In the cell membrane are located Na +, k + -atfase, sodium and potassium channels.

Na +, K + -ATFAZ Due to the energy of ATP constantly pumps Na + outward and k + inside, creating a transmembrane gradient of concentrations of these ions. The sodium pump is inhibited by Wabaine.

Sodium and potassium channels Can pass Na + and K + in gradients of their concentrations. Sodium channels are blocked by novocaine, tetrodotoxin, and potassium - tetraethylammonium.

The work of Na +, k + -atfase, sodium and potassium channels can create peace and potential on the membrane .

Potential rest - This is the potential difference between the outer and the inner membrane in peace conditions, when sodium and potassium channels are closed. Its value is -70mv, it is created mainly by the concentration of K + and depends on Na + and Cl -. The concentration of K + inside the cell is 150 mmol / l, outside 4-5 mmol / l. The concentration of Na + inside the cell is 14 mmol / l, outside 140 mmol / l. The negative charge inside the cells create anions (glutamate, aspartate, phosphates), for which the cell membrane is impenetrable. The potential of rest is the same throughout the fiber and is not a specific peculiarity of nerve cells.

Nerve irritation may result in the action potential.

Action potential - This is a short-term change in the potential difference between the outer and the inner membrane at the time of excitation. The action potential depends on the concentration of Na + and arises according to the principle of "all or nothing."

The action potential consists of the following stages:

1. Local answer . If under the action of the stimulus, there is a change in the potential of rest to the threshold value of -50MV, soda channels are opened, which have a higher bandwidth than potassium.

2. Stage depolarization. The Na + stream inside the cell leads first to depolarization of the membrane to 0 mV, and then to the inversion of polarity to + 50mv.

3. Repolarization stage. Sodium channels are closed, and potassium open. The output of K + from the cell restores the membrane potential to the level of rest potential.

Ion channels open for a short time and after their closure, the sodium pump restores the initial distribution of ions on the sides of the membrane.

Nervous impulse

In contrast to the potential of rest, the potential of action covers only a very small section of the axon (in the myelinated fibers - from one interception of Ranvier to the neighboring). Arriving in one axon site, the action potential due to diffusion of ions from this site along the fiber reduces the rest potential in the neighboring site and causes the same development potential here. Thanks to this mechanism, the potential of action is distributed by nervous fibers and is called nerve impulse .

In the myelinized nerve fiber, sodium and potassium ion channels are located in non-cellinized areas of interceptions in Ranvier, where the axon membrane is in contact with the intercellular fluid. As a result, the nerve impulse moves "jumps": Na + ions entering inside when opening channels in one interception, diffuse along the axon along the potential gradient until the next interception, reduce the potential to the threshold values \u200b\u200band thereby induce the action potential. Thanks to such a device, the rate of impulse behavior in the myelinized fiber is 5-6 times more than in non-cellular fibers, where the ion channels are uniformly along the entire length of the fiber and the potential of the action is moved not to jumps, and smoothly.

SINAPS: species, structure and functions

Walder in 1891 Formulated neural theory according to which the nervous system consists of a variety of individual cells - neurons. It remained unclear the question: What is the mechanism of communication between single neurons? Cherry Sherngton in 1887. To explain the mechanism of interaction of neurons, the term "synaps" and "synaptic transmission" introduced.

Nervous impulse (lat. nervus nerve; lat. impulsus blow, push) - excitation wave propagating by nerve fiber; Unit of propagating excitation.

Nervous impulse ensures the transfer of information from receptors to nervous centers and from them to the executive bodies - skeletal muscles, smooth muscles of internal organs and vessels, glands of internal and external secretion, etc.

Complicated information about irritation on the body is encoded in the form of individual groups of nerve pulses - rows. According to the law "All or nothing" (see) amplitude and duration of individual nerve impulses passing through the same fiber, constant, and the frequency and number of nerve pulses in the row depend on the intensity of irritation. This method of transmitting information is the most interrectant, i.e., in broad limits, it does not depend on the state of the conductive fibers.

The propagation of nerve impulses is identified with the performance of the potentials (see bioelectric potentials). The occurrence of excitation can be the result of irritation (see), for example, the effect of light on the visual receptor, sound on the hearing receptor, or processes occurring in the tissues (spontaneous occurrence of N. and.). In these cases, N. and. Provide the agreed work of the organs during the flow of any physiological process (for example, in the process of breathing N. and. cause reducing skeletal muscles and diaphragms, resulting in breath and exhale, etc.).

In living organisms, the transmission of information can be carried out and humoral by emissions in the blood stream of hormones, mediators, etc. However, the advantage of information transmitted using N. and is that it is more targeted, transmitted quickly and can be More precisely coded than signals sent by a humoral system.

