The cerebellum - comparative anatomy and evolution. cerebellum - comparative anatomy and evolution Anatomy of the human cerebellum

(lat. Cerebellum- literally "small brain") - the part of the brain of vertebrates responsible for the coordination of movements, the regulation of balance and muscle tone. In humans, it is located behind the medulla oblongata and the pons, under the occipital lobe of the cerebral hemispheres. With the help of three pairs of legs, the cerebellum receives information from the cerebral cortex, the basal ganglia of the extrapyramidal system, the brain stem and spinal cord. In different taxa of vertebrates, the relationship with other parts of the brain can vary.

In vertebrates with cerebral cortex, the cerebellum is a functional offshoot of the main cortex-spinal cord axis. The cerebellum receives a copy of the 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 one signals the current state of the regulated variable (muscle tone, position of the body and limbs in space), and the second one gives an idea of ​​the desired final state of the variable. Correlating the first and second, the cerebellar cortex can calculate the error reported by the motor centers. Thus, the cerebellum smoothly corrects both spontaneous and automatic movements.

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

Comparative anatomy and evolution

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

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

The cerebellum is present in representatives of all classes of vertebrates, including cyclostomes, in which it changes the shape of the transverse plate, spreads through the anterior part 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 similar brain formations.

There is a significant variety of shapes and sizes in different biological species. For example, the cerebellum of lower vertebrates is connected to the hindbrain by a continuous plate, in which fiber bundles are not anatomically distinguished. In mammals, these bundles form three pairs of structures called the cerebellar peduncles. Through the legs of the cerebellum, the connections of the cerebellum with other parts of the central nervous system occur.

Cyclostomes and fish

The cerebellum has the widest 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 factors. The most obvious has to do with pelagic lifestyles, predation, or the ability to swim effectively through the water column. The cerebellum reaches its greatest development in pelagic sharks. It forms real furrows 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 provision of the vestibular apparatus and the sensorimotor system. This conclusion is confirmed by the study of the brain of sharks, lead a benthic lifestyle. The nurse shark does not have a developed cerebellum, and the cavity of the IV ventricle is completely open. Its habitat and way of life does not impose such strict requirements as in long-winged sharks. The result was a relatively modest size of the cerebellum.

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

The size and shape of the cerebellum in primordial vertebrates may differ not only in connection with the pelagic or relatively sedentary way of life. Since the cerebellum is the center of somatic sensitivity analysis, it takes the most active part in the processing of electroreceptor signals. A lot of first-water vertebrates have electroreception (70 species of fish have developed electroreceptors, 500 can generate electrical discharges of various powers, 20 are capable of both generating and receptive electric fields). In all fish with electroreception, the cerebellum is extremely well developed. If the main system of afferentation becomes electroreception of its own electromagnetic field or external electromagnetic fields, then the cerebellum begins to play the role of a sensory and motor center. Often the size of their cerebellum is so large that it covers the entire brain from the dorsal (back) surface.

Many vertebrate species have areas of the brain that are similar to the cerebellum in terms of cellular cytoarchitectonics and neurochemistry. Most species of fish and amphibians have a lateral line, an organ that senses changes in water pressure. The part of the brain that receives information from the lateral line, the so-called octavolateral nucleus, has a structure similar to the cerebellum.

Amphibians and reptiles

In amphibians, the cerebellum is 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 is an evolutionary justification. A suitable environment for the formation of the nervous system in reptiles could be giant coal blockages, consisting mainly of club mosses, horsetails and ferns. In such multi-meter blockages from rotten or hollow tree trunks, ideal conditions could have developed for the evolution of reptiles. Modern deposits of coal directly indicate that such blockages from tree trunks were very widespread and could become a large-scale transitional environment for amphibians to reptiles. In order to take advantage of the biological benefits of tree blockages, several special characteristics had to be acquired. First, it was necessary to learn how to navigate well in three-dimensional space. For amphibians, this is not an easy task, since their cerebellum is quite small. Even in specialized tree frogs, which are a dead end branch of evolution, the cerebellum is much smaller than in reptiles. In reptiles, neuronal interconnections are formed between the cerebellum and the cerebral cortex.

