lability functional

From Big Medical Encyclopedia

LABILITY functional (Latin labilis mobile, unstable) — functional mobility; the speed of course of elementary physiological reactions defining a functional condition of live substrate. Entered the concept «lability» into physiology of H. E. Vvedensky (1892), which under L. understood «the high or smaller speed of elementary reactions by which physiological activity of this substrate is followed». A. A. Ukhtomsky defined L. as speed, about a cut manages to pass this substrate from a condition of rest to a condition of excitement and back to full readiness for new action. Sometimes L. consider as the speed of the transmembrane ion fluxes defining extent of polarization of membranes, level funkts, conditions of cells and their systems (N. V. Golikov). In applied medicine and in chemistry the term «lability» designates instability, easy variability funkts, properties of substrate. In physiology, on the contrary,' size L. it is usually proportional to stability, resistance. A. A. Ukhtomsky emphasized that high physiological L. can serve as expression of resistance of excitable system to the alteriruyushchy (changing) factors. Having opened the law of increase of L. in process onto-and phylogenetic development, A. A. Ukhtomsky (1937) noted that in connection with increase of L. the indifferent excitability with low thresholds which was so reminding itself irritable weakness, or isteriozis (i.e. patol, increase in excitability of neurons at lowered by their L.), in development is replaced by special responsiveness to short incentives of the environment. As the best measure of lability of H. E. Vvedensky (1892, 1901) offered «the largest frequency of electric oscillations (action potentials) which this substrate can develop in unit of time, remaining in strict accordance with the frequency of the maximum irritation». The limit of synchronization of a rhythm of action potentials with a rhythm of irritation offered H. E. Vvedensky as a measure of L., corresponds to the capacity of a communication channel in sovr, theories of communication. As a measure also maximum rhythm of local electric answers (evoked potentials), synchronous with a rhythm of stimulation, duration of separate action potential, size of an absolute refractory phase, effective time, chronaxia can serve. The L is measured. and the speed of the ascending and descending phases of action potential.

Level L. characterizes the speed of emergence and compensation of excitement in any cells and their level funkts, states. It is possible to measure L. membranes, cells, bodies, and in system L. is defined by L. its least labile link. So, if L. a motor axon of a frog apprx. 500 reductions in 1 sec., L. muscle fiber apprx. 200, and L. a synapse apprx. 100, L. neuromuscular system will be apprx. 100 reductions in 1 sec. Owing to various L. various sites of a membrane of neuron of its L., measured from various synoptic entrances, will be various. L. various reflex arcs it is not identical and in the course of activity can change on the course of reaction both towards increase, and towards decrease. During the strengthening of active ionic transport and at hyperpolarization of membranes of L. increases, at depolarization of membranes of L. decreases with emergence at first of excitement, and then pessimal (ultraboundary) braking. Excitement and rhythmic activity arise at average, optimum level of L. and polarization of neurons. L. it is measured at registration of the caused bioelectric activity of cells, fabrics and bodies in the conditions of macroelectrode (total) and microelectrode (out of - and intracellular) assignments in a lab. and a wedge, practice for assessment funkts, conditions of various bodies (see. Bioelectric potential , Elektrokardiografiya , Electromyography , Elektroentsefalografiya ). By means of various funkts, tests, in particular rhythmic adequate stimulation of sense bodys, the L is defined. respective cortical fields and even separate neurons (reaction of following to a rhythm).

In 1928 A. A. Ukhtomsky described the phenomena of assimilation of a rhythm of irritations nerve centers later designated by the term «synchronization of activity of neurons». In a number of neurons process of assimilation of a rhythm is followed by reorganization of conformational features of receptive structures with formation is long the remaining selectively high responsiveness to an impulsation of a certain rhythm and a certain spatio-temporal characteristic (long-term memory). Changes of L., causing assimilation of a rhythm, provide formation of system reactions of a brain and phenomena of recruitment and switching off of separate neural groups in konstellyation of the dominating centers.

Disturbance of lability. Decrease in L., shown in the form of reduction or disappearance of answers to the second and the subsequent incentives at rhythmic irritation (the maximum adequate frequency), confirms disturbance of ability of structure to recover the power and plastic stocks necessary for implementation of full reaction. However and increase in ability of structure to react to high-frequency stimulation not always testifies to its optimum state; such phenomenon is more often it is observed at exaltation and can speak about so-called irritable weakness, or an isteriozisa. In such cases quickly there comes the exhaustion or exhaustion of reserves of the reacting structure.

At considerable loadings or in unfavorable conditions a part of excitable systems usually is reversibly damaged also by L. these structures, naturally, decreases. In the conditions of reversible disturbance of carrying out in neuromuscular synapses (partial blocking of secretion of a mediator) the muscle is capable to answer stimulation of a nerve with a bigger frequency, than normal. At the same time amplitude of answers of a muscle can increase. This results from the fact that the synchronous excitation wave, reaching neuromuscular synapses, finds them in various funkts, a state — a part of synapses transfers excitement to a muscle, other part (reversibly the damaged synapses) did not recover initial funkts, level yet. The impulse of excitement can pass, therefore. only through synapses of the first group. The following impulse finds them already in a condition of not excitability (refrakternost). Reversibly the damaged synapses by the time of arrival of the second impulse can recover the excitability thanks to influence of the first impulse which though does not cause transfer of excitement, but increases L. these synapses. In it the reason that at reversible damage of a part of synapses ability of the neuromuscular device to give reaction due to nonsynchronous inclusion in reaction of various groups of muscle fibers increases lies. In the conditions of norm already on the first incentive react almost all muscle fibers as they and their synoptic device are practically in an identical funkts, a state. From this it follows that so-called pessimal reaction of a muscle (normal) in the form of abrupt falling of amplitude of answers to the first incentives at high-frequency superthreshold irritation of a nerve is not an indicator of pathology. On the contrary, such reaction says that all groups of muscle fibers have high and identical reactivity.

Thus, usual criteria of L. not always adequately reflect funkts, a condition of fabric, especially a condition of difficult educations, napr, the nerve centers possessing special mechanisms of regulation funkts, a fortune of the elements making them (see. Nervous system ). The L used for studying. the test of assimilation of a rhythm shall be applied with the known care since it is impossible to identify mechanisms of assimilation of a rhythm in an elementary fiziol. to structure and in the complex system possessing the special mechanism of regulation of activity and being under integrative control from other systems. The applied criteria of L. are suitable only for the characteristic of working opportunities and a recovery rate of reactivity elementary fiziol, structures.

See also Excitement , Braking .

Bibliography: Vvedensky N. E. Ratios between rhythmic processes and functional activity of the excited neuromuscular device, Half-N of SOBR. soch., t. 3, page 84, L., 1952; it, Excitement, braking and anesthesia, in the same place, t. 4, page 9, L., 1953; N. V Brooms. Physiological lability and its changes at the basic nervous processes, L., 1950, bibliogr.; Kryzha-n about in with to and y G. N., Pozdnyakov O. M. and P about l of and r A. A. Patologiya of the synoptic device of a muscle, M., 1974, bibliogr.; At x t about m with to and y A. A. Collected works, t. 2, page 33, etc., L., 1951, t. 6, page 168, L., 1962.

N. V. Golikov; G. N. Kryzhanovsky (stalemate. physical.).