Cerebellar legs. The cerebellum is a small brain. to RF of the midbrain - cerebellar-reticular

External structure. The cerebellum develops from the dorsal wall of the hindbrain and is the largest, after the cerebral hemispheres, part of the brain.

Together with the medulla oblongata and the pons, the cerebellum is located in the posterior cranial fossa. The cerebellum has a rhomboid shape with a predominance of transverse size. In it, the middle part is distinguished - a worm, two side voluminous parts - the hemispheres. Based on the development of the cerebellum in phylogeny, a small formation should be distinguished, adjacent to the ventral side of the hemisphere - a patch. In the vermis and cerebellar hemispheres, two surfaces are distinguished - the upper and lower (Fig. 3.11).

Figure: 3.11.

a - upper surface: 1 - anterior notch of the cerebellum; 2 - plates of the cerebellum; 3 - horizontal groove; 4 - posterior notch of the cerebellum; 5 - grooves of the cerebellum; 6 - upper worm; b - lower surface: 1 - lower worm; 2 - the superior cerebellar pedicle; 3 - middle cerebellar pedicle; 4 - a piece; 5 - the leg of the scrap; 6 - knot; 7 - cerebellar valley; 8 - horizontal groove; 9 - vascular plate of the IV ventricle; 10 - upper cerebral sail

The superior surface of the cerebellum faces upward and backward. It is convex and has a longitudinal elevation in the middle, called the upper worm. The worm passes into the hemispheres from the lateral sides. The lower surface of the cerebellum is directed downward and forward. It is adjacent to the occipital bone. On the lower surface there is a longitudinal depression called the cerebellar valley. The bottom worm is located in this depression.

The surface of the cerebellum is lined with a large number of parallel cracks (grooves), which have a transverse direction and different depths. Small grooves divide the surface of the cerebellum into plates (gyrus). Deeper grooves divide the groups of plates into plates, which are called "cerebellar laminae". Finally, the deepest grooves divide the surface of the cerebellum into lobules.

Among the furrows separating the cerebellar lobules, the deepest is the horizontal slit. It runs along the entire circumference of the cerebellum and separates the upper and lower surfaces of the hemispheres. The grooves of the cerebellum, without interruption, pass from the worm to the hemispheres.

The division of the cerebellum into lobules was given on the basis of the premise of the presence of connections between individual parts of the hemispheres and certain parts of the worm. Eight lobules are isolated in the worm and hemispheres. The anterior lobule of the lower worm is a nodule. A piece is a small group of plates of the cerebellar hemispheres adjacent to its middle pedicle.

Modern studies of the conducting pathways of the cerebellum allow us to consider it more rational to isolate parts, the function of which was formed in the process of phylo- and ontogenesis. So, in the cerebellum, a phylogenetically ancient part (ancient cerebellum) is isolated, which includes a clump and a nodule; the old part (old cerebellum), which includes the worm, with the exception of the nodule, and the new part of the cerebellum (new cerebellum), which includes the cerebellar hemispheres, developing from the middle part of the worm.

Internal structure. The sections clearly show the gray matter located on the surface, which forms the cerebellar cortex, under the cortex is the white matter of the cerebellum, from which processes extend to the surface, penetrating into the lobules and plates of the cerebellum. In the midline section, the white matter has a leaf-like shape, which is associated with the figurative name "tree of life of the cerebellum".

Three layers are distinguished in the cerebellar cortex: the outer layer is molecular, the middle layer is the layer of piriform neurons (the layer of Purkinje cells), and the inner layer is granular. This layered arrangement of neurons is a characteristic morphological feature of the integration centers of the brain, one of which is the cerebellum. This explains the numerous complex connections of the cerebellum with other parts of the central nervous system.

Figure: 3.12.

1 - the superior cerebellar pedicle; 2 - worm; 3 - the core of the tent; 4 - cerebellar cortex; 5 - toothed core; 6 - spherical core; 7 - corky core; 8 - lower mound; 9 - upper mound

In the thickness of the white matter of the cerebellum, there are accumulations of gray matter that make up the nucleus of the cerebellum (Figure 3.12). In the vermis of the cerebellum, on either side of the midline is the core of the tent. Lateral to it is the second small nucleus, called spherical. The corky nucleus lies even more laterally. In the white matter of the hemispheres is the largest - the dentate nucleus.

The tent nucleus belongs to the ancient cerebellum, the globular and corky nuclei are phylogenetically later formations (refer to the old cerebellum), and the dentate nucleus belongs to the new cerebellum.

The white matter of the cerebellum contains afferent and efferent fibers that connect the cerebellum to the brainstem and form the cerebellar peduncles. There are three pairs of cerebellar legs - upper, middle and lower. The upper cerebellar legs connect it with the midbrain, the middle ones - with the bridge, and the lower ones - with the medulla oblongata (Fig. 3.13). The superior and inferior cerebellar peduncles are visible from the dorsal surface of the brainstem, and the middle ones from its ventral surface.

