Article for Competition "Bio / Mol / Text": People's potential is an important phenomenon in the life of all organism cells, and it is important to know how it is formed. However, this is a complex dynamic process, difficult to perceive entirely, especially for students of junior courses (biological, medical and psychological specialties) and unprepared readers. However, when considering the points, it is quite possible to understand its basic details and stages. The work introduced the concept of resting potential and highlights the main stages of its formation using figurative metaphors, helping to understand and remember the molecular mechanisms for the formation of rest potential.

Membrane transport structures - sodium-potassium pumps - create prerequisites for the occurrence of resting potential. The prerequisites are the difference in the concentration of ions on the inner and outer sides of the cell membrane. Separately shows itself the difference in sodium concentration and the difference in concentration according to Kalia. Attempting potassium ions (K +) to align their concentration on both sides of the membrane leads to its leakage from the cell and loss with them positive electrical chargesDue to which the general negative charge of the cell internal cell surface is significantly enhanced. This "potassium" negativeness is most of the rest potential (-60 mV average), and a smaller part of it (-10 mV) is "exchange" negativity caused by the electricality of the ion exchange pump itself.

Let's deal with more.

Why do we need to know what kind of rest potential and how does it occur?

Do you know what "Animal electricity" is? Where in the body take "biotoki"? how live cell.located in an aquatic environment, can turn into an "electric battery" and why does it instantly discharge?

These questions can only be answered if you know how the cell creates the difference in electrical potentials (resting potential) on the membrane.

It is clear that for understanding how the nervous system works, it is necessary to figure out first, as its separate nervous cell - neuron works. The main thing is that the neuron is based on the movement of electrical charges through its membrane and the appearance of electric potentials on the membrane. It can be said that neuron, preparing for its nervous work, first pokes energy in electrical form, and then uses it in the process of conducting and transmitting nervous excitement.

Thus, our very first step towards studying the work of the nervous system is to understand how the electrical potential appears on the membrane of nerve cells. We will deal with this, and let's call this process. the formation of the potential of rest.

Determination of the concept of "rest potential"

Normally, when the nervous cell is in physiological peace and is ready to work, it has already had a redistribution of electrical charges between the inner and outer sides of the membrane. Due to this, an electric field arose, and electric potential appeared on the membrane - the membrane potential of rest.

Thus, the membrane turns out to be polarized. This means that it has a different electrical potential of the outer and internal surfaces. The difference between these potentials is possible to register.

This can be verified if you enter the microelectrod cell inside, connected to the registering installation. As soon as the electrode falls inside the cell, it instantly acquires some permanent electronegative potential with respect to the electrode located in the surrounding fluid cell. The magnitude of the intracellular electric potential at nerve cells and fibers, for example, giant squid nerve fibers, at rest is about -70 mV. This magnitude is called the diaphragm potential of peace (MPP). At all points of axoplasm, this potential is almost the same.

Nostdrachev A.D. and others. The start of physiology.

Some more physics. Macroscopic physical bodies are usually electrically neutral, i.e. They are in equal amounts are contained both positive and negative charges. You can charge the body by creating an excess of charged particles of one species in it, for example, friction about another body, in which the excess of the opposite type charges is formed. Considering the presence of an elementary charge ( e.), full electrical charge of any body can be represented as q. \u003d ± N × e.where n is an integer.

Potential rest - This is the difference in the electrical potentials existing on the inner and outer sides of the membrane, when the cell is in a state of physiological rest. Its value is measured from the inside of the cell, it is negative and is an average -70 MV (Milvolt), although in different cells may be different: from -35 mV to -90 mV.

It is important to take into account that in nervous system Electrical charges are not shown by electrons, as in conventional metal wires, but by ions - chemical particles having an electric charge. And in general in aqueous solutions electric current Not electrons move, but ions. Therefore, all electrical currents in cells and the environment surrounding them are ion Toki..

So, from the inside the cell is charged negatively, and the outside is positive. It is characteristic of all living cells, except, except, red blood cells, which, on the contrary, are charged negatively outside. To speak more specifically, it turns out that positive ions (Na + and K + cations) will prevail around the cell, and inside negative ions (organic acid anions that are not able to move freely through the membrane as Na + and K +).

Now we have just left to explain how it all turned out exactly that way. Although, of course, it is unpleasant to realize that all our cells besides erythrocytes only look positive outside, and inside they are negative.

The term "negativeness", which we will be used to characterize the electric potential inside the cell, will be useful for us for simplicity of explaining changes in the level of rest potential. In this term, it is valuable that the following is intuitive: the more negativity inside the cell - the lower in negative side The potential is shifted from zero, and the less negativeness - the closer the negative potential to zero. This is much easier to understand what the expression "potential increases is exactly what it means - an increase in the absolute value (or" module ") will mean the offset of the rest potential down from zero, and simply" increasing "- potential displacement up to zero. The term "negativeness" does not create such problems of ambiguity of understanding.

The essence of the formation of rest potential

Let's try to figure out where the electrical charge of nerve cells is taken from, although nobody rubs them, as physicists do in their experiments with electric charges.

Here the researcher and the student waits one of the logical traps: the internal negativity of the cell occurs not due to advent of unnecessary negative particles (anions), but, on the contrary, due to losses of some number of positive particles (Cations)!

So where are positively charged particles from the cage? Let me remind you that it has left the cell and the sodium ions accumulated outside the outside - Na + - and potassium - K +.

The main secret of the appearance of negativity inside the cell

We will immediately open this secret and say that the cell is deprived of parts of its positive particles and is charged negatively due to two processes:

1. at first, she exchanges "his" sodium on "someone else's" potassium (yes, one positive ions on the other, the same positive);
2. then the leakage of these "impatient" positive potassium ions occurs, together with which the positive charges are dried out of the cell.

These two processes we need to explain.

The first stage of creating an internal negativity: exchange Na + on K +

In the membrane of the nervous cell constantly work protein exchanges pumps(adenosyntriphosphatase, or Na + / k + -atphase) embedded in the membrane. They change the "own" sodium cells on the outdoor "alien" potassium.

