In order to perceive internal and external stimuli, the nervous system has sensory structures located in the analyzers. These structures will include certain devices capable of receiving information:
1. Proprioceptors. They collect all information regarding the condition of muscles, bones, fascia, joints, and the presence of fiber.
2. Exteroceptors. They are located in human skin, sensory organs, and mucous membranes. Able to perceive irritating factors received from the surrounding external environment.
3. Interoreceptors. Located in tissues and internal organs. Responsible for the perception of biochemical changes received from the external environment.
Basic meaning and functions of the nervous system
It is important to note that with the help of the nervous system, perception and analysis of information about stimuli from the external world and internal organs is carried out. She is also responsible for responses to these irritations.
The human body, the subtlety of its adaptation to changes in the surrounding world, is accomplished primarily through the interaction of humoral and nervous mechanisms.
The main functions include:
1. Definition of a person’s mental health and activities, which are the basis of his social life.
2. Regulation of the normal functioning of organs, their systems, tissues.
3. Integration of the body, its unification into a single whole.
4. Maintaining the relationship of the whole organism with the environment. If environmental conditions change, the nervous system adapts to these conditions.
In order to accurately understand the importance of the nervous system, it is necessary to delve into the meaning and main functions of the central and peripheral nervous systems.
The importance of the central nervous system
It is the main part of the nervous system of both humans and animals. Its main function is the implementation of various levels of complexity of reactions called reflexes.
Thanks to the activity of the central nervous system, the brain is able to consciously reflect changes in the external conscious world. Its significance is that it regulates various kinds of reflexes and is able to perceive stimuli received both from internal organs and from the external world.
The importance of the peripheral nervous system
The PNS connects the central nervous system to the limbs and organs. Its neurons are located far beyond the central nervous system - the spinal cord and brain.
It is not protected by bones, which can lead to mechanical damage or harmful effects of toxins
Thanks to the proper functioning of the PNS, the body's movements are coordinated. This system is responsible for conscious control of the actions of the entire organism. Responsible for responding to stressful situations and danger. Increases heart rate. In case of excitement, it increases the level of adrenaline.
It is important to remember that you should always take care of your health. After all, when a person leads a healthy lifestyle, adheres to the correct daily routine, he does not burden his body in any way and thereby remains healthy.
Nervous system
Functions of the nervous system. The nervous system performs the following functions:
· Sensory – perceiving, transmitting and processing information, the nervous system communicates with the external and internal environment and ensures adaptation to living conditions;
· Motor – regulates the motor functions of organs and systems of the human body;
· Integrative – ensures fast and coordinated interaction between organs, thanks to which the human body functions as a single whole;
· Mental - the central section of the nervous system is the substrate of higher mental manifestations - consciousness, speech, thinking, memory, learning, with the help of which people communicate with each other and learn about the environment.
General plan of the structure of the nervous system. The nervous system is topographically divided into central And peripheral , and functionally – on somatic And vegetative . The central nervous system (CNS) includes the spinal cord and brain, and the peripheral nervous system includes nerves and ganglia.
The central nervous system is formed by neurons and neuroglia. In the brain and spinal cord, neurons can be arranged in the form
· Clusters called nuclei (for example, the nuclei of the cranial nerves);
· Clusters called nerve centers. These centers are necessary for the implementation of a certain reflex or regulation of a particular function (for example, the breathing center in the medulla oblongata);
· Networks, that is, diffusely (for example, neurons of the reticular formation);
· Parallel horizontal layers (for example, in the cerebral cortex and cerebellum);
· Vertical columns (for example, in the cerebral cortex).
The processes of central neurons within the brain form its pathways and connections in neural networks. The processes of neurons located outside the brain form peripheral nerves.
The central nervous system analyzes information coming from the external and internal environment of the body, and forms its response to this information.
Ganglia of the peripheral nervous system are also clusters of neurons surrounded by neuroglial cells. There are spinal and cranial ganglia.
Nerves are formed by long processes of neurons. The peripheral nerves include 12 pairs of cranial nerves and 31 pairs of spinal nerves. The cranial nerves innervate mainly the structures of the head and neck, except for the vagus nerve, which innervates the internal organs. Spinal nerves innervate the muscles of the trunk and limbs. Some nerves carry information from receptors to the central nervous system and are called sensory, or afferent . Other nerves transmit signals from the central nervous system to all organs and systems of the body and are called motor, or efferent . Most peripheral nerves are mixed: they contain both afferent and efferent fibers.
Somatic nervous system provides tone, body posture, motor reactions and innervation of the skin.
Vegetative, or autonomic nervous system regulates the functioning of internal organs. It is associated with the maintenance of homeostasis, metabolism, growth and development of the body, neuroendocrine regulation and trophic innervation of skeletal muscles, skin and the nervous system itself. The autonomic nervous system is divided into sympathetic and parasympathetic divisions.
Both the somatic nervous system and the autonomic nervous system have central and peripheral sections. The central section is located in the spinal cord and brain and is represented by nuclei, and the peripheral section is located outside the central nervous system and is represented by nerves.
