The membrane potential of the neuron at rest is equal. Cell membrane potential, or resting potential

Table of contents of the topic "Endocytosis. Exocytosis. Regulation of cellular functions.":
1. Effect of the Na/K pump (sodium potassium pump) on membrane potential and cell volume. Constant cell volume.
2. Sodium (Na) concentration gradient as the driving force for membrane transport.
3. Endocytosis. Exocytosis.
4. Diffusion in the transport of substances within the cell. The importance of diffusion in endocytosis and exocytosis.
5. Active transport in organelle membranes.
6. Transport in cell vesicles.
7. Transport through the formation and destruction of organelles. Microfilaments.
8. Microtubules. Active movements of the cytoskeleton.
9. Axon transport. Fast axon transport. Slow axon transport.
10. Regulation of cellular functions. Regulatory effects on the cell membrane. Membrane potential.
11. Extracellular regulatory substances. Synaptic mediators. Local chemical agents (histamine, growth factor, hormones, antigens).
12. Intracellular communication with the participation of second messengers. Calcium.
13. Cyclic adenosine monophosphate, cAMP. cAMP in the regulation of cell function.
14. Inositol phosphate "IF3". Inositol triphosphate. Diacylglycerol.

Effect of the Na/K pump (sodium potassium pump) on membrane potential and cell volume. Constant cell volume.

Rice. 1.9. Diagram showing the concentrations of Na+, K+ and CI inside and outside the cell and the pathways for the penetration of these ions through the cell membrane (through specific ion channels or using a Na/K pump. At these concentration gradients, the equilibrium potentials E(Na), E(K) and E(Cl) are equal to those indicated, the membrane potential Et = - 90 mV

In Fig. 1.9 shows the various components membrane current and given intracellular ion concentrations that ensure their existence. An outward current of potassium ions is observed through potassium channels, since the membrane potential is slightly more electropositive than the equilibrium potential for potassium ions. Total sodium channel conductance much lower than potassium, i.e. sodium channels are open much less frequently than potassium channels at resting potential; however, approximately the same number of sodium ions enter the cell as potassium ions exit the cell, because large concentration and potential gradients are required for sodium ions to diffuse into the cell. The Na/K pump provides ideal compensation for passive diffusion currents, as it transports sodium ions out of the cell and potassium ions into it. Thus, the pump is electrogenic due to the difference in the number of charges transferred into and out of the cell, which, at its normal speed of operation, creates a membrane potential that is approximately 10 mV more electronegative than if it were formed only due to passive ion flows. As a result, the membrane potential approaches the potassium equilibrium potential, which reduces the leakage of potassium ions. Na/K pump activity regulated intracellular concentration of sodium ions. The speed of the pump slows down as the concentration of sodium ions to be removed from the cell decreases (Fig. 1.8), so that the pump operation and the flow of sodium ions into the cell balance each other, maintaining the intracellular concentration of sodium ions at a level of approximately 10 mmol/L.

To maintain balance between pumping and passive membrane currents, many more Na/K pump molecules are needed than channel proteins for potassium and sodium ions. When the channel is open, tens of thousands of ions pass through it in a few milliseconds, and since the channel usually opens several times per second, in total more than 105 ions pass through it during this time. A single pump protein moves several hundred sodium ions per second, so the plasma membrane must contain about 1000 times more pump molecules than channel molecules. Measurements of channel currents at rest showed an average of one potassium and one sodium open channel per 1 µm2 membrane; It follows from this that about 1000 molecules of the Na/K pump should be present in the same space, i.e. the distance between them is on average 34 nm; The diameter of the pump protein, like the channel protein, is 8-10 nm. Thus, the membrane is quite densely saturated with pumping molecules.

