From Big Medical Encyclopedia

THE POTENTIAL CAUSED — fluctuations of bioelectric potential in any structures of a head and spinal cord at receipt of the nervous impulses resulting from irritation of receptors, esodic nerves or other structures of the central nervous system. Also such changes of bioelectric activity of a brain as reaction of involvement, reaction of assimilation of a rhythm, answers to direct electric irritation of structures of a brain belong to P. century.

P.'s registration is widely used in neyrofiziol, researches for the analysis and understanding of mechanisms of work of c century. N of page. In Kliniko-fiziol, researches P.'s analysis of century serves as additional diagnostic test at topical diagnosis patol, process in a brain, and also is used for studying of a pathogeny of nervous and mental diseases, etc. With the advent of highly sensitive electronic amplifiers and implementation of the specialized averaging computers the method of registration of P. of century began to be used widely at psikhol, researches. P.'s registration at the person allows to compare century objective parameters of bioelectric reactions with subjective reports of examinees. Similar researches are conducted for the purpose of studying fiziol, mechanisms of perception, emotional reactions, characterologic features of the personality, etc.

In 1875 R. Caton showed that in a brain in response to irritation of any perceiving touch body there are electric potentials. In 1913 V. Pravdich-Neminsky in experience on a dog registered in a cerebral cortex P.'s emergence of century at irritation of a sciatic nerve. In the late forties developed 20 century a method of registration of P. of century at the person from the surface of head skin.

In total P. differ century on a configuration of separate components at graphic registration, on stage of latency of emergence, on localization and the nature of changes under the influence of various factors. Have the largest amplitude and short stage of latency of P. of century in those sites (structures) of a brain where afferent impulses from the corresponding receptors arrive. Projective zones of bark of big hemispheres (visual, acoustical, somatosensory, etc.) and specific kernels of a thalamus (lateral and medial cranked bodies and back ventral kernels) belong to such structures. The items of century noted in these structures of a brain are called primary answers. They consist of the primary and positive phase of evoked potential and a pervichnootritsatelny phase of evoked potential having amplitude 400 — 600 mkv and stage of latency from 10 to 20 ms.

In bark of big hemispheres secondary P. are registered century (local and generalized), among to-rykh allocate 3 — 4 various look. All secondary local responses, as a rule, arise after primary answers, but can appear also in the absence of primary answers. Secondary local responses can be various duration with stage of latency of 40 ms and more, with an amplitude from 100 to 500 mkv.

There is no uniform point of view on origins of P. of a century yet. Consider that phases of primary answer and secondary responses are connected with consecutive inflow of vozbuzhdeniye to aksosomatichesky and akso-dentritic synapses of neurons of various structures of a brain. The primary and positive phase of primary answer reflects excitement of postsynaptic membranes in bodies of neurons, and the primary and negative phase of primary answer is expression of local excitement of dendritic branchings. Believe that phases of primary answer reflect receipt in a brain of information on physical parameters of an incentive: about its intensity, temporary characteristics, topography in relation to the receptive field. Fiziol, mechanisms of the secondary responses arising in 100 — 120 ms from the moment of influence of an irritant are connected by hl. obr. with gradual spread of activation on som of neurons also reflect processes of interaction between various structures of a brain.

See also Bioelectric potential .

Vibliogr.: Brezhe M. Electric activity of a nervous system, the lane with English, page 198, M., 1979; Ivanitsky A. M. Brain mechanisms of assessment of signals, page 69, M., 1976; Methods of clinical neurophysiology (studying of physiology of a brain of the person), under the editorship of V. B. Grechin, page 122, L., 1977; Roytbak A. I. The bioelectric phenomena in bark of big hemispheres, p.1, Tbilisi, 1955; Shagas Ch. Evoked potentials of a brain are normal also of pathology, the lane with English, M., 1975; Caton R. The electric currents of the brain, Brit. med. J., v. 2, p. 278, 1875; Prawdicz-Ne-m i n s k i W. W. Ein Versuch der Re-gistrierung der elektrischen Gehirnerschei-nung, Zbl. Physiol., Bd 27, S. 951, 1913.

Yu. A. Fadeyev.