The human nervous system. Definition, general characteristics, classification. Lek nervous system

Nerve endings are located throughout the human body. They carry out the most important function and are an integral part of the entire system. The structure of the human nervous system is a complex branched structure that runs through the entire body.

The physiology of the nervous system is a complex composite structure.

The neuron is considered the basic structural and functional unit of the nervous system. Its processes form fibers, which are excited upon exposure and transmit impulse. The impulses reach the centers where they are analyzed. After analyzing the received signal, the brain transmits the necessary response to the stimulus to the corresponding organs or parts of the body. The human nervous system is briefly described by the following functions:

• providing reflexes;
• regulation of internal organs;
• ensuring the interaction of the body with the external environment, by adapting the body to changing external conditions and stimuli;
• interaction of all organs.

The importance of the nervous system is to ensure the vital activity of all parts of the body, as well as the interaction of a person with the outside world. The structure and functions of the nervous system are studied by neurology.

CNS structure

The anatomy of the central nervous system (CNS) is a collection of neuronal cells and neural processes in the spinal cord and brain. A neuron is a unit of the nervous system.

The function of the central nervous system is to provide reflex activity and the processing of impulses from the PNS.

Structural features of PNS

Thanks to PNS, the activity of the whole human body is regulated. The PNS consists of cranial and spinal neurons and fibers that form the ganglia.

Its structure and functions are very complex, so any slightest damage, for example, damage to blood vessels on the legs, can cause serious disruption of its work. Thanks to the PNS, all parts of the body are monitored and the vital activity of all organs is ensured. The importance of this nervous system for the body cannot be overestimated.

The PNS is divided into two divisions - the somatic and vegetative systems of the PNS.

Performs double work - collecting information from the senses, and further transmitting this data to the central nervous system, as well as providing motor activity the body, by transmitting impulses from the central nervous system to the muscles. Thus, it is nervous system somatic is an instrument of human interaction with the outside world, as it processes signals received from the organs of vision, hearing and taste buds.

Provides the performance of the functions of all organs. It controls the heartbeat, blood supply, and respiratory activity. It contains only motor nerves that regulate muscle contraction.

To ensure the heartbeat and blood supply, the efforts of the person himself are not required - it is the vegetative part of the PNS that controls this. The principles of the structure and function of the PNS are studied in neurology.

PNS departments

The PNS also consists of the afferent nervous system and the efferent division.

The afferent region is a collection of sensory fibers that process information from receptors and transmit it to the brain. The work of this department begins when the receptor is irritated due to some kind of influence.

The efferent system differs in that it processes impulses transmitted from the brain to the effectors, that is, the muscles and glands.

One of the important parts of the vegetative part of the PNS is the enteric nervous system. The enteric nervous system is formed from fibers located in the gastrointestinal tract and urinary tract. The enteric nervous system provides motility to the small and large intestine. This department also regulates the secretion secreted in the gastrointestinal tract and provides local blood supply.

The importance of the nervous system lies in ensuring the work of internal organs, intellectual function, motor skills, sensitivity and reflex activity. The central nervous system of a child develops not only during the prenatal period, but also during the first year of life. Ontogenesis of the nervous system begins from the first week after conception.

The basis for the development of the brain is formed as early as the third week after conception. The main functional nodes are indicated by the third month of pregnancy. By this time, the hemispheres, trunk and spinal cord have already been formed. By the sixth month, the higher regions of the brain are already better developed than the spinal region.

By the time the baby is born, the brain is the most developed. The size of the brain in a newborn is about one-eighth of the weight of a child and fluctuates around 400 g.

The activity of the central nervous system and PNS is greatly reduced in the first few days after birth. This may consist in the abundance of new irritating factors for the baby. This is how the plasticity of the nervous system manifests itself, that is, the ability of this structure to rebuild. As a rule, the increase in excitability occurs gradually, starting from the first seven days of life. The plasticity of the nervous system deteriorates with age.

CNS types

In the centers located in the cerebral cortex, two processes interact simultaneously - inhibition and excitation. The rate at which these states change determines the types of the nervous system. While one part of the central nervous system is excited, the other slows down. This determines the features of intellectual activity, such as attention, memory, concentration.

The types of the nervous system describe the differences between the speed of the processes of inhibition and excitation of the central nervous system in different people.

People can differ in character and temperament, depending on the characteristics of the processes in the central nervous system. Its features include the speed of switching neurons from the inhibition process to the excitation process, and vice versa.

The types of the nervous system are divided into four types.

• The weak type, or melancholic, is considered the most susceptible to the onset of neurological and psychoemotional disorders. It is characterized by slow processes of excitation and inhibition. The strong and unbalanced type is choleric. This type is distinguished by the predominance of excitation processes over inhibition processes.
• Strong and agile is a type of sanguine person. All processes occurring in the cerebral cortex are strong and active. A strong, but inert, or phlegmatic type, is characterized by a low speed of switching of nervous processes.

The types of the nervous system are interconnected with temperaments, but these concepts should be distinguished, because temperament characterizes a set of psycho-emotional qualities, and the type of the central nervous system describes the physiological characteristics of the processes occurring in the central nervous system.

CNS protection

The anatomy of the nervous system is very complex. The CNS and PNS are affected by stress, overexertion, and nutritional deficiencies. For the normal functioning of the central nervous system, vitamins, amino acids and minerals are needed. Amino acids take part in the work of the brain and are building material for neurons. Having figured out why and for what vitamins and amino acids are needed, it becomes clear how important it is to provide the body with the necessary amount of these substances. Glutamic acid, glycine and tyrosine are especially important for humans. The scheme of taking vitamin-mineral complexes for the prevention of diseases of the central nervous system and PNS is selected individually by the attending physician.

Damage to the bundles, congenital pathologies and abnormalities of the brain, as well as the action of infections and viruses - all this leads to disruption of the central nervous system and PNS and the development of various pathological conditions. Such pathologies can cause a number of very dangerous diseases- immobilization, paresis, muscle atrophy, encephalitis and much more.

Malignant neoplasms in the brain or spinal cord lead to a number of neurological disorders. If you suspect cancer The central nervous system is assigned an analysis - the histology of the affected sections, that is, an examination of the composition of the tissue. A neuron as part of a cell can also mutate. Such mutations can be detected by histology. Histological analysis is carried out according to the testimony of a doctor and consists in the collection of the affected tissue and its further study. For benign lesions, histology is also performed.

There are many nerve endings in the human body, damage to which can cause a number of problems. Damage often results in impaired mobility of a part of the body. For example, an injury to the hand can lead to pain and impaired movement of the fingers. Osteochondrosis of the spine provoke pain in the foot due to the fact that an irritated or transmitted nerve sends pain impulses to receptors. If the foot hurts, people often look for the cause in a long walk or injury, but pain syndrome can be triggered by an injury in the spine.

If there is a suspicion of damage to the PNS, as well as in case of any accompanying problems, it is necessary to undergo an examination by a specialist.

NERVOUS SYSTEM
a complex network of structures that permeates the entire body and provides self-regulation of its vital activity due to the ability to respond to external and internal influences (stimuli). The main functions of the nervous system are receiving, storing and processing information from the external and internal environment, regulation and coordination of the activities of all organs and organ systems. In humans, as in all mammals, the nervous system includes three main components: 1) nerve cells (neurons); 2) glial cells associated with them, in particular neuroglia cells, as well as cells that form neurilemma; 3) connective tissue. Neurons provide the conduction of nerve impulses; neuroglia performs supporting, protective and trophic functions both in the brain and in the spinal cord, and neurilemma, consisting mainly of specialized, so-called. Schwann cells, participates in the formation of the sheaths of the fibers of the peripheral nerves; connective tissue supports and binds together the various parts of the nervous system. The human nervous system is subdivided in different ways. Anatomically, it consists of the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system includes the brain and spinal cord, and the PNS, which provides communication between the central nervous system and various parts of the body, includes the cranial and spinal nerves, as well as the nerve nodes (ganglia) and nerve plexuses lying outside the spinal cord and brain.

