What does innervation mean? Motor innervation of muscle fibers of skeletal muscles. Dictionary of medical terms

Types of innervation

Distinguish between innervation afferent(sensitive) and efferent(motor). Signals about the state of the organ and the processes occurring in it are perceived by sensitive nerve endings (receptors) and transmitted to the central nervous system via centripetal fibers. The centrifugal nerves transmit response signals that regulate the functioning of organs, thanks to which the central nervous system constantly monitors and changes the activity of organs and tissues in accordance with the needs of the body.

Role of the central nervous system

The role of the central nervous system in regulating the functions of different organs is different. In some organs (for example, in skeletal muscle or the salivary gland), signals coming from the central nervous system determine all their vital functions; therefore, complete disconnection from the central nervous system - denervation- leads to organ atrophy. Some other organs (for example, heart, intestines) have the ability to function under the influence of impulses arising in the organ itself (see automatism). In such cases, denervation does not lead to atrophy, but only limits adaptive reactions to one degree or another, which, however, are preserved not only due to humoral regulation, but also due to the presence of the intraorgan nervous system. Renal nerve denervation is used for cardiovascular diseases. The denervation method is radiofrequency ablation of the sympathetic renal nerves.

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Notes

Excerpt characterizing innervation

Motor and sensory somatic innervation of muscle fibers of skeletal muscles is carried out respectively by alpha and gamma motor neurons of the anterior horns of the spinal cord and motor nuclei of the cranial nerves and pseudounipolar sensory neurons of the spinal ganglia and sensory nuclei of the cranial nerves.

Autonomic innervation no muscle fibers were found in skeletal muscles, but the SMC walls of muscle blood vessels have sympathetic adrenergic innervation.

Motor innervation

Each extrafusal muscle fiber has direct motor innervation - neuromuscular synapses formed by the terminal branches of the axons of alpha motor neurons and specialized areas of the muscle fiber plasmalemma (end plate, postsynaptic membrane).

Extrafusal muscle fibers are part of neuromotor (motor) units and provide contractile function of muscles.

Intrafusal muscle fibers form neuromuscular synapses with efferent fibers of gamma motor neurons.

Rice. 7–6.

(Fig. 7–6) includes one motor neuron and a group of extrafusal muscle fibers innervated by it. The number and size of motor units in different muscles varies significantly.

Since, during contraction, phasic muscle fibers obey the “all or nothing” law, the force developed by the muscle depends on the number of activated (i.e., participating in the contraction of the muscle fiber) motor units.

Each motor unit formed only by fast-twitch or only slow-twitch muscle fibers (see below).

Polyneuron innervation

Formation motor units occurs in the postnatal period, and before birth, each muscle fiber is innervated by several motor neurons. A similar situation occurs when a muscle is denervated (for example, when a nerve is damaged) with subsequent reinnervation of muscle fibers. It is clear that in these situations the efficiency of the contractile function of the muscle suffers.

Neuromuscular junction

Physiology neuromuscular junctions discussed in Chapters 4 (see Fig. 4–8) and 6 (see Fig. 6–2 in the article Synapses And 6–3 in the article Organization and function of synapse).

Like any synapse, the neuromuscular junction consists of three parts: presynaptic region, postsynaptic region and synaptic cleft .

Presynaptic region

The motor nerve terminal of the neuromuscular junction is externally covered by a Schwann cell, has a diameter of 1–1.5 μm, and forms the presynaptic region of the neuromuscular junction. In the presynaptic region there are large numbers of synaptic vesicles filled with acetylcholine (5–15 thousand molecules in one vesicle) and having a diameter of about 50 nm.

Postsynaptic region

On the postsynaptic membrane, a specialized part of the muscle fiber plasmalemma, there are numerous invaginations, from which postsynaptic folds extend to a depth of 0.5–1.0 μm, thereby significantly increasing the membrane area. Built into the postsynaptic membrane n?cholinergic receptors, their concentration reaches 20–30 thousand per 1 micron 2.

Postsynaptic n?cholinergic receptors(Fig. 7–7) The diameter of the open channel within the receptor is 0.65 nm, which is quite sufficient for the free passage of all necessary cations: Na+, K+, Ca2+. Negative ions such as Cl– do not pass through the channel due to the strong negative charge at the mouth of the channel.

Rice. 7–7. . A - the receptor is not activated, the ion channel is closed. B - after the receptor binds to acetylcholine, the channel opens briefly. In reality, predominantly Na+ ions pass through the channel due to the following circumstances: - in the environment surrounding the acetylcholine receptor, there are only two positively charged ions in sufficiently high concentrations: in the extracellular fluid Na+ and in the intracellular fluid K+; - the strong negative charge on the inner surface of the muscle membrane (from –80 to –90 mV) attracts positively charged sodium ions into the muscle membrane, while simultaneously preventing potassium ions from attempting to move out.

Extrasynaptic cholinergic receptors. Cholinergic receptors are also present in the muscle fiber membrane outside the synapse, but here their concentration is an order of magnitude lower than in the postsynaptic membrane.