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

Birds

The cerebellum of birds consists of a large posterior part and two small lateral appendages. It completely covers the rhomboid fossa. The middle part of the cerebellum is divided by transverse grooves into numerous leaflets. The ratio of the mass of the cerebellum to the mass of the entire brain is the largest in birds. This is due to the need for fast and accurate coordination of movements in flight.

In birds, the cerebellum consists of a massive middle part (worm), crossed mainly by 9 convolutions, and two small particles that are homologous to the cerebellar bundle of mammals, including humans. Birds are characterized by the perfection of the vestibular apparatus and the system of coordination of movements. The result of the intensive development of the coordination sensorimotor centers was the appearance of a large cerebellum with real folds - furrows and convolutions. The cerebellum of birds became the first structure of the brain of vertebrates, which was supposed to be measles and a folded structure. Complex movements in three-dimensional space caused the development of the cerebellum of birds as a sensorimotor center for coordinating movements.

mammals

A characteristic feature of the mammalian cerebellum is the enlargement of the lateral parts of the cerebellum, which mainly interact with the cerebral cortex. In the context of evolution, the enlargement of the lateral portions of the cerebellum (neocerebelum) goes hand in hand with the enlargement of the frontal lobes of the cerebral cortex.

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

In monotremes, as in birds, the middle section of the cerebellum predominates over the lateral ones, which are located in the form of insignificant appendages. In marsupials, edentulous, bats and rodents, the middle section is not inferior to the lateral ones. Only in carnivores and ungulates are the lateral parts larger than the middle section, forming the cerebellar hemispheres. In primates, the middle section, in comparison with the hemispheres, is rather undeveloped.

The predecessors of man and lat. Homo sapiens time of the Pleistocene, the increase in the frontal lobes took place at a faster pace than in the cerebellum.

Anatomy of the human cerebellum

A feature of the human cerebellum is that, like the brain, it consists of the right and left hemispheres (lat. Hemispheria cerebelli) and an odd structure, they are connected by a “worm” (lat. Vermis cerebelli). The cerebellum occupies almost the entire posterior cranial fossa. The transverse size of the cerebellum (9-10 cm) is much larger than its anterior-posterior size (3-4 cm).

The mass of the cerebellum in an adult ranges from 120 to 160 grams. By the time of birth, the cerebellum is less developed than the cerebral hemispheres, but in the first year of life it develops faster than other parts of the brain. A pronounced increase in the cerebellum is noted between the fifth and eleventh months of life, when the child learns to sit and walk. The mass of the cerebellum of an infant is about 20 grams, 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 up to 6 years of age, its mass reaches the lower limit of the normal adult - 120 grams.

Above the cerebellum lie the occipital lobes of the cerebral hemispheres. The cerebellum is delimited from the cerebrum by a deep fissure into which a process of the dura mater of the brain is wedged - the tent of the cerebellum (lat. Tentorium cerebelli) stretched over the posterior cranial fossa. Anterior to the cerebellum is the pons and medulla oblongata.

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

Horizontal slot (lat. Fissura horizontalis) that goes from the middle legs of the cerebellum to the posterior notch of the cerebellum, divides each hemisphere of the cerebellum into two surfaces: the upper one, obliquely descending along the edges and a relatively flat and convex lower one. 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 valley of the cerebellum (lat. Vallecula cerebelli) at the bottom of which is a worm.

On the cerebellar vermis, the upper and lower surfaces are distinguished. Furrows running along the sides of the worm separate it from the cerebellar hemispheres: on the front surface - the smallest, on the back - deeper.

The cerebellum consists of gray and white matter. The gray matter of the hemispheres and the cerebellar vermis, located in the surface layer, forms the cerebellar cortex (lat. Cortex cerebelli) and the accumulation of gray matter in the depths of the cerebellum - the nucleus of the cerebellum (lat. Nuclei cerebelli). White matter - the brain body of the cerebellum (lat. Corpus medullare cerebelli), lies in the thickness of the cerebellum and, through the mediation of three pairs of cerebellar peduncles (upper, middle and lower), connects the gray matter of the cerebellum with the brain stem and spinal cord.

Worm

The cerebellar vermis governs posture, tone, supportive movement, and body balance. Worm dysfunction in humans manifests itself in the form of static-locomotor ataxia (impaired standing and walking).

