological abnormalities, the signs and symptoms of which appear in the first months of life, which is why they are in dire need of rehabilitation and treatment. In such a situation, neurologists usually prescribe developmental massage, exercises for the development of the vestibular apparatus, as well as taking neurostimulating drugs.

Diagnosis of disorders of the structures of this organ begins in the neurologist’s office, with the help of tests and special exercises indicating the development of any pathology. Thus, when one hemisphere of the cerebellum is destroyed, the damaged lobe is identified using the finger-nose test, when the deviation of the finger will indicate the affected area. If the ancient cerebellum or archicerebellum is damaged, then the patient experiences a lack of coordination of eye movements and the balance of the body in space is lost.

Diagnosis of cerebellar ataxia caused by tumors of various natures is carried out in conjunction with other medical specialists, such as a neurologist, endocrinologist, traumatologist and oncologist. Typically, examination of the cerebellum, like other parts of the brain, involves the use of a large amount of equipment and may include:

• spinal puncture and cerebrospinal fluid analysis;
• CT and MRI of the head;
• dopplerography;
• electronystagmography (allows you to evaluate the conduction pathways);
• DNA diagnostics.

Adenomas and cysts are detected using MRI of the brain. This diagnostic method makes it possible to identify cerebellar disease at an early stage of development. Therapy in this case depends on the size and quality of the tumor. Thus, when treating a malignant tumor, radiation therapy or surgical removal of the tumor can be used.

It is important to realize that disturbances in the functioning of the cerebellum and its dysfunction require careful attention, since the connection of this part of the brain with other structures of the human body is obvious. And treatment with folk remedies will only worsen the disease, so at the first signs of damage to this organ you need to consult a specialist.

Video

The cerebellum is a part of the vertebrate brain responsible for coordinating movements, regulating balance and muscle tone. In humans, it is located behind the medulla oblongata and the pons, under the occipital lobes of the cerebral hemispheres. Through three pairs of peduncles, the cerebellum receives information from the cerebral cortex, the basal ganglia of the extrapyramidal system, the brain stem and the spinal cord. In different vertebrate taxa, relationships with other parts of the brain may vary.

In vertebrates with a cerebral cortex, the cerebellum is a functional branch of the main axis of the cerebral cortex - the spinal cord. The cerebellum receives a copy of afferent information transmitted from the spinal cord to the cerebral cortex, as well as efferent information from the motor centers of the cerebral cortex to the spinal cord. The first signals the current state of the controlled variable, and the second gives an idea of ​​the required final state. By comparing the first and second, the cerebellar cortex can calculate the error, which it reports to the motor centers. In this way, the cerebellum continuously corrects both voluntary and automatic movements.

Although the cerebellum is connected to the cerebral cortex, its activity is not controlled by consciousness.

Cerebellum - Comparative Anatomy and Evolution

The cerebellum developed phylogenetically in multicellular organisms due to the improvement of voluntary movements and the complication of the structure of body control. The interaction of the cerebellum with other parts of the central nervous system allows this part of the brain to provide precise and coordinated body movements in various external conditions.

The cerebellum varies greatly in size and shape across different groups of animals. The degree of its development correlates with the degree of complexity of body movements.

Representatives of all classes of vertebrates have a cerebellum, including cyclostomes, in which it has the shape of a transverse plate extending across the anterior section of the rhomboid fossa.

The functions of the cerebellum are similar in all classes of vertebrates, including fish, reptiles, birds and mammals. Even cephalopods have a similar brain structure.

There are significant differences in shape and size among different species. For example, the cerebellum of lower vertebrates is connected to the hindbrain by a continuous plate in which the fiber bundles are not anatomically distinguished. In mammals, these bundles form three pairs of structures called the cerebellar peduncles. Through the cerebellar peduncles, the cerebellum communicates with other parts of the central nervous system.

Cyclostomes and fish

The cerebellum has the greatest range of variability among the sensorimotor centers of the brain. It is located at the anterior edge of the hindbrain and can reach enormous sizes, covering the entire brain. Its development depends on several reasons. The most obvious is related to pelagic lifestyle, predation, or the ability to swim efficiently in the water column. The cerebellum reaches its greatest development in pelagic sharks. It forms real grooves and convolutions, which are absent in most bony fish. In this case, the development of the cerebellum is caused by the complex movement of sharks in the three-dimensional environment of the world's oceans. The requirements for spatial orientation are too great for it not to affect the neuromorphological support of the vestibular apparatus and sensorimotor system. This conclusion is confirmed by a study of the brains of sharks that live near the bottom. The nurse shark does not have a developed cerebellum, and the cavity of the fourth ventricle is completely open. Its habitat and way of life do not impose such stringent requirements for spatial orientation as those of the long-tipped shark. The consequence was the relatively modest size of the cerebellum.

The internal structure of the cerebellum in fish is different from that of humans. The fish cerebellum does not contain deep nuclei and there are no Purkinje cells.