The fact that the nervous trunks are the way, the effects of the brain towards the muscles and in the opposite direction are transmitted, was known in the era of antiquity. In the Middle Ages and up to the middle of the 17th century. It was believed that some substance, such a liquid or flame, is applied by nerves. The idea of \u200b\u200bthe electrical nature of N. and. originated in the 18th century. The first studies of electrical phenomena in the living tissues associated with the occurrence and propagation of excitation were carried out by L. Galvani. G. Helmgoltz showed that the speed of distribution N. and., K-Rui was previously considered close to the speed of light, it has a final value and can be accurately measured. Hermann (L. Hermann) introduced the concept of action potential into the physiology. An explanation of the mechanism of occurrence and conduct of excitation has become possible after the creation of S. Arrhenius the theory of electrolytic dissociation. In accordance with this theory Bernstein (J. Bernstein) suggested that the emergence and holding of N. and. due to the movement of ions between the nervous fiber and the environment. English Researchers A. Hodgkin, B. Katz and E. Huxley investigated in detail transmembrane ionic currents underlying the development of the action potential. Later, the mechanisms of operation of ion channels were intensively studied, the ions are exchanged between the axon and the environment, and the mechanisms that ensure the ability of nerve fibers to carry out the rows of N. and. Different rhythm and duration.

N. and. It spreads at the expense of local currents arising between excited and unexcited areas of the nervous fiber. The current coming out of the fiber outside in a resting plot serves as an irritant. Coming after excitation in this section of the nervous fiber refractory causes the translational movement N. and.

Quantitatively, the ratios of different phases of the development of the action potential can be characterized by comparing them by amplitude and duration in time. So, for example, for the myelin nerve fibers of the group, a mammalian fiber diameter is in the range of 1-22 MK, the speed of carrying out - 5-120 m / s, the duration and amplitude of the high-voltage part (peak, or spike) - 0,4-0, 5 ms and 100-120 mV, respectively, trace negative potential - 12-20 ms (3-5% of the amplitude of spike), trace positive potential - 40-60 ms (0.2% of the spike amplitude).

The possibilities of transmitting a variety of information are expanded by increasing the rate of development of the potential of action, the spread rate, as well as by increasing the lability (see) - that is, the ability of excitations to reproduce high rhythms of excitation per unit of time.

Specific features of the distribution of N. and. associated with the structure of nerve fibers (see). The core of the fiber (axoplasma) has low resistance and, accordingly, good conductivity, and the plasma membrane surrounding the Axoplasum is greater resistance. Especially great electrical resistance of the outer layer in the myelinated fibers, in which they are free from the thick myelin shell only the interceptions of Ranvier. In messenger fibers N. and. Moves continuously, and in myelines - hopped (sifting).

Discern the decrement and impervious distribution of excitation wave. Decorate, i.e., the conduct of excitement with the extinction is observed in messenger fibers. In such fibers, the speed of N. and. It is small and as it removed from the place of irritation, the annoying effect of local currents gradually decreases until full of extinction. Decorative conducting characteristic of fibers innervating internal organs with low function, mobility. Without a decrementary conduct, it is characteristic of myelin and those silent fibers, which transmit signals to organs with high reactivity (eg, heart muscle). In case of reimbursement of N. and. It takes all the way from the place of irritation to the place of implementation of information without attenuation.

The maximum speed of N. and., Registered in the mammalian speed-conducting nerve fibers, is 120 m / s. High pulse velocities can be achieved due to an increase in the diameter of the nerve fiber (at messenger fibers) or by increasing the degree of myelinization. Distribution of single N. and. In itself, it does not require immediate energy costs, since at a certain level of polarization of the membrane, each section of the nervous fiber is in a state of readiness for conducting and an irritating incentive plays the role of "trigger". However, restoring the initial state of the nervous fiber and maintaining it in readiness for the new N. and. It is associated with the considerable energy of biochemical reactions occurring in the nervous fiber. Recovery processes are gaining great importance in the case of N. Rows. When conducting rhythmic excitation (pulse rows) in nerve fibers, the heat-product and oxygen consumption increases, the macro-ergic phosphates is consumed and the activity of Na is increased, the K-ATF-Ase K-Rui is identified with the sodium pump. Changing the intensity of the flow of various physicals. and biochemical processes depends on the nature of rhythmic excitation (the duration of the rows of impulses and the frequency of their follow) and the physiological state of the nerve. When carrying out a large number of N. and. In a high rhythm in nerve fibers, "Metabolic debt" can accumulate (this is reflected in the increase in total trace potentials), and then the recovery processes are delayed. But under these conditions, the ability of nerve fibers to conduct N. and. For a long time remains unchanged.