31.Structure and physiological functions of a neuron.
A neuron is a cell soms(body) from which several short processes extend - dendrites With spines at the ends there is one long process - axon, which branches to form collaterals. Collaterals and spines are necessary to increase the area of contact of one neuron with other neurons
The neuron has a specialized plasma membrane that conducts impulses. The cytoplasm of a neuron, like any eukaryotic cell, contains a nucleus and organelles. The peculiarity of the internal structure of a neuron is that in the neuroplasm of the latter, in addition to the usual organelles, there are special structures - neurofibrils. The cytoplasm of a neuron also contains pigment substances on which the color of the neuron depends. In addition, the neuron contains a large number of mitochondria and an endoplasmic reticulum that changes in volume, depending on the functional activity.
The soma and dendrites of a neuron do not have a myelin sheath (the myelin sheath is formed by a white fat-like substance), so they are gray in color in the brain mass. The substance they form is called gray matter brain Axons covered with a myelin sheath form white matter The brain is a collection of pathways. The myelin sheath of the axon is not continuous; at certain intervals it is interrupted - these places are called Ranvier interceptions. The portion of the soma from which the axon arises is called axon hillock. The axon hillock does not have a myelin sheath.
Depending on the number of processes, all neurons are divided into
1. bipolar, which have one axon and one dendrite and are located in the retina of the eye and in the sound-receiving apparatus of the inner ear;
2. polypolar – have one axon and many dendrites, located in the brain;
3. false unipolar - one process departs from the soma, which then at some distance is divided into two: an axon and a relatively long dendrite; located in peripheral ganglia;
4. unipolar - have one process, are present in the human body only in the prenatal period.
Depending on the shape of the soma, neurons are divided into
1. pyramidal - the catfish has the shape of a pyramid;
2. star-shaped - the catfish has the appearance of a star;
3. spindle-shaped - the catfish has the appearance of a spindle.
The main function of neurons is the reception, transformation and transmission of information, which is encoded in the form of electrical potentials propagating along the processes of the neuron - action potentials (AP). The neuron has an electrically excitable membrane that is negatively charged relative to the surrounding extracellular fluid. Membrane charge – membrane potential, or resting potential (RP), - is not the same for different neurons and depends on a number of factors. The membrane charge is created due to different concentrations of sodium, potassium, and chlorine ions inside and outside the cell. When excited, a neuron generates an AP, or nerve impulse. In this case, depolarization of the membrane occurs, and currents appear in the dendrites and soma directed towards the axon hillock. In the area of the axon hillock, a nerve impulse is generated, which spreads along the axon. If the axon is covered with a myelin sheath, then the AP causes excitation only at the nodes of Ranvier; if the axon is not covered with a sheath, then the AP causes excitation at each adjacent point of the fiber. The speed of PD propagation depends on
1. axon diameter - the thicker the axon, the higher the speed of propagation;
2. the presence of a myelinated membrane;
3. PP values - the higher the PP, the higher the propagation speed;
4. PD values – the higher the PD, the higher the propagation speed.
A neuron works as a signal transducer: it sums up many incoming stimuli and forms its response on this basis. A neuron does not generate a single impulse, but a series of several impulses that occur at a certain frequency. This frequency conversion is one of the main ways of encoding information in the nervous system.
Functionally, all neurons are divided into
1. afferent (sensitive), carrying information from the external and internal environment to the central nervous system;
2. efferent (motor), carrying an information response from the central nervous system to the organs;
3. associative (intercalary) – neurons that connect afferent and efferent cells with each other.
To transmit and process information, neurons interact with each other and with the cells of the executive organs using special contacts - synapses . The synapse is divided into a presynaptic membrane, a synaptic cleft, and a postsynaptic membrane. According to the nature of their influence on the cell, synapses are divided into excitatory and inhibitory, and according to the method of signal transmission - electrical and chemical. In humans, only chemical synapses are present. Substances that transmit signals through synaptic contact are called mediators . These include acetylcholine, adrenaline, serotonin, histamine, norepinephrine, and gamma-aminobutyric acid (GABA). Mediators pass through the presynaptic membrane, bind to receptors on the postsynaptic membrane, thereby changing it membrane potential(resting potential - PP ). Thus, at synapses, a chemical signal is converted into an electrical signal.
Synaptic contacts can be: axosomatic, axodendritic, axo-axonal and dendro-dendritic. The synapses between the axon terminal and the muscle are called neuromuscular, or end plates.
The formation of new synapses underlies the property of the nervous system - plasticity. The development of the child’s brain, learning and memory processes depend on this property.
Nerve fibers
Nerve fibers- processes of nerve cells (neurons) that have a membrane and are capable of conducting nerve impulses.
The main component of the nerve fiber is the process of the neuron, which forms, as it were, the axis of the fiber. Mostly this is an axon. The nerve process is surrounded by a membrane of complex structure, together with which it forms a fiber. The thickness of the nerve fiber in the human body, as a rule, does not exceed 30 micrometers.
