Development of the nervous system. Nervous system of vertebrates

Age of fetus (weeks)	Development of the nervous system
2,5	There is a neural groove
3.5	Formation of the neural tube and nerve cords
3 brain bubbles are formed; nerves and ganglia are formed
5 brain bubbles form
The meninges are outlined
Hemispheres of the brain reach a large size
Typical neurons appear in the cortex
The internal structure of the spinal cord is formed
Common structural features of the brain are formed; neuroglial cell differentiation begins
Distinguishable lobes of the brain
20-40	Myelination of the spinal cord begins (20 weeks), layers of the cortex appear (25 weeks), furrows and convolutions form (28-30 weeks), myelination of the brain begins (36-40 weeks)

Thus, the development of the brain in the prenatal period occurs continuously and in parallel, however, it is characterized by heterochrony: the rate of growth and development of phylogenetically older formations is greater than that of phylogenetically younger formations.

Genetic factors play a leading role in the growth and development of the nervous system during the prenatal period. The average brain weight of a newborn is approximately 350 g.

Morpho-functional maturation of the nervous system continues in the postnatal period. By the end of the first year of life, the weight of the brain reaches 1000 g, while in an adult the weight of the brain is on average 1400 g. Consequently, the main increase in brain mass occurs in the first year of a child's life.

The increase in brain mass in the postnatal period occurs mainly due to an increase in the number of glial cells. The number of neurons does not increase, as they lose the ability to divide already in the prenatal period. The total density of neurons (the number of cells per unit volume) decreases due to the growth of the soma and processes. The number of branches increases in dendrites.

In the postnatal period, myelination of nerve fibers also continues both in the central nervous system and the nerve fibers that make up the peripheral nerves (cranial and spinal.).

The growth of the spinal nerves is associated with the development of the musculoskeletal system and the formation of neuromuscular synapses, and the growth of the cranial nerves with the maturation of the sense organs.

Thus, if in the prenatal period the development of the nervous system occurs under the control of the genotype and practically does not depend on the influence of the external environment, then in the postnatal period, external stimuli become increasingly important. Irritation of receptors causes afferent streams of impulses that stimulate the morpho-functional maturation of the brain.

Under the influence of afferent impulses, spines are formed on the dendrites of cortical neurons - outgrowths, which are special postsynaptic membranes. The more spines, the more synapses and the more involved the neuron is in information processing.

Throughout the entire postnatal ontogenesis up to the pubertal period, as well as in the prenatal period, the development of the brain occurs heterochronously. So, the final maturation of the spinal cord occurs earlier than the brain. The development of stem and subcortical structures, earlier than cortical ones, the growth and development of excitatory neurons overtakes the growth and development of inhibitory neurons. These are general biological patterns of growth and development of the nervous system.

Morphological maturation of the nervous system correlates with the features of its functioning at each stage of ontogenesis. Thus, the earlier differentiation of excitatory neurons compared to inhibitory neurons ensures the predominance of flexor muscle tone over extensor tone. The arms and legs of the fetus are in a flexed position, which results in a posture that provides minimal volume, so that the fetus takes up less space in the uterus.

Improving the coordination of movements associated with the formation of nerve fibers occurs throughout the entire preschool and school periods, which is manifested in the consistent mastering of the posture of sitting, standing, walking, writing, etc.

An increase in the speed of movements is mainly due to the processes of myelination of peripheral nerve fibers and an increase in the speed of excitation of nerve impulses.

The earlier maturation of subcortical structures compared to cortical ones, many of which are part of the limbic structure, determines the peculiarities of the emotional development of children (the greater intensity of emotions, the inability to restrain them is associated with the immaturity of the cortex and its weak inhibitory effect).

In the elderly and senile age, anatomical and histological changes in the brain occur. Often there is atrophy of the cortex of the frontal and upper parietal lobes. The furrows become wider, the ventricles of the brain increase, the volume of white matter decreases. There is a thickening of the meninges.

With age, neurons decrease in size, while the number of nuclei in cells may increase. In neurons, the content of RNA, which is necessary for the synthesis of proteins and enzymes, also decreases. This impairs the trophic functions of neurons. It is suggested that such neurons tire faster.

In old age, the blood supply to the brain is also disturbed, the walls of blood vessels thicken and cholesterol plaques (atherosclerosis) are deposited on them. It also impairs the activity of the nervous system.

LITERATURE

Atlas “Human Nervous System”. Comp. V.M. Astashev. M., 1997.

Blum F., Leyzerson A., Hofstadter L. Brain, mind and behavior. M.: Mir, 1988.

Borzyak E.I., Bocharov V.Ya., Sapina M.R. Human anatomy. — M.: Medicine, 1993. V.2. 2nd ed., revised. and additional

Zagorskaya V.N., Popova N.P. Anatomy of the nervous system. Course program. MOSU, M., 1995.

Kishsh-Sentagothai. Anatomical atlas of the human body. - Budapest, 1972. 45th ed. T. 3.

Kurepina M.M., Vokken G.G. Human anatomy. - M .: Education, 1997. Atlas. 2nd edition.

Krylova N.V., Iskrenko I.A. Brain and pathways (Human anatomy in diagrams and drawings). M.: Publishing House of the Peoples' Friendship University of Russia, 1998.

Brain. Per. from English. Ed. Simonova P.V. — M.: Mir, 1982.

Human morphology. Ed. B.A. Nikityuk, V.P. Chtetsov. - M .: Publishing House of Moscow State University, 1990. S. 252-290.

Prives M.G., Lysenkov N.K., Bushkovich V.I. Human anatomy. - L .: Medicine, 1968. S. 573-731.

Saveliev S.V. Stereoscopic atlas of the human brain. M., 1996.

Sapin M.R., Bilich G.L. Human anatomy. - M .: Higher school, 1989.

Sinelnikov R.D. Atlas of human anatomy. - M .: Medicine, 1996. 6th ed. T. 4.

Sade J., Ford D. Fundamentals of neurology. — M.: Mir, 1982.

SECTION I. CYTOLOGICAL AND HISTOLOGICAL CHARACTERISTICS OF THE NERVOUS SYSTEM 3

SECTION II. STRUCTURE OF THE CENTRAL NERVOUS SYSTEM. thirty

SECTION III. BRAIN………………………………………………………… 46

SECTION IV. DEVELOPMENT OF THE NERVOUS SYSTEM……………………………. 92

LITERATURE…………………………………………………………………………………….. 102

Publishing license:
series ID No. 00865, registration date: 25.01.2000

Publisher address: 109383, Moscow, st. Highway, 86

Socio-Technological Institute of MGUS

Tissue is a collection of cells and intercellular substance similar in structure, origin and functions.

2 Some anatomists do not include the medulla oblongata in the hindbrain, but distinguish it as an independent department.

DEVELOPMENT OF THE NERVOUS SYSTEM IN ONTOGENESIS

Ontogeny, or the individual development of an organism, is divided into two periods: prenatal(intrauterine) and postnatal(after birth).

The first continues from the moment of conception and the formation of the zygote until birth; the second is from birth to death.

prenatal period in turn is divided into three periods: initial, embryonic and fetal.

Elementary The (pre-implantation) period in humans covers the first week of development (from the moment of fertilization to implantation in the uterine mucosa). Embryonic(prefetal, embryonic) period - from the beginning of the second week to the end of the eighth week (from the moment of implantation to the completion of organ laying).

Fetal The (fetal) period begins at the ninth week and lasts until birth. At this time, there is an increased growth of the body.

postnatal period ontogenesis is divided into eleven periods: 1st - 10th day - newborns; 10th day - 1 year - infancy; 1-3 years - early childhood; 4-7 years - the first childhood; 8-12 years - the second childhood; 13-16 years - adolescence; 17–21 years old - adolescence; 22-35 years - the first mature age; 36-60 years - the second mature age; 61-74 years - old age; from 75 years old - senile age, after 90 years old - centenarians.

Ontogeny ends with natural death.

The prenatal period of ontogenesis begins from the moment of the fusion of male and female germ cells and the formation zygotes. The zygote divides successively, forming a spherical blastula. At the blastula stage, further fragmentation and the formation of a primary cavity take place - blastocoel.

Then the process of gastrulation begins, as a result of which cells move in various ways into the blastocoel, with the formation bilayer embryo.

The outer layer of cells is called ectoderm, internal - endoderm. Inside the cavity of the primary intestine is formed - gastrocoel.

This is the gastrula stage. At the stage of neurula are formed neural tube, chord, somites and other embryonic rudiments.

The rudiment of the nervous system begins to develop at the end of the gastrula stage.

Rice. 16. Neural tube laying (schematic representation and cross-sectional view):

A-A'- level of the transverse cut; a- the initial stage of immersion of the medullary plate and the formation of the neural tube: 1 - neural tube; 2 - ganglionic plate; 3 - somite; b - completion of the formation of the neural tube and its immersion inside the embryo: 4 - ectoderm; 5 - central channel; 6 - white matter of the spinal cord; 7 - gray matter of the spinal cord; 8 - anlage of the spinal cord; 9 - bookmark of the brain

The cellular material of the ectoderm, located on the dorsal surface of the embryo, thickens, forming the medullary plate (Fig.

17, 2 ). This plate is limited laterally by medullary ridges. Cleavage of cells of the medullary plate (medulloblasts) and medullary ridges leads to the bending of the plate into a groove, and then to the closing of the edges of the groove and the formation of a medullary tube (Fig. 16a, 1 ). When the medullary ridges are connected, a ganglionic plate is formed, which then divides into ganglionic ridges.

17. Prenatal development of the human nervous system:

1 - neural crest; 2 - neural plate; 3 - neural tube; 4 - ectoderm; 5 - midbrain; 6 - spinal cord; 7 - spinal nerves; 8 - eye vesicle; 9 - forebrain; 10 - diencephalon; 11 - bridge; 12 - cerebellum; 13 - telencephalon

At the same time, the neural tube is immersed inside the embryo (Fig.

16c; 17, 3 ).

Homogeneous primary cells of the wall of the medullary tube - medulloblasts - differentiate into primary nerve cells (neuroblasts) and the original neuroglial cells (spongioblasts).

The cells of the inner layer of medulloblasts adjacent to the cavity of the tube turn into ependymal cells that line the lumen of the brain cavities. All primary cells are actively dividing, increasing the wall thickness of the brain tube and reducing the lumen of the nerve canal. Neuroblasts differentiate into neurons, spongioblasts into astrocytes and oligodendrocytes, ependymal cells into ependymal cells (at this stage of ontogenesis, ependymal cells can form neuroblasts and spongioblasts).

During the differentiation of neuroblasts, the processes elongate and turn into dendrites and an axon, which at this stage are devoid of myelin sheaths.

Myelination begins from the fifth month of prenatal development and is fully completed only at the age of 5–7 years. Synapses appear in the fifth month. The myelin sheath is formed within the CNS by oligodendrocytes, and in the peripheral nervous system by Schwann cells.

In the process of embryonic development, processes are also formed in macroglial cells (astrocytes and oligodendrocytes).

Microglial cells are formed from the mesenchyme and appear in the CNS along with the germination of blood vessels into it.

The cells of the ganglionic ridges differentiate first into bipolar, and then into pseudo-unipolar sensory nerve cells, the central process of which goes to the central nervous system, and the peripheral process goes to the receptors of other tissues and organs, forming the afferent part of the peripheral somatic nervous system.

The efferent part of the nervous system consists of axons of motor neurons of the ventral parts of the neural tube.

In the first months of postnatal ontogenesis, the intensive growth of axons and dendrites continues, and the number of synapses sharply increases due to the development of neural networks.

brain embryogenesis begins with the development in the anterior (rostral) part of the brain tube of two primary cerebral vesicles resulting from uneven growth of the walls of the neural tube (archencephalon and deuterencephalon).

The deuterencephalon, like the back of the brain tube (later the spinal cord), is located above the notochord. Archencephalon is laid in front of her. Then, at the beginning of the fourth week, the deuterencephalon in the embryo divides into the middle ( mesencephalon) and diamond-shaped ( rhombencephalon) bubbles.

And the archencephalon turns at this (three-bladder) stage into the anterior cerebral bladder ( prosencephalon) (rice.

