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change in the condition of a nerve, muscle, or excitable tissue after exposure to a direct current of electricity. The phenomenon was first discovered in 1859 by the German physiologist E. Pflüger, who showed that excitability decreases in the region of the anode upon closure of the circuit (anelectrotonus) but increases in the region of the cathode (catelectrotonus). After gradual intensification of the current, closure of the circuit gives rise to action potential in the region of the cathode, whereas a decrease in excitability in the region of the anode may block conduction.
The Russian physiologist B. F. Verigo (1883, 1888), who significantly supplemented Pflüger’s data, found that upon prolonged exposure to a current the initial catelectrotonic increase in excitability gives way to “cathodic depression,” that is, excitability decreases, while a decrease in excitability in the region of the anode is converted to “anodic exaltation.”
Electrotonus can spread through nerve or muscle cells (perielectrotonus). The nature of the primary (after brief action of a current) and secondary (after prolonged action) electrotonic changes in excitability and conduction varies. Primary catelectrotonus and anelectrotonus are caused by shifts in membrane potential of excitable cells, depending on whether they are closer to or farther from the critical level at which action potential is generated. Secondary electrotonic phenomena result from action on the processes of inactivation of sodium permeability and activation of potassium permeability of the membrane of an excitable cell. By participating in the mechanisms responsible for the functioning of the nervous system, electrotonic phenomena play an important role in propagating impulses through the neural networks.
Research on electrotonus led to the development of techniques for stimulating the human motor apparatus. They are now used in the electrodiagnosis of diseases of the peripheral nervous and muscular systems.
L. G. MAGAZANIK