«Physiology-1» Topic: «Laws of irritation of excitable tissues »
Purpose : • To disassemble laws of irritation excitable tissues
situational problem • How is changed the excitability of the tissue, if the membrane potential increased by 20%, and the critical level of depolarization on - 30%? • Baseline values: Eo = 90 m. V. , Ek = 60 m. V.
Laws stimulation of excitable tissues • The laws establish the dependence of the response of tissue parameters from the stimulus. • This behavior is typical for a highly organized tissues. • There are three laws of stimulation of excitable tissues: • 1) the law of force stimulation; • 2) the law of the duration of stimulation; • (the law Strength—duration) • 3) the law of the gradient stimulation. • 4) polar law
BIOELECTRICITY AND EXCITABLE TISSUE
THE RESTING CELL • • • HIGH POTASSIUM LOW SODIUM NA/K ATPASE PUMP RESTING POTENTIAL ABOUT 90 - 120 MV OSMOTICALLY BALANCED (CONSTANT VOLUME)
BIOELECTRICITY THE ORIGIN OF THE MEMBRANE POTENTIAL
MOBILITY OF IONS DEPENDS ON HYDRATED SIZE • IONS WITH SMALLER CRYSTAL RADIUS HAVE A HIGHER CHARGE DENSITY • THE HIGHER CHARGE DENSITY ATTRACTS MORE WATER OF HYDRATION • THUS THE SMALLER THE CRYSTAL RADIUS, THE LOWER THE MOBILITY IN WATER
IONS MOVE WITH THEIR HYDRATION SHELLS - - + + - - +- + + + - - + + - + - - Hydration Shells + + - - + +
ELECTRONEUTRAL DIFFUSSION LOW SALT CONCEMTRATION HIGH SALT CONCEMTRATION + + - + - - - BARRIER SEPARATES THE TWO SOLUTIONS
ELECTRONEUTRAL DIFFUSSION HIGH SALT CONCEMTRATION + + + - + - LOW SALT CONCEMTRATION + - - - + BARRIER REMOVED CHARGE SEPARATION = ELECTRICAL POTENTIAL
ELECTRICAL POTENTIAL=CHARGE SEPARATION In water, without a membrane hydrated Chloride is smaller than hydrated Sodium, therefore faster: + Cl- Na+ The resulting separation of charge is called an ELECTRICAL POTENTIAL -
THE MEMBRANE POTENTIAL Extracellular Fluid K+ Na+ Potassium channel is more open causing potassium to be faster + M E M B R A N E Intracellular Fluid Sodium channel is less open causing sodium to be slower - MEMRANE POTENTIAL (ABOUT 90 -120 mv)
THE ORIGIN OF BIOELECTRICITY • POTASSIUM CHANNELS ALLOW HIGH MOBILITY • SODIUM CHANNELS LESS OPEN • CHARGE SEPARATION OCCURS UNTIL BOTH MOVE AT SAME SPEED • STEADY IS ACHIEVED WITH A CONSTANT MEMBRANE POTENTIAL
THE RESTING CELL • • • HIGH POTASSIUM LOW SODIUM NA/K ATPASE PUMP RESTING POTENTIAL ABOUT 90 - 120 MV OSMOTICALLY BALANCED (CONSTANT VOLUME)
ACTIVE TRANSPORT ADP ATP
ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGY • • USUALLY IN THE FORM OF ATPase IS INVOLVED SOME ASYMMETRY IS NECESSARY CAN PUMP UPHILL
EXCITABLE TISSUES • NERVE AND MUSCLE • VOLTAGE GATED CHANNELS • DEPOLARIZATION LESS THAN THRESHOLD IS GRADED • DEPOLARIZATION BEYOND THRESHOLD LEADS TO ACTION POTENTIAL • ACTION POTENTIAL IS ALL OR NONE
THE NERVE CELL AXON CELL BODY AXON TERMINALS AXON HILLOCK DENDRITES
EXCITABLE TISSUES: THE ACTION POTENTIAL • THE MEMBRANE USES VOLTAGE GATED CHANNELS TO SWITCH FROM A POTASSIUM DOMINATED TO A SODIUM DOMINATED POTENTIAL • IT THEN INACTIVATES AND RETURNS TO THE RESTING STATE • THE RESPONSE IS “ALL OR NONE”
EQUILIBRIUM POTENTIALS FOR IONS FOR EACH CONCENTRATION DIFFERENCE ACROSS THE MEMBRANE THERE IS AN ELECTRIC POTENTIAL DIFFERENCE WHICH WILL PRODUCE EQUILIBRIUM. AT EQUILIBRIUM NO NET ION FLOW OCCURS
THE EQUILIBRIUM MEMBRANE POTENTIAL FOR POTASSIUM IS -90 m. V - + K+ + K CONCENTRATION POTENTIAL IN
THE EQUILIBRIUM MEMBRANE POTENTIAL FOR SODIUM IS + 60 m. V - + + Na OUT CONCENTRATION Na+ POTENTIAL IN
THE RESTING POTENTIAL IS NEAR THE POTASSIUM EQUILIBRIUM POTENTIAL • AT REST THE POTASSIUM CHANNELS ARE MORE OPEN AND THE POTASSIUM IONS MAKE THE INSIDE OF THE CELL NEGATIVE • THE SODIUM CHANNELS ARE MORE CLOSED AND THE SODIUM MOVES SLOWER
EVENTS DURING EXCITATION • DEPOLARIZATION EXCEEDS THRESHOLD • SODIUM CHANNELS OPEN • MEMBRANE POTENTIAL SHIFTS FROM POTASSIUM CONTROLLED (-90 MV) TO SODIUM CONTROLLED (+60 MV) • AS MEMBRANE POTENTIAL REACHES THE SODIUM POTENTIAL, THE SODIUM CHANNELS CLOSE AND ARE INACTIVATED • POTASSIUM CHANNELS OPEN TO REPOLARIZE THE MEMBRANE