But after all, when exchanging one positive charge (Na +), there is no deficiency of positive charges in the cell to occur on another positive charge (K +)! Right. But, nevertheless, because of this, there is very little sodium ions in the cell, because they almost all left out. And at the same time, the cell is overwhelmed with potassium ions, which molecular pumps were pumped into it. If we could try to taste the cytoplasm of the cell, we would notice that as a result of the operation of exchange pumps, it turned out of salty in bitter-salty, because sodium chloride solid taste was replaced by a difficult taste of a concentrated solution of potassium chloride. In the cell, potassium concentration reaches 0.4 mol / l. Solutions of potassium chloride in the range of 0.009-0.02 mol / l have a sweet taste, 0.03-0.04 - bitter, 0.05-0.1 - bitter and salty, and starting from 0.2 and higher - a complex taste consisting of salty, bitter and sour.

Important here is that sodium exchange for potassium - unequal. For every cell three sodium ions She gets everything two potassium ions. This leads to a loss of one positive charge with each ion exchange act. So already at this stage due to an unequal exchange of the cell loses more "pluses" than it receives in return. In electrical terms, this is approximately -10 mV of negativity inside the cell. (But remember that we still need to find an explanation for the remaining -60 MV!)

To make it easier to remember the work of exchange pumps, it is figuratively to be expressed as follows: "The cell loves potassium!"Therefore, the cell also lines potassium to himself, despite the fact that it is full of it. And so it disadvantageously shares it on sodium, giving 3 sodium ions for 2 potassium ions. And so she spends on this exchange energy ATP. And how does it spend! Up to 70% of all neuron energy consumption can go to the work of sodium-potassium pumps. (That's what love does, let her even do not real!)

By the way, it is interesting that the cell is not born with the finished potential of rest. She still needs to be created. For example, when differentiating and merging myoblasts, the potential of their membrane varies from -10 to -70 mV, i.e. Their membrane becomes more negative - polarizes in the differentiation process. And in experiments on multipotent mesenchymal stromal bone marrow cells, artificial depolarization, opposing the resting potential and reducing cell negativeness, even inhibited (oppressed) cell differentiation.

Figuratively speaking, it can be expressed like this: creating the potential of peace, the cell "charges with love." This is love for two things:

1. love cells to potassium (therefore the cell is forcibly shutting it to him);
2. love potassium to freedom (therefore, potassium leaves the captured cell).

We have already explained the saturation mechanism of cage cells (this is the work of exchangeback pumps), and the mechanism of potassium care from the cell is explained below when we turn to the description of the second stage of creating intracellular negativity. So, the result of the activities of membrane ion exchange pumps at the first stage of the formation of the potential of peace is:

1. Sodium deficiency (Na +) in the cell.
2. Excess potassium (K +) in the cell.
3. The appearance on the membrane of a weak electric potential (-10 mV).

It can be said: at the first stage, the membrane ionic pumps create the difference of ion concentrations, or a gradient (differential) of the concentration, between the intracellular and extracellular medium.

The second stage of creating a negativity: leakage of k + ions from the cell

So, what starts in a cage after the membrane sodium-potassium exchange pumps work with ions?

Because of the sodium deficit inside the cell, this ion is tormented at each other case. to rush into: Dissolved substances always tend to align their concentration in the entire volume of the solution. But this sodium turns out badly, since ion sodium channels are usually closed and open only under certain conditions: under the influence of special substances (transmitters) or with a decrease in negativity in the cell (membrane depolarization).

At the same time, the cell has an excess of potassium ions compared to the outer medium - because the membrane pumps forcibly pumped into a cage. And he, too, striving to equalize its concentration inside and outside, strives, on the contrary, exit the cage. And it turns out!

Potassium ions K + leave the cell under the action of a chemical gradient of their concentration on different sides Membranes (membrane is much more permeable for k + than for Na +) and carry positive charges with them. Because of this, negativity increases inside the cell.

It is still important to understand what sodium and potassium ions are "do not notice" each other, they react only "on themselves." Those. Sodium reacts to sodium concentration, but "does not pay attention" to how many potassium around. Conversely, potassium reacts only to the concentration of potassium and "doesn't notice" sodium. It turns out that to understand the behavior of ions, it is necessary separately to consider the concentrations of sodium and potassium ions. Those. It is necessary to separately compare the sodium concentration inside and outside the cell and separately - the concentration according to potassium inside and outside the cell, but it does not make sense to compare sodium with potassium, as it happens, is done in textbooks.

According to the law of alignment of chemical concentrations, which acts in solutions, sodium "wants" from the outside to enter the cell; There is also an electric force in the same way (as we remember, the cytoplasm is negatively charged). Hoothing he wants, but can not, since the membrane in the usual state misses it. Sodium ion channels available in the membrane are normal. If he still comes in a little bit, the cell immediately exchanges it on the outdoor potassium with the help of its sodium-potassium exchange pumps. It turns out that sodium ions pass through the cage as if transit and do not delay in it. Therefore, sodium in neurons is always shortage.

But Potassium just can easily leave the cell outside! It is fully in the cage, and she can't hold it. It goes out through special channels in the membrane - "potassium leakage channels", which are normally open and produce potassium.

K + leak-channels are constantly open at normal regimens of the membrane restacity of peace and exhibit explosives of activity during the shears of the membrane potential, which lasts a few minutes and are observed with all potential values. The reinforcement of K + -OPs leaks leads to hyperpolarization of the membrane, while their suppression is to depolarization. ... However, the existence of a channel mechanism responsible for leakage currents for a long time remained. Only now it became clear that the potassium leakage is a current through special potassium channels.

Zephyrov A.L. and Sitdikova G.F. Ion channels excitable cells (structure, function, pathology).

From chemical - to electric

And now - once again the most important thing. We must consciously move from movement chemical particles To movement electrical charges.

Potassium (K +) is positively charged, and therefore he, when it comes out of the cage, makes out of it not only himself, but also a positive charge. Behind him, from the inside the cells to the membrane stretch "minuses" - negative charges. But they cannot leak through the membrane - unlike potassium ions - because For them there are no suitable ion channels, and the membrane does not miss them. Remember the remaining -60 MV of negativity that remains -60. This is the most part of the membrane rest potential, which is created by the leak of potassium ions from the cell! And this is most of the potential of rest.

