A person acts as a kind of coordinator in our body. It transmits commands from the brain to muscles, organs, tissues and processes the signals coming from them. A nerve impulse is used as a kind of data carrier. What does he represent? At what speed does it work? These and a number of other questions can be answered in this article.
What is a nerve impulse?
This is the name of the wave of excitation that propagates through the fibers as a response to irritation of neurons. Thanks to this mechanism, information is transmitted from various receptors to the central nervous system. And from it, in turn, to different organs (muscles and glands). But what is this process at the physiological level? The mechanism of transmission of a nerve impulse is that the membranes of neurons can change their electrochemical potential. And the process of interest to us takes place in the area of synapses. The speed of a nerve impulse can vary from 3 to 12 meters per second. In more detail about it, as well as about the factors that influence it, we will talk later.
Study of the structure and work
For the first time, the passage of a nerve impulse was demonstrated by the German scientists E. Goering and G. Helmholtz using a frog as an example. At the same time, it was found that the bioelectric signal propagates at the previously indicated speed. In general, this is possible due to the special construction. In some ways, they resemble an electrical cable. So, if we draw parallels with it, then the conductors are the axons, and the insulators are their myelin sheaths (they are the membrane of the Schwann cell, which is wound in several layers). Moreover, the speed of the nerve impulse depends primarily on the diameter of the fibers. The second most important is the quality of electrical insulation. By the way, the body uses myelin lipoprotein, which has the properties of a dielectric, as a material. Ceteris paribus, the larger its layer, the faster the nerve impulses will pass. Even at the moment it cannot be said that this system has been fully investigated. Much that relates to nerves and impulses still remains a mystery and a subject of research.
Features of the structure and functioning
If we talk about the path of a nerve impulse, then it should be noted that the fiber is not covered along its entire length. The design features are such that the current situation can best be compared with the creation of insulating ceramic sleeves that are tightly strung on the rod of an electrical cable (although in this case on the axon). As a result, there are small non-isolated electrical sections from which the ion current can safely flow out of the axon into the environment (or vice versa). This irritates the membrane. As a result, generation is caused in areas that are not isolated. This process is called the intercept of Ranvier. The presence of such a mechanism makes it possible to make the nerve impulse propagate much faster. Let's talk about this with examples. So, the speed of nerve impulse conduction in a thick myelinated fiber, the diameter of which fluctuates within 10-20 microns, is 70-120 meters per second. Whereas for those who have a suboptimal structure, this figure is 60 times less!
Where are they created?
Nerve impulses originate in neurons. The ability to create such "messages" is one of their main properties. The nerve impulse ensures the rapid propagation of the same type of signals along the axons to long distance. Therefore, this is the most important tool organism for the exchange of information in it. Data on irritation are transmitted by changing the frequency of their repetition. A complex system of periodicals works here, which can count hundreds of nerve impulses in one second. According to a somewhat similar principle, although much more complicated, computer electronics work. So, when nerve impulses arise in neurons, they are encoded in a certain way, and only then are they transmitted. In this case, the information is grouped into special "packs", which have a different number and nature of the sequence. All this, put together, is the basis for the rhythmic electrical activity of our brain, which can be registered thanks to the electroencephalogram.
Cell types
Speaking about the sequence of passage of a nerve impulse, one cannot ignore (neurons), through which the transmission of electrical signals occurs. So, thanks to them, different parts of our body exchange information. Depending on their structure and functionality, three types are distinguished:
- Receptor (sensitive). They encode and turn into nerve impulses all temperature, chemical, sound, mechanical and light stimuli.
- Plug-in (also called conductor or closing). They serve to process and switch impulses. Most of them are found in the human brain and spinal cord.
- Effector (motor). They receive commands from the central nervous system to perform certain actions (in the bright sun, close your eyes with your hand, and so on).
Each neuron has a cell body and a process. The path of a nerve impulse through the body begins precisely with the latter. Branches are of two types:
- Dendrites. They are entrusted with the function of perceiving irritation of the receptors located on them.
- Axons. Thanks to them, nerve impulses are transmitted from cells to the working organ.
Speaking about the conduction of a nerve impulse by cells, it is difficult not to talk about one interesting point. So when they're at rest, let's say the sodium-potassium pump is busy moving the ions around in such a way as to achieve the effect of fresh water on the inside and salty on the outside. Due to the resulting imbalance of the potential difference across the membrane, up to 70 millivolts can be observed. For comparison, this is 5% of the usual ones. But as soon as the state of the cell changes, the resulting balance is disturbed, and the ions begin to change places. This happens when the path of a nerve impulse passes through it. Due to the active action of ions, this action is also called the action potential. When it reaches a certain value, then reverse processes begin, and the cell reaches a state of rest.
About the action potential
Speaking about the transformation of a nerve impulse and its propagation, it should be noted that it could be miserable millimeters per second. Then the signals from the hand to the brain would reach in minutes, which is clearly not good. This is where the previously discussed myelin sheath plays its role in strengthening the action potential. And all its "passes" are placed in such a way that they only have a positive effect on the speed of signal transmission. So, when an impulse reaches the end of the main part of one axon body, it is transmitted either to the next cell, or (if we talk about the brain) to numerous branches of neurons. In the latter cases, a slightly different principle works.
How does everything work in the brain?
Let's talk about which nerve impulse transmission sequence works in the most important parts of our central nervous system. Here, neurons are separated from their neighbors by small gaps, which are called synapses. The action potential cannot cross them, so it looks for another way to get to the next nerve cell. At the end of each process are small sacs called presynaptic vesicles. Each of them has special compounds - neurotransmitters. When an action potential arrives at them, molecules are released from the sacs. They cross the synapse and attach to special molecular receptors that are located on the membrane. In this case, the balance is disturbed and, probably, a new action potential appears. This is not yet known for certain, neurophysiologists are studying the issue to this day.
The work of neurotransmitters
When they transmit nerve impulses, there are several options for what will happen to them:
- They will diffuse.
- subjected to chemical degradation.
- Return back to their bubbles (this is called recapture).
At the end of the 20th century, a startling discovery was made. Scientists have learned that drugs that affect neurotransmitters (as well as their release and reuptake) can change a person's mental state in a fundamental way. So, for example, a number of antidepressants like Prozac block the reuptake of serotonin. There are some reasons to believe that a deficiency in the brain neurotransmitter dopamine is to blame for Parkinson's disease.
