Summary: Nervous system. Nervous system

The nervous system is one, but conditionally it is divided into parts. According to the topographic principle, the nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes nerves extending from the brain (12 pairs of cranial nerves), and nerves extending from the spinal cord (31 pairs of spinal nerves), as well as nerve nodes. The CNS is built from cells and fibers that have developed from the dorsally located neural tube (Table 11.3). Peripheral nervous system - nerve fibers that connect the CNS and the body, as well as groups of cells that lie outside the CNS and are called ganglia (Table 11.4).

According to the functional principle, the nervous system is divided into somatic (animal) and autonomous (vegetative) parts. The first innervates the striated muscles of the skeleton and some organs - the tongue, pharynx, larynx, etc., and also provides sensitive innervation of the whole body. Through the somatic nervous system, a person can control movements, arbitrarily cause or stop them. The autonomic, or autonomic, nervous system innervates all the smooth muscles of the body, providing motor and secretory innervation of the internal organs, motor innervation of the cardiovascular system, and trophic innervation of the striated muscles. The work of the autonomic nervous system is not subject to the will of man. It is impossible, for example, to stop the heart at will, to speed up the process of digestion, to delay sweating.

The autonomic nervous system, in turn, is divided into two divisions: sympathetic and parasympathetic. As a rule, they have opposite effects on the organs. For example, the sympathetic nerve increases and speeds up the work of the heart, while the parasympathetic nerve slows and weakens it. The autonomic nervous system affects the processes common to animals and plants (metabolism, respiration, excretion, etc.), which is why its name comes from (vegetative - vegetable).

Table 11.3. General plan of the structure of the central nervous system

Table 11.4. General plan of the structure of the central nervous system

test questions

1. What classifications of the nervous system do you know?

2. How does an axon differ from a dendrite (in structure and function)?

3. What types of nerve cells are distinguished (by structure and function)?

4. Name the types of synapses known to you.

5. Explain the structure of the synapse and the mechanism of occurrence of a nerve impulse (postsynaptic potential).

6. What types of neuroglia exist?

7. How is the sheath of myelinated and unmyelinated nerve fibers built?

8. Tell the structure and significance of the blood-brain barrier.

9. Define and tell the structure of the reflex arc.

10. Tell us the features of the phylo- and ontogenetic development of the nervous system.

The nervous system plays an important role in the human body. Since it is responsible for coordinating the activities and implementation of the functions of other systems of the human body, as well as individual organs. That is, the nervous system is the control center of the whole organism. It controls the work of other organs and systems, allowing a person to live comfortably. The divisions of the human nervous system are responsible for various tasks, and also perform different functions. This allows a person not only to control and perform their actions, but also to interact with the external environment. A person feels a change in temperature and weather conditions precisely thanks to the nervous system. The human nervous system consists of departments that allow you to control the entire body in an appropriate way. This allows not to disturb the functions of the nervous system. Since each department is responsible for different tasks.

Central part of the nervous system

The central section consists of the spinal cord and brain, as well as white and gray matter. The spinal cord is located in the spinal canal and is made up of nerve tissue. Numerous nerves depart from it, performing a connecting function with all organs. The brain is a complex system, which includes different departments.

Vegetative part of the nervous system

The autonomic system performs a regulatory function in relation to the internal organs. That is, it is she who controls and regulates their work. Control over the lymphatic and blood vessels, as well as over the glands of external and internal secretion, is carried out precisely from the vegetative department.

Sympathetic division of the nervous system

The sympathetic division has a direct connection with the parasympathetic division in the nervous system of the human body. Motor and sensory nerve fibers underlie this department. They allow you to deliver information from organs to the central nervous system and vice versa. The main function of the somatic system is communication.

Parasympathetic division of the nervous system

The fibers of the parasympathetic division are located in the middle part of the brain, as well as in the lower part of the spinal cord, since they are directed to various organs. It allows you to control energy and circulate blood. Therefore, the parasympathetic department is very closely related to the work of the heart. Based on the impulses received from the brain, the parasympathetic system regulates the tone of the blood vessels. With brain injury, this function is impaired.

Somatic division of the nervous system

The somatic part of the nervous system is responsible for all the processes that are necessary for a person to communicate with the environment. That is, it is responsible for the behavior of the body.

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM

Centers of the nervous system

Inhibition processes in the CNS

Reflex and reflex arc. Types of reflex

Functions and divisions of the nervous system

The body is a complex highly organized system consisting of functionally interconnected cells, tissues, organs and their systems. Management of their functions, as well as their integration (relationship) provides nervous system. The NS also communicates the organism with the external environment by analyzing and synthesizing various information coming to it from receptors. It provides movement and performs the functions of a regulator of behavior necessary in specific conditions of existence. This ensures adequate adaptation to the surrounding world. In addition, the processes underlying the mental activity of a person (attention, memory, emotions, thinking, etc.) are associated with the functions of the central nervous system.

In this way, nervous system functions:

Regulates all processes occurring in the body;

Carries out the relationship (integration) of cells, tissues, organs and systems;

Carries out the analysis and synthesis of information entering the body;

Regulates behavior;

Provides the processes underlying the mental activity of a person.

According to morphological principle central(brain and spinal cord) and peripheral(paired spinal and cranial nerves, their roots, branches, nerve endings, plexuses and ganglia, lying in all parts of the human body).

By functional principle the nervous system is divided into somatic and vegetative. The somatic nervous system provides innervation mainly to the organs of the body (soma) - skeletal muscles, skin, etc. This section of the nervous system connects the body with the external environment using the sense organs, provides movement. The autonomic nervous system innervates internal organs, blood vessels, glands, including endocrine, smooth muscles, regulates metabolic processes in all organs and tissues. The autonomic nervous system includes sympathetic, parasympathetic and metasympathetic departments.