Nerve fibers are divided into pulpy (myelinated) and non-myelinated (non-myelinated). The former have a myelin sheath covering the axon, the latter lack a myelin sheath.
Myelin fibers predominate in both the peripheral and central nervous systems. Nerve fibers lacking myelin are located predominantly in the sympathetic division of the autonomic nervous system. At the point where the nerve fiber departs from the cell and in the area of its transition into the final branches, the nerve fibers can be devoid of any membranes, and then they are called bare axial cylinders.
Depending on the nature of the signal carried through them, nerve fibers are divided into motor autonomic, sensory and motor somatic.
The structure of nerve fibers
Myelinated nerve fiber contains the following elements (structures):
1) an axial cylinder located in the very center of the nerve fiber,
2) the myelin sheath covering the axial cylinder,
3) Schwann shell.
The axial cylinder consists of neurofibrils. The pulpy membrane contains a large amount of lipoid substances known as myelin. Myelin ensures the speed of nerve impulses. The myelin sheath does not cover the entire axial cylinder, forming gaps called nodes of Ranvier. In the area of the nodes of Ranvier, the axial cylinder of the nerve fiber is adjacent to the superior Schwann membrane.
The fiber space located between two nodes of Ranvier is called a fiber segment. In each such segment, the nucleus of the Schwann membrane can be seen on stained preparations. It lies approximately in the middle of the segment and is surrounded by the protoplasm of the Schwann cell, the loops of which contain myelin. Between the nodes of Ranvier, the myelin sheath is also not continuous. In its thickness, so-called Schmidt-Lanterman notches are found, running in an oblique direction.
Schwann membrane cells, as well as neurons with processes, develop from the ectoderm. They cover the axial cylinder of the nerve fiber of the peripheral nervous system, similar to how glial cells cover the nerve fiber in the central nervous system. As a result, they may be called peripheral glial cells.
In the central nervous system, nerve fibers do not have Schwann sheaths. The role of Schwann cells here is performed by elements of oligodendroglia. An unmyelinated (unmyelinated) nerve fiber lacks a myelin sheath and consists only of an axial cylinder and a Schwann sheath.
Function of nerve fibers
The main function of nerve fibers is the transmission of nerve impulses. Currently, two types of nerve transmission have been studied: pulsed and non-pulse. Impulse transmission is provided by electrolyte and neurotransmitter mechanisms. The speed of nerve impulse transmission in myelinated fibers is much higher than in nonmyelinated fibers. In its implementation, the most important role is played by myelin. This substance is capable of isolating a nerve impulse, as a result of which signal transmission along the nerve fiber occurs spasmodically, from one node of Ranvier to another.
Pulseless transmission is carried out by axoplasmic current along special axon microtubules containing trophogens - substances that have a trophic effect on the innervated organ.
The function of the nervous system is to control the activities of various systems and apparatuses that make up the whole organism, to coordinate the processes occurring in it, to establish relationships between the body and the external environment. The great Russian physiologist I.P. Pavlov wrote: “The activity of the nervous system is directed, on the one hand, to unify, integrate the work of all parts of the body, and on the other, to connect the body with the environment, to balance the body system with external conditions.”
Nerves penetrate into all organs and tissues, form numerous branches with receptor (sensory) and effector (motor, secretory) endings, and together with the central sections (brain and spinal cord) ensure the unification of all parts of the body into a single whole. The nervous system regulates the functions of movement, digestion, respiration, excretion, blood circulation, lymphatic drainage, immune (protective) and metabolic processes (metabolism), etc.
The activity of the nervous system, according to I.M. Sechenov, is reflexive in nature. Reflex (Latin reflexus - reflected) is the body's response to a particular irritation (external or internal influence), which occurs with the participation of the central nervous system (CNS). The human body, living in its external environment, interacts with it. The environment influences the body, and the body, in turn, reacts appropriately to these influences. Processes occurring in the body itself also cause a response. Thus, the nervous system ensures the interconnection and unity of the organism and the environment.
The structural and functional unit of the nervous system is the neuron (nerve cell, neurocyte). A neuron consists of a body and processes. The processes that conduct nerve impulses to the body of the nerve cell are called dendrites. From the neuron body, the nerve impulse is sent to another nerve cell or to working tissue along a process called an axon, or neurite. A nerve cell is dynamically polarized, that is, it is capable of transmitting a nerve impulse in only one direction - from the dendrite through the cell body to the axon (neurite).
Neurons in the nervous system, coming into contact with each other, form chains along which nerve impulses are transmitted (moved). The transmission of a nerve impulse from one neuron to another occurs at the places of their contacts and is ensured by a special kind of formations called interneuron synapses. A distinction is made between axsomatic synapses, when the axon endings of one neuron form contacts with the body of the next, and axodendritic synapses, when the axon comes into contact with the dendrites of another neuron. The contact type of relationships in a synapse under various physiological conditions can, obviously, either be “created” or “destroyed,” providing the possibility of a selective reaction to any stimulation. In addition, the contact construction of chains of neurons creates the opportunity to conduct a nerve impulse in a certain direction. Due to the presence of contacts in some synapses and disconnection in others, the conduction of the impulse may be disrupted.