Now researchers who study borderline states human psyche trying to figure out how it all affects the human mind. In the meantime, we do not have an answer to such a fundamental question: what causes a neuron to create an action potential? So far, the mechanism of "launching" this cell is a secret for us. Particularly interesting from the point of view of this riddle is the work of neurons in the main brain.
In short, they can work with thousands of neurotransmitters that are sent by their neighbors. Details regarding the processing and integration of this type of impulses are almost unknown to us. Although many research groups are working on this. At the moment, it turned out to find out that all received impulses are integrated, and the neuron makes a decision - whether it is necessary to maintain the action potential and transmit them further. The functioning of the human brain is based on this fundamental process. Well, then it is not surprising that we do not know the answer to this riddle.
Some theoretical features
In the article, "nerve impulse" and "action potential" were used as synonyms. Theoretically, this is true, although in some cases it is necessary to take into account some features. So, if you go into details, then the action potential is only part of the nerve impulse. With a detailed examination of scientific books, you can find out that this is only the change in the charge of the membrane from positive to negative, and vice versa. Whereas a nerve impulse is understood as a complex structural and electrochemical process. It spreads across the neuron membrane like a traveling wave of changes. An action potential is just an electrical component in a nerve impulse. It characterizes the changes that occur with the charge of a local section of the membrane.
Where are nerve impulses created?
Where do they start their journey? The answer to this question can be given by any student who diligently studied the physiology of arousal. There are four options:
- Receptor ending of a dendrite. If it exists (which is not a fact), then the presence of an adequate stimulus is possible, which will first create a generator potential, and then a nerve impulse. Pain receptors work in a similar way.
- The membrane of the excitatory synapse. As a rule, this is possible only in the presence of strong irritation or their summation.
- Trigger zone of the dentrid. In this case, local excitatory postsynaptic potentials are formed as a response to a stimulus. If the first node of Ranvier is myelinated, then they are summed up on it. Due to the presence of a section of the membrane there, which has increased sensitivity, a nerve impulse occurs here.
- Axon hillock. This is the name of the place where the axon begins. The mound is the most frequent create impulses on a neuron. In all other places that were considered earlier, their occurrence is much less likely. This is due to the fact that here the membrane has an increased sensitivity, as well as a reduced one. Therefore, when the summation of numerous excitatory postsynaptic potentials begins, the hillock reacts to them first of all.
An example of a spreading excitation
The story in medical terms can cause misunderstanding of certain points. To eliminate this, it is worth briefly going through the stated knowledge. Let's take a fire as an example.
Think back to last summer's news bulletins (you might hear it again soon too). The fire is spreading! At the same time, trees and shrubs that burn remain in their places. But the front of the fire goes further and further from the place where the fire was. The nervous system works the same way.
It is often necessary to calm the excitation of the nervous system that has begun. But this is not so easy to do, as in the case of fire. To do this, artificial interference is made in the work of the neuron (in medicinal purposes) or use various physiological means. This can be compared to pouring water on a fire.
Synaptic transmission is the interaction of brain cells.
Neurons produce electrochemical perturbations that travel along their fibers. These disturbances, called nerve impulses or action potentials, are generated by small electrical currents along the nerve cell membrane. Neurons are capable of producing up to a thousand action potentials per second, in the sequence and duration of which information is encoded.
Nerve impulses - electrochemical disturbances transmitted along nerve fibers; through them neurons interact with each other and with the rest of the body. The electrical nature of nerve impulses is determined by the structure of the cell membrane, which consists of two layers separated by a small gap. The membrane also acts as a capacitor - it accumulates electric charge, collecting ions on itself, and as resistance, blocking the current. In a neuron at rest, a cloud of negatively charged ions forms along the inner surface of the membrane, and positive ions along the outer surface.
A neuron, when activated, emits (also called "generates") a nerve impulse. It occurs in response to signals received from other cells, and is a brief reverse change in the potential difference of the membrane: inside it becomes positively charged for a moment, after which it quickly returns to a state of rest. During a nerve impulse, the membrane of a nerve cell lets in certain types of ions. Since the ions are electrically charged, their movement is an electric current through the membrane.
neurons at rest. There are ions inside the neurons, but the neurons themselves are surrounded by ions in other concentrations. It is natural for particles to move from an area of high concentration to an area of low concentration, but the nerve cell membrane prevents this movement because it is basically impermeable.
It turns out that some ions are concentrated outside the membrane, while others are inside. As a result, the outer surface of the membrane is positively charged, while the inner surface is negatively charged. The membrane is thus polarized.
It all started with a squid. The mechanism of the action potential - waves of excitation on the cell membrane - was discovered in the early 1950s, in a classic experiment with microelectrodes inserted into the axons of a giant squid. These experiments proved that the action potential is generated by successive movements of ions across the membrane.
In the first phase of the action potential, the membrane briefly becomes permeable to sodium ions, and they fill the cell. This causes depolarization of the cell - the potential difference across the membrane is reversed, and the inner surface of the membrane is positively charged. Following this, potassium ions rapidly leave the cell and the potential difference of the membrane returns to its original state. The penetration of potassium ions inside makes the charge on the membrane more negative than at rest, and the cell is thus hyperpolarized. During the so-called refractory period, the neuron cannot produce the next action potential, but quickly returns to a resting state.
Action potentials are generated at a structure called the axon hillock, which is where the axon grows out of the cell body. Action potentials move along the axon because depolarization of one segment of the fiber causes depolarization of the adjacent one. This wave of depolarization rolls away from the cell body and, upon reaching the terminal of the nerve cell, causes the release of neurotransmitters.
A single pulse lasts one thousandth of a second; Neurons encode information with a precisely timed sequence of impulses (spike discharges), but it is still unclear exactly how information is encoded. Neurons often fire action potentials in response to signals from other cells, but they also fire without any external signals. The frequency of basal pulsations, or spontaneous action potentials, varies in different types of neurons and can change depending on the signals of other cells.
Few will pass. Ions cross the nerve cell membrane through barrel-shaped proteins called ion channels. They penetrate the membrane and form through pores. Ion channels have sensors that recognize changes in the potential difference of the membrane, and they open and close in response to these changes.
Human neurons contain more than a dozen different types such channels, and each of them passes only one type of ions. The activity of all these ion channels during the action potential is strictly regulated. They open and close in a certain order - so that neurons, in response to signals received from other cells, can generate sequences of nerve impulses.
Ohm's law.
Ohm's law explains how the electrical properties of the brain change with input. It describes the relationship between the potential difference (voltage) of the nerve cell membrane, its resistance, and the current flowing through it. According to this relationship, the current is directly proportional to the membrane voltage and is described by the equation I = U/R, where I is the electric current, U is the potential difference, and R is the resistance.