Shares

The surfaces of the hemispheres and the cerebellar vermis are divided by more or less deep cerebellar fissures (lat. Fissurae cerebelli) on various in size numerous arcuately curved leaves of the cerebellum (lat. Folia cerebelli) most of which are located almost parallel to each other. The depth of these furrows 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 separate lobes of the cerebellum. The lobes of the same name of both hemispheres are delimited by another groove, which passes from the worm from one hemisphere to another, as a result of which two - right and left - lobes of the same name of the hemispheres correspond to a certain share of the worm.

Individual particles form parts of the cerebellum. There are three such parts: anterior, posterior and shred-nodular.

The worm and hemispheres are covered with gray matter (cerebellar cortex), inside which is white matter. The white matter, branching, penetrates into each gyrus in the form of white stripes (lat. Laminae albae). Arrow-like sections of the cerebellum show a peculiar pattern, called the "tree of life" (lat. Arbor vitae cerebelli). The subcortical nuclei of the cerebellum lie within the white matter.

The cerebellum is connected to neighboring brain structures through three pairs of legs. Cerebellar peduncles (lat. Pedunculi cerebellares) are systems of driveways, the fibers of which go towards the cerebellum and from it:

1. Inferior cerebellar peduncles (lat. Pedunculi cerebellares inferiores) go from the medulla oblongata to the cerebellum.
2. Middle cerebellar peduncles (lat. Pedunculi cerebellares medii)- from the pons to the cerebellum.
3. Superior cerebellar peduncles (lat. Pedunculi cerebellares superiores)- go to the midbrain.

Nuclei

The nuclei of the cerebellum are paired accumulations of gray matter, which lie in the thickness of the white, closer to the middle, that is, the cerebellar vermis. There are the following cores:

1. dentate nucleus (lat. Nucleus dentatus) lies in the medial-lower areas of the white matter. This nucleus is a wave-like plate of gray matter with a small break in the middle region, which is called the gate of the dentate nucleus (lat. Hilum nuclei dentait). The jagged core is like a butter core. This similarity is not accidental, since both nuclei are connected by conductive pathways, lead-cerebellar fibers (lat. Fibrae olivocerebellares), and each twist of the oil core is similar to the twist of the other.
2. Korkopodibne kernel (lat. Nucleus emboliformis) located medially and parallel to the dentate nucleus.
3. Spherical nucleus (lat. Nucleus globosus) lies somewhat in the middle of the crust-like nucleus and can be presented in the section in the form of several small balls.
4. The core of the tent (lat. Nucleus fastigii) 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 IV ventricle.

The nucleus of the tent, being the most medial, is located on the sides of the midline in the area where the tent is pressed into the cerebellum (lat. fastigium). Bichnishe from it is respectively spherical, crust-like and dentate nuclei. These nuclei have different phylogenetic ages: nucleus fastigii refers to the ancient part of the cerebellum (lat. Archicerebellum) connected to the vestibular apparatus; nuclei emboliformis et globosus - up to old part (lat. Paleocerebellum), which arose in connection with the movements of the body, and nucleus dentatus - to the new (lat. neocerebellum), developed in connection with movement with the help of limbs. Therefore, when each of these parts is damaged, various aspects of the motor function are violated, corresponding to different stages of phylogenesis, namely: archicerebellum balance of the body is disturbed, with injuries paleocerebellum the work of the muscles of the neck and trunk is disrupted, if damaged neocerebellum - work of the muscles of the limbs.

The nucleus of the tent is located in the white matter of the worm, the remaining nuclei lie in the hemispheres of the cerebellum. Almost all information coming from the cerebellum is switched to its nuclei (with the exception of the connection of the glomerular-nodular lobule with the vestibular nucleus of Deiters).

Cerebellum(lat. cerebellum- literally "small brain") - the part of the brain of vertebrates responsible for the coordination of movements, the regulation of balance and muscle tone. In humans, it is located behind the pons, under the occipital lobes of the brain. Through three pairs of legs, the cerebellum receives information from the cerebral cortex, basal ganglia, brain stem and. Relationships with other parts of the brain may vary in different taxa of vertebrates.

In vertebrates that possess a cortex, the cerebellum is a functional offshoot of the main "cortex-spinal cord" axis. The cerebellum receives a copy of the afferent information transmitted from the cortex of the cerebral hemispheres, as well as efferent - from the motor centers of the cerebral cortex to. The first one signals the current state of the regulated variable (muscle tone, position of the body and limbs in space), and the second one gives an idea of ​​the required final state. Comparing the first and second, the cerebellar cortex can calculate, which reports to the motor centers. So the cerebellum continuously corrects both voluntary and automatic movements.

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

In different groups of animals, the cerebellum varies greatly in size and shape. 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 lampreys), in which it has the form of a transverse plate that spreads over the anterior section.

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

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

Cyclostomes and fish

The cerebellum has the largest 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 factors. The most obvious is associated with pelagic lifestyle, predation or the ability to swim efficiently in the water column. The cerebellum reaches its greatest development in pelagic sharks. Real furrows and convolutions are formed in it, 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 provision of the vestibular apparatus and the sensorimotor system. This conclusion is confirmed by the study of the brain of sharks that live near the bottom. The nurse shark does not have a developed cerebellum, and the cavity of the IV ventricle is completely open. Its habitat and way of life does not impose such stringent requirements on spatial orientation as those of the long-winged shark. The result was a relatively modest size of the cerebellum.

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

The size and shape of the cerebellum in primary aquatic vertebrates can change not only in connection with a pelagic or relatively sedentary lifestyle. Since the cerebellum is the center of somatic sensitivity analysis, it takes an active part in the processing of electroreceptor signals. Very many primary aquatic vertebrates have electroreception (70 species of fish have developed electroreceptors, 500 can generate electrical discharges of various powers, 20 are able to both generate and recieve electric fields). In all fish with electroreception, the cerebellum is extremely well developed. If the main system of afferentation becomes the electroreception of its own electromagnetic field or external electromagnetic fields, then the cerebellum begins to play the role of a sensory (sensitive) and motor center. Often, their cerebellum is so large that it covers the entire brain from the dorsal (posterior) surface.

Many vertebrate species have areas of the brain that are similar to the cerebellum in terms of cellular cytoarchitectonics and neurochemistry. Most fish and amphibian species have a lateral line organ that senses changes in water pressure. The part of the brain that receives information from this organ, the so-called octavolateral 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, an increase in the size of the cerebellum is noted, which has an evolutionary justification. A suitable environment for the formation of the nervous system in reptiles could be giant coal blockages, consisting mainly of club mosses, horsetails and ferns. In such multi-meter blockages from rotten or hollow tree trunks, ideal conditions could have developed for the evolution of reptiles. Modern deposits of coal directly indicate that such blockages from tree trunks were very widespread and could become a large-scale transitional environment for amphibians to reptiles. In order to take advantage of the biological benefits of tree blockages, it was necessary to acquire several specific qualities. First, it was necessary to learn how to navigate well in a three-dimensional environment. For amphibians, this is not an easy task, since their cerebellum is very small. Even specialized tree frogs, which are a dead-end evolutionary branch, have a much smaller cerebellum than reptiles. In reptiles, neuronal interconnections are formed between the cerebellum and the cerebral cortex.

The cerebellum in snakes and lizards, as well 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. At the same time, in crocodiles, its middle part differs in size and bulge.

Birds

The cerebellum of birds consists of a larger middle part and two small lateral appendages. It completely covers the rhomboid fossa. The middle part of the cerebellum is divided by transverse grooves into numerous leaflets. The ratio of the mass of the cerebellum to the mass of the entire brain is the highest in birds. This is due to the need for fast and accurate coordination of movements in flight.

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

mammals

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

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

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

The predecessors of man and lat. homo sapiens During the Pleistocene, the increase in the frontal lobes occurred at a faster rate than in the cerebellum.

Shark brain. The cerebellum is highlighted in blue

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

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

The cerebellum is present in representatives of all classes of vertebrates, including cyclostomes, in which it has the form of a transverse plate that spreads over the anterior part 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 formation.

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

Cyclostomes and fish

The cerebellum has the largest 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 factors. The most obvious is associated with pelagic lifestyle, predation or the ability to swim efficiently in the water column. The cerebellum reaches its greatest development in pelagic sharks. Real furrows and convolutions are formed in it, 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 provision of the vestibular apparatus and the sensorimotor system. This conclusion is confirmed by the study of the brain of sharks that live near the bottom. The nurse shark does not have a developed cerebellum, and the cavity of the IV ventricle is completely open. Its habitat and way of life does not impose such stringent requirements on spatial orientation as those of the long-winged shark. The result was a relatively modest size of the cerebellum.

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

The size and shape of the cerebellum in primary aquatic vertebrates can change not only in connection with a pelagic or relatively sedentary lifestyle. Since the cerebellum is the center of somatic sensitivity analysis, it takes an active part in the processing of electroreceptor signals. Very many primary aquatic vertebrates possess electroreception. In all fish with electroreception, the cerebellum is extremely well developed. If the electroreception of one's own electromagnetic field or external electromagnetic fields becomes the main afferent system, then the cerebellum begins to play the role of a sensory and motor center. Their cerebellum is often so large that it covers the entire brain from the dorsal surface.

Many vertebrate species have areas of the brain that are similar to the cerebellum in terms of cellular cytoarchitectonics and neurochemistry. Most fish and amphibian species have a lateral line organ that senses changes in water pressure. The part of the brain that receives information from this organ, the so-called octavolateral 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, an increase in the size of the cerebellum is noted, which has an evolutionary justification. A suitable environment for the formation of the nervous system in reptiles could be giant coal blockages, consisting mainly of club mosses, horsetails and ferns. In such multi-meter blockages from rotten or hollow tree trunks, ideal conditions could have developed for the evolution of reptiles. Modern deposits of coal directly indicate that such blockages from tree trunks were very widespread and could become a large-scale transitional environment for amphibians to reptiles. In order to take advantage of the biological benefits of tree blockages, it was necessary to acquire several specific qualities. First, it was necessary to learn how to navigate well in a three-dimensional environment. For amphibians, this is not an easy task, since their cerebellum is very small. Even specialized tree frogs, which are a dead-end evolutionary branch, have a much smaller cerebellum than reptiles. In reptiles, neuronal interconnections are formed between the cerebellum and the cerebral cortex.

The cerebellum in snakes and lizards, as well 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. At the same time, in crocodiles, its middle part differs in size and bulge.

Birds

The cerebellum of birds consists of a larger middle part and two small lateral appendages. It completely covers the rhomboid fossa. The middle part of the cerebellum is divided by transverse grooves into numerous leaflets. The ratio of the mass of the cerebellum to the mass of the entire brain is the highest in birds. This is due to the need for fast and accurate coordination of movements in flight.

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

mammals

A distinctive feature of the mammalian cerebellum is the enlargement of the lateral parts of the cerebellum, which mainly 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 a vermis and paired hemispheres. Mammals are also characterized by an increase in the surface area of ​​the cerebellum due to the formation of furrows and folds.

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

The predecessors of man and lat. Homo sapiens of the Pleistocene time, the increase in the frontal lobes occurred at a faster rate compared to the cerebellum.

The cerebellum (cerebellum; a synonym for the small brain) is an unpaired part of the brain that is in charge of coordinating voluntary, involuntary and reflex movements; located under the cerebellar mantle in the posterior cranial fossa.

Comparative anatomy and embryology

The cerebellum is present in all vertebrates, although it is developed differently in representatives of the same class. Its development is determined by the lifestyle of the animal, the peculiarities of its movements - the more complex they are, the more developed the cerebellum. It reaches great development in birds; their cerebellum is represented almost exclusively by the middle lobe; only some birds have hemispheres. The cerebellar hemispheres are a formation characteristic of mammals. In parallel with the development of the cerebral hemispheres, the lateral parts of the cerebellum developed, which, together with the middle sections of the worm, formed a new cerebellum (neocerebellum). The special development of neocerebellum in mammals is associated primarily with changes in the nature of motor skills, since the cerebral cortex organizes elementary motor acts, and not their complexes. Phylogenetically, there is a basis for the division of the cerebellum (respectively, the emergence of motility based on the principle of continuity, discontinuity and cortical motility) into the ancient vestibular sections (archicerebellum), its older sections, in which the bulk of the spinal-cerebellar fibers (paleocerebellum) ends, and the newest departments (neocerebellum).

The common anthropometric classification is based on the external shape of the organ without regard to functional features. Larsell (O. Larsell, 1947) proposed a diagram of the cerebellum, in which the anatomical and comparative anatomical classifications are compared (Fig. 1).