The fact that flow of sodium ions into the cell, A potassium ions - from the cell compensated by the operation of the pump, has another consequence, which is the maintenance of stable osmotic pressure and constant volume. Inside the cell there is a high concentration of large anions, mainly proteins (A in Table 1.1), which are not able to penetrate the membrane (or penetrate it very slowly) and are therefore a fixed component inside the cell. To balance the charge of these anions, an equal number of cations is needed. Thanks to action of the Na/K pump These cations are mainly potassium ions. Significant increase intracellular ion concentration could only occur with an increase in the concentration of anions due to the flow of Cl along the concentration gradient into the cell (Table 1.1), but the membrane potential counteracts this. An inward Cl current is observed only until the equilibrium potential for chloride ions is reached; this is observed when the chlorine ion gradient is almost opposite to the potassium ion gradient, since chlorine ions are negatively charged. Thus, a low intracellular concentration of chlorine ions is established, corresponding to a low extracellular concentration of potassium ions. The result is a limitation of the total number of ions in the cell. If the membrane potential drops when the Na/K pump is blocked, for example during anoxia, then the equilibrium potential for chloride ions decreases, and the intracellular concentration of chloride ions increases accordingly. Restoring the balance of charges, potassium ions also enter the cell; the total concentration of ions in the cell increases, which increases osmotic pressure; this forces water into the cell. The cell swells. This swelling is observed in vivo under conditions of energy deficiency.

The main physiological function of sodium in the human body is to regulate the volume of extracellular fluid, thereby determining blood volume and blood pressure. This function is directly related to sodium and fluid metabolism. In addition, sodium is involved in the process of bone tissue formation, conduction of nerve impulses, etc.

In medicine, in the event of various kinds of electrolyte imbalances, in order to find out the causes of this condition, tests are carried out to determine the concentration of sodium, as well as monitoring the fluid balance (its intake and excretion).

In the human body, the mass of fluid occupies approximately 60%, that is, a person weighing 70 kg contains approximately 40 liters of fluid, of which about 25 liters are contained in the cells (intracellular fluid - CL) and 14 liters are outside the cells (extracellular fluid - ExtraQoL). Of the total amount of extracellular fluid, approximately 3.5 liters is occupied by blood plasma (blood fluid located inside the vascular system) and about 10.5 liters by interstitial fluid (IF), filling the space in the tissues between cells (see Fig. 1)

Figure 1. Fluid distribution in the body of an adult weighing 70 kg

The total amount of fluid in the body and maintaining a constant level of its distribution between compartments help ensure the full functioning of all organs and systems, which, undoubtedly, is the key to good health. The exchange of water between intracellular fluid and extracellular fluid occurs through cell membranes. The osmolarity of the fluid solutions on both sides of the membrane directly influences this exchange. Under the condition of osmotic equilibrium, the liquid will not move, that is, its volumes in the compartments will not change. In a healthy person, the osmolarity of intracellular fluid and blood plasma (extracellular fluid) is maintained at approximately 80-295 mOsmol/kg.

The role of sodium in the regulation of extracellular fluid volume

Osmolarity is the sum of the concentration of all kinetic particles in 1 liter of solution, that is, it depends on the total concentration of dissolved ions. In the human body, osmolarity is determined by electrolytes, since in liquid media (intra- and extracellular fluid) ions are in relatively high concentrations compared to other dissolved components. Figure 2 demonstrates the distribution of electrolytes between intracellular and extracellular fluids.

Figure 2. Concentration of dissolved components in intracellular and extracellular fluids

It is important to note that for monovalent ions (potassium, sodium) meq/l = mmol/l, and for divalent ions, to calculate the number of mmol/l, meq should be divided by 2.

The left side of the figure (Ex-QF) shows the composition of blood plasma, which is very similar in composition to interstitial fluid (except for the low protein concentration and high chloride concentration)

It can be concluded that the sodium concentration in the blood plasma is a determining indicator of the volume of extracellular fluid and, as a consequence, the volume of blood.

The extracellular fluid is high in sodium and low in potassium. On the contrary, the cells contain little sodium - the main intracellular cation is potassium. This difference in the concentrations of electrolytes in the extracellular and intracellular fluids is maintained by the mechanism of active ion transport with the participation of the sodium-potassium pump (pump) (see Fig. 3).

Figure 3. Maintaining sodium and potassium concentrations in the QoL and extraQoL

The sodium-potassium pump, localized on cell membranes, is an energy-independent system found in all types of cells. Thanks to this system, sodium ions are removed from cells in exchange for potassium ions. Without such a transport system, potassium and sodium ions would remain in a state of passive diffusion through the cell membrane, which would result in ionic equilibrium between the extracellular and intracellular fluids.

High osmolarity of the extracellular fluid is ensured due to the active transport of sodium ions from the cell, which ensures their high content in the extracellular fluid. Given the fact that osmolarity influences the distribution of fluid between the ECF and the CL, therefore, the volume of extracellular fluid is directly dependent on the sodium concentration.