Transmission N. and. From the nervous fiber on the muscular or any other effector is carried out through synapses (see). In vertebrate animals, in the overwhelming majority of cases, the transfer of excitation to the effector occurs with the help of acetylcholine isolate (skeletal muscles neuromuscular synapses, synaptic compounds in the heart, etc.). For such synapses, it is characterized by strictly unilateral conducting pulse and the presence of a temporary delay of excitation transmission.

In synapses, in the synaptic slit of which electric current resistance due to the large area of \u200b\u200bcontacting surfaces is small, an electrical excitation transmission occurs. They do not have a synaptic delay of holding and possible bilateral conduct. Such synapses are peculiar to invertebrate animals.

Registration N. and. Found a wide application in biol, research and wedge, practice. For registration, cobweets are used and more often cathode oscilloscopes (see oscillography). With the help of microelectrode technology (see the microelectrode research method), N. is recorded. In single excitable formations - neurons and axes. Opportunities to study the mechanism of the emergence and distribution of N. and. Significantly expanded after the development of the potential fixation method. This method obtained basic data on ionic currents (see bioelectric potentials).

Violation of N. and. It occurs during damage to the nerve trunks, for example, with mechanical injuries, squeezing as a result of the expansion of the tumor or in inflammatory processes. Such violations of N. and. Often there are irreversible. The consequence of termination of innervation may be heavy functional and trophic disorders (eg, atrophy of the skeletal muscles of the limbs after the cessation of the arrival of N. and. Due to the irreversible injury of the nervous trunk). Reversible termination of N. and. may be caused specifically, for therapeutic purposes. For example, with the help of anesthetics, the impulse is blocked by painful receptors in C. n. from. Reversible termination of N. and. Causes a novocainal blockade. Temporary termination of the transfer of N. and. On nervous conductors there is also observed during general anesthesia.

Bibliography: Burzh M. A. Electric activity of the nervous system, trans. from English, M., 1979; Zhukov E. K. Essays in neuromuscular physiology, L., 1969; Connel K. Recovery processes and metabolism in Nerve, in the book: Sovar, Probl. biophysics, per. from English, ed. G. M. Frank and A. G. Pasynsky, vol. 2, p. 211, M., 1961; Sostor P. G. Physiology of the central nervous system, Kiev, 1977; Latmanizova L.V. Sketch of the physiology of excitement, M., 1972; General physiology of the nervous system, ed. P. G. Kostyka, L., 1979; Tasaki I. Nervous excitement, per. from English, M., 1971; Hodgkin A. Nervous impulse, per. from English, M., 1965; Hodorov B.I. General physiology of excitable membranes, M., 1975.

A person acts as a kind of coordinator in our body. It transmits the command from the brain musculature, organs, tissues and processes the signals coming from them. Nervous impulse is used as a kind of data media. What does he represent? How fast does it work? These, as well as a number of other issues, you can find an answer in this article.

What is a nervous impulse?

So call the excitation wave, which spreads through the fibers as an answer to irritation of neurons. Thanks to this mechanism, information transfer from various receptors to the central nervous system is ensured. And from her, in turn, to different organs (muscles and glands). And what is this process at the physiological level? The mechanism of transmission of the nervous impulse is that neuron membranes can change their electrochemical potential. And the process of interest to us is performed in the field of synapses. The speed of the nervous impulse may vary within 3 to 12 meters per second. More detailed about it, as well as about the factors that they influence it, we will still talk.

Study of structure and work

For the first time, the passage of the nerve impulse was demonstrated by German scientists by E. Goering and G. Helmholz on the example of a frog. Then it was found that the bioelectric signal applies to the previously indicated speed. In general, this is possible due to the special construction in some way they resemble the electrical cable. So, if you carry out parallels with it, then the conductors are axons, and the insulators are their myelin shells (they are a membrane of the Schwann cell, which is wound in several layers). Moreover, the velocity of the nervous pulse depends primarily from the diameter of the fibers. The second most important is the quality of electrical insulation. By the way, the organism is used by the organism a lipoproteide of myelin, which has the properties of the dielectric. All other things being equal, the more it will be the layer, the faster the nerve impulses will pass. Even at the moment it is impossible to say that this system is fully investigated. Much, which relates to nerves and impulses, still remains a mystery and subject matter.

Features of the structure and operation

If we talk about the path of the nervous impulse, it should be noted that the fiber is not covered in all its length. The composition of the construction is such that the current situation will be best compared with the creation of insulating ceramic couplings, which is tightly rods on the terminal of the electrical cable (although in this case per axon). As a result, there are small uninsulated electric sections, from which the ion current can calmly pour out the axon to the environment (or vice versa). In this case, the membrane irritates. As a result, generation is caused in sites that are not isolated. This process is called Ranvier interception. The presence of such a mechanism allows you to make the nervous impulse to spread much faster. Let's talk about this on the examples. Thus, the rate of conducting a nervous pulse in a thick myelinized fiber, the diameter of which fluctuates in 10-20 microns, is 70-120 meters per second. Whereas those who have a non-optimal structure, this figure is less than 60 times!

Where are they created?

Nervous impulses occur in neurons. The ability to create such "messages" is one of their main properties. Nervous impulse ensures the rapid spread of the same type of axon on a long distance. Therefore, this is the most important means of the body for sharing information in it. Data on irritation is transmitted by changing the frequency of their following. There is a complex period of periodicals, which can have hundreds of nerve impulses in one second. A somewhat similar principle, although a significantly complicated, computer electronics works. So, when the nerve impulses occur in neurons, then they are encoded in a certain way, and only then are already transmitted. At the same time, the information is grouped into special "packs" that have a different number and nature of the following. All this, folded together, and is the basis for the rhythmic electrical activity of our brain, which can be registered thanks to the electroencephalogram.

Types of cells

Speaking about the sequence of passing the nerve impulse, it is impossible to be bypass (neurons), for which the transmission of electrical signals occurs. So, thanks to them exchange information from various parts of our body. Depending on their structure and the functional, three types are isolated:

1. Receptor (sensitive). They are encoded and turning into nervous impulses all temperature, chemical, sound, mechanical and light stimuli.
2. Inserts (also called conductor or closure). They serve in order to process and switch pulses. Their largest number is in the human head and spinal cord.
3. Effective (motor). They receive commands from the central nervous system to ensure that certain actions were made (with a bright sun, close the eye and so on).

Each neuron has a cell body and process. The path of the nervous impulse on the body begins precisely from the last. The processes are of two types:

1. Dendriti. They are entrusted with the function of perceiving irritation of receptors located on them.
2. Axons. Thanks to them, nerve impulses are transmitted from cells to the worker.

Speaking about carrying a nervous pulse by cells, it is difficult not to tell about one interesting moment. So, when they are alone, then, let's say, the sodium-potassium pump is engaged in moving ions in such a way as to achieve the effect of fresh water inside and salty externally. Due to the imbalance gained, the difference in the membrane can be observed up to 70 Milvololt. For comparison, it is 5% of ordinary, but as soon as the cell condition changes, the resulting equilibrium is broken, and the ions begin to change places. This happens when the path of the nervous impulse passes through it. Due to the active action of ions, this action is also called the potential of action. When it reaches a definite indicator, the inverse processes begin, and the cell reaches the state of rest.

On the potential of action

Speaking about the transformation of the nervous impulse and its distribution, it should be noted that it might be a pitiful millimeters per second. Then the signals from the hand to the brain would reach the moments, which is clearly not good. Here it also plays a role in strengthening the potential of the action previously earlier shell from myelin. And all of its "skips" is placed in such a way that they only have a positive effect on the speed of signal transmission. So, when the impulse is reached the end of the main part of the axon's body, it is transmitted either the next cell, or (if we talk about the brain) with numerous neurons branches. In the last cases, there is a slightly different principle.

How does everything work in the brain?

Let's talk, what a gear sequence of the nervous impulse works in the most important parts of our CNS. Here neurons from their neighbors are separated by small slits, as they are called synapses. The action potential cannot move through them, so it is looking for a different way to get to the next nervous cell. At the end of each process there are small bags, which are called presynaptic bubbles. In each of them there are special connections - neurotransmitters. When the action potential arrives, then the molecule bags are released. They cross the synaps and join special molecular receptors that are located on the membrane. At the same time, equilibrium is disturbed and, probably, a new action potential appears. It is more reliable yet, neurophysiologists are engaged in studying the issue to this day.

The work of neurotransmitters

When they transmit nerve impulses, there are several options that will happen to them:

1. They will diffundated.
2. Subjected to chemical splitting.
3. Return back to their bubbles (this is called reverse capture).

At the end of the 20th century, a striking discovery was made. Scientists have learned that medicines that affect neurotransmitters (as well as their release and reverse seizure), may change the human mental state to a radically. So, for example, a number of antidepressants like the "Prose" block the reverse seizure of serotonin. There are certain reasons to believe that the deficiency in the brain of the neurotransmitter of dopamine is to blame for Parkinson's disease.