2. Structural and functional elements of the National Assembly

The main structural and functional unit of the NS is neuron with its offshoots. Their functions consist in the perception of information from the periphery or from other neurons, its processing and transmission to neighboring neurons or executive organs. In a neuron there are body (som) and processes (dendrites and axon). Dendrites are numerous strongly branching protoplasmic outgrowths near the soma, along which excitation is conducted to the body of the neuron. Their initial segments have a larger diameter and are devoid of spines (outgrowths of the cytoplasm). Axon - the only axial - cylindrical process of a neuron, having a length of several microns to 1 m, the diameter of which is relatively constant throughout its length. The terminal sections of the axon are divided into terminal branches, through which excitation is transmitted from the body of the neuron to another neuron or working organ.

The union of neurons in the nervous system occurs with the help of interneuronal synapses.

Neuron functions:

1. Perception of information (dendrites and neuron body).

2. Integration, storage and reproduction of information (neuron body). Integrative activity of a neuron consists in the intracellular transformation of the multitude of heterogeneous excitations coming to the neuron and the formation of a single response.

3. Synthesis of biologically active substances (neuron body and synaptic endings).

4. Generation of electrical impulses (axon hillock - the base of the axon).

5. Axon transport and conduction of excitation (axon).

6. Transmission of excitations (synaptic endings).

There are several classifications of neurons.

According to morphological classification Neurons are distinguished by the shape of the soma. Allocate neurons granular, pyramidal, stellate neurons, etc. According to the number of neurons extending from the body, processes are distinguished unipolar neurons (one process), pseudo-unipolar neurons (T-shaped branching process), bipolar neurons (two processes), multipolar neurons (one axon and many dendrites).

Functional classification neurons is based on the nature of the function they perform. Allocate afferent (sensitive, receptor) neurons (pseudo-unipolar), efferent (motor neurons, motor) neurons (multipolar) and associative (intercalary, interneurons) neurons (mostly multipolar).

Biochemical classification neurons is carried out taking into account the nature of the produced mediator. Based on this, distinguish cholinergic(transmitter acetylcholine), monoaminergic(adrenaline, norepinephrine, serotonin, dopamine), GABAergic(gamma-aminobutyric acid), peptidergic(substance P, enkephalins, endorphins, other neuropeptides), etc. Based on this classification, four main diffuse modulators systems:

1. Serotonergic the system originates in the raphe nuclei and releases the neurotransmitter serotonin. Serotonin is the precursor of melatonin, which is formed in the pineal gland; may be involved in the formation of endogenous opiates. Serotonin plays a major role in mood regulation. The development of mental disorders, manifested by depression and anxiety, suicidal behavior, is associated with impaired function of the serotonergic system. An excess of serotonin usually causes panic. Antidepressants of the latest generation are based on the mechanisms of blocking the reuptake of serotonin from the synaptic cleft. The serotonergic neurons of the raphe nuclei are central to the control of the sleep-wake cycle, it initiates REM sleep. The serotonergic system of the brain is involved in the regulation of sexual behavior: an increase in the level of serotonin in the brain is accompanied by inhibition of sexual activity, and a decrease in its content leads to its increase.

2. Noradrenergic the system originates in the blue spot of the bridge and functions as an "alarm center" that becomes most active when new environmental stimuli appear. Noradrenergic neurons are widely distributed throughout the CNS and provide an increase in the overall level of excitation, initiate vegetative manifestations of the stress response.

3. Dopaminergic neurons are widely distributed in the CNS. Dopaminergic neurons play an important role in the brain's satisfaction system (pleasure system). This system underlies addiction to drugs (including cocaine, amphetamines, ecstasy, alcohol, nicotine and cocaine). The development of Parkinson's disease is based on the progressive degeneration of dopamine-containing pigment neurons of the substantia nigra and the blue spot. It is assumed that in schizophrenia there is an increase in the activity of the dopamine system of the brain with an increase in the release of dopamine, amphetamine-type dopamine agonists can cause psychoses similar to paranoid schizophrenia. Psychomotor processes (exploratory behavior, motor skills) are closely related to dopamine metabolism.

4. Cholinergic neurons are widely distributed in the central nervous system, especially in the basal ganglia and brainstem. Cholinergic neurons are involved in the mechanisms of selective attention to a particular task and are important for learning and memory. Cholinergic neurons are involved in the pathogenesis of Alzheimer's disease.

One of the components of the CNS is neuroglia(glial cells). It makes up almost 90% of NS cells and consists of two types: macroglia, represented by astrocytes, oligodendrocytes and ependymocytes, and microglia. Astrocytes- large stellate cells perform supporting and trophic (nutritional) functions. Astrocytes ensure the constancy of the ionic composition of the medium. Oligodendrocytes form the myelin sheath of CNS axons. Oligodendrocytes outside the CNS are called Schwann cells, they take part in axon regeneration. Ependymocytes line the ventricles of the brain and the spinal canal (these are cavities filled with cerebral fluid secreted by epidimocytes). Cells microglia can turn into mobile forms, migrate through the central nervous system to the site of damage to the nervous tissue and phagocytize decay products. Unlike neurons, glial cells do not generate an action potential, but can influence excitatory processes.

According to the histological principle, in the structures of the NS, one can distinguish white and Gray matter. Gray matter- this is the cerebral cortex and cerebellum, various nuclei of the brain and spinal cord, peripheral (i.e. located outside the central nervous system) ganglia. Gray matter is formed by clusters of neuron bodies and their dendrites. It follows that it is responsible for reflex functions: perception and processing of incoming signals, as well as the formation of a response. The remaining structures of the nervous system are formed by white matter. white matter formed by myelinated axons (hence the color and name), the function of which is - conducting nerve impulses.

3. Features of the spread of excitation in the central nervous system

Excitation in the central nervous system is not only transmitted from one nerve cell to another, but is also characterized by a number of features. These are convergence and divergence of nerve pathways, phenomena of irradiation, spatial and temporal relief and occlusion.

Divergence paths are the contact of one neuron with many neurons of higher orders.

So, in vertebrates, there is a division of the axon of a sensitive neuron entering the spinal cord into many branches (collaterals) that go to different segments of the spinal cord and to different parts of the brain. Signal divergence is also observed in output nerve cells. So, in humans, one motor neuron excites dozens of muscle fibers (in the eye muscles) and even thousands of them (in the muscles of the limbs).