Neuron. The structural and functional unit of the nervous system is a nerve cell - a neuron. It is estimated that there are over 100 billion neurons in the human nervous system. A typical neuron consists of a body (i.e., a nuclear part) and processes, one usually unbranching process, an axon, and several branching ones - dendrites. The impulses travel along the axon from the cell body to the muscles, glands or other neurons, while along the dendrites they enter the cell body. In a neuron, as in other cells, there is a nucleus and a number of tiny structures - organelles (see also CELL). These include the endoplasmic reticulum, ribosomes, Nissl corpuscles (tigroid), mitochondria, Golgi complex, lysosomes, filaments (neurofilaments and microtubules).

Nervous impulse. If the stimulation of a neuron exceeds a certain threshold value, then at the point of stimulation, a series of chemical and electrical changes occurs that spread throughout the neuron. Transmitted electrical changes are called nerve impulses. Unlike a simple electrical discharge, which, due to the resistance of the neuron, will gradually weaken and will be able to overcome only a short distance, a much slower "running" nerve impulse is constantly restored (regenerated) during the propagation process. The concentrations of ions (electrically charged atoms) - mainly sodium and potassium, as well as organic substances - outside the neuron and inside it are not the same, therefore, the nerve cell at rest is negatively charged from the inside, and positively from the outside; as a result, a potential difference arises on the cell membrane (the so-called "resting potential" is approximately -70 millivolts). Any changes that reduce the negative charge inside the cell and thus the potential difference across the membrane are called depolarization. The plasma membrane that surrounds a neuron is a complex formation consisting of lipids (fats), proteins and carbohydrates. It is practically impervious to ions. But some of the protein molecules of the membrane form channels through which certain ions can pass. However, these channels, called ionic, are not constantly open, but, like gates, can open and close. When a neuron is stimulated, some of the sodium (Na +) channels open at the point of stimulation, allowing sodium ions to enter the cell. The influx of these positively charged ions reduces the negative charge of the inner surface of the membrane in the channel region, which leads to depolarization, which is accompanied by a sharp change in voltage and discharge - a so-called. "action potential", i.e. nervous impulse. Then the sodium channels are closed. In many neurons, depolarization also causes the opening of potassium (K +) channels, as a result of which potassium ions leave the cell. The loss of these positively charged ions again increases the negative charge on the inner surface of the membrane. Then the potassium channels are closed. Other membrane proteins also start to work - the so-called. potassium-sodium pumps, which ensure the movement of Na + from the cell, and K + into the cell, which, along with the activity of potassium channels, restores the initial electrochemical state (resting potential) at the point of stimulation. Electrochemical changes at the point of stimulation cause depolarization at the adjacent point of the membrane, triggering the same cycle of changes in it. This process is constantly repeated, and at each new point, where depolarization occurs, an impulse of the same magnitude is generated as at the previous point. Thus, together with the renewed electrochemical cycle, the nerve impulse propagates along the neuron from point to point. Nerves, nerve fibers and ganglia. A nerve is a bundle of fibers, each of which functions independently of the others. The fibers in the nerve are organized into groups, surrounded by specialized connective tissue, in which the vessels pass, supplying the nerve fibers with nutrients and oxygen and removing carbon dioxide and decay products. Nerve fibers along which impulses propagate from peripheral receptors to the central nervous system (afferent) are called sensitive or sensory. Fibers that transmit impulses from the central nervous system to muscles or glands (efferent) are called motor or motor fibers. Most of the nerves are mixed and consist of both sensory and motor fibers. A ganglion (ganglion) is a collection of neuronal bodies in the peripheral nervous system. Axon fibers in the PNS are surrounded by neurilemma - a sheath of Schwann cells, which are located along the axon, like beads on a thread. A significant number of these axons are covered with an additional coat of myelin (protein-lipid complex); they are called myelinated (fleshy). Fibers surrounded by neurilemma cells, but not covered by the myelin sheath, are called unmyelinated (non-fleshy). Myelinated fibers are found only in vertebrates. The myelin sheath is formed from the plasma membrane of Schwann cells, which is wound around the axon like a coil of tape, forming layer by layer. The section of an axon where two adjacent Schwann cells touch each other is called a Ranvier intercept. In the central nervous system, the myelin sheath of nerve fibers is formed by a special type of glial cells - oligodendroglia. Each of these cells forms the myelin sheath of several axons at once. Unmyelinated fibers in the CNS lack a sheath of any special cells. The myelin sheath speeds up the conduction of nerve impulses that "jump" from one interception of Ranvier to another, using this sheath as a connecting electrical cable. The speed of impulse conduction increases with the thickening of the myelin sheath and ranges from 2 m / s (for unmyelinated fibers) to 120 m / s (for fibers, especially rich in myelin). For comparison: the speed of propagation electric current on metal wires - from 300 to 3000 km / s.
Synapse. Each neuron has a specialized connection to muscles, glands, or other neurons. The area of ​​functional contact between two neurons is called a synapse. Interneuronal synapses are formed between different parts of two nerve cells: between an axon and a dendrite, between an axon and a cell body, between a dendrite and a dendrite, between an axon and an axon. The neuron that sends an impulse to the synapse is called presynaptic; the neuron receiving the impulse is postsynaptic. The synaptic space is shaped like a slit. A nerve impulse propagating along the membrane of a presynaptic neuron reaches the synapse and stimulates the release of a special substance - a neurotransmitter - into a narrow synaptic cleft. Neurotransmitter molecules diffuse through the gap and bind to receptors on the membrane of the postsynaptic neuron. If a neurotransmitter stimulates a postsynaptic neuron, its action is called excitatory; if it suppresses, it is called inhibitory. The result of the summation of hundreds and thousands of excitatory and inhibitory impulses simultaneously flowing to a neuron is the main factor that determines whether this postsynaptic neuron will generate a nerve impulse at a given moment. In a number of animals (for example, in the lobster), a particularly close connection is established between the neurons of certain nerves with the formation of either an unusually narrow synapse, the so-called. gap junction, or, if neurons are in direct contact with each other, tight junction. Nerve impulses pass through these connections not with the participation of a neurotransmitter, but directly, by means of electrical transmission. Few dense connections of neurons are found in mammals, including humans.
Regeneration. By the time a person is born, all his neurons and most of the interneuronal connections have already been formed, and in the future, only a few new neurons are formed. When a neuron dies, it is not replaced by a new one. However, the remaining ones can take on the functions of the lost cell, forming new processes that form synapses with those neurons, muscles or glands with which the lost neuron was connected. Cut or damaged fibers of PNS neurons, surrounded by neurilemma, can regenerate if the cell body remains intact. Below the transection site, the neurilemma remains in the form of a tubular structure, and the part of the axon that remains connected to the cell body grows along this tube until it reaches the nerve ending. Thus, the function of the damaged neuron is restored. Axons in the central nervous system that are not surrounded by neurilemma, apparently, are not able to germinate again to the place of their former termination. However, many neurons in the central nervous system can give rise to new short processes - branches of axons and dendrites that form new synapses.
CENTRAL NERVOUS SYSTEM