REGULATION OF WATER BALANCE

The intake of fluid into the human body must be adequate to its removal, otherwise overhydration or dehydration may occur. In order for the excretion (removal) of toxic substances (toxic substances formed in the body during metabolism) to occur, the kidneys must excrete at least 500 ml of urine daily. To this amount you need to add 400 ml of liquid, which is excreted daily through the lungs during breathing, 500 ml - excreted through the skin, and 100 ml - with fecal matter. As a result, the human body loses an average of 1500 ml (1.5 l) of fluid daily.

Note that daily in the human body in the process of metabolism (as a result of a by-product of metabolism) approximately 400 ml of water is synthesized. Thus, in order to maintain a minimum level of water balance, the body must receive at least 1100 ml of water per day. In fact, the daily volume of incoming fluid often exceeds the specified minimum level, while the kidneys, in the process of regulating water balance, do an excellent job of removing excess fluid.

For most people, the average daily urine volume is approximately 1200-1500 ml. If necessary, the kidneys can produce significantly more urine.

Blood plasma osmolarity is associated with the flow of fluid into the body and the process of formation and excretion of urine. For example, if fluid loss is not adequately replaced, extracellular fluid volume decreases and osmolarity increases, resulting in an increase in fluid flow from body cells into the extracellular fluid, thereby restoring its osmolarity and volume to the required level. However, such internal distribution of fluid is effective only for a limited period of time, since this process leads to dehydration (dehydration) of cells, as a result of which the body needs more fluid from outside.

Figure 4 schematically represents the physiological response to fluid deficiency in the body.

Figure 4. Maintaining normal water balance in the body is regulated by the hypothalamic-pituitary system, the feeling of thirst, adequate synthesis of antidiuretic hormone and the full functioning of the kidneys

When there is a deficiency of fluid in the body, high-osmolar blood plasma flows through the hypothalamus, in which osmoreceptors (special cells) analyze the state of the plasma and give a signal to trigger the mechanism of reducing osmolarity by stimulating the secretion of antidiuretic hormone (ADH) in the pituitary gland and the emergence of a feeling of thirst. When thirsty, a person tries to compensate for the lack of fluid from outside by consuming drinks or water. Antidiuretic hormone affects kidney function, thereby preventing the removal of fluid from the body. ADH promotes increased reabsorption (reabsorption) of fluid from the collecting ducts and distal tubules of the kidneys, resulting in the production of relatively small amounts of higher concentration urine. Despite these changes in the blood plasma, modern diagnostic analyzers can assess the degree of hemolysis and measure the actual level of potassium in the plasma of hemolyzed blood samples.

When a large amount of fluid enters the body, the osmolarity of the extracellular fluid decreases. In this case, there is no stimulation of osmoreceptors in the hypothalamus - the person does not experience a feeling of thirst and the level of antidiuretic hormone does not increase. In order to prevent excessive water load, a large amount of dilute urine is formed in the kidneys.

Note that approximately 8000 ml (8 liters) of fluid enters the gastrointestinal tract daily in the form of gastric, intestinal and pancreatic juices, bile, and saliva. Under normal conditions, approximately 99% of this fluid is reabsorbed and only 100 ml is excreted in the feces. However, disruption of the water conservation function contained in these secretions can lead to water imbalance, which will cause serious disorders of the entire body.

Let us once again pay attention to the factors influencing the normal regulation of water balance in the human body:

Feeling thirsty(for thirst to manifest, a person must be conscious)
Full functioning of the pituitary gland and hypothalamus
Full kidney function
Full functioning of the gastrointestinal tract

REGULATION OF SODIUM BALANCE

For the normal functioning and health of the body, maintaining sodium balance is as important as maintaining water balance. In a normal state, the adult human body contains approximately 3000 mmol of sodium. Most of the sodium is contained in the extracellular fluid: blood plasma and interstitial fluid (sodium concentration in them is about 140 mmol/l).

Daily sodium loss is at least 10 mmol/l. To maintain normal balance in the body, these losses must be compensated (replenished). Through diet, people receive significantly more sodium than the body needs to compensate (with food, usually in the form of salty seasonings, a person receives an average of 100-200 mmol of sodium daily). However, despite the wide variability in sodium intake, renal regulation ensures that excess sodium is excreted in the urine, thereby maintaining physiological balance.