Faster than Usain Bolt.
The axons of the spinal cord and brain are isolated by thick myelin tissue produced by brain cells called oligodendrocytes. The oligodendrocyte has few branches, and each consists of a large, flat sheet of myelin repeatedly wrapped around a small segment of the axon belonging to another neuron. The myelin sheath along the length of the entire axon is uneven: it is interrupted at regular intervals, and the points of these interruptions are called nodes of Ranvier. Ion channels thicken just at these points, thereby ensuring the jumping of action potentials from one intercept to another. This accelerates the entire process of movement of action potentials along the axon - it occurs at a speed of up to 100 m / s.
RESEARCH WORK
The electrical nature of the nerve impulse
Introduction 3
Experiments by L. Galvani and A. Volta 3
Biocurrents in living organisms 4
Annoyance effect. 5
Nerve cell and nerve impulse transmission 6
The action of a nerve impulse on various parts of the body
Exposure to electrical activity for medical purposes 9
Reaction speed 10
Conclusion 11
Literature 11
Appendix
Introduction
“No matter how wonderful the laws and phenomena
electricity,
appearing to us in the world
inorganic or
dead matter, interest,
which they
represent, can hardly
compare with that
which is inherent in the same force
in connection with the nervous
system and life
M. Faraday
The purpose of the work: To determine the factors affecting the propagation of a nerve impulse.
This work was faced with the following tasks:
1. To study the history of the development of the science of bioelectricity.
2. Consider electrical phenomena in wildlife.
3. Investigate the transmission of a nerve impulse.
4. Check in practice what affects the speed of transmission of a nerve impulse.
Experiments by L. Galvani and A. Volta
Back in the 18th century Italian physician Luigi Galvani (1737-1787) discovered that if you bring a frog to a decapitated body electrical voltage, then contractions of her paws are observed. So he showed the effect of electric current on muscles, so he is rightfully called the father of electrophysiology. In other experiments, he hung the leg of a dissected frog on a brass hook. At the moment when, swinging, the paw touched the iron grating of the balcony where the experiments were carried out, contraction of the paw was again observed. Galvani suggested the existence of a potential difference between the nerve and the foot - "animal electricity". He explained the contraction of the muscle by the action of an electric current that occurs in the tissues of the frog when the circuit is closed through the metal.
Galvani's compatriot, Alessandro Volta (1745-1827), carefully studied the electrical circuit used by Galvani and proved that it contains two dissimilar metals that are closed through a saline solution, i.e. on the face of a complete likeness of a chemical current source. The neuromuscular preparation, he argued, in this experiment serves only as a sensitive galvanometer.
Galvani could not admit his defeat. He threw a nerve on the muscle under various conditions in order to prove that even without metal it is possible to obtain muscle contraction due to electricity of "animal origin". One of his followers finally succeeded. It turned out that an electric current occurs when a nerve is thrown onto a damaged muscle. Thus, electric currents between healthy and damaged tissue were discovered. That's what they were named...fault currents. Later it was shown that any activity of nerves, muscles and other tissues is accompanied by the generation of electrical currents.
Thus, the presence of biocurrents in living organisms has been proven. Nowadays, they are recorded and examined by sensitive instruments - oscilloscopes.
Biocurrents in living organisms
The first information about the study of electrical phenomena in living nature is interesting. The objects of observation were electric fish. Through experiments on an electric skate, Faraday established that the electricity created by a special organ of this fish is completely identical to the electricity received from a chemical or other source, although it is a product of the activity of a living cell. Subsequent observations showed that many fish have special electrical organs, a kind of "batteries" that generate high voltages. So, a giant stingray creates a voltage in the discharge of 50-60 V, the Nile electric catfish 350 V, and the electrophorus eel - over 500 V. Nevertheless, this high voltage has no effect on the body of the fish itself!
The electrical organs of these fish consist of muscles that have lost their ability to contract: muscle tissue serves as a conductor, and connective tissue serves as an insulator. Nerves from the spinal cord go to the organ, and in general it is a small-lamellar structure of alternating elements. For example, an eel has between 6,000 and 10,000 connected in series elements forming a column, and about 70 columns in each organ located along the body. In adults, this organ accounts for about 40% of the total body weight. The role of electric organs is great, they serve for defense and attack, and are also part of a very sensitive navigation and location system.
Annoyance effect.
One of the most important bodily functions, calledirritability - the ability to respond to changes in the environment. The highest irritability is in animals and humans, which have specialized cells that form nervous tissue. Nerve cells - neurons - are adapted for a quick and specific response to a variety of stimuli coming from the external environment and the tissues of the body itself. The reception and transmission of stimuli occurs with the help of electrical impulses propagating along certain paths.
Nerve cell and nerve impulse transmission
A nerve cell, a neuron, is a star-shaped body and consists of thin processes - axons and dendrites. The end of the axon passes into thin fibers that end in the muscle or synapses. In an adult, the length of the axon can reach 1-1.5 m with a thickness of about 0.01 mm. The cell membrane plays a special role in the formation and transmission of nerve impulses.
The fact that the nerve impulse is an impulse of electric current was proved onlyby the middle of the 20th century, mainly by the works of A. Hodgkin's group. In 1963, A. Hodgkin, E. Huxley and J. Eccles were awarded the Nobel Prize in Physiology or Medicine "for discoveries concerning ionic mechanisms involved in excitation and inhibition in the peripheral and central regions of the nerve cell membrane." The experiments were carried out on giant neurons (diameter 0.5 mm) - squid axons.
Certain parts of the membrane have semiconductor and ion-selective properties - they pass ions of the same sign or one element. The appearance of the membrane potential, on which the work of the information and energy-converting systems of the body depends, is based on such a selective ability. In an external solution, more than 90% of the charged particles are sodium and chloride ions. In the solution inside the cell, the main part of the positive ions are potassium ions, and the negative ones are large organic ions. The concentration of sodium ions outside is 10 times higher than inside, and potassium ions inside are 30 times higher than outside. This creates a double electrical layer on the cell wall. Since the membrane at rest is well permeable, a potential difference of 60-100 mV arises between the internal part and the external environment, and the internal part is negatively charged. This potential difference is calledresting potential.
When the cell is irritated, the electrical double layer is partially discharged. When the resting potential drops to 15–20 mV, the membrane's permeability increases, and sodium ions rush into the cell. As soon as a positive potential difference between both surfaces of the membrane is reached, the flow of sodium ions dries up. At the same moment, channels for potassium ions open, and the potential shifts to the negative side. This, in turn, reduces the sodium ion conductance, and the potential returns to the resting state.