Numerous synaptic contacts of one axon of a nerve cell with a large number of dendrites of several neurons are the structural basis of the phenomenon. irradiation excitation (expanding the scope of the signal). Irradiation happens directed when a certain group of neurons is covered by excitation, and diffuse. An example of the latter is an increase in the excitability of one receptor site (for example, the right leg of a frog) when another is irritated (pain affects the left leg).

Convergence is the convergence of many neural pathways to the same neurons. The most common in the CNS is multisensory convergence, which is characterized by the interaction on individual neurons of several afferent excitations of various sensory modality (visual, auditory, tactile, temperature, etc.).

The convergence of many neural pathways to a single neuron makes that neuron integrator of the corresponding signals. If it's about motoneurone, i.e. the final link of the nerve pathway to the muscles, they talk about common destination. The presence of convergence of many paths, i.e. nerve chains, on one group of motor neurons underlies the phenomena of spatial relief and occlusion.

Spatial and temporal relief is the excess of the effect of the simultaneous action of several relatively weak (subthreshold) excitations over the sum of their separate effects. The phenomenon is explained by spatial and temporal summation.

Occlusion is a phenomenon opposite to spatial relief. Here, two strong (superthreshold) excitations together cause an excitation of such a force that is less than the arithmetic sum of these excitations separately.

The reason for the occlusion is that these afferent inputs, by virtue of convergence, partly excite the same structures, and therefore each can create almost the same suprathreshold excitation in them as they can together.

Centers of the nervous system

A functionally connected set of neurons located in one or more structures of the central nervous system and providing the regulation of a particular function or the implementation of a holistic reaction of the body is called center of the nervous system. Physiological concept of the nerve center different from the anatomical representation of the nucleus, where closely located neurons are united by common morphological features.

In the human body, the work of all its organs is closely interconnected, and therefore the body functions as a whole. The coordination of the functions of the internal organs is provided by the nervous system. In addition, the nervous system communicates between the external environment and the regulatory body, responding to external stimuli with appropriate reactions.

The perception of changes occurring in the external and internal environment occurs through nerve endings - receptors.

Any irritation (mechanical, light, sound, chemical, electrical, temperature) perceived by the receptor is converted (transformed) into the process of excitation. Excitation is transmitted along sensitive - centripetal nerve fibers to the central nervous system, where an urgent process of processing nerve impulses takes place. From here, impulses are sent along the fibers of centrifugal neurons (motor) to the executive organs that implement the response - the corresponding adaptive act.

This is how a reflex is performed (from the Latin "reflexus" - reflection) - a natural reaction of the body to changes in the external or internal environment, carried out through the central nervous system in response to irritation of the receptors.

Reflex reactions are diverse: this is the narrowing of the pupil in bright light, the release of saliva when food enters the oral cavity, etc.

The path along which nerve impulses (excitation) pass from receptors to the executive organ during the implementation of any reflex is called reflex arc.

The arcs of the reflexes close in the segmental apparatus of the spinal cord and brainstem, but they can also close higher, for example, in the subcortical ganglia or in the cortex.

Based on the foregoing, there are:

• central nervous system (brain and spinal cord) and
• peripheral nervous system, represented by nerves extending from the brain and spinal cord and other elements that lie outside the spinal cord and brain.

The peripheral nervous system is divided into somatic (animal) and autonomic (or autonomic).

• The somatic nervous system mainly carries out the connection of the body with the external environment: the perception of stimuli, the regulation of movements of the striated muscles of the skeleton, etc.
• vegetative - regulates metabolism and the functioning of internal organs: heartbeat, peristaltic contractions of the intestines, secretion of various glands, etc.

The autonomic nervous system, in turn, based on the segmental principle of structure, is divided into two levels:

• segmental - includes sympathetic, anatomically associated with the spinal cord, and parasympathetic, formed by accumulations of nerve cells in the midbrain and medulla oblongata, nervous systems
• suprasegmental level - includes the reticular formation of the brain stem, hypothalamus, thalamus, amygdala and hippocampus - limbic-reticular complex

The somatic and autonomic nervous systems function in close interaction, however, the autonomic nervous system has some independence (autonomy), controlling many involuntary functions.

CENTRAL NERVOUS SYSTEM

Represented by the brain and spinal cord. The brain is made up of gray and white matter.

Gray matter is a collection of neurons and their short processes. In the spinal cord, it is located in the center, surrounding the spinal canal. In the brain, on the contrary, gray matter is located on its surface, forming a cortex (cloak) and separate clusters, called nuclei, concentrated in white matter.

The white matter is under the gray and is composed of sheathed nerve fibers. Nerve fibers, connecting, compose nerve bundles, and several such bundles form individual nerves.

The nerves through which excitation is transmitted from the central nervous system to the organs are called centrifugal, and the nerves that conduct excitation from the periphery to the central nervous system are called centripetal.

The brain and spinal cord are surrounded by three membranes: hard, arachnoid and vascular.

• Solid - external, connective tissue, lines the internal cavity of the skull and spinal canal.
• The arachnoid is located under the solid - it is a thin shell with a small number of nerves and blood vessels.
• The choroid is fused with the brain, enters the furrows and contains many blood vessels.

Cavities filled with cerebral fluid form between the vascular and arachnoid membranes.

Spinal cord located in the spinal canal and has the appearance of a white cord, stretching from the occipital foramen to the lower back. Longitudinal grooves are located along the anterior and posterior surfaces of the spinal cord, in the center there is a spinal canal, around which gray matter is concentrated - an accumulation of a huge number of nerve cells that form the contour of a butterfly. On the outer surface of the cord of the spinal cord is white matter - an accumulation of bundles of long processes of nerve cells.

The gray matter is divided into anterior, posterior and lateral horns. In the anterior horns lie motor neurons, in the posterior - intercalary, which carry out the connection between sensory and motor neurons. Sensory neurons lie outside the cord, in the spinal nodes along the sensory nerves.

