Theory of nerve impulse conduction

nerve impulse

A wave of excitation that spreads along a nerve fiber and manifests itself in electricity. (action potential), ionic, mechanical, thermal. and other changes. Provides information transfer from peripherals. receptor endings to nerve centers within the central nervous system and from them to effectors. It is characterized by a short-term decrease in the potential difference (relative to the initial one), resulting from a local shift in the ionic permeability of the excitable membrane. The energy necessary for the transmission of N. and. is released in the nerve itself. N. and. arises according to the “all or nothing” law, i.e. it does not depend on the strength and quality of the stimulus, and is capable of spreading spasmodically along the nerve fiber at a speed of 0.2 to 180 m/s. At the time of N.'s spread and. internal part of the nerve fiber is charged positively and the potential difference between the axoplasm and the outside. environment can reach 40-50 mV. Decrease in potential difference (depolarization) at the moment of N. and. depends on the concentration of Ca2+ and Mg2+ ions in the environment. Duration N. and. and the speed of its conduction depend on the temperature, diameter and structure of the nerve fiber. An important property of excitable tissue is refractoriness. The duration of the refractory period limits the ability of the nerve cell to reproduce rhythmic rhythms. impulses, i.e. determines its lability. In natural under conditions, series of N. and. continuously run along the nerve fibers. The frequency of these rhythmic discharges depends on the strength of the stimulus that caused them. Yes, move. neurons can conduct without distortion for approx. 500 N. and. per second, intermediate ones - up to 1000. After the refractory period, long-term trace changes in excitability follow, that is, aftereffects, which in the body of the nerve cell are expressed almost 10 times more strongly than in the axon. N. and. capable of self-propagation due to those electrical the currents that he creates; In this way, undistorted information is carried along the nerve fibers, encoded either by the frequency of action potentials or by the “pattern” of the discharge, that is, by a certain sequence of N. and. within the overall cell response time. About the transition of N. and. from neuron to neuron or to executive organs (see synapses).

Source: Biological encyclopedic dictionary on Gufo.me

Meanings in other dictionaries

Nerve impulse - See nerve impulse. Great Soviet Encyclopedia
NERVE IMPULSE - NERVE IMPULSE, an electrical signal propagating along the Axons of nerve cells. Nerve impulses transmit information throughout the NERVOUS SYSTEM. Scientific and technical dictionary
NERVE IMPULSE - NERVE IMPULSE - a wave of excitation propagating along a nerve fiber in response to irritation of neurons. Provides the transmission of information from receptors to the central nervous system and from it to the executive organs (muscles, glands). Large encyclopedic dictionary

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Deism

, a term originally used in the same sense as the term “theism”, and denoting belief in one supreme God, and at the end of the 17th century. acquired independent meaning and was used to denote such faith in God, which can only be justified by reason.

Lord Herbert Cherbury

, who is usually called the “father of deism,” sought the basis for a rationalistic religion in those primordial ideas that are shared by all people, regardless of their religion. S. Clark distinguished four varieties of deism, of which only one came close to orthodox Christianity.

John Locke, due to his conviction that only reason is the final criterion of all knowledge, was often classified as a deist, but he himself strongly insisted on the difference between his position and the position of such deists as J. Toland, since in his system Toland did not leave room for miracles . In other words, Locke adhered to a broader interpretation of reason than was typical of thinkers who are usually called deists.

Over time, the rationalistic ideal acquired a natural-scientific coloring, and deists began to look for evidence of the existence of God in the world around us, considering it as the creation of God. Therefore, later deism is associated mainly with the idea of God as a transcendental “mechanic” who designed the world.

All deists subordinated Revelation to reason. Some, such as M. Tyndale (1655-1733), assigned Revelation the role of a source of alternative popular evidence of the truth of the teaching, which for more educated people can be justified by purely rational means (for example, the resurrection of Christ is a proof of immortality based on sensory evidence ).

Others, such as E. Collins and T. Woolston, on the contrary, resolutely rejected Revelation and everything on which belief in it is based - first of all, miracles and the fulfillment of prophecies. All deists were critical of the institution of the priesthood and of the clergy, whom they suspected of having a hidden interest in maintaining an atmosphere of mystery and ignorance among the people. It was precisely because of their recognition of the supreme authority of reason and their expressed hatred of the priesthood that thinkers such as Voltaire and T. Paine were classified as deists.

Sources:

Around the World - encyclopedia;
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The Tree is an open Orthodox encyclopedia;
Yandex dictionaries;
Web portal of BPSU named after. V.M.Shukshina - portal of Biysk Pedagogical University.

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→ What is Christianity?

→What is the meaning of Ludwig Feuerbach's philosophy?

→What is Islam?

→What is Buddhism?

→What is Protestantism?

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The scientist, true to his professional character, refuses to deal with phenomena or objects that he cannot measure or at least observe. Only by listening to the answers given by nature to the questions posed to it, and asking further questions according to these answers, can the scientist rely on this faceless witness to learn more and more.

The problem of measuring nerve impulses. To study nerve impulses, it is necessary to have some index or measure. Nerve impulses remained mysterious for centuries due to the absence of visible signs of their passage along nerve fibers. The contraction of the isolated gastrocnemius muscle of the frog during irritation of the sciatic nerve can be used as an indicator of the movement of impulses along the nerve (contraction occurs with each irritation of the nerve, even if a section of the nerve that is significantly remote from the muscle - more than 6 cm - is exposed to irritation). However, observations carried out even under a microscope do not reveal any changes in the nerve itself when it is irritated. Moreover, until recently, attempts to detect, by measuring heat production, oxygen consumption, or observing any chemical reactions, an increase in the metabolic activity of the nerve during the conduction of impulses remained completely unsuccessful.

Therefore, it is not surprising that physiologists imagined nerves as passive pathways or conductors that only allow the excitation that arises during stimulation to move from one end of the nerve to the other. Water flowing through a pipe, or electric current passing through a wire - not to mention cars driving along a road - are not in any way dependent on the path along which they move. The amount of flowing water, its speed, pulsation, and developed pressure vary depending on the strength of the pump moving it. For a long time it was believed that nerve impulses are a stream of a special fluid passing through the invisible pores of the nerve, which was called “animal force” or “vital spirit” and the behavior of which is very similar to the behavior of water flowing through pipes. Such entertaining but useless fantasies arise from the fact that the deepest minds try to go too far ahead of existing real knowledge.

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Electrical phenomena and speed. The beginning of our actual knowledge of the nature of the nerve impulse was laid by the following experiment by Galvani, performed about one and a half hundred years ago. While observing a frog's leg suspended from an iron stand on a copper wire hook placed under the sciatic nerve, Galvani accidentally discovered that, no matter where the hanging leg touched the iron stand, its muscles would contract. The compound of iron and copper is a weak battery, and therefore when the frog's leg tissue completes the circuit, the resulting current irritates the nerve and causes muscle contraction. Thus, at the same time, firstly, a new method of producing current, known to this day under the name galvanic, and, secondly, the important fact of the possibility of irritating a nerve using electric current were discovered. Over the next 50 years, electrophysicists constructed a sensitive galvanometer (named after Galvani) and a variety of electrical equipment, and one physiologist showed that nerve and muscle (and virtually any tissue) are not only irritated by electric current, but, much more instructively, , being in an active state (no matter how it is caused), they themselves produce an electric current.

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This discovery shocked the scientific world, and it was quickly concluded that nerve impulses are electrical currents. And since it was known that electricity moves at enormous speed, Müller, the leading physiologist of that time, confidently predicted that it would never be possible to measure the speed of a nerve impulse on a short segment of a nerve. And yet, despite this, his student Helmholtz, one of the great minds of all time, measured the speed of a nerve impulse in less than 10 years. And although this was done almost a hundred years ago, the accuracy of the definition is not inferior to modern ones. It turned out that making such a measurement is not so difficult, because we are talking about a very moderate speed: along the nerve of a frog, impulses move at a speed of 30 m per second, or about 2 km per minute, along the nerves of a person about four times faster.

You can reproduce Helmholtz's experiment yourself and determine the speed of nerve impulses. To do this, one pair of electrical wires is placed on the nerve near the muscle, the second - on its other end, at a distance of, say, 6 cm. The muscle will contract in response to irritation coming from any pair of wires, but when using distant electrodes, the contraction will begin later, than when using loved ones. The contraction will be delayed just by the time required for the nerve impulse to travel a distance of 6 cm. The time difference, based on the speed of the nerve impulse we now know, should be about 0.002 sec.

To record muscle contractions, a special muscle lever is made that draws white lines on smoked paper mounted on a fairly quickly moving drum. By placing the smoked paper in the same position during each test and giving stimulation at the same time, it can be found that the second contraction curve will be shifted in the protocol compared to the first. Knowing the speed of the paper, equal to, for example, 100 cm per second, and the magnitude of the resulting displacement, we can calculate the speed of the nerve impulse.

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The experiment described clearly shows that a nerve impulse is not an ordinary electric current, since it moves at a much lower speed. However, the fact remains undoubtedly true that the nerve impulse is accompanied by electrical changes. It was soon shown by placing measuring electrodes on various parts of the stimulated nerve that electrical changes, or currents of action as they are called, move along the nerve at the same speed as the nerve impulse. It can be assumed that although action currents accompany a nerve impulse, they, like the noise of a moving car, are only random and meaningless phenomena. However, numerous experiments in which a wide variety of criteria were used have shown that action currents invariably accompany the nerve impulse, their intensity, shape and other characteristic features exactly correspond to the intensity and other properties of the nerve impulse.

Therefore, there is every reason to believe that electrical changes are an integral part of the nerve impulse itself. A nerve impulse can be studied in detail using precise measurements of action currents, which is quite possible with the use of modern radio amplifiers and oscilloscopes. Thus, action currents represent that much-needed signal that indicates the passage of nerve impulses. Useful: sexual disharmony in the family