17, 9 ). In the lower part of the forebrain, the olfactory lobes protrude (from which the olfactory epithelium of the nasal cavity, olfactory bulbs and tracts develop). Two ophthalmic vesicles protrude from the dorsolateral walls of the anterior cerebral vesicle.

In the future, the retina, optic nerves and tracts develop from them.

At the sixth week of embryonic development, the anterior and rhomboid bladders each divide into two and the five-vesicle stage begins (Fig. 17).

Front bubble - telencephalon- divided by a longitudinal fissure into two hemispheres. The cavity also divides, forming the lateral ventricles. The medulla increases unevenly, and numerous folds form on the surface of the hemispheres - convolutions, separated from each other by more or less deep grooves and crevices (Fig.

eighteen). Each hemisphere is divided into four lobes, in accordance with this, the cavities of the lateral ventricles are also divided into 4 parts: the central section and the three horns of the ventricle. From the mesenchyme surrounding the brain of the embryo, the membranes of the brain develop.

The gray matter is located both on the periphery, forming the cortex of the cerebral hemispheres, and at the base of the hemispheres, forming the subcortical nuclei.

Rice. 18. Stages of development of the human brain

The back of the anterior bladder remains undivided and is now called diencephalon(rice.

17, 10 ). Functionally and morphologically, it is associated with the organ of vision. At the stage when the boundaries with the telencephalon are poorly expressed, paired outgrowths are formed from the basal part of the side walls - eye bubbles (Fig. 17, 8 ), which are connected to their place of origin with the help of eye stalks, which subsequently turn into optic nerves. The greatest thickness is reached by the lateral walls of the diencephalon, which are transformed into visual tubercles, or thalamus.

In accordance with this, the cavity of the third ventricle turns into a narrow sagittal fissure. In the ventral region (hypothalamus), an unpaired protrusion is formed - a funnel, from the lower end of which comes the posterior cerebral lobe of the pituitary gland - the neurohypophysis.

The third brain vesicle turns into midbrain(rice.

17, 5), which develops most simply and lags behind in growth. Its walls thicken evenly, and the cavity turns into a narrow canal - the Sylvius aqueduct, connecting the III and IV ventricles.

The quadrigemina develops from the dorsal wall, and the legs of the midbrain develop from the ventral wall.

The rhomboid brain is divided into posterior and accessory. The cerebellum is formed from the posterior (Fig. 17, 12 ) - first the cerebellar vermis, and then the hemispheres, as well as the bridge (Fig. 17, 11 ). The accessory brain turns into the medulla oblongata. The walls of the rhomboid brain thicken - both from the sides and at the bottom, only the roof remains in the form of the thinnest plate.

The cavity turns into the IV ventricle, which communicates with the aqueduct of Sylvius and with the central canal of the spinal cord.

As a result of the uneven development of the cerebral vesicles, the brain tube begins to bend (at the level of the midbrain - the parietal deflection, in the region of the hindbrain - the bridge, and at the point of transition of the accessory brain into the dorsal - the occipital deflection).

The parietal and occipital deflections are turned outward, and the bridge - inward (Fig. 17; 18).

The structures of the brain that form from the primary brain bladder: the middle, hindbrain, and accessory brain make up the brainstem ( truncus cer e bri). It is a rostral continuation of the spinal cord and has structural features in common with it.

Passing along the lateral walls of the spinal cord and the brain stem, a paired border groove ( s u lcus limits) divides the brain tube into the main (ventral) and pterygoid (dorsal) plates. Motor structures (anterior horns of the spinal cord, motor nuclei of the cranial nerves) are formed from the main plate.

Sensory structures (posterior horns of the spinal cord, sensory nuclei of the brainstem) develop above the borderline sulcus from the pterygoid plate, and centers of the autonomic nervous system develop within the borderline sulcus itself.

Archencephalon derivatives ( telenc e phalon and diencephalon) create subcortical structures and cortex.

There is no main plate here (it ends in the midbrain), therefore, there are no motor and autonomic nuclei.

The entire forebrain develops from the pterygoid plate, so it contains only sensory structures (see Fig. 18).

Postnatal ontogeny of the human nervous system begins from the moment the child is born. The brain of a newborn weighs 300-400 g. Shortly after birth, the formation of new neurons from neuroblasts stops, the neurons themselves do not divide. However, by the eighth month after birth, the weight of the brain doubles, and by the age of 4–5 it triples.

The mass of the brain grows mainly due to an increase in the number of processes and their myelination. The brain of men reaches its maximum weight by the age of 20-29, and of women by 15-19. After 50 years, the brain flattens, its weight falls and in old age it can decrease by 100 g.

Perm Institute of Humanities and Technology

Faculty of Humanities

TEST

in the discipline "ANATOMY OF THE CNS"

on the topic

"The main stages of the evolutionary development of the central nervous system"

Perm, 2007

Stages of development of the central nervous system

This interaction can be carried out both in a humoral way through the entry of hormones and metabolic products into the blood, lymph and tissue fluid, and due to the function of the nervous system, which ensures the rapid transmission of excitation addressed to well-defined targets.

Nervous system of invertebrates

The nervous system as a specialized integration system on the path of structural and functional development passes through several stages, which in protostomes and deuterostomes can be characterized by features of parallelism and phylogenetic plasticity of choice.

Among invertebrates, the most primitive type of nervous system in the form diffuse neural network found in the intestinal type.

Their nervous network is an accumulation of multipolar and bipolar neurons, the processes of which can cross, adjoin each other and lack functional differentiation into axons and dendrites. The diffuse nervous network is not divided into central and peripheral sections and can be localized in the ectoderm and endoderm.

epidermal nerve plexuses resembling the nervous networks of coelenterates can also be found in more highly organized invertebrates (flatworms and annelids), but here they occupy a subordinate position in relation to the central nervous system (CNS), which stands out as an independent department.

As an example of such centralization and concentration of nerve elements, one can cite orthogonal nervous system flatworms.

The orthogon of higher turbellarians is an ordered structure, which consists of associative and motor cells, which together form several pairs of longitudinal cords, or trunks, connected by a large number of transverse and annular commissural trunks.

The concentration of nerve elements is accompanied by their immersion into the depths of the body.

These turbellarian receptors include pigment eyes, olfactory pits, statocysts, and sensory cells of the integument, the presence of which contributes to the concentration of nervous tissue at the anterior end of the body. This process leads to the formation head ganglion, which, according to the apt expression of Ch.

Sherrington, can be considered as a ganglion superstructure over the systems of reception at a distance.

Ganglionization of nerve elements is further developed in higher invertebrates, annelids, mollusks and arthropods.

In most annelids, the abdominal trunks are ganglionized in such a way that one pair of ganglia is formed in each segment of the body, connected by connectives to another pair located in the adjacent segment.

The ganglia of one segment in primitive annelids are interconnected by transverse commissures, and this leads to the formation ladder nervous system. In more advanced orders of annelids, there is a tendency for the abdominal trunks to converge up to the complete fusion of the ganglia of the right and left sides and the transition from the scalariform to the chain nervous system. An identical, chain type of structure of the nervous system also exists in arthropods with a different concentration of nerve elements, which can be carried out not only due to the fusion of neighboring ganglia of one segment, but also due to the fusion of successive ganglia of different segments.

It is no coincidence that modern literature notes the tendency to compare the ventral nerve cord with the spinal cord of vertebrates. As in the spinal cord, in the ganglia, a superficial arrangement of pathways is found, the differentiation of the neuropil into motor, sensory, and associative areas.

This similarity, which is an example of parallelism in the evolution of tissue structures, does not, however, exclude the peculiarity of the anatomical organization.

For example, the location of the trunk brain of annelids and arthropods on the ventral side of the body determined the localization of the motor neuropil on the dorsal side of the ganglion, and not on the ventral side, as is the case in vertebrates.

The process of ganglionization in invertebrates can lead to the formation scattered-nodular nervous system, found in molluscs. Within this numerous phylum, there are phylogenetically primitive forms with a nervous system comparable to the orthogon of flatworms (lateral nerve molluscs) and advanced classes (cephalopods) in which fused ganglia form a differentiated brain.

The progressive development of the brain in cephalopods and insects creates a prerequisite for the emergence of a kind of hierarchy of behavior control command systems.

The lowest level of integration in the segmental ganglia of insects and in the subpharyngeal mass of the brain of mollusks, it serves as the basis for autonomous activity and coordination of elementary motor acts. At the same time, the brain is the following, a higher level of integration, where inter-analyzer synthesis and assessment of the biological significance of information can be carried out.

On the basis of these processes, descending commands are formed that provide the variability in the launch of neurons of segmental centers. Obviously, the interaction of two levels of integration underlies the plasticity of the behavior of higher invertebrates, including innate and acquired reactions.

In general, speaking about the evolution of the nervous system of invertebrates, it would be an oversimplification to represent it as a linear process.

The facts obtained in neurodevelopmental studies of invertebrates make it possible to assume a multiple (polygenetic) origin of the nervous tissue of invertebrates. Consequently, the evolution of the nervous system of invertebrates could proceed on a broad front from several sources with initial diversity.

At the early stages of phylogenetic development, a the second trunk of the evolutionary tree, which gave rise to echinoderms and chordates.

The main criterion for distinguishing the type of chordates is the presence of a chord, pharyngeal gill slits and a dorsal nerve cord - the neural tube, which is a derivative of the outer germ layer - the ectoderm.

Tubular type of nervous system vertebrates, according to the basic principles of organization, is different from the ganglionic or nodal type of the nervous system of higher invertebrates.

Nervous system of vertebrates

In the most ancient chordates (non-cranial), the brain is absent and the neural tube is presented in an undifferentiated state.

According to L.

A. Orbeli, S. Herrick, A. I.

Karamyan, this critical stage in the development of the central nervous system is designated as spinal. The neural tube of a modern non-cranial (lancelet), like the spinal cord of more highly organized vertebrates, has a metameric structure and consists of 62-64 segments, in the center of which passes spinal canal. The abdominal (motor) and dorsal (sensory) roots depart from each segment, which do not form mixed nerves, but go in the form of separate trunks.

In the head and tail sections of the neural tube, giant Rode cells are localized, the thick axons of which form the conduction apparatus. The light-sensitive eyes of Hess are associated with Rode cells, the excitation of which causes negative phototaxis.

In the head part of the neural tube of the lancelet there are large ganglionic cells of Ovsyannikov, which have synaptic contacts with bipolar sensory cells of the olfactory fossa.

Recently, neurosecretory cells resembling the pituitary system of higher vertebrates have been identified in the head of the neural tube. However, an analysis of the perception and simple forms of learning in the lancelet shows that at this stage of development the CNS functions according to the principle of equipotentiality, and the statement about the specificity of the head section of the neural tube does not have sufficient grounds.

During the period of phylogenetic development from the level of non-cranial to the level of cyclostomes the brain is formed as a superstructure over systems of distant reception.

A study of the central nervous system of modern cyclostomes shows that their rudimentary brain contains all the main structural elements.

The development of the vestibulolateral system associated with the semicircular canals and lateral line receptors, the emergence of nuclei of the vagus nerve and the respiratory center create the basis for the formation hindbrain. The hindbrain of the lamprey includes the medulla oblongata and cerebellum in the form of small protrusions of the neural tube.

General development of the nervous system

The phylogeny of the nervous system in brief outlines is as follows. The simplest unicellular organisms (amoeba) do not yet have a nervous system, and communication with the environment is carried out with the help of fluids inside and outside the body - humoral (humor - liquid), pre-nervous form of regulation.

In the future, when the nervous system arises, another form of regulation appears - the nervous one.

As the nervous system develops, nervous regulation more and more subjugates humoral regulation, so that a single neurohumoral regulation is formed with the leading role of the nervous system. The latter goes through a number of main stages in the process of phylogenesis (Fig.

Stage I - reticulate nervous system. At this stage, the (intestinal) nervous system, such as hydra, consists of nerve cells, the numerous processes of which are connected to each other in different directions, forming a network that diffusely permeates the entire body of the animal.