Long processes depart from the motor neurons of the anterior horns - the anterior roots, which form the motor nerve fibers. Axons of sensitive neurons approach the posterior horns, forming the posterior roots, which enter the spinal cord and transmit excitation from the periphery to the spinal cord. Here, the excitation switches to the intercalary neuron, and from it to the short processes of the motor neuron, from which it is then transmitted along the axon to the working organ.

In the intervertebral foramina, the motor and sensory roots connect to form mixed nerves, which then split into anterior and posterior branches. Each of them consists of sensory and motor nerve fibers. Thus, at the level of each vertebra, only 31 pairs of spinal nerves of a mixed type depart from the spinal cord in both directions.

The white matter of the spinal cord forms pathways that stretch along the spinal cord, connecting both its individual segments to each other, and the spinal cord to the brain. Some pathways are called ascending or sensitive, transmitting excitation to the brain, others are descending or motor, which conduct impulses from the brain to certain segments of the spinal cord.

The function of the spinal cord. The spinal cord has two functions:

1. reflex [show] .

   Each reflex is carried out by a strictly defined part of the central nervous system - the nerve center. The nerve center is a collection of nerve cells located in one of the parts of the brain and regulating the activity of any organ or system. For example, the center of the knee-jerk reflex is located in the lumbar spinal cord, the center of urination is in the sacral, and the center of pupil dilation is in the upper thoracic segment of the spinal cord. The vital motor center of the diaphragm is localized in the III-IV cervical segments. Other centers - respiratory, vasomotor - are located in the medulla oblongata.

   The nerve center consists of many intercalary neurons. It processes the information that comes from the corresponding receptors and generates impulses that are transmitted to the executive organs - the heart, blood vessels, skeletal muscles, glands, etc. As a result, their functional state changes. To regulate the reflex, its accuracy, the participation of the higher parts of the central nervous system, including the cerebral cortex, is also necessary.

   The nerve centers of the spinal cord are directly connected with the receptors and executive organs of the body. The motor neurons of the spinal cord provide contraction of the muscles of the trunk and limbs, as well as the respiratory muscles - the diaphragm and intercostals. In addition to the motor centers of skeletal muscles, there are a number of autonomic centers in the spinal cord.

2. conductive [show] .

The bundles of nerve fibers that form the white matter connect the various parts of the spinal cord to each other and the brain to the spinal cord. There are ascending pathways, carrying impulses to the brain, and descending, carrying impulses from the brain to the spinal cord. According to the first, the excitation that occurs in the receptors of the skin, muscles, and internal organs is carried along the spinal nerves to the posterior roots of the spinal cord, is perceived by the sensitive neurons of the spinal ganglions, and from here it is sent either to the posterior horns of the spinal cord, or as part of the white matter reaches the trunk, and then the cerebral cortex.

Descending pathways conduct excitation from the brain to the motor neurons of the spinal cord. From here, the excitation is transmitted along the spinal nerves to the executive organs. The activity of the spinal cord is under the control of the brain, which regulates spinal reflexes.

Brain located in the medulla of the skull. Its average weight is 1300 - 1400 g. After the birth of a person, brain growth continues up to 20 years. It consists of five sections: the anterior (large hemispheres), intermediate, middle, hindbrain and medulla oblongata. Inside the brain there are four interconnected cavities - cerebral ventricles. They are filled with cerebrospinal fluid. I and II ventricles are located in the cerebral hemispheres, III - in the diencephalon, and IV - in the medulla oblongata.

The hemispheres (the newest part in evolutionary terms) reach high development in humans, accounting for 80% of the mass of the brain. The phylogenetically older part is the brain stem. The trunk includes the medulla oblongata, the medullary (varoli) bridge, the midbrain and the diencephalon.

Numerous nuclei of gray matter lie in the white matter of the trunk. The nuclei of 12 pairs of cranial nerves also lie in the brainstem. The brain stem is covered by the cerebral hemispheres.

Medulla- a continuation of the dorsal and repeats its structure: furrows also lie on the anterior and posterior surfaces. It consists of white matter (conducting bundles), where clusters of gray matter are scattered - the nuclei from which the cranial nerves originate - from the IX to XII pair, including the glossopharyngeal (IX pair), vagus (X pair), innervating organs respiration, circulation, digestion and other systems, sublingual (XII pair). At the top, the medulla oblongata continues into a thickening - the pons varolii, and from the sides the lower legs of the cerebellum depart from it. From above and from the sides, almost the entire medulla oblongata is covered by the cerebral hemispheres and the cerebellum.

In the gray matter of the medulla oblongata lie vital centers that regulate cardiac activity, breathing, swallowing, carrying out protective reflexes (sneezing, coughing, vomiting, tearing), secretion of saliva, gastric and pancreatic juice, etc. Damage to the medulla oblongata can be the cause of death due to the cessation heart activity and respiration.

Hind brain includes the pons and cerebellum. The pons of Varolii is limited from below by the medulla oblongata, from above it passes into the legs of the brain, its lateral sections form the middle legs of the cerebellum. In the substance of the pons, there are nuclei from the V to VIII pair of cranial nerves (trigeminal, abducent, facial, auditory).