For this component part of the rest potential there is even a special name - the concentration potential. Concentration potential - This is part of the rest potential, created by a shortage of positive charges inside the cell, formed by leakage from her positive potassium ions.

Well, now some physicists, chemistry and mathematics for accuracy lovers.

Electrical forces are associated with chemicals according to the Goldman equation. Its special case is a simpler nerve equation, by which the formula of which can calculate the transmembrane diffusion difference of potentials based on different concentrations of the ions of one species on different sides of the membrane. So, knowing the concentration of potassium ions outside and inside the cell, you can calculate the potassium equilibrium potential E. K:

where E.k - equilibrium potential R. - Gas constant, T. - absolute temperature, F. - Permanent Faraday, K + external and k + internal ion concentrations to + outside and inside the cell, respectively. According to the formula, it is clear that the concentration of ions of one species is compared to calculate the potential - K +.

A more accurate final value of the total diffusion potential, which is created by the leakage of several types of ions, is calculated using the Goldman-Hodgkin-Katza formula. It takes into account that the care potential depends on the three factors: (1) the polarity of the electrical charge of each ion; (2) membrane permeability R for each ion; (3) [concentrations of the corresponding ions] inside (internal) and outside the membrane (external). For the Diambrane A axon squid alone R K: PNA :P. CL \u003d 1: 0.04: 0.45.

Conclusion

So, the sweat of the rest nial consists of two parts:

1. -10 MVthat are obtained from the "asymmetric" work of the membrane exchange rate of the exchanger (after all, it pumps out the positive charges from the cell (Na +) than he downloads back with potassium).
2. The second part is all the time dried out potassium cells, carrying positive charges. His contribution - the main: -60 MV.. In sum, it gives the desired -70 mV.

What is interesting, potassium will cease to leave the cell (more precisely, its input and yield is equalized) only at the level of negativeness of the cell -90 mV. In this case, chemical and electrical powers that push potassium through the membrane, but guides it in opposite sides. But this interferes constantly leaking in the cell sodium, which brings with it positive charges and reduces the negativeness for which potassium fights. And as a result, the cell maintains an equilibrium state at -70 mV.

Now the recreation potential of rest is finally formed.

Scheme of work Na + / k + -atphase Visually illustrates the "asymmetric" exchange of Na + on k +: the pumping out of the excessive "plus" in each cycle of the enzyme work leads to a negative charge of the inner surface of the membrane. What is not said in this video, so this is the fact that the ATPAZ is responsible for less than 20% of the rest potential (-10 mV): the remaining "negativeness" (-60 MV) appears due to the exit of the cell through the "Kaliya Diver Channels" of the K + seeking to align their concentration inside the cell and outside it.

Literature

1. Jacqueline Fischer-Lougheed, Jian-Hui Liu, Estelle Espinos, David Mordasini, Charles R. Bader, ET. Al .. (2001). Human Myoblast Fusion Requires Expression of Functional Inward Rectifier Kir2.1 Channels. J Cell Biol.. 153 , 677-686;
2. Liu J.h., Bijlenga P., Fischer-Lougheed J. et al. (1998). Role of An Inward Rectifier K + Current and of Hyperpolarization in Human Myoblast Fusion. J. Physiol. 510 , 467–476;
3. Sarah Sundelacruz, Michael Levin, David L. Kaplan. (2008). Membrane Potential Controls Adipogenic and Osteogenic Differentiation of Mesenchymal Stem Cells. PLOS ONE. 3 , E3737;
4. Pavlovskaya M.V. and Mamyakin A.I. Electrostatics. Dielectrics and conductors in the electric field. Permanent current / Electronic manual According to the general course of physics. St. Petersburg: St. Petersburg State Electrotechnical University;
5. Nosdraachev A.D., Bazhenov Yu.I., Barannikova I.A., Batuev A.S. and others. Start physiology: Textbook for universities / ed. Acad. HELL. Nostrhachev. St. Petersburg: Lan, 2001. - 1088 p.;
6. Makarov A.M. and Luneva L.A. Basics of electromagnetism / physics in technical University. T. 3;
7. Zephyrov A.L. and Sitdikova G.F. Ion channels excitable cells (structure, function, pathology). Kazan: Art Cafe, 2010. - 271 p.;
8. Motherland T.G. Sensory analysis of food products. Tutorial for students of universities. M.: Academy, 2004. - 208 p.;
9. Colman Ya. And Rem K.-g. Visual biochemistry. M.: Mir, 2004. - 469 p.;
10. Schulgovsky V.V. Basics of neurophysiology: Tutorial for university students. M.: Aspect Press, 2000. - 277 s ..

Any live cell is covered with a semipermeable membrane through which passive movement is carried out and active electoral transport of positive and negatively charged ions. Due to this transfer between the outer and the inner surface of the membrane, there is a difference in electrical charges (potentials) - membrane potential. There are three different manifestations of membrane potential - membrane Potential Peace, Local Potential, or local answer, I. action potential.

If there are no external stimuli on the cage, the membrane potential is long saved constant. The membrane potential of such a resting cell is called the membrane potential of rest. For the outer surface of the cell membrane, the potential of rest is always positive, and for the inner surface of the cell membrane is always negative. It is customary to measure the potential of rest on the inner surface of the membrane, because The ion composition of cytoplasm cells is more stable than the intercellular fluid. The quantity of rest potential is relatively constant for each cell type. For transverse muscle cells, it ranges from -50 to -90 mV, and for nerve cells from -50 to -80 mV.

The causes of the occurrence of resting potential are different concentration of cations and anions outside and inside the cell as well electoral permeability For them, cell membrane. The cytoplasm of the resting nervous and muscular cell contains about 30-50 times more potassium cations, 5-15 times less sodium cations and 10-50 times less chlorine anions than extracellular liquid.