Now researchers who study the border states of the human psyche, try to figure out how it all affects human mind. In the meantime, we have no answer to such a fundamental question: what makes the neuron create the potential of action? While the mechanism of "launch" of this cell is a secret for us. Especially interesting from the point of view of this riddle is the work of neurons of the main brain.

If briefly, they can work with thousands of neurotransmitters that are sent by their neighbors. Details regarding the processing and integration of this type of pulses are almost not known. Although there is a lot of research groups over it. At the moment it turned out to find out that all the obtained impulses are integrated, and neuron makes a solution - whether it is necessary to maintain the potential of action and transmit them further. On this fundamental process is based on the functioning of the human brain. Well, then it is not surprising that we do not know the answer to this riddle.

Some theoretical features

The article "Nervous impulse" and "action potential" was used as synonyms. Theoretically, this is true, although in some cases it is necessary to take into account some features. So, if you go to the details, then the potential of action is only part of the nervous pulse. With detailed consideration of scientists, books can be found that only the change in the charge of the membrane with a positive to negative, and vice versa. Whereas under the nervous impulse understand the complex structural and electrochemical process. It applies to the neuron membrane as a running wave of change. The potential of action is just an electrical component in the neural impulse. It characterizes changes that occur with the charge of the local area of \u200b\u200bthe membrane.

Where are the nerve impulses create?

How do they start their journey? Answer to this question can give any student who diligently studied the physiology of excitement. There are four options:

1. Receptor ending of dendrita. If it is (which is not a fact), then the presence of an adequate stimulus is possible, which will first create the generator potential, and then the nervous impulse. In a similar way, pain receptors are working.
2. Membrane exciting synapse. As a rule, this is possible only in the presence of strong irritation or summation.
3. Dentrid's trigger zone. In this case, local exciting postsynaptic potentials are formed as an answer to the stimulus. If the first interception is myelinized, they are summed on it. Due to the presence of the membrane site there, which has increased sensitivity, a nervous impulse arises here.
4. Aksona Holmik. So call the place where Akson begins. Hollyk is the most frequent creation of pulses on neuron. In all other places, which were considered earlier, their emergence is much less likely. This is due to the fact that the membrane has increased sensitivity, as well as lowered therefore, when the summation of numerous exciting postsynaptic potentials begins, then the Holloik reacts before them.

Example of extending excitation

The story of medical terms can cause a misunderstanding of certain points. To eliminate it, it is worthwhile to go through the stated knowledge. As an example, take a fire.

Remember the reports from the news of last summer (it will also be possible to hear again). The fire applies! At the same time, trees and shrubs who are burning remain in their places. But the front of the fire goes farther from the place where the hearth is the hearth. The nervous system works in a similar way.

Often it is necessary to calm the starting the initiation of the nervous system. But it is not so easy to do, as in the case of fire. For this, artificial intervention in the work of neuron (for therapeutic purposes) or use various physiological means. This can be compared with the flood of fire with water.

The potential of action or nerve impulse, a specific reaction flowing in the form of an exciting wave and occurs throughout the nervous path. This reaction is an answer to the stimulus. The main task is to transfer data from the receptor to the nervous system, and after that it sends this information to the necessary muscles, glands and tissues. After passing the pulse, the surface part of the membrane becomes negatively charged, and its internal part remains positive. Thus, the nerve impulse is called sequentially transmitted electrical changes.

The excitation effect and its distribution is subject to physicochemical nature. Energy for carrying out this process is formed directly in the nerve itself. This is due to the fact that the passage of the impulse entails the formation of heat. As soon as he passed, silence or reference state begins. In which only a fraction of a second, the nerve cannot carry out an incentive. The speed with which the impulse can act from 3 m / s to 120 m / s.

Fibers for which excitation passes, have a specific shell. Roughly speaking, this system resembles an electrical cable. In terms of its composition, the shell can be a myelin and silent. The most important component of myelin shell is a myelin that plays the role of a dielectric.

The speed of the pulse depends on several factors, for example, from the thickness of the fiber, and it is thicker, the speed is developing faster. Another factor in increasing the rate of conduct is myelin himself. But at the same time it is not located over the entire surface, but by plots, as if rolling. Accordingly, between these sites there are those that remain "bare". There is a current leakage from Akson.

The axon is called the process, using it is provided with data transmission from one cell to the rest. This process is regulated using synapse - direct communication between neurons or neuron and cell. There is still a so-called synaptic space or gap. When the irritable impulse comes to neurons, neurotransmitters (chemical molecules) are released during the reaction. They pass through the synaptic hole, as a result, entering the neuron receptors or cells that the data should be conveyed. For the nervous impulse, calcium ions are needed, since without this, the neurotransmitter is not released.