As part of the lower cerebellar legs the following paths pass.

• 1. The posterior spinal cord (afferent) is formed by the axons of the cells of the thoracic nucleus. All fibers of this pathway, without crossing, go along their side in the posterolateral part of the lateral cord of the spinal cord. They end on the neurons of the cortex of the lower part of the cerebellar vermis.
• 2. Bulbar-cerebellar pathway (afferent) is formed by the axons of a part of neurons located in the nuclei of the thin and wedge-shaped tubercles. The tract ends on the neurons of the cortex of the middle part of the cerebellar worm.
• 3. The vestibular cerebellar pathway (afferent) is formed by the axons of the cells of the vestibular nuclei of the pons (mainly the Deiters nucleus and the Bechterew nucleus). The tract ends at the cells of the cortex of the worm's nodule and shred.

Figure: 3.13.

• 1 - upper mound; 2 - lower mound; 3 - the superior cerebellar pedicle; 4 - superior cerebral sail; 5 - middle cerebellar pedicle; 6 - the leg of the scrap; 7 - lower cerebral sail; 8 - hole Mozhandi; 9 - wedge-shaped bundle; 10 - thin bundle; 11 - vascular plate of the IV ventricle; 12 - lower cerebellar pedicle; 13 - Lyushka's hole; 14 - a scrap; 15 - knot
• 4. Olive-cerebellar pathway (afferent) is formed by axons of cells of the olives of the medulla oblongata. The tract ends on the neurons of the cortex of the cerebellar hemispheres on the opposite side.
• 5. The nuclear cerebellar pathway (afferent) is formed by the axons of a part of the neurons of the sensory nuclei of the cranial nerves (pairs V, VII, IX and X). The tract ends on the cells of the cortex of the middle part of the cerebellar worm.
• 6. The cerebellar vestibular pathway (efferent) is formed by the axons of the cells of the cortical cortex and the vermis of the cerebellum. This path ends on those neurons of the Deiters nucleus, the axons of which form the vestibular-spinal path.
• 7. The cerebellar-olive path (associative) is formed by the axons of the cells of the cortex of the cerebellar hemispheres. Ends in the nuclei of the olive of the medulla oblongata.
• 8. The cerebellar-reticular pathway (efferent) is formed by the axons of the neurons of the tent nucleus, the spherical and corky nuclei. Ends on the cells of the reticular formation of the medulla oblongata and spinal cord, the axons of which form the reticular-spinal path.

As part of the middle cerebellar legs only the pontine-cerebellar pathway (associative) passes, which is formed by the axons of the pons' own nuclei. It ends on the cells of the cortex of the cerebellar hemispheres of the opposite side.

As part of the upper cerebellar legs the following paths pass.

• 1. The anterior spinal-cerebellar pathway (afferent) is formed by the axons of the cells of the intermediate-medial nuclei of its own and opposite sides. The axons on the opposite side return to their side through the superior cerebral sail. The fibers of this tract end on the cells of the cortex of the upper part of the cerebellar vermis.
• 2. The dentate-red-nuclear pathway (associative) is formed by the axons of the cells of the dentate nucleus of the cerebellum. The tract makes a complete intersection at the level of the lower mounds of the midbrain (Werneking's cross) and ends on the cells of the red nucleus of the midbrain.
• 3. The dentate thalamic pathway (associative) is formed by the axons of the cells of the dentate nucleus of the cerebellum, which end on the neurons of the central nuclei of the thalamus.

The main manifestations of cerebellar lesions

In case of damage to the cerebellum (traumatic brain injury, vascular pathology, neuroinfection, intoxication), disorders occur, which are called syndrome "Four A".

• 1. Ataxia - violation of coordination of movements, their accuracy and speed. Movements become awkward, sweeping and abrupt. These disorders are the result of a violation of the coordinated work of muscles, the so-called asynergy. Fine motor skills are impaired, for example, the handwriting changes, the letters become large, uneven. Speech becomes irregular, chanted, words are pronounced indistinctly, which indicates a violation of the coordination of the muscles of the larynx, tongue, lips.
• 2. Atony - decrease or absence of muscle tone, inability to maintain a posture and perform movements.
• 3. Asthenia - the emergence of rapidly emerging fatigue, both during physical and intellectual exertion.
• 4. Astasia - violation of statics and statokinetics, manifested in the form of tremors of the limbs and head, the so-called tremor. In this case, the muscles lose the ability to coordinated movements, which manifests itself in instability when standing (in fact astasia) and especially when walking ( abasia). In this case, the head and body sway in different directions. In patients with lesions of the cerebellum, the so-called "drunk gait" develops.

Finally, a fairly common symptom of cerebellar lesions is dizziness and nausea, resulting from a violation of the functional connections of the cerebellum with the vestibular apparatus.