Synaptic cleft

Through synaptic cleft passes through the synaptic basement membrane. It holds the axon terminal in the synapse area and controls the location of cholinergic receptors in the form of clusters in the postsynaptic membrane. The synaptic cleft also contains the enzyme acetylcholinesterase, which breaks down acetylcholine into choline and acetic acid.

Stages of neuromuscular transmission

Neuromuscular transmission excitation consists of several stages.

1. The AP along the axon reaches the region of the motor nerve ending.
2. Depolarization of the membrane of the nerve ending leads to the opening of voltage-gated Ca2+ channels and the entry of Ca2+ into the motor nerve ending.
3. An increase in Ca2+ concentration triggers the exocytosis of acetylcholine quanta from synaptic vesicles.
4. Acetylcholine enters the synaptic cleft, where it reaches receptors on the postsynaptic membrane by diffusion. At the neuromuscular synapse, in response to one AP, about 100–150 quanta of acetylcholine are released.
5. Activation of n?cholinergic receptors of the postsynaptic membrane. When the n-cholinergic receptor channels open, an incoming Na current occurs, which leads to depolarization of the postsynaptic membrane. An end plate potential appears, which, when a critical level of depolarization is reached, causes an action potential in the muscle fiber.
6. Acetylcholinesterase breaks down acetylcholine and the action of the released portion of the neurotransmitter on the postsynaptic membrane ceases.

Reliability of synaptic transmission

Under physiological conditions, each nerve impulse entering the neuromuscular junction causes an endplate potential to occur, the amplitude of which is three times greater than that required for the occurrence of AP. The appearance of such potential is associated with excess release of the mediator. By excess we mean the release into the synaptic cleft of a significantly larger amount of acetylcholine than is required to trigger AP on the postsynaptic membrane. This ensures that each action of a motor neuron will cause a reaction in the MV innervated by it.

Substances that activate excitation transmission

Cholinomimetics. Methacholine, carbachol and nicotine have the same effect on the muscle as acetylcholine. The difference is that these substances are not destroyed by acetylcholinesterase or are destroyed more slowly, over many minutes or even hours.

Anticholinesterase compounds. Neostigmine, physostigmine and diisopropyl fluorophosphate inactivate the enzyme in such a way that the acetylcholinesterase present in the synapse loses the ability to hydrolyze acetylcholine released in the motor end plate. As a result, acetylcholine accumulates, which in some cases can cause muscle spasm. This can be fatal due to laryngeal spasm in smokers. Neostigmine and physostigmine inactivate acetylcholinesterase for several hours, after which their effect wears off and synaptic acetylcholinesterase resumes its activity. Diisopropyl fluorophosphate, a nerve gas, blocks acetylcholinesterase for weeks, making the substance deadly.

Substances that block the transmission of excitation

• Peripheral muscle relaxants(curare and curare-like drugs) are widely used in anesthesiology. Tubocurarine interferes with the depolarizing effect of acetylcholine. Ditilin leads to a myopalytic effect, causing persistent depolarization of the postsynaptic membrane.
• Botulinum toxin and tetanus toxin block the secretion of mediators from nerve terminals.
• beta and gamma bungarotoxins block cholinergic receptors.

Neuromuscular transmission disorders

• Myasthenia gravis pseudoparalytic(myasthenia gravis) is an autoimmune disease in which antibodies to n?cholinergic receptors are formed. Antibodies circulating in the blood bind to the cholinergic receptors of the postsynaptic membrane of the MV, prevent the interaction of cholinergic receptors with acetylcholine and inhibit their function, which leads to disruption of synaptic transmission and the development of muscle weakness. A number of forms of myasthenia gravis cause the appearance of antibodies to calcium channels of nerve endings at the neuromuscular junction.
• Muscle denervation. With motor denervation, there is a significant increase in the sensitivity of muscle fibers to the effects of acetylcholine due to increased synthesis of acetylcholine receptors and their integration into the plasma membrane over the entire surface of the muscle fiber.

Muscle fiber action potential

The nature and mechanism of the occurrence of the action potential are discussed in Chapter 5. The MV AP lasts 1–5 ms, the speed of its conduction along the sarcolemma, including

(innervatio; In- + Nerve)
providing nerves and, therefore, communication with the central nervous system of organs, areas and parts of the body.

View value Innervation in other dictionaries

Innervation J.— 1. Connection of organs and tissues with the central nervous system through nerves (in anatomy).
Explanatory Dictionary by Efremova

Innervation- [ne], -i; and. [from lat. in - in and nervus - nerve] Anat. Provision of organs and tissues with nerve cells. I. muscles.
Kuznetsov's Explanatory Dictionary

Innervation- (innervatio; in- + nerve) providing nerves and, therefore, communication with the central nervous system of organs, areas and parts of the body.
Large medical dictionary

Innervation- (from Latin in - in - inside and nerves), connection of organs and tissues with the central nervous system using nerves. A distinction is made between afferent or centripetal innervation (from........
Large encyclopedic dictionary

Mutual Innervation— See innervation, mutual.
Psychological Encyclopedia

Innervation- (innervation) - connection of nerve fibers with any organ or part of the body; these fibers either transmit motor impulses going towards the tissue or sensory impulses........
Psychological Encyclopedia

Innervation, Reciprocal- Innervation of a pair of antagonist muscles, as a result of which nