Action potential or nerve impulse, a specific response that occurs in the form of an excitatory wave and flows along the entire nerve pathway. This reaction is a response to a stimulus. The main task is to transmit data from the receptor to the nervous system, and after that it directs this information to the desired muscles, glands and tissues. After the passage of the pulse, the surface part of the membrane becomes negatively charged, while its inner part remains positive. Thus, a nerve impulse is a sequentially transmitted electrical change.
The exciting effect and its distribution are subject to physico-chemical nature. The energy for this process is generated directly in the nerve itself. This happens due to the fact that the passage of an impulse leads to the formation of heat. Once it has passed, the attenuation or reference state begins. In which only a fraction of a second the nerve cannot conduct a stimulus. The speed at which the pulse can be delivered ranges from 3 m/s to 120 m/s.
The fibers through which excitation passes have a specific sheath. Roughly speaking, this system resembles an electrical cable. The composition of the membrane can be myelin or non-myelin. The most important component of the myelin sheath is myelin, which plays the role of a dielectric.
The speed of the pulse depends on several factors, for example, on the thickness of the fibers; the thicker it is, the faster the speed develops. Another factor in increasing conduction speed is the myelin itself. But at the same time, it is not located over the entire surface, but in sections, as if strung together. Accordingly, between these areas there are those that remain “bare”. They cause current leakage from the axon.
An axon is a process that is used to transmit data from one cell to the rest. This process is regulated by a synapse - a direct connection between neurons or a neuron and a cell. There is also a so-called synaptic space or cleft. When an irritating impulse arrives at a neuron, neurotransmitters (molecules of a chemical composition) are released during the reaction. They pass through the synaptic opening, eventually reaching the receptors of the neuron or cell to which the data needs to be conveyed. Calcium ions are necessary for the conduction of a nerve impulse, since without this the neurotransmitter cannot be released.
The autonomic system is provided mainly by non-myelinated tissues. Excitement spreads through them constantly and continuously.
The transmission principle is based on the appearance of an electric field, so a potential arises that irritates the membrane of the adjacent section and so on throughout the fiber.
In this case, the action potential does not move, but appears and disappears in one place. The transmission speed through such fibers is 1-2 m/s. 
Laws of conduct
There are four basic laws in medicine:
- Anatomical and physiological value. Excitation is carried out only if there is no violation in the integrity of the fiber itself. If unity is not ensured, for example, due to infringement, drug use, then the conduction of a nerve impulse is impossible.
- Isolated conduction of irritation. Excitation can be transmitted along, in no way, without spreading to neighboring ones.
- Bilateral conduction. The path of impulse conduction can be of only two types - centrifugal and centripetal. But in reality, the direction occurs in one of the options.
- Non-decremental implementation. The impulses do not subside, in other words, they are carried out without decrement.
Chemistry of impulse conduction
The irritation process is also controlled by ions, mainly potassium, sodium and some organic compounds. The concentration of these substances is different, the cell is negatively charged inside itself, and positively charged on the surface. This process will be called potential difference. When a negative charge oscillates, for example, when it decreases, a potential difference is provoked and this process is called depolarization.
Stimulation of a neuron entails the opening of sodium channels at the site of stimulation. This may facilitate the entry of positively charged particles into the cell. Accordingly, the negative charge is reduced and an action potential or nerve impulse occurs. After this, the sodium channels close again.
It is often found that it is the weakening of polarization that promotes the opening of potassium channels, which provokes the release of positively charged potassium ions. This action reduces the negative charge on the cell surface.
The resting potential or electrochemical state is restored when potassium-sodium pumps are activated, with the help of which sodium ions leave the cell and potassium ions enter it.
As a result, we can say that when electrochemical processes are resumed, impulses occur that travel along the fibers.
Nerve fiber structure. The conduction of nerve impulses is a specialized function of nerve fibers, i.e. processes of nerve cells.