In a nerve chain, different neurons have different functions. In this regard, three main types of neurons are distinguished according to their morphofunctional characteristics.
1Sensitive, receptor, or afferent neurons. The bodies of these nerve cells always lie outside the brain or spinal cord, in the nodes (ganglia) of the peripheral nervous system. One of the processes extending from the body of the nerve cell follows to the periphery of one or another organ and ends there with one or another sensitive ending - a receptor that is capable of transforming the energy of external influence (irritation) into a nerve impulse. The second process is directed to the central nervous system, spinal cord or to the brainstem as part of the dorsal roots of the spinal nerves or corresponding cranial nerves.
The following types of receptors are distinguished depending on location:
1 exteroceptors perceive irritation from the external environment. They are located in the outer integument of the body, in the skin and mucous membranes, in the sensory organs;
2interoceptors receive irritation mainly due to changes in the chemical composition of the internal environment of the body and pressure in tissues and organs;
3proprioceptors perceive irritations in muscles, tendons, ligaments, fascia, and joint capsules.
Reception, i.e., the perception of irritation and the beginning of the spread of a nerve impulse along nerve conductors to the centers, I. P. Pavlov attributed to the beginning of the analysis process.
2Closing, intercalary, associative, or conductor neuron. This neuron transmits excitation from the afferent (sensitive) neuron to the efferent ones. The essence of this process is the transmission of the signal received by the afferent neuron to the efferent neuron for execution in the form of a response. I. P. Pavlov defined this action as “the phenomenon of nervous closure.” Closing (intercalary) neurons lie within the central nervous system.
3. Effector, efferent (motor or secretory) neuron. The bodies of these neurons are located in the central nervous system (or on the periphery - in the sympathetic, parasympathetic nodes). The axons (neurites) of these cells continue in the form of nerve fibers to the working organs (voluntary - skeletal and involuntary - smooth muscles, glands).
After these general remarks, let us consider in more detail the reflex arc and the reflex act as the basic principle of the activity of the nervous system. Reflex arc is a chain of nerve cells, including afferent (sensitive) and effector (motor or secretory) neurons, along which the nerve impulse moves from the place of its origin (from the receptor) to the working organ (effector). Most reflexes are carried out with the participation of reflex arcs, which are formed by neurons of the lower parts of the central nervous system - neurons of the spinal cord.
The simplest reflex arc (Fig. 108) consists of only two neurons - afferent and effector (efferent). The body of the first neuron (receptor, afferent), as noted, is located outside the CNS. Usually this is a pseudounipolar (unipolar) neuron, the body of which is located in the spinal ganglion (ganglion spindle) or sensory ganglion of cranial nerves (ganglion sensoriale nn. cranialii). The peripheral process of this cell follows as part of the spinal nerves or cranial nerves with sensory fibers and their branches and ends with a receptor that perceives external (from the external environment) or internal (in organs, tissues) irritation. This irritation is transformed by the receptor into a nerve impulse, which reaches the body of the nerve cell, and then along the central process (the set of such processes forms the posterior, or sensitive, roots of the spinal nerves) is sent to the spinal cord or along the corresponding cranial nerves to the brain. In the gray matter of the spinal cord or in the motor nucleus of the brain, this process of the sensitive cell forms a synapse with the body of the second neuron (efferent, effector). In the interneuron synapse, with the help of mediators, nerve excitation is transferred from a sensitive (afferent) neuron to a motor (efferent) neuron, the process of which leaves the spinal cord as part of the anterior roots of the spinal nerves or motor (secretory) nerve fibers of the cranial nerves and is directed to the working organ, causing muscle contraction, or inhibition or increased secretion of the gland.
As a rule, the reflex arc does not consist of two neurons, but is much more complex. Between two neurons - receptor (afferent) and effector (afferent) - there is one or more closing (intercalary) neurons. In this case, excitation from the receptor neuron along its central process is transmitted not directly to the effector nerve cell, but to one or more interneurons. The role of interneurons in the spinal cord is performed by cells lying in the gray matter of the posterior columns. Some of these cells have an axon (neurite), which is directed to the motor cells of the anterior horns of the spinal cord at the same level and closes the reflex arc at the level of this segment of the spinal cord. The axon of other cells can pre-divide in a T-shape in the spinal cord into descending and ascending branches, which are directed to the motor nerve cells of the anterior horns of neighboring, superior or underlying segments. Along the route, each of the marked ascending or descending branches can send collaterals to the motor cells of these and other neighboring segments. In this regard, it becomes clear that stimulation of even the smallest number of receptors can be transmitted not only to the nerve cells of a particular segment of the spinal cord, but also spread to the cells of several neighboring segments. As a result, the response is a contraction of not one muscle or even one group of muscles, but several groups at once. Thus, in response to irritation, a complex reflex movement occurs. This is one of the body’s responses (reflex) in response to external or internal irritation.