The size and shape of the cerebellum in proto-aquatic vertebrates can change not only due to a pelagic or relatively sedentary lifestyle. Since the cerebellum is the center of analysis of somatic sensitivity, it takes an active part in the processing of electroreceptor signals. Many proto-aquatic vertebrates have electroreception. In all fish that have electroreception, the cerebellum is extremely well developed. If electroreception of one’s own electromagnetic field or external electromagnetic fields becomes the main afferentation system, then the cerebellum begins to serve as a sensory and motor center. Often the size of their cerebellum is so large that it covers the entire brain from the dorsal surface.

Many vertebrate species have brain regions that are similar to the cerebellum in terms of cellular cytoarchitecture and neurochemistry. Most species of fish and amphibians have a lateral line organ that detects changes in water pressure. The area of ​​the brain that receives information from this organ, the so-called octavollateral nucleus, has a structure similar to the cerebellum.

Amphibians and reptiles

In amphibians, the cerebellum is very poorly developed and consists of a narrow transverse plate above the rhomboid fossa. In reptiles, there is an increase in the size of the cerebellum, which has an evolutionary basis. A suitable environment for the formation of the nervous system in reptiles could be giant coal heaps, consisting mainly of club mosses, horsetails and ferns. In such multi-meter rubble of rotten or hollow tree trunks, ideal conditions could have developed for the evolution of reptiles. Modern coal deposits directly indicate that such tree trunk debris was very widespread and could become a large-scale transitional environment for amphibians to reptiles. To take advantage of the biological benefits of woody debris, it was necessary to acquire several specific qualities. Firstly, it was necessary to learn to navigate well in a three-dimensional environment. This is not an easy task for amphibians because their cerebellum is very small. Even the specialized tree frogs, which are a dead-end evolutionary lineage, have a much smaller cerebellum than reptiles. In reptiles, neuronal connections are formed between the cerebellum and the cerebral cortex.

The cerebellum in snakes and lizards, as in amphibians, is located in the form of a narrow vertical plate above the anterior edge of the rhomboid fossa; in turtles and crocodiles it is much wider. Moreover, in crocodiles its middle part differs in size and convexity.

Birds

The avian cerebellum consists of a larger middle part and two small lateral appendages. It completely covers the diamond-shaped fossa. The middle part of the cerebellum is divided by transverse grooves into numerous leaves. The ratio of the mass of the cerebellum to the mass of the entire brain is greatest in birds. This is due to the need for quick and accurate coordination of movements in flight.

In birds, the cerebellum consists of a massive middle part, usually intersected by 9 convolutions, and two small lobes, which are homologous to the cerebellum of mammals, including humans. Birds are characterized by a high perfection of the vestibular apparatus and movement coordination system. A consequence of the intensive development of coordinating sensorimotor centers was the appearance of a large cerebellum with real folds - grooves and convolutions. The avian cerebellum was the first structure of the vertebrate brain to have a cortex and a folded structure. Complex movements in a three-dimensional environment have led to the development of the avian cerebellum as a sensorimotor center for coordination of movements.

Mammals

A distinctive feature of the mammalian cerebellum is the enlargement of the lateral portions of the cerebellum, which primarily interact with the cerebral cortex. In the context of evolution, the enlargement of the lateral cerebellum occurs along with the enlargement of the frontal lobes of the cerebral cortex.

In mammals, the cerebellum consists of the vermis and paired hemispheres. Mammals are also characterized by an increase in the surface area of ​​the cerebellum due to the formation of grooves and folds.

In monotremes, as in birds, the middle section of the cerebellum predominates over the lateral sections, which are located in the form of minor appendages. In marsupials, edentates, chiropterans and rodents, the middle section is not inferior to the lateral ones. Only in carnivores and ungulates the lateral parts become larger than the middle section, forming the cerebellar hemispheres. In primates, the middle section is already very undeveloped in comparison with the hemispheres.

In the predecessors of man and lat. homo sapiens during the Pleistocene, the expansion of the frontal lobes occurred at a faster rate compared to the cerebellum.

Cerebellum - Anatomy of the human cerebellum

A peculiarity of the human cerebellum is that, like the cerebrum, it consists of the right and left hemispheres and an unpaired structure connecting them - the “worm”. The cerebellum occupies almost the entire posterior cranial fossa. The diameter of the cerebellum is significantly larger than its anteroposterior size.

The mass of the cerebellum in an adult ranges from 120 to 160 g. By the time of birth, the cerebellum is less developed compared to the cerebral hemispheres, but in the first year of life it develops faster than other parts of the brain. A pronounced enlargement of the cerebellum is observed between the 5th and 11th months of life, when the child learns to sit and walk. The mass of the cerebellum of a newborn is about 20 g, at 3 months it doubles, at 5 months it increases 3 times, at the end of the 9th month - 4 times. Then the cerebellum grows more slowly, and by the age of 6 years its weight reaches the lower limit of the adult norm - 120 g.