The process of excretion (removal) of sodium through the kidneys depends directly on GFR (glomerular filtration rate). A high glomerular filtration rate increases the amount of sodium excreted in the body, and a low GFR rate delays it. Approximately 95-99% of the sodium filtered by the glomerulus is actively reabsorbed as urine passes through the proximal convoluted tubule. By the time the ultrafiltrate enters the distal convoluted tubule, the amount of sodium already filtered in the glomeruli is 1-5%. Whether the remaining sodium is excreted in the urine or reabsorbed into the blood depends directly on the concentration of the adrenal hormone aldosterone in the blood.

Aldosterone enhances the reabsorption of sodium in exchange for hydrogen or potassium ions, thereby affecting the cells of the distal tubules of the kidneys. That is, under conditions of high aldosterone levels in the blood, most of the remaining sodium is reabsorbed; at low concentrations, sodium is excreted in the urine in large quantities.

Figure 5.

Controls the process of aldosterone production (see Figure 5). Renin- an enzyme that is produced by the kidneys in the cells of the juxtaglomerular apparatus in response to a decrease in blood flow through the renal glomeruli. Since the rate of renal blood flow, like blood flow through other organs, depends on blood volume, and therefore on the concentration of sodium in the blood, renin secretion in the kidneys increases when plasma sodium levels decrease.

Thanks to renin, the enzymatic breakdown of protein, also known as renin substrate. One of the products of this splitting is angiotensinI- a peptide containing 10 amino acids.

Another enzyme is ACE ( angiotensin converting enzyme), which is synthesized mainly in the lungs. During metabolism, ACE separates two amino acids from angiotensin I, which leads to the formation of octopeptide - the hormone angiotensin II .

AngiotensinII has very important properties for the body:

Vasoconstriction- constriction of blood vessels, which increases blood pressure and restores normal renal blood flow
Stimulates aldosterone production in the cells of the adrenal cortex, thereby activating sodium reabsorption, which helps restore normal blood flow through the kidneys and the total blood volume in the body.

When blood volume and blood pressure increase, heart cells secrete a hormone that is an aldosterone antagonist - ANP ( atrial natriuretic peptide, or PNP). ANP helps reduce sodium reabsorption in the distal tubules of the kidneys, thereby increasing its excretion in the urine. That is, the “feedback” system ensures clear regulation of sodium balance in the body.

Experts say that approximately 1,500 mmol of sodium enters the human body through the gastrointestinal tract every day. Approximately 10 mmol of sodium that is excreted in the feces is reabsorbed. In case of dysfunction of the gastrointestinal tract, the amount of sodium reabsorbed decreases, which leads to its deficiency in the body. When the renal compensation mechanism is impaired, signs of this deficiency begin to appear.

Maintaining a normal sodium balance in the body depends on 3 main factors:

Kidney functions
Aldosterone secretion
Functioning of the gastrointestinal tract

POTASSIUM

Potassium is involved in the conduction of nerve impulses, the process of muscle contraction, and ensures the action of many enzymes. The human body contains on average 3000 mmol of potassium, most of which is found in cells. The potassium concentration in blood plasma is approximately 0.4%. Although its concentration in the blood can be measured, the test result will not objectively reflect the total potassium content in the body. However, to maintain the overall balance of potassium, it is necessary to maintain the desired level of concentration of this element in the blood plasma.

Regulation of potassium balance

The body loses at least 40 mmol of potassium daily in feces, urine and then. Maintaining the necessary potassium balance requires replenishing these losses. A diet that contains vegetables, fruit, meat and bread provides approximately 100 mmol of potassium per day. To ensure the necessary balance, excess potassium is excreted in the urine. The process of filtration of potassium, like sodium, occurs in the renal glomeruli (as a rule, it is reabsorbed in the proximal (initial) part of the renal tubules. Fine regulation occurs in the collecting glomeruli and distal tubules (potassium can be reabsorbed or secreted in exchange for sodium ions).

The renin-angiotensin-aldosterone system regulates sodium-potassium metabolism, or rather, stimulates it (aldosterone triggers sodium reabsorption and the process of potassium excretion in the urine).

In addition, the amount of potassium excreted in the urine is determined by the function of the kidneys in regulating the acid-base balance (pH) of the blood within physiological normal limits. For example, one mechanism to prevent blood oxidation is to remove excess hydrogen ions from the body in the urine (this occurs by exchanging hydrogen ions for sodium ions in the distal renal tubules). Thus, in acidosis, less sodium can be exchanged for potassium, resulting in the kidneys excreting less potassium. There are other ways of interaction between acid-base status and potassium.