TO central nervous system (CNS) include the spinal cord and brain, which consist of gray and white matter. The gray matter of the spinal cord and brain is a collection of nerve cells along with the nearest branches of their processes. White matter is nerve fibers, processes of nerve cells that have a myelin sheath (hence the white color of the fibers). Nerve fibers form the pathways of the spinal cord and brain and connect various parts of the central nervous system and various nuclei (nerve centers) with each other.
Peripheral nervous system consists of roots, spinal and cranial nerves, their branches, plexuses and nodes lying in various parts of the human body.
According to another, anatomical and functional classification, the unified nervous system is also conventionally divided into two parts: somatic and autonomic, or autonomic. Somatic nervous system provides innervation mainly to the telosoma, namely the skin and skeletal (voluntary) muscles. This section of the nervous system performs the functions of connecting the body with the external environment through skin sensitivity and sensory organs.
Autonomic (autonomic) nervous system innervates all the insides, glands, including endocrine ones, involuntary muscles of organs, skin, blood vessels, heart, and also regulates metabolic processes in all organs and tissues.
The autonomic nervous system is in turn divided into the parasympathetic part, pars parasympathica, and the sympathetic part, pars sympathica. In each of these parts, as in the somatic nervous system, there are central and peripheral sections.
This division of the nervous system, despite its conventionality, has developed traditionally and seems quite convenient for studying the nervous system as a whole and its individual parts. In this regard, in the future we will also adhere to this classification in the presentation of the material.
STRUCTURE OF THE NERVOUS SYSTEM
Central and peripheral nervous system. The human nervous system consists of central and peripheral parts. The central part includes the brain and spinal cord, the peripheral part includes nerves and nerve ganglia.
The nervous system is made up of neurons and other cells of nervous tissue. There are sensory, executive and mixed nerves.
Signals travel through sensory nerves to the central nervous system. They inform the brain about the state of the internal environment and events occurring in the outside world. Executive nerves carry signals from the brain to organs, controlling their activities. Mixed nerves include both sensory and executive nerve fibers.
The brain is located in the skull. The cell bodies of neurons in the brain are located in the gray matter of the cortex and nuclei scattered among the white matter of the brain. White matter consists of nerve fibers connecting various centers of the brain and spinal cord.
All parts of the brain perform conduction and reflex functions. In the frontal lobes of the cerebral cortex, activity goals are formed and an action program is developed; through the lower parts of the brain, its “orders” are sent to the organs, and through feedback from the organs, signals are sent about the implementation of these “orders” and their effectiveness.
Spinal cord - located in the spinal canal. At the top, the spinal cord passes into the brain, at the bottom it ends at the level of the second lumbar vertebra, with a bundle of nerves extending from it, reminiscent of a horse’s tail.
The spinal cord is found in the cerebrospinal fluid. It acts as a tissue fluid, ensuring a constant internal environment, and protects the spinal cord from shocks and shocks.
The cell bodies of the spinal cord neurons are concentrated in the gray columns, which occupy the central part of the spinal cord and stretch along the entire spine.
There are ascending nerve pathways, along which nerve impulses go to the brain, and descending nerve pathways, along which excitation goes from the brain to the centers of the spinal cord.
The spinal cord performs reflex and conductive functions.
Connection between the spinal cord and the brain. The centers of the spinal cord work under the control of the brain. The impulses coming from it stimulate the activity of the spinal cord centers and maintain their tone. If the connection between the spinal cord and the brain is disrupted, as happens when the spine is damaged, shock occurs. In shock, all reflexes, the centers of which lie below the spinal cord lesions, disappear, and voluntary movements become impossible.
Somatic and autonomous (vegetative) departments. Functionally, the nervous system forms two sections: somatic and autonomic.
Somatic the department regulates human behavior in the external environment; it is associated with the work of skeletal muscles, which are controlled by the desires and will of a person.
Autonomous The department regulates the functioning of smooth muscles, internal organs, and blood vessels. It is weakly subject to volitional control and acts according to a program formed as a result of natural selection and fixed by the heredity of the body.
The autonomous department consists of two sub-departments - sympathetic And parasympathetic, which operate on the principle of complementarity. Thanks to their joint work, the optimal mode of operation of the internal organs is established for each specific situation.
FUNCTIONS AND IMPORTANCE OF THE NERVOUS SYSTEM
The nervous system ensures the relative constancy of the internal environment of the body.
Metabolism in every body occurs continuously. Some substances are consumed and excreted from the body, others come from outside.
The brain, and with it the endocrine glands, automatically maintain a balance between the intake and use of substances, ensuring that vital signs fluctuate within acceptable limits.
Thanks to the nervous system, the body maintains homeostasis, a relative constancy of the internal environment: acid-base balance, the amount of mineral salts, oxygen and carbon dioxide, breakdown products and nutrients, in the blood - blood pressure and body temperature.
The nervous system coordinates the work of all organs.