OPENING THE SODIUM CHANNELS ALLOWS SODIUM TO RUSH IN • THE MEMBRANE DEPOLARIZES AND THEN THE MEMBRANE POTENTIAL APPROACHES THE SODIUM EQUILIBRIUM POTENTIAL • THIS RADICAL CHANGE IN MEMBRANE POTENTIAL CAUSES THE SODIUM CHANNELS TO CLOSE (INACTIVATION) AND THE POTASSIUM CHANNELS TO OPEN REPOLARIZING THE MEMBRANE • THERE IS A SLIGHT OVERSHOOT (HYPERPOLARIZATION) DUE TO THE POTASSIUM CHANNELS BEING MORE OPEN
GRADED VS ALL OR NONE • A RECEPTOR’S RESPONSE TO A STIMULUS IS GRADED • IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL RESULTING IS ALL OR NONE
PROPAGATION OF THE ACTION POTENTIAL OUTSIDE ---- +++++++ AXON MEMBRANE +++++ ----------DEPOLARIZING CURRENT INSIDE
PROPAGATION OF THE ACTION POTENTIAL OUTSIDE ---- +++++++ AXON MEMBRANE +++++ ----------DEPOLARIZING CURRENT INSIDE
PROPAGATION OF THE ACTION POTENTIAL OUTSIDE ACTION POTENTIAL ++-----+++++ AXON MEMBRANE --+++ +++---------DEPOLARIZING CURRENT INSIDE
PROPAGATION OF THE ACTION POTENTIAL OUTSIDE +++++ ------++++ AXON MEMBRANE ---- ++++++------DEPOLARIZING CURRENT INSIDE
SALTATORY CONDUCTION OUTSIDE ACTION POTENTIAL ---- NODE OF RANVIER +++++ DEPOLARIZING CURRENT MYELIN +++++ AXON MEMBRANE NODE OF RANVIER -------INSIDE
NORMALLY A NERVE IS EXCITED BY A SYNAPSE OR BY A RECEPTOR • MANY NERVES SYNAPSE ON ANY GIVEN NERVE • RECEPTORS HAVE GENERATOR POTENTIALS WHICH ARE GRADED • IN EITHER CASE WHEN THE NERVE IS DEPOLARIZED BEYOND THRESHOLD IT FIRE AN ALL-OR-NONE ACTION POTENTIAL AT THE FIRST NODE OF RANVIER
THE SYNAPSE • • • JUNCTION BETWEEN TWO NEURONS CHEMICAL TRANSMITTER MAY BE 100, 000 ON A SINGLE CNS NEURON SPATIAL AND TEMPORAL SUMMATION CAN BE EXCITATORY OR INHIBITORY
THE SYNAPSE INCOMING ACTION POTENTIAL CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
THE SYNAPSE INCOMING ACTION POTENTIAL CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
THE SYNAPSE INCOMING ACTION POTENTIAL CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
THE SYNAPSE CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • • • • RECEPTOR • • • ENZYME ION CHANNEL
THE SYNAPSE CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
THE SYNAPSE CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
THE SYNAPSE CALCIUM CHANNEL • • • SYNAPTIC VESSICLES • • • RECEPTOR • • • • • • ENZYME ION CHANNEL
POSTSYNAPTIC POTENTIALS IPSP RESTING POTENTIAL TIME EPSP
TEMPORAL SUMMATION TOO FAR APART IN TIME: NO SUMMATION TIME
TEMPORAL SUMMATION CLOSER IN TIME: SUMMATION BUT BELOW THRESHOLD TIME
TEMPORAL SUMMATION STILL CLOSER IN TIME: ABOVE THRESHOLD TIME
SPATIAL SUMMATION SIMULTANEOUS INPUT FROM TWO SYNAPSES: ABOVE THRESHOLD TIME
EPSP-IPSP CANCELLATION
NEURO TRANSMITTERS • • • ACETYL CHOLINE DOPAMINE NOREPINEPHRINE SEROTONIN • • HISTAMINE GLYCINE GLUTAMINE GAMMAAMINOBUTYRIC ACID (GABA)
• Therefore, to stimulus caused excitation, it should grow fairly quickly. • With its slow increase in the excitability threshold is increased, so slowly rising stimulus must reach a much greater magnitude than the instantaneous build-up it. • The dependence of the threshold on the speed of its rise also is hyperbolic (inversely - proportional relationship). • Stimuli with a very low rate of increase may not cause a response in the form of propagating excitation. This increase in excitability threshold of the action of slowly increasing incentives is the name of accommodation. • The mechanism of accommodation associated with more rapid an early increase in the critical level of depolarization compared with the development of local depolarizing membrane processes. Na - membrane system at the same time is inactivated before the potential reaches a critical level
• There is for each of excitable tissue minimum gradient - the minimum rate of growth of the stimulus, in which the fabric is able to respond to the excitation of this stimulus. Nerve, having a higher excitability than skeletal muscle, faster akkomodiruet. Its unit - rheobase / sec. • The practical significance of this law: Given the ability of tissue to the accommodation for the assessment of the functional state of tissues used rectangular elektrostimuly. • This law has other aspects - how to use drugs, hardening.