The signal arising in the cell propagates along the axon due to the conductivity of the electrolyte inside it. If the axon has a special insulation - the myelin sheath - then the electrical impulse passes through these areas faster, and the overall speed is determined by the size and number of uninsulated areas. The speed of the impulse in the axon is 100 m/s.
How is the signal transmitted through the gap? It turned out that the synapse membrane is heterogeneous in structure - in the central regions it has "windows" with low resistance, and near the edge the resistance is high. Membrane heterogeneity is created in a special way: with the help of a special protein - coppectin. The molecules of this protein form a special structure - kopnexon, which, in turn, consists of six molecules and has a channel inside. Thus, the synapse connects two cells with many small tubes passing inside the protein molecules. The gap between the membranes is filled with an insulator. In birds, the protein myelin acts as an insulator.
When the change in potentials in the muscle fiber reaches the excitation threshold of the electrically excitable membrane, an action potential arises in it and the muscle fiber contracts.
The action of a nerve impulse on various parts of the body
Mankind has been puzzling over what is happening in the brain of every person for more than one millennium. It is now known that in the brain of thoughtare born under the action of an electric current, but the mechanism has not been studied. Thinking about the interaction of chemical and physical phenomena, Faraday said: "Wonderful as the laws and phenomena of electricity that we observed in the world of inorganic matter and inanimate nature, the interest they represent can hardly be compared with that which causes the same force in combination with life."
In humans, an electromagnetic field was also found, generated by bioelectric potentials on the surface of cells. The Soviet inventor S.D. Kirlian managed to make this phenomenon visual in the truest sense of the word. He suggested photographing the human body by placing it between two large metal walls to which an alternating electrical voltage was applied. In an environment with an increased electromagnetic field, microcharges appear on the human skin, and the most active are those places where the nerve endings come out. In photographs taken using the Kirlian method, they are visible as small, brightly glowing dots. These points, as it turned out, are located exactly in those places of the body in which it is recommended to immerse silver needles during acupuncture treatment.
Thus, using the recording of brain biocurrents as feedback, you can assess the degree of prayer immersion of the patient.
We now know that some areas of the brain are responsible for emotions and for creative activity. It is possible to determine whether this or that area of the brain is in an excited state, but it is impossible to decipher these signals, so it can be said with certainty that humanity will not soon learn to read minds.
A human thought is a product of the work of the brain associated with bioelectrical phenomena in it and in other parts of the body. It is the biocurrents that arise in the muscles of a person who thinks about clenching his fingers into a fist, caught and amplified by the appropriate equipment, that clench the fingers of a mechanical hand.
Academics psychiatristVladimir Mikhailovich Bekhterev and biophysicistPyotr Petrovich Lazarev recognized that under some special conditions, not yet known to science exactly, the electrical energy of one brain can act at a distance on the brain of another person. If this brain was "tuned" accordingly, they supposed, it would be possible to evoke in it "resonant" bioelectrical phenomena and, as a result of them, the corresponding representations.
The study of electrical phenomena in the body has brought significant benefits. We list the most famous.
Exposure to electrical activity for medical purposes
О Electrochemistry is widely used in medicine and physiology. The potential difference between two points of the cell is determined using microelectrodes. With their help, you can measure the oxygen content in the blood: a catheter is introduced into the blood, the basis of which is a platinum electrode, placed together with the reference electrode in an electrolyte solution, which is separated from the analyzed blood by a porous hydrophobic Teflon film; oxygen dissolved in the blood diffuses through the pores of the Teflon film to the platinum electrode and is reduced on it.
О In the process of vital activity, the state of an organ, and, consequently, its electrical activity, change over time. The method of studying their work, based on the registration of potentials electric field on the surface of the body, called electrography. The name of the electrogram indicates the organs or tissues being studied: the heart - an electrocardiogram, the brain - an electroencephalogram, the muscles - an electromyogram, the skin - a galvanic skin reaction, etc.
О In medical practice, electrophoresis is widely used - to separate proteins, amino acids, antibiotics, enzymes in order to control the course of the disease. Iontophoresis is just as common.
A The well-known apparatus "artificial kidney", to which a patient is connected in case of acute renal failure, is based on the phenomenon of electrodialysis. Blood flows in a narrow gap between two membranes, washed with saline, while toxins are removed from it - products of metabolism and tissue decay.
A Researchers in the US have proposed electrical stimulation to treat epilepsy. To do this, a tiny device is sewn under the skin in the upper chest, programmed to stimulate the vagus nerve for 30 hours with an interval of 5-15 minutes. Its action has been tested in the USA, Canada, Germany. In patients who were not helped by drugs, after 3 months the number of seizures decreased by 25%, after 1.5 years - by 50%.
Speed reaction
One of the features that characterize the brain is the speed of reaction. It is determined by the time during which the first impulse travels from the receptors of the organ that received the irritation to the organ that produces the body's response. From the survey I conducted, it follows that many factors influence the speed of reaction and attentiveness. In particular, it may decrease for the following reasons: uninteresting and (or) monotonous teaching material presented by the teacher; poor discipline in the classroom; ambiguity of the purpose and plan of the lesson; stale air in the room; too high or too low temperature in the classroom; extraneous noise; the presence of new unnecessary benefits, fatigue by the end of the day.
There are also individual reasons for inattention: too easy or too difficult assimilation of the material; unpleasant family events; illness, overwork; watching a large number of movies; late sleep.
Conclusion
Words have a huge influence on the nervous activity of a person. The more the listeners trust the speaker, the brighter the emotional coloring of the words they perceive and the stronger their effect. The patient trusts the doctor, the student trusts the teacher, therefore, one should carefully choose the words - stimuli of the second signaling system. So, a well-flying cadet of the flight school suddenly began to experience overwhelming fear. It turned out that an authoritative pilot instructor for him, leaving, left him a note: “I hope to see you soon, but be careful with the corkscrew.”
In a word, you can both cause a disease and successfully cure it. Treatment with a word - logotherapy - is a part of psychotherapy. My next experience is direct proof of that. I asked two people to perform the following actions: at the same time, with one hand, stroke the stomach in a circular motion, with the other, touch the head along a straight line. It turned out that this is quite difficult to do - the movements were either simultaneously circular or linear. However, I influenced the subjects in different ways: I told one that he was about to succeed, and the other that he would not succeed. After a while, the first one succeeded, while the other did not succeed.
Personal indicators should be guided when choosing a profession. If the reaction rate is low, then it is better not to choose professions that require a lot of attention, a quick analysis of the situation (pilot, driver, etc.).
Literature
Voronkov G.Ya.Electricity in the world of chemistry. - M.: Knowledge, 1987.
Tretyakova S.V.The human nervous system. - Physics ("PS"), No. 47.
Platonov K.Entertaining psychology. - M.: Liter, 1997.
Berkinblit M.B., Glagoleva E.G.Electricity in living organisms. - M.: Nauka, 1988.
The effect of fatigue on the nervous electrical impulse
Purpose: to test the effect of physical activity on the reaction rate.
Research progress:The usual time for a simple reaction is 100–200 ms to light, 120–150 ms to sound, and 100–150 ms to an electrocutaneous stimulus. I conducted an experiment according to the method of Academician Platonov.At the beginning of the lesson physical education, we recorded the reaction time when catching the ball, then checked this reaction after physical exertion.
Name, Surname 11A Class of secondary school No. 22Reaction time to exercise
Reaction time after exercise Loads
Kocharyan Karen
0.13s
0.15s
Nikolaev Valery
0.15s
0.16s
Kazakov Vadim
0.14s
0.16s
Kuzmin Nikita
0.8s
0.1s
Safiullin Timur
0.13s
0.15s
Tukhvatullin Rishat
0.9s
0.11s
Farafonov Artur
0.9s
0.11s
Conclusion: We recorded the reaction time before and after exercise. We concluded that fatigue slows down reaction time.Based on this, teachers can be advised when scheduling subjects that require maximum attention to be set in the middle of the school day, when students are not yet tired and are capable of full-fledged mental activity.
NERVE IMPULSE
NERVE IMPULSE
A wave of excitation, which spreads along the nerve fiber and serves to transmit information from the periphery. receptor (sensitive) endings to the nerve centers, inside the center. nervous system and from it to the executive apparatus - the muscles and glands. N.'s passage and. accompanied by transient electric. processes, to-rye it is possible to register both extracellular, and intracellular electrodes.
Generation, transfer and processing N. and. carried out by the nervous system. Main a structural element of the nervous system of higher organisms is a nerve cell, or a neuron, consisting of a cell body and numerous. processes - dendrites (Fig. 1). One of the processes in non-ripheric. neurons has a large length - this is a nerve fiber, or axon, the length of which is ~ 1 m, and the thickness is from 0.5 to 30 microns. There are two classes of nerve fibers: pulpy (myelinated) and amyelinated. The pulpy fibers have myelin, formed by special. a membrane, edges like isolation is wound on an axon. The length of sections of a continuous myelin sheath is from 200 microns to 1 mm, they are interrupted by the so-called. interceptions of Ranvier with a width of 1 μm. The myelin sheath plays the role of insulation; the nerve fiber in these areas is passive, electrically active only in the nodes of Ranvier. Meleless fibers do not have insulated. plots; their structure is homogeneous along the entire length, and the membrane has an electric. activity over the entire surface.
Nerve fibers end on the bodies or dendrites of other nerve cells, but are separated from them by an intermediate
an eerie width of ~10 nm. This area of contact between two cells is called. synapse. The axon membrane entering the synapse is called. presynaptic, and the corresponding dendritic or muscle membrane is post-synaptic (see Fig. Cell structures).
Under normal conditions, a series of N. and. constantly run along the nerve fiber, arising on the dendrites or the cell body and spreading along the axon in the direction from the cell body (the axon can conduct N. and. in both directions). The frequency of these periodic discharges carries information about the strength of the irritation that caused them; eg, with moderate activity, the frequency is ~ 50-100 impulses / s. There are cells, to-rye are discharged with a frequency of ~ 1500 impulses/s.
Speed of distribution of N. and. u .
depends on the type of nerve fiber and its diameter d, u .
~ d 1/2. In the thin fibers of the human nervous system u .
~ 1 m/s, and in thick fibers u .
~ 100-120 m/s.
Each N. and. occurs as a result of irritation of the body of a nerve cell or nerve fiber. N. and. always has the same characteristics (shape and speed) regardless of the strength of irritation, i.e., with subthreshold stimulation of N. and. does not occur at all, but with suprathreshold - has a full amplitude.
After excitation, a refractory period occurs, during which the excitability of the nerve fiber is reduced. Distinguish abs. the refractory period, when the fiber cannot be excited by any stimuli, and refers. refractory period, when possible, but its threshold is above normal. Abs. the refractory period limits the transmission frequency of N. from above and. The nerve fiber has the property of accommodation, that is, it gets used to constantly acting irritation, which is expressed in a gradual increase in the threshold of excitability. This leads to a decrease in N.'s frequency and. and even to their complete disappearance. If irritation builds up slowly, then excitation may not occur even after reaching the threshold.
Fig.1. Diagram of the structure of a nerve cell.
Along N.'s nerve fiber and. distributed in the form of electricity. potential. In the synapse, there is a change in the propagation mechanism. When N. and. reaches the presynaptic endings, in synaptic. the gap is allocated active chem. - m e d i a t o r. The mediator diffuses through the synaptic. gap and changes the permeability of postsynaptic. membrane, as a result of which it appears, again generating a propagating . This is how chemo works. synapse. There is also an electric synapse when . the neuron is electrically excited.
N.'s excitation and. Phys. ideas about the appearance of electric. potentials in cells are based on the so-called. membrane theory. Cell membranes separate electrolytes of different concentrations and possess is-Byrate. permeability for certain ions. Thus, the axon membrane is a thin layer of lipids and proteins with a thickness of ~7 nm. Her electric resistance at rest ~ 0.1 ohm. m 2, and the capacity is ~ 10 mf / m 2. Inside the axon, there is a high concentration of K + ions and a low concentration of Na + and Cl - ions, and in environment- vice versa.
At rest, the axon membrane is permeable to K + ions. Due to the difference in concentrations C 0 K .
in ext. and C in ext. solutions, a potassium membrane potential is established on the membrane
where T - abs. pace-pa, e - charge of an electron. On the axon membrane, a resting potential of ~ -60 mV is indeed observed, corresponding to the indicated f-le.
Ions Na + and Cl - penetrate the membrane. To maintain the necessary non-equilibrium distribution of ions, the cell uses an active transport system, which uses cellular energy to work. Therefore, the state of rest of the nerve fiber is not thermodynamically equilibrium. It is stationary due to the action of ion pumps, and the membrane potential in open circuit conditions is determined from the equality to zero of the total electric. current.
The process of nervous excitation develops as follows (see also Biophysics). If a weak current pulse is passed through the axon, leading to depolarization of the membrane, then after removing the external. exposure potential monotonously returns to the initial level. Under these conditions, the axon behaves like a passive electrical circuit. circuit consisting of a capacitor and a DC. resistance.
Rice. 2. Development of the action potential in the nervous systemlokne: a- subthreshold ( 1
) and suprathreshold (2) irritation; b-membrane response; with supra-threshold irritation, full sweat appearsaction cycle; v is the ion current flowing through membrane when excited; G - approximation ion current in a simple analytical model.
If the current pulse exceeds a certain threshold value, the potential continues to change even after the disturbance is turned off; the potential becomes positive and only then returns to the level of rest, and at first it even skips a little (the region of hyperpolarization, Fig. 2). The response of the membrane does not depend on the perturbation; this impulse is called action potential. At the same time, an ion current flows through the membrane, directed first inward and then outward (Fig. 2, v).
Phenomenological interpretation of the mechanism of occurrence of N. and. was given by A. L. Hodg-kin and A. F. Huxley in 1952. The total ion current is made up of three components: potassium, sodium, and leakage current. When the membrane potential is shifted by the threshold value j* (~ 20mV), the membrane becomes permeable to Na + ions. Na + ions rush into the fiber, shifting the membrane potential until it reaches the equilibrium sodium potential:
component ~ 60 mV. Therefore, the full amplitude of the action potential reaches ~ 120 mV. By the time the max. potential in the membrane begins to develop potassium (and at the same time decrease sodium). As a result, the sodium current is replaced by a potassium current directed outward. This current corresponds to a decrease in the action potential.
The empirical ur-tion for the description of sodium and potassium currents. The behavior of the membrane potential during spatially homogeneous excitation of the fiber is determined by the equation:
where WITH - membrane capacity, I- ion current, consisting of potassium, sodium and leakage current. These currents are determined by the post. emf j K , j Na and j l and conductivities g K , g Na and gl:
the value gl considered constant, conductivity g Na and g K is described using parameters m, h and P:
g Na, g K - constants; parameters t, h and P satisfy the linear equations
Coefficient dependence. a .
and b on the membrane potential j (Fig. 3) are selected from the condition of the best match
Rice. 3. Dependence of coefficientsa.
andbfrom membranespotential.
calculated and measured curves I(t). The choice of parameters is caused by the same considerations. Dependence of stationary values t, h and P on the membrane potential is shown in fig. 4. There are models with a large number parameters. Thus, the nerve fiber membrane is a non-linear ionic conductor, the properties of which significantly depend on the electric. fields. The mechanism of excitation generation is poorly understood. The Hodgkin-Huxley Urn gives only a successful empirical. description of the phenomenon, for which there is no specific physical. models. Therefore, an important task is to study the mechanisms of the flow of electric. current through membranes, in particular through controlled electric. field ion channels.
Rice. 4. Dependence of stationary values t, h and P
from the membrane potential.
N.'s distribution and. N. and. can propagate along the fiber without attenuation and with post. speed. This is due to the fact that the energy necessary for signal transmission does not come from a single center, but is drawn in place, at each point of the fiber. In accordance with the two types of fibers, there are two ways of N.'s transmission and
In the case of nonmyelination membrane potential fibers j( x, t) is determined by the equation:
where WITH - membrane capacitance per unit fiber length, R- the sum of longitudinal (intracellular and extracellular) resistances per unit fiber length, I- ion current flowing through the membrane of a fiber of unit length. Electric current I is a functional of the potential j, which depends on time t and coordinates X. This dependence is determined by equations (2) - (4).
Type of functionality I specific to a biologically excitable environment. However, equation (5), apart from the form I, has a more general character and describes many physical. phenomena, eg. combustion process. Therefore N.'s transfer and. likened to the burning of a powder cord. If in a running flame the process of ignition is carried out due to thermal conductivity, then in N. and. excitation occurs with the help of the so-called. local currents (Fig. 5).
Rice. 5. Local currents providing distributionnerve impulse.
Ur-tion of Hodgkin - Huxley for N.'s distribution and. solved numerically. The solutions obtained, together with the accumulated experiments. data showed that N.'s distribution and. does not depend on the details of the excitation process. Qualities. a picture of N.'s distribution and. can be obtained using simple models that reflect only the general properties of excitation. Such approach allowed to count also the N.'s form and. in a homogeneous fiber, their change in the presence of inhomogeneities, and even complex modes of propagation of excitation in active media, for example. in the heart muscle. There are several math. models of this kind. The simplest of them is this. The ion current flowing through the membrane during the passage of N. and. is sign-alternating: at first it flows into the fiber, and then out. Therefore, it can be approximated by a piecewise constant function (Fig. 2, G). Excitation occurs when the membrane potential is shifted by the threshold value j*. At this moment, a current appears, directed inside the fiber and equal in absolute value j". After t "the current changes to the opposite, equal to j". This continues for time ~t". The self-similar solution of equation (5) can be found as a function of the variable t = x/ u ,
where u -
speed of distribution of N. and. (Fig. 2, b).
In real fibers, the time t" is large enough, so only it determines the speed u ,
for which the f-la is valid: 
. Given that j" ~ ~d, R~d 2 and WITH~ d, where d- fiber diameter, we find, in agreement with experiment, that u ~d 1/2 .
Using a piecewise constant approximation, the shape of the action potential is found.
Ur-tion (5) for the spreading N. and. actually admits two solutions. The second solution turns out to be unstable; it gives N. and. with a much lower speed and potential amplitude. The presence of the second, unstable solution has an analogy in the theory of combustion. When a flame propagates with a lateral heat sink, an unstable regime may also occur. A simple analytic N.'s model and. can be improved, taking into account the additions. details.
At change of section and at branching of nervous fibers N.'s passage and. may be difficult or even completely blocked. In an expanding fiber (Fig. 6), the pulse velocity decreases as it approaches expansion, and after expansion, it begins to increase until it reaches a new stationary value. N.'s delay and. the stronger, the greater the difference in cross sections. With a sufficiently large expansion of N. and. stops. There is a critical expansion of a fiber, a cut detains N. and.
At the return movement of N. and. (from wide fiber to narrow) there is no blocking, but the change in speed is the opposite. At the approach to narrowing N.'s speed and. increases and then begins to fall to a new stationary value. On the speed graph (Fig., 6 a) results in a kind of hysteresis loop.