Schemes of functional localization in the cerebellum are based on the study of phylogenesis, anatomical connections of the cerebellum, experimental and clinical observations.

The study of the distribution of fibers of the afferent systems made it possible to distinguish three main parts in the cerebellum of mammals: the most ancient vestibular, spinal-cerebellar region and the phylogenetically newest middle lobe, in which mainly the fibers from the pons nuclei terminate.

According to another scheme, based on the study of the distribution of afferent and afferent fibers of the cerebellum of mammals and humans, it is divided into two main parts (Fig. 2): flocculo-nodular lobule (lobus flocculonodularis) - the vestibular section of the cerebellum, damage to which causes imbalance without disturbing asymmetric movements in the limbs, and the body (corpus cerebelli).

Rice. 1. Human cerebellum (diagram). The usual anatomical classification is shown on the right, comparative anatomical - on the left. (According to Larsell.)

Rice. 2. Cerebellar cortex. Diagram showing the division of the mammalian cerebellum and the distribution of afferent connections.

The cerebellum develops from the posterior cerebral bladder (metencephalon). At the end of the 2nd month of intrauterine life, the lateral (pterygoid) plates of the brain tube in the region of the hindbrain are interconnected by a curved leaf; the bulge of this leaflet protruding into the cavity of the IV ventricle is a vestige of the cerebellar vermis. The cerebellar vermis gradually thickens and in the 3rd month of intrauterine life already has 3-4 sulci and convolutions; the gyrus of the cerebellar hemisphere begins to stand out only in the middle of the 4th month. Nuclei dentatus et fastigii appear at the end of the 3rd month. At the 5th month, the cerebellum already receives its main form, and over the last months of intrauterine life, the size of the cerebellum, the number of grooves and grooves that divide the main lobes of the cerebellum into smaller lobules increase, which determine the characteristic complexity of the structure of the cerebellum and folding, which is especially clearly visible on sections of the cerebellum.

Goals:

• reveal the features of the nervous system of vertebrates, its role in the regulation of vital processes and their relationship with the environment;
• to develop the ability of students to distinguish classes of animals, arrange them in order of complexity in the process of evolution.

Equipment and equipment of the lesson:

• Program and textbook by N.I. Sonin “Biology. Living organism". 6th grade.
• Handout - a table-grid "Departments of the brain of vertebrates."
• Vertebrate brain models.
• Inscriptions (names of classes of animals).
• Drawings depicting representatives of these classes.

During the classes.

I. Organizational moment.

II. Repetition of homework (frontal survey):

1. What systems regulate the activity of the animal organism?
2. What is irritability or sensitivity?
3. What is a reflex?
4. What are reflexes?
5. What are these reflexes?
   a) saliva is produced by the smell of food?
   b) does the person turn on the light despite the absence of a light bulb?
   c) Does the cat run to the sound of the refrigerator door opening?
   d) does the dog yawn?
6. What is the nervous system of a hydra?
7. How is the nervous system of an earthworm arranged?

III. New material:

(? - questions asked to the class during the explanation)

We are studying now Section 17, what is it called?
Coordination and regulation of what?
What animals did we talk about in class?
Are they invertebrates or vertebrates?
What groups of animals do you see on the board?

Today in the lesson we will study the regulation of the life processes of vertebrates.

Topic:“Regulation in vertebrates(write in notebook).

Our goal will be to consider the structure of the nervous system of different vertebrates. At the end of the lesson, we will be able to answer the following questions:

1. How is the behavior of animals related to the structure of the nervous system?
2. Why is it easier to train a dog than a bird or a lizard?
3. Why do doves in the air can roll over during the flight?

During the lesson, we will fill in the table, so everyone has a piece of paper with a table on their desk.

Where is the nervous system located in annelids and insects?

In vertebrates, the nervous system is located on the dorsal side of the body. It consists of the brain, spinal cord and nerves.

? 1) Where is the spinal cord located?

2) Where is the brain located?

It distinguishes between the anterior, middle, hindbrain and some other departments. In different animals, these departments are developed in different ways. This is due to their lifestyle and the level of their organization.