The vegetative system is provided mainly by messenger tissues. On them, the excitement applies constantly and continuously.

The principle of transmission is based on the occurrence of the electric field, therefore the potential occurs, irritating the membrane of the neighboring area and so on all over the fiber.

At the same time, the potential of the action does not move, but appears and disappears in one place. The transfer rate of such fibers is 1-2 m / s.

Conduct laws

There are four fundamental laws in medicine:

• Anatomy-physiological value. Excited is carried out only if there is no violation in the integrity of the fiber itself. If you do not provide unity, for example, due to infringement, drug adoption, then the nervous impulse is impossible.
• Isolated irritation. The excitation can be transmitted along the nerve fiber, in any way without extinguing the adjacent one.
• Bilateral conduct. The path of the pulse can be only two species - centrifugal and centripetal. But in reality, the direction occurs in one of the options.
• Requirement. The pulses do not subside, in other words, are carried out without a decrement.

Chemistry of impulse

The process of irritation is also controlled by ions, mainly by potassium, sodium and some organic compounds. The concentration of these substances is different, the cell is charged inside the negative, and on the surface is positive. This process will be called the difference in potentials. When hesitation of a negative charge, for example, its reduction is provoked by the difference of potentials and this process is called depolarization.

Neuron irritation entails the opening of sodium channels at the place of irritation. This can contribute to the entry of positively charged particles inside the cell. Accordingly, the negative charge decreases and the action potential occurs or a nervous impulse occurs. After that, sodium channels are covered again.

It is often found that it is the weakening of polarization that contributes to the discovery of potassium channels, which provokes the release of positively charged potassium ions. This action reduces the negative charge on the cell surface.

People's potential or electrochemical state is restored when potassium-sodium pumps are included in operation, with which sodium ions come out of the cell, and potassium come into it.

As a result, it can be said - with the resumption of electrochemical processes and impulses are taking place, striving for fibers.

Candidate of Biological Sciences L. Chaylakhyan, Researcher at the Institute of Biophysics and USSR

The reader of the magazine L. Gorbunova (Tsybino village, Moscow region) writes to us: "I am interested in the mechanism, the transmission of signals on nervous, cells."

Laureates of the Nobel Prize of 1963 (from left to right): A. Khodgkin, E. Huxley, D. Eccles.

Presentations of scientists about the mechanism of transmission of the nervous impulse have undergone a substantial change recently. Until recently, Bernstein's views were dominated in science.

Man's brain, no doubt, the highest achievement of nature. In a kilogram of the nervous tissue, the quintessence of the whole person was concluded, ranging from the regulation of life functions - the work of the heart, the lungs, the digestive tract, the liver - and ending with his spiritual world. Here - our mental abilities, all our worldview, memory, mind, our self-awareness, our "I". The knowledge of the mechanisms of brain work is the knowledge of oneself.

The target is great and tempting, but the object of the study is incredibly complicated. Joke say, this kilogram of tissue is a complex communication system of tens of billions of nerve cells.

However, the first essential step towards the knowledge of the brain is already made. Maybe he is one of the lightest, but it is extremely important for everything further.

I mean the study of the mechanism of transmission of nerve impulses - signals running around the nerves, both by wire. It is these signals that are the alphabet of the brain, with which the sense authorities are sent to the central nervous system of information-dispatch about events in the external world. The nerve impulses encrypts the brain their orders to muscles and various internal organs. Finally, in the language of these signals, individual nerve cells and nervous centers speak among themselves.

Nervous cells - the main element of the brain is diverse in size, in form, but in principle, they have a single structure. Each nervous cell consists of three parts: from the body, the long nerve fiber - axon (the length of his person from several millimeters to the meter) and several short branching proceedings - dendrites. Nervous cells are isolated from each other with shells. But still cells interact with each other. It happens at the place of the cell of the cell; This joint is called Synaps. In the synapse there are axon of one nervous cell and body or dendrites of another cell. Moreover, it is interesting that the excitation can be transmitted only in one direction: from the axon to the body or dendrituit, but in no case back. Synaps is like Kenotron: it skips the signals in only one direction.

In the problem of studying the mechanism of the nervous impulse and its distribution, two main questions can be distinguished: the nature of the nerve pulse or excitation within the same cell is the fiber and the mechanism of transmitting the nerve pulse from the cell to the cell - through synapses.

What is the nature of signals transmitted from the cell to the nervous fiber cell?