The central nervous system consists of the brain and spinal cord and their protective membranes. The outermost is the dura mater, underneath is the arachnoid (arachnoid), and then the pia mater, fused to the surface of the brain. Between the pia mater and the arachnoid is the subarachnoid (subarachnoid) space containing the cerebrospinal fluid, in which both the brain and spinal cord literally float. The action of the buoyant force of the liquid leads to the fact that, for example, the brain of an adult, weighing on average 1500 g, inside the skull actually weighs 50-100 g. The cerebral membranes and cerebrospinal fluid also play the role of shock absorbers that soften all kinds of shocks and shocks that experiences the body and which could damage the nervous system. The central nervous system is formed from gray and white matter. Gray matter is made up of cell bodies, dendrites and unmyelinated axons, organized into complexes that include countless synapses and serve as information processing centers, providing many functions of the nervous system. White matter consists of myelinated and unmyelinated axons, which act as conductors that transmit impulses from one center to another. Glia cells are also part of the gray and white matter. The neurons of the central nervous system form many circuits that perform two main functions: they provide reflex activity, as well as complex information processing in the higher brain centers. These higher centers, such as the visual cortex (visual cortex), receive incoming information, process it and transmit a response signal along the axons. The result of the activity of the nervous system is this or that activity, which is based on the contraction or relaxation of muscles or the secretion or cessation of the secretion of glands. It is with the work of muscles and glands that any way of our self-expression is associated. The incoming sensory information is processed, passing through a sequence of centers connected by long axons, which form specific pathways, for example, painful, visual, auditory. Sensory (ascending) pathways go in an ascending direction to the centers of the brain. Motor (descending) pathways connect the brain to the motor neurons of the cranial and spinal nerves. Pathways are usually organized in such a way that information (for example, pain or tactile) from the right side of the body enters the left side of the brain and vice versa. This rule also applies to the descending motor paths: the right half of the brain controls the movements of the left half of the body, and the left half controls the movement of the right. There are, however, a few exceptions to this general rule. The brain consists of three main structures: the cerebral hemispheres, the cerebellum, and the trunk. The cerebral hemispheres - the largest part of the brain - contain the higher nerve centers that form the basis of consciousness, intelligence, personality, speech, understanding. In each of the large hemispheres, the following formations are distinguished: lying in the depth, isolated clusters (nuclei) of gray matter, which contain many important centers; located above them a large mass of white matter; covering the hemispheres outside a thick layer of gray matter with numerous convolutions, which makes up the cerebral cortex. The cerebellum also consists of a deep gray matter, an intermediate array of white matter and an outer thick layer of gray matter that forms many convolutions. The cerebellum provides mainly coordination of movements. The brain stem is formed by a mass of gray and white matter, not divided into layers. The trunk is closely connected with the cerebral hemispheres, cerebellum and spinal cord and contains numerous centers of sensory and motor pathways. The first two pairs of cranial nerves depart from the cerebral hemispheres, while the remaining ten pairs - from the trunk. The trunk regulates vital functions such as breathing and circulation.
see also HUMAN BRAIN.
Spinal cord. The spinal cord located inside the spinal column and protected by its bone tissue has a cylindrical shape and is covered with three membranes. In cross section, the gray matter has the shape of the letter H or a butterfly. The gray matter is surrounded by white matter. The sensory fibers of the spinal nerves end in the dorsal (posterior) sections of the gray matter - the posterior horns (at the ends of the H facing the back). The bodies of the motor neurons of the spinal nerves are located in the ventral (anterior) sections of the gray matter - the anterior horns (at the ends of the H, remote from the back). In the white matter, there are ascending sensory pathways ending in the gray matter of the spinal cord, and the descending motor paths coming from the gray matter. In addition, many fibers in the white matter bind different parts of the gray matter of the spinal cord.
PERIPHERAL NERVOUS SYSTEM
PNS provides two-way communication of the central parts of the nervous system with organs and systems of the body. Anatomically, the PNS is represented by cranial (cranial) and spinal nerves, as well as a relatively autonomous enteric nervous system localized in the intestinal wall. All cranial nerves (12 pairs) are divided into motor, sensory, or mixed. The motor nerves begin in the motor nuclei of the trunk, formed by the bodies of the motor neurons themselves, and the sensory nerves are formed from the fibers of those neurons whose bodies lie in the ganglia outside the brain. 31 pairs of spinal nerves depart from the spinal cord: 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. They are designated in accordance with the position of the vertebrae adjacent to the intervertebral foramen, from which these nerves exit. Each spinal nerve has anterior and posterior roots, which merge to form the nerve itself. The dorsal spine contains sensitive fibers; it is closely associated with the spinal ganglion (dorsal root ganglion), which consists of the bodies of neurons, the axons of which form these fibers. The anterior root consists of motor fibers formed by neurons, whose cell bodies lie in the spinal cord.
VEGETATIVE NERVOUS SYSTEM
The vegetative, or autonomic, nervous system regulates the activity of the involuntary muscles, heart muscle, and various glands. Its structures are located both in the central nervous system and in the peripheral. The activity of the autonomic nervous system is aimed at maintaining homeostasis, i.e. a relatively stable state of the internal environment of the body, for example, a constant body temperature or blood pressure corresponding to the needs of the body. Signals from the central nervous system go to the working (effector) organs through pairs of neurons connected in series. The bodies of the first level neurons are located in the central nervous system, and their axons end in the autonomic ganglia lying outside the central nervous system, and here they form synapses with the bodies of the second level neurons, the axons of which are in direct contact with the effector organs. The first neurons are called preganglionic, the second - postganglionic. In that part of the autonomic nervous system, which is called the sympathetic, the bodies of preganglionic neurons are located in the gray matter of the thoracic (thoracic) and lumbar (lumbar) spinal cord. Therefore, the sympathetic system is also called thoraco-lumbar. The axons of her preganglionic neurons terminate and form synapses with postganglionic neurons in the ganglia located in a chain along the spine. Axons of postganglionic neurons are in contact with effector organs. The endings of postganglionic fibers secrete norepinephrine (a substance close to adrenaline) as a neurotransmitter, and therefore the sympathetic system is also defined as adrenergic. The sympathetic system is complemented by the parasympathetic nervous system. The bodies of her preganglinar neurons are located in the brain stem (intracranially, i.e. inside the skull) and the sacral (sacral) part of the spinal cord. Therefore, the parasympathetic system is also called cranio-sacral. The axons of the preganglionic parasympathetic neurons terminate and form synapses with postganglionic neurons in the ganglia located near the working organs. The endings of the postganglionic parasympathetic fibers secrete the neurotransmitter acetylcholine, on the basis of which the parasympathetic system is also called cholinergic. As a rule, the sympathetic system stimulates those processes that are aimed at mobilizing the body's forces in extreme situations or under stress. The parasympathetic system contributes to the accumulation or restoration of the body's energy resources. The reactions of the sympathetic system are accompanied by a waste of energy resources, an increase in the frequency and strength of heart contractions, an increase in blood pressure and blood sugar, as well as an increase in blood flow to skeletal muscles by reducing its flow to internal organs and skin. All of these changes are characteristic of the "fear, flight, or fight" response. The parasympathetic system, on the other hand, reduces the heart rate and strength of the heart, lowers blood pressure, and stimulates the digestive system. The sympathetic and parasympathetic systems act in a coordinated manner and should not be considered antagonistic. Together they support the functioning of internal organs and tissues at a level corresponding to the intensity of stress and the emotional state of a person. Both systems operate continuously, but their levels of activity fluctuate depending on the situation.
REFLEXES
When an adequate stimulus acts on the receptor of a sensory neuron, a burst of impulses arises in it, triggering a response called a reflex act (reflex). Reflexes underlie most of the manifestations of the vital activity of our body. The reflex act is carried out by the so-called. reflex arc; this term denotes the path of transmission of nerve impulses from the point of initial stimulation on the body to the organ that performs a response. The arc of the reflex that causes contraction of the skeletal muscle consists of at least two neurons: a sensory neuron, whose body is located in the ganglion, and the axon forms a synapse with neurons of the spinal cord or brain stem, and a motor (lower, or peripheral, motor neuron), whose body is located in the gray matter, and the axon ends with a motor end plate on skeletal muscle fibers. A third, intermediate, neuron located in the gray matter can also be included in the reflex arc between the sensory and motor neurons. The arcs of many reflexes contain two or more intermediate neurons. Reflex actions are carried out involuntarily, many of them are not realized. The knee reflex, for example, is triggered by tapping the tendon of the quadriceps muscle in the knee area. This is a two-neuron reflex, its reflex arc consists of muscle spindles (muscle receptors), a sensory neuron, a peripheral motor neuron, and muscle. Another example is reflexive withdrawal of the hand from a hot object: the arc of this reflex includes a sensitive neuron, one or more intermediate neurons in the gray matter of the spinal cord, a peripheral motor neuron, and a muscle. Many reflex acts have a much more complex mechanism. The so-called intersegmental reflexes consist of combinations of simpler reflexes, in the implementation of which many segments of the spinal cord take part. Thanks to such reflexes, for example, coordination of movements of the arms and legs when walking is ensured. Complex reflexes that are closed in the brain include movements associated with maintaining balance. Visceral reflexes, i.e. reflex reactions of internal organs, mediated by the autonomic nervous system; they provide emptying Bladder and many processes in the digestive system.
see also REFLEX.
DISEASES OF THE NERVOUS SYSTEM
Damage to the nervous system occurs in organic diseases or injuries of the brain and spinal cord, meninges, peripheral nerves. Diagnostics and treatment of diseases and injuries of the nervous system are the subject of a special branch of medicine - neurology. Psychiatry and clinical psychology deal mainly with mental disorders. The areas of these medical disciplines often overlap. See individual diseases of the nervous system: ALZHEIMER'S DISEASE;
STROKE ;
Meningitis;
NOT BELIEVE;
PARALYCH;
PARKINSON'S DISEASE;
POLIOMYELITIS;
MULTIPLE SCLEROSIS ;
TETANUS;
CEREBRAL PALSY ;
Chorea;
ENCEPHALIT;
EPILEPSY.
see also
ANATOMY COMPARATIVE;
HUMAN ANATOMY .
LITERATURE
Bloom F., Leiserson A., Hofstedter L. Brain, Mind and Behavior. M., 1988 Human Physiology, ed. R. Schmidt, G. Tevs, t. 1. M., 1996

Collier's Encyclopedia. - Open Society. 2000 .