The nervous system is responsible for the coordinated activity of various organs and systems, as well as for the regulation of body functions. It determines the order of contraction of muscle groups, the intensity of breathing and cardiac activity, and monitors and corrects the results of the action. The nervous system is responsible for sensitivity, motor activity and the functioning of the endocrine and immune systems.
Higher nervous activity ensures the most perfect adaptation of the body to the external environment. In humans, it provides higher mental functions: cognitive, emotional and volitional processes, speech, thinking, consciousness, ability to work and creativity.
Through direct connections there are “orders” of the brain addressed to the organs, and through feedback connections there are signals to the brain from the organs, informing how successfully these “orders” have been carried out. The subsequent action will not take place until the previous one is completed and a positive effect is achieved.
Parasympathetic innervation (supply of nerves) of all organs and tissues is carried out by branches
The nervous system ensures the survival of the organism as a whole.
To survive, the body needs to receive information about objects in the external world. When entering life, a person constantly encounters certain objects, phenomena, and situations. Some of them are necessary for him, some are dangerous, others are indifferent.
With the help of the senses, the nervous system recognizes objects in the external world, evaluates them, remembers and processes the received information aimed at satisfying emerging needs.
OUR NERVOUS SYSTEM LOVES:
1. Fresh air.
2. Movement (long walks).
3. Positive emotions (feelings of joy, change of impressions).
4. Long sleep (9-10 hours).
5. Alternation of physical and mental labor.
6. Water treatments.
7. Simple food: Wholemeal bread, cereals (buckwheat, oatmeal), legumes, fish, meat and offal (liver, heart, kidneys), dried porcini mushrooms.
8. Vitamins of group “B” and Nicotinic acid.
OUR NERVOUS SYSTEM DOESN'T LIKE:
1. Stress(arising as a result of prolonged negative emotions, fasting, prolonged exposure to the hot sun).
2. Noise- anyone annoying.
3. Infections and mechanical damage(diseases of the ears, teeth, squeezing pimples, insect bites - ticks, head contusion).
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A very important condition for normal human life is the coordinated work of all organ systems. As soon as the increased activity of the mouse begins, breathing and the rhythm of heart contractions immediately increase. At the same time, the blood vessels of the internal organs narrow, and in the muscles and skin they expand: blood flow to the muscles and skin increases. Sweat glands increase sweat production. The activity of the digestive system is inhibited.
This is how the nervous system ensures the unity of the body, its integrity. By changing the work of some organs, it, accordingly, changes the work of all other systems of the body, coordinating their functioning.
Adaptation of the body's activity to environmental conditions. Through the sense organs and numerous nerve endings - receptors - located in the skin, the nervous system, perceiving irritations, connects the human body with the external environment. Sounds, colors, smells, temperature changes and other stimuli, acting on receptors and sensory organs, cause responses in the body. A decrease in air temperature increases metabolism, and an increase leads to a decrease in metabolism and increased sweating. The sight and smell of food increases salivation. Imminent danger causes rapid movements.
The nervous system, perceiving changes occurring in the environment, changes the activity of the body, adapting it to these constantly changing conditions.
Thus, the nervous system, regulating and coordinating the activities of organs, adapts their work to changes in the external environment.
The role of the nervous system in human labor activity. Science has proven that work is a need of the human body. It is necessary for the proper functioning and development of all its organs, including the brain. In any work activity, the nervous system plays a major role. With the help of the nervous system, work skills are mastered, the purpose and results of work are realized.
Meaning:
1. Ensures coordinated functioning of all organs and systems of the body.
2. Provides orientation of the body in the external environment and adaptive response to its changes.
3. Constitutes the material basis of mental activity: speech, thinking, social behavior. Nerves- an accumulation of nerve cell processes outside the central nervous system enclosed in a common connective tissue sheath and conducting nerve impulses.
Meaning: The main functions of the nervous system are the fast, accurate transmission of information and its integration; it ensures the relationship between organs and organ systems, the functioning of the body as a whole, and its interaction with the external environment. It regulates and coordinates the activities of various organs, adapts the activity of the entire organism as an integral system to changing environmental conditions. With the help of the nervous system, various signals from the environment and internal organs are received and analyzed, and responses to these signals are formed. The activities of the higher parts of the nervous system are associated with the implementation of mental functions - awareness of signals from the surrounding world, their memorization, decision-making and organization of goal-directed behavior, abstract thinking and speech. All these complex functions are carried out by a huge number of nerve cells - neurons, united into complex neural circuits and centers.
General plan of the NS structure. The NS is functionally and structurally divided into peripheral And central NS. CNS - a collection of interconnected neurons. It is represented by the brain and spinal cord. In a section of the brain and spinal cord, areas of a darker color are distinguished - Gray matter(formed by the bodies of nerve cells) and white areas - white matter brain (a collection of nerve fibers covered with a myelin sheath). Peripheral NS - educated nerves- bundles of nerve fibers covered on top with a common connective membrane. The peripheral NS includes ganglia, or ganglia, - a collection of nerve cells outside the spinal cord and brain. If a nerve contains nerve fibers that transmit excitation from the central nervous system to the innervated organ (effector), then such nerves are called centrifugal or efferent. There are nerves that are formed by sensory nerve fibers through which excitation spreads to the central nervous system. Such nerves are called centripetal or afferent. Most nerves are mixed, they contain both centripetal and centrifugal nerve fibers. The division of the nervous system into central and peripheral is largely arbitrary, since the nervous system functions as a single whole.