The functions of the cerebellum and the appearance of these symptoms are checked by various neurological tests, for example:

• 1) Romberg's test - standing, with closed eyes, heels and socks together, arms extended forward, fingers apart;
• 2) the complicated Romberg test is performed similarly to the previous one, but the legs are on the same line, the right foot is in front of the left;
• 3) test of "one plate" - it is proposed to walk in a straight line with open and closed eyes;
• 4) a test for adiadochokinesis - the loss of the ability to produce movements that require successive muscle contractions of agonists and antagonists: the patient fails to quickly change opposite movements - pronation and supination, flexion and extension;
• 5) the finger-nose test is based on the fact that when the subject tries with his eyes closed to touch the tip of the nose with his index finger, there is a miss and (or) trembling of the index finger.

What is the cerebellum responsible for in the body? This small formation, like the large brain, consists of white and gray matter (cells and conductive fibers). This structure is located behind and below the cerebral hemispheres, between the middle and oblong sections and the bridge. The functions of the cerebellum are the regulation of movements, their coordination, the implementation of articulation. Cerebellum (cerebellum) connects the parts of the central nervous system with each other, ensures their integration.

Structure

Where is the cerebellum of the human brain, look at the photo: it is located in the skull, its posterior fossa, adjacent to the middle and medulla oblongata. In this structure, there is a rhomboid fossa - the bottom of the fourth ventricle, a cavity with fluid. Consists of two hemispheres and a worm between them, its weight is about 120 g, its transverse dimensions are about 10 cm.

Each hemisphere has three lobes separated by furrows. The surface is not smooth, covered with grooves, similar to the convolutions of the cerebral hemispheres. The worm is connected to the lobes of the hemispheres by white fibers, which diverge to form the "tree of life." In cerebellum, there are accumulations of gray matter: jagged roof cores, tent cores, corky core and spherical.

Kernel functions:

1. Serrated nuclei are necessary for the implementation of the beginning of movements, their control, planning.
2. The cores of the tent are responsible for maintaining balance and saccadic (jump-like) movement of the eyeballs. This formation contains GABAergic neurons (inhibitory).

The globular nucleus is located deep, is an ancient formation, belongs to the old cerebellum. The anterior inferior cerebellar artery feeds the cerebellum anteriorly and inferiorly. There is also the posterior inferior cerebellar artery, the superior cerebellar artery.

The cerebellum, whose structure is similar to the cerebral hemispheres, has "legs" - nerve fibers. These are the pathways that connect it with the neighboring sections: the bridge, the medulla oblongata, and the midbrain. It is connected to the spinal cord to transmit impulses to its anterior horns, which provide transmission of the signal to the skeletal muscles. The connection with the reticular formation provides a role in the regulation of autonomic functions.

Important! The structure and function of the cerebellum connected: it integrates all departments in the process of coordinating complex motor acts, being a connecting element.

The intensive development of this department occurs in childhood, when the child masters the basic movements. The accumulation of experience with motor acts leads to the establishment of communication between different parts of the central nervous system. Cerebellum is the link between the motor centers of the cerebral hemispheres and the motor neurons of the spinal cord located in their anterior horns.

What is it for?

What is the cerebellum of the brain responsible for? First of all, it regulates gait, other actions with stereotyped movements, keeps the body in balance, in the required posture. In addition, this section is necessary for the regulation of the tone of the flexors, extensors, and other antagonist muscles.

The functions of the cerebellum of the human brain include the regulation of speech through the coordinated control of the muscles of the tongue and lips, fine motor skills (handwriting).

In trauma, hemorrhagic and inflammatory processes, multiple sclerosis, tumors, the cortex or nerve fibers can be damaged. The pathways are affected; adequate transmission of the nerve impulse to the spinal cord motor neurons does not occur.

Symptoms of defeat

When the structure of the cerebellum is destroyed, a disorder of the sense of balance appears, as evidenced by nystagmus: trembling of the eyeballs when they are taken to the side, as well as unsteadiness of gait, dizziness. The disorder of coordination of motor acts is called cerebellar.

Speech is disturbed: it becomes incoherent, but rhythmic (chanted), the language seems to be braided. When an organ is damaged, the patient emphasizes the words not according to the rules of orthoepy, but in accordance with the rhythm of speech.

Cerebellum regulates the coordinated work of muscles: thanks to it, antagonist muscles work apart, without interfering with each other. However, with pathological processes, this function is disturbed, asynergy develops. There is a decrease in muscle tone.

Intentional and postural - another consequence of the defeat of the cerebellum and trunk. Postural tremor of the body or its limbs occurs when the patient tries to maintain the desired posture. Intentional tremor is an involuntary oscillatory movement made towards a specific object for a specific purpose.

Strengthening of jitter, an increase in its amplitude, sweeping occurs when approaching the target object. This dyskinesia does not allow the person suffering from cerebellar lesion to pick up the necessary objects in his hands, to perform complex acts that require coordination. The neurologist checks for intentional tremor by asking the patient to touch the tip of their nose with their eyes closed.