Above the cerebellum lie the occipital lobes of the cerebral hemispheres. The cerebellum is separated from the cerebrum by a deep fissure, into which a process of the dura mater of the brain is wedged - the tentorium cerebellum, stretched over the posterior cranial fossa. In front of the cerebellum is the pons and medulla oblongata.

The cerebellar vermis is shorter than the hemispheres, therefore, notches are formed at the corresponding edges of the cerebellum: on the anterior edge - anterior, on the posterior edge - posterior. The most protruding sections of the anterior and posterior edges form the corresponding anterior and posterior corners, and the most protruding lateral sections form the lateral corners.

The horizontal fissure, running from the middle cerebellar peduncles to the posterior notch of the cerebellum, divides each hemisphere of the cerebellum into two surfaces: the upper, relatively flat and obliquely descending to the edges, and the convex lower. With its lower surface, the cerebellum is adjacent to the medulla oblongata, so that the latter is pressed into the cerebellum, forming an invagination - the cerebellar valley, at the bottom of which the vermis is located.

The cerebellar vermis has superior and inferior surfaces. Grooves running longitudinally along the sides of the vermis: shallower on the anterior surface and deeper on the posterior surface—separate it from the cerebellar hemispheres.

The cerebellum consists of gray and white matter. The gray matter of the hemispheres and the cerebellar vermis, located in the superficial layer, forms the cerebellar cortex, and the accumulation of gray matter in the depths of the cerebellum forms the cerebellar nuclei. White matter - the cerebellar body of the cerebellum, lies deep in the cerebellum and, through three pairs of cerebellar peduncles, connects the gray matter of the cerebellum with the brain stem and spinal cord.

Worm

The cerebellar vermis controls posture, tone, supporting movements and balance of the body. Worm dysfunction in humans manifests itself in the form of static-locomotor ataxia.

Slices

The surfaces of the hemispheres and the cerebellar vermis are divided by more or less deep cerebellar fissures into numerous arched cerebellar sheets of various sizes, most of which are located almost parallel to one another. The depth of these grooves does not exceed 2.5 cm. If it were possible to straighten the leaves of the cerebellum, then the area of ​​its cortex would be 17 x 120 cm. Groups of convolutions form individual lobules of the cerebellum. The lobules of the same name in both hemispheres are delimited by the same groove, which passes through the vermis from one hemisphere to the other, as a result of which the two - right and left - lobules of the same name in both hemispheres correspond to a certain lobe of the vermis.

The individual lobules form the lobes of the cerebellum. There are three such lobes: anterior, posterior and flocnodular.

The vermis and hemispheres are covered with gray matter, within which there is white matter. The white matter branches out and penetrates into each gyrus in the form of white stripes. On sagittal sections of the cerebellum, a peculiar pattern is visible, called the “tree of life.” The subcortical nuclei of the cerebellum lie within the white matter.

10. tree of life of the cerebellum
11. Cerebellum medulla
12. white stripes
13. cerebellar cortex
18. dentate nucleus
19. dentate core gate
20. corky nucleus
21. globular nucleus
22. tent core

The cerebellum is connected to neighboring brain structures through three pairs of peduncles. The cerebellar peduncles are systems of pathways whose fibers run to and from the cerebellum:

1. The inferior cerebellar peduncles extend from the medulla oblongata to the cerebellum.
2. Middle cerebellar peduncles - from the pons to the cerebellum.
3. The superior cerebellar peduncles lead to the midbrain.

Cores

The cerebellar nuclei are paired clusters of gray matter, located in the thickness of the white matter, closer to the middle, that is, the cerebellar vermis. The following kernels are distinguished:

1. the dentate lies in the medial-inferior areas of the white matter. This nucleus is a wave-like curved plate of gray matter with a small break in the medial section, which is called the hilum of the dentate nucleus. The serrated nucleus is similar to the olive nucleus. This similarity is not accidental, since both nuclei are connected by pathways, olivocerebellar fibers, and each gyrus of one nucleus is similar to the gyrus of the other.
2. corky is located medially and parallel to the dentate nucleus.
3. the globular lies somewhat medial to the corky nucleus and on a section can be presented in the form of several small balls.
4. the tent core is localized in the white matter of the worm, on both sides of its median plane, under the uvula lobule and the central lobule, in the roof of the fourth ventricle.

The tent nucleus, being the most medial, is located on the sides of the midline in the area where the tent protrudes into the cerebellum. Lateral to it are the spherical, cork-shaped and dentate nuclei, respectively. The named nuclei have different phylogenetic ages: nucleus fastigii belongs to the most ancient part of the cerebellum, associated with the vestibular apparatus; nuclei emboliformis et globosus - to the old part, which arose in connection with movements of the body, and nucleus dentatus - to the youngest, developed in connection with movement with the help of the limbs. Therefore, when each of these parts is damaged, various aspects of the motor function are disrupted, corresponding to different stages of phylogenesis, namely: when the archicerebellum is damaged, the balance of the body is disturbed, when paleocerebellum is damaged, the work of the muscles of the neck and torso is disrupted, and when neocerebellum is damaged, the work of the muscles of the limbs is disrupted.