Nerve fibers separate soft, or myelinated, And pulpless, or unmyelinated. Pulp, sensory and motor fibers are part of the nerves supplying the sensory organs and skeletal muscles; they are also present in the autonomic nervous system. Non-pulp fibers in vertebrates belong mainly to the sympathetic nervous system.
Nerves usually consist of both pulpy and non-pulphate fibers, and their ratio in different nerves is different. For example, in many cutaneous nerves the predominant nerve fibers predominate. Thus, in the nerves of the autonomic nervous system, for example in the vagus nerve, the number of soft fibers reaches 80-95%. In contrast, the nerves innervating skeletal muscles contain only a relatively small number of non-pulp fibers.
As electron microscopic studies have shown, the myelin sheath is created as a result of the fact that the myelocyte (Schwann cell) repeatedly wraps the axial cylinder (Fig. 2.27"), its layers merge, forming a dense fatty sheath - the myelin sheath. The myelin sheath through gaps of equal length are interrupted, leaving open areas of the membrane approximately 1 μm wide. These areas are called Ranvier interceptions.
Rice. 2.27. The role of the myelocyte (Schwann cell) in the formation of the myelin sheath in the pulpy nerve fibers: successive stages of the spiral-shaped twisting of the myelocyte around the axon (I); mutual arrangement of myelocytes and axons in non-pulp nerve fibers (II)
The length of the interstitial areas covered by the myelin sheath is approximately proportional to the diameter of the fiber. Thus, in nerve fibers with a diameter of 10-20 microns, the length of the gap between the interceptions is 1-2 mm. In the thinnest fibers (diameter
1-2 µm) these areas are about 0.2 mm long.
Non-pulp nerve fibers do not have a myelin sheath; they are isolated from each other only by Schwann cells. In the simplest case, a single myelocyte surrounds one pulpless fiber. Often, however, several thin, pulpless fibers appear in the folds of the myelocyte.
The myelin sheath has a dual function: an electrical insulator function and a trophic function. The insulating properties of the myelin sheath are due to the fact that myelin, as a substance of lipid nature, prevents the passage of ions and therefore has a very high resistance. Due to the existence of the myelin sheath, the occurrence of excitation in the pulpal nerve fibers is not possible throughout the entire length of the axial cylinder, but only in limited areas - the nodes of Ranvier. This is important for the propagation of the nerve impulse along the fiber.
The trophic function of the myelin sheath, apparently, is that it takes part in the processes of regulation of metabolism and growth of the axial cylinder.
Conduction of excitation in unmyelinated and myelinated nerve fibers. In soft nerve fibers, excitation spreads continuously along the entire membrane, from one excited area to another located nearby. In contrast, in myelinated fibers the action potential can propagate only spasmodically, “jumping” through sections of the fiber covered with an insulating myelin sheath. This is called salipatory.
Direct electrophysiological studies carried out by Kato (1924) and then by Tasaki (1953) on single myelinated frog nerve fibers showed that action potentials in these fibers arise only at the nodes, and the myelin-covered areas between the nodes are practically inexcitable.
The density of sodium channels in the interceptions is very high: there are about 10,000 sodium channels per 1 µm2 membrane, which is 200 times higher than their density in the membrane of the giant squid axon. A high density of sodium channels is the most important condition for saltatory conduction of excitation. In Fig. Figure 2.28 shows how a nerve impulse “jumps” from one interception to another.
At rest, the outer surface of the excitable membrane of all nodes of Ranvier is positively charged. There is no potential difference between adjacent interceptions. At the moment of excitation, the surface of the interception membrane WITH becomes charged electronegatively with respect to the membrane surface of the adjacent interception D. This leads to the emergence of local (lo 
Rice. 2.28.