When any point of the body is stimulated, the excitation spreads throughout the entire nervous network, and the animal reacts with the movement of the whole body. A reflection of this stage in humans is the network-like structure of the intramural nervous system.

Stage II - the nodal nervous system.

At this stage (higher worms), nerve cells converge into separate clusters or groups, and clusters of cell bodies produce nerve nodes - centers, and clusters of processes - nerve trunks - nerves. At the same time, the number of processes in each cell decreases, and they receive a certain direction.

According to the segmental structure of the body of an animal, for example, in an annelids, in each segment there are segmental nerve nodes and nerve trunks. The latter connect the nodes in two directions, the transverse shafts connect the nodes of a given segment, and the longitudinal ones connect the nodes of different segments.

Due to this, nerve impulses that occur at any point in the body do not spread throughout the body, but spread along transverse trunks within this segment.

Longitudinal trunks connect nerve segments into one whole. At the head end of the animal, which, when moving forward, comes into contact with various objects of the surrounding world, sensory organs develop, and therefore the head nodes develop more strongly than the others, being a prototype of the future brain.

A reflection of this stage is the preservation of primitive features in humans (dispersion of nodes and microganglia on the periphery) in the structure of the autonomic nervous system.

III stage - tubular nervous system. At the initial stage of animal development, a particularly important role was played by the apparatus of movement, on the perfection of which depends the main condition for the existence of an animal - nutrition (movement in search of food, capturing and absorbing it).

In lower multicellular organisms, a peristaltic mode of movement has developed, which is associated with smooth muscles and its local nervous apparatus.

At a higher level, the peristaltic method is replaced by skeletal motility, i.e., movement with the help of a system of rigid levers - over the muscles (arthropods) and inside the muscles (vertebrates).

The consequence of this was the formation of striated muscles and the central nervous system, which coordinates the movement of individual levers of the motor skeleton.

Such a central nervous system in chordates (lancelet) arose in the form of a metamerically built neural tube with segmental nerves extending from it to all segments of the body, including the apparatus of movement - the trunk brain.

In vertebrates and humans, the trunk brain becomes the spinal cord. Thus, the appearance of the trunk brain is associated with the improvement, first of all, of the motor armament of the animal.

Along with this, the lancelet already has receptors (olfactory, light). The further development of the nervous system and the emergence of the brain are due primarily to the improvement of the receptor armament.

Since most of the sense organs arise at that end of the animal’s body that is turned in the direction of movement, i.e. forward, the anterior end of the trunk brain develops to perceive the external stimuli coming through them and the brain is formed, which coincides with the isolation of the anterior end of the body in the form of the head - cephalization (cephal - head).

K. Sepp in the manual on nervous diseases gives a simplified, but convenient for studying, scheme of the phylogeny of the brain, which we present. According to this scheme, at the first stage of development, the brain consists of three sections: posterior, middle and anterior, and from these sections in the first place (in lower fish) the posterior, or rhomboid, brain (rhombencephalon) especially develops.

The development of the hindbrain occurs under the influence of acoustic and static receptors (receptors of the VIII pair of head nerves), which are of leading importance for orientation in the aquatic environment.

In further evolution, the hindbrain differentiates into the medulla oblongata, which is a transitional section from the spinal cord to the brain and is therefore called myelencephalon (myelos - spinal cord, encephalon - brain), and the hindbrain proper - metencephalon, from which the cerebellum and bridge develop.

In the process of adapting the organism to the environment by changing the metabolism in the hindbrain, as the most developed section of the central nervous system at this stage, control centers for vital processes of plant life arise, associated, in particular, with the gill apparatus (respiration, blood circulation, digestion, etc.). ).

Therefore, nuclei of gill nerves arise in the medulla oblongata (group X of the pair - vagus). These vital centers of respiration and circulation remain in the human medulla oblongata, which explains the death that occurs when the medulla oblongata is damaged. At stage II (still in fish), under the influence of the visual receptor, the midbrain, mesencephalon, especially develops. At stage III, in connection with the final transition of animals from the aquatic environment to the air, the olfactory receptor develops intensively, perceiving chemicals contained in the air, signaling with their smell about prey, danger and other vital phenomena of the surrounding nature.

Under the influence of the olfactory receptor, the forebrain, the prosencephalon, develops, initially having the character of a purely olfactory brain.

In the future, the forebrain grows and differentiates into the intermediate - diencephalon and the final - telencephalon.

In the telencephalon, as in the highest part of the central nervous system, centers appear for all types of sensitivity. However, the underlying centers do not disappear, but remain, obeying the centers of the overlying floor. Consequently, with each new stage in the development of the brain, new centers arise that subjugate the old ones.

There is a kind of movement of functional centers to the head end and the simultaneous subordination of phylogenetically old rudiments to new ones. As a result, the centers of hearing that first appeared in the hindbrain are also present in the middle and forebrain, the centers of vision that arose in the middle are also present in the forebrain, and the centers of smell are only in the forebrain.

Under the influence of the olfactory receptor, a small part of the forebrain develops, which is therefore called the olfactory brain (rhinencephalon), which is covered with a bark of gray matter - the old cortex (paleocortex).

The improvement of the receptors leads to the progressive development of the forebrain, which gradually becomes the organ that controls the entire behavior of the animal.

There are two forms of animal behavior: instinctive, based on specific reactions (unconditioned reflexes), and individual, based on the experience of the individual (conditioned reflexes).

Corresponding to these two forms of behavior, two groups of gray matter centers develop in the telencephalon: subcortical bonds, which have the structure of nuclei (nuclear centers), and the gray matter cortex, which has the structure of a continuous screen (screen centers). In this case, the “subcortex” develops first, and then the cortex. The bark arises during the transition of an animal from an aquatic to a terrestrial lifestyle and is clearly found in amphibians and reptiles.

The further evolution of the nervous system is characterized by the fact that the cerebral cortex more and more subjugates the functions of all underlying centers, there is a gradual corticolization of functions.

Pneumatosis of the stomach

A necessary formation for the implementation of higher nervous activity is the new cortex, located on the surface of the hemispheres and acquiring a six-layer structure in the process of phylogenesis.

Due to the increased development of the new cortex, the telencephalon in higher vertebrates surpasses all other parts of the brain, covering them like a cloak (pallium). The developing new brain (neencephalon) pushes the old brain (olfactory) into the depths, which, as it were, curls up in the form of an ammon horn (cornu Ammoni or pes hyppocampi), which remains the olfactory center. As a result, the cloak, i.e., the new brain (neencephalon), sharply prevails over the rest of the brain - the old brain (paleencephalon).

So, the development of the brain takes place under the influence of the development of receptors, which explains that the highest part of the brain - the gray matter cortex - represents, as I.

P. Pavlov, the totality of the cortical ends of the analyzers, i.e., a continuous perceiving (receptor) surface.

The further development of the human brain is subject to other patterns associated with its social nature. In addition to the natural organs of the body, which are also found in animals, man began to use tools.

Tools of labor, which became artificial organs, supplemented the natural organs of the body and constituted the technical armament of man.

With the help of this weapon, man acquired the opportunity not only to adapt himself to nature, as animals do, but also to adapt nature to his needs.

Labor, as mentioned above, was a decisive factor in the formation of man, and in the process of social labor, a means necessary for communication between people arose - speech. “First work, and then articulate speech along with it, were the two most important stimuli, under the influence of which the monkey brain gradually turned into a human brain, which, for all its resemblance to the monkey, far surpasses it in size and perfection.”

This perfection is due to the maximum development of the telencephalon, especially its cortex - the new cortex (neocortex).

In addition to analyzers that perceive various stimuli of the external world and constitute the material substrate of concrete-visual thinking characteristic of animals (the first signal system of reality), a person has the ability to abstract, abstract thinking with the help of a word, first heard (oral speech) and later visible (written language). speech).

This constituted the second signaling system, according to I.P. Pavlov, which in the developing animal world was "an extraordinary addition to the mechanisms of nervous activity." The surface layers of the new crust became the material substrate of the second signaling system. Therefore, the cerebral cortex reaches its highest development in humans.

Thus, the entire evolution of the nervous system is reduced to the progressive development of the telencephalon, which in higher vertebrates and especially in humans, due to the complication of nervous functions, reaches enormous proportions.

The stated patterns of phylogenesis determine the embryogenesis of the human nervous system. The nervous system originates from the outer germ layer, or ectoderm. This latter forms a longitudinal thickening called the medullary plate (Fig.

The medullary plate soon deepens into the medullary groove, the edges of which (medullary ridges) gradually become higher and then fuse with each other, turning the groove into a tube (brain tube).

The brain tube is the rudiment of the central part of the nervous system. The posterior end of the tube forms the rudiment of the spinal cord, while its anterior expanded end is divided by constrictions into three primary cerebral vesicles, from which the brain in all its complexity originates.

The medullary plate initially consists of only one layer of epithelial cells.

During its closing into the brain tube, the number of cells in the walls of the latter increases, so that three layers appear: the inner one (facing into the cavity of the tube), from which the epithelial lining of the brain cavities (ependyma of the central canal of the spinal cord and ventricles of the brain) comes from; the middle one, from which the gray matter of the brain develops (nerve cells - neuroblasts), and finally, the outer, almost not containing cell nuclei, developing into white matter (the processes of nerve cells - neurites).

Bundles of neurites of neuroblasts spread either in the thickness of the brain tube, forming the white matter of the brain, or they go into the mesoderm and then connect with young muscle cells (myoblasts). In this way motor nerves arise.

Sensory nerves arise from the rudiments of the spinal nodes, which are already visible along the edges of the medullary groove at the place where it passes into the skin ectoderm. When the groove closes into the brain tube, the rudiments are displaced to its dorsal side, located along the midline.

Then the cells of these rudiments move ventrally and are again located on the sides of the brain tube in the form of the so-called ganglionic ridges. Both ganglion ridges are clearly laced along the segments of the dorsal side of the embryo, as a result of which a number of spinal nodes, ganglia spinalia s, are obtained on each side.

intervertebral. In the head part of the brain tube, they reach only the region of the posterior cerebral vesicle, where they form the rudiments of nodes of sensitive head nerves. In the ganglionic rudiments, neuroblasts develop, taking the form of bipolar nerve cells, one of the processes of which grows into the brain tube, the other goes to the periphery, forming a sensory nerve. Due to fusion at some distance from the beginning of both processes, the so-called false unipolar cells with one process dividing in the shape of the letter “T” are obtained from bipolar ones, which are characteristic of the intervertebral nodes of an adult.

The central processes of cells penetrating the spinal cord make up the posterior roots of the spinal nerves, and the peripheral processes, growing ventrally, form (together with the efferent fibers that come out of the spinal cord and make up the anterior root) a mixed spinal nerve.

Ontogenesis (ontogenesis; Greek op, ontos - existing + genesis - origin, origin) - the process of individual development of the organism from the moment of its inception (conception) to death. Allocate: embryonic(embryonic, or prenatal) - the time from fertilization to birth and postembryonic(post-embryonic, or postnatal) - from birth to death, periods of development.

The human nervous system develops from the ectoderm - the outer germ layer.

At the end of the second week of embryonic development, a section of the epithelium separates in the dorsal parts of the body - neural (medullary) plate, cells of which intensively multiply and differentiate. The accelerated growth of the lateral sections of the neural plate leads to the fact that its edges first rise, then approach each other, and finally, at the end of the third week, grow together, forming the primary brain tube.

After that, the brain tube gradually sinks into the mesoderm.

Fig.1. Formation of the neural tube.

The neural tube is the embryonic germ of the entire human nervous system.

From it, the brain and spinal cord, as well as the peripheral parts of the nervous system, are subsequently formed. When the neural groove closes on the sides in the region of its raised edges (neural folds), a group of cells is isolated on each side, which, as the neural tube separates from the skin ectoderm, forms a continuous layer between the neural folds and ectoderm - the ganglionic plate.

The latter serves as the starting material for cells of sensitive nerve nodes (spinal and cranial ganglia) and nodes of the autonomic nervous system that innervates internal organs.

The neural tube at an early stage of its development consists of one layer of cylindrical cells, which subsequently intensively multiply by mitosis and their number increases; as a result, the wall of the neural tube thickens.