The nucleus of the tent is located in the white matter of the “worm”, the remaining nuclei lie in the cerebellar hemispheres. Almost all information leaving the cerebellum is switched to its nuclei.

Blood supply

Arteries

Three large paired arteries originate from the vertebrates and the basilar artery, delivering blood to the cerebellum:

1. superior cerebellar artery;
2. anterior inferior cerebellar artery;
3. posterior inferior cerebellar artery.

The cerebellar arteries pass along the ridges of the cerebellar convolutions, without forming loops in its grooves, as do the arteries of the cerebral hemispheres. Instead, small vascular branches extend from them into almost every groove.

Superior cerebellar artery

It arises from the upper part of the basilar artery at the border of the pons and the cerebral peduncle before its division into the posterior cerebral arteries. The artery goes below the trunk of the oculomotor nerve, bends around the anterior peduncle of the cerebellum from above and at the level of the quadrigeminal, under the tentorium, turns back at a right angle, branching on the upper surface of the cerebellum. Branches depart from the artery that supply blood to:

• inferior colliculus of the quadrigeminal;
• superior cerebellar peduncles;
• dentate nucleus of the cerebellum;
• upper parts of the vermis and cerebellar hemispheres.

The initial parts of the branches supplying blood to the upper parts of the vermis and the surrounding areas may be located within the posterior part of the tentorium notch, depending on the individual size of the tentorial foramen and the degree of physiological protrusion of the vermis into it. Then they cross the edge of the tentorium of the cerebellum and go to the dorsal and lateral parts of the upper parts of the hemispheres. This topographical feature makes the vessels vulnerable to possible compression by the most elevated part of the vermis when the cerebellum herniates into the posterior part of the tentorial foramen. The result of such compression is partial and even complete infarctions of the cortex of the upper hemispheres and the cerebellar vermis.

The branches of the superior cerebellar artery widely anastomose with the branches of both inferior cerebellar arteries.

Anterior inferior cerebellar artery

It arises from the initial part of the basilar artery. In most cases, the artery passes along the lower edge of the pons in an arch with its convexity facing downwards. The main trunk of the artery is most often located anterior to the abducens nerve root, goes outward and passes between the roots of the facial and vestibulocochlear nerves. Next, the artery bends around the flocculus from above and branches on the anteroinferior surface of the cerebellum. In the area of ​​the flocculus there can often be two loops formed by the cerebellar arteries: one - the posterior inferior, the other - the anterior inferior.

The anterior inferior cerebellar artery, passing between the roots of the facial and vestibulocochlear nerves, gives off the labyrinthine artery, which goes to the internal auditory canal and, together with the auditory nerve, penetrates the inner ear. In other cases, the labyrinthine artery arises from the basilar artery. The terminal branches of the anterior inferior cerebellar artery supply the roots of the VII-VIII nerves, the middle cerebellar peduncle, the flocculus, the anterior inferior parts of the cerebellar hemisphere cortex, and the choroid plexus of the fourth ventricle.

The anterior villous branch of the fourth ventricle departs from the artery at the level of the flocculus and penetrates the plexus through the lateral aperture.

Thus, the anterior inferior cerebellar artery supplies blood to:

• inner ear;
• roots of the facial and vestibulocochlear nerves;
• middle cerebellar peduncle;
• flocculo-nodular lobule;
• choroid plexus of the fourth ventricle.

The area of ​​their blood supply in comparison with the rest of the cerebellar arteries is the smallest.

Posterior inferior cerebellar artery

It arises from the vertebral artery at the level of the decussation of the pyramids or at the lower edge of the olive. The diameter of the main trunk of the posterior inferior cerebellar artery is 1.5-2 mm. The artery goes around the olive, rises up, turns and passes between the roots of the glossopharyngeal and vagus nerves, forming loops, then descends between the inferior cerebellar peduncle and the inner surface of the tonsil. Then the artery turns outward and passes to the cerebellum, where it diverges into internal and external branches, the first of which rises along the vermis, and the second goes to the lower surface of the cerebellar hemisphere.

The artery can form up to three loops. The first loop, convexly directed downward, is formed in the area of ​​the groove between the pons and the pyramid, the second loop with convexity upward is formed on the inferior cerebellar peduncle, and the third loop directed downward lies on the inner surface of the amygdala. From the trunk of the posterior inferior cerebellar artery branches go to:

• ventrolateral surface of the medulla oblongata. Damage to these branches causes the development of Wallenberg-Zakharchenko syndrome;
• amygdala;
• the inferior surface of the cerebellum and its nuclei;
• roots of the glossopharyngeal and vagus nerves;
• choroid plexus of the fourth ventricle through its median aperture in the form of the posterior villous branch of the fourth ventricle).

Vienna

The veins of the cerebellum form a wide network on its surface. They anastomose with the veins of the cerebrum, brain stem, spinal cord and flow into nearby sinuses.