A- unmyelinated fiber; IN- myelinated fiber. The arrows show the direction of the current
cal) electric current that passes through the interstitial fluid surrounding the fiber, membrane and axoplasm in the direction shown in the figure by the arrow. Coming out through interception D the current excites it, causing the membrane to recharge. In interception WITH the excitement still continues, and he becomes refractory for a while. Therefore interception D is capable of bringing into a state of excitation only the next interception, etc.
“Jumping” of the action potential across the interinterceptor region is possible only because the amplitude of the action potential in each interception is 5-6 times higher than the threshold value required to excite the neighboring interception. Under certain conditions, the action potential can “jump” not only through one, but also through two interinterceptor sections - in particular, if the excitability of the adjacent interception is reduced by some pharmacological agent, for example, novocaine, cocaine, etc.
The assumption about the spasmodic propagation of excitation in nerve fibers was first expressed by B.F. Verigo (1899). This method of conduction has a number of advantages compared to continuous conduction in non-pulp fibers: firstly, by “jumping” over relatively large sections of the fiber, excitation can spread at a much higher speed than with continuous conduction along a non-pulp fiber of the same diameter; secondly, abrupt propagation is energetically more economical, since not the entire membrane comes into a state of activity, but only its small sections in the interception area, having a width of less than 1 μm. The losses of ions (per unit fiber length) accompanying the occurrence of an action potential in such limited areas of the membrane are very small, and therefore the energy costs for the operation of the sodium-potassium pump, necessary to restore the altered ionic ratios between the internal contents of the nerve fiber and tissue fluid.
- See: Human Physiology / Ed. A. Kositsky.
Lecture No. 3 Conducting
nervous
impulse
Synapse structure
Nerve fibers
Pulpy(myelinated)
Pulpless
(unmyelized)
Sensory and motor
fibers.
Mainly owned
sympathetic n.s.
PD spreads spasmodically
(saltatory conduction).
PD is spreading continuously.
in the presence of even weak myelination
with the same fiber diameter - 1520 m/s. More often with a larger diameter 120
m/sec.
With a fiber diameter of about 2 µm and
lack of myelin sheath
the speed of conduction will be
~1 m/s
I – unmyelinated fiber II – myelinated fiber
According to the speed of conduction, all nerve fibers are divided:
Type A fibers – α, β, γ, δ.Myelinated. The thickest α.
Excitation speed 70-120m/sec
Conduct stimulation to skeletal muscles.
β, γ, δ fibers. They have a smaller diameter, smaller
speed, longer PD. Mostly
sensory fibers of tactile, pain
temperature receptors, internal receptors
organs. Type B fibers are covered with myelin
shell. Speed from 3 –18 m/sec
- predominantly preganglionic
fiber of the autonomic nervous system.
Type C fibers are pulpless. Very
small diameter. Conduction speed
excitation from 0-3 m/sec. This
postganglionic fibers
sympathetic nervous system and
sensory fibers of some
receptors.
Laws of conduction of excitation in nerves.
1) The law of anatomical andphysiological continuity
fibers. For any nerve damage
(transection) or its blockade
(novocaine), nerve stimulation is not
held. 2) The law of 2-sided conduct.
Excitation is carried along the nerve from
sites of irritation in both
sides are the same.
3) Law of isolated conduction
excitement. In the peripheral nerve
impulses spread through each
fiber in isolation, i.e. without moving from
one fiber to another and exert
action only on those cells ending
nerve fibers which are in contact
Sequence of processes leading to blockade of nerve impulses under the influence of local anesthetic
1.Diffusion of anesthetic through the nerve sheath andnerve membrane.
2. Fixation of the anesthetic in the sodium receptor zone
channel.
3. Blockade of the sodium channel and inhibition of permeability
membranes for sodium.
4. Decrease in the speed and degree of the depolarization phase
action potential.
5. Inability to achieve the threshold level and
action potential development.
6. Conductor blockade.
Synapse.
Synapse - (from the Greek “to connect, bind”).This concept was introduced in 1897 by Sherrington
General plan of the structure of a synapse
Basic properties of synapses:
1. Unilateral conduction of excitation.2. Delay in excitation.
3. Summation and transformation. Allocable
small doses of the mediator are summed up and
cause excitement.
As a result, the frequency of nerve
impulses coming along the axon
transforms into a different frequency. 4. In all synapses of one neuron
one mediator stands out or
excitatory or inhibitory effect.
5. Synapses are characterized by low lability
and high sensitivity to chemicals
substances.
Classification of synapses
By mechanism:Chemical
Electric
Electrochemical
By location:
1. neuromuscular By sign:
-exciting
2. Nervous
- axo-somatic - inhibitory
- axo-dendritic
- axo-axonal
- dendro-dendritic
The mechanism of excitation in the synapse.
Sequencing:
* Receipt of excitation in the form of PD tothe end of the nerve fiber.
* presynaptic depolarization
membranes and release of Ca++ ions
from the sarcoplasmic reticulum
membranes.
*Receipt of Ca++ upon admission to
synaptic plaque promotes
release of mediator from vesicles.
CONDUCTING A NERVE IMPULSE
nerve impulse, the transmission of a signal in the form of an excitation wave within one neuron and from one cell to another. P.n. And. along nerve conductors occurs with the help of electrotonic potentials and action potentials, which propagate along the fiber in both directions, without passing to neighboring fibers (see Bioelectric potentials, Nerve impulse). The transmission of intercellular signals occurs through synapses, most often with the help of mediators that cause the appearance of postsynaptic potentials. Nerve conductors can be thought of as cables that have a relatively low axial resistance (axoplasmic resistance - ri) and a higher sheath resistance (membrane resistance - rm). The nerve impulse propagates along the nerve conductor through the passage of current between the resting and active sections of the nerve (local currents). In a conductor, as the distance from the point of excitation increases, a gradual, and in the case of a homogeneous structure of the conductor, exponential decay of the pulse occurs, which decreases by 2.7 times at a distance l (length constant). Since rm and ri are in inverse ratio to the diameter of the conductor, the attenuation of the nerve impulse in thin fibers occurs earlier than in thick ones. The imperfection of the cable properties of nerve conductors is compensated by the fact that they have excitability. The main condition for excitation is the presence of a resting potential in the nerves. If a local current through a resting region causes depolarization of the membrane reaching a critical level (threshold), this will lead to the occurrence of a propagating action potential (AP). The ratio of the level of threshold depolarization and AP amplitude, usually at least 1: 5, ensures high reliability of conduction: sections of the conductor that have the ability to generate AP can be separated from each other at such a distance, overcoming which the nerve impulse reduces its amplitude by almost 5 times. This weakened signal will be amplified again to a standard level (AP amplitude) and will be able to continue its path along the nerve.
Speed P. n. And. depends on the speed with which the membrane capacitance in the area ahead of the impulse is discharged to the level of the AP generation threshold, which, in turn, is determined by the geometric features of the nerves, changes in their diameter, and the presence of branching nodes. In particular, thin fibers have a higher ri and a greater surface capacity, and therefore the rate of transfer. And. on them below. At the same time, the thickness of the nerve fibers limits the possibility of the existence of a large number of parallel communication channels. The conflict between the physical properties of nerve conductors and the requirements for the “compactness” of the nervous system was resolved by the appearance during the evolution of vertebrates so-called. pulpy (myelinated) fibers (see Nerves). Speed P. n. And. in myelinated fibers of warm-blooded animals (despite their small diameter - 4-20 microns) reaches 100-120 m/sec. The generation of PD occurs only in limited areas of their surface - the nodes of Ranvier, and along the inter-intercept areas of the P. and. And. carried out electrotonically (see Saltatory conduction). Some medicinal substances, such as anesthetics, greatly slow down the process until it completely blocks P. n. And. This is used in practical medicine for pain relief.
Lit. see under articles Excitation, Synapses.
L. G. Magazanik.
Great Soviet Encyclopedia, TSB. 2012
See also interpretations, synonyms, meanings of the word and what CONDUCTING A NERVOUS IMPULSE is in Russian in dictionaries, encyclopedias and reference books:
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conducting, conducting, conducting, conducting, conducting, conducting, conducting, conducting, conducting, conducting, conducting, … - CONDUCT in the Russian Synonyms dictionary:
fulfillment, performance, tracing, deception, implementation, design, construction, wire, wiring, work, laying, laying, drawing, ... - CONDUCT in the New Explanatory Dictionary of the Russian Language by Efremova:
Wed The process of action by value. verb: to carry out (1*), ... - CONDUCT in Lopatin’s Dictionary of the Russian Language:
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carrying out Wed. The process of action by value. verb: to carry out (1*), ... - CONDUCT in the New Dictionary of the Russian Language by Efremova:
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Wed process of action according to ch. carry out I, ... - SALTATORY CONDUCT
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Synapses- these are structures designed to transmit impulses from one neuron to another or to muscle and glandular structures. Synapses provide polarization of impulse transmission along a chain of neurons. Depending on the method of impulse transmission synapses can be chemical or electrical (electrotonic).
Chemical synapses transmit an impulse to another cell with the help of special biologically active substances - neurotransmitters located in synaptic vesicles. The axon terminal is the presynaptic portion, and the region of the second neuron, or other innervated cell, with which it contacts is the postsynaptic portion. The area of synaptic contact between two neurons consists of a presynaptic membrane, a synaptic cleft, and a postsynaptic membrane.
Electrical, or electrotonic, synapses are relatively rare in the mammalian nervous system. In the area of such synapses, the cytoplasms of neighboring neurons are connected by gap-like junctions (contacts), ensuring the passage of ions from one cell to another, and, consequently, the electrical interaction of these cells.
The speed of impulse transmission by myelinated fibers is greater than that of non-myelinated fibers. Thin fibers poor in myelin and unmyelinated fibers conduct nerve impulses at a speed of 1-2 m/s, while thick myelin fibers conduct a nerve impulse at a speed of 5-120 m/s.
In an unmyelinated fiber, the wave of membrane depolarization travels along the entire axolemma without interruption, but in a myelinated fiber it occurs only in the area of interception. Thus, myelinated fibers are characterized by saltatory conduction of excitation, i.e. jumping. Between the interceptions there is an electric current, the speed of which is higher than the passage of the depolarization wave along the axolemma.
No. 36 Comparative characteristics of the structural organization of reflex arcs of the somatic and autonomic nervous systems.
Reflex arc- this is a chain of nerve cells, necessarily including the first - sensitive and the last - motor (or secretory) neurons. The simplest reflex arcs are two- and three-neuron, closing at the level of one segment of the spinal cord. In a three-neuron reflex arc, the first neuron is represented by a sensitive cell, which moves first along the peripheral process and then along the central one, heading to one of the nuclei of the dorsal horn of the spinal cord. Here the impulse is transmitted to the next neuron, the process of which is directed from the posterior horn to the anterior horn, to the cells of the nuclei (motor) of the anterior horn. This neuron performs a conductor function. It transmits an impulse from a sensory (afferent) neuron to a motor (efferent) one. The body of the third neuron (efferent, effector, motor) lies in the anterior horn of the spinal cord, and its axon is part of the anterior root, and then the spinal nerve extends to the working organ (muscle).
With the development of the spinal cord and brain, the connections in the nervous system also became more complex. Formed multineuron complex reflex arcs, in the construction and functions of which nerve cells located in the overlying segments of the spinal cord, in the nuclei of the brain stem, hemispheres and even in the cerebral cortex participate. The processes of nerve cells that conduct nerve impulses from the spinal cord to the nuclei and cortex of the brain and in the opposite direction form bundles, fasciculi.