Adiadochokinesis - the inability of a person to switch between opposite movements, that is, a person suffering from cerebellar disorder is unable to alternately flex and extend, adduction, abduction, pronation, supination. Switching between the activity of opposite muscle groups is slow.

The dentate nuclei are connected by conductive fibers with the red nucleus of the midbrain. If this connection is violated, extrapyramidal disorders occur in the form of various hyperkinesis: athetoses,.

If the lower olive of the medulla oblongata (medulla oblongata) is affected, its communication with the dentate nucleus, then myoclonic disorders arise in the form of twitching of the tongue, muscles of the palate, pharynx. Swallowing disorders are possible.

If the worm is affected, gait and posture disturbances dominate. The defeat of the hemispheres leads to a mismatch in the movements of the limbs of the same name. Symptoms of damage often include mental health problems.

Conclusion

Cerebellum is an important formation of the central nervous system, which is responsible for performing motor acts and maintaining balance. His defeat is a serious problem leading to a person's disability.

The part of the brain responsible for coordinating movements, maintaining body balance and regulating muscle tone. In a newborn, the mass of the cerebellum is approximately 20 g, or 5.4% of the total body weight. By 5 months of life, it increases 3 times, and by 9 months - 4 times. The intensive growth of the cerebellum in the first year of life is determined by the formation of differentiation and coordination of movements during this period. In the future, the rate of its growth decreases. By about 15 years of age, the cerebellum reaches the size of an adult.

The structure of the cerebellum

It is located behind the medulla oblongata and is placed under the occipital lobes of the cerebral hemispheres, in the cranial fossa. It distinguishes between lateral parts, or hemispheres, and a worm located between them. Unlike the spinal cord and the trunk, the gray matter (cortex) is on the surface of the cerebellum, and the white matter is inside.

The gray matter consists of cells arranged in three layers:

• outer layer - consists of stellate and basket-like cells;
• middle layer - represented by large ganglion cells;
• inner granular layer - consists of granular cells, between which large stellate cells are found.

In the thickness of the cerebellum there are also paired nuclei of the gray matter. In the area of \u200b\u200bthe worm is the core of the tent, in the hemispheres, outward from the core of the tent - the intercalary nucleus, consisting of spherical and cork-shaped nuclei. In the center of the hemispheres is the dentate nucleus, which is involved in the implementation of the balance function. The defeat of one or another nucleus leads to various disorders of motor function. The destruction of the core of the tent is accompanied by an imbalance in the body; damage to the worm, corky and spherical nuclei - disruption of the muscles of the neck and trunk; destruction of the hemispheres and the dentate nucleus leads to disruption of the muscles of the limbs.

The white matter of the cerebellum is composed of all sorts of nerve fibers. Some of them connect the convolutions and lobules, others stretch from the cortex to the inner nuclei, and still others connect the cerebellum with other parts of the brain. The latter type of fibers forms the lower, middle and upper pairs of legs. As part of the lower legs, fibers from the medulla oblongata and olives stretch to the cerebellum, they end in the cortex of the worm and the hemispheres. The fibers of the middle legs are directed towards the bridge. The fibers of the upper legs extend to the roof of the midbrain. They run in both directions, connecting the cerebellum with the red nucleus and thalamus, as well as with the spinal cord.

Cerebellar functions

As mentioned above, the cerebellum provides coordination of movements. With his lesions, various disorders of motor activity and muscle tone develop, as well as autonomic disorders. Cerebellar failure is manifested by muscle atony and an inability to maintain body position. So, when a passively hanging limb is displaced, it does not return to its original position, but swings like a pendulum. Purposeful movements are performed impulsively, with misses.

Typical manifestations of cerebellar insufficiency are:

• tremor - oscillations of small amplitude occur synchronously in different parts of the body;
• ataxia - violation of the speed and direction of movement, which leads to a loss of smoothness and stability of motor reactions.

Impaired coordination of movements in lesions of the cerebellum is explained by its close connection with the brain stem, as well as with the thalamus and the sensorimotor region of the cerebral cortex. The cerebellum receives information from various components of the motor apparatus, processes it and transmits corrective influences to the neurons of the brainstem and spinal motor centers. In addition, due to numerous synaptic contacts with the reticular formation, the cerebellum plays a significant role in the regulation of autonomic functions.

The main coordinating center of a person is his brain. And it consists of certain parts. This article will discuss what the cerebellum is: the functions and structure of this organ.

What it is?

At the very beginning, you need to understand the concepts that will be actively used in this article. So what is the cerebellum of the brain? It is a specific structure that sits at the back of the head. Namely, over the bridge and the medulla oblongata, behind the cerebral hemispheres.