The superior vein of the cerebellar vermis collects blood from the superior vermis and adjacent parts of the cortex of the superior surface of the cerebellum and, above the quadrigeminal area, flows into the greater cerebral vein below.

The inferior vein of the cerebellar vermis receives blood from the inferior vermis, the inferior surface of the cerebellum and the tonsil. The vein runs posteriorly and upward along the groove between the cerebellar hemispheres and flows into the straight sinus, less often into the transverse sinus or into the sinus drainage.

The superior cerebellar veins pass along the superolateral surface of the brain and empty into the transverse sinus.

The inferior cerebellar veins, collecting blood from the inferolateral surface of the cerebellar hemispheres, flow into the sigmoid sinus and the superior petrosal vein.

Cerebellum - Neurophysiology

The cerebellum is a functional branch of the main axis “cerebral cortex - spinal cord”. On the one hand, sensory feedback is closed in it, that is, it receives a copy of afferentation, on the other hand, a copy of efferentation from motor centers also comes here. In technical terms, the first signals the current state of the controlled variable, and the second gives an idea of ​​​​the desired final state. By comparing the first and second, the cerebellar cortex can calculate the error, which it reports to the motor centers. In this way, the cerebellum continuously corrects both intentional and automatic movements. In lower vertebrates, information also comes to the cerebellum from the acoustic region, which registers sensations related to balance supplied by the ear and lateral line, and in some even from the olfactory organ.

Phylogenetically, the most ancient part of the cerebellum consists of a flocculus and a nodule. Vestibular inputs predominate here. In evolutionary terms, the structures of the archicerebellum appear in the class of cyclostomes in lampreys, in the form of a transverse plate spreading across the anterior section of the rhomboid fossa. In lower vertebrates, the archicerebellum is represented by paired ear-shaped parts. In the process of evolution, a decrease in the size of the structures of the ancient part of the cerebellum is noted. Archicerebellum is the most important component of the vestibular apparatus.

The “old” structures in humans also include the region of the vermis in the anterior lobe of the cerebellum, the pyramid, the uvula of the vermis and the periclotch. The paleocerebellum receives signals mainly from the spinal cord. Paleocerebellum structures appear in fish and are present in other vertebrates.

The medial elements of the cerebellum give projections to the tent nucleus, as well as to the spherical and cortical nuclei, which in turn form connections mainly with the stem motor centers. Deiters' nucleus, the vestibular motor center, also directly receives signals from the vermis and the flocculonodular lobe.

Damage to the archi- and paleocerebellum leads primarily to imbalances, as with pathology of the vestibular apparatus. A person experiences dizziness, nausea and vomiting. Oculomotor disorders in the form of nystagmus are also typical. It is difficult for patients to stand and walk, especially in the dark, to do this they have to grab onto something with their hands; the gait becomes unsteady, as if in a state of intoxication.

The lateral elements of the cerebellum receive signals mainly from the cerebral cortex through the nuclei of the pons and inferior olive. Purkinje cells of the cerebellar hemispheres give projections through the lateral dentate nuclei to the motor nuclei of the thalamus and further to the motor areas of the cerebral cortex. Through these two inputs, the cerebellar hemispheres receive information from cortical areas that are activated during the preparation phase for movement, that is, participating in its “programming.” Neocerebellum structures are found only in mammals. At the same time, in humans, due to upright posture and improvement of hand movements, they have achieved the greatest development in comparison with other animals.

Thus, some of the impulses generated in the cerebral cortex reach the opposite hemisphere of the cerebellum, bringing information not about what was done, but only about the active movement planned for execution. Having received such information, the cerebellum instantly sends impulses that correct voluntary movement mainly by extinguishing inertia and the most rational regulation of muscle tone of agonists and antagonists. As a result, clarity and precision of voluntary movements are ensured, and any inappropriate components are eliminated.

Functional plasticity, motor adaptation and motor learning

The role of the cerebellum in motor adaptation has been demonstrated experimentally. If vision is impaired, the vestibulo-ocular reflex of compensatory eye movement when turning the head will no longer correspond to the visual information received by the brain. A subject wearing prism glasses initially finds it very difficult to move correctly in the environment, but after a few days he adapts to the anomalous visual information. At the same time, clear quantitative changes in the vestibulo-ocular reflex and its long-term adaptation were noted. Experiments with the destruction of nerve structures showed that such motor adaptation is impossible without the participation of the cerebellum. The plasticity of cerebellar functions and motor learning, the definition of their neural mechanisms, was described by David Marr and James Albus.

The plasticity of the cerebellar function is also responsible for motor learning and the development of stereotypical movements, such as writing, typing on a keyboard, etc.

Although the cerebellum is connected to the cerebral cortex, its activity is not controlled by consciousness.

Functions

The functions of the cerebellum are similar across species, including humans. This is confirmed by their disruption during damage to the cerebellum in experiments in animals and by the results of clinical observations in diseases affecting the cerebellum in humans. The cerebellum is a brain center that is extremely important for coordinating and regulating motor activity and maintaining posture. The cerebellum works mainly reflexively, maintaining the balance of the body and its orientation in space. It also plays an important role in locomotion.