Rie. 6. Passage of nerve impulses by expandingrunning fiber: a - change in pulse speed in depending on its direction; b- schematic image of an expanding fiber.
Another type of heterogeneity is fiber branching. In the branch node, various options for passing and blocking impulses. At the nonsynchronous N.'s approach and. the blocking condition depends on the time offset. If the time between pulses is small, then they help each other to penetrate into the wide third fiber. If the shift is large enough, then N. and. interfere with each other. This is due to the fact that N. and., who came up first, but failed to excite the third fiber, partially transfers the node into a refractory state. Besides, there is a synchronization effect: in process of N.'s approach and. to the node, their delay relative to each other decreases.
N.'s interaction and. Nerve fibers in the body are combined into bundles or nerve trunks, forming a kind of stranded cable. All fibers in a bundle are independent. communication lines, but have one common "wire" - intercellular. When N. and runs along any of the fibers, it creates an electric current in the intercellular fluid. , a cut influences membrane potential of the next fibers. Usually such an influence is negligible and the communication lines work without mutual interference, but it manifests itself in the pathological. and arts. conditions. Processing nerve trunks special. chem. substances, it is possible to observe not only mutual interference, but also the transfer of excitation to neighboring fibers.
Known experiments on the interaction of two nerve fibers placed in a limited volume of external. solution. If N. runs along one of the fibers and., then the excitability of the second fiber changes at the same time. Change goes through three stages. At first, the excitability of the second fiber falls (the excitation threshold rises). This decrease in excitability precedes the action potential traveling along the first fiber and lasts approximately until the potential in the first fiber reaches its maximum. Then the excitability grows, this stage coincides in time with the process of reducing the potential in the first fiber. Excitability decreases again when a slight hyperpolarization of the membrane occurs in the first fiber.
At the same time N.'s passage and. on two fibers it was sometimes possible to achieve their synchronization. Despite the fact that own N.'s speeds and. in different fibers are different, at the same time. excitation could arise collective N. and. If own. speeds were the same, then the collective impulse had a lower speed. With a noticeable difference in property. speeds, the collective speed had an intermediate value. Only N. and. could synchronize, the speeds of which did not differ too much.
Matem. the description of this phenomenon is given by the system of equations for the membrane potentials of two parallel fibers j 1 and j 2:
where R 1 and R 2 - longitudinal resistances of the first and second fibers, R 3 -
longitudinal resistance of the environment, g = R 1 R 2 + R 1 R 3 .
+ R 2 R 3 .
Ionic currents I 1 and I 2 can be described by one or another model of nervous excitation.
When using a simple analytic model solution leads to the following. picture. When one fiber is excited, an alternating membrane potential is induced in the adjacent one: first, the fiber is hyperpolarized, then depolarized, and finally hyperpolarized again. These three phases correspond to a decrease, an increase, and a new decrease in the excitability of the fiber. At normal values of the parameters, the shift of the membrane potential in the second phase towards depolarization does not reach the threshold, so there is no transfer of excitation to the adjacent fiber. At the same time excitation of two fibers, system (6) allows a joint self-similar solution, which corresponds to two N. and. moving at the same speed per post. distance from each other. If there is a slow N. and. ahead, then it slows down the fast impulse, not releasing it forward; both are moving at a relatively slow speed. If there is a fast II ahead. and., then it pulls up a slow impulse. The collective velocity turns out to be close to the intrinsic velocity. fast impulse speed. In complex neural structures, the appearance of auto will.
excitable environments. Nerve cells in the body are combined into neural networks, which, depending on the frequency of branching of the fibers, are divided into rare and dense. In a rare network are excited independently of each other and interact only at branch nodes, as described above.
In a dense network, the excitation covers many elements at once, so that their detailed structure and the way they are interconnected turn out to be insignificant. The network behaves like a continuous excitable medium, the parameters of which determine the occurrence and propagation of excitation.
The excitable medium can be three-dimensional, although it is more often considered as two-dimensional. The excitement which arose in to. point on the surface, propagates in all directions in the form of an annular wave. The excitation wave can go around obstacles, but cannot be reflected from them, nor is it reflected from the boundary of the medium. When waves collide with each other, their mutual annihilation occurs; these waves cannot pass through each other due to the presence of a refractory region behind the excitation front.
An example of an excitable environment is cardiac neuromuscular syncytium - the union of nerve and muscle fibers into a single conducting system capable of transmitting excitation in any direction. Neuromuscular syncytia contract synchronously, obeying a wave of excitation, which is sent by a single control center - the pacemaker. A single rhythm is sometimes disturbed, arrhythmias occur. One of these modes is called atrial flutter: these are autonomous contractions caused by the circulation of excitation around an obstacle, for example. superior or inferior vein. For the occurrence of such a regime, the perimeter of the obstacle must exceed the wavelength of excitation, which is ~ 5 cm in the human atrium. atrial contraction with a frequency of 3-5 Hz. A more complex mode of excitation is ventricular fibrillation of the heart, when otd. elements of the heart muscle begin to contract without external. commands and without communication with neighboring elements with a frequency of ~ 10 Hz. Fibrillation leads to the cessation of blood circulation.
The emergence and maintenance of spontaneous activity of an excitable medium are inextricably linked with the emergence of wave sources. The simplest source of waves (spontaneously excited cells) can provide periodic. pulsation of activity, this is how the pacemaker of the heart works.
Sources of excitation can also arise due to complex spaces. organization of the excitation mode, for example. reverberator of the type of a rotating spiral wave, appearing in the simplest excitable medium. Another kind of reverb occurs in an environment consisting of two types of elements with different excitation thresholds; the reverb periodically excites one or the other elements, while changing the direction of its movement and generating plane waves.
The third type of source is the leading center (echo source), which appears in an environment that is inhomogeneous in terms of refractoriness or excitation threshold. In this case, a reflected wave (echo) appears on the inhomogeneity. The presence of such wave sources leads to the appearance of complex excitation regimes, which are studied in the theory of autowaves.
Lit.: Hodgkin A., Nerve impulse, trans. from English, M., 1965; Katz B., Nerve, muscle and synapse, trans. from English, M., 1968; Khodorov B. I., The problem of excitability, L., 1969; Tasaki I., Nervous excitement, trans. from English, M., 1971; V. S. Markin, V. F. Pastushenko, Yu. A. Chizmadzhev, Theory of Excitable Media, Moscow, 1981. V. S. Markin.
NERNSTA THEOREM- the same as Third law of thermodynamics.