Structure

Be sure to also consider the structure of the cerebellum. So, this body consists of two main parts:

1. The so-called worm - an elongated component part.
2. Two hemispheres.

These parts - the two hemispheres and the worm - are fragmented into certain parts, the so-called lobules, by transverse grooves. You also need to clarify that the cerebellum itself consists of white and gray matter. The latter forms paired nuclei and cerebellar cortex. The white matter, penetrating into the mass of gray, forms, as it were, branched stripes, resembling a tree in section.

Numbers

What is the weight and size of the cerebellum?

1. Dimensions. The diameter of the cerebellum is approximately 9-10 cm. The anteroposterior part is 3-4 cm. It should be said here that the cerebellum occupies almost the entire posterior cranial fossa.
2. The weight. The mass of this organ of an adult is approximately 120-160 g.

Together with the change in indicators, the development of the cerebellum can also be traced. For example, by the time a child is born, he is less developed than the hemispheres of the brain. But during the first year of life, it develops faster than other parts of the brain as a whole. The cerebellum changes especially actively during the period from 5 to 11 months of the baby, when the baby learns to walk, move.

As for weight, in newborns, the cerebellum weighs only 20 grams. By about the third month of life, its weight doubles, by six months it triples, and by 9 months it becomes four times more. Further, the active growth of the cerebellum decreases. By the age of six, the child is gaining weight 120 grams, which is equal to the weight of this part of the brain of an adult.

Cerebellar connections

Considering the structure of the cerebellum, one must also consider all the connections of this organ:

1. Vestibular nerves and their nuclei.
2. Somatosensory pathways that run primarily from the spinal cord.
3. Descending pathways that move from the cerebral cortex. All motor signals go to the cerebellar hemispheres.

Based on this, it is also necessary to clarify that three pairs of cerebellar legs depart from the cerebellum:

1. Lower: heading to the medulla oblongata.
2. Medium: going to the bridge.
3. Upper: directed towards the quadruple.

Through these parts, the cerebellum comes into contact with other important parts of the human body.

Bark

You also need to consider the most different parts of the cerebellum. You can start with its bark. So, it consists exclusively of gray matter, its size is 1-2.5 mm. Bark layers:

1. Molecular, i.e. outer. Only small neurons are located here.
2. Medium, i.e. ganglionic (pear-shaped layer of neurons). There are also quite large neurons, also called Purkinje cells. It is they who integrate all the information that comes from the cerebral cortex to the cerebellum.
3. Internal, which is also called grainy. This layer contains large stellate neurons, which are also called Golgi cells.

The brains (or leaves) of the cerebellum are another component of this organ. It is a thin layer of white matter that covers the gray. The size of the leaves is approximately 1-2.5 mm.

Functions

Looking at the cerebellum, function is also something to talk about. It is worth clarifying here that this organ is not associated with the body's receptors. He has contact exclusively with the central nervous system. Multiple sensory pathways are directed to it, which carry impulses from muscles, ligaments, tendons, vestibular nuclei. The cerebellum itself can send impulses to all parts of the central nervous system.

Function exploration

If we talk about such an organ as the cerebellum, its functions were studied by stimulating it. Or complete removal and further - the study of bioelectric phenomena. This is what the Italian scientist Luciani investigated. He was able to describe the consequences of removal by a triad:

1. Astasia.
2. Atony.
3. Asthenia.

Scientists who have conducted similar studies have added another symptom: ataxia.

All experiments were carried out on dogs, and the results were quite interesting:

1. A dog without a cerebellum stands on widely spaced legs, while swaying slightly from side to side. This is astasia.
2. The tone of the flexor and extensor muscles is disturbed - this is atony.
3. All movements of the dog are sharp, sweeping, wide. This symptom is called ataxia.
4. Also, the dog cannot regulate its movements. She does not hit the bowl with her muzzle, all the movements are very tedious. This is asthenia.

However, over time, all sharp movements in a dog without a cerebellum are smoothed out. She learns to eat on her own, walks normally (defects are visible only if you look closely).

A team of scientists has also shown that all kinds of autonomic functions are impaired in cerebellar dogs. Vascular tone, blood constant changes, the work of the digestive tract is transformed.

Small summary regarding functions

Considering the above studies, you can draw certain conclusions about what the cerebellum is doing. Its functions are as follows:

1. Coordination of all human movements.
2. Regulation of muscle tone.
3. Balance regulation.

It should be said here that this organ is of the greatest importance for the life of mammals. After all, it is he who helps animals move in space.

Diagnosing problems

How to understand that a person has a damaged cerebellum or other problems with this organ? There are several research methods for this:

1. Study of a person's gait, his movements. Here they can take samples to identify dynamic and static ataxia, study muscle tone. In this case, two main methods will be relevant: plantography and ichnography. The gait and shape of a person's feet will be considered based on their prints (the paper lies on a metal base covered with paint).
2. To clarify the diagnosis or the nature of the damage, the same diagnostic methods can be used as in the study of the brain: radiography, echoencephalography, etc.