At this stage of development, three layers can be distinguished in it: the inner one (later it will form the ependymal lining), the middle layer (the gray matter of the brain, the cellular elements of this layer differentiate in two directions: some of them turn into neurons, the other part into glial cells ) and the outer layer (white matter of the brain).

Fig.2.

Stages of development of the human brain.

The neural tube develops unevenly. Due to the intensive development of its anterior part, the brain begins to form, cerebral bubbles form: first two bubbles appear, then the back bubble divides into two more. As a result, in four-week-old embryos, the brain consists of three brain bubbles(front, middle and rhomboid brain).

At the fifth week, the anterior cerebral vesicle is subdivided into the telencephalon and diencephalon, and the rhomboid - into the posterior and medulla oblongata ( stage five brain bubbles). At the same time, the neural tube forms several bends in the sagittal plane.

The spinal cord with the spinal canal develops from the undifferentiated posterior part of the medullary tube. Formation occurs from the cavities of the embryonic brain brain ventricles.

The cavity of the rhomboid brain is transformed into the IV ventricle, the cavity of the midbrain forms the cerebral aqueduct, the cavity of the diencephalon forms the III ventricle of the brain, and the cavity of the forebrain forms the lateral ventricles of the brain with a complex configuration.

After the formation of five cerebral vesicles in the structures of the nervous system, complex processes of internal differentiation and growth of various parts of the brain take place.

At 5-10 weeks, growth and differentiation of the telencephalon is observed: cortical and subcortical centers are formed, and the cortex is stratified. Meninges are formed. The spinal cord acquires a definitive state. At 10-20 weeks, the migration processes are completed, all the main parts of the brain are formed, and differentiation processes come to the fore.

The end brain develops most actively. The cerebral hemispheres become the largest part of the nervous system. At the 4th month of human fetal development, a transverse fissure of the large brain appears, at the 6th - the central sulcus and other main sulci, in the following months - secondary and after birth - the smallest sulci.

In the process of development of the nervous system, myelination of nerve fibers plays an important role, as a result of which the nerve fibers are covered with a protective layer of myelin and the speed of nerve impulses increases significantly.

By the end of the 4th month of intrauterine development, myelin is detected in the nerve fibers that make up the ascending, or afferent (sensory) systems of the lateral cords of the spinal cord, while in the fibers of the descending, or efferent (motor) systems, myelin is found at the 6th month.

At about the same time, myelination of the nerve fibers of the posterior cords occurs. Myelination of nerve fibers of the cortico-spinal tract begins in the last month of intrauterine life and continues for a year after birth.

This indicates that the process of myelination of nerve fibers extends first to phylogenetically older structures and then to younger structures. The order of formation of their functions depends on the sequence of myelination of certain nerve structures.

The formation of function and also depends on the differentiation of cellular elements and their gradual maturation, which lasts for the first decade.

By the time the baby is born, nerve cells reach maturity and are no longer capable of dividing. As a result, their number will not increase in the future.

In the postnatal period, the final maturation of the entire nervous system gradually occurs, in particular its most complex section - the cerebral cortex, which plays a special role in the brain mechanisms of conditioned reflex activity, which is formed from the first days of life.

Another important stage in ontogenesis is the period of puberty, when the sexual differentiation of the brain also takes place.

Throughout a person's life, the brain is actively changing, adapting to the conditions of the external and internal environment, some of these changes are genetically programmed, some are a relatively free reaction to the conditions of existence. The ontogenesis of the nervous system ends only with the death of a person.

Among invertebrates, the most primitive type of nervous system in the form of a diffuse nervous network is found in coelenterates (see Fig. 1.2). Their nervous network is a cluster of multipolar and bipolar neurons, the processes of which can cross, adjoin each other and lack functional differentiation on axon s and dendrite. The diffuse nervous network is not divided into central and peripheral sections and can be localized in the ectoderm and endoderm.
Epidermal nerve plexuses, resembling the nervous networks of intestinal cavities, can also be found in more highly organized invertebrates (flatworms and annelids), but here they occupy a subordinate position in relation to the central nervous system, which stands out as an independent department.
... Ganglionization of nerve elements is further developed in higher invertebrates, annelids, mollusks and arthropods. In most annelids, the abdominal trunks are ganglionized in such a way that one pair of ganglia is formed in each segment of the body, connected by connectives to another pair located in the adjacent segment.
...The evolution of the nervous system of invertebrates goes not only along the path of concentration of nerve elements, but also in the direction of complication of structural relationships within the ganglia. It is no coincidence that the ventral nerve cord is compared with the spinal cord of vertebrates. As in the spinal cord, in the ganglia, a superficial arrangement of pathways is found, the differentiation of the neuropil into motor, sensory, and associative areas.
...The progressive development of the brain in cephalopods and insects creates the prerequisite for the emergence of a kind of hierarchy of command systems for controlling behavior. The lowest level of integration in the segmental ganglia of insects and in the subpharyngeal mass of the brain of mollusks serves as the basis for autonomous activity and coordination of elementary motor acts. At the same time, the brain represents the next, higher level of integration, where inter-analyzer synthesis and assessment of biological significance information. Based on these processes, descending commands are formed that provide launch variability neurons segment centers. Obviously, the interaction of two levels of integration underlies the plasticity of the behavior of higher invertebrates, including innate and acquired reactions.
... The nervous system of vertebrates is laid down in the form of a continuous neural tube, which in the process of onto- and phylogenesis differentiates into various sections and is also a source of peripheral sympathetic, parasympathetic and metasympathetic ganglions. In the most ancient chordates (non-cranial), the brain is absent, and the neural tube is presented in an undifferentiated state.
... In the course of further evolution, some functions and systems of integration are observed to move from the spinal cord to the brain - the process of encephalization, which was discussed above using the example of invertebrates. During the period of phylogenetic development from the level of non-cranial to the level of cyclostomes, the brain is formed as a superstructure over the systems of distant reception.
...For a long time, the forebrain of cyclostomes was considered purely olfactory. However, recent studies have shown that the olfactory inputs to the forebrain are not the only ones, but are complemented by sensory inputs from other modalities. Obviously, already at the early stages of vertebrate phylogenesis, the forebrain begins to participate in information processing and behavior control. However, encephalization magicians st The traditional direction of brain development does not exclude evolutionary transformations in the spinal cord of cyclostomes. Unlike the skullless neurons skin sensitivity are released from the spinal cord and concentrated in the spinal ganglion. Improvement of the conductive part of the spinal cord is observed. The conductive fibers of the side pillars have contacts with a powerful dendrite noah network of motoneurons. Downward connections of the brain with the spinal cord are formed through the Müllerian fibers - giant axon s cells in the midbrain and medulla oblongata.
... The most significant evolutionary changes occur in the diencephalon of amphibians. Here the thalamus (thalamic thalamus) separates, the structured nuclei (the lateral geniculate body) and the ascending pathways that connect the thalamus with the cortex (thalamocortical pathway) differentiate.
In the hemispheres of the forebrain, further differentiation of the rudiments of the old and ancient cortex occurs. In the old cortex (archeocortex), stellate and pyramidal cells are found. In the gap between the old and ancient cortex, a strip of cloak appears, which is the forerunner of the new cortex (neocortex).
On the whole, the development of the forebrain creates the preconditions for the transition from the mesencephalocerebral system of integration characteristic of fish to the diencephalotelencephalic system, where the forebrain becomes the leading part, and the thalamus of the diencephalon turns into a collector of all afferent signals. This system of integration is fully represented in the sauropsid type of the brain in reptiles and marks the next stage in the morphofunctional evolution of the brain.
The development of the thalamocortical system of connections in reptiles leads to the formation of new conducting pathways, as if pulling up to phylogenetically young brain formations.
In the lateral columns of the spinal cord of reptiles, the ascending spinal-thalamic pathway separates, which conducts information about temperature and pain sensitivity to the brain. Here, in the side columns, a new descending path is formed - the red-nuclear-spinal (Monakova). It connects the motor neurons of the spinal cord with the red nucleus of the midbrain, which is included in the ancient extrapyramidal system of motor regulation. This multi-link system combines the influence of the forebrain, cerebellum, brainstem reticular formation, nuclei of the vestibular complex and coordinates motor activity. In reptiles, as truly terrestrial animals, the role of visual and acoustic information increases, and it becomes necessary to compare this information with olfactory and gustatory information. Corresponding to these biological changes, a number of structural changes occur in the reptile brainstem. In the medulla oblongata, the auditory nuclei differentiate, in addition to the cochlear nucleus, an angular nucleus appears, connected with the midbrain. In the midbrain, the colliculus is transformed into the quadrigemina, in the rostral hills of which there are acoustic centers.
There is a further differentiation of the connections of the roof of the midbrain with the thalamus, which is, as it were, the vestibule of the entrance to the cortex of all ascending sensory pathways. In the thalamus itself, there is a further separation of nuclear structures and the establishment of specialized connections between them.
...In mammals, the development of the forebrain was accompanied by a rapid growth of the neocortex, which is in close functional connection with the thalamus of the diencephalon. Efferent pyramidal cells are laid in the cortex, sending their long axon s to the motor neurons of the spinal cord.
Thus, along with the multilink extrapyramidal system, direct pyramidal pathways appear that provide direct control over motor acts. Cortical regulation of movements in mammals leads to the development of the phylogenetically youngest part of the cerebellum - the anterior part of the posterior lobes of the hemispheres, or neocerebellum. The neocerebellum acquires bilateral connections with the neocortex.
The growth of the new cortex in mammals is so intense that the old and ancient cortex is pushed in the medial direction to the cerebral septum. The rapid growth of the crust is compensated by the formation of folding. In the most poorly organized monotremes (platypus), the first two permanent furrows are laid on the surface of the hemisphere, while the rest of the surface remains smooth (lissencephalic type of cortex).
Neurophysiological studies have shown that the brain of monotremes and marsupials is devoid of the corpus callosum that still connects the hemispheres and is characterized by overlapping sensory projections in the neocortex. There is no clear localization of motor, visual and auditory projections here.
In placental, mammals (insectivores and rodents), the development of a clearer localization of the projection zones in the cortex is noted. Along with the projection zones, associative zones are formed in the neocortex, however, the boundaries of the first and second ones can overlap. The brain of insectivores and rodents is characterized by the presence of a corpus callosum and a further increase in the total area of the new cortex, the development of furrows and convolutions (girencephalic type of cortex).
In the process of parallel-adaptive evolution, carnivorous mammals develop parietal and frontal associative fields, which are responsible for assessing biologically meaningful oh information, motivation of behavior and programming of complex behavioral acts. Further development of folding of the new crust is observed.
Finally, primates show the highest level of organization of the cerebral cortex. The bark of primates is characterized by six layers, the absence of overlap of associative and projection zones. In primates, connections are formed between the frontal and parietal associative fields and, thus, an integral integrative system of the cerebral hemispheres arises.

Perm Institute of Humanities and Technology

Faculty of Humanities

TEST

in the discipline "ANATOMY OF THE CNS"

on the topic

"The main stages of the evolutionary development of the central nervous system"

Perm, 2007

Stages of development of the central nervous system

The appearance of multicellular organisms was the primary stimulus for the differentiation of communication systems that ensure the integrity of the body's reactions, the interaction between its tissues and organs. This interaction can be carried out both in a humoral way through the entry of hormones and metabolic products into the blood, lymph and tissue fluid, and due to the function of the nervous system, which ensures the rapid transmission of excitation addressed to well-defined targets.

Nervous system of invertebrates

Among invertebrates, the most primitive type of nervous system in the form diffuse neural network found in the intestinal type. Their nervous network is an accumulation of multipolar and bipolar neurons, the processes of which can cross, adjoin each other and lack functional differentiation into axons and dendrites. The diffuse nervous network is not divided into central and peripheral sections and can be localized in the ectoderm and endoderm.

As an example of such centralization and concentration of nerve elements, one can cite orthogonal nervous system flatworms. The orthogon of higher turbellarians is an ordered structure, which consists of associative and motor cells, which together form several pairs of longitudinal cords, or trunks, connected by a large number of transverse and annular commissural trunks. The concentration of nerve elements is accompanied by their immersion into the depths of the body.