Under normal conditions, approximately 60 mmol of potassium is released into the gastrointestinal tract, where most of it is reabsorbed (the body loses about 10 mmol of potassium in feces). In case of dysfunction of the gastrointestinal tract, the reabsorption mechanism is disrupted, which can lead to potassium deficiency.

Transport of potassium across cell membranes

Low potassium concentrations in the extracellular fluid and high potassium concentrations in the intracellular fluid are regulated by the sodium-potassium pump. Inhibition (inhibition) or stimulation (intensification) of this mechanism affects the concentration of potassium in the blood plasma, as the ratio of concentrations in extracellular and intracellular fluids changes. Note that hydrogen ions compete with potassium ions when passing through cell membranes, that is, the level of potassium in the blood plasma affects the acid-base balance.

A significant decrease or increase in the concentration of potassium in the blood plasma does not at all indicate a deficiency or excess of this element in the body as a whole - it may indicate a violation of the necessary balance of extra- and intracellular potassium.

Regulation of potassium concentration in blood plasma occurs due to the following factors:

Potassium intake from food
Kidney functions
Functions of the gastrointestinal tract
Aldosterone production
Acid-base balance
Sodium-potassium pump

Between the outer surface of the cell and its cytoplasm at rest there is a potential difference of about 0.06-0.09 V, and the cell surface is charged electropositively with respect to the cytoplasm. This potential difference is called resting potential or membrane potential. Accurate measurement of the resting potential is only possible with the help of microelectrodes designed for intracellular current drainage, very powerful amplifiers and sensitive recording instruments - oscilloscopes.

The microelectrode (Fig. 67, 69) is a thin glass capillary, the tip of which has a diameter of about 1 micron. This capillary is filled with saline solution, a metal electrode is immersed in it and connected to an amplifier and an oscilloscope (Fig. 68). As soon as the microelectrode pierces the membrane covering the cell, the oscilloscope beam is deflected down from its original position and established at a new level. This indicates the presence of a potential difference between the outer and inner surfaces of the cell membrane.

The origin of the resting potential is most fully explained by the so-called membrane-ion theory. According to this theory, all cells are covered with a membrane that is unequally permeable to different ions. In this regard, inside the cell in the cytoplasm there are 30-50 times more potassium ions, 8-10 times less sodium ions and 50 times less chlorine ions than on the surface. At rest, the cell membrane is more permeable to potassium ions than to sodium ions. The diffusion of positively charged potassium ions from the cytoplasm to the cell surface gives the outer surface of the membrane a positive charge.

Thus, the surface of the cell at rest carries a positive charge, while the inner side of the membrane turns out to be negatively charged due to chlorine ions, amino acids and other large organic anions that practically do not penetrate the membrane (Fig. 70).

Action potential

If a section of a nerve or muscle fiber is exposed to a sufficiently strong stimulus, then excitation occurs in this section, manifested in a rapid oscillation of the membrane potential and called action potential.

The action potential can be recorded either using electrodes applied to the outer surface of the fiber (extracellular lead) or a microelectrode inserted into the cytoplasm (intracellular lead).

With extracellular abduction, one can find that the surface of the excited area for a very short period, measured in thousandths of a second, becomes charged electronegatively with respect to the resting area.

The reason for the occurrence of an action potential is a change in the ionic permeability of the membrane. When irritated, the permeability of the cell membrane to sodium ions increases. Sodium ions tend to enter the cell because, firstly, they are positively charged and are drawn inward by electrostatic forces, and secondly, their concentration inside the cell is low. At rest, the cell membrane was poorly permeable to sodium ions. Irritation has changed the permeability of the membrane, and the flow of positively charged sodium ions from the external environment of the cell into the cytoplasm significantly exceeds the flow of potassium ions from the cell to the outside. As a result, the inner surface of the membrane becomes positively charged, and the outer surface becomes negatively charged due to the loss of positively charged sodium ions. At this moment the peak of the action potential is recorded.

The increase in membrane permeability to sodium ions lasts for a very short time. Following this, reduction processes occur in the cell, leading to the fact that the permeability of the membrane for sodium ions again decreases, and for potassium ions increases. Since potassium ions are also positively charged, when they leave the cell, they restore the original relationship between the outside and inside the cell.