Symptoms

What will a person who has problems with the cerebellum feel? Symptoms in this case may be as follows:

1. Coordination of movements (ataxia) will be impaired.
2. A person will quickly get tired, a little physical activity will require a break (asthenia).
3. Muscle tone will be significantly reduced (atony).
4. A person will not be able to make smooth movements, they will be sharp. Long-term muscle contraction (astasia) will become impossible.
5. Also, a person will not be able to quickly change the direction of movement, he will have to think about this (adiadochokinesis).
6. The patient's movement accuracy will be impaired (dysmetria).

Other symptoms that are also observed with damage to the cerebellum:

1. Tremor, i.e. trembling (if there are violations of connections with red and serrated nuclei).
2. There may be myoclonus (muscle twitching) of the pharynx, tongue, upper palate.
3. Pendulum reflexes may occur.
4. Hypertensive crises (increased intracranial pressure). It occurs most often as a result of tumors, injuries, cysts and hematomas of the cerebellum.

As a conclusion, I would like to say that although the cerebellum is not a very large part of the brain, it is, however, responsible for multiple essential functions in the human body. At the moment, research is still underway, because modern scientists do not know everything about this part of the brain.

Cerebellum - a part of the brain related to the hindbrain proper, involved 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 Varoliev Bridge.

In the cerebellum, the middle part is distinguished - the worm and two hemispheres located on the sides of it. The surface of the cerebellum is made of gray matter called the cortex. Inside the cerebellum is a white matter, which is a process of neurons. On the surface of the cerebellum, there are many folds, or sheets, formed by the complex bends of its cortex.

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

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

The 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 middle and medulla oblongata, as well as through the motor neurons of the spinal cord.

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

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

The auditory and visual zones are located in the cerebellar cortex.

The cerebellum is also part of the visceral function monitoring system. Its irritation causes several autonomic reflexes: increased blood pressure, dilated pupils, etc. In case of damage to the cerebellum, disturbances in the activity of the cardiovascular system, the secretory function of the gastrointestinal tract and other systems occur.

Cerebellum structure

Cerebellum located rostrally from the cerebellar tentorium, caudally to the foramen magnum and occupies most of the posterior cranial fossa. Downward and ventrally, it is separated by the cavity of the IV ventricle from the bridge.

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

• vestibulocerebellum;
• spinocerebellum;
• cerebrocerebellum.

Vestibulocerebellum (archcerebellum) is the most ancient part of the cerebellum, represented in humans by the flocculonodular lobe and part of the worm, associated mainly with the vestibular system. The department is connected by reciprocal connections with the vestibular and reticular nuclei of the brainstem, which is the basis for its participation in the control of body balance, as well as coordination of eye and head movements. This is realized through the regulation and distribution of the tonus of the axial muscles of the body by the vestibular part of the cerebellum. Damage to vetibulocerebellum may be accompanied by impaired coordination of muscle contraction, the development of ataxic (drunken) gait, as well as nystagmus of the eyes.

Spinocerebellum (paleocerebellum) is represented by the anterior and small part of the posterior lobe of the cerebellum. It is connected by spinocerebellar pathways with the spinal cord, from where it receives somatotopically organized information from the spinal cord. Using the received signals, 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 section of the human cerebellum. The neurons in this part of the cerebellum receive signals along the axons of neurons, many fields. Therefore, neocerebellum is also called cerebrocerebellum. It modulates signals received from the motor cortex of the brain and is involved in the planning and regulation of limb movements. Each side of the neocerebellum modulates signals from the motor cortex on the opposite side. Since this contralateral side of the cortex controls the movement of the ipsilateral limb, neocerebellum regulates the motor activity of 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 - with basket and stellate neurons, the middle - with Purkinje cells, the inner layer - with 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 nuclei of the cerebellum and other areas of the brain. Purkinje cells have an extremely highly branched dendritic tree.

Cerebellar afferent connections

The neurons of the cerebellum receive signals through afferent fibers from various parts of the CIS, 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 the afferent and efferent fibers of the cerebellum, which is 40: 1. The spinocerebellar pathways, mainly through the lower legs of the cerebellum, receive information from the proprioceptors about the state of activity of the spinal cord motor neurons, the state of the muscles, the tension of the tendons, the position of the joints. Afferent signals entering the cerebellum from the vestibular apparatus and vestibular nuclei of the brainstem bring information about the position of the body and its parts in space (body posture) and the state of balance. The corticocerebellar descending pathways are interrupted on the neurons of the nuclei of the pons (cortico-pontocerebellar pathway), the red nucleus and the inferior olive path (cortico-olivocerebellar pathway), reticular nuclei (corticoreticulocerebellar pathway) and hypothalamic nuclei, and after their processing they follow the cerebellar neurons These pathways provide the cerebellum with information about planning, initiating, and executing movements.

Afferent signals enter the cerebellum through two types of fibers - mossy and curly (climbing, liana-like). Mossy fibers originate in different areas of the brain, while climbing fibers come from the lower olivary nucleus. Mossy fibers that exocyte acetylcholine diverge widely and end on the dendrites of the granular cells of the cerebellar cortex. Afferent pathways formed by climbing fibers are characterized by low divergence. The excitatory neurotransmitter aspartate is used in the synapses they form on Purkinje cells.

The axons of the granular cells follow to the Purkinje cells and to the interneurons and exert an excitatory effect on them through the release of aspartate. Ultimately, through neural connections, mossy fibers (granular cells) and through climbing fibers, excitation of Purkinje cells is achieved. These cells have an exciting 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 discharges of Purkinje cells changes in response to the receipt of sensory signals along afferent fibers or from proprioceptors when the activity of spinal cord motoneurons changes. Purkinje cells are efferent neurons of the cerebellar cortex that release GABA, so their effect on neurons in other brain structures is inhibitory. Most of the Purkinje cells send axons to the neurons of the deep (dentate, cork-shaped, spherical, tent) nuclei of the cerebellum, and some to the neurons of the lateral vestibular nuclei.

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

Table. Functional connections of the cerebellar cortex.

Efferent pathways of the cerebellum

They are subdivided into intracerebellar and extracerebellar. The intracerebellar pathways are represented by the axons of Purkinje cells, following to the neurons of the deep nuclei. The main number of extracerebellar efferent connections is represented by the axons of the neurons of the deep cerebellar nuclei, emerging as part of the nerve fibers of the cerebellar pedicles and ending in synapses on the neurons of the reticular nuclei, red nucleus, inferior olives, thalamus and hypothalamus. Through the neurons of the stem and thalamic nuclei, the cerebellum can influence the activity of neurons in the motor areas of the cerebral cortex, which form the descending pathways of the medial system: corticospinal, corticorubal, corticorsticular, etc. In addition, the cerebellum is connected by efferent pathways with neurons in the parietal and temporal associative areas of the brain brain.

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

Cerebellar functions and consequences of their violation

The main functions of the cerebellum:

• Regulation of posture and muscle tone
• Correction of slow, purposeful movements and their coordination with reflexes of maintaining posture
• Correct execution of fast targeted movements according to the commands of the cerebral hemispheres in the structure of the general program of movements
• 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 departments 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 basal nuclei in the formations of the central nervous system that organize and control movements. Both of these structures of the central nervous system are involved in the control of movements, but do not initiate them; they are built into 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 evaluating and comparing signals of the speed of eye movement in the orbit, head and body movements coming to it from the retina, proprioceptors of the eye muscles, the vestibular analyzer, and proprioceptors of skeletal muscles during combined movements of the eyes, head, and trunk. It is likely that such combined signal processing is carried out by the neurons of the worm, in which the selective activity of Purkinje cells on the character, direction, and speed of movement is recorded. The cerebellum plays an exceptional role in calculating the speed and amplitude of forthcoming movements in the preparation of their motor programs, as well as in controlling the accuracy of the execution of the movement parameters that were laid down in these programs.

Characteristics of cerebellar dysfunctions

Triad Luciani: atony, asthenia, astasia.

Dysarthria - disorder of the organization of speech motor skills.

Adiadochokinesis - slowing down of reactions when changing one type of movement to directly opposite ones.

Dystonia - an involuntary increase or decrease in muscle tone.

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

Ataxia - impaired coordination of movements.

Dysmetry - 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 violation that occurs after damage to the cerebellum. The main manifestation of these disorders is the classic triad of symptoms - asthenia, ataxia and atony. The emergence of the latter is a consequence of a violation of the main function of the cerebellum - control and coordination of motor activity of the motor centers located at different levels of the central nervous system. Normally, our movements are always coordinated, various muscles are involved in their implementation, contracting or relaxing with the necessary force at the necessary time. A high degree of coordination of muscle contraction predetermines 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. When the cerebellum is damaged, such coordination is impaired - the movements become uncertain, jerky, abrupt.

One of the manifestations of impaired coordination of movements is the development ataxia - unnatural, shaky gait with legs wide apart, balancing arms abducted, with the help of which the patient maintains body balance. The movements are uncertain, accompanied by excessive jerky throws from side to side. The patient cannot stand and walk on toes or heels.

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

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

A delay in the termination of an already initiated contraction of one of the antagonistic muscle groups leads to dysmetria and the impossibility of performing precise actions.

Continuously receiving sensory information from the proprioceptors of the locomotor apparatus at rest and during the exercise of movements, as well as information from the cerebral cortex, the cerebellum uses it to regulate, through feedback channels, the strength and temporal characteristics of movements initiated and controlled by the cerebral cortex. Violation of this function of the cerebellum, when damaged, leads to tremor. A characteristic of a tremor of cerebellar origin is its intensification at the final stage of movement - intentional tremor. This distinguishes it from the tremor that occurs when the basal nuclei are damaged, which manifests itself rather at rest and weakens with movements.

