EFAPS

From Big Medical Encyclopedia

EFAPS (Greek ephapsis touch; the synonym an electric synapse) — the site of contact of membranes of shoots of two neurons, excitement from one cell to another is transferred to Krom by means of electric current.

For the first time electric transfer in a synapse between a huge axon of a belly nervous chain and a motor nerve in cancer was found by E. J. Furshpan and D. D. Potter in 1957.

On morphology E. have the same structural organization, as well as synapses with the chemical mechanism of transfer of excitement (see the Synapse). However in E. a synaptic gap already, than in chemical synapses, and distance between periblasts of membranes in E. makes

only 2 nanometers. Under a microscope sites of rapprochement of membranes have an appearance of roundish plates, to-rye are called slot-hole contacts (neksusa). Electronic microscopic examinations revealed nek-ry features of their ultrastructure. On surfaces of the membranes adjoining on a crack there are structures which are densely packed in the form of a polygonal grid. Consider that these educations serve as cytoplasmatic channels for communication between internal environments of the contacting cells. It is experimentally proved that molecules of nek-ry dyes can pass through E, from one cell in another, without leaving on extracellular Wednesday. Possibly, intercellular channels can have additional value in transfer of molecules RNA, cyclic AMF and other macromolecules.

As well as synapses, AA. divide on aksosomatichesky, akso dentritic, dendro-dentritic, somato-somatic, dendrosomatichesky and akso-axonal. They are found in different types of animals in bark of a cerebellum and in huge neurons of a kernel of Deyters, in an olfactory bulb and a ventral cochlear kernel of a brain of a rat, in a neocortex and ganglionic cells of a retina of primacies etc. Mechanism of transfer of excitement E. in principle it is similar to the mechanism of distribution of a bioelectric impulse on nerve fibrils. From a presynaptic bombway of an axon electric current through slot-hole contact «flows» into a postsynaptic cell and «follows» outside through its membrane, creating postsynaptic potential. One of the main sizes characterizing functional properties E., the coefficient of transfer, i.e. size of the relation of the potentials arising in pre-and postsynaptic membranes in the course of excitement is. Unlike a chemical synapse, in Krom the size of postsynaptic potential depends on the membrane potential of a cell, in E. postsynaptic potential does not depend on this factor. Similar mechanism of work E. provides transition of excitement from presynaptic structures to postsynaptic practically without delay characteristic of a chemical synapse. Unlike a chemical synapse E. it is not blocked pharmakol. substances, and also ions of magnesium and cobalt. AA. practically we do not tire since in it there is no synthesis of a mediator (see) that in combination with lack of a synaptic delay provides reliability E. and its constant availability for service. Important property E. the orientation of transfer of the depolarizing current since E is. passes current only from presynaptic structure to postsynaptic, and not vice versa. At the same time the hyper polarizing potentials easily pass also in the opposite (antidromic) direction. The investigator-on, efaps has the straightening properties and relative polarity of carrying out excitement.

Communication of neurons in c. N of page by means of E. provides synchronism in their work, edges it is most often observed among the motor-neurons managing work of effector bodies.

By the main method of studying of an efap-s as well as studying of a chemical synapse, the micro electrode method of a research is (see).

Bibliography: Kuffler S. V. and Nichols Dzh. G. From neuron to a brain, the lane with English, M., 1979; General physiology of a nervous system, under the editorship of V. N. Chernigovsky, L., 1979; E to l with D. Physiology of synapses, the lane with English, M., 1966; Furshpan E. J. a. Potter D. D. Transmission at the giant motor synapses of the crayfish, J. Physiol. (Lond.), v. 145, p. 289, 1959; they, Slow post synaptic potentials recorded from the giant motor fiber of the crayfish, ibid., p. 326; Structure and function of synapses, ed. by G. D. Pappas a. D. P. Purpura, N. Y., 1972. Yu. A. Fadeyev.

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