In evolution, the nervous system has undergone several stages of development, which have become turning points in the qualitative organization of its activity. These stages differ in the number and types of neuronal formations, synapses, signs of their functional specialization, in the formation of groups of neurons related to each other by a common function. There are three main stages of the structural organization of the nervous system: diffuse, nodular, tubular.

Diffuse the nervous system is the most ancient; it is found in coelenterates (hydra) animals. Such a nervous system is characterized by a multiplicity of connections between neighboring elements, which allows excitation to spread freely along the nervous network in all directions.

This type of nervous system provides wide interchangeability and thus greater reliability of functioning, however, these reactions are imprecise, vague in nature.

Nodal the type of nervous system is typical for worms, molluscs, crustaceans.

It is characterized by the fact that the connections of nerve cells are organized in a certain way, the excitation passes along strictly defined paths. This organization of the nervous system is more vulnerable. Damage to one node causes a violation of the functions of the whole organism as a whole, but in its qualities it is faster and more accurate.

Tubular the nervous system is characteristic of chordates, it includes features of the diffuse and nodal types. The nervous system of higher animals took all the best: high reliability of the diffuse type, accuracy, locality, and the speed of organizing nodal type reactions.

The leading role of the nervous system

At the first stage of the development of the world of living beings, the interaction between the simplest organisms was carried out through aquatic environment the primitive ocean, which received the chemicals released by them. The first ancient form of interaction between the cells of a multicellular organism is chemical interaction through metabolic products entering the body fluids. Such metabolic products, or metabolites, are the breakdown products of proteins, carbon dioxide, etc. these are the humoral transmission of influences, the humoral mechanism of correlation, or communication between organs.

The humoral connection is characterized by the following features:

• the lack of an exact address to which the chemical is directed to enter the blood or other body fluids;
• the chemical spreads slowly;
• the chemical acts in negligible amounts and is usually rapidly degraded or excreted from the body.

Humoral connections are common to both the animal world and the plant world. At a certain stage in the development of the animal world, in connection with the appearance of the nervous system, a new, nervous form of connections and regulation is formed, which qualitatively distinguishes the animal world from the plant world. The higher in its development the organism of an animal, the more important is the interaction of organs through the nervous system, which is designated as reflex. In higher living organisms, the nervous system regulates humoral connections. In contrast to the humoral connection, the neural connection has a precise orientation towards a specific organ and even a group of cells; communication takes place hundreds of times faster than the rate at which chemicals spread. The transition from a humoral connection to a nervous one was accompanied not by the destruction of the humoral connection between the cells of the body, but by submission to the nervous connections and the emergence of neuro-humoral connections.

At the next stage in the development of living beings, special organs appear - glands, in which hormones are produced, which are formed from the nutrients entering the body. The main function of the nervous system is both in the regulation of the activity of individual organs among themselves, and in the interaction of the organism as a whole with its surrounding external environment. Any effect of the external environment on the body is primarily on the receptors (sense organs) and is carried out through changes caused by the external environment and the nervous system. As the nervous system develops, its higher section - the cerebral hemispheres - becomes "the manager and distributor of all the body's activities."

The structure of the nervous system

The nervous system is formed by nervous tissue, which consists of a huge amount neurons- a nerve cell with processes.

The nervous system is conventionally divided into central and peripheral.

central nervous system includes the brain and spinal cord, and peripheral nervous system- nerves extending from them.

The brain and spinal cord are a collection of neurons. On a transverse section of the brain, white and gray matter are distinguished. The gray matter consists of nerve cells, and the white matter consists of nerve fibers, which are processes of nerve cells. In different parts of the central nervous system, the location of the white and gray matter is not the same. In the spinal cord, the gray matter is inside, and the white matter is outside, in the brain (cerebral hemispheres, cerebellum), on the contrary, the gray matter is outside, white is inside. In different parts of the brain, there are separate clusters of nerve cells (gray matter) located inside the white matter - kernels... Clusters of nerve cells are also found outside the central nervous system. They're called knots and belong to the peripheral nervous system.

Reflex activity of the nervous system

The main form of activity of the nervous system is the reflex. Reflex- the reaction of the body to a change in the internal or external environment, carried out with the participation of the central nervous system in response to irritation of the receptors.

With any irritation, excitation from the receptors is transmitted along the centripetal nerve fibers to the central nervous system, from where, through the intercalary neuron along the centrifugal fibers, it goes to the periphery to one or another organ, the activity of which changes. This entire path through the central nervous system to the working organ is called reflex arc usually formed by three neurons: sensory, intercalary and motor. A reflex is a complex act, in the implementation of which it takes part significantly large quantity neurons. Excitation, getting into the central nervous system, spreads to many parts of the spinal cord and reaches the brain. As a result of the interaction of many neurons, the body responds to stimulation.

Spinal cord

Spinal cord- a strand about 45 cm long, 1 cm in diameter, located in the canal of the spine, covered with three meninges: hard, arachnoid and soft (vascular).

Spinal cord is located in the spinal canal and is a cord that passes into the medulla oblongata at the top, and ends at the bottom at the level of the second lumbar vertebra. The spinal cord consists of gray matter, which contains nerve cells, and white matter, which contains nerve fibers. The gray matter is located inside the spinal cord and is surrounded on all sides by white matter.

In cross section, the gray matter resembles the letter N. In it, anterior and posterior horns are distinguished, as well as a connecting bar, in the center of which is a narrow canal of the spinal cord containing cerebrospinal fluid. In the thoracic region, lateral horns are distinguished. They contain the bodies of neurons that innervate the internal organs. The white matter of the spinal cord is formed by nerve processes. Short processes connect parts of the spinal cord, and long ones make up the conductive apparatus of bilateral connections with the brain.

The spinal cord has two thickenings - the cervical and lumbar, from which nerves extend to the upper and lower extremities. 31 pairs of spinal nerves depart from the spinal cord. Each nerve starts from the spinal cord with two roots - anterior and posterior. Back roots - sensitive consist of processes of centripetal neurons. Their bodies are located in the spinal nodes. Front roots - motor- are the processes of centrifugal neurons located in the gray matter of the spinal cord. As a result of the fusion of the anterior and posterior roots, a mixed spinal nerve is formed. The spinal cord contains centers that regulate the simplest reflex acts. The main functions of the spinal cord are reflex activity and conduction of arousal.

The human spinal cord contains the reflex centers of the muscles of the upper and lower extremities, perspiration and urination. The function of conducting excitation is that impulses pass through the spinal cord from the brain to all areas of the body and vice versa. Along the ascending pathways, centripetal impulses from organs (skin, muscles) are transmitted to the brain. In descending paths, centrifugal impulses are transmitted from the brain to the spinal cord, then to the periphery, to the organs. If the pathways are damaged, there is a loss of sensitivity in various parts of the body, a violation of voluntary muscle contractions and the ability to move.

Evolution of the vertebrate brain

The formation of the central nervous system in the form of a neural tube first appears in chordates. Have lower chordates the neural tube persists throughout life, in higher- vertebrates - in the embryonic stage, a neural plate is laid on the dorsal side, which is immersed under the skin and coiled into a tube. In the embryonic stage of development, the neural tube forms three swellings in the anterior part - three cerebral vesicles, from which the parts of the brain develop: the anterior vesicle gives the forebrain and diencephalon, the middle bladder turns into the midbrain, the posterior bladder forms the cerebellum and medulla oblongata... These five brain regions are characteristic of all vertebrates.