The cerebellum is located posterior to the pons and medulla oblongata. Its surface consists of gray matter (bark). Under the cerebellar cortex is white matter, in which there are accumulations of gray matter - the nucleus. The entire cerebellum is represented by two hemispheres, the middle part is a worm and three pairs of legs formed by nerve fibers, through which it is connected with other parts of the brain. The main function of the cerebellum is the unconditional reflex coordination of movements, which determines their clarity, smoothness and maintaining body balance, as well as maintaining muscle tone. Through the spinal cord along the pathways, impulses from the cerebellum arrive at the muscles. The activity of the cerebellum is controlled by the cerebral cortex.

midbrain located in front of the pons, it is represented by the quadrigemina and the legs of the brain. In the center of it is a narrow canal (aqueduct of the brain), which connects the III and IV ventricles. The cerebral aqueduct is surrounded by gray matter, which contains the nuclei of the III and IV pairs of cranial nerves. In the legs of the brain, pathways continue from the medulla oblongata and the pons to the cerebral hemispheres. The midbrain plays an important role in the regulation of tone and in the implementation of reflexes, due to which standing and walking are possible. The sensitive nuclei of the midbrain are located in the tubercles of the quadrigemina: the nuclei associated with the organs of vision are enclosed in the upper ones, and the nuclei associated with the organs of hearing are in the lower ones. With their participation, orienting reflexes to light and sound are carried out.

diencephalon occupies the highest position in the trunk and lies anterior to the legs of the brain. It consists of two visual hillocks, supratuberous, hypothalamic region and geniculate bodies. On the periphery of the diencephalon is white matter, and in its thickness - the nuclei of gray matter. Visual hillocks are the main subcortical centers of sensitivity: impulses from all receptors of the body arrive here along ascending paths, and from here to the cerebral cortex. In the hypothalamic part (hypothalamus) there are centers, the totality of which is the highest subcortical center of the autonomic nervous system, which regulates the metabolism in the body, heat transfer, and the constancy of the internal environment. Parasympathetic centers are located in the anterior hypothalamus, and sympathetic centers in the posterior. The subcortical visual and auditory centers are concentrated in the nuclei of the geniculate bodies.

The 2nd pair of cranial nerves - optic nerves - goes to the geniculate bodies. The brain stem is connected to the environment and to the organs of the body by cranial nerves. By their nature, they can be sensitive (I, II, VIII pairs), motor (III, IV, VI, XI, XII pairs) and mixed (V, VII, IX, X pairs).

forebrain consists of strongly developed hemispheres and the middle part connecting them. The right and left hemispheres are separated from each other by a deep fissure, at the bottom of which lies the corpus callosum. The corpus callosum connects both hemispheres through long processes of neurons that form pathways.

The cavities of the hemispheres are represented by the lateral ventricles (I and II). The surface of the hemispheres is formed by gray matter or the cerebral cortex, represented by neurons and their processes, under the cortex lies white matter - pathways. Pathways connect individual centers within the same hemisphere, or the right and left halves of the brain and spinal cord, or different floors of the central nervous system. In the white matter there are also clusters of nerve cells that form the subcortical nuclei of the gray matter. Part of the cerebral hemispheres is the olfactory brain with a pair of olfactory nerves extending from it (I pair).

The total surface of the cerebral cortex is 2000-2500 cm 2, its thickness is 1.5-4 mm. Despite its small thickness, the cerebral cortex has a very complex structure.

The cortex includes more than 14 billion nerve cells, arranged in six layers that differ in shape, size of neurons and connections. The microscopic structure of the cortex was first studied by V. A. Betz. He discovered pyramidal neurons, which were later given his name (Betz cells).

In a three-month-old embryo, the surface of the hemispheres is smooth, but the cortex grows faster than the brain box, so the cortex forms folds - convolutions limited by furrows; they contain about 70% of the surface of the cortex. Furrows divide the surface of the hemispheres into lobes.

There are four lobes in each hemisphere:

• frontal
• parietal
• temporal
• occipital.

The deepest furrows are the central one, which runs across both hemispheres, and the temporal one, which separates the temporal lobe of the brain from the rest; the parieto-occipital sulcus separates the parietal lobe from the occipital lobe.

Anterior to the central sulcus (Roland sulcus) in the frontal lobe is the anterior central gyrus, behind it is the posterior central gyrus. The lower surface of the hemispheres and the brain stem is called the base of the brain.

Based on experiments with partial removal of different parts of the cortex in animals and observations on people with affected cortex, it was possible to establish the functions of different parts of the cortex. So, in the cortex of the occipital lobe of the hemispheres is the visual center, in the upper part of the temporal lobe - the auditory. The musculocutaneous zone, which perceives irritations from the skin of all parts of the body and controls the voluntary movements of the skeletal muscles, occupies a portion of the cortex on both sides of the central sulcus.

Each part of the body corresponds to its own section of the cortex, and the representation of the palms and fingers, lips and tongue, as the most mobile and sensitive parts of the body, occupies almost the same area of ​​​​the cortex in a person as the representation of all other parts of the body combined.

In the cortex there are centers of all sensitive (receptor) systems, representations of all organs and parts of the body. In this regard, centripetal nerve impulses from all internal organs or parts of the body are suitable for the corresponding sensitive areas of the cerebral cortex, where analysis is carried out and a specific sensation is formed - visual, olfactory, etc., and it can control their work.

A functional system consisting of a receptor, a sensitive pathway and a cortical zone where this type of sensitivity is projected, I. P. Pavlov called the analyzer.

The analysis and synthesis of the received information is carried out in a strictly defined area - the zone of the cerebral cortex. The most important areas of the cortex are motor, sensory, visual, auditory, olfactory. The motor zone is located in the anterior central gyrus in front of the central sulcus of the frontal lobe, the zone of musculoskeletal sensitivity is located behind the central sulcus, in the posterior central gyrus of the parietal lobe. The visual zone is concentrated in the occipital lobe, the auditory zone is in the superior temporal gyrus of the temporal lobe, and the olfactory and gustatory zones are in the anterior temporal lobe.

In the cerebral cortex, many nervous processes are carried out. Their purpose is twofold: the interaction of the body with the external environment (behavioral reactions) and the unification of body functions, the nervous regulation of all organs. The activity of the cerebral cortex of humans and higher animals was defined by I. P. Pavlov as the highest nervous activity, which is a conditioned reflex function of the cerebral cortex.

PERIPHERAL NERVOUS SYSTEM

The peripheral nervous system is formed by nerves emerging from the central nervous system, and nerve nodes and plexuses located mainly near the brain and spinal cord, as well as next to various internal organs or in the wall of these organs. In the peripheral nervous system, somatic and autonomic divisions are distinguished.

somatic nervous system

This system is formed by sensory nerve fibers going to the central nervous system from various receptors, and motor nerve fibers innervating skeletal muscles. The characteristic features of the fibers of the somatic nervous system are that they are not interrupted anywhere from the central nervous system to the receptor or skeletal muscle, they have a relatively large diameter and a high speed of excitation conduction. These fibers make up most of the nerves that emerge from the CNS and form the peripheral nervous system.