Accordingly, the main functions of the cerebellum are:

1. coordination of movements
2. balance regulation
3. regulation of muscle tone

Pathways

The cerebellum is connected to other parts of the nervous system through numerous pathways that pass through the cerebellar peduncles. There are afferent and efferent pathways. Efferent pathways are present only in the upper legs.

The cerebellar pathways do not cross at all or cross twice. Therefore, with half damage to the cerebellum itself or unilateral damage to the cerebellar peduncles, the symptoms of the lesion develop on the affected sides.

Upper legs

Efferent pathways pass through the superior cerebellar peduncles, with the exception of the Gowers afferent pathway.

1. Anterior spinocerebellar tract - the first neuron of this tract starts from the proprioceptors of muscles, joints, tendons and periosteum and is located in the spinal ganglion. The second neuron is the cells of the posterior horn of the spinal cord, the axons of which pass to the opposite side and rise up in the anterior part of the lateral column, pass the medulla oblongata, the pons, then cross again and through the upper legs enter the cortex of the cerebellar hemispheres, and then into the dentate nucleus .
2. Dentate red tract - originates from the dentate nucleus and passes through the superior cerebellar peduncles. These pathways cross-cross twice and end at the red nuclei. Axons of neurons from the red nuclei form the rubrospinal tract. After leaving the red nucleus, this pathway crosses again, descends in the brain stem, as part of the lateral column of the spinal cord, and reaches the α- and γ-motoneurons of the spinal cord.
3. Cerebellothalamic tract - goes to the nuclei of the thalamus. Through them, the cerebellum connects with the extrapyramidal system and the cerebral cortex.
4. Cerebellar-reticular tract - connects the cerebellum with the reticular formation, from which the reticular-spinal tract begins.
5. The cerebellar-vestibular tract is a special pathway because, unlike other pathways that begin in the cerebellar nuclei, it consists of axons of Purkinje cells heading to the lateral vestibular nucleus of Deiters.

Middle legs

The middle cerebellar peduncles carry afferent pathways that connect the cerebellum to the cerebral cortex.

1. Fronto-pontine-cerebellar pathway - starts from the anterior and middle frontal gyri, passes through the anterior thigh of the internal capsule to the opposite side and switches to the cells of the pons, which represent the second neuron of this pathway. From them it enters the contralateral middle cerebellar peduncle and ends on the Purkinje cells of its hemispheres.
2. Temporopontine-cerebellar tract - starts from the cells of the cortex of the temporal lobes of the brain. Otherwise, its course is similar to that of the fronto-pontine-cerebellar pathway.
3. The occipital-pontine-cerebellar tract begins from the cells of the cortex of the occipital lobe of the brain. Transmits visual information to the cerebellum.

Lower legs

In the lower cerebellar peduncles there are afferent pathways running from the spinal cord and brain stem to the cerebellar cortex.

1. The posterior spinocerebellar tract connects the cerebellum to the spinal cord. Conducts impulses from proprioceptors of muscles, joints, tendons and periosteum, which reach the posterior horns of the spinal cord as part of sensory fibers and dorsal roots of the spinal nerves. In the posterior horns of the spinal cord they switch to the so-called. Clark cells, which are the second neuron of deep sensitivity. Clark cell axons form the Flexig pathway. They pass in the posterior part of the lateral column on their side and, as part of the lower cerebellar peduncles, reach its cortex.
2. Olive-cerebellar tract - begins in the inferior olive nucleus on the opposite side and ends on the Purkinje cells of the cerebellar cortex. The olivocerebellar tract is represented by climbing fibers. The inferior olive nucleus receives information directly from the cerebral cortex and thus conducts information from its premotor zones, that is, the areas responsible for planning movements.
3. The vestibulocerebellar tract begins from the superior vestibular nucleus of Bechterew and through the inferior peduncle reaches the cerebellar cortex of the flocculonodular region. Information from the vestibulo-cerebellar pathway switches on Purkinje cells and reaches the tent nucleus.
4. Reticulo-cerebellar tract - starts from the reticular formation of the brain stem and reaches the cortex of the cerebellar vermis. Connects the cerebellum and the basal ganglia of the extrapyramidal system.

Cerebellum - Symptoms of lesions

Damage to the cerebellum is characterized by disorders of statics and coordination of movements, as well as muscle hypotonia. This triad is characteristic of both humans and other vertebrates. At the same time, the symptoms of cerebellar damage are described in the most detail for humans, since they have direct applied significance in medicine.

