Excitation

Excitation, like inhibition, is one of the basic neurophysiological processes. The essence of these processes is currently far from sufficiently understood. Physiological study of these processes in various levels of the nervous system, as well as physicochemical study of their nature, have led to a multitude of various theories. The most studied area is the field of neuromuscular physiology, where the most well-known are the law of Dubois-Reymon (now outdated), establishing the connection between excitation and the speed of oscillation of electric current, the electro-polar law of Pflüger (Pfliiger), related to physiological electroton, measurement of the speed of excitation (Helmholtz) and others. Physicochemical study of nerve processes reduces to ion theories. The starting point of ion theories is that agents, causing various physiological effects in tissues, act through ions, by changing their concentration ratio. The most well-known are the theories of Nernst, Horweg, Loeb, Ber, Bershtegon, Lazarev. The question of the relationship between the strength of stimulation and the strength of the response divides physiologists into two camps—supporters and opponents of the 'all-or-nothing' law. Supporters of this law believe that stimulation either gives no effect at all (if it is subminimal) or immediately gives a maximal effect (if it reaches the threshold). Closely connected with the 'all-or-nothing' law is the nutritive theory of Verworn, explaining nerve processes by the states of assimilation and dissimilation of nervous tissue, then the Cambridge school, explaining them by states of facilitated conduction and passive resistance, and finally, Nernst's ion theory. The 'all-or-nothing' law was first formulated by Wundt. The essence of this theory is that a nerve or muscle, being in an inactive state (refractory phase), does not react at all to stimulations received at that time. On the contrary, during the active state, a nerve or muscle reacts maximally in response to any threshold stimulus, discharging completely the active potentials of the tissue. Having expended all its energy, the tissue naturally loses sensitivity to stimuli until the moment when, due to certain conditions, the tissue again acquires the energy needed for discharge. In accordance with the 'all-or-nothing' law, the refractory phase is conceived as a passive, inactive state of the tissue. Verworn, starting from the known thought of Claude Bernard that life consists of two different states—assimilation and dissimilation—built a theory according to which excitation corresponds to dissimilation, and the refractory phase to assimilation. The Cambridge school, also adhering to the 'all-or-nothing' law, explains the refractory phase somewhat differently. It treats the relative refractory phase as increased resistance experienced by excitation on its path. Finally, Nernst's ion theory is based on the position that subthreshold stimulations never summate. Opponents of the 'all-or-nothing' law adhere to one degree or another to Vvedensky's theory of parabiosis. According to this theory, nerve processes are in strict dependence on the state of the apparatus (tissue). The excitability of nervous tissue is connected with its lability or functional mobility. The degree of lability of nervous tissue is measured by its ability to conduct waves of high rhythm of oscillations. Every stimulation either increases the lability of the tissue, leaving behind increased excitability (corroboration), or decreases its lability (parabiotic action). Every stimulation, reaching a certain strength and frequency, in connection with the state of the apparatus, begins to act parabiotically. Parabiosis—a transitional state from excitation to inhibition—represents a stable, non-oscillating excitation, while according to this theory, inhibition is a stagnant wave of excitation. Thus, every, even negligible, stimulation in one way or another affects excitability, and conversely, excitability in one way or another affects the effect of stimulation. The starting position of Vvedensky's theory was the view of the refractory phase as an active active state resulting from the struggle of two waves of excitation approaching each other or meeting. The sequential development of this idea through the application of exceptionally illustrative experiments led him to the position of the stagnation of excitation waves as a result of changes in the properties (lability) of the tissue. The watershed between Vvedensky's theory and theories adhering to the 'all-or-nothing' law was Vvedensky's initial position on the activity of inhibition. Vvedensky's theory is close in direction to the theories of Sherrington and Pavlov. Directly connected with it is Uktomsky's theory of dominance. According to Uktomsky, dominance represents a dominant focus of excitation, accumulating in itself excitation from distant sources and inhibiting the work of other centers. According to the teaching of Sherrington, excitation and inhibition are connected in time and space (induction). The theory of reciprocal innervation of muscles (connected with the principle of 'common final path') states that simultaneously with the excitation in the spinal cord of the flexor muscles center, there occurs inhibition of the extensor muscles center of the same joint (and vice versa). According to Pavlov's theory, activities related to the cessation of the response are reduced to a single process of inhibition. Between excitation and inhibition there exists a time-space connection. One under certain conditions causes the opposite (induction) and transitions into this opposite (paradoxical phase). The cerebral cortex possesses the property of higher reactivity and variability, while at the same time having a certain stability of certain relationships. The theories of Pavlov and Vvedensky are the starting point for studying various forms of psychopathic excitation, and Zal'shon. Pathology of excitation. States of excitation in various mental diseases are apparently connected with the state of lability of nervous tissue. An example can be the so-called states of irritable weakness, expressed in the rapid change of increased excitability by states of inhibition. As for the symptomatology of states of excitation in the mentally ill, of course, what is most striking is motor excitation (inability of the patient to lie still, tendency to run, inclination to produce various movements, finally, generally increased need for activity). A particular form of it is speech excitation (incessant chatter, singing, cries, pronunciation of a meaningless set of words, etc.). In motor and speech discharges find their external expression also such forms of excitation as intellectual (flight of ideas: influx of thoughts and their frequent change, distractibility of attention to new and new subjects) and affective (excessive ease of occurrence and violent manifestation of affects, usually accompanied by their instability). More profound differences form the basis for distinguishing such types of excitation as catatonic, characterized by stereotypy and meaningless character (psychic unproductivity), manic, arising mainly from weakening of inhibitions (insufficiency of inhibitory processes), epileptic, for which complete clouding of consciousness, convulsive manifestations and aggressiveness are so characteristic, hysterical, with its ostentatious character and theatrical effects, etc. - Excited depression, see Melancholia. P. Zinoviev.