For lower vertebrates- fish and amphibians - the predominance of the midbrain over the other sections is characteristic. Have amphibians the forebrain slightly increases and a thin layer of nerve cells is formed in the roof of the hemispheres - the primary cerebral vault, the ancient cortex. Have reptiles the forebrain is significantly enlarged due to the accumulation of nerve cells. Most of the roof of the hemispheres is occupied by the ancient crust. For the first time, the rudiment of a new bark appears in reptiles. The hemispheres of the forebrain creep into other parts, as a result of which a bend is formed in the diencephalon. Since the ancient reptiles, the cerebral hemispheres have become the largest part of the brain.

In the structure of the brain birds and reptiles much in common. On the roof of the brain is the primary cortex, the midbrain is well developed. However, in birds, compared to reptiles, the total brain mass and the relative size of the forebrain increase. The cerebellum is large and has a folded structure. Have mammals the forebrain reaches its greatest size and complexity. Most of the brain matter is the new cortex, which serves as the center of higher nervous activity. The intermediate and middle parts of the brain in mammals are small. The expanding hemispheres of the forebrain cover them and crush them under themselves. Some mammals have a smooth brain, without grooves and convolutions, but most mammals have grooves and convolutions in the cerebral cortex. The appearance of grooves and convolutions occurs due to the growth of the brain with a limited size of the skull. Further growth of the cortex leads to the appearance of folding in the form of grooves and convolutions.

Brain

If the spinal cord in all vertebrates is more or less developed in the same way, then the brain will differ significantly in size and complexity of structure in different animals. The forebrain undergoes especially drastic changes in the course of evolution. In lower vertebrates, the forebrain is poorly developed. In fish, it is represented by the olfactory lobes and nuclei of gray matter in the thickness of the brain. The intensive development of the forebrain is associated with the emergence of animals on land. It differentiates into the diencephalon and into two symmetrical hemispheres, which are called terminal brain... The gray matter on the surface of the forebrain (cortex) first appears in reptiles, further developing in birds and especially in mammals. Really large hemispheres of the forebrain become only in birds and mammals. In the latter, they cover almost all other parts of the brain.

The brain is located in the cranial cavity. It includes the trunk and the telencephalon (cerebral cortex).

Brain stem consists of the medulla oblongata, pons varoli, midbrain and diencephalon.

Medulla is a direct continuation of the spinal cord and expanding, passes into the hindbrain. It basically retains the shape and structure of the spinal cord. In the thickness of the medulla oblongata, there are accumulations of gray matter - the nuclei of the cranial nerves. The rear axle includes cerebellum and pons... The cerebellum is located above the medulla oblongata and has complex structure... On the surface of the cerebellar hemispheres, the gray matter forms the cortex, and inside the cerebellum, its nuclei. Like the spinal medulla oblongata, it performs two functions: reflex and conduction. However, the reflexes of the medulla oblongata are more complex. This is expressed in an important meaning in the regulation of cardiac activity, the state of blood vessels, respiration, and sweating. The centers of all these functions are located in the medulla oblongata. There are also centers for chewing, sucking, swallowing, saliva and gastric juice. Despite its small size (2.5–3 cm), the medulla oblongata is a vital part of the central nervous system. Damage to it can cause death due to cessation of breathing and heart activity. The conductive function of the medulla oblongata and the pons varoli is to transmit impulses from the spinal cord to the brain and vice versa.

V midbrain the primary (subcortical) centers of vision and hearing are located, which carry out reflex orientational reactions to light and sound stimuli. These reactions are expressed in various movements of the trunk, head and eyes towards stimuli. The midbrain consists of the legs of the brain and the quadruple. The midbrain regulates and distributes the tone (tension) of the skeletal muscles.

Diencephalon consists of two departments - thalamus and hypothalamus, each of which consists of a large number of nuclei of the optic hillocks and the sub-hillock area. Through the visual hillocks, centripetal impulses are transmitted to the cerebral cortex from all receptors in the body. Not a single centripetal impulse, wherever it comes from, can pass to the cortex, bypassing the visual hillocks. Thus, through the diencephalon, all receptors communicate with the cerebral cortex. In the sub-tuberous region, there are centers that affect metabolism, thermoregulation and endocrine glands.

Cerebellum located behind the medulla oblongata. It is composed of gray and white matter. However, unlike the spinal cord and the trunk, the gray matter - the cortex - is located on the surface of the cerebellum, and the white matter is located inside, under the cortex. The cerebellum coordinates movements, makes them clear and smooth, plays an important role in maintaining the balance of the body in space, and also affects muscle tone. With damage to the cerebellum, a person experiences a drop in muscle tone, movement disorder and a change in gait, speech slows down, etc. However, after a while, movement and muscle tone are restored due to the fact that the intact parts of the central nervous system take over the functions of the cerebellum.

Large hemispheres- the largest and most developed part of the brain. In humans, they form the bulk of the brain and are covered with bark over their entire surface. The gray matter covers the outside hemispheres and forms the cerebral cortex. The cortex of the human hemispheres has a thickness of 2 to 4 mm and is composed of 6-8 layers formed by 14-16 billion cells, different in shape, size and functions. There is a white substance under the bark. It consists of nerve fibers that connect the cortex with the lower parts of the central nervous system and individual lobes of the hemispheres among themselves.

The cerebral cortex has convolutions, separated by grooves, which significantly increase its surface. The three deepest grooves divide the hemispheres into lobes. There are four lobes in each hemisphere: frontal, parietal, temporal, occipital... Excitation of different receptors goes to the corresponding perceiving areas of the cortex, called zones, and from here they are transmitted to a specific organ, prompting it to action. The following zones are distinguished in the bark. Auditory zone located in the temporal lobe, receives impulses from the auditory receptors.

Visual zone lies in the occipital region. This is where impulses come from the eye receptors.

Olfactory zone is located on the inner surface of the temporal lobe and is associated with receptors in the nasal cavity.

Sensory-motor the zone is located in the frontal and parietal lobes. This zone contains the main centers of movement of the legs, trunk, arms, neck, tongue and lips. The center of speech also lies here.

The cerebral hemispheres are the highest part of the central nervous system that controls the functioning of all organs in mammals. The significance of the cerebral hemispheres in humans also lies in the fact that they represent the material basis of mental activity. I.P. Pavlov showed that mental activity is based on physiological processes occurring in the cerebral cortex. Thinking is associated with the activity of the entire cerebral cortex, and not only with the function of its individual areas.

Department of the brain	Functions
Medulla	Conductor	The connection between the spinal cord and the overlying parts of the brain.
	Reflex	Regulation of the activity of the respiratory, cardiovascular, digestive systems: food reflexes, reflexes of salivation, swallowing; protective reflexes: sneezing, blinking, coughing, vomiting.
Pons	Conductor	It connects the cerebellar hemispheres to each other and to the cerebral cortex.
Cerebellum	The coordinating	Coordination of voluntary movements and maintaining the position of the body in space. Regulation of muscle tone and balance
Midbrain	Conductor	Orientation reflexes to visual, sound stimuli ( turns of the head and torso).
	Reflex	Regulation of muscle tone and body posture; coordination of complex motor acts ( finger and hand movements) etc.
Diencephalon	thalamus collection and evaluation of incoming information from the sense organs, transmission of the most important information to the cerebral cortex; regulation of emotional behavior, pain. hypothalamus controls the work of the endocrine glands, cardiovascular system, metabolism ( thirst, hunger), body temperature, sleep and wakefulness; gives the behavior an emotional coloring ( fear, rage, pleasure, discontent)

Cerebral cortex

Surface cerebral cortex in humans, it is about 1500 cm 2, which is many times larger than the inner surface of the skull. Such a large surface of the cortex was formed due to the development of a large number of grooves and convolutions, as a result of which most of the cortex (about 70%) is concentrated in the grooves. The largest grooves of the cerebral hemispheres - central that runs across both hemispheres, and temporal separating the temporal lobe from the rest. The cerebral cortex, despite its small thickness (1.5–3 mm), has a very complex structure. It has six main layers, which differ in the structure, shape and size of neurons and connections. In the cortex are the 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 approach the cortex, and it can control their work. Through the cerebral cortex, a closure of conditioned reflexes occurs, through which the body constantly, throughout its life, very accurately adapts to the changing conditions of existence, to the environment.

