Electrophysiology

Electrophysiology, the doctrine of the origin and role of electrical energy in the organism. Historically, E. is in the closest connection with the development of the doctrine of electricity in physics. Its beginning was laid by the Italian physicist Galvani with his famous "balcony experiment" of 1786; dissected frog legs, long used as an electroscope for detecting currents of physical origin, when suspended by nerves to a metal balcony and swaying in the wind, reveal the appearance of an irritating electric current each time the ends of the legs come into contact with the metal balusters of the balcony. At this moment the circuit is closed, which includes, first, the metal parts of the balcony, and second, the tissues of the legs. Galvani claimed that the source of the current was the frog's leg. His contemporary, the physicist Volta, pointed out that the source of the current could be the metal parts of the balcony. Galvani's view, assuming a normal source of electromotive force in living tissue, can be called theory I. The view, according to which there is no need to attribute electrical tensions to the tissue, as they can arise in the rest of the experimental setup, can be called theory II. Subsequently, these two theories continued to oppose each other with varying success, until science had exact theoretical foundations that would force one to accept that electrical tensions in living tissue must exist and cannot not exist. The famous "Untersuehungen uber thierische Electricitat" (1848-1849) by Emil du Bois-Reymond, which raised E. to the level of exact scientific knowledge, stood on the point of view of theory I: in living substance, polarly charged molecules are assumed, and the arrangement and movement of which in the tissues determine the measurable electrical activity of the latter in rest ("resting current") and in excitation ("negative oscillation"). A critical review of the question led Hermann to the so-called alteration theory (1867), according to which in a fully physiologically balanced and resting tissue there are no electrical tensions, but they are introduced into it by injury ("demarcation current") and excitation ("action current"). This is an example of theory II. The solution theory of van't Hoff (1885), Arrhenius's theory of electrolytic dissociation of dissolved molecules (1887) and W. Ostwald's concept (1890) of the role of semipermeable to ions membranes turned the whole question in a new direction. The constant presence of mobile electric charges (ions) in any animal and plant tissue became the basic principle of the theory. The tensions with which ions of opposite sign tend to distribute themselves with the greatest electrical neutralization in the solution, where their equilibrium is disturbed, determine the electromotive forces in external circuits. For the new theory, the question is not how electrical activity can arise in a medium where there are ions, but how equilibria in solutions containing ions are disrupted. Ionic equilibria are disrupted due to the condensation of ions of the same sign in one or another area of the solution. Such condensation should arise, for example, on the surface of division between two immiscible solvents, if one of the ions is more soluble in the other phase than its partner; or if one of the partners is not chemically indifferent to the new phase; or if one of the partners more easily penetrates into the other phase. The retention of one of the partners near the surface of division will create the condition for the accumulation of the other partner at the same surface and the latter will serve as the place for the "potential jump". As models of bioelectric tensions, the Haber and Clemenceau potential (acid of different concentration, stratified by thin glass), the Beutner potential (salt solutions of different concentration, stratified by oil), the Bethe and Toropov potential (salt solutions penetrating through a porous barrier) have been reproduced and studied. One should distinguish between "surface potentials", depending on the formation of "double layers" on the surfaces of division between phases and on the one-sided adsorption to the surface of ions of one sign, and "membrane potentials", depending on the different permeability of the barrier to partner ions. Stationary potentials, undoubtedly present in the complex heterogeneous architecture of animal and plant tissue, may not manifest themselves as currents in the external circuit when the ionic layers on a closed circuit are arranged symmetrically. Violations of symmetry in the distribution of charges will lead to electromotive effects. Thus currents arise in the galvanic cells of the special organs of electric fish and fundamentally in the same way "demarcation currents" and "action currents" arise in muscles, nerves, nerve centers and in other animal and plant tissues. Stationary asymmetry in the distribution of ions leads to stationary electrical activity in tissues. Such a stationary asymmetry can arise if a barrier permeable to salt ions but impermeable to colloids serves as the occasion for the accumulation, for example, of protein on one side. Protein, having a certain charge and not having the possibility to penetrate through the membrane, will create an attraction for ions of the opposite sign to its side; and this attraction will lead to a stationary maintained asymmetry in the distribution of penetrating ions on both sides of the membrane (Donnan potential). Thus, between the protein-rich blood plasma and the protein-poor aqueous humor of the eye, a stationary current of 4-12 mV is maintained, as is predicted by the theory that sets the magnitude of the electromotive force of the bioelectric current depending on the condensation of ions in individual areas of the liquid conductor. If the potential is created by the adsorption of gaseous or liquid particles by the surface of a solid body, the density of particles outside the adsorption area is P_i, the density of them at point i, taken in the adsorption area P_a, the work required to transfer a particle from point a to point i, i.e., the adsorption potential at point i, will reach