This problem has been interested in this problem for a long time, Descartes assumed that the spread of the signal is associated with the transfusion of the fluid on the nerves, like on the tubes. Newton thought it was a purely mechanical process. When an electromagnetic theory appeared, scientists decided that the nerve impulse was similar to the current movement on the conductor at a speed close to the speed of the propagation of electromagnetic oscillations. Finally, the development of the biochemistry appeared point of view that the movement of the nervous pulse is the propagation along the nervous fiber of a special biochemical reaction.

And yet none of these ideas was justified.

Currently, the nature of the nervous impulse is disclosed: this is a surprisingly thin electrochemical process, which is based on the movement of ions through the cell shell.

A great contribution to the disclosure of this nature was made by the work of three scientists: Alan Hodgkin, Professor of the Biophysics of the University of Cambridge; Andrew Huxley, Professor of Physiology of the University of London, and John Eccles, Professor Physiology of the Australian University in Canberre. They awarded the Nobel Medicine Premium for 1963,

For the first time, the suggestion of the nervous impulse was expressed by the famous German physiologist Bernstein at the beginning of our century.

By the beginning of the twentieth century, it was quite aware of the nervous excitation. Scientists have already known that the nervous fiber can be excited by electric shock, and the excitement always occurs under the cathode - under the cons. It was known that the excited area of \u200b\u200bthe nerve charges negatively relative to the unexcited area. It was found that the nerve impulse at each point lasts only 0.001-0.002 seconds, which the magnitude of the excitation does not depend on the force of irritation, as the volume of the call in our apartment does not depend on how much we pressed the button. Finally, scientists found that electrical current carriers in living tissues are ions; Moreover, inside the cell of the main electrolyte - potassium salts, and in the tissue fluid - sodium salts. Inside most cells, the concentration of potassium ions is 30-50 times greater than in the blood and in the intercellular fluid, washing cell.

And on the basis of all these data, Bernstein suggested that the shell of nerve and muscle cells is a special semi-permeable membrane. It permeates only for ions to +; For all other ions, including for the negatively charged anions inside the cell, the path is closed. It is clear that potassium according to the diffusion laws will strive to get out of the cell, an excess of anions occur in the cell, and on both sides of the membrane, the difference in potentials will appear: outside - plus (excess of cations), inside - minus (excess anions). This potential difference received the name of peace potential. Thus, at rest, in an unexcited state, the inner part of the cell is always charged negatively compared with the outer solution.

Bernstein suggested that at the time of the excitation of the nervous fiber, structural changes of the surface membrane occur, its pores, as it were, increase, and it becomes permeable for all ions. At the same time, naturally, the potential difference disappears. This causes a nervous signal.

The Bernsteum membrane theory quickly won recognition and existed over 40 years, up to the middle of our century.

But at the end of the 30s the theory of Bernstein met with insurmountable contradictions. A strong blow she was inflicted in 1939 by subtle experiments of Hodgkin and Huxley. These scientists first measured the absolute values \u200b\u200bof the membrane potential of the nerve fiber at rest and when excited. It turned out that when excited, the membrane potential was not simply decreased to zero, but passed through zero to several dozen Milvololt. That is, the inner part of the fiber from the negative becomes positive.

But it is not enough to unsubstate the theory, it is necessary to replace it with another: science does not tolerate vacuum. And Hodgkin, Huxley, Katz in 1949-1953 offer a new theory. She gets the name of sodium.

Here the reader has the right to be surprised: so far there was no speech about sodium. This is all the matter. Scientists have established with the help of labeled atoms, which in the transmission of the nerve impulse not only potassium and anions, but also sodium and chlorine ions are mixed.

In the body, sodium and chlorine ions are enough, everyone knows that the blood is salty taste. Moreover, sodium in the intercellular fluid is 5-10 times greater than inside the nervous fiber.

What can this mean? Scientists suggested that when excited at the first moment, the permeability of the membrane only increases for sodium. Permeability becomes ten times more than for potassium ions. And since sodium is 5-10 more sodium than inside, it will strive to enter the nervous fiber. And then the inner part of the fiber will be positive.

And after some time - after excitement - the balance is restored: the membrane begins to pass potassium ions. And they go out. Thus, they compensate for the positive charge that was introduced inside the fiber sodium ions.

It was completely difficult to come to such ideas. And this is why: the diameter of sodium ion in the solution is one and a half more diameter of potassium and chlorine ions. And it is completely incomprehensible how larger than the Ion passes where the smaller can pass.