At rest, almost all sodium cells of the cell membrane are closed, and most potassium channels are open. Whenever potassium ions are running onto an open channel, they pass through the membrane. Since potassium ion cells are much larger, the osmotic force pushes them out of the cell. Potassium cations increased a positive charge on the outer surface of the cell membrane. As a result of the output of potassium ions from the cell, their concentration inside and out of the cell would soon be equal. However, this prevents the electrical force repulsion of positive potassium ions from a positively charged outer surface of the membrane.

The more the value of a positive charge on the outer surface of the membrane becomes, the more difficult to go from cytoplasm through the membrane. Potassium ions will leave the cell until the electric repulsion force becomes equal to the power of osmotic pressure to +. With this level of potential on the membrane, the entry and output of potassium ions from the cell are in equilibrium, so the electric charge on the membrane is called at that moment kalive equilibrium potential. For neurons, it is equal to -80 to -90 mV.

Since almost all sodium membrane sodium channels are closed, then NA + ions come into a cell at a concentration gradient in minor quantities. They only reimburse the loss of a positive charge of the inner medium of the cell caused by the output of potassium ions, but cannot significantly compensate for this loss. Therefore, penetration into the cell (leakage) of sodium ions leads only to a minor reduction in the membrane potential, as a result of which the recreation potential of rest has a slightly smaller value compared with the potassium equilibrium potential.

Thus, the cations of potassium cations together with the excess of sodium cations in the extracellular fluid create a positive potential on the outer surface of the diaphragm of the resting cell.

In a state of rest, the plasma membrane cell is well permeable for chlorine anions. Chlorine anions, which are larger in extracellular fluid, diffuse inside the cell and carry a negative charge with them. The complete equalization of the concentrations of chlorine ions outside and inside the cell does not occur, because This prevents the power of the electric mutual repulsion of the same names. Created chlorine equilibrium potential In which the entrance of chlorine ions into the cell and their output from it is equilibrium.

The cell membrane is practically impermeable for large anions of organic acids. Therefore, they remain in the cytoplasm and together with incoming chlorine anions provide a negative potential on the inner surface of the membrane of the resting nervous cell.

The most important meaning of the membrane rest potential is that it creates an electric field that affects the macromolecules of the membrane and gives them to the charged groups a certain position in space. It is especially important that this electric field determines the closed state of the activation gate of sodium channels and the open state of their inactivational gates (Fig. 61, a). This ensures the condition of the cage and its readiness to excitement. Even a relatively small decrease in the dying potential of rest opens the activation "gate" of sodium channels, which displays a cell from the state of rest and gives rise to excitation.

To signal from the preceding cell to the subsequent, neuron generates electrical signals within itself. Your movements with your eyes when reading this paragraph, the feeling of a soft chair under the booty, the perception of music from headphones and much more are based on the fact that hundreds of billions of electrical signals pass within you. Such a signal may be born in the spinal cord and go to the tip of the finger on the long axon. Or it can overcome a negligible distance in the depths of the brain, limited to the limits of an interneyrone with short processes. Any neuron that received a signal runs it through its body and grow out, and this signal has an electric nature.

Back in 1859, scientists were able to measure the speed with which these electrical signals are transmitted. It turned out that electricity transmitted by the living axon is fundamentally different from electric current in metals. By metallic wire, the electrical signal is transmitted at a speed close to the speed of light (300,000 kilometers per second), because in the metal there are many free electrons. However, despite this speed, the signal relatively weakens, overcoming long distances. If on acesons, the signals were transmitted in the same way that were transmitted in metals, then the nervous impulse, which comes from the nervous end in the skin of the thumb of your foot, would completely fucked, without reaching your brain - the electrical resistance of the organic matter is too large, and the signal is too weak .

Studies have shown that electricity is transmitted on axons much slower than on the wires, and that at the heart of this transmission lies an unknown mechanism earlier, as a result of which the signal applies at a speed of about 30 meters per second. Electrical signals running around the nerves, in contrast to signals going on wires, do not weaken along their movement. The reason for this is that the nerve endings do not pass through themselves the signal passively, simply allowing the charged particles available in them to transmit it to each other. They are in each of its point the active emitter of this signal, relaying it, and detailed description This mechanism will require a separate chapter. Thus, sacrificing the high speed of nerve impulses, due to the active transmission of the neuron signal, it receives a guarantee that big finger Legs signal will reach the spinal cord, not at all weakening.

To observe the passage of an electrical excitation wave, or action potential (action Potential ['ækʃʃn Pə'Tenʃʃl]), in a living cage, a fairly simple device: one end of a thin metal wire is placed on the outer surface of the axon of the touch neuron of the skin, and the other is supplied to the recorder, drawing line up when the signal is gained, and down when weakening. Each touch of leather causes one or several potentials of action. If each potential occurs, the recorder draws a narrow long peak.

The potential of the action of the sensory neuron lasts only about 0.001 seconds and includes two phases: rapid increases, reaching peak, and then almost as quick decay of the excitation leading to the original position. And then the recorder informs an unexpected fact: all the potentials of actions arising in the same nervous cell are about the same. It can be seen in the picture on the left: all the peaks drawn by the recorder have about the same shape and amplitude, regardless of how strong or long there was a touch to the skin, which caused them. Weak stroking or tangible plugs will be transferred by the potentials of the action of the same value. The action potential is a permanent signal, subject to the "All or Nothing" principle: after exceeding the irritant of a certain threshold value, it always occurs about the same signal, not more and not less than usual. And if the stimulus is less than the threshold value, the signal will not be transmitted at all: for example, you can so easily touch the skin of the pen with the tip, that this touch will not be felt.

The principle of "all or nothing" in the occurrence of the action potential causes new questions. How Touch Neuron reports the strength of the stimulus - strong or weak pressure, bright or low light? How does he report the duration of the irritant? Finally, how neurons are distinguished by one type of sensory information from the other - for example, how do they distinguish touch from pain, light, smell or sound? And how do they distinguish sensory information to perceive from motor information for action?