Includes organs of the central nervous system (brain and spinal cord) and organs of the peripheral nervous system (peripheral nerve nodes, peripheral nerves, receptor and effector nerve endings).

Functionally, the nervous system is subdivided into the somatic one, which innervates the skeletal muscle tissue, that is, it is controlled by consciousness and vegetative (autonomous), which regulates the activity of internal organs, blood vessels and glands, i.e. does not depend on consciousness.

The functions of the nervous system are regulatory and integrating.

It is laid in the 3rd week of embryogenesis in the form of a neural plate, which is transformed into a neural groove, from which a neural tube is formed. There are 3 layers in its wall:

Internal - ependymal:

Medium - raincoat. Later it is converted to gray matter.

Outer - marginal. It forms a white substance.

In the cranial part of the neural tube, an extension is formed, from which 3 cerebral vesicles are formed at the beginning, and later - five. The latter give rise to five brain regions.

The spinal cord is formed from the trunk of the neural tube.

In the first half of embryogenesis, there is an intensive proliferation of young glial and nerve cells. Later, radial glia is formed in the cloak layer of the cranial region. Its thin, long processes penetrate the wall of the neural tube. Young neurons migrate along these processes. The formation of the centers of the brain occurs (especially intensively from 15 to 20 weeks - the critical period). Gradually, in the second half of embryogenesis, proliferation and migration attenuate. After birth, division stops. When a neural tube is formed, cells are evicted from the nerve folds (closing areas), which are located between the ectoderm and the neural tube, forming a neural crest. The latter is split into 2 leaves:

1 - under the ectoderm, pigmentocytes (skin cells) are formed from it;

2 - around the neural tube - ganglion plate. From it, peripheral nerve nodes (ganglia), adrenal medulla, areas of chromaffin tissue (along the spine) are formed. After birth, there is an intensive growth of the processes of nerve cells: axons and dendrites, synapses between neurons, neural circuits (strictly ordered interneuronal communication) are formed, which make up reflex arcs (sequentially located cells that transmit information) that provide reflex activity of a person (especially the first 5 years of life child, so stimuli are needed to form connections). Also, in the first years of a child's life, myelination is the most intensive - the formation of nerve fibers.

PERIPHERAL NERVOUS SYSTEM (PNS).

Peripheral nerve trunks are part of the neurovascular bundle. They are mixed in function, contain sensory and motor nerve fibers (afferent and efferent). Myelinic nerve fibers predominate, and myelin-free - in small quantities. Around each nerve fiber is a thin layer of loose connective tissue with blood and lymphatic vessels - endoneurium. Around the bundle of nerve fibers is a sheath of loose fibrous connective tissue - perineurium - with a small number of vessels (it mainly performs a frame function). Around the entire peripheral nerve there is a sheath of loose connective tissue with larger vessels - epineurium. Peripheral nerves regenerate well, even after complete damage. Regeneration is carried out through the growth of peripheral nerve fibers. The growth rate is 1-2 mm per day (the ability to regenerate is a genetically fixed process).

Spinal cord

It is a continuation (part) of the dorsal root of the spinal cord. Functionally sensitive. The outside is covered with a connective tissue capsule. Inside - connective tissue layers with blood and lymphatic vessels, nerve fibers (vegetative). In the center are myelinic nerve fibers of pseudo-unipolar neurons located along the periphery of the spinal cord. Pseudo-unipolar neurons have a large rounded body, a large nucleus, well-developed organelles, especially a protein-synthesizing apparatus. A long cytoplasmic outgrowth departs from the body of the neuron - this is a part of the body of the neuron, from which one dendrite and one axon depart. Dendrite - long, forms a nerve fiber that goes as part of the peripheral mixed nerve to the periphery. Sensory nerve fibers end at the periphery with a receptor, i.e. sensitive nerve endings. Axons are short and form the posterior root of the spinal cord. In the posterior horns of the spinal cord, axons form synapses with intercalary neurons. Sensory (pseudo-unipolar) neurons make up the first (afferent) link of the somatic reflex arc. All cell bodies are located in the ganglia.

Spinal cord

Outside, it is covered with the pia mater, which contains blood vessels that penetrate into the brain substance. Conventionally, 2 halves are distinguished, which are separated by the anterior median fissure and the posterior median connective tissue septum. In the center is the central canal of the spinal cord, which is located in the gray matter, lined with ependyma, contains cerebrospinal fluid, which is in constant motion. On the periphery, there is a white matter, where bundles of nerve myelin fibers are located, which form pathways. They are separated by glial connective tissue septa. In the white matter, anterior, lateral and posterior cords are distinguished.

In the middle part there is a gray matter, in which the posterior, lateral (in the thoracic and lumbar segments) and anterior horns are distinguished. The halves of the gray matter are connected by the anterior and posterior commissures of the gray matter. In gray matter, there are a large number glial and nerve cells. Gray matter neurons are divided into:

1) Internal neurons, completely (with processes) are located within the gray matter, are intercalary and are located mainly in the posterior and lateral horns. There are:

a) Associative. Are located within one half.

b) Commissural. Their processes go to the other half of the gray matter.

2) Bundle neurons. They are located in the hind horns and in the lateral horns. They form nuclei or are diffusely located. Their axons go into the white matter and form bundles of nerve fibers in the ascending direction. Are intercalated.

3) Root neurons. They are located in the lateral nuclei (nuclei of the lateral horns), in the anterior horns. Their axons extend beyond the spinal cord and form the anterior roots of the spinal cord.

In the superficial part of the posterior horns, there is a spongy layer, which contains a large number of small intercalary neurons.

Deeper than this strip is a gelatinous substance containing mainly glial cells, small neurons (the latter are in small numbers).

In the middle part is the own nucleus of the hind horns. It contains large bundle neurons. Their axons go into the white matter of the opposite half and form the dorsal-cerebellar anterior and dorsal-thalamic posterior pathways.

Nuclear cells provide exteroceptive sensitivity.

At the base of the posterior horns is the thoracic nucleus (Clark-Shutting column), which contains large bundle neurons. Their axons go to the white matter of the same half and are involved in the formation of the posterior spinal cord. Cells this path provide proprioceptive sensitivity.

In the intermediate zone, there are the lateral and medial nuclei. The medial intermediate nucleus contains large bundle neurons. Their axons go into the white matter of the same half and form the anterior cerebellar pathway, which provides visceral sensitivity.

The lateral intermediate nucleus belongs to the autonomic nervous system. In the thoracic and upper lumbar regions it is the sympathetic nucleus, and in the sacral it is the nucleus of the parasympathetic nervous system. It contains an intercalary neuron, which is the first neuron of the efferent link of the reflex arc. This is a radicular neuron. Its axons emerge as part of the anterior roots of the spinal cord.

The anterior horns contain large motor nuclei, which contain motor radicular neurons with short dendrites and a long axon. The axon emerges as part of the anterior roots of the spinal cord, and then goes as part of a peripheral mixed nerve, represents motor nerve fibers and is pumped at the periphery by a neuromuscular synapse on skeletal muscle fibers. Are effector. Forms the third effector link of the somatic reflex arc.

In the anterior horns, the medial group of nuclei is isolated. It is developed in the thoracic region and provides innervation to the muscles of the trunk. The lateral group of nuclei is located in the cervical and lumbar regions and innervates the upper and lower extremities.

The gray matter of the spinal cord contains a large number of diffuse bundle neurons (in the posterior horns). Their axons go into white matter and immediately split into two branches that branch up and down. The branches through 2-3 segments of the spinal cord return back to the gray matter and form synapses on the motor neurons of the anterior horns. These cells form their own apparatus of the spinal cord, which provides communication between adjacent 4-5 segments of the spinal cord, due to which a response of a muscle group is provided (an evolutionarily developed defense reaction).

The white matter contains ascending (sensory) pathways that are located in the posterior cords and in the peripheral part of the lateral horns. Descending nerve pathways (motor) are located in the anterior cords and in the inner part of the lateral cords.

Regeneration. It regenerates gray matter very poorly. Regeneration of the white matter is possible, but the process is very long.

Histophysiology of the cerebellum. The cerebellum belongs to the structures of the brain stem, i.e. is an older formation that is part of the brain.

Performs a number of functions:

Equilibrium;

The centers of the autonomic nervous system (ANS) (intestinal motility, blood pressure control) are concentrated here.

The outside is covered with meninges. The surface is embossed due to deep grooves and convolutions, which are deeper than in the cerebral cortex (CBP).

The cut is represented by the so-called "tree of life".

The gray matter is located mainly on the periphery and inside, forming nuclei.

In each gyrus, the central part is occupied by a white matter, in which 3 layers are clearly visible:

1 - surface - molecular.

2 - middle - ganglionic.

3 - internal - grainy.

1. The molecular layer is represented by small cells, among which basket-like and stellate (small and large) cells are distinguished.

Basket cells are located closer to the ganglion cells of the middle layer, i.e. in the inner part of the layer. They have small bodies, their dendrites branch out in the molecular layer, in a plane transverse to the course of the gyrus. Neurites run parallel to the gyrus plane above the bodies of the piriform cells (ganglionic layer), forming numerous branches and contacts with the dendrites of piriform cells. Their branches are twisted around the bodies of pear-shaped cells in the form of baskets. Excitation of basket cells leads to inhibition of pear cells.

Outside, stellate cells are located, the dendrites of which branch out here, and the neurites participate in the formation of the basket and connect by synapses with dendrites and the bodies of pear-shaped cells.

Thus, the basket and stellate cells of this layer are associative (binding) and inhibitory.

2. Ganglionic layer. Here are located large ganglion cells (diameter = 30-60 microns) - Purkine cells. These cells are located strictly in one row. The cell bodies are pear-shaped, there is a large nucleus, the cytoplasm contains EPS, mitochondria, the Golgi complex is poorly expressed. One neurite departs from the base of the cell, which passes through the granular layer, then into the white matter and ends at the nuclei of the cerebellum with synapses. This neuritis is the first link in the efferent (descending) pathways. 2-3 dendrites depart from the apical part of the cell, which intensively branch in the molecular layer, while the branching of the dendrites proceeds in a plane transverse to the course of the gyrus.

Piriform cells are the main effector cells of the cerebellum, where an inhibitory impulse is produced.

3. Granular layer, saturated with cellular elements, among which cells - grains stand out. These are small cells with a diameter of 10-12 microns. They have one neurite, which goes into the molecular layer, where it comes into contact with the cells of this layer. Dendrites (2-3) are short and branch with numerous bird's-foot branches. These dendrites come into contact with afferent fibers, mossy fibers. The latter also branch out and come into contact with the branching of the dendrites of the cells - grains, forming glomeruli of thin weaves like moss. In this case, one mossy fiber is in contact with many cells - grains. And vice versa - the cell - the grain is also in contact with many mossy fibers.

Mossy fibers come here from the olives and the bridge, i.e. bring here information, which through associative neurons goes to pear-shaped neurons. There are also large stellate cells that lie closer to the pear-shaped cells. Their processes come into contact with the granule cells proximal to the bryophyte glomeruli and in this case block the transmission of the impulse.

Other cells can also be found in this layer: stellate cells with a long neurite that goes into the white matter and further into the neighboring gyrus (Golgi cells are large stellate cells).

Afferent climbing fibers, liana-like, enter the cerebellum. They come here as part of the spinocerebellar tract. Further, they crawl along the bodies of pear-shaped cells and along their processes, with which they form numerous synapses in the molecular layer. Here they carry the impulse directly to the pear-shaped cells.

Efferent fibers emerge from the cerebellum, which are the axons of the pear-shaped cells.

The cerebellum has a large number of glial elements: astrocytes, oligodendrogliocytes, which perform supporting, trophic, restrictive and other functions. A large amount of serotonin is secreted in the cerebellum, thus. the endocrine function of the cerebellum can also be distinguished.

The cerebral cortex (CBP)

This is a newer part of the brain. (It is believed that KBP is not a vital organ.) It has great plasticity.

The thickness can be 3-5mm. The area occupied by the cortex is increased by furrows and convolutions. Differentiation of KBP ends by the age of 18, and then the processes of accumulation and use of information follow. The mental abilities of an individual also depend on the genetic program, but in the end it all depends on the number of synaptic connections formed.

There are 6 layers in the bark:

1. Molecular.

2. Outer granular.

3. Pyramid.

4. Internal granular.

5. Ganglionic.

6. Polymorphic.

White matter is located deeper than the sixth layer. The bark is divided into granular and agranular (according to the severity of the granular layers).

In KBP, cells have different shapes and sizes, ranging in diameter from 10-15 to 140 microns. The main cellular elements are pyramidal cells, which have a pointed apex. Dendrites extend from the lateral surface, and one neurite extends from the base. Pyramidal cells can be small, medium, large, giant.

In addition to pyramidal cells, there are arachnids, cells - grains, horizontal.

The arrangement of cells in the cortex is called cytoarchitectonics. Fibers that form myelin pathways or various systems of associative, commissural, etc. form the myeloarchitectonics of the cortex.

1. In the molecular layer, cells are found in small numbers. The processes of these cells: the dendrites go here, and the neurites form the outer tangential path, which also includes the processes of the underlying cells.

2. Outer granular layer. There are many small cellular elements of pyramidal, star-shaped, and other forms. Dendrites either branch out here, or pass into another layer; neurites go to the tangential layer.

3. Pyramid layer. Extensive enough. Basically, small and medium-sized pyramidal cells are found here, the processes of which branch out in the molecular layer, and the neurites of large cells can go into the white matter.

4. Inner granular layer. Well expressed in the sensitive area of ​​the cortex (granular type of bark). It is represented by many small neurons. Cells of all four layers are associative and transmit information to other departments from the underlying departments.

5. Ganglionic layer. Mainly large and giant pyramidal cells are located here. These are mainly effector cells, because the neurites of these neurons go into the white matter, being the first links of the effector pathway. They can give off collaterals, which can return to the cortex, forming associative nerve fibers. Some processes - commissural - go through the commissure to the neighboring hemisphere. Some neurites are switched either on the nuclei of the cortex, or in the medulla oblongata, in the cerebellum, or can reach the spinal cord (1r. Corrosive motor nuclei). These fibers form the so-called. projection paths.

6. The layer of polymorphic cells is located on the border with the white matter. There are large neurons of various shapes. Their neurites can return in the form of collaterals to the same layer, or to another gyrus, or to the myelin tract.

The entire cortex is subdivided into morpho-functional structural units - columns. Allocate 3-4 million columns, each of which contains about 100 neurons. The column goes through all 6 layers. The cellular elements of each column are concentrated around the glide column; a group of neurons is included that can process a unit of information. This includes afferent fibers from the thalamus, and cortico-cortical fibers from the adjacent column or from the adjacent gyrus. From here efferent fibers come out. Due to collaterals in each hemisphere, 3 columns are interconnected. Through commissural fibers, each column is connected to two columns of the neighboring hemisphere.

All organs of the nervous system are covered with membranes:

1. The pia mater is formed by loose connective tissue, due to which grooves are formed, carries blood vessels and is delimited by glial membranes.

2. The arachnoid membrane is represented by delicate fibrous structures.

Between the soft and arachnoid membranes, there is a subarachnoid space filled with cerebral fluid.

3. The dura mater is formed from coarse fibrous connective tissue. It is fused with bone tissue in the region of the skull, and is more mobile in the region of the spinal cord, where the space filled with cerebrospinal fluid is located.

The gray matter is located on the periphery, and also forms nuclei in the white matter.

Autonomic nervous system (ANS)

Subdivided into:

The sympathetic part,

The parasympathetic part.

Allocate the central nuclei: the nuclei of the lateral horns of the spinal cord, medulla oblongata, midbrain.

On the periphery, nodes can form in the organs (paravertebral, prevertebral, paraorgan, intramural).

The reflex arc is represented by the afferent part, which is common, and the efferent part is the preganglionic and postganglionic links (they can be multi-storey).

In the peripheral ganglia of the ANS, various cells can be located in structure and function:

Motor (according to Dogel - type I):

Associative (type II)

Sensitive, the processes of which reach the neighboring ganglia and spread far beyond.