Damage to the cerebellum, primarily to its vermis, usually leads to a violation of the statics of the body - the ability to maintain a stable position of its center of gravity, ensuring stability. When this function is disrupted, static ataxia occurs. The patient becomes unstable, so in a standing position he tends to spread his legs wide and balance with his arms. Static ataxia manifests itself especially clearly in the Romberg position. The patient is asked to stand with his feet tightly together, slightly raise his head and stretch his arms forward. In the presence of cerebellar disorders, the patient in this position turns out to be unstable, his body sways. The patient may fall. In case of damage to the cerebellar vermis, the patient usually sways from side to side and more often falls back; with pathology of the cerebellar hemisphere, he leans mainly towards the pathological focus. If the static disorder is moderately expressed, it is easier to identify it in a patient in the so-called complicated or sensitized Romberg position. In this case, the patient is asked to place his feet in one line so that the toe of one foot rests on the heel of the other. The stability assessment is the same as in the usual Romberg position.

Normally, when a person stands, the muscles of his legs are tense; if there is a threat of falling to the side, his leg on this side moves in the same direction, and the other leg comes off the floor. When the cerebellum, mainly its vermis, is damaged, the patient’s support and jump reactions are disrupted. Impaired support response is manifested by the patient's instability in a standing position, especially if his legs are closely moved. A violation of the jump reaction leads to the fact that if the doctor, standing behind the patient and securing him, pushes the patient in one direction or another, then the latter falls with a slight push.

The gait of a patient with cerebellar pathology is very characteristic and is called “cerebellar.” Due to the instability of the body, the patient walks unsteadily, spreading his legs wide apart, while being “thrown” from side to side, and if the cerebellar hemisphere is damaged, he deviates when walking from the given direction towards the pathological focus. The instability is especially noticeable when turning. When walking, the human torso is excessively straightened. The gait of a patient with cerebellar damage is in many ways reminiscent of the gait of a drunk person.

If static ataxia turns out to be pronounced, then patients completely lose the ability to control their body and cannot not only walk and stand, but even sit.

Predominant damage to the cerebellar hemispheres leads to a breakdown of its anti-inertial influences and, in particular, to the occurrence of dynamic ataxia. It is manifested by clumsiness in the movements of the limbs, which is especially pronounced during movements that require precision. To identify dynamic ataxia, a series of coordination tests are performed.

Muscular hypotonia is detected during passive movements performed by the examiner in various joints of the patient’s limbs. Damage to the cerebellar vermis usually leads to diffuse muscle hypotonia, while with damage to the cerebellar hemisphere, a decrease in muscle tone is noted on the side of the pathological focus.

Pendulum-like reflexes are also caused by hypotension. When examining the knee reflex in a sitting position with legs hanging freely from the couch after a blow with a hammer, several “rocking” movements of the lower leg are observed.

Asynergy is the loss of physiological synergistic movements during complex motor acts.

The most common tests for asynergy are:

1. The patient, standing with his legs together, is asked to bend back. Normally, at the same time as the head is thrown back, the legs bend synergistically at the knee joints, which helps maintain body stability. With cerebellar pathology, there is no conjugal movement in the knee joints and, throwing the head back, the patient immediately loses balance and falls in the same direction.
2. The patient, standing with his legs together, is asked to rest on the palms of the doctor, who then suddenly removes them. If a patient has cerebellar asynergia, he falls forward. Normally, there is a slight deviation of the body back or the person remains motionless.
3. The patient, lying on his back on a hard bed without a pillow with his legs spread shoulder-width apart, is asked to cross his arms over his chest and then sit down. Due to the absence of conjugal contractions of the gluteal muscles, a patient with cerebellar pathology cannot fix his legs and pelvis to the support area; as a result, he is unable to sit down, while the patient’s legs lift up from the bed.

Cerebellum - Pathology

Cerebellar lesions occur in a wide range of diseases. Based on ICD-10 data, the cerebellum is directly affected in the following pathologies:

Neoplasms

Cerebellar neoplasms are most often represented by medulloblastomas, astrocytomas and hemangioblastomas.

Abscess

Cerebellar abscesses account for 29% of all brain abscesses. They are most often localized in the cerebellar hemispheres at a depth of 1-2 cm. They are small in size, round or oval in shape.

There are metastatic and contact cerebellar abscesses. Metastatic abscesses are rare; develop as a result of purulent diseases of distant parts of the body. Sometimes the source of the infection cannot be determined.

Contact abscesses of otogenic origin are more common. The routes of infection in them are either the bone canals of the temporal bone or the vessels that drain blood from the middle and inner ear.

Hereditary diseases

A group of hereditary diseases is accompanied by the development of ataxia.

In some of them, a predominant lesion of the cerebellum is noted.

Hereditary cerebellar ataxia of Pierre Marie

A hereditary degenerative disease with predominant damage to the cerebellum and its pathways. The type of inheritance is autosomal dominant.

With this disease, degenerative damage to the cells of the cortex and cerebellar nuclei, spinocerebellar tracts in the lateral cords of the spinal cord, in the nuclei of the pons and medulla oblongata is determined.

Olivopontocerebellar degenerations

A group of hereditary diseases of the nervous system, characterized by degenerative changes in the cerebellum, nuclei of the inferior olives and pons, in rare cases - the nuclei of the cranial nerves of the caudal group, and to a lesser extent - damage to the pathways and cells of the anterior horns of the spinal cord, basal ganglia. The diseases differ in the type of inheritance and different combinations of clinical symptoms.

Alcoholic cerebellar degeneration

Alcoholic cerebellar degeneration is one of the most common complications of alcohol abuse. It develops more often in the 5th decade of life after many years of ethanol abuse. It is caused by both the direct toxic effect of alcohol and electrolyte disturbances caused by alcoholism. Severe atrophy of the anterior lobes and the upper part of the cerebellar vermis develops. In the affected areas, almost complete loss of neurons is detected in both the granular and molecular layers of the cerebellar cortex. In advanced cases, the dentate nuclei may also be involved.

Multiple sclerosis

Multiple sclerosis is a chronic demyelinating disease. With it, multifocal damage to the white matter of the central nervous system is observed.

Morphologically, the pathological process in multiple sclerosis is characterized by numerous changes in the brain and spinal cord. The favorite localization of lesions is the periventricular white matter, the lateral and posterior cords of the cervical and thoracic spinal cord, the cerebellum and the brainstem.

Cerebrovascular disorders

Hemorrhage into the cerebellum

Cerebral circulation disorders in the cerebellum can be either ischemic or hemorrhagic.

Cerebellar infarction occurs when the vertebral, basilar or cerebellar arteries are blocked and, with extensive damage, is accompanied by severe cerebral symptoms and impaired consciousness. Blockage of the anterior inferior cerebellar artery leads to an infarction in the cerebellum and pons, which can cause dizziness, tinnitus, nausea on the affected side - paresis of facial muscles, cerebellar ataxia, Horner's syndrome. When the superior cerebellar artery is blocked, dizziness and cerebellar ataxia on the side of the lesion often occur.

Hemorrhage into the cerebellum usually manifests as dizziness, nausea, and repeated vomiting while maintaining consciousness. Patients are often bothered by headaches in the occipital region; they usually exhibit nystagmus and ataxia in the extremities. When a cerebellar-tentorial displacement occurs or herniation of the cerebellar tonsils into the foramen magnum, a disturbance of consciousness develops up to coma, hemi- or tetraparesis, damage to the facial and abducens nerves.

Traumatic brain injury

Cerebellar contusions dominate among lesions of the posterior cranial fossa. Focal cerebellar injuries are usually caused by an impact mechanism of injury, as evidenced by frequent fractures of the occipital bone below the transverse sinus.

General cerebral symptoms in cases of cerebellar damage often have an occlusive coloration due to the proximity to the cerebrospinal fluid outflow pathways from the brain.

Among the focal symptoms of cerebellar contusions, unilateral or bilateral muscle hypotonia, impaired coordination, and large tonic spontaneous nystagmus dominate. The localization of pain in the occipital region with irradiation to other areas of the head is typical. Often, one or another symptomatology from the brain stem and cranial nerves manifests itself simultaneously. With severe damage to the cerebellum, breathing disorders, hormetonia and other life-threatening conditions occur.

Due to the limited subtentorial space, even with a relatively small amount of damage to the cerebellum, dislocation syndromes often develop with entrapment of the medulla oblongata by the cerebellar tonsils at the level of the occipito-cervical dural infundibulum or entrapment of the midbrain at the level of the tentorium due to the upper parts of the cerebellum being displaced from bottom to top.

Developmental defects

MRI. Arnold-Chiari syndrome I. The arrow indicates the protrusion of the cerebellar tonsils into the lumen of the spinal canal

Cerebellar malformations include several diseases.

There are total and subtotal cerebellar agenesis. Total cerebellar agenesis is rare and is combined with other severe anomalies of the development of the nervous system. Most often, subtotal agenesis is observed, combined with malformations of other parts of the brain. Hypoplasia of the cerebellum occurs, as a rule, in two variants: reduction of the entire cerebellum and hypoplasia of individual parts while maintaining the normal structure of its remaining parts. They can be unilateral or bilateral, as well as lobar, lobular and intracortical. There are various changes in the configuration of the leaves - allogyry, polygyry, agyry.

Dandy-Walker syndrome

Dandy-Walker syndrome is characterized by a combination of cystic dilatation of the fourth ventricle, total or partial aplasia of the cerebellar vermis, and supratentorial hydrocephalus.

Arnold-Chiari syndrome

Arnold-Chiari syndrome includes 4 types of diseases, respectively designated Arnold-Chiari syndrome I, II, III and IV.

Arnold-Chiari syndrome I is a descent of the cerebellar tonsils more than 5 mm beyond the foramen magnum into the spinal canal.

Arnold-Chiari II syndrome is a descent into the spinal canal of the cerebellar and brainstem structures, myelomeningocele and hydrocephalus.

Arnold-Chiari syndrome III is an occipital encephalocele in combination with signs of Arnold-Chiari II syndrome.

Arnold-Chiari IV syndrome is aplasia or hypoplasia of the cerebellum.