Electrophysiology

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electrophysiology

[i‚lek·trō‚fiz·ē′ä·lə·jē]
(physiology)
The branch of physiology concerned with determining the basic mechanisms by which electric currents are generated within living organisms.

Electrophysiology

 

the branch of physiology concerned with electric phenomena in living tissues (bioelectric potentials) and the mechanism of action of electric current on tissues.

The earliest work on “animal electricity” was done in 1791 by L. Galvani, who discovered that encircling an exposed frog nerve and muscle with a metal conductor causes muscle contraction. He interpreted the phenomenon to be a result of the action of electricity arising in living tissue. Galvani’s experiment was denounced by A. Volta, who maintained that the muscle had been stimulated by electricity arising in an external circuit consisting of heterogeneous metals. Galvani, however, subsequently induced muscle contraction without the use of a metal conductor: he touched the muscle to the injured portion of the nerve, thereby demonstrating beyond any doubt that living tissue is a source of electricity. Galvani’s experiments were confirmed in 1797 by the German scientist A. von Humboldt. In 1837 the Italian physiologist C. Matteucci showed that there is a difference in electric potentials between injured and intact portions of muscle; he also found that muscle contraction creates an electric current sufficient to stimulate other myoneural connections. In 1948, E. Dubois-Reymond, using a more advanced technique, confirmed that an injury to a muscle or nerve invariably results in a difference in potentials that decreases upon excitation. He discovered action potential (or negative variation, as it was called at the time), one of the main types of electric processes in excitable tissues.

Further progress was made in electrophysiology after the development of technical methods of recording weak and transient electric oscillations. In 1888 the German physiologist J. Bernstein proposed a differential rheotome for use in studying action currents in living tissues; the device measured the latent period and time of increase and decrease in action potentials. With the invention of the capillary electrometer, which measures low electromotive force, the study of action currents was repeated with greater precision by the French scientist E. J. Marey (1875) on the heart and by A. F. Samoilov (1908) on skeletal muscle. N. E. Vvedenskii (1884) used a telephone to listen to action potentials. The Soviet physiologist V. Iu. Chagovets played an important role in the development of electrophysiology; he was the first to use (1896) the theory of electrolytic dissociation to elucidate the mechanism responsible for the appearance of electric potentials in living tissues. In 1902, Bernstein formulated the principal elements of the membrane theory of excitation; Bernstein’s work was subsequently extended by the British scientists P. Boyle and E. Conway in 1941 and by A. Hodgkin, B. Katz, and A. Huxley in 1949.

In the early 20th century a string, or thread, galvanometer was used in electrophysiological research; the device overcame to a large extent the drift of other recording devices. W. Einthoven and Samoilov used the string galvanometer to identify the detailed characteristics of electric processes in a variety of living tissues. Undistorted recording of any forms of bioelectric potentials was not possible until the introduction of electronic amplifiers and oscillographs in the 1930’s-1940’s (G. Bishop, J. Erlanger, and H. Gasser in the United States). The use of these devices, the basis of electrophysiological technology, made it possible to lead off electric potentials both from the surface of living tissues and from deep-lying structures by means of buried electrodes (recording of electric activity of individual cells and derivation from within cells). Later electronic computers were widely used to distinguish very weak electric signals against a noisy background, to do an automatic statistical analysis of a large quantity of electrophysiological data, and to simulate electrophysiological processes. Many Russian and Soviet physiologists, including I. G. Tarkhanov, B. F. Verigo, V. Ia. Danilevskii, D. S. Vorontsov, A. B. Kogan, P. G. Kostiuk, and M. N. Livanov, made significant contributions to the development of electrophysiology.

Since electric potentials underlie the mechanism of generation of such processes as excitation, inhibition, and secretion, the electrophysiological method of recording electric potentials arising during active physiological functions in all living tissues is the most convenient and accurate method for studying these processes and measuring their temporal characteristics and spatial distribution. Moreover, electric current is the most universal stimulus of living structures. Chemical, mechanical, and other stimuli are also transformed on cell membranes into electrical changes after acting on tissue. Therefore, electrophysiological methods are widely used in all branches of physiology to induce and record the activity of various organs and systems. They are also widely used in pathophysiological studies and in clinical practice to determine functional impairment of vital functions. Some electrophysiological procedures, for example, electrocardiography, electroencephalography, electromyography, electroretinography, and electrodermography, have become valuable diagnostic aids.

The principal concerns of modern electrophysiology are (1) the physicochemical processes on the cell membrane that give rise to electric potentials and changes therein during active physiological processes, (2) the biochemical processes that supply energy for the transport of ions across membranes and for the creation of ion gradients—the basis for the generation of these potentials, (3) the molecular structure of membrane channels that selectively allow certain ions to cross the membrane and thereby trigger various forms of active cell reactions, and (4) the simulation of bioelectric phenomena on artificial membranes.

REFERENCES

Galvani, A., and A. Volta. Izbrannye raboty o zhivotnom elektrichestve. Moscow-Leningrad, 1937.
Brazier, M. Elektricheskaia aktivnost’ nervnoi sistemy. Moscow, 1955. (Translated from English.)
Beritov, I. S. Obshchaia fiziologiia myshevhnoi i nervnoi sistemy, 3rd ed., vols. 1–2. Moscow, 1959–66.
Vorontsov, D. S. Obshchaia elektrofiziologiia. Moscow, 1961.
Hodgkin, A. Nervnyi impul’s. Moscow, 1965. (Translated from English.)
Katz, B. Nerv, myshtsa i sinaps. Moscow, 1968. (Translated from English.)
Hodorov, B. I. Obshchaia fiziologiia vozbudimykh membran. Moscow, 1975.
Kostiuk, P. G. Fiziologiia tsentral’noi nervnoi sistemy, 2nd ed. Kiev, 1977.
Erlanger, J., and H. S. Gasser. Electrical Signs of Nervous Activity. Philadelphia, 1937.
Schaefer, H. Elektrophysiologie, vols. 1–2. Vienna, 1940–42.
Hubbard, J., R. Llinás, and D. Quastel. Electrophysiological Analysis of Synaptic Transmission. London, 1969.

P. G. KOSTIUK

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