Flatworms are bilaterally symmetrical animals with a well-defined longitudinal body axis. Movement in free-living forms is carried out mainly towards the head end, where receptors are concentrated, signaling the approach of a source of irritation. These turbellarian receptors include pigment eyes, olfactory pits, statocysts, and sensory cells of the integument, the presence of which contributes to the concentration of nervous tissue at the anterior end of the body. This process leads to the formation head ganglion, which, according to the apt expression of Ch. Sherrington, can be considered as a ganglion superstructure over the systems of reception at a distance.

Ganglionization of nerve elements is further developed in higher invertebrates, annelids, mollusks and arthropods. In most annelids, the abdominal trunks are ganglionized in such a way that one pair of ganglia is formed in each segment of the body, connected by connectives to another pair located in the adjacent segment.

The evolution of the nervous system of invertebrates goes not only along the path of concentration of nerve elements, but also in the direction of complication of structural relationships within the ganglia. It is no coincidence that modern literature notes the tendency to compare the ventral nerve cord with the spinal cord of vertebrates. As in the spinal cord, in the ganglia, a superficial arrangement of pathways is found, the differentiation of the neuropil into motor, sensory, and associative areas. This similarity, which is an example of parallelism in the evolution of tissue structures, does not, however, exclude the peculiarity of the anatomical organization. For example, the location of the trunk brain of annelids and arthropods on the ventral side of the body determined the localization of the motor neuropil on the dorsal side of the ganglion, and not on the ventral side, as is the case in vertebrates.

The progressive development of the brain in cephalopods and insects creates a prerequisite for the emergence of a kind of hierarchy of behavior control command systems. The lowest level of integration in the segmental ganglia of insects and in the subpharyngeal mass of the brain of mollusks, it serves as the basis for autonomous activity and coordination of elementary motor acts. At the same time, the brain is the following, a higher level of integration, where inter-analyzer synthesis and assessment of the biological significance of information can be carried out. On the basis of these processes, descending commands are formed that provide the variability in the launch of neurons of segmental centers. Obviously, the interaction of two levels of integration underlies the plasticity of the behavior of higher invertebrates, including innate and acquired reactions.

In general, speaking about the evolution of the nervous system of invertebrates, it would be an oversimplification to represent it as a linear process. The facts obtained in neurodevelopmental studies of invertebrates make it possible to assume a multiple (polygenetic) origin of the nervous tissue of invertebrates. Consequently, the evolution of the nervous system of invertebrates could proceed on a broad front from several sources with initial diversity.

At the early stages of phylogenetic development, a the second trunk of the evolutionary tree, which gave rise to echinoderms and chordates. The main criterion for distinguishing the type of chordates is the presence of a chord, pharyngeal gill slits and a dorsal nerve cord - the neural tube, which is a derivative of the outer germ layer - the ectoderm. Tubular type of nervous system vertebrates, according to the basic principles of organization, is different from the ganglionic or nodal type of the nervous system of higher invertebrates.

Nervous system of vertebrates

Nervous system of vertebrates is laid in the form of a continuous neural tube, which in the process of ontogenesis and phylogenesis differentiates into various sections and is also a source of peripheral sympathetic and parasympathetic ganglions. In the most ancient chordates (non-cranial), the brain is absent and the neural tube is presented in an undifferentiated state.

According to the ideas of L. A. Orbeli, S. Herrick, A. I. Karamyan, this critical stage in the development of the central nervous system is designated as spinal. The neural tube of a modern non-cranial (lancelet), like the spinal cord of more highly organized vertebrates, has a metameric structure and consists of 62-64 segments, in the center of which passes spinal canal. The abdominal (motor) and dorsal (sensory) roots depart from each segment, which do not form mixed nerves, but go in the form of separate trunks. In the head and tail sections of the neural tube, giant Rode cells are localized, the thick axons of which form the conduction apparatus. The light-sensitive eyes of Hess are associated with Rode cells, the excitation of which causes negative phototaxis.

In the head part of the neural tube of the lancelet there are large ganglionic cells of Ovsyannikov, which have synaptic contacts with bipolar sensory cells of the olfactory fossa. Recently, neurosecretory cells resembling the pituitary system of higher vertebrates have been identified in the head of the neural tube. However, an analysis of the perception and simple forms of learning in the lancelet shows that at this stage of development the CNS functions according to the principle of equipotentiality, and the statement about the specificity of the head section of the neural tube does not have sufficient grounds.

In the course of further evolution, there is a movement of some functions and integration systems from the spinal cord to the brain - encephalization process, which was considered on the example of invertebrates. During the period of phylogenetic development from the level of non-cranial to the level of cyclostomes the brain is formed as a superstructure over systems of distant reception.

A study of the central nervous system of modern cyclostomes shows that their rudimentary brain contains all the main structural elements. The development of the vestibulolateral system associated with the semicircular canals and lateral line receptors, the emergence of nuclei of the vagus nerve and the respiratory center create the basis for the formation hindbrain. The hindbrain of the lamprey includes the medulla oblongata and cerebellum in the form of small protrusions of the neural tube.

The nervous system is of ectodermal origin, i.e., it develops from an external germinal sheet with a thickness of a single-cell layer due to the formation and division of the medullary tube.

In the evolution of the nervous system, the following stages can be schematically distinguished:

1. Reticulate, diffuse, or asynaptic, nervous system. It arises in freshwater hydra, has the shape of a grid, which is formed by the connection of process cells and is evenly distributed throughout the body, thickening around the oral appendages. The cells that make up this network differ significantly from the nerve cells of higher animals: they are small in size, do not have a nucleus and a chromatophilic substance characteristic of a nerve cell. This nervous system conducts excitations diffusely, in all directions, providing global reflex reactions. At further stages of the development of multicellular animals, it loses its significance as a single form of the nervous system, but in the human body it remains in the form of the Meissner and Auerbach plexuses of the digestive tract.

2. The ganglionic nervous system (in worm-like) is synaptic, conducts excitation in one direction and provides differentiated adaptive reactions. This corresponds to the highest degree of evolution of the nervous system: special organs of movement and receptor organs develop, groups of nerve cells appear in the network, the bodies of which contain a chromatophilic substance. It tends to disintegrate during cell excitation and recover at rest. Cells with a chromatophilic substance are located in groups or nodes of ganglia, therefore they are called ganglionic. So, at the second stage of development, the nervous system from the reticular system turned into the ganglion-network. In humans, this type of structure of the nervous system has been preserved in the form of paravertebral trunks and peripheral nodes (ganglia), which have vegetative functions.

3. The tubular nervous system (in vertebrates) differs from the nervous system of worm-like ones in that skeletal motor apparatuses with striated muscles arose in vertebrates. This led to the development of the central nervous system, the individual parts and structures of which are formed in the process of evolution gradually and in a certain sequence. First, the segmental apparatus of the spinal cord is formed from the caudal, undifferentiated part of the medullary tube, and the main parts of the brain are formed from the anterior part of the brain tube due to cephalization (from the Greek kephale - head).

A reflex is a natural reaction of the body in response to irritation of receptors, which is carried out by a reflex arc with the participation of the central nervous system. This is an adaptive reaction of the body in response to a change in the internal or environment. Reflex reactions ensure the integrity of the body and the constancy of its internal environment, the reflex arc is the main unit of integrative reflex activity.

A significant contribution to the development of the reflex theory was made by I.M. Sechenov (1829-1905). He was the first to use the reflex principle to study the physiological mechanisms of mental processes. In the work "Reflexes of the brain" (1863) I.M. Sechenov argued that the mental activity of humans and animals is carried out according to the mechanism of reflex reactions that occur in the brain, including the most complex of them - the formation of behavior and thinking. Based on his research, he concluded that all acts of conscious and unconscious life are reflex. Reflex theory I.M. Sechenov served as the basis on which the teachings of I.P. Pavlov (1849-1936) on higher nervous activity.

The method of conditioned reflexes developed by him expanded the scientific understanding of the role of the cerebral cortex as a material substratum of the psyche. I.P. Pavlov formulated a reflex theory of the brain, which is based on three principles: causality, structure, unity of analysis and synthesis. PK Anokhin (1898-1974) proved the importance of feedback in the reflex activity of the organism. Its essence lies in the fact that during the implementation of any reflex act, the process is not limited to the effector, but is accompanied by the excitation of the receptors of the working organ, from which information about the consequences of the action is supplied by afferent pathways to the central nervous system. There were ideas about the "reflex ring", "feedback".

Reflex mechanisms play an essential role in the behavior of living organisms, ensuring their adequate response to environmental signals. For animals, reality is signaled almost exclusively by stimuli. This is the first signal system of reality, common to man and animals. I.P. Pavlov proved that for a person, unlike animals, the object of display is not only the environment, but also social factors. Therefore, for him, the second signal system acquires decisive importance - the word as a signal of the first signals.

The conditioned reflex underlies the higher nervous activity of man and animals. It is always included as an essential component in the most complex manifestations of behavior. However, not all forms of behavior of a living organism can be explained from the point of view of the reflex theory, which reveals only the mechanisms of action. The reflex principle does not answer the question of the expediency of human and animal behavior, does not take into account the result of the action.

Therefore, over the past decades, on the basis of reflex ideas, a concept has been formed regarding the leading role of needs as the driving force behind the behavior of humans and animals. The presence of needs is a necessary prerequisite for any activity. The activity of the organism acquires a certain direction only if there is a goal that meets this need. Each behavioral act is preceded by needs that arose in the process of phylogenetic development under the influence of environmental conditions. That is why the behavior of a living organism is determined not so much by the reaction to external influences as by the need to implement the intended program, plan, aimed at satisfying a particular need of a person or animal.

PC. Anokhin (1955) developed the theory of functional systems, which provides a systematic approach to the study of the mechanisms of the brain, in particular, the development of problems of the structural and functional basis of behavior, the physiology of motivations and emotions. The essence of the concept is that the brain can not only adequately respond to external stimuli, but also foresee the future, actively plan its behavior and implement them. The theory of functional systems does not exclude the method of conditioned reflexes from the sphere of higher nervous activity and does not replace it with something else. It makes it possible to delve deeper into the physiological essence of the reflex. Instead of the physiology of individual organs or structures of the brain, the systematic approach considers the activity of the organism as a whole. For any behavioral act of a person or animal, such an organization of all brain structures is needed that will provide the desired end result. So, in the theory of functional systems, the useful result of an action occupies a central place. Actually, the factors that are the basis for achieving the goal are formed according to the type of versatile reflex processes.

One of the important mechanisms of the activity of the central nervous system is the principle of integration. Thanks to the integration of somatic and autonomic functions, which is carried out by the cerebral cortex through the structures of the limbic-reticular complex, various adaptive reactions and behavioral acts are realized. The highest level of integration of functions in humans is the frontal cortex.

An important role in the mental activity of humans and animals is played by the principle of dominance, developed by O. O. Ukhtomsky (1875-1942). Dominant (from Latin dominari to dominate) is an excitation that is superior in the central nervous system, which is formed under the influence of stimuli from the environment or internal environment and at a certain moment subordinates the activity of other centers.

The brain with its highest department - the cerebral cortex - is a complex self-regulating system built on the interaction of excitatory and inhibitory processes. The principle of self-regulation is carried out at different levels of the analyzer systems - from the cortical sections to the level of receptors with the constant subordination of the lower sections of the nervous system to the higher ones.

Studying the principles of the functioning of the nervous system, not without reason, the brain is compared with an electronic computer. As you know, the basis of the operation of cybernetic equipment is the reception, transmission, processing and storage of information (memory) with its further reproduction. Information must be encoded for transmission and decoded for playback. Using cybernetic concepts, we can assume that the analyzer receives, transmits, processes and, possibly, stores information. In the cortical sections, its decoding is carried out. This is probably enough to make it possible to attempt to compare the brain with a computer.