There are 12 pairs of cranial nerves that emerge from the brain. The characteristics of these nerves are given in Table 1. [show] .

Table 1. Cranial nerves

Each segment of the spinal cord gives off one pair of nerves containing sensory and motor fibers. All sensory, or centripetal, fibers enter the spinal cord through the posterior roots, on which there are thickenings - nerve nodes. In these nodes are the bodies of centripetal neurons.

The fibers of the motor, or centrifugal, neurons exit the spinal cord through the anterior roots. Each segment of the spinal cord corresponds to a certain part of the body - metamere. However, the innervation of the metameres occurs in such a way that each pair of spinal nerves innervates three adjacent metameres, and each metamere is innervated by three adjacent segments of the spinal cord. Therefore, in order to completely denervate any metamere of the body, it is necessary to cut the nerves of three neighboring segments of the spinal cord.

The autonomic nervous system is a section of the peripheral nervous system that innervates internal organs: the heart, stomach, intestines, kidneys, liver, etc. It does not have its own special sensitive pathways. Sensitive impulses from organs are transmitted through sensory fibers, which also pass through the peripheral nerves, are common to the somatic and autonomic nervous systems, but make up a smaller part of them.

Unlike the somatic nervous system, autonomic nerve fibers are thinner and conduct excitation much more slowly. On the way from the central nervous system to the innervated organ, they are necessarily interrupted with the formation of a synapse.

Thus, the centrifugal pathway in the autonomic nervous system includes two neurons - preganglionic and postganglionic. The body of the first neuron is located in the central nervous system, and the body of the second is outside it, in the nerve nodes (ganglia). There are many more postganglionic neurons than preganglionic ones. As a result, each preganglionic fiber in the ganglion fits and transmits its excitation to many (10 or more) postganglionic neurons. This phenomenon is called animation.

According to a number of signs, the sympathetic and parasympathetic divisions are distinguished in the autonomic nervous system.

Sympathetic department The autonomic nervous system is formed by two sympathetic chains of nerve nodes (paired border trunk - vertebral ganglia), located on both sides of the spine, and nerve branches that depart from these nodes and go to all organs and tissues as part of mixed nerves. The nuclei of the sympathetic nervous system are located in the lateral horns of the spinal cord, from the 1st thoracic to the 3rd lumbar segments.

The impulses coming through the sympathetic fibers to the organs provide reflex regulation of their activity. In addition to the internal organs, sympathetic fibers innervate blood vessels in them, as well as in the skin and skeletal muscles. They increase and speed up heart contractions, cause a rapid redistribution of blood by constricting some vessels and expanding others.

Parasympathetic department represented by a number of nerves, among which the vagus nerve is the largest. It innervates almost all organs of the chest and abdominal cavity.

The nuclei of the parasympathetic nerves lie in the middle, oblong sections of the brain and sacral spinal cord. Unlike the sympathetic nervous system, all parasympathetic nerves reach the peripheral nerve nodes located in the internal organs or on the outskirts of them. The impulses carried out by these nerves cause weakening and slowing of cardiac activity, constriction of the coronary vessels of the heart and brain vessels, dilation of the vessels of the salivary and other digestive glands, which stimulates the secretion of these glands, and increases the contraction of the muscles of the stomach and intestines.

The main differences between the sympathetic and parasympathetic divisions of the autonomic nervous system are given in Table. 2. [show] .

Table 2. Autonomic nervous system

Most of the internal organs receive a double autonomic innervation, that is, both sympathetic and parasympathetic nerve fibers approach them, which function in close interaction, having the opposite effect on the organs. This is of great importance in adapting the body to constantly changing environmental conditions.

A significant contribution to the study of the autonomic nervous system was made by L. A. Orbeli [show] .

Orbeli Leon Abgarovich (1882-1958) - Soviet physiologist, student of I.P. Pavlov. Acad. Academy of Sciences of the USSR, Academy of Sciences of the ArmSSR and the Academy of Medical Sciences of the USSR. Head of the Military Medical Academy, Institute of Physiology. I, P. Pavlov of the USSR Academy of Sciences, Institute of Evolutionary Physiology, Vice-President of the USSR Academy of Sciences.

The main direction of research is the physiology of the autonomic nervous system.

L. A. Orbeli created and developed the doctrine of the adaptive-trophic function of the sympathetic nervous system. He also carried out research on the coordination of the activity of the spinal cord, on the physiology of the cerebellum, and on higher nervous activity.

Nervous system

Functions of the nervous system. plays an important role in the life of the human body nervous system- a set of various structures of the nervous tissue. Functions nervous system are: 1) regulation vital activity of tissues, organs and their systems; 2) association (integration) organism into a single whole; 3) implementation the relationship of the organism with the external environment and its adaptation to changing environmental conditions; 4) definition mental activity of a person as the basis of his social existence.

In contrast to the humoral regulation of vital processes carried out by the endocrine glands, the nervous system ensures the rapid transmission of information (excitation) to well-defined cells, tissues, and organs.

Divisions of the nervous system. The nervous system - a single structural and functional formation - is conventionally divided into central and peripheral parts. To central nervous system(CNS) refers to the brain and spinal cord, to peripheral- formations lying outside the central nervous system, namely: nerves, nodes (ganglia), nerve plexuses and receptor apparatus extending from the central nervous system.

Depending on the structural and functional features of the innervated organs, the somatic and autonomic parts of the nervous system are distinguished. Somatic nervous system - part of the nervous system that regulates the activity of the skeletal (voluntary) muscles. autonomic nervous system- part of the nervous system that regulates the activity of smooth (involuntary) muscles of internal organs, blood vessels, skin, heart muscles and glands. In turn, depending on the anatomical and functional features, the autonomic nervous system is divided into two sections: sympathetic and parasympathetic.