the magnitude: φ_i = RTln|P_i/P_a|, where T is the absolute temperature, and R is the Clapeyron constant: 0.0821 liter atmospheres. Similarly, if the concentration of an ion on one side of the membrane is C₁, and on the other side it has increased to C₂, the electromotive force is given by the Nernst relation: E = RTln(C₂/C₁). As can be seen, the regularities for the adsorption potential and for the concentration potential near the membrane are homogeneous here. The special organs of electric fish can develop voltages up to 800 V (Gymnotus electricus). This is very much, if one recalls that the maximum voltage of a muscle element is about 80 mV (du Bois-Reymond), and the highest voltage of the action current in a single nerve fiber is 16 mV (Erlanger and Gasser), 14-18 mV (Rosenberg), 30 mV (Schaefer). However, the difference is not so striking if one takes the voltages of individual cells in the fish organ: 0.14 V for Gymnotus electricus, 0.08 V for Torpedo, 0.048 V for Malopterurus. The order of magnitude of actual bioelectric voltages corresponds to the predictions of the theory. Further deepening of the bioelectric theory must go with the transfer into it of the methods of the latest "electronic physics and so-called chemical physics. E., its problematic and significance for physiology develop in the closest dependence on the current technical means. The following historical stages are noted here: 1) the invention of the galvanometer by Nobili - the first determinations of the directions of physiological currents; 2) du Bois-Reymond's multiplier - the discovery of the resting current and the negative oscillation during excitation; 3) Weidemann's compass with mirror mounting - the development of the famous electrophysiological schools in Berlin (du Bois-Reymond) and Königsberg (Hermann); 4) physiological application of the telephone - the study of rhythmic currents of the muscle during tetanus (Bernstein), the discovery of rhythmic currents in the tetanized nerve, the non-fatigability of the nerve, the transfer of the rhythm of excitations as they pass through devices of decreasing excitability (Vvedensky); 5) Lippmann's capillary electrometer - the development of the Cambridge school of Gotch and K. Lucas; 6) Einthoven's string galvanometer - the development of cardiography, the introduction of bioelectric research into clinical practice, the study of central rhythms, in our country the works of Yudin, Samoylov, Pravdich-Neminsky, Beritov, Vorontsov; 7) physiological application of Brown cathode tubes, as oscillographs, with amplifiers - the works of Americans: Bishop, Erlanger and Gasser; 8) oscillographs of Matthews, Siemens and others - with amplifiers - current research by Adrian on centers and receptors, in our country the study of currents in the cortex (Sarkisov, Livanov). The most outstanding discoveries in E. of recent times are the following: the action current of the nerve, known until now, was the summated effect of a bundle of fibers entering the nerve trunk. Gasser, Erlanger and Bishop (1922-33) managed to capture with the oscillograph the effects of individual fibers. Individual fibers of the trunk conduct impulses at different speeds, and at some distance from the site of irritation the impulses of individual fibers manage to diverge noticeably in time. Excitability, conduction velocities and the magnitude of the current amplitude are in direct dependence on the thickness of the fiber.

The most powerful, excitable, and rapidly conducting are found to be efferent motor pathways, and among afferent pathways, apparently proprioceptive ones (Matthews), in second place are tactile pathways, followed by temperature pathways (Ranson) and pain pathways (Erlanger). Adrian and Zotterman (1926) ground up the m. sterno-cleido-mastoideus of a frog to the point where only a single proprioceptive nerve ending remained. When the muscle was stretched, the stronger the stretching, the more frequent afferent impulses occurred. The natural central rhythm of impulses is always lower than that obtained by electrical stimulation of afferent nerves and is not synchronized with it, as the latter is (Gasser, 1928). In the nerve centers of the medulla oblongata, a gradual and smooth periodic increase in potential has been established, indicating the occurrence of excitations in the form of long periods (Adrian, 1929). A single nerve impulse is not limited to the long-established brief action current of 1-2 ms. It is followed by a prolonged low-voltage potential lasting up to 100 ms, with an even longer positive after-potential up to 5 sec. (Emberson and Downing, 1929). Apparently the entire reconstructive metabolism of the nerve, oxygen consumption and heat production fall on this prolonged after-effect of a single impulse (Hill, 1932-33). A single nerve impulse is now depicted as a comet, in which the action current plays the role of the head, followed by a very long tail, on which the metabolic recovery process and the secondary electrical potential fall. During the formation of tetanus, the tails of individual impulses must intertwine in time, while the heads remain discrete. Thus, tetanus is not a simple product of superposition and not a simple summation of constant units; a frequent series of impulses, causing a frequent series of action currents, stimulates a collective metabolic wave, and the latter more completely restores the polarized structure of the nerve, making it more polarizable, capable of shorter intervals of excitation. - The recordings of bioelectric oscillations of the cerebral cortex are extremely remarkable, recently oscillographic with amplifying equipment (S. A. Sarkisov, 1933, Adrian, 1934), with harmonic analysis of electrocerebrograms, according to Fourier and according to N. A. Bernstein. The electrocerebrogram apparently represents the result of the summation of many and diverse periodic components, varying in individual areas of the cortex mainly in the magnitude of amplitudes. Strong peripheral irritations apparently cause an effect similar to putting the periodic components in the same phase with a simultaneous increase in amplitude (M. N. Livanov, 1935).