Each organ or system in the human body plays its role. Moreover, they are all interconnected. The importance of the nervous system cannot be overestimated. It is responsible for the correlation between all organs and their systems and for the functioning of the body as a whole. At school, they begin early to become familiar with such a multifaceted concept as the nervous system. 4th grade – these are still young children who cannot deeply understand many complex scientific concepts.
Structural units
The main structural and functional units of the nervous system (NS) are neurons. They are complex excitable secreting cells with processes and perceive nervous stimulation, process it and transmit it to other cells. Neurons can also have modulatory or inhibitory effects on target cells. They are an integral part of the bio- and chemoregulation of the body. From a functional point of view, neurons are one of the foundations of the organization of the nervous system. They combine several other levels (molecular, subcellular, synaptic, supracellular).
Neurons consist of a body (soma), a long process (axon), and small branching processes (dendrites). In different parts of the nervous system they have different shapes and sizes. In some of them, the length of the axon can reach 1.5 m. Up to 1000 dendrites extend from one neuron. Through them, excitation spreads from the receptors to the cell body. The axon carries impulses to effector cells or other neurons.
In science there is a concept “synapse”. The axons of neurons, approaching other cells, begin to branch and form numerous endings on them. Such places are called synapses. Axons form them not only on nerve cells. There are synapses on muscle fibers. These organs of the nervous system are even present on the cells of the endocrine glands and blood capillaries. Nerve fibers are processes of neurons covered with glial sheaths. They perform a conducting function.
Nerve endings
These are specialized formations located at the tips of nerve fiber processes. They provide information transmission in the form of an impulse. Nerve endings participate in the formation of transmitting and receiving end apparatuses of different structural organizations. By functional purpose they are distinguished:
Synapses, which transmit nerve impulses between nerve cells;
Receptors (afferent endings) that direct information from the site of action of an internal or external environmental factor;
Effectors that transmit impulses from nerve cells to other tissues.
Activity of the nervous system
The nervous system (NS) is an integral complex of several interconnected structures. It promotes the coordinated regulation of the activities of all organs and ensures a response to changing conditions. The human nervous system, a photo of which is presented in the article, links together motor activity, sensitivity and the work of other regulatory systems (immune, endocrine). The activities of the NS are related to:
Anatomical penetration into all organs and tissues;
Establishing and optimizing the relationship between the body and the surrounding external environment (ecological, social);
Coordinating all metabolic processes;
Management of organ systems.
Structure
The anatomy of the nervous system is very complex. It contains many structures, different in structure and purpose. The nervous system, photos of which indicate its penetration into all organs and tissues of the body, plays an important role as a receiver of internal and external stimuli. For this purpose, special sensory structures are designed, which are located in the so-called analyzers. They include special neural devices that are capable of perceiving incoming information. These include the following:
Proprioceptors, which collect information regarding the condition of muscles, fascia, joints, bones;
Exteroreceptors, located in the skin, mucous membranes and sensory organs, capable of perceiving irritating factors received from the external environment;
Interoreceptors located in internal organs and tissues and responsible for the adoption of biochemical changes.
Basic meaning of the nervous system
The work of the nervous system is closely connected both with the surrounding world and with the functioning of the body itself. With its help, information is perceived and analyzed. Thanks to it, irritants of internal organs and signals coming from outside are recognized. The nervous system is responsible for the body's reactions to received information. It is thanks to its interaction with humoral regulatory mechanisms that a person’s adaptability to the surrounding world is ensured.
The importance of the nervous system is to ensure coordination of individual parts of the body and maintain its homeostasis (equilibrium state). Thanks to its work, the body adapts to any changes, called adaptive behavior (state).
Basic functions of the NS
The functions of the nervous system are quite numerous. The main ones include the following:
Regulation of the vital functions of tissues, organs and their systems in a normal manner;
Unification (integration) of the body;
Preserving the relationship between man and the environment;
Control over the condition of individual organs and the body as a whole;
Ensuring activation and maintenance of tone (working condition);
Determination of people's activities and their mental health, which are the basis of social life.
The human nervous system, the photo of which is presented above, provides the following thought processes:
Perception, assimilation and processing of information;
Analysis and synthesis;
Formation of motivation;
Comparison with existing experience;
Goal setting and planning;
Action correction (error correction);
Performance evaluation;
Formation of judgments, conclusions and conclusions, general (abstract) concepts.
In addition to signaling, the nervous system also performs a trophic function. Thanks to it, biologically active substances released by the body ensure the vital activity of innervated organs. Organs that are deprived of such nourishment atrophy and die over time. The functions of the nervous system are very important for humans. When existing environmental conditions change, they help the body adapt to new circumstances.