It was necessary to resolutely change the look at the mechanism of the transition of ions through the membranes. It is clear that only reasoning about the pores in the membrane does not do here. And then the idea was expressed that ions can cross the membrane in a completely different way, with the help of mystery to the time before the time of allies - singular organic carriers hidden in the membrane itself. With this molecule, ions can cross the membrane anywhere, and not only through the pores. Moreover, these molecules are well distinguished by their passengers, they do not confuse sodium ions with potassium ions.

Then the general picture of the spread of the nervous impulse will have the following form. In peace of carrier molecules, charged negatively, the membrane potential is pressed against the outer border of the membrane. Therefore, sodium permeability is very small: 10-20 times less than for potassium ions. Potassium can cross the membrane through the pores. When the excitation wave approaches the pressure of the electric field on the carriers molecules is reduced; They reset their electrostatic "shackles" and begin to carry sodium ions inside the cell. It further reduces the membrane potential. It goes like a chain process recharge process membrane. And this process continuously spreads along the nerve fiber.

Interestingly, nerve fibers spend on their main work - carrying out nerve impulses - only about 15 minutes a day. However, ready for this fiber at any second: all elements of the nervous fiber work without a break - 24 hours a day. Nervous fibers in this sense are similar to interceptual aircraft, which continuously work motors for instant departure, but the departure itself can take place only once a few months.

We now became acquainted with the first half of the mysterious act of passing the nerve impulse - along the same fiber. But how is the excitation from the cell to the cell, through the joints of the joints - synapses. This issue was investigated in the brilliant experiments of the Third Nobel laureate, John Eccles.

The excitation cannot directly move from the nerve endings of one cell on the body or dendritis of another cell. Virtually the entire current flows through the synaptic slit into the outer fluid, and the negative share is incapacitated to the adjacent cell through synaps, unable to cause excitation. Thus, in the field of synapses, electrical continuity in the propagation of the nervous pulse is broken. Here, at the junction of two cells, a completely different mechanism comes into force.

When the excitation comes to the termination of the cell, to the site of synapse, physiologically active substances are distinguished into the intercellular fluid - mediators, or intermediaries. They become a link in the transmission of information from the cell to the cell. The mediator chemically interacts with the second nervous cell, changes the ion permeability of its membrane - as it would break through the gap, in which many ions are rushed, including sodium ions.

So, thanks to the works of Hodgkin, Huxley and Eccles, the most important states of the nervous cell - excitation and braking - can be described in terms of ion processes, in terms of the structural-chemical rearrangements of surface membranes. Based on these works, you can already make assumptions about possible mechanisms for short-term and long-term memory, the plastic properties of the nervous tissue. However, this is a conversation about mechanisms within one or several cells. It is only a brain alphabet. Apparently, the next stage may be much more difficult - the opening of the laws on which the coordinating activity of thousands of nerve cells is being built, language recognition on which the nervous centers speak among themselves.

We are now in the knowledge of the brain's work at the level of the child, who recognized the letters of the alphabet, but does not know how to bind them into words. However, it is not far a while, when scientists with a code - elementary biochemical acts occurring in the nervous cell, read the fascinating dialogue between the nerve brain centers.

Detailed description of illustrations

Presentations of scientists about the mechanism of transmission of the nervous impulse have undergone a substantial change recently. Until recently, Bernstein's views were dominated in science. In his opinion, at rest (1), the nervous fiber is charged positively outside and negatively inside. This was due to the fact that through the pores in the wall of the fiber can be held only positively charged potassium ions (K +); Large-dimensional negatively dressed anions (A -) are forced to stay inside and create an excess of negative charges. The excitation (3) on Bernstein is reduced to the disappearance of the potential difference, which is caused by the fact that the pore size increases, the anions outward and align the ion balance: the number of positive ions becomes equal to the number of negative. The work of the Nobel Prize laureates of 1963 A. Khodjkpna, E. Huxley and D. Ecclesa changed our previous ideas. It has been proven that positive sodium ions (Na +) are also involved in the nervous excitation, negative non-chlorine (CL) and negatively charged carrier molecules. The resting state (3) is formed in principle, just as it was thought before: an excess of positive ions - outside the nervous fiber, an excess of negative - inside. However, it was established that when excited (4), no alignment of charges occur, and recharge: an excess of negative ions is formed outside, and inside is an excess of positive. It is explained by the fact that when the carrier molecule is excited, the positive sodium ions are beginning to transport through the wall. Thus, the nerve impulse (5) is moving along the fiber reloading a double electric layer. And from the cell to the cell, the excitation is transmitted by a peculiar chemical "taran" (6) - acetylcholine molecule, which helps ions break through the wall of the neighboring nerve fiber.