Accumulation of sodium ions inside the cell during repeated excitation does not occur because sodium ions are constantly evacuated from it due to the action of a special biochemical mechanism called the “sodium pump”. There is also evidence of active transport of potassium ions using the “sodium-potassium pump”.

Thus, according to the membrane-ion theory, the selective permeability of the cell membrane is of decisive importance in the origin of bioelectric phenomena, which determines the different ionic composition on the surface and inside the cell, and, consequently, the different charge of these surfaces. It should be noted that many provisions of the membrane-ion theory are still debatable and require further development.

History of discovery

In 1902, Julius Bernstein put forward a hypothesis according to which the cell membrane allows K + ions into the cell, and they accumulate in the cytoplasm. The calculation of the resting potential value using the Nernst equation for the potassium electrode satisfactorily coincided with the measured potential between the muscle sarcoplasm and the environment, which was about -70 mV.

According to the theory of Yu. Bernstein, when a cell is excited, its membrane is damaged, and K + ions flow out of the cell along a concentration gradient until the membrane potential becomes zero. The membrane then restores its integrity and the potential returns to the resting potential level. This claim, which relates rather to the action potential, was refuted by Hodgkin and Huxley in 1939.

Bernstein's theory of the resting potential was confirmed by Kenneth Stewart Cole, sometimes erroneously spelled K.C. Cole, because of his nickname, Casey ("Kacy"). PP and PD are depicted in a famous illustration by Cole and Curtis, 1939. This drawing became the emblem of the Membrane Biophysics Group of the Biophysical Society (see illustration).

General provisions

In order for a potential difference to be maintained across the membrane, it is necessary that there be a certain difference in the concentration of various ions inside and outside the cell.

Ion concentrations in the skeletal muscle cell and in the extracellular environment

The resting potential for most neurons is on the order of −60 mV - −70 mV. Cells of non-excitable tissues also have a potential difference on the membrane, which is different for cells of different tissues and organisms.

Formation of the resting potential

The PP is formed in two stages.

First stage: the creation of slight (-10 mV) negativity inside the cell due to the unequal asymmetric exchange of Na + for K + in a ratio of 3: 2. As a result, more positive charges leave the cell with sodium than return to it with potassium. This feature of the sodium-potassium pump, which exchanges these ions through the membrane with the expenditure of ATP energy, ensures its electrogenicity.

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

1. Deficiency of sodium ions (Na +) in the cell.

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

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

Second phase: creation of significant (-60 mV) negativity inside the cell due to the leakage of K + ions from it through the membrane. Potassium ions K+ leave the cell and take away positive charges from it, bringing the negative charge to -70 mV.

So, the resting membrane potential is a deficiency of positive electrical charges inside the cell, resulting from the leakage of positive potassium ions from it and the electrogenic action of the sodium-potassium pump.

Notes

Links

Dudel J, Rüegg J, Schmidt R, et al. Human physiology: in 3 volumes. Per. from English / edited by R. Schmidt and G. Teus. - 3. - M.: Mir, 2007. - T. 1. - 323 with illustrations. With. - 1500 copies. - ISBN 5-03-000575-3

Wikimedia Foundation. 2010.

See what “Rest potential” is in other dictionaries:

RESTING POTENTIAL, the electrical potential between the internal and external environment of the cell, arising on its membrane; in neurons and muscle cells reaches a value of 0.05–0.09 V; arises due to the uneven distribution and accumulation of ions in different... encyclopedic Dictionary

Resting membrane potential, the potential difference that exists in living cells in a state of physiology. rest, between their cytoplasm and extracellular fluid. In nerve and muscle cells, P. p. usually varies in the range of 60–90 mV, and internal. side …

resting potential- resting voltage - [Ya.N.Luginsky, M.S.Fezi Zhilinskaya, Yu.S.Kabirov. English-Russian dictionary of electrical engineering and power engineering, Moscow, 1999] Topics electrical engineering, basic concepts Synonyms rest voltage EN rest potentialresting... ... Technical Translator's Guide

resting potential- Rest(ing) Potential The potential that exists between the environment in which the cell is located and its contents ... Explanatory English-Russian dictionary on nanotechnology. - M.

Resting potential- Potential of an inactive neuron. Also called membrane potential... Psychology of sensations: glossary

resting potential- the potential difference between the cell contents and the extracellular fluid. In nerve cells pp. participates in maintaining the cell’s readiness for excitation. * * * Membrane bioelectric potential (about 70 mV) in a nerve cell located in... ... Encyclopedic Dictionary of Psychology and Pedagogy

Resting potential- – the difference in electrical charges between the outer and inner surfaces of the membrane in a state of physiological rest of the cell, recorded before the onset of the stimulus... Glossary of terms on the physiology of farm animals

Membrane potential recorded before the onset of the stimulus... Large medical dictionary

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

A rapid oscillation (spike) of the membrane potential that occurs upon excitation of nerve, muscle, and certain glandular and vegetative cells; electric a signal that ensures rapid transmission of information in the body. Subject to the “all or nothing” rule... ... Biological encyclopedic dictionary

Books

100 ways to change your life. Part 1, Parfentyeva Larisa. About the book A collection of inspiring stories about how to change your life for the better, from a man who managed to turn his own life 180 degrees. This book was born from a weekly column...

Any living cell is covered with a semi-permeable membrane, through which passive movement and active selective transport of positively and negatively charged ions occur. Due to this transfer, there is a difference in electrical charges (potentials) between the outer and inner surfaces of the membrane - the membrane potential. There are three distinct manifestations of membrane potential: resting membrane potential, local potential, or local response, And action potential.

If the cell is not affected by external stimuli, then the membrane potential remains constant for a long time. The membrane potential of such a resting cell is called the resting membrane potential. For the outer surface of the cell membrane, the resting potential is always positive, and for the inner surface of the cell membrane it is always negative. It is customary to measure the resting potential on the inner surface of the membrane, because The ionic composition of the cell cytoplasm is more stable than that of the intercellular fluid. The magnitude of the resting potential is relatively constant for each cell type. For striated muscle cells it ranges from –50 to –90 mV, and for nerve cells from –50 to –80 mV.

The causes of the resting potential are different concentrations of cations and anions outside and inside the cell, as well as selective permeability for them the cell membrane. The cytoplasm of a resting nerve and muscle cell contains approximately 30–50 times more potassium cations, 5–15 times less sodium cations and 10–50 times less chlorine anions than the extracellular fluid.

At rest, almost all sodium channels of the cell membrane are closed, and most potassium channels are open. Whenever potassium ions encounter an open channel, they pass through the membrane. Since there are much more potassium ions inside the cell, the osmotic force pushes them out of the cell. The released potassium cations increase the positive charge on the outer surface of the cell membrane. As a result of the release of potassium ions from the cell, their concentrations inside and outside the cell would soon be equalized. However, this is prevented by the electrical force of repulsion of positive potassium ions from the positively charged outer surface of the membrane.

The greater the positive charge on the outer surface of the membrane becomes, the more difficult it is for potassium ions to pass from the cytoplasm through the membrane. Potassium ions will leave the cell until the force of electrical repulsion becomes equal to the force of osmotic pressure K+. At this level of potential on the membrane, the entrance and exit of potassium ions from the cell are in equilibrium, therefore the electric charge on the membrane at this moment is called potassium equilibrium potential. For neurons it is from –80 to –90 mV.

Since in a resting cell almost all sodium channels of the membrane are closed, Na+ ions enter the cell along the concentration gradient in small quantities. They only to a very small extent compensate for the loss of positive charge in the internal environment of the cell caused by the release of potassium ions, but cannot significantly compensate for this loss. Therefore, the penetration (leakage) of sodium ions into the cell leads to only a slight decrease in the membrane potential, as a result of which the resting membrane potential has a slightly lower value compared to the potassium equilibrium potential.

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

At rest, the plasma membrane of the cell is highly permeable to chlorine anions. Chlorine anions, which are more abundant in the extracellular fluid, diffuse into the cell and carry with them a negative charge. Complete equalization of the concentrations of chlorine ions outside and inside the cell does not occur, because this is prevented by the force of electrical mutual repulsion of like charges. Created chlorine equilibrium potential, in which the entry of chlorine ions into the cell and their exit from it are in equilibrium.

The cell membrane is practically impermeable to 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 a resting nerve cell.

The most important significance of the resting membrane potential is that it creates an electric field that acts on the macromolecules of the membrane and gives their charged groups a certain position in space. It is especially important that this electric field determines the closed state of the activation gates of sodium channels and the open state of their inactivation gates (Fig. 61, A). This ensures that the cell is in a state of rest and is ready to be excited. Even a relatively small decrease in the resting membrane potential opens the activation “gate” of sodium channels, which removes the cell from the resting state and gives rise to excitation.