Processes occurring in the NS
The human nervous system, the diagram of which is quite simple and understandable, is responsible for the interaction of the body and the environment. To ensure this, the following processes are carried out:
Transduction, which is the transformation of irritation into nervous excitation;
Transformation, during which the incoming excitation with one characteristics is converted into an outgoing flow with other properties;
Distribution of excitation in different directions;
Modeling, which is the construction of an image of irritation that replaces its source itself;
Modulation that changes the nervous system or its activity.
The importance of the human nervous system also lies in the interaction of the body with the external environment. In this case, various responses to any type of stimulus arise. Main types of modulation:
Excitation (activation), which consists in increasing the activity of the nervous structure (this state is dominant);
Inhibition, depression (inhibition), consisting of a decrease in the activity of the nervous structure;
Temporary neural connection, which represents the creation of new pathways for the transmission of excitation;
Plastic restructuring, which is represented by sensitization (improved transmission of excitation) and habituation (deterioration of transmission);
Activation of the organ that provides the reflex reaction of the human body.
Tasks of the National Assembly
The main tasks of the nervous system:
Reception – capturing changes in the internal or external environment. It is carried out by sensory systems with the help of receptors and represents the perception of mechanical, thermal, chemical, electromagnetic and other types of stimuli.
Transduction is the transformation (coding) of an incoming signal into nervous excitation, which is a stream of impulses with characteristics characteristic of irritation.
Carrying out conduction, which consists in delivering excitation along the nerve pathways to the necessary areas of the nervous system and to effectors (executive organs).
Perception is the creation of a nervous model of irritation (construction of its sensory image). This process forms a subjective picture of the world.
Transformation is the transformation of excitation from sensory to effector. Its goal is to implement the body’s response to the environmental change that has occurred. In this case, there is a transfer of descending excitation from the higher parts of the central nervous system to the lower ones or to the PNS (working organs, tissues).
Assessment of the result of the activity of the nervous system using feedback and afferentation (transmission of sensory information).
NS structure
The human nervous system, the diagram of which is presented above, is divided structurally and functionally. The work of a neural network cannot be fully understood without understanding the functions of its main types. Only by studying their purpose can one understand the complexity of the entire mechanism. The nervous system is divided into:
Central (CNS), which carries out reactions of varying levels of complexity, called reflexes. It perceives stimuli received from the external environment and from organs. It includes the brain and spinal cord.
Peripheral (PNS), connecting the central nervous system with organs and limbs. Its neurons are located far from the brain and spinal cord. It is not protected by bones, so it is susceptible to mechanical damage. Only thanks to the normal functioning of the PNS is coordination of human movements possible. This system is responsible for the body's response to danger and stressful situations. Thanks to it, in such situations, the pulse quickens and the level of adrenaline increases. Diseases of the peripheral nervous system affect the functioning of the central nervous system.
The PNS consists of bundles of nerve fibers. They go far beyond the spinal cord and brain and are directed to various organs. They are called nerves. The PNS includes ganglia (nodes). They are a collection of nerve cells.
Diseases of the peripheral nervous system are divided according to the following principles: topographic-anatomical, etiological, pathogenesis, pathomorphology. These include:
Radiculitis;
Plexites;
Funiculitis;
Mono-, poly- and multineuritis.
According to the etiology of diseases, they are divided into infectious (microbial, viral), toxic
logical, allergic, discirculatory, dysmetabolic, traumatic, hereditary, idiopathic, compression-ischemic, vertebrogenic. Diseases of the PNS can be primary (leprosy, leptospirosis, syphilis) and secondary (after childhood infections, mononucleosis, periarteritis nodosa). According to pathomorphology and pathogenesis, they are divided into neuropathies (radiculopathy), neuritis (radiculitis) and neuralgia.
Reflex activity is largely determined by the properties of the nerve centers, which represent a set of structures of the central nervous system. Their coordinated activity ensures the regulation of various body functions or reflex acts. Nerve centers have several common properties determined by the structure and function of synaptic formations (contact between neurons and other tissues):
One-sidedness of the excitation process. It spreads along the reflex arc in one direction.
Irradiation of excitation, which consists in the fact that with a significant increase in the strength of the stimulus, the area of neurons involved in this process expands.
Summation of excitation. This process is facilitated by the presence of a huge number of synaptic contacts.
High fatigue. With prolonged repeated stimulation, the reflex reaction weakens.
Synaptic delay. The time of the reflex reaction depends entirely on the speed of movement and the time of propagation of excitation through the synapse. In humans, one such delay is about 1 ms.
Tone, which represents the presence of background activity.
Plasticity, which is the functional ability to significantly modify the overall picture of reflex reactions.
Convergence of nerve signals, which determines the physiological mechanism of the passage of afferent information (a constant flow of nerve impulses).
Integration of cell functions in nerve centers.
The property of a dominant nerve focus, characterized by increased excitability, the ability to excite and summation.
Cephalization of the nervous system, which consists in moving, coordinating the activity of the body in the main sections of the central nervous system and concentrating the regulatory function in them.