Now we will listen to reports on the structure of the nervous system of different classes of vertebrates. And you make notes in the table: does this group of animals have this part of the brain or not, how developed is it compared to other animals? After filling out the table remains with you.

(The table must be printed in advance according to the number of students in the class)

Table. Parts of the brain of vertebrates.

Before the lesson, inscriptions and drawings are attached to the board. During the answers, students hold models of the brain of vertebrates in their hands and show the departments they are talking about. After each answer, the model is placed on a demonstration table near the board under the inscription and drawing of the corresponding group of animals. It turns out something like this scheme ...

Scheme:

AT

Spinal cord. The central nervous system of fish, like that of the lancelet, has the form of a tube. Its posterior section - the spinal cord - is located in the spinal canal, formed by the upper bodies and arches of the vertebrae. From the spinal cord, between each pair of vertebrae, nerves depart to the right and left, which control the work of the muscles of the body and the fins and organs located in the body cavity.

The nerves from the sensory cells on the body of the fish send signals of irritation to the spinal cord.

Brain. The anterior part of the neural tube of fish and other vertebrates is modified into a brain, protected by the bones of the cranium. In the brain of vertebrates, departments are distinguished: forebrain, diencephalon, midbrain, cerebellum and medulla oblongata. All these parts of the brain are of great importance in the life of the fish. For example, the cerebellum controls the coordination of movement and balance of the animal. The medulla oblongata gradually passes into the spinal cord. It plays a large role in controlling respiration, circulation, digestion and other essential bodily functions.

! Let's see what you wrote down?

The central nervous system and sense organs of amphibians consist of the same departments as those of fish. The forebrain is more developed than in fish, and two swellings can be distinguished in it - large hemispheres. The body of amphibians is close to the ground, and they do not have to maintain balance. In connection with this, the cerebellum, which controls the coordination of movements, is less developed in them than in fish. The nervous system of the lizard is similar in structure to the corresponding systems of amphibians. In the brain, the cerebellum, which is in charge of balance and coordination of movements, is more developed than in amphibians, which is associated with greater mobility of the lizard and a significant variety of its movements.

Nervous system. The optic tubercles of the midbrain are well developed in the brain. The cerebellum is much larger than in other vertebrates, as it is the center of coordination and coordination of movements, and birds in flight make very complex movements.

Compared with fish, amphibians and reptiles, birds have enlarged forebrain hemispheres.

The mammalian brain consists of the same sections as those of other vertebrates. However, the large hemispheres of the forebrain have a more complex structure. The outer layer of the cerebral hemispheres consists of nerve cells that form the cerebral cortex. In many mammals, including the dog, the cerebral cortex is so enlarged that it does not lie in an even layer, but forms folds - convolutions. The more nerve cells in the cerebral cortex, the more it is developed, the more convolutions in it. If the cerebral cortex is removed from the experimental dog, then the animal retains its innate instincts, but conditioned reflexes are never formed.

The cerebellum is well developed and, like the cerebral hemispheres, has many convolutions. The development of the cerebellum is associated with the coordination of complex movements in mammals.

Conclusion on the table (questions to the class):

1. What parts of the brain do all classes of animals have?
2. Which animals will have the most developed cerebellum?
3. Forebrain?
4. Which have a cortex on the hemispheres?
5. Why is the cerebellum less developed in frogs than in fish?

Now consider the structure of the sense organs of these animals, their behavior, in connection with such a structure of the nervous system (tell the same students who talked about the structure of the brain):

The sense organs allow fish to navigate well in the environment. The eyes play an important role in this. The perch sees only at a relatively close distance, but distinguishes the shape and color of objects.

In front of each eye of a perch, two nostril openings are placed, leading to a blind sac with sensitive cells. This is the organ of smell.

The organs of hearing are not visible from the outside, they are placed on the right and left of the skull, in the bones of its back. Due to the density of water, sound waves are well transmitted through the bones of the skull and are perceived by the fish's hearing organs. Experiments have shown that fish can hear the steps of a person walking along the shore, the ringing of a bell, a shot.

Taste organs are sensitive cells. They are located in the perch, like other fish, not only in the oral cavity, but are also scattered over the entire surface of the body. There are also tactile cells. Some fish (for example, catfish, carp, cod) have tactile antennae on their heads.