About that, a person learns in school years. Biology lessons provide general information about the body as a whole and about individual organs in particular. As part of the school curriculum, children learn that the normal functioning of the body depends on the state of the nervous system. If there are failures in it, the work of other organs is disrupted. Exists different factors who, to one degree or another, to this influence. Nervous system characterized as one of the most important parts of the body. It determines the functional unity of the internal structures of a person and the relationship of the body with the external environment. Let's take a closer look at what is

Structure

To understand what the nervous system is, it is necessary to study all its elements separately. A neuron acts as a structural unit. It is a cell that has processes. Circuits are formed from neurons. Speaking about what the nervous system is, it should also be said that it consists of two sections: central and peripheral. The first includes the spinal cord and brain, the second - the nerves and nodes extending from them. The nervous system is conventionally divided into autonomic and somatic.

Cells

They are divided into 2 large groups: afferent and efferent. The activity of the nervous system starts with receptors. They perceive light, sound, smells. Efferent - motor - cells generate and direct impulses to certain organs. They consist of a body and a nucleus, numerous processes called dendrites. A fiber is isolated - an axon. Its length can be 1-1.5 mm. Axons provide impulse transmission. In the membranes of cells responsible for the perception of smell and taste, there are special compounds. They react to certain substances by changing their state.

Vegetative department

The activity of the nervous system ensures the work of internal organs, glands, lymph and blood vessels. To a certain extent, it also determines the functioning of the muscles. In the autonomic system, the parasympathetic and sympathetic divisions are distinguished. The latter provides expansion of the pupil and small bronchi, increased pressure, increased heart rate, etc. The parasympathetic section is responsible for the functioning of the genitals, bladder, rectum. From it emanate impulses that activate other glossopharyngeal, for example). The centers are located in the brainstem and sacral spinal cord.

Pathology

Diseases of the autonomic system can be caused by various factors. Quite often, disorders are a consequence of other pathologies, such as TBI, poisoning, infections. Disruptions in the vegetative system can be caused by a lack of vitamins, frequent stress. Often, diseases are "masked" by other pathologies. For example, if the functioning of the thoracic or cervical nodes of the trunk is dysfunctional, pain in the sternum, radiating to the shoulder, is noted. Such symptoms are characteristic of heart disease, so patients often confuse pathologies.

Spinal cord

Outwardly, it resembles a heavy. The length of this section in an adult is about 41-45 cm. There are two thickenings in the spinal cord: lumbar and cervical. In them, the so-called innervation structures of the lower and upper extremities are formed. The following sections are distinguished: sacral, lumbar, thoracic, cervical. Throughout its length, it is covered with soft, hard and arachnoid shells.

Brain

It is located in the skull. The brain consists of the right and left hemispheres, the trunk and the cerebellum. It was found that its weight in men is greater than that of women. The brain begins its development in the embryonic period. The organ reaches its real size by about 20 years. By the end of life, the weight of the brain decreases. It is divided into departments:

1. Finite.
2. Intermediate.
3. Average.
4. Rear.
5. Oblong.

Hemispheres

They also contain the olfactory center. The outer shell of the hemispheres has a rather complex pattern. This is due to the presence of ridges and grooves. They form a kind of "convolutions". Each person has an individual drawing. However, there are several furrows that are the same for everyone. They allow you to distinguish five lobes: frontal, parietal, occipital, temporal and hidden.

Unconditioned reflexes

Nervous system processes- response to stimuli. Unconditioned reflexes were studied by such a prominent Russian scientist as I.P. Pavlov. These reactions are focused mainly on the body's self-preservation. The main ones are food, indicative, and defensive ones. Unconditioned reflexes are innate.

Classification

Unconditioned reflexes were studied by Simonov. The scientist identified 3 classes of innate reactions corresponding to the development of a specific area of ​​the environment:

Orientation reflex

It manifests itself in involuntary sensory attention, accompanied by increased muscle tone. A reflex is triggered by a new or unexpected stimulus. Scientists call this reaction "alertness", anxiety, surprise. There are three phases of its development:

1. Termination of current activities, posture fixation. Simonov calls this general (preventive) inhibition. It occurs when any stimulus with an unknown signal appears.
2. Transition to the "activation" reaction. At this stage, the body is transferred to a reflex readiness for a probable meeting with emergency... This is manifested in a general increase in muscle tone. In this phase, a multicomponent reaction takes place. It includes turning the head and eyes towards the stimulus.
3. Fixation of the stimulus field for the start of differentiated signal analysis and selection of a response.

Meaning

The orienting reflex is part of the structure of exploratory behavior. This is especially evident in the new environment. Research activities can be focused on the development of novelty, and on the search for an object that can satisfy curiosity. In addition, it can provide an analysis of the significance of the stimulus. In such a situation, an increase in the sensitivity of the analyzers is noted.

Mechanism

The realization of the orienting reflex is a consequence of the dynamic interaction of many formations of nonspecific and specific elements of the central nervous system. The general activation phase, for example, is associated with the onset and onset of generalized excitation of the cortex. When analyzing the stimulus, cortical-limbic-thalamic integration is of primary importance. The hippocampus plays an important role in this.

Conditioned reflexes

At the turn of the 19th and 20th centuries. Pavlov, who for a long time studied the work of the digestive glands, revealed the following phenomenon in experimental animals. An increase in the secretion of gastric juice and saliva occurred regularly, not only with direct ingestion of food into the gastrointestinal tract, but also while waiting for it to be received. At that time, the mechanism of this phenomenon was not known. Scientists attributed it to the "psychic excitement" of the glands. In the course of subsequent research, Pavlov attributed this reaction to conditioned (acquired) reflexes. They can appear and disappear during a person's life. For the appearance of a conditioned reaction, it is necessary that two stimuli coincide. One of them, in any conditions, provokes a natural response - an unconditioned reflex. The second, due to its routine, does not provoke any reaction. He is defined as indifferent (indifferent). For a conditioned reflex to arise, the second stimulus must start acting earlier than the unconditioned one, a few seconds. Moreover, the biological significance of the former should be less.

Nervous system protection

As you know, the body is affected by a variety of factors. The state of the nervous system affects the work of other organs. Even seemingly insignificant failures can cause serious illnesses... Moreover, they will not always be associated with the activity of the nervous system. In this regard, great attention should be paid to preventive measures. The first step is to reduce irritating factors. It is known that constant stress, experiences are one of the causes of cardiac pathologies. Treatment of these diseases includes not only medicines, but also physiotherapy, exercise therapy, etc. The diet is of particular importance. From proper nutrition the state of all human systems and organs depends. Food must contain sufficient amounts of vitamins. Experts recommend including plant foods, herbs, vegetables and fruits in the diet.

Vitamin C

It has a beneficial effect on all body systems, including the nervous one. Due to vitamin C at the cellular level, energy production is provided. This compound is involved in the synthesis of ATP (adenosine triphosphoric acid). Vitamin C is considered one of the strongest antioxidants, it neutralizes negative impact free radicals by binding them. In addition, the substance is capable of enhancing the activity of other antioxidants. These include vitamin E and selenium.

Lecithin

It ensures the normal course of processes in the nervous system. Lecithin is the main nutrient for cells. The content in the peripheral section is about 17%, in the brain - 30%. With insufficient intake of lecithin, nervous exhaustion occurs. The person becomes irritable, which often leads to nervous breakdowns. Lecithin is essential for all cells in the body. It is included in the B-vitamin group and promotes energy production. In addition, lecithin is involved in the production of acetylcholine.

Music to calm the nervous system

As mentioned above, for diseases of the central nervous system, therapeutic measures may include not only medication. The therapeutic course is selected depending on the severity of the violations. Meanwhile, relaxation of the nervous system often achieved without consulting a doctor. A person can independently find ways to relieve irritation. For example, there are different melodies. As a rule, these are slow compositions, often without words. However, some people can be reassured by the march. When choosing melodies, you should be guided by your own preferences. You just need to make sure that the music is not depressing. A special relaxing genre has become quite popular today. It combines classics, folk melodies. The main sign of relaxing music is quiet monotony. It "envelops" the listener, creating a soft but durable "cocoon" that protects a person from external irritations. Relaxing music can be classical, but not symphonic. Usually it is performed with one instrument: piano, guitar, violin, flute. It can also be a song with repetitive recitative and simple words.

Sounds of nature are very popular - rustling of leaves, the sound of rain, birdsong. In combination with the melody of several instruments, they take a person away from the daily hustle and bustle, the rhythm of the metropolis, remove the nervous and muscle tension... When listening, thoughts are ordered, excitement is replaced by tranquility.