At the same time, the work of the brain cannot be identified with a computer: “... the brain is the most capricious machine in the world. Let us be modest and cautious with conclusions” (I.M. Sechenov, 1863). A computer is a machine and nothing more. All cybernetic devices operate on the principle of electrical or electronic interaction, and in the brain, which was created through evolutionary development, in addition, complex biochemical and bioelectrical processes take place. They can only be carried out in living tissue. The brain, unlike electronic systems, does not function according to the principle of “all or nothing”, but takes into account a great many gradations between these two extremes. These gradations are due not to electronic, but to biochemical processes. This is the essential difference between the physical and the biological.

The brain has qualities that go beyond those that a computer has. It should be added that the behavioral reactions of the body are largely determined by intercellular interactions in the central nervous system. As a rule, processes from hundreds or thousands of other neurons approach one neuron, and it, in turn, branches off into hundreds or thousands of other neurons. No one can say how many synapses are in the brain, but the number 10 14 (one hundred trillion) does not seem incredible (D. Hubel, 1982). The computer contains much fewer elements. The functioning of the brain and the vital activity of the body are carried out in specific environmental conditions. Therefore, the satisfaction of certain needs can be achieved provided that this activity is adequate to the existing external environmental conditions.

For the convenience of studying the basic patterns of functioning, the brain is divided into three main blocks, each of which performs its own specific functions.

The first block is the phylogenetically most ancient structures of the limbic-reticular complex, which are located in the stem and deep parts of the brain. They include the cingulate gyrus, the seahorse (hippocampus), the papillary body, the anterior nuclei of the thalamus, the hypothalamus, and the reticular formation. They provide the regulation of vital functions - respiration, blood circulation, metabolism, as well as general tone. Regarding behavioral acts, these formations take part in the regulation of functions aimed at ensuring eating and sexual behavior, species preservation processes, in the regulation of systems that provide sleep and wakefulness, emotional activity, memory processes. The second block is a set of formations located behind central sulcus: somatosensory, visual and auditory areas of the cerebral cortex.

Their main functions are receiving, processing and storing information. The neurons of the system, which are located mainly anterior to the central sulcus and are associated with effector functions, the implementation of motor programs, constitute the third block. Nevertheless, it should be recognized that it is impossible to draw a clear line between the sensory and motor structures of the brain. The postcentral gyrus, which is a sensitive projection area, is closely interconnected with the precentral motor area, forming a single sensorimotor field. Therefore, it is necessary to clearly understand that one or another human activity requires the simultaneous participation of all parts of the nervous system. Moreover, the system as a whole performs functions that go beyond the functions inherent in each of these blocks.

Anatomical and physiological characteristics and pathology of the cranial nerves

The cranial nerves, which extend from the brain in an amount of 12 pairs, innervate the skin, muscles, organs of the head and neck, as well as some organs of the chest and abdominal cavities. Of these, III, IV,

VI, XI, XII pairs are motor, V, VII, IX, X are mixed, pairs I, II and VIII are sensitive, providing, respectively, specific innervation of the organs of smell, vision and hearing; Pairs I and II are derivatives of the brain, they do not have nuclei in the brain stem. All other cranial nerves exit or enter the brain stem where their motor, sensory, and autonomic nuclei are located. So, the nuclei of III and IV pairs of cranial nerves are located in the brain stem, V, VI, VII, VIII pairs - mainly in the pons, IX, X, XI, XII pairs - in the medulla oblongata.

cerebral cortex

The brain (encephalon, cerebrum) includes the right and left hemispheres and the brain stem. Each hemisphere has three poles: frontal, occipital and temporal. Four lobes are distinguished in each hemisphere: frontal, parietal, occipital, temporal and insula (see Fig. 2).

The hemispheres of the brain (hemispheritae cerebri) are called even more, or the final brain, the normal functioning of which predetermines signs specific to a person. The human brain consists of multipolar nerve cells - neurons, the number of which reaches 10 11 (one hundred billion). This is approximately the same as the number of stars in our galaxy. The average mass of the brain of an adult is 1450 g. It is characterized by significant individual fluctuations. For example, such prominent people as the writer I.S. Turgenev (63 years old), the poet Byron (36 years old), it was 2016 and 2238, respectively, for others, no less talented - the French writer A. France (80 years old) and the political scientist and philosopher G.V. Plekhanov (62 years old) - respectively 1017 and 1180. The study of the brain of great people did not reveal the secret of intelligence. There was no dependence of brain mass on the creative level of a person. The absolute mass of the brain of women is 100-150 g less than the mass of the brain of men.

The human brain differs from the brain of apes and other higher animals not only in greater mass, but also in the significant development of the frontal lobes, which makes up 29% of the total mass of the brain. Significantly outpacing the growth of other lobes, the frontal lobes continue to increase throughout the first 7-8 years of a child's life. Obviously, this is due to the fact that they are associated with motor function. It is from the frontal lobes that the pyramidal path originates. The importance of the frontal lobe and in the implementation of higher nervous activity. In contrast to the animal, in the parietal lobe of the human brain, the lower parietal lobule is differentiated. Its development is associated with the appearance of speech function.

The human brain is the most perfect of all that nature has created. At the same time, it is the most difficult object for knowledge. What apparatus, in general terms, enables the brain to perform its extremely complex function? The number of neurons in the brain is about 10 11 , the number of synapses, or contacts between neurons, is about 10 15 . On average, each neuron has several thousand separate inputs, and it itself sends connections to many other neurons (F. Crick, 1982). These are just some of the main provisions of the doctrine of the brain. Scientific research on the brain is progressing, albeit slowly. However, this does not mean that at some point in the future there will not be a discovery or series of discoveries that will reveal the secrets of how the brain works.

This question concerns the very essence of man, and therefore fundamental changes in our views on the human brain will significantly affect ourselves, the world around us and other areas of scientific research, and will answer a number of biological and philosophical questions. However, these are still prospects for the development of brain science. Their implementation will be similar to those revolutions that were made by Copernicus, who proved that the Earth is not the center of the Universe; Darwin, who established that man is related to all other living beings; Einstein, who introduced new concepts regarding time and space, mass and energy; Watson and Crick, who showed that biological heredity can be explained by physical and chemical concepts (D. Huebel, 1982).

The cerebral cortex covers its hemispheres, has grooves that divide it into lobes and convolutions, as a result of which its area increases significantly. On the upper lateral (outer) surface of the cerebral hemisphere there are two largest primary sulci - the central sulcus (sulcus centralis), which separates the frontal lobe from the parietal, and the lateral sulcus (sulcus lateralis), which is often called the sylvian sulcus; it separates the frontal and parietal lobes from the temporal (see Fig. 2). On the medial surface of the cerebral hemisphere, a parietal-occipital sulcus (sulcus parietooccipitalis) is distinguished, which separates the parietal lobe from the occipital lobe (see Fig. 4). Each cerebral hemisphere also has a lower (basal) surface.

The cerebral cortex is evolutionarily the youngest formation, the most complex in structure and function. It is extremely important in the organization of the life of the body. The cerebral cortex developed as an apparatus for adapting to changing environmental conditions. Adaptive reactions are determined by the interaction of somatic and vegetative functions. It is the cerebral cortex that ensures the integration of these functions through the limbic-reticular complex. It does not have a direct connection with receptors, but receives the most important afferent information, partially already processed at the level of the spinal cord, in the brain stem and subcortical region. In the cortex, sensitive information lends itself to analysis and synthesis. Even according to the most cautious estimates, about 10 11 elementary operations are carried out in the human brain during 1 second (O. Forster, 1982). It is in the cortex that nerve cells, interconnected by many processes, analyze the signals that enter the body, and decisions are made regarding their implementation.

Emphasizing the leading role of the cerebral cortex in neurophysiological processes, it should be noted that this higher department of the central nervous system can function normally only with close interaction with subcortical formations, the mesh formation of the brain stem. Here it is appropriate to recall the statement of P.K. Anokhin (1955) that, on the one hand, the cerebral cortex develops, and, on the other hand, its energy supply, i.e., network formation. The latter controls all the signals that are sent to the cerebral cortex, skips a certain number of them; excess signals are cumulated, and in case of information hunger are added to the general flow.

Cytoarchitectonics of the cerebral cortex

The cerebral cortex is the gray matter of the surface of the cerebral hemispheres 3 mm thick. It reaches its maximum development in the precentral gyrus, where its thickness approaches 5 mm. The human cerebral cortex contains about 70% of all neurons of the central nervous system. The mass of the cerebral cortex in an adult is 580 g, or 40% of the total mass of the brain. The total area of the cortex is about 2200 cm 2, which is 3 times the area of the inner surface of the cerebral skull, to which it is adjacent. Two-thirds of the area of the cerebral cortex is hidden in a large number of furrows (sulci cerebri).

The first rudiments of the cerebral cortex are formed in the human embryo at the 3rd month of embryonic development, at the 7th month most of the cortex consists of 6 plates, or layers. The German neurologist K. Brodmann (1903) gave the following names to the layers: molecular plate (lamina molecularis), outer granular plate (lamina granulans externa), outer pyramidal plate (lamina pyramidal is externa), inner granular plate (lamina granulans interna), internal pyramidal plate (lamina pyramidalis interna seu ganglionaris) and multiform plate (lamina miltiformis).

The structure of the cerebral cortex:

a - layers of cells; b - layers of fibers; I - molecular plate; II - external granular plate; III - external pyramidal plate; IV - internal granular plate; V - internal pyramidal (ganglion) plate; VI - multiform plate (Via - triangular cells; VIb - spindle-shaped cells)

The morphological structure of the cerebral cortex in its different parts was described in detail by Professor of Kiev University I.O. Betz in 1874. He first described giant pyramidal cells in the fifth layer of the cortex of the precentral gyrus. These cells are known as Betz cells. Their axons are sent to the motor nuclei of the brainstem and spinal cord, forming a pyramidal pathway. IN. Betz first introduced the term "cytoarchitecture of the cortex". This is the science of the cellular structure of the cortex, the number, shape and arrangement of cells in its different layers. The cytoarchitectonic features of the structure of different parts of the cerebral cortex are the basis for its distribution into areas, subareas, fields and subfields. Individual fields of the cortex are responsible for certain manifestations of higher nervous activity: speech, vision, hearing, smell, etc. The topography of the fields of the human cerebral cortex was studied in detail by K. Brodman, who compiled the corresponding maps of the cortex. The entire surface of the cortex, according to K. Brodman, is divided into 11 sections and 52 fields, which differ in the features of the cellular composition, structure and executive function.

In humans, there are three formations of the cerebral cortex: new, ancient and old. They differ significantly in their structure. The new cortex (neocortex) makes up approximately 96% of the entire surface of the cerebrum and includes the occipital lobe, superior and inferior parietal, precentral and postcentral gyrus, as well as the frontal and temporal lobes of the brain, the insula. This is a homotopic cortex, it has a lamellar type of structure and consists mainly of six layers. Records vary in the power of their development in different fields. In particular, in the precentral gyrus, which is the motor center of the cerebral cortex, the outer pyramidal, inner pyramidal and multiform plates are well developed, and worse - the outer and inner granular plates.

The ancient cortex (paleocortex) includes the olfactory tubercle, the transparent septum, the periamygdala and prepiriform regions. It is connected with the ancient functions of the brain, relating to smell, taste. The ancient bark differs from the bark of the new formation in that it is covered with a white layer of fibers, part of which consists of fibers of the olfactory pathway (tractus olfactorius). The limbic cortex is also an ancient part of the cortex, it has a three-layer structure.

Old bark (archicortex) includes ammonium horn, dentate gyrus. It is closely connected with the area of the hypothalamus (corpus mammillare) and the limbic cortex. The old bark differs from the ancient one in that it is clearly separated from the subcortical formations. Functionally, it is connected with emotional reactions.

The ancient and aged cortex makes up approximately 4% of the cerebral cortex. It does not pass in the embryonic development of the period of the six-layer structure. Such a cortex has a three- or one-layer structure and is called heterotopic.

Almost simultaneously with the study of the cellular architectonics of the cortex, the study of its myeloarchitectonics began, that is, the study of the fibrous structure of the cortex in terms of determining those differences that exist in its individual sections. The myeloarchitectonics of the cortex is characterized by the presence of six layers of fibers within the boundaries of the cerebral cortex with different lines of their myelination (Fig. b). different hemispheres, and projection, connecting the cortex with the lower parts of the central nervous system.

Thus, the cerebral cortex is divided into sections and fields. All of them have a special, specific, inherent structure. As for functions, there are three main types of cortical activity. The first type is associated with the activities of individual analyzers and provides the simplest forms of cognition. This is the first signal system. The second type includes a second signaling system, the operation of which is closely related to the function of all analyzers. This is a more complex level of cortical activity, which directly concerns the speech function. Words for a person are the same conditioned stimulus as signals of reality. The third type of cortical activity provides purposefulness of actions, the possibility of their long-term planning, which is functionally connected with the frontal lobes of the cerebral hemispheres.

Thus, a person perceives the world around him on the basis of the first signal system, and logical, abstract thinking is associated with the second signal system, which is the highest form of human nervous activity.

Autonomic (vegetative) nervous system

As already noted in previous chapters, the sensory and motor systems perceive irritation, carry out a sensitive connection of the body with the environment, and provide movement by contracting skeletal muscles. This part of the general nervous system is called the somatic. At the same time, there is a second part of the nervous system, which is responsible for the process of nutrition of the body, metabolism, excretion, growth, reproduction, circulation of fluids, i.e., regulates the activity of internal organs. It is called the autonomic (vegetative) nervous system.

There are different terminological designations for this part of the nervous system. According to the International Anatomical Nomenclature, the generally accepted term is "autonomous nervous system". However, in the domestic literature, the former name is traditionally used - the autonomic nervous system. The division of the general nervous system into two closely interconnected parts reflects its specialization while maintaining the integrative function of the central nervous system as the basis of the body's integrity.

Functions of the autonomic nervous system:

Trophotropic - regulation of the activity of internal organs, maintaining the constancy of the internal environment of the body - homeostasis;

Ergotropic vegetative support of the processes of adaptation of the body to environmental conditions, i.e., the provision of various forms of mental and physical activity of the body: increased blood pressure, increased heart rate, deepening of breathing, increased blood glucose levels, release of adrenal hormones and other functions. These physiological functions are regulated independently (autonomously), without arbitrary control of them.

Thomas Willis singled out a borderline sympathetic trunk from the vagus nerve, and Jacob Winslow (1732) described in detail its structure, connection with internal organs, noting that "... one part of the body affects another, sensations arise - sympathy." This is how the term “sympathetic system” arose, that is, a system that connects organs to each other and to the central nervous system. In 1800, the French anatomist M. Bisha divided the nervous system into two sections: animal (animal) and vegetative (vegetative). The latter provides the metabolic processes necessary for the existence of both an animal organism and plants. Although at that time such ideas were not fully perceived, and then were generally discarded, the proposed term "vegetative nervous system" was widely used and has survived to the present.

The English scientist John Langley established that different nervous vegetative conductor systems exercise opposite influences on organs. Based on these functional differences in the autonomic nervous system, two divisions were identified: sympathetic and parasympathetic. The sympathetic division of the autonomic nervous system activates the activity of the organism as a whole, provides protective functions (immune processes, barrier mechanisms, thermoregulation), the parasympathetic division maintains homeostasis in the body. In its function, the parasympathetic nervous system is anabolic, it contributes to the accumulation of energy.

In addition, some of the internal organs also have metasympathetic neurons that carry out local mechanisms of regulation of internal organs. The sympathetic nervous system innervates all organs and tissues of the body, while the sphere of activity of the parasympathetic nervous system refers mainly to the internal organs. Most internal organs have dual, sympathetic and parasympathetic, innervation. The exceptions are the central nervous system, most of the vessels, the uterus, the adrenal medulla, the sweat glands, which do not have parasympathetic innervation.

The first anatomical descriptions of the structures of the autonomic nervous system were made by Galen and Vesalius, who studied the anatomy and function of the vagus nerve, although they mistakenly attributed other formations to it. In the XVII century.

Anatomy

According to anatomical criteria, the autonomic nervous system is divided into segmental and suprasegmental sections.

The segmental division of the autonomic nervous system provides autonomic innervation of individual segments of the body and the internal organs that belong to them. It is divided into sympathetic and parasympathetic parts.

The central link of the sympathetic part of the autonomic nervous system is the Jacobson's nucleus neurons of the lateral horns of the spinal cord from the lower cervical (C8) to the lumbar (L2-L4) segments. The axons of these cells leave the spinal cord as part of the anterior spinal roots. Then they in the form of preganglionic fibers (white connecting branches) go to the sympathetic nodes of the border (sympathetic) trunk, where they break.

The sympathetic trunk is located on both sides of the spine and is formed by paravertebral nodes, of which 3 are cervical, 10-12 thoracic, 3-4 lumbar and 4 sacral. In the nodes of the sympathetic trunk, part of the fibers (preganglionic) ends. The other part of the fibers, without interruption, goes to the prevertebral plexuses (on the aorta and its branches - the abdominal, or solar plexus). From the sympathetic trunk and intermediate nodes originate postgangio fibers (gray connecting branches), which do not have a myelin sheath. They innervate various organs and tissues.

Scheme of the structure of the segmental division of the autonomic (vegetative) nervous system:

1 - craniobulbar division of the parasympathetic nervous system (nuclei III, VII, IX, X pairs of cranial nerves); 2 - sacral (sacral) section of the parasympathetic nervous system (lateral horns of S2-S4 segments); 3 - sympathetic department (lateral horns of the spinal cord at the level of C8-L3 segments); 4 - ciliary knot; 5 - pterygopalatine node; 6 - submaxillary node; 7 - ear knot; 8 - sympathetic trunk.

In the lateral horns of the spinal cord at the level of C8-T2 is the ciliospinal center Budge, from which the cervical sympathetic nerve originates. The preganglionic sympathetic fibers from this center are sent to the superior cervical sympathetic ganglion. From it, the postganglionic fibers rise up, form the sympathetic plexus of the carotid artery, the ophthalmic artery (a. ophtalmica), then penetrate into the orbit, where they innervate the smooth muscles of the eye. With damage to the lateral horns at this level or the cervical sympathetic nerve, Bernard-Horner syndrome occurs. The latter is characterized by partial ptosis (narrowing of the palpebral fissure), miosis (narrowing of the pupil) and enophthalmos (retraction of the eyeball). Irritation of sympathetic fibers leads to the appearance of the opposite Pourfure du Petit syndrome: expansion of the palpebral fissure, mydriasis, exophthalmos.

Sympathetic fibers that start from the stellate ganglion (cervicothoracic ganglion, gangl. stellatum) form the plexus of the vertebral artery and the sympathetic plexus in the heart. They provide innervation of the vessels of the vertebrobasilar basin, and also give branches to the heart and larynx. The thoracic section of the sympathetic trunk gives off branches that innervate the aorta, bronchi, lungs, pleura, and abdominal organs. From the lumbar nodes, sympathetic fibers are sent to the organs and vessels of the small pelvis. On the extremities, sympathetic fibers go along with the peripheral nerves, spreading in the distal regions along with small arterial vessels.

The parasympathetic part of the autonomic nervous system is divided into craniobulbar and sacral divisions. The craniobulbar region is represented by neurons of the nuclei of the brain stem: III, UP, IX, X pairs of cranial nerves. The vegetative nuclei of the oculomotor nerve - the accessory (Yakubovich's nucleus) and the central posterior (Perlia's nucleus) are located at the level of the midbrain. Their axons, as part of the oculomotor nerve, go to the ciliary ganglion (gangl. ciliarae), which is located in the posterior part of the orbit. From it, postganglionic fibers as part of short ciliary nerves (nn. ciliaris brevis) innervate the smooth muscles of the eye: the muscle that narrows the pupil (m. sphincter pupillae) and the ciliary muscle (t. ciliaris), the contraction of which provides accommodation.

In the region of the bridge there are secretory lacrimal cells, the axons of which, as part of the facial nerve, go to the pterygopalatine ganglion (gangl. pterygopalatinum) and innervate the lacrimal gland. The upper and lower secretory salivary nuclei are also localized in the brain stem, the axons from which go with the glossopharyngeal nerve to the parotid node (gangl. oticum) and with the intermediate nerve to the submandibular and sublingual nodes (gangl. submandibularis, gangl. sublingualis) and innervate the corresponding salivary glands.

At the level of the medulla oblongata is the posterior (visceral) nucleus of the vagus nerve (nucl. dorsalis n.vagus), the parasympathetic fibers of which innervate the heart, alimentary canal, gastric glands and other internal organs (except for the pelvic organs).

Scheme of efferent parasympathetic innervation:

1 - parasympathetic nuclei of the oculomotor nerve; 2 - upper salivary nucleus; 3 - lower salivary nucleus; 4 - posterior nucleus of a wandering non-ditch; 5 - lateral intermediate nucleus of the sacral spinal cord; b - oculomotor nerve; 7 - facial nerve; 8 - glossopharyngeal nerve; 9 - vagus nerve; 10 - pelvic nerves; 11 - ciliary knot; 12 - pterygopalatine node; 13 - ear knot; 14 - submandibular node; 15 - sublingual node; 16 - nodes of the pulmonary plexus; 17 - nodes of the cardiac plexus; 18 - abdominal nodes; 19 - nodes of the gastric and intestinal plexuses; 20 - nodes of the pelvic plexus.

On the surface or inside the internal organs there are intraorganic nerve plexuses (the metasympathetic division of the autonomic nervous system), which act as a collector - they switch and transform all the impulses that come to the internal organs and adapt their activity to the changes that have occurred, i.e. e. provide adaptive and compensatory processes (for example, after surgery).

The sacral (sacral) part of the autonomic nervous system is represented by cells that are located in the lateral horns of the spinal cord at the level of S2-S4 segments (lateral intermediate nucleus). The axons of these cells form the pelvic nerves (nn. pelvici), which innervate the bladder, rectum and genitals.

The sympathetic and parasympathetic parts of the autonomic nervous system have the opposite effect on the organs: dilatation or contraction of the pupil, acceleration or deceleration of the heartbeat, opposite changes in secretion, peristalsis, etc. An increase in the activity of one department under physiological conditions leads to a compensatory tension in another . This returns the functional system to its original state.

The differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are as follows:

1. The parasympathetic ganglia are located near or in the organs that they innervate, and the sympathetic ganglia are at a considerable distance from them. Therefore, the postganglionic fibers of the sympathetic system are of considerable length, and when they are stimulated, the clinical symptoms are not local, but diffuse. The manifestations of the pathology of the parasympathetic part of the autonomic nervous system are more local, often covering only one organ.

2. Different nature of mediators: the mediator of preganglionic fibers of both departments (sympathetic and parasympathetic) is acetylcholine. In the synapses of the postganglionic fibers of the sympathetic part, sympathy is released (a mixture of adrenaline and norepinephrine), parasympathetic - acetylcholine.

3. The parasympathetic department is evolutionarily older, it performs a trophotropic function and is more autonomous. The sympathetic department is newer, performs an adaptive (ergotropic) function. It is less autonomous, depends on the function of the central nervous system, endocrine system and other processes.

4. The scope of functioning of the parasympathetic part of the autonomic nervous system is more limited and concerns mainly the internal organs; sympathetic fibers provide innervation to all organs and tissues of the body.

The suprasegmental division of the autonomic nervous system is not divided into sympathetic and parasympathetic parts. In the structure of the supra-segmental department, ergotropic and trophotropic systems are distinguished, as well as systems proposed by the English researcher Ged. The ergotropic system intensifies its activity at moments that require a certain tension, vigorous activity from the body. In this case, blood pressure rises, the coronary arteries expand, the pulse quickens, the respiratory rate increases, the bronchi expand, pulmonary ventilation increases, intestinal peristalsis decreases, the kidney vessels constrict, the pupils expand, the excitability of receptors and attention increase.

The body is ready to defend or to resist. To implement these functions, the ergotropic system mainly includes segmental apparatuses of the sympathetic part of the autonomic nervous system. In such cases, humoral mechanisms are also included in the process - adrenaline is released into the blood. Most of these centers are located in the frontal and parietal lobes. For example, the motor centers of innervation of smooth muscles, internal organs, blood vessels, sweating, trophism, and metabolism are located in the frontal lobes of the brain (fields 4, 6, 8). The innervation of the respiratory organs is associated with the cortex of the insula, the abdominal organs - with the cortex of the postcentral gyrus (field 5).

