ELECTROTONIC PHENOMENA (a synonym electrotone physiological) — change of excitability and conductivity in body tissues under the influence of direct electric current.
For the first time E. I. were found by E. Pflyuger in 1859 in an experiment on nerve-muscle preparation. Irritating a nervous trunk with direct electric current, he found out that at closing of the circuit of a direct current excitement in a nerve arose only under the cathode, and at the time of disconnection — only under the anode. Afterwards the established dependence received the name of the law of electrotone of Pflyuger, or the polar law (see). E. Pflyuger established also change of excitability under the cathode and the anode during passing of direct electric current through excitable fabric. Further B. F. Verigo described the decrease in conductivity under the cathode which received the name of a katodichesky depression. Studying a parabiotic condition of nerves, N. E. Vvedensky found fluctuations of excitability on nek-rum distance from poles of the operating direct current, to-rye them were called perielektrotony. Studying E. I. it was continued by the Soviet physiologists L. L. Vasilyev, D. S. Vorontsov, V. S. Rusinov, etc.
At action by direct electric current on nerve fibril or a muscle directly under the cathode (a negative pole) and in the neighboring sites of fabric excitability (catelectrotonus) increases that is shown by decrease in threshold force of the testing irritant; under the anode (a positive pole), and also in the neighboring sites of excitable fabric, on the contrary, there is a decrease in excitability (anelektroton). If direct electric current affects fabric long enough, then the nature of change of excitability is perverted: under the cathode initial increase in excitability is replaced by decrease (a katodichesky depression), and the excitability under the anode lowered gradually increases (apodichesky exaltation). With the advent of a method of direct registration of membrane potentials of cells (see. A microelectrode method of a research) became possible to study the mechanism of change of excitability at action by direct electric current on excitable fabric. Passing of direct electric current through living excitable cells is followed by changes of polarization of their membrane both towards reduction (depolarization), and towards increase (hyperpolarization), and also change of size of a critical level of depolarization. The similar subthreshold not extending changes of membrane potential registered near the irritating electrode received the name of electrotonic potentials. Electrotonic changes of membrane potential are not connected with active changes of permeability for ions. Electrotone has purely physical nature, is defined by passive characteristics of a membrane and cable properties of excitable nerve or muscle fiber (see. Nerve fibrils). At short action of a direct current increase in excitability under the cathode is a direct consequence of depolarization of a membrane and approach of level of threshold potential to a critical level of depolarization. Decrease in excitability under the anode results from increase in rest potential (hyperpolarization) and its distances from the level of critical depolarization of a membrane. Long action of a direct current on excitable fabric leads not only to shift of a membrane poteptsial, but also to change of a critical level of depolarization. Under the cathode there is a reduction of these sizes, but on an absolute value of an izmeeneniye of a critical level of depolarization it is more, than membrane potential that leads to increase of threshold potential and, therefore, to decrease in excitability. Under the anode increase in membrane potential and a critical level of depolarization is observed, but owing to bigger increase in a critical level of polarization there is a reduction of threshold potential that leads to increase in excitability. At long action by a subthreshold direct current the critical level of polarization under the cathode decreases so that threshold potential becomes more reference value, and amplitude of action potential as a result decreases up to its total disappearance, i.e. the Catholic depression of Verigo (fig.) develops. According to the membrane theory of excitement (see) the reason observed E. I. the inactivation of permeability of ions of sodium through a membrane caused by its long depolarization is. At the same time considerably permeability of a membrane for potassium ions increases.
Change of excitability under poles of the operating direct current is followed by conductivity change. Under the cathode at increase in excitability the speed of carrying out nervous impulse on nerve fibril increases, and during a Catholic depression the speed of carrying out decreases and the full block of carrying out develops. Under the anode decrease in excitability leads to speed drop of carrying out excitement.
The possibility of change of excitability of nerves and muscles with direct electric current is applied in experimental neurophysiology to studying of membrane mechanisms of excitement. In neurologic and neurosurgical practice influence by poles of a direct current on excitable fabrics is used for the directed change of a functional condition of nerves, muscles and c. N of page.
Bibliography: Latmanizova L. V. Sketch of physiology of excitement, M., 1972; General physiology of a nervous system, under the editorship of P. G. Kostiuk, L., 1979; Hodorov B. I. General physiology of excitable membranes, M., 1975; Pfluger E. F. W. Untersuchungen uber die Pbysiologie des Electrotonus, B., 1859.
Yu. A. Fadeyev.