Evolution solved the question of how to report the strength of the stimulus, using the use of the same type of signals of the same value: this force is determined frequency (Frequency ['friːkwənsɪ]), with which the potentials of the action are emitted. Weak stimulus, for example, a slight touch towards hand, leads to the emission of only two or three potentials of action per second, while strong pressure, as when a pinch or shock is shred, can cause a queue of hundreds of potentials per second. In this case, the duration of the sensation is determined by the duration of the occurrence of the potentials of action.

Are the neurons of different electrical codes, telling the brain, which carry information about different stimuli, such as pain, light or sound? It turned out that there is no! This is surprising, but between the potentials of the action generated by neurons from various sensory systems (for example, visual or tactile), the difference is very insignificant! Thus, the nature and nature of the sensation does not depend on the differences in the potentials of the action (which opens a rather exciting perspective to reflect on the "matrix" theme from the film of the same name). Neuron, transmitting auditory information, is arranged in the same way as the neuron from the visual nervous chain, and they are spent the same action potentials, in the same way. Without knowledge, some nervous chain owns a specific neuron, it is not possible to determine which information it carries.

The nature of the transmitted information depends primarily on the type of nerve fibers and the specific brain systems with which these fibers are connected. The sensations of each type are transmitted according to their conductive paths, and the type of information transmitted by neuron is depends on the path, which includes this neuron. In any sensory carrying path, the information is transmitted from the first sensory neuron (the receptor reacting to the external stimulus, such as touch, smell or light) to specialized neurons in the dorsal or brain. Thus, visual information differs from the auditory only by what is transmitted by other conductive paths beginning in the retina of the eye and ending in the brain area, which is responsible for visual perception.

The signals sent from the motor neurons of the brain to the muscles are also almost identical to the sensory neurons from the skin into the brain. They obey the same principle of "all or nothing", also transmit the signal intensity using the frequency of action potentials, and also the result of the signal depends only on which neuron is included in which neuro chain. Thus, a quick series of potentials of action, which runs on a specific conductive path, causes the movement of your fingers, and not, say, the perception of multi-colored lights, only because this path is associated with the muscles of the hands, and not with the retina.

The versatility of the potentials of action is not limited to the similarity of their manifestations in different neurons located within one organism. They are so the same among different animals that even a wise experience researcher is not able to accurately distinguish the recording of the potential of the nervous fiber of China, mouse, monkey or it scientific leader. Nevertheless, the potentials of the action in different cells are not identical: a small difference in their amplitude and duration is still there, and the approval "all potentials of action is as inaccurately, as well as" all bougainvilleans are the same. "

So, each neuron transmits a signal through its body and the process in the same way. All variety of information we receive from sensory neurons, all movements that can make our body is the result of the transmission of a single type of signals within neurons. Lost "trifle": understand what is the signal and how it is transmitted.

We are familiar to all that we consider living nature, including yourself, from "non-living" things, including metal and transmitting electric currents. The more surprising to realize that in our bodies the metals are not simply present - they are needed, without them the body will not be able to exist. Electric current - a phenomenon is not one-time, but continuously arising in a hundred billion of neurons that have penetrated by their processes all our body. Right now you can experience a variety of signs of his presence: the fact that you realize this text is the result of countless electric current gears. The feeling of hunger and the pleasure of the smell of preparing food, the perception of this smell, the touch of a wind flush into your skin ... can be listed infinitely. And the desire to understand how it all occurs, also consists of electrical pulses arising in neurons.

Since the purpose of this chapter is the message of only the most general information on the passage of the nervous impulse, here it is also necessary to consider the environment in which it arises, those conditions in the cell that make it possible to occur and transmit. Therefore, it is worth starting with the study of a bridgehead, on which events will develop, namely from Neron condition of rest (dORMANT STATE ['Dɔːmənt Steɪt]).

Back in the middle of the last century, scientists have found a way to establish in which part of the neuron there is an electric charge. For this use voltmeter (voltmeter ['vəultˌmiːtə]) (voltage measurement device electric field) With two electrodes. One electrode is placed inside the neuron, having it close to the cell membrane, and the second electrode is in the environment of the neuron, on the other side of the same membrane. Voltmeter shows that from different sides of the cell membrane exist electric charges, negative inside the cell and positive outside. The existence of such diverse electrical charges on both sides of the membrane creates an electric field, which is an important characteristic of which is potential. Potential, speaking by a simple language, this is the ability to work, for example, work on dragging the charged particle from place to place. The more negative charges accumulated on one side, and the more positive - on the other side of the membrane, the stronger the electric field created by them, and the more powerful particles are capable of dragging there. The difference between external and internal electrical charges is called membrane potential (membrane Potential ['Membreɪn Pə'Tenʃʃl]) rest. For neuron, it is approximately 70 mV (Milvolt), that is, 70 thousand volts or seven hundredths of Volta. For comparison, the potential difference in AA battery is 1.5 volts - 20 times more. That is, the membrane potential of the neuron rest is only 20 times weaker than between the AA battery terminals - quite large, it turns out. Electric potential exists only on the membrane, and in the other parts of the neuron neutron neutron.

If you write more accurately, the membrane potential of neuron's rest is -70 MV (minus seventy Millivolt). The minus sign means only the negative charge is precisely inside the cell, and not outside, and thus the generated electric field is capable of dragging through the membrane inside the cell positively charged ions.

Acting persons in the creation of the MEMBRAN POTENTIAL OF OCHOY:

1 . IN cell membrane Neuron There are channels for which the air charges can travel through it. At the same time, the membrane is not only a passive "partition" between the inner medium of the neuron and the surrounding fluid: special proteins embedded in the membrane flesh open and close these channels, and thus the membrane controls the passage of ions of atoms that have an electrical charge. Accumulating negatively charged ions inside the cell, neuron increases the number of negative charges inside, thereby leading to an increase in positive charges outside, and thus electric potential increases. Since the proton has a positive charge, and the electoral electron is obtained, then with an excess of protons, a positively charged ion is obtained, and with an excess of electrons - negatively charged. If you want more detailed information about atoms and ions, you can return to. It is important to understand that the membrane potential exists on the boundary of the cell membrane, and the fluids are generally inside and outside the neuron remain electrically neutral. The ions for which the membrane permeates remain near it, since positive and negative charges are mutually attracted to each other. As a result, the membrane is formed by a layer of "sitting" on it positive ions, and inside - negative. Thus, the membrane plays the role of an electric container separating charges, inside which has an electric field. Membrane, therefore, is a natural capacitor.