Spinal cord. It is located in the spinal canal and is a white cord slightly flattened in the anteroposterior direction, 40-45 cm long and about 1 cm thick. In its upper part, it passes into the medulla oblongata, and in the lower part it ends at the level of the 2nd lumbar vertebra. The spinal cord is divided by longitudinal grooves into mirror-symmetrical right and left halves. There is a cavity in the center spinal canal, filled with liquid. The spinal cord is covered with three membranes: outer - hard, middle - arachnoid, and inner - vascular. hard shell- a dense and durable connective tissue membrane of the brain, consisting of two layers. The outer layer lines the bones of the skull and the spinal canal, while the inner, smooth and shiny, faces the brain. The function of the hard shell is protective. Arachnoid is a thin membrane that separates the dura from the vascular. Internal choroid rich in blood vessels penetrating the medulla. It fits snugly to the brain, going into the furrows on its surface. Between the arachnoid and choroid there is a space filled with cerebrospinal fluid. Its purpose is to soften shocks and bruises of the spinal cord.

A cross section of the spinal cord (Fig. 13.1) shows that its inner part, located around the central spinal canal, looks like a butterfly. She is educated gray matter, containing bodies of intercalary and centrifugal neurons. Short and wide protrusions of gray matter leading to the anterior surface of the brain are called front horns; in the opposite direction, narrow rear horns. In the thoracic segments of the spinal cord there are still small protrusions of gray matter —side horns.

Rice. 13.1. Cross section of the spinal cord: 1 — anterior root of the spinal nerve; 2 — spinal mixed nerve; 3 — spinal node; four — posterior root of the spinal nerve; 5 — posterior longitudinal furrow; 6 —spinal canal; 7$ — white and gray matter of the brain, respectively; 9 — anterior longitudinal furrow.

The outer layer of the spinal cord is white matter, made up of neurons. Some processes stretch along the spinal cord and partially pass into the brain, forming pathways, connecting the nerve centers of different segments of the spinal cord with each other and with the nerve centers of the brain. Pathways are divided into ascending(sensitive), transmitting excitation to the brain, and descending(motor), conducting nerve impulses from the brain to the working organs. Other processes of neurons extend beyond the spinal cord, where they form front and back roots. The anterior roots are formed by the processes of motor neurons, and the posterior roots are sensory. Thickenings - ganglia - on the posterior roots are formed by accumulations of bodies of sensitive neurons. Leaving the spinal canal through the intervertebral foramina, the anterior and posterior roots unite with each other and form a pair mixed spinal nerves. Their total number is 31 pairs. Each pair innervates a specific group of skeletal muscles and a limited area of ​​the skin. In places where the spinal nerves exit to the upper and lower extremities, the spinal cord has two thickenings - cervical and lumbar.

Spinal Cord Functions- reflex and conductive. In the spinal cord there are nerve centers (motor centers of skeletal muscles, vasomotor centers, centers of sweating, urination, defecation, sexual activity, etc.), which are directly connected with receptors and executive (working) organs. Thanks to these centers, many simple reflexes that do not affect the brain are carried out. An example of such a reflex is the knee reflex: with a light blow to the tendon under the patella, a sharp extension of the bent leg occurs. All spinal reflexes are innate, unconditional. They are inherited and persist throughout life.

The conductive function of the spinal cord is to conduct centripetal impulses to the brain and centrifugal impulses from the brain to all parts of the body. The activity of the spinal cord is controlled by the brain, which has a regulatory effect on spinal reflexes.

Brain. It is located in the brain region of the skull, which protects it from mechanical damage. Outside, the brain is covered with three meninges. The mass of the brain in an adult is usually about 1400-1600 g (in newborns, its mass is 330-400 g).

According to the structure and function, the brain is divided into five sections: anterior, intermediate, middle, cerebellum and oblong(Fig. 13.2). All parts of the brain, excluding the forebrain, are brain stem, consisting of white matter, in which there are accumulations of gray matter - core, which are the centers of various reflex acts. In accordance with the functions performed, various more sensitive centers are distinguished, centers of vegetative functions, motor centers1, centers of mental functions, etc.

Rice. 13.2. Longitudinal section of the brain: 1 — medulla; 2 — pons; 3 — midbrain; four —diencephalon; 5 — pituitary; 6 — quadrigemina; 7 — corpus callosum; eight — hemisphere; 9 - cerebellum; ten — worm.

12 pairs depart from accumulations of gray matter in different parts of the brain cranial nerves: olfactory, visual, facial, auditory, etc. All parts of the brain are connected to each other FROM other and with the spinal cord conducting pathways, which ensures the functioning of the central nervous system as a whole. The spinal canal continues into the brain, where it forms four fluid-filled expansions (ventricles).

Medulla- a vital part of the central nervous system, which is a continuation of the spinal cord. Here are the centers of regulation of respiration (centers of inhalation and exhalation), cardiovascular activity, as well as centers of digestive (salivation, separation of gastric and pancreatic juice, chewing, sucking, swallowing, etc.) and protective reflexes (sneezing, coughing, vomiting, etc. .). Damage to the medulla oblongata leads to instant death as a result of cessation of breathing and cardiac arrest.