Fish have a special sense organ - lateral line. A series of holes are visible outside the body. These holes are connected to a channel located in the skin. The canal contains sensory cells connected to a nerve running under the skin.

The lateral line senses the direction and strength of the water current. Thanks to the lateral line, even a blinded fish does not run into obstacles and is able to catch moving prey.

? Why can't you talk loudly while fishing?

2. Amphibians.

The structure of the sense organs corresponds to the terrestrial environment. For example, by blinking its eyelids, the frog removes dust particles adhering to the eye and moistens the surface of the eye. Like fish, frogs have an inner ear. However, sound waves travel much worse in air than in water. Therefore, for better hearing, the frog has also developed middle ear. It begins with the sound-perceiving eardrum - a thin round film behind the eye. From her sound vibrations through auditory ossicle transmitted to the inner ear.

When hunting, sight plays a major role. Noticing any insect or other small animal, the frog throws out a wide sticky tongue from its mouth, to which the victim sticks. Frogs grab only moving prey.

The hind legs are much longer and stronger than the front legs, they play a major role in movement. The sitting frog rests on slightly bent forelimbs, while the hind limbs are folded and located on the sides of the body. Quickly straightening them, the frog makes a jump. The front legs at the same time protect the animal from hitting the ground. The frog swims, pulling and straightening the hind limbs, while pressing the front to the body.

? How do frogs move in water and on land?

3. Birds.

Sense organs. Vision is best developed - when moving quickly in the air, only with the help of the eyes can one assess the situation from a distance. The sensitivity of the eyes is very high. In some birds, it is 100 times greater than in humans. In addition, birds can clearly see objects that are far away, and distinguish details that are only a few centimeters from the eye. Birds have color vision, better developed than other animals. They distinguish not only primary colors, but also their shades, combinations.

Birds hear well, but their sense of smell is weak.

The behavior of birds is very complex. True, many of their actions are innate, instinctive. Such, for example, are the behavioral features associated with reproduction: pair formation, nest building, incubation. However, during the life of birds, more and more conditioned reflexes appear. For example, young chicks are often not afraid of humans at all, and with age they begin to treat people with caution. Moreover, many learn to determine the degree of danger: they are little afraid of the unarmed, and they fly away from a man with a gun. Domestic and tame birds quickly get used to recognizing the person who feeds them. Trained birds are able to perform various tricks at the direction of the trainer, and some (for example, parrots, lanes, crows) learn to repeat various words of human speech quite clearly.

Sense organs. Mammals have a developed sense of smell, hearing, sight, touch and taste, but the degree of development of each of these senses in different species is not the same and depends on the lifestyle and habitat. So, a mole living in the complete darkness of underground passages has underdeveloped eyes. Dolphins and whales almost do not distinguish smells. Most land mammals have a very sensitive sense of smell. Predators, including the dog, it helps to find prey on the trail; herbivores at a great distance can smell a creeping enemy; Animals smell each other. Hearing in most mammals is also well developed. This is facilitated by sound-catching auricles, which are mobile in many animals. Those animals that are active at night have especially delicate hearing. Vision is less important for mammals than for birds. Not all animals distinguish colors. The same gamut of colors that a person sees only monkeys.

The organs of touch are special long and stiff hair (the so-called "whiskers"). Most of them are located near the nose and eyes. Bringing their head closer to the object under study, mammals simultaneously sniff, examine and touch it. In monkeys, like in humans, the main organs of touch are the fingertips. The taste is especially developed in herbivores, which, thanks to this, easily distinguish edible plants from poisonous ones.
The behavior of mammals is no less complex than that of birds. Along with complex instincts, it is largely determined by higher nervous activity, based on the formation of conditioned reflexes during life. Conditioned reflexes are developed especially easily and quickly in species with a well-developed cerebral cortex.

From the first days of life, young mammals recognize their mother. As they grow, their personal experience in dealing with the environment is continuously enriched. The games of young animals (fighting, mutual pursuit, jumping, running) serve as good training for them and contribute to the development of individual methods of attack and defense. Such games are typical only for mammals.

Due to the fact that the environment is extremely changeable, new conditioned reflexes are constantly developed in mammals, and those that are not reinforced by conditioned stimuli are lost. This feature allows mammals to quickly and very well adapt to environmental conditions.

?What animals are the easiest to train? Why?