2 . negatively charged proteinsInside the neuron near the inner surface of the membrane. The Protein charge always remains the same and is only part of the total charge of the inner surface of the membrane. Unlike ions, proteins cannot leave the cell and enter it - for this they are too big. The general charge varies depending on the number of positively charged ions located near the membrane, the concentration of which may vary through their transition from the cell outside, and from the outside.

3 . Positively charged potassium ions (K +) can move freely between the inner and external environment when the neuron is at rest. They move through constantly open flowing potassium canals (flow Potassium Passage.) Through which only ions K + can pass, and nothing else. The flowable channels that do not have a gate are called, which means open with any state of the neuron. Inside potassium ions is much larger than outside. This happens due to the permanent work of the sodium-potassium pump (it will be described below), so in the state of the neuron of ions K + begin to move into an external environment, since the concentration of the same substance seeks to align in the general system. If we are in the pool with water in one corner of some substance, then its concentration in this corner will be very large, and in other parts of the pool - zero or very small. However, after some time, we find that the concentration of this substance was leveled throughout the basin at the expense of Brownian movement. In this case, they talk about "partial pressure" of a substance, whether it is liquid or gas. If alcohol will be poured in one corner of the pool, then a big difference is formed at the alcohol concentration between this angle and the rest of the pool. The partial pressure of alcohol molecules will occur, and they will gradually distribute evenly through the pool so that partial pressure will disappear, since the concentration of alcohol molecules is leveled everywhere. Thus, ions K + carry a positive charge from the neuron, leaving the outside by partial pressure, which is stronger than the strength of attraction of negatively charged proteins, if the difference in the concentration of ions inside and outside the cell is large enough. Since negatively charged proteins remain inside, thus, a negative charge is formed on the inside of the membrane. For a clear understanding of the work of cellular mechanisms, it is important to remember that despite the permanent flow of potassium ions from the cell, they are always greater inside the neuron than outside.

4 . Positively charged sodium ions (Na +) are located on the outside of the membrane and create a positive charge there. During the Phase of Niron Sodium Channels Cells closed, and Na + can not go inside, and their concentration outside increases due to the work of the sodium-potassium pump, outlining them from the neuron.

5 . The role is negatively charged chlorine ions (Cl -) and positively charged calcium ions (CA 2+) To create a membrane potential is small, so their behavior will remain behind the scenes.

Formation of the diaphragmal potential of rest Passes in two stages:

Stage I.. A small (-10 mV) is created) the difference of potentials with sodium-potassium pump.

Unlike other channels of the membrane, the sodium-potassium canal is able to pass through itself and sodium ions, and potassium ions. And Na + can only pass through it from the cell outside, and to + outside inside. One cycle of this channel is included in 4 steps:

1 . The "gate" of the sodium-potassium channel is open only from the inside of the membrane, and 3 Na + go there

2 . The presence of Na + inside the channel affects it so that it can partially destroy one molecule ATF (ATP) ( adenosineRithosphate), (aDENOSINE TRIPHOSPHATE [ə'dɛnəsiːn trai'fɔsfeɪt]) A "battery" cells, stocking energy and give it if necessary. With such a partial destruction, which consists in cleaving from the end of the molecule of one phosphate group PO 4 3-, the energy is distinguished, which is just spent on the transfer of Na + to the external space.

3 . When the channel opens in order for Na + to outward, it remains open, and two ions fall into + - negative chargers of proteins from the inside are attracted. The fact that in the channel that contains three sodium ions is placed only two potassium ions, it is quite logical: potassium atom has a larger diameter.

4 . The presence of potassium ions now, in turn, affects the channel so that the external "gate" is closed, and the internal opens, and K + come into the inner medium of the neuron.

Thus, the sodium-potassium pump, "exchanging" three sodium ions into two potassium ions. Since the electrical charge in Na + and K + is the same, it turns out that three positive charges are derived from the cell, and only two falls inside. Due to this, the internal positive charge of the cell membrane is reduced, and external - increases. In addition, the difference is created at the concentration of Na + and K + along different sides of the membrane:

\u003d) Outside the cells are many sodium ions, and inside - little. At the same time, sodium channels are closed, and it cannot get back into the Na + cell, and it does not leave the membrane, as it is attracted by the membrane existing on the inside.

\u003d) There are a lot of potassium ions inside the cell, but there are few of them outside, and this leads to the flow of K + from the cellular channels open during the maintenance phase of the neuron.

Stage II. The formation of the diaphragmal potential of peace is just based on this flowing of potassium ions from neuron. The figure below shows the ion composition of the membrane at the beginning of the second stage of the formation of the rest potential: the set of K + and adversely charged proteins (designated a 4-) inside, and the membrane seeded outside Na +. Moving to the external environment, potassium ions are carrying their positive charges from the cell, while the total charge of the inner membrane is reduced. Just as the positive sodium ions, flowing out of the cells of potassium ions remain outside the membrane attracted by an internal negative charge, and an external positive charge of the membrane folds from the amount of charges Na + and K +. Despite the flowing channels through the flow channels, there are always more inside the cells of potassium ions than outside.

The question arises: why potassium ions do not continue to flow out until the amount of their amount inside the cell and outside it becomes the same, that is, until the partial pressure created by these ions disappears? The reason for this lies in the fact that when the cell leaves, the positive charge is increasing outside, and an excess of negative charge is formed inside. This reduces the desire of potassium ions to leave the cell, because the outdoor positive charge pushes them, and the inner negative attracts. Therefore, after a while, K + cease to flow, despite the fact that in the external environment, their concentration is lower than in the inner: the influence of charges on different sides of the membrane exceeds the force of partial pressure, that is, exceeds the desire to + distribute uniform in the liquid inside and out Neuron. At the time of this equilibrium, the membrane potential of the neuron and stops about -70 mV.