The trophotropic system helps to maintain internal balance and homeostasis. It provides nutritional benefits. The activity of the trophotropic system is associated with the state of rest, rest, sleep, and the processes of digestion. In this case, the heart rate, breathing slows down, blood pressure decreases, the bronchi narrow, the peristalsis of the intestines and the secretion of digestive juices increase. The actions of the trophotropic system are realized through the formation of the segmental division of the parasympathetic part of the autonomic nervous system.

The activity of both these functions (ergo- and trophotropic) proceeds synergistically. In each specific case, the predominance of one of them can be noted, and the adaptation of the organism to changing environmental conditions depends on their functional relationship.

Supra-segmental autonomic centers are located in the cerebral cortex, subcortical structures, cerebellum and brain stem. For example, such vegetative centers as the innervation of smooth muscles, internal organs, blood vessels, sweating, trophism, and metabolism are located in the frontal lobes of the brain. A special place among the higher vegetative centers is occupied by the limbic-reticular complex.

The limbic system is a complex of brain structures, which includes: the cortex of the posterior and mediobasal surface of the frontal lobe, the olfactory brain (olfactory bulb, olfactory pathways, olfactory tubercle), hippocampus, dentate, cingulate gyrus, septal nuclei, anterior thalamic nuclei , hypothalamus, amygdala. The limbic system is closely related to the reticular formation of the brain stem. Therefore, all these formations and their connections are called the limbic-reticular complex. The central parts of the limbic system are the olfactory brain, the hippocampus, and the amygdala.

The whole complex of structures of the limbic system, despite their phylogenetic and morphological differences, ensures the integrity of many body functions. At this level, the primary synthesis of all sensitivity takes place, the state of the internal environment is analyzed, elementary needs, motivations, and emotions are formed. The limbic system provides integrative functions, the interaction of all motor, sensory, and vegetative systems of the brain. The level of consciousness, attention, memory, the ability to navigate in space, motor and mental activity, the ability to perform automated movements, speech, the state of alertness or sleep depend on its state.

A significant place among the subcortical structures of the limbic system is assigned to the hypothalamus. It regulates the function of digestion, respiration, cardiovascular, endocrine systems, metabolism, thermoregulation.

Ensures the constancy of the indicators of the internal environment (BP, blood glucose, body temperature, gas concentration, electrolytes, etc.), i.e. is the main central mechanism for the regulation of homeostasis, ensures the regulation of the tone of the sympathetic and parasympathetic divisions of the autonomic nervous system. Thanks to connections with many structures of the central nervous system, the hypothalamus integrates the somatic and autonomic functions of the body. Moreover, these connections are carried out on the principle of feedback, bilateral control.

An important role among the structures of the suprasegmental division of the autonomic nervous system is played by the reticular formation of the brain stem. It has an independent meaning, but is a component of the limbic-reticular complex - the integrative apparatus of the brain. The nuclei of the reticular formation (there are about 100 of them) form suprasegmental centers of vital functions: respiration, vasomotor, cardiac activity, swallowing, vomiting, etc. In addition, it controls the state of sleep and wakefulness, phasic and tonic muscle tone, deciphers information signals from environment. The interaction of the reticular formation with the limbic system ensures the organization of expedient human behavior to changing environmental conditions.

Sheaths of the brain and spinal cord

The brain and spinal cord are covered with three membranes: hard (dura mater encephali), arachnoid (arachnoidea encephali) and soft (pia mater encephali).

The hard shell of the brain consists of dense fibrous tissue, in which the outer and inner surfaces are distinguished. Its outer surface is well vascularized and is directly connected to the bones of the skull, acting as an internal periosteum. In the cavity of the skull, the hard shell forms folds (duplicatures), which are commonly called processes.

There are such processes of the dura mater:

The crescent of the brain (falx cerebri), located in the sagittal plane between the cerebral hemispheres;

The sickle of the cerebellum (falx cerebelli), located between the hemispheres of the cerebellum;

The tentorium cerebellum (tentorium cerebelli), stretched in a horizontal plane above the posterior cranial fossa, between the upper corner of the pyramid of the temporal bone and the transverse groove of the occipital bone, delimits the occipital lobes of the cerebrum from the upper surface of the cerebellar hemispheres;

Aperture of the Turkish saddle (diaphragma sellae turcicae); this process is stretched over the Turkish saddle, it forms its ceiling (operculum sellae).

Between the sheets of the dura mater and its processes are cavities that collect blood from the brain and are called the sinuses of the dura matris (sinus dures matris).

There are the following sinuses:

Superior sagittal sinus (sinus sagittalis superior), through which blood is discharged into the transverse sinus (sinus transversus). It is located along the protruding side of the upper edge of the greater falciform process;

The lower sagittal sinus (sinus sagittalis inferior) lies along the lower edge of the large crescent process and flows into the straight sinus (sinus rectus);

The transverse sinus (sinus transversus) is contained in the sulcus de occipital bone of the same name; bending around the mastoid angle of the parietal bone, it passes into the sigmoid sinus (sinus sigmoideus);

The direct sinus (sinus rectus) runs along the line of connection of the large falciform process with the cerebellum tenon. Together with the superior sagittal sinus, it brings venous blood into the transverse sinus;

Cavernous sinus (sinus cavernosus) is located on the sides of the Turkish saddle.

In cross section, it looks like a triangle. Three walls are distinguished in it: upper, outer and inner. The oculomotor nerve passes through the upper wall (p.

1) Dorsal induction or Primary neurulation - a period of 3-4 weeks of gestation;
2) Ventral induction - the period of 5-6 weeks of gestation;
3) Neuronal proliferation - a period of 2-4 months of gestation;
4) Migration - a period of 3-5 months of gestation;
5) Organization - a period of 6-9 months of fetal development;
6) Myelination - takes the period from the moment of birth and in the subsequent period of postnatal adaptation.

AT first trimester of pregnancy the following stages of development of the nervous system of the fetus occur:

Dorsal induction or Primary neurulation - due to individual developmental characteristics, it may vary in time, but always adheres to 3-4 weeks (18-27 days after conception) of gestation. During this period, the formation of the neural plate occurs, which, after closing its edges, turns into a neural tube (4-7 weeks of gestation).

Ventral induction - this stage of the formation of the fetal nervous system reaches its peak at 5-6 weeks of gestation. During this period, 3 expanded cavities appear at the neural tube (at its anterior end), from which are then formed:

from the 1st (cranial cavity) - the brain;

from the 2nd and 3rd cavity - the spinal cord.

Due to the division into three bubbles, the nervous system develops further and the rudiment of the fetal brain from three bubbles turns into five by division.

From the forebrain, the telencephalon and the diencephalon are formed.

From the posterior cerebral bladder - the laying of the cerebellum and medulla oblongata.

Partial neuronal proliferation also occurs in the first trimester of pregnancy.

The spinal cord develops faster than the brain, and, therefore, it also begins to function faster, which is why it plays a more important role in the initial stages of fetal development.

But in the first trimester of pregnancy, the development of the vestibular analyzer deserves special attention. He is a highly specialized analyzer, which is responsible for the fetus for the perception of movement in space and the sensation of a change in position. This analyzer is formed already at the 7th week of intrauterine development (earlier than other analyzers!), and by the 12th week nerve fibers are already approaching it. Myelination of nerve fibers begins by the time the first movements appear in the fetus - at 14 weeks of gestation. But in order to conduct impulses from the vestibular nuclei to the motor cells of the anterior horns of the spinal cord, the vestibulo-spinal tract must be myelinated. Its myelination occurs after 1-2 weeks (15 - 16 weeks of gestation).

Therefore, due to the early formation of the vestibular reflex, when a pregnant woman moves in space, the fetus moves into the uterine cavity. At the same time, the movement of the fetus in space is an “irritating” factor for the vestibular receptor, which sends impulses for the further development of the fetal nervous system.

Violations of the development of the fetus from the influence of various factors during this period leads to violations of the vestibular apparatus in a newborn child.

Until the 2nd month of gestation, the fetus has a smooth surface of the brain, covered with an ependymal layer consisting of medulloblasts. By the 2nd month of intrauterine development, the cerebral cortex begins to form by migration of neuroblasts to the overlying marginal layer, and thus forming the anlage of the gray matter of the brain.

All adverse factors in the first trimester of the development of the fetal nervous system lead to severe and, in most cases, irreversible impairments in the functioning and further formation of the fetal nervous system.

Second trimester of pregnancy.

If in the first trimester of pregnancy the main laying of the nervous system occurs, then in the second trimester its intensive development occurs.

Neuronal proliferation is the main process of ontogeny.

At this stage of development, physiological dropsy of the cerebral vesicles occurs. This is due to the fact that the cerebrospinal fluid, entering the brain bubbles, expands them.

By the end of the 5th month of gestation, all the main sulci of the brain are formed, and Luschka's foramina also appear, through which the cerebrospinal fluid enters the outer surface of the brain and washes it.

Within 4-5 months of brain development, the cerebellum develops intensively. It acquires its characteristic sinuosity, and divides across, forming its main parts: anterior, posterior and follicle-nodular lobes.

Also in the second trimester of pregnancy, the stage of cell migration takes place (month 5), as a result of which zonality appears. The fetal brain becomes more similar to the brain of an adult child.

Under the influence of unfavorable factors on the fetus during the second period of pregnancy, disorders occur that are compatible with life, since the laying of the nervous system took place in the first trimester. At this stage, disorders are associated with underdevelopment of brain structures.

Third trimester of pregnancy.

During this period, the organization and myelination of brain structures occurs. Furrows and convolutions in their development are approaching the final stage (7-8 months of gestation).

The stage of organization of nervous structures is understood as morphological differentiation and the emergence of specific neurons. In connection with the development of the cytoplasm of cells and an increase in intracellular organelles, there is an increase in the formation of metabolic products that are necessary for the development of nervous structures: proteins, enzymes, glycolipids, mediators, etc. In parallel with these processes, the formation of axons and dendrites occurs to ensure synoptic contacts between neurons.

Myelination of nervous structures begins from 4-5 months of gestation and ends by the end of the first, beginning of the second year of a child's life, when the child begins to walk.

Under the influence of unfavorable factors in the third trimester of pregnancy, as well as during the first year of life, when the processes of myelination of the pyramidal tracts end, no serious disturbances occur. There may be slight changes in the structure, which are determined only by histological examination.

The development of cerebrospinal fluid and the circulatory system of the brain and spinal cord.

In the first trimester of pregnancy (1 - 2 months of gestation), when the formation of five cerebral vesicles occurs, the formation of vascular plexuses occurs in the cavity of the first, second and fifth cerebral vesicles. These plexuses begin to secrete highly concentrated cerebrospinal fluid, which is, in fact, a nutrient medium due to the high content of protein and glycogen in its composition (exceeds 20 times, unlike adults). Liquor - in this period is the main source of nutrients for the development of the structures of the nervous system.

While the development of brain structures supports the CSF, at 3-4 weeks of gestation, the first vessels of the circulatory system are formed, which are located in the soft arachnoid membrane. Initially, the oxygen content in the arteries is very low, but during the 1st to 2nd month of intrauterine development, the circulatory system becomes more mature. And in the second month of gestation, blood vessels begin to grow into the medulla, forming a circulatory network.

By the 5th month of development of the nervous system, the anterior, middle and posterior cerebral arteries appear, which are interconnected by anastomoses and represent a complete structure of the brain.

The blood supply to the spinal cord comes from more sources than to the brain. Blood to the spinal cord comes from two vertebral arteries, which branch into three arterial tracts, which, in turn, run along the entire spinal cord, feeding it. The anterior horns receive more nutrients.

The venous system eliminates the formation of collaterals and is more isolated, which contributes to the rapid removal of the end products of metabolism through the central veins to the surface of the spinal cord and into the venous plexuses of the spine.

A feature of the blood supply to the third, fourth and lateral ventricles in the fetus is the wider size of the capillaries that pass through these structures. This leads to slower blood flow, which leads to more intense nutrition.

Portal for the student. Self-training