NERNSTA EFFECT(longitudinal galvanothermomagnetic effect) - the appearance in the conductor, through which current flows j , located in the magnet. field H | j , temperature gradient T , directed along the current j ; temperature gradient does not change sign when field direction changes H to the opposite (even effect). Opened by W. G. Nernst (W. H. Nernst) in 1886. N. e. occurs as a result of the fact that current transfer (the flow of charge carriers) is accompanied by a heat flow. Actually N. e. represents Peltier effect under conditions when the temperature difference arising at the ends of the sample leads to compensation for the heat flux associated with the current j , the flow of heat due to thermal conductivity. N. e. observed also in the absence of a magnet. fields.
NERNSTA-ETTINGSHAUSEN EFFECT- the appearance of electricity. fields E ne in the conductor, in which there is a temperature gradient T
,
in a direction perpendicular to the magnetic field H
.
Distinguish between transverse and longitudinal effects.
Transverse H.-E. e. consists in the appearance of electricity. fields E ne |
(potential difference V ne |
) in a direction perpendicular to H
and T
. In the absence of a magnet. fields of thermoelectric the field compensates for the flow of charge carriers created by the temperature gradient, and compensation takes place only for the total current: electrons with an energy greater than the average (hot) move from the hot end of the sample to the cold one, electrons with an energy less than the average (cold) - in the opposite direction. The Lorentz force deflects these groups of carriers in a direction perpendicular to T
and magn. field, in different directions; the deflection angle (Hall angle) is determined by the relaxation time t of a given group of carriers, i.e., it differs for hot and cold carriers if t depends on the energy. In this case, the currents of cold and hot carriers in the transverse direction ( |
T
and |
H
) cannot cancel each other out. This gives rise to a field E |
ne ,
the value of which is determined from the condition of equality 0 of the total current j = 0.
Field value E |
does not depend on T, H and properties of the substance, characterized by the coefficient. Nernst-Ettingsha-Usen N |
:
V semiconductors Under the influence T charge carriers of different signs move in the same direction, and in the magnetic. the field is deflected in opposite directions. As a result, the direction of the Nernst-Ettingshausen field created by charges of different signs does not depend on the sign of the carriers. This significantly distinguishes the transverse N.-E. e. from hall effect, where the direction of the Hall field is different for charges of different signs.
Since the coefficient N |
is determined by the dependence of the relaxation time t of carriers on their energy, then N.-E. e. sensitive to the mechanism scattering of charge carriers. Scattering of charge carriers reduces the influence of the magnetic. fields. If t ~ , then at r> 0 hot carriers scatter less often than cold ones and the direction of the field E |
ne is determined by the direction of deflection in magn. field of hot carriers. At r < 0 направление E |
ne is opposite and is determined by cold carriers.
V metals, where the current is carried by electrons with energies in the interval ~ kT near Fermi surfaces, magnitude N |
is given by the derivative d t /d.
on the Fermi surface = const (usually for metals N |
> 0, but, for example, copper N |
< 0).
Measurements N.-E. e. in semiconductors allow you to determine r, i.e. restore the function t(). Usually at high temp-pax in the area of own. semiconductor conductivity N |
<
0 due to the scattering of carriers on the optical. phonons. When the temperature drops, an area appears with N |
> 0, corresponding to the impurity conductivity and scattering of carriers Chap. arr. on phonons ( r< < 0). При ещё более низких T ionization scattering dominates. impurities with N |
< 0 (r > 0).
In weak magnetic fields (w with t<< 1, где w с - cyclotron frequency carriers) N |
does not depend on H. In strong fields (w c t >> 1) coefficient. N |
proportional one/ H 2. In anisotropic conductors, the coefficient. N |
-
tensor. By the amount N |
affect the drag of electrons by photons (increases N |
),
anisotropy of the Fermi surface, etc.
Longitudinal H.-E. e. consists in the occurrence of electric-rich. fields E || ne (potential difference V || ne) along T
in the presence of H
|
T
. Because along T
there is a thermo-electric. field E a =
a T
,
where a is the coefficient. thermoelectric fields, then the appearance will complement. fields along T
is equivalent to changing the field E a .
when applying a magnet. fields:
Magn. field, bending the trajectories of electrons (see above), reduces their mean free path l in the direction T . Since the mean free path (relaxation time t) depends on the energy of the electrons, the decrease l is not the same for hot and cold carriers: it is smaller for the group for which m is smaller. T. o., magn. field changes the role of fast and slow carriers in energy transfer, and thermoelectric. the field that ensures the absence of charge during energy transfer must change. At the same time, the coefficient N || also depends on the carrier scattering mechanism. Thermoelectric the current increases if m decreases with increasing carrier energy (during scattering of carriers by acoustic phonons), or decreases if m increases with increasing (during scattering by impurities). If electrons with different energies have the same t, the effect disappears ( N|| = 0). Therefore, in metals, where the energy range of electrons involved in the transfer processes is small (~ kT), N || small: In a semiconductor with two types of carriers N ||~ ~ g/kT. At low temp-pax N|| can also increase due to the influence of electron drag by phonons. In strong magnetic fields total thermoelectric field in magn. the field "saturates" and is independent of the carrier scattering mechanism. In ferromagnet. metals N.-E. e. has features associated with the presence of spontaneous magnetization.
A wave of excitation propagating along a nerve fiber and manifesting itself in an electric. (action potential), ionic, mechanical, thermal. and other changes. Provides information transfer from peripherals. receptor endings to the nerve centers inside ... ... Biological encyclopedic dictionary
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A nerve impulse is an electrical impulse that propagates along a nerve fiber. With the help of the transmission of nerve impulses, information is exchanged between neurons and information is transmitted from neurons to cells of other body tissues. Nervous ... ... Wikipedia
A wave of excitation propagating along a nerve fiber in response to stimulation of neurons. Provides information transfer from receptors to the central nervous system and from it to the executive organs (muscles, glands). Conducting a nervous ... ... encyclopedic Dictionary
nerve impulse- a wave of excitation that propagates along nerve fibers and through the body of nerve cells in response to irritation of neurons and serves to transmit a signal from receptors to the central nervous system, and from it to the executive organs (muscles, ... ... Beginnings of modern natural science
nerve impulse- nervinis impulsas statusas T sritis Kūno kultūra ir sportas apibrėžtis Jaudinimo banga, plintanti nerviniu audiniu. Atsiranda padirginus nervų ląsteles. Perduoda signalus iš jautriųjų periferinių nervų galūnių (receptorių) į centrinę nervų… … Sporto terminų žodynas
See Nervous Impulse... Great Soviet Encyclopedia
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