As soon as the neuron is achieved by the membrane potential of peace, it is ready for the emergence and conduct of the potential of action, which will be discussed in the next cytological chapter.

Thus, summarize: The uneven distribution of potassium and sodium ion distribution on both sides of the membrane is caused by the action of two rival forces: a) by the power of electric attraction and repulsion, and b) by the force of partial pressure arising from the difference in concentrations. The work of these two rival forces proceeds in the conditions of the existence of differently arranged sodium, potassium and sodium-potassium channels, which act as regulators of the action of these forces. The potassium channel is flowing, that is, it is always open at the rest of the neuron, so the ions K + can quietly walk there and here under the influence of the power of the electric repulsion / attraction and under the influence of force caused by partial pressure, that is, the difference in the concentration of these ions. The sodium channel is always closed in a state of rest of the neuron, so that the Na + ions can not walk through them. And finally, the sodium-potassium canal arranged in such a way that it works as a pump, which, with each cycle, he catches three sodium ions outward, and pens two potassium ions inside.

All this design and ensures the occurrence of the membrane potential of the neuron rest: i.e. The states at which two things are achieved:

a) inside there is a negative charge, and outside - positive.

b) inside a lot of ions K +, shuffled negatively charged parts of proteins, and thus the potassium partial pressure occurs - the desire of potassium ions to exit to align the concentration.

c) Outside a lot of Na + ions that form partly a pair with CL ions. And thus sodium partial pressure occurs - the desire of sodium ions enter inside the cell to align the concentration.

As a result of the work of the potassium-sodium pump, we get three forces that exist on the membrane: the power of the electric field and the strength of two partial pressures. These forces and begin to work when neuron leaves the state of rest.

History opening

In 1902, Julius Bernstein highlighted the hypothesis, according to which the cell membrane passes inside the ions cells to +, and they accumulate in the cytoplasm. The calculation of the magnitude of the care potential according to the Nernst equation for the potential electrode satisfactorily coincided with the measured potential between the sarcoplasma muscle and environmentalwhich was about 70 mV.

According to Y. Bernstein theory, when the cell is excited, its membrane is damaged, and ions K + leak out of the cell at a concentration gradient until the membrane potential becomes equal to zero. The membrane then restores its integrity, and the potential returns to the level of rest potential. This statement relating rather to the potential of action was refuted by Hodgkin and Huxley in 1939.

Bernstein's theory regarding the care potential confirmed Kenneth Stewart Cole (Kenneth Stewart Cole), sometimes his initials are mistakenly written as k.c. Cole, because of his nickname, Casey ("Kacy"). PP and PD are depicted on the well-known illustration of COUL and CURTIS, 1939. This picture has become the emblem of Membrane Biophysics Group of the Biophysical Society (see illustration).

General provisions

In order for the membrane to be supported by the potential difference, it is necessary that a certain difference in the concentration of different ions inside and outside the cell is.

The concentration of ions in the skeletal muscle cell and in the extracellular medium

People's potential for most neurons is about -60 mV - -70 mV. In the cells of non-professional tissues, the membrane also has a difference in potentials, different for cells of different tissues and organisms.

The formation of rest potential

PP is formed in two stages.

First stage: The creation of a minor (-10 mV) of negativity inside the cell due to the unequal asymmetric exchange of Na + on K + in the ratio of 3: 2. As a result, the cell leaves more positive charges with sodium than returned to it with potassium. Such a feature of the work of the sodium-potassium pump, performing the interchange of these ions through the membrane with the cost of ATP energy, provides its electricality.

The results of the activities of membrane ion exchange pumps at the first stage of the formation of PP are as follows:

1. Sodium ion deficiency (Na +) in the cell.

2. Excess potassium ions (K +) in the cell.

3. The appearance on the membrane of the weak electric potential (-10 mV).

Second phase: The creation of a significant (-60 mV) of negativity inside the cell due to leakage from it through the membrane of K + ions. Kaliya K + ions leave the cage and carry out positive charges with them, bringing negate to -70 mV.

So, the membrane care potential is a deficiency of positive electrical charges inside the cell, which occurs due to leakage from it positive potassium ions and the electrical action of the sodium-potassium pump.

see also

Notes

Links

Dudel J., Roegg J., Schmidt R., etc. Human physiology: in 3 volumes. Per. from English / near Ed R. Schmidt and the city of Tevs. - 3. - m .: Mir, 2007. - T. 1. - 323 s Ill. from. - 1500 copies. - ISBN 5-03-000575-3

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Watch what is the "Potential of Peace" in other dictionaries:

Resting potential, the electrical potential between the inner and outer medium, occurs on its membrane; Neurons and muscle cells reaches a value of 0.05 0.09 V; It occurs because of the uneven distribution and accumulation of ions in different ... encyclopedic Dictionary

The membrane potential of peace, the potential difference existing in the living cells in the physiol state. People, between their cytoplasm and extracellular fluid. Nervous and muscular cells P. p. Various usually in the range of 60,90 mV, and internal. Side ...

potential rest - The stress of rest - [Ya.N. Luginsky, M.S.Fesi Zhilinskaya, Yu.S. Kabirov. English Russian Dictionary for Electrical Engineering and Electric Power Industry, Moscow, 1999] Electrical Equipment Topics, Basic Concepts Synonyms Powers EN REST POTENTIALRESTING ... Technical translator directory

potential rest - REST (ING) Potential rest potential potential existing between the medium in which the cell is located and its contents ... Explanatory english-Russian dictionary on nanotechnology. - M.