The conductor function of the medulla oblongata is to transmit impulses from the spinal cord to the brain and vice versa.

cerebellum and the pons form the hindbrain. Nerve pathways pass through the bridge, connecting the forebrain and midbrain with the medulla oblongata and spinal cord. The cerebellum is made up of two hemispheres connected by a small formation - worm. The gray matter of the brain is located on the surface, forming a sinuous cortex, and the white matter is located inside the cerebellum, under the cortex. The nuclei of the cerebellum provide coordination of movements, maintaining balance and posture of the body, and regulating muscle tone. Damage to the cerebellum is accompanied by a decrease in muscle tone, the disappearance of accuracy and direction of movements. The activity of the cerebellum is associated with the implementation of unconditioned reflexes and is controlled by the cerebral cortex.

midbrain placed between the pons, into which the medulla oblongata passes, and the diencephalon. On the upper side of the midbrain lie two pairs of tubercles quadrigemina, in the thickness of which gray matter is located, and on the surface - white. In the anterior pair of tubercles of the quadrigemina are primary(subcortical) reflex centers of vision, and in the posterior pair of tubercles - primary reflex centers of hearing. They provide indicative reflex reactions to light and auditory stimuli, expressed in various movements of the body, head, eyes in the direction of a new sound or auditory stimulus. In the midbrain there are also clusters of nerve cell bodies (red nucleus) that take part in regulation of skeletal muscle tone.

diencephalon located above the midbrain and below the cerebral hemispheres of the forebrain. It has two main departments: visual tubercles (thalamus) and hypothalamic region (hypothalamus). In the visual hillocks there are neurons, the processes of which go to the cortex of the cerebral hemispheres. On the other hand, the fibers of the pathways from all centripetal neurons approach them. Therefore, not a single centripetal impulse, no matter where it comes from, can pass to the cerebral cortex, bypassing the visual tubercles. Thus, through this part of the brain stem, connection of all receptors with the cerebral cortex. With the destruction of the thalamus, a complete loss of sensitivity is observed.

The hypothalamus contains centers that regulate all types of metabolism(protein, fat, carbohydrate, water-salt), heat production and heat transfer (thermoregulation center), activity of endocrine glands. The hypothalamus contains subcortical centers of regulation of vegetative functions, maintaining constancy of the parameters of the internal environment of the body (homeostasis). The hypothalamus also contains centers satiety, hunger, thirst, pleasure. The nuclei of the hypothalamus are involved in the regulation alternation of sleep and wakefulness.

forebrain- the largest and most developed part of the brain. He is represented large hemispheres and corpus callosum. outside the hemisphere covered with bark- a layer of gray matter of the brain, the thickness of which is 1.5-4.5 mm. About 16 billion cells of the cerebral cortex are arranged in six layers. They vary in shape, size and function. Some of them are sensitive perceiving excitation coming from the periphery from different organs. Excitation motor cells is transmitted through the spinal cord to the appropriate organs, such as muscles. association cells connect different parts of the cortex with their processes, providing a connection between the sensory and motor areas of the cortex. As a result, an adequate form of human response is formed.

The cerebral cortex It has convolutions and furrows, which significantly increase its surface - up to about 1700-2500 cm 2. The three deepest grooves divide each hemisphere into four lobes: frontal, parietal, temporal th occipital. Cells of the cortex of three different types and functions are distributed unevenly in different parts of it, due to which the so-called zones (fields) of the cortex. So, auditory zone the cortex is located in the temporal lobes and receives impulses from auditory receptors. visual area lies in the occipital lobes. She perceives visual signals and forms visual images. Olfactory zone located on the inner surface of the temporal lobes. sensitive area(pain, temperature, tactile sensitivity) is located in the parietal lobes; its defeat leads to loss of sensitivity. Motor center of speech lies in the frontal lobe of the left hemisphere. The most anterior part of the frontal lobes of the cortex has centers involved in the formation of personal qualities, creative processes and human drives. Conditioned reflex connections are closed in the cortex, therefore it is an organ for acquiring and accumulating life experience and adapting the body to constantly changing environmental conditions.

Thus, the cerebral cortex of the forebrain is the highest department of the central nervous system, regulating and coordinating the work of all organs. It is also the material basis of human mental activity.

autonomic nervous system. According to its structure and properties autonomic nervous system (ANS) is different from somatic(SNA) the following features:

1. The centers of the ANS are located in different parts of the CNS: in the middle and oblong parts of the brain, sternolumbar and sacral segments of the spinal cord. Nerve fibers extending from the nuclei of the middle and medulla oblongata and from the sacral segments of the spinal cord form parasympathetic division of the ANS. Fibers emerging from the nuclei of the lateral horns of the sternolumbar segments of the spinal cord form sympathetic division of the ANS.

2. Nerve fibers, leaving the CNS, do not reach the innervated organ, but are interrupted and come into contact with the dendrite of another nerve cell, the nerve fiber of which already reaches the innervated organ. In places of contact, accumulations of bodies of nerve cells form nodes, or ganglia, of the ANS. Thus, the peripheral part of the motor sympathetic and parasympathetic nerve pathways is built from two consecutively following each other neurons (Fig. 13.3). The body of the first neuron is located in the central nervous system, the body of the second - in the autonomic ganglion (ganglion). The nerve fibers of the first neuron are called preganglionic mi, second -postganglionic

.

Rice. 13.3. Scheme of the reflex arc of somatic (a) and vegetative (6) reflexes: 1 — receptor; 2 - sensitive nerve; 3 — central nervous system; 4 - motor nerve; 5 —working body — muscle, gland; To — contact (insert) neuron; G — vegetative ganglion; 6.7 — pre- and postganglionic nerve fibers.

3. Ganglia of the sympathetic division of the ANS are located on both sides of the spine, forming two symmetrical chains of nerve nodes connected to each other. The ganglia of the parasympathetic division of the ANS are located in the walls of the innervated organs or near them. Therefore, in the parasympathetic division of the ANS, the post-ganglionic fibers, in contrast to the sympathetic ones, are short.

4. The nerve fibers of the ANS are 2-5 times thinner than the fibers of the SNS. Their diameter is 0.002-0.007 mm, so the speed of excitation through them is lower than through the SNS fibers, and reaches only 0.5-18 m/s (for SNS fibers - 30-120 m/s). Most of the internal organs have a dual innervation, i.e., nerve fibers of both the sympathetic and parasympathetic divisions of the ANS are suitable for each of them. They have the opposite effect on the work of organs. So, excitation of sympathetic nerves speeds up the rhythm of contractions of the heart muscle, narrows the lumen of blood vessels. The opposite effect is associated with the excitation of the parasympathetic nerves. The meaning of the double innervation of the internal organs lies in the involuntary contractions of the smooth muscles of the walls. In this case, reliable regulation of their activity can only be ensured by double innervation, which has the opposite effect.