The law of force stimulation • establishes the strength of stimulus dependence of response on the strength of the stimulus. • This dependence is not the same for individual cells and entire tissues. For single cell dependence called "all or nothing". • The nature of the response depends on a sufficient threshold stimulus. • Under the influence of subliminal stimuli magnitude of response there will be no (nothing). • When the stimulation threshold response occurs, it will be the same under the action threshold and supra-threshold quantities of any stimulus (part of the law - all). • For the aggregate of cells (for tissues), this dependence is different, the response of tissue is directly proportional to a certain limit the power of the applied stimulus. • The increase in response due to the fact that an increasing number of structures involved in response.
Law of the duration of stimuli. • The response of tissue depends on the duration of stimulation, but there is within certain limits and is directly proportional. There is a correlation between the intensity of stimulation and the time of his actions. This dependence is expressed in the form of a curve and time. • This curve is called the curve Goorvega Weiss Lapicque. • The curve shows that no matter how strong would have been a stimulus, it must act in a certain period of time. If a time interval small, the response does not occur. If the stimulus is weak, then how long would he not acted, the response does not occur. Stimulus strength is gradually increased, and at some point there is a response of tissue. This force reaches a threshold called the rheobase (the minimal intensity of stimulation, which causes the primary response). The time during which operates the current equal to rheobase, is a useful time.
Law gradient stimulation. • Gradient - a steep increase of stimulation. The response of tissue depends to a certain limit on the gradient of stimulation. If a strong stimulus for about the third time causing irritation response occurs rapidly, because it has a strong gradient. If you gradually increase threshold of stimulation, the tissue there is the phenomenon of accommodation. Accommodation - an adaptation of tissue to slowly increases with stimulus strength. This phenomenon is associated with the rapid development of inactivation of Nachannels. Gradually increases the threshold of stimulation, and stimulus always remains subliminal, ie, the stimulation threshold increases.
Nervous and muscular excitability determining in dentistry. • Chronaxymetry - at electrical current application on muscle current is coming also through nervous fibers located in it. That is why by chronaxy level determining one can tell about motor nerve fibers injure. Irritation threshold (rheobase) and chronaxy of nervous fibers are lower than in muscles. That is why at normal muscle chronaxy determining we in fact measure chronaxy of nervous fiber innervating it. If nerve is injured than nervous fiber is degenerated and under such conditions electrical stimulus applying to the muscle shows muscular fibers chronaxy (such chronaxy is longer in time).
• Between the irritation character and the answer-back reaction of an alive tissue there are close mutual relations, which find expression in the irritation laws.
• Irritation force law : the more force of an irritation, the more strong is answer- back reaction (up to known limits). The further stimulus force augmentation any more does not lead to the answer-back reaction increasing, and even cause return reaction, down to its disappearance. It is explained by the fact that each functional unit of tissues (for example, muscular) has its exaltation threshold. That's • 6 why while working the threshold stimulus, those fibers, for which this stimulus is of a such size are only involved in the answer. Others do not react.
• At stimulus force augmentation the new fibers are involved, for which the given stimulus is a threshold etc. Further, when the stimulus force will exceed the opportunities of all fibers of the given tissue, its answer-back reaction to the force augmentation will not change (the resources are settled!). Such stimuli, which cause the maximal answer-back reaction, are named in physiology maximal or optimal. At the even greater stimulus force augmentation the answer-back reaction even will decrease, as at such a stimulus force the separate functional fibers of excitable tissues even can be injured. In a result, the answer-back reaction decreases and this phenomenon in physiology is named pessimum, and the stimuli causing it - pessimal.
• The law "nothing" or "everything" ("all" or "nothing") is shown, first of all, at the cardiac muscle work analysis. According to this law, subliminal stimuli, acting to a cardiac muscle, do not cause an answer in it (it is "nothing"), and threshold and epiliminal stimuli cause answer-back reaction of the same size (it is named "everything"). Under the same law the functional unit of any excitable tissue works. Let's take, for example, a muscular fiber and we shall imagine, that threshold stimulus at it is 2 V (electrical current strain or voltage). If we act the stimulus of 1 V to it, we naturally shall not receive any reaction ("nothing"), and if we take the stimulus of 4 V, the muscle will give the same answer-back reaction, as well as on 2 V ("all"). Naturally, "nothing" and "everything" are relative concepts, as at the subliminal stimulus action there is a local answer (local potential), therefore it already cannot be treated as "anything".
• The law of force-time - with the augmentation of a stimulus force it is required less time of its influence to tissue for answer-back reaction reception. The relation between the duration and force can be expressed by hyperbolic curve, the both branches of which go at any stage in parallel to axes of coordinates. This last circumstance forms the basis that the stimuli of a very small size (less than the threshold) can not cause the answer-back reaction.
• The excitability curve demonstrates the exact relationship between the strength and the duration of a stimulus. So, it is also called the strength—duration curve (Fig. 1).
• Characteristic Features of the Curve The shape of the curve is similar in almost all excitable tissues. Following are some of the important points to be studied in the excitability curve: - Rheobase: This is the least possible, i. e. minimum, strength (voltage) of stimulus which can excite the tissue. The voltage below this cannot excite the tissue, whatever may be the duration of stimulus. - Utilization time: It is the minimum time required for a rheobasic strength (threshold strength) to excite the tissue. - Chronaxie: It is the minimum time, at which a stimulus with double the rheobasic strength (voltage) can excite the tissue.
7 - Fig. 1. Strength—duration curve.
Importance of Chronaxie • The value of chronaxie is used to compare the excitability in different tissues. • The measurement of chronaxie determines the excitability of tissue. • Longer the chronaxie, lesser is the excitability. Chronaxie in human skeletal muscles varies from 0. 08 milliseconds to 0. 32 milliseconds. • In frog's skeletal muscle, it is about 3 milliseconds. • Chronaxie is 10 times more in skeletal muscles of infants than in the skeletal muscles of adults.
• Chronaxie is shortened by increased temperature and prolonged in cold temperature. It is shorter in homoiothermic animals than in poikilothermic animals. Chronaxie is shorter in red muscles than in white muscles.
• In physiology they determine one more property of excitable tissues, which has received the name a lability. It is a functional mobility of tissues, its parameter is the potentials action maximal number, which the excitable tissue is capable to generate per 1 second according to a rhythm of a submitted boring (irritation). The normal size of a lability, e. g. , for a nervous tissue makes 500 -1000 impulses per second, and for skeletal muscles - 150 -200 impulses per second. There is a skeletal muscles lability rising with ageing. It is shown in augmentation of irritation frequency, at which the gear (incomplete) tetanus turns in smooth. In newborn's muscles it occurs at a stimulus frequency 4 -20 per second, at adulthood - 50 -100 impulses per second.
• Electrical changes during muscular contraction When the muscle is stimulated, electrical changes occur before onset of mechanical changes. Usually the electrical events in a muscle (or any living tissue) are measured by using a Cathode Ray Oscilloscope. Nowadays, sophisti cated electronic equipments like computerized polygraph are available to record analyze the electrical activities of any tissue.
• RESTING MEMBRANE POTENTIAL The potential difference between inside and outside of the cell under resting condition is known as resting membrane potential.
Fig. 2. Resting membrane potential
Laws stimulation of excitable tissues • 1) the law of force stimulation; 2) the law of the duration of stimulation; 3) the law of the gradient stimulation.
Law of stimulation I law: the stronger the stimulation, the stronger - the response of tissue. (up to certain limits) Open E. Du. Bois - Reymond (Emil Du Bois - Reymond, a disciple of J. Mueller, author of 3 part "Studies on animal electricity" (1848, 1849, 1869) Unilateral conduct excitation.
II Law of force-time "stimulus. • The reaction of tissue reveals the dependence not only on the strength of stimulation, but the time of its impact. • The more prolonged stimulation, the stronger the response of living tissue.
Strength—duration curve (by Lapik) The minimum time at which the rheobase can cause excitation of tissue called a useful time. The least useful time inherent in the peripheral somatic NS and skeletal muscle. R - rheobase 2 - twice the rheobase UT - useful time of the current C - chronaxie Lapik introduced the concept of physiological science chronaxie and continued use as a unit of the threshold of stimulation does not force, and the time of stimulation. Determination of the useful time is difficult in practice, so the study chronaxy has been used in practic
Chronaxie • - this is the minimum time at which the current tension in 2 rheobase, causes excitement. • Chronaxie measured in milliseconds or sigma. • Chronaxie nerve and muscle fibers is equal to the thousandth person and decimal fractions of seconds. • In smooth muscle it is much more.
• • When short-term stimulation of the curve of force - time becomes parallel to the Y-axis, ie, the excitation does not occur with any strength of the stimulus. Approximation of the curve asymptotically to a line parallel to the abscissa, does not allow enough time to accurately determine useful because Minor variations in the rheobase, reflecting changes in the functional state of biological membranes at rest, followed by large fluctuations in time of stimulation. In connection with this proposed measure Lapik etc. datum - H, ie, the duration of the stimulus, equal to twice the rheobase [in the figure corresponds to the segment OD (EF)]. For a given value of the stimulus the least time of its action, in which possible threshold effect, the same OF. Found that the shape of the curve characterizing the excitability of the tissue, depending on the intensity and duration of the stimulus, similar for a variety of tissues. The differences between them concern only the absolute values of the variables and the first time, ie excitable tissues differ in the time constant irritation.
• There are chronaxy subordinate (sibling) and constitutional (isolated tissue).
There are chronaxy subordinate (sibling) 2/17/2018 • constitutional (isolated tissue). . 82
Hronaksometriya • Hronaksometriya - (time axia - number metreo measured) method for determining the excitability of the tissue or organs by identifying the relationship between the threshold intensity of stimulation, which causes excitation, and prolonged its action. Chronaxie used in the diagnosis of lesions of the central and peripheral NA, musculo - skeletal system, delineation of the pathological focus and the functional state of individual brain structures during surgical operations. The relative simplicity of the method and sufficiently clear interpretation of the results made it possible to use chronaxy in sports medicine, physiology of labor, industrial and sanitary hygiene. In fact determined by the subordinate chronaxie. If the nerve is damaged or lost motor neurons of the spinal cord, chronaxy already revealed constitutional.
III law: the gradient of the stimulus • Among the very important aspects of the impact of the external world on tissue is a rapid increase in the stimulus in time. This relationship was noticed even Du. Bois - Reymond in the nerve - muscle preparation frog, and further studies in the 80's of last century B. Verity and later in the 30 years of this century - A. Hill, which enabled us to clarify the existence of the relationship between speed growth stimulation and response of tissues. • The essence of the law: the higher the gradient of the stimulus, the stronger the reaction of tissue
• When two electrodes are connected to a cathode ray oscilloscope through a suitable amplifier and placed over the surface of the muscle fiber, there is no potential difference. There is zero potential difference. But, if one of the electrodes is inserted into the interior of the muscle fiber, potential difference is observed across the sarcolemma (cell membrane). There is negativity inside the muscle fiber in relation to the outside. This potential difference is constant and is called resting membrane potential. The condition of the muscle during resting membrane potential is called polarized state. In human skeletal muscle, the resting membrane potential is -90 m. V.
• To make tissue passed from a state of physiological rest in the state of excitation, the stimulus must be of sufficient strength to act adequate time and its magnitude should increase fairly quickly.
• Act I: the stronger the stimulus, the stronger (up to certain limits) and the response of tissue. Open Dubois - Reymond (Emil Du Bois - Reymond, a disciple of J. Mueller, author of 3 books "Studies on animal electricity" (1848, 1849, 1869). Du Bois tried to irritate the muscle by a direct current of different strength. He was able to measure the minimal current strength, which makes muscles shrink - this is the threshold intensity of stimulation. Thus, he introduced one of the basic concepts electrobiology. Du Bois - Reymond discovered that the thresholds are not absolute constant: different muscles have different thresholds. The threshold of excitability (TE) with intracellular stimulation ≈ 10 -7 - 10 -9.
• Since experimental physiology as a stimulus uses an electric current, denoted by TE in dimensions, or amperage, or, more likely to stress. Since the research of L. Lapin TE is denoted by the term rheobase. The strength of the threshold stimulus - one of the criteria for evaluating excitability, as higher the excitability of the tissue, the lower the threshold, ie force threshold of stimulation - a measure of excitability of the tissue.
• Irritating, whose strength is below the threshold, is called subliminal. the action of very weak stimulus, the response is not observed. Effects of subliminal stimulus causes certain changes in energy metabolism and tissue, and the more, the more the strength of the stimulus. However, the resultant shifts do not reach the critical level, which is required for the emergence of AP. Stimulus strength is greater than the threshold, called supra. At suprathreshold stimulation magnitude of the response increases. Increased response of tissue runs parallel to the increase in strength of stimulation, but to a certain limit (for each tissue). Once the response reaches a maximum value, further increase the strength of stimulation becomes ineffective or may be accompanied by depression ( "pessimum" by A. V. Vedenskiy), irreversible structural changes and even loss of the object.
• The value of the "law of force": the indicator "irritation threshold" allows us to study the excitability of the tissues and to compare it with other excitable. In physiology there is a representation of the possibility of some structures to respond to the law "all or nothing".
• On the effect of subliminal stimuli structure does not meet ( "none"), and increased strength of the threshold stimulus is not accompanied by the growth response ( "all"). This law was formulated in the 70 years of the last century by the English physiologist H. Boudichem in the study of cardiac muscle, and its position in the early 20 century. Used to explain the activity of all living entities.
• Law "all or nothing" is just for a single entity (neuron, axon, a single muscle fiber). If we are talking about general education (the nerve trunk, muscle), the total electrical activity in a certain range will increase (the dependence is gradual). • Criticism: AA Ukhtomsky, based on the works of British and Japanese physiologists, K. Lucas (1906), increasing the strength of stimulation, was increased contractions, ie at a low threshold intensity of reaction, only the most excitable fibers. A gradual increase in the strength of stimulation involves less excitable fibers. Consequently, each muscle fiber responds to the law "all or nothing".
• H. Kato (1934): The law is valid for the isolated muscle fibers. Thus It was shown that the organism is typical dependence of the reaction on the strength of stimulation and response in an "all or nothing" - a special case of response, a kind of trigger for functional items of the nervous and muscular tissues.
• Act II of "power time" stimulus. The reaction of tissue reveals the dependence not only on the strength of stimulation, but also the time of its impact. The longer stimulus, the stronger and the response of living tissue. Du Bois - Reymond trying to figure out how to affect the muscle action of the current time and from - the imperfect instruments (inertia galvanometers) came to the conclusion that the duration of the current role is not played) - and wrong.
• A. Fick (1863) (Professor, University of Zurich) on the muscle of the bezzubka mollusc (slowly instituted) was able to establish the inverse relationship. a I = - + ba, b - const I - current strength t - time of t T. Entelman (1870) - had a parallel experience in the ureter.
• In the early 20 century. The relationship between the forces of time studying Goorveg J. (1892), Weiss M. (1901) and L. Lapik (1909). They found that the TE is inversely related to duration. Lapik used the original instructional techniques (gun, coupling and uncoupling circuit, capacitors). These studies have shown that these ratios are determined by a hyperbolic curve. The minimum time at which the rheobase can cause excitation of tissue is a useful time.
• The least useful time characteristic of the peripheral somatic NS and skeletal muscle. Lapik introduced the concept of Physiological Sciences chronaxie and continued use as a unit of the threshold of stimulation does not force, and the time of stimulation. Defining a useful time to practice is difficult, therefore chronaxie study has found application in practice.
• Chronaxie - is the minimum time, with current voltage in 2 rheobase, causes excitement. Chronaxie measured in milliseconds or sigma. Chronaxie nerve and muscle fibers of man is thousandths and ten thousand shares of a second. In smooth muscle it is much more. Distinguish chronaxy subordinated (sibling) and constitutional (isolated tissue).
• Chronaxiemetria - (time + axia - number + metreo measured) method for determining the excitability of the tissues or organs by identifying the relationship between the threshold strength of stimulation, causing the process of excitation, and prolonged its action.
• Chronaxie used in the diagnosis of lesions of the central and peripheral NS, mobility - the locomotive system, delineation of the pathological focus and the functional state of individual brain structures in the process of conducting surgical operations. The relative simplicity of the method and sufficiently clear interpretation of the results allowed us to use chronaxy in sports medicine, physiology of labor, industrial and sanitary hygiene. In fact determined subordinated chronaxie. If the nerve is damaged or lost motor neurons of the spinal cord, chronaxy detected already constitutional.
• III of the gradient force. Among the very important aspects of the impact of the external world on the live tissue is a rapid increase of the stimulus in time. This dependence has been noticed yet Dubois - Reymond on nerve - muscle preparation of a frog, and further studies in the 80's of last century B. believes, and later in the 30 -ies of the century - A. Hill, which allowed us to clarify the existence of the relationship between speed growth stimulation and response of tissues.
• The essence of the law: the higher the gradient of the stimulus, the stronger the reaction of tissue. Therefore, to the stimulus caused excitation, it should grow fairly quickly. With its slow build-up raises the threshold of excitability, therefore, slowly rising stimulus must reach a much greater magnitude than the instantaneous build-up it. The dependence of the threshold on the speed of its rise also has a hyperbolic character (inversely - proportional dependence).
• Stimulus with a very low rate of increase might not trigger a response in the form of propagating excitation. This increase in excitability threshold by the action of slowly increasing incentives is the name of accommodation.
• The mechanism of accommodation associated with more rapid and more rapid increase in the critical level of depolarization compared with the development of local depolarizing the membrane processes. Na + - system membrane with inactivated before the potential reaches a critical level.
• There is for each of excitable tissue minimum gradient - the minimum rate of increase of the stimulus, in which the fabric is able to respond to the excitation of this stimulus. Nerve, having a higher excitability than skeletal muscle, accommodates faster. Its unit - rheobase / sec. The practical significance of this law: Given the ability of tissue to the accommodation for the assessment of functional state of tissues used rectangular electro stimulus. This law has other aspects - how to use drugs, tempering.
• Features of the DC on the fabric. Even in 1859, Pfluger, studying the action of direct current to the tissue, established a number of laws that were formulated in the form of three laws.
I. Polar Law irritation. • DC has a stimulating effect on the fabric only at the time of closure under the cathode, but at the time of breaking under the anode. Threshold of irritation when disconnecting when stimulation occurs under the anode. Pfluger only found these patterns, but the study of the mechanism of DC in tissues has been possible only through the microelectrode technique. It was found that in the application to the fabric surface of the anode + - positive potential on the outer side of the membrane increases - is in this place passive giperpolation, while apposition of the cathode - - positive potential on the outer side of the membrane decreases, and at this point there is a passive depolarization. They are called passive because of the tissue there is a change in membrane potential is not due to changes in ion permeability of the membrane itself, but under the influence of the cathode and anode
I. Polar Law irritation. • Excitation is produced at time of switch on electrical circuit - under Cathode • Excitation is produced at time of switch off electrical circuit - under Anode • Curve of potential Curve of exitability C A
• • Increase in membrane potential at the anode (passive hyperpolarization) is not accompanied by increases in ion permeability of the membrane even with a large force of the applied current. Therefore, the closure of the DC excitation under the anode does not occur. In contrast, the decrease in membrane potential at the cathode (passive depolarization) involves a transient increase in membrane permeability to sodium ions and slow-growing and persistent increase its permeability to potassium ions. So - then the closure of the DC excitation occurs under the cathode. Thus, the momentary closure leads to a gradual increase in polarization at the anode (hyperpolarization) and reduce the polarization at the cathode (depolarization). When disconnecting a slow return of membrane potential to its initial level. As already mentioned, Pfluger found that the reflex-forming impact reflexunforming efficiently, ie stimulation threshold for the closure of lower than when disconnecting. This is explained by the fact that if the initial depolarization at the cathode need very little stimulus to cause further depolarization, ie initial depolarization under the cathode, quickly reaches a critical level.
• Act II physiological galvanotonus. According to this law during prolonged passage of direct current in the excitability of the tissue changes. She rises at the cathode and it is called katelektroton, the anode is reduced excitability and it is called anelektroton. Excitability increases not only directly under the cathode, but also in neighboring areas. Similarly anelektroton means a decrease in excitability, not only directly under the anode, but also in neighboring sites with one difference, however, that a change in the excitability of the distance from the cathode and anode, less significant than in areas where applied directly to the anode and cathode. Make sure this is possible, defining the threshold of stimulation in the nerve fiber to the passage of DC and after prolonged its effects.
• With this in place of the application of the cathode and in neighboring areas of the stimulation threshold is lowered, while in the field of anelektroton it becomes higher. B. F. Verigo complement the established laws of Pfluger and showed that under prolonged dc electrotonic changes in excitability are distorted: a cathode, the initial increase in excitability (katelektroton) followed by its decrease - catodic depression and reduced excitability under the anode is gradually increased. • In the light of modern data due to electrotonic changes as follows. Electrotonic current in the conductor of the second kind, which are all living tissue, causing the movement of ions: negatively charged ions to the anode, a positively charged - to the cathode. This leads to more passive changes in membrane hyperpolarization and an increase in membrane potential at the anode and cathode polarization is a decrease (depolarization) and the membrane potential is also reduced.
• Thus, membrane hyperpolarization is the essence of anelektroton, membrane depolarization - katelektroton. This physical galvanotonus (movement of ions) leads to a change in physiological properties - excitability and conduction at the poles of the stimulating current. The resulting passive membrane depolarization under the cathode increases its permeability to sodium. This increase in sodium permeability of the membrane depolarization and accompanied by a mean increase in excitability. Increased sodium permeability lasts 0. 4 milliseconds, and then there is the process of sodium inactivation caused by prolonged depolarization of the membrane. However, significantly increases the permeability of the membrane for potassium ions. As soon as the current of sodium ions decreases and increases the current of the potassium ion membrane excitability under the cathode decreases and there catodic depression, open chains.
• III. Muscle contraction depends on the strength of direct current and its direction. Pfluger, depending on the location of the electrodes of direct current to the nerve - muscle preparation distinguish upward and downward direction of current. If the cathode is located farther from the muscle, and the anode closer to the muscle, then this upward trend of current. And if the cathode is closer to the muscle, and the anode is on, then this direction - downward. ↑ + and - to ↓ - K + and Ascending Descending
• He is also distinguished by a current of the weak and the threshold, the average - slightly above threshold and strong, which causes a sufficiently rapid movement of ions toward the poles (physical galvanotonus).
amperage strong current medium current direction ↓ - к +а + + + ↑ + weak current + + - +а -к + + -
• Regardless of the direction of the weak current causes the excitation of nerve and muscle only at the circuit, because He is a threshold, and when closing the excitatory effect is absent, because according to the law when closing the polar current is weaker, it will be subliminal and therefore has no exciting effect.
• The average current - a current above threshold. It is enough to cause excitement not only for the closure, but also when disconnecting, regardless of the direction of current. Under the influence of the strong current has the value of its direction. Thus, in a downward direction closer to the muscle is the cathode, while the anode is further away from it. With the closure of the excitation occurs at the cathode and easily reaches the muscle, causing it to decrease. At the anode part at this moment, excitability and conductivity decreases because value of the membrane potential increases as a result of hyperpolarization. There is a kind of block. However, since
• • This site is located on the muscle on the cathode, it does not preclude the holding of excitation arising at the cathode and the muscle is reduced. When a downward direction, but at the moment of breaking the muscle contraction does not occur, because at this moment there is excitement at the anode, which is located further away from the muscles, and the cathode on the way to the excitation coming from the anode to the muscle, because of the disappearance of katelektroton, excitability and conductivity sharply decreases and the cathodic area is a sort of block for the excitation. Therefore, when disconnecting a strong downward current muscular contraction does not occur. When the upward direction at the time of closure the excitation arising at the cathode, located farther from the muscle on its way to extinguish the muscle of the anode, where the excitability and conduction depressed, and the effect of reducing it. When closing the same in the area under the anode occurs anode - reflex-unforming excitement which easily reaches the muscle and cause its decline. According to current under the action of a very strong direct current in the area under the anode is accompanied by the breaking of the anode - reflex-unforming excitation and is accompanied by the appearance of action potential, because anode weakens inactivation sodium permeability of the membrane. Because in this case, enhancing the ability of the membrane to pass into the sodium and potassium also reduced permeability, which contributes to depolarization of the membrane.
• Practical use: if you want to block conduction of excitation along the nerve (pain), then you can use direct current, while the excitability of the anode will be reduced, leading to a block of excitation. DC has a wide application in medicine.
• For therapeutic purposes, using low voltage direct current (30 m. A) and low power (up to 50 m. A). This method is called galvanization. Arising under the action of the DC in the mucosa of the mouth vascular reactions contribute to the improvement of local metabolism, regeneration of the epithelium. With the help of DC probably more effective introduction of medicinal substances, particularly in the tooth and periodontal tissue. This method of drug electrophoresis. Phenomena galvanotonus underlie method electro anesthetizing. Practical use: if you want to block the excitation of the nerve (pain), you can use direct current, while the excitability of the anode will be reduced, leading to a block of excitation. In addition to the above-mentioned methods of direct current is used in physiotherapy units to supply the numerous electrodiagnostic devices (EKGraf, EEG, EMG, oximeter, p. H-meters, etc. ).
situational problem • How is changed the excitability of the tissue, if the membrane potential increased by 20%, and the critical level of depolarization on - 30%? Baseline values: Eo = - 90 m. V. , Ek = - 60 m. V. • response • In this case, the new membrane potential was set to 108 m. V, and the critical level of depolarization of - 78 m. V. • The initial values of these indicators (- 90 m. V) and (-60 m. V). • Consequently, the initial difference between membrane potential and the critical level of depolarization did not change and remained equal to 30 m. V. • This means that the excitability of the membrane has not changed.
Control questions (feedback) • 1. What is the threshold force? • 2. How excitation depends on force of stimulus? • 3. How correspond among themselves force of stimulus and time of its action? • 4. For what tissues the law « all or none» is used? • 5. What occurs with excitable tissues at slow increase of force stimulus? • 6. What is the polar law of irritation?
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