Potential rest - The potential of inactive neuron. It is also called membrane potential ... Psychology of sensations: Glossary

potential rest - The potential difference between the contents of the cell and the extracellular fluid. In nerve cells P.P. Participates in maintaining the readiness of the cell to excitement. * * * Membrane bioelectric potential (about 70mB) in the nervous cell located in ... ... Encyclopedic Dictionary of Psychology and Pedagogy

Potential rest - - the difference of electrical charges between the outer and the inner surfaces of the membrane in the state of the physiological side of the cell, registered before the start of the irritant ... Dictionary of terms in physiology of farm animals

The membrane potential registered before the start of the irritant ... Big Medical Dictionary

- (physiological) potential difference between the contents of the cell (fiber) and extracellular liquid; The potential jump is localized on the surface membrane, with it, the inner side is charged electronegatively with respect to ... ... Great Soviet Encyclopedia

Rapid oscillation (spike) of the membrane potential arising from the excitation of nervous, muscle, non-ryy glands and growing, cells; Electric. Signal providing quick transmission of information in the body. Obeys the rule "all or nothing" ... ... Biological Encyclopedic Dictionary

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It has been established that the most important ions that determine the membrane cell potentials are inorganic ions K +, Na +, SG, as well as in some cases of Ca 2 +. It is well known that the concentrations of these ions in the cytoplasm and in the intercellular fluid differ in tens of times.

From table. 11.1 It can be seen that the concentration of ions to + inside the cell is 40-60 times higher than in the intercellular fluid, whereas for Na + and SG the distribution of concentrations is the opposite. The uneven distribution of the concentrations of these ions on both sides of the membrane is ensured by both their different permeability and a strong electric membrane field, which is determined by its rest potential.

Indeed, in a state of rest, the total flow of ions through the membrane is zero, and then from the equation of the non-rhine - the plank it follows that

Thus, at rest gradients concentration - and

electric potential - on the membrane directed

opposite to each other and therefore in a resting cell high and constant difference of the concentrations of the main ions ensures that the cells of the electrical voltage cell on the membrane is called, which is called equilibrium membrane potential.

In turn, the peak potential occurring on the membrane prevents the ion exit from the K + cell and the excessive entry into it of the SG, thereby maintaining their concentration gradients on the membrane.

The complete expression for the membrane potential, which takes into account the diffusion flows of these three types of ions, was obtained by Goldman, Hodgkin and Katz:

where R k P Na, p C1 - the permeability of the membrane for the corresponding ions.

Equation (11.3) with high accuracy determines the membrane potentials of rest different cells. It follows from it that for the membrane potential of rest is not important absolute values The permeability of the membrane for various ions, and their relationship, since, dividing both parts of the fraction under the sign of the logarithm, for example, on the R K, we move on to the relative permeability of ions.

In cases where the permeability of one of these ions is significantly larger than others, equation (11.3) enters the Nernst equation (11.1) for this ion.

From table. 11.1 It can be seen that the membrane potential of the cells of cells is close to the potential of Nernsta for ions K + and CV, but is significantly different from it by Na +. This is evidence

0 The fact that in the rest of the membrane is well permeable for ions K + and SG, whereas for Na ions + its permeability is very low.

Despite the fact that the equilibrium potential of Nernsta for the SG is closest to the potential of the cage rest, the latter has predominantly potassium nature. This is due to the fact that a high intracellular concentration of K + cannot significantly decrease, since ions K + should balancing inside the cell volumetric negative anion charge. Intracellular anions are mostly large organic molecules (proteins, residues of organic acids IT.P.), which can not pass through the channels in the cell membrane. The concentration of these anions in the cell is almost constant and their total negative charge prevents the significance of potassium output from the cell, maintaining its high intracellular concentration along with the Na-K pump. However, the main role in the initial establishment within the cell of the high concentration of potassium ions and the low sodium ion concentrations belongs to the Na-k-pump.

The distribution of ions C1 is established in accordance with the membrane potential, since there are no special mechanisms for maintaining the concentration of SG in the cell. Therefore, due to the negative chlorine charge, its distribution is reverse with respect to the distribution of potassium on the membrane (see Table 11.1). Thus, the concentration diffusion of K + from the cell and C1 into the cell is practically equalized by the membrane potential of the cell rest.

As for Na +, then its diffusion is directed into a cell under the action of both the concentration gradient and the membrane electric field and the input of Na + into the cell is limited to a closer only the permeability of the membrane for sodium (sodium channels are closed). Indeed, Hodgkin and Katz experimentally found that in a state of rest of the permeability of the axon membrane of a squid for K +, Na + and SGs refer to as 1: 0.04: 0.45. Thus, in a state of rest, the cell membrane is only permeable for Na +, and for SG it permeates almost as good as for K +. In the nervous cells, permeability for the SG is usually lower than for K +, but in muscle fibers, permeability for SG is even somewhat prevalent.

Despite the small permeability of the cell membrane for Na + alone, there is, although very small, passive transfer of Na + into the cell. This current Na + would have to lead to a decrease in the potential difference on the membrane and to the exit to + from the cell, which would ultimately believe to align the concentrations of Na + and K + on both sides of the membrane. This does not occur due to the work of Na + - K + -Pasos, compensating for the leakage currents Na + and K + and maintaining normal values Intracellular concentrations of these ions and, therefore, the normal amount of cell rest potential.

For most cells, the membrane resting potential is (-beyond) - (- Yuo) MV. At first glance it may seem that this is a small value, but it is necessary to consider that the membrane thickness is also small (8-10 nm), so that the electric field strength in the cell membrane is enormous and is about 10 million volts per 1 m (or 100 square meters on 1 cm):

Air, for example, does not withstand such an electric field strength (electric breakdown in the air occurs at 30 kV / cm), and the membrane can withstand. This is the normal condition of its activity, since it is precisely such an electric field to maintain the difference in sodium ions concentrations, potassium and chlorine on the membrane.

The magnitude of the potential of peace, different in cells, can change when the conditions change their livelihoods. Thus, the violation of bioenergy processes in a cell, accompanied by a drop in the intracellular level of macro-ergic compounds (in particular, ATP), primarily eliminates the peak potential component associated with the work of Ma + -K + -atf-Ase.

Cell damage causes usually to increase the permeability of cell membranes, as a result of which the differences in the permeability of the membrane for potassium and sodium ions decrease; The resting potential is reduced, which may cause a violation of a number of cell functions, such as excitability.

• Since the intracellular concentration of potassium is supported by almost constant, even relatively small changes in extracellular concentration to * can have a noticeable effect on potential perception and cell activity. Similar changes in the concentration K "in the blood plasma occur in some pathologies (for example, episherative failure).