Neocerebellum is involved in motor learning, planning and control of voluntary movement. This is confirmed by observations that changes in neuronal activity in the deep nuclei of the cerebellum occur simultaneously with those in the pyramidal neurons of the motor cortex even before the start of movements. Vestibulocerebellum and spinocerebellum affect motor functions through the neurons of 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 y-motor neurons of the spinal cord. In this way, the cerebellum controls the sensitivity of the muscle spindle receptors to decreased tone and muscle stretching. With damage to the cerebellum, its tonic effect on y-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 y- and a-motor neurons during contraction. Ultimately, this leads to a decrease in muscle tone at rest (hypotension), as well as to a violation of the smoothness and accuracy of movements.

At the same time, in some muscles, another variant of changes in tone develops, when, when the interaction of y- and a-motor neurons is disturbed, the tone of the latter becomes high at rest. This is accompanied by the development of a-rigidity in individual muscles and an uneven distribution of tone. This combination of hypotension in some muscles with hypertension in others is called dystonia. It is obvious that the presence of dystonia and impaired coordination in the patient makes his movements uneconomical, high energy consumption. For this reason, patients develop asthenia - rapid fatigue and decreased muscle strength.

One of the frequent manifestations of the lack of coordination function with damage to a number of parts of the cerebellum is imbalance in the body and gait. In particular, damage to the shred, nodule and the anterior lobe of the cerebellum may develop imbalance and posture, dystonia, impaired coordination of semi-automatic movements and gait instability, spontaneous nystagmus of the eyes.

If the connections of the cerebellar hemispheres with the motor areas of the cerebral hemispheres are damaged, the execution of voluntary movements may be impaired - they develop ataxia and dysmetria. In this case, the patient loses the ability to complete the started movement in time. At the final stage of the movement, tremor, uncertainty, additional movements occur, with the help of which the patient seeks to correct the inaccuracy of the movement being performed. These changes are characteristic of cerebellar dysfunctions and help to differentiate them from movement disorders in case of damage to the basal nuclei, when patients have difficulty starting movements and muscle tremor in mowing. To detect dysmetria, the subject is asked to perform a knee-heel or finger-nose test. In the latter case, a person with closed eyes should slowly bring the previously abducted hand and touch the tip of the nose with the index finger. If the cerebellum is damaged, the smoothness of the hand movement is lost and its trajectory can be zigzag. At the final stage of the movement, additional hesitation and finger misses the target may occur.

Cerebellar damage can be accompanied by the development asynergiescharacterized by the collapse of complex movements; dysdiadochokinesia, manifested by difficulty or inability to perform synchronized actions with two hands. The degree of dysdiadochokinesia increases with an increase in the frequency of performing the same type of movements. Often, as a result of a violation of the coordination of the muscles of the speech motor apparatus (respiratory muscles, muscles of the larynx), patients develop speech ataxia or dysarthria.

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

From the above examples of movement disorders after damage to the cerebellum, it follows that it performs or directly participates in the performance of a number of motor functions. Among them are the maintenance of muscle tone and posture, participation in maintaining the balance of the body in space, programming the forthcoming movements and their implementation (participation in the selection of muscles, control of the duration and strength of contraction of the muscles performing the movement), participation in the organization and coordination of complex movements (coordination of the 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 associated with numerous afferent connections with many structures of the central nervous system. Recent data obtained by the methods of functional magnetic resonance imaging, positron emission tomography and clinical observations have given grounds to believe that the motor function of the cerebellum is not its only function. The cerebellum is actively involved in the continuous tracking and analysis of sensory, cognitive and motor information, in preliminary calculations of the probability of certain events, associative and anticipatory learning, thereby releasing the higher parts of the brain and the cortex to carry out higher-order functions and, in particular, consciousness.

One of the important functions of Purkinje cells VI-VII of the cerebellar lobules is participation in the implementation of the processes of the latent phase of orientation and visual-spatial attention. The cerebellum prepares the internal systems of the brain for upcoming events, supporting the work of a wide range of brain systems involved in motor and non-motor functions (the inclusion of systems of prediction, orientation and attention). An increase in neural activity in the posterior regions of the cerebellum is recorded in healthy subjects in the course of their visual selection of goals when solving problems requiring attention without a motor component, when solving problems in conditions of shifting attention, solving spatial or temporal problems.

Clinical observations of the consequences that develop in humans after suffering cerebellar diseases confirm the possibility of the cerebellum performing these functions. It turned out that in cerebellar diseases, along with movement disorders, the latent orientation of visual-spatial attention slows down. A healthy person, when solving problems requiring spatial attention, orients attention approximately 100 ms after the presentation of the task. Patients with cerebellar injuries show clear signs of attention orientation only after 800-1200 ms; their ability to quickly switch attention is impaired. Disorder of attention becomes especially pronounced after damage to the cerebellar worm. Damage to the cerebellum is accompanied by a decrease in cognitive functions, impaired social and cognitive development of the child.