the weakening of an excitation according to the extent of its distribution along a nerve or muscle fiber.
In normal nerve and skeletal-muscle (striated) fibers of vertebrate animals, an excitation or, specifically, its electrical component—the activity potential—conforms to the so-called all-or-none rule—that is, it arises only after the stimulus attains threshold intensity; once it arises, it is distributed further without decrement. In certain tissues (for example, in many arthropod muscles) excitation is distributed with decrement even under normal conditions. According to the membrane theory of excitation, nondecremental conduction of excitation is converted to decremental conduction in all cases when there is a decrease in regenerative depolarization, which is basic for the formation of the activity potential. This takes place, for example, when a nerve or muscle is under the influence of anesthetics or narcotics and when there is cessation of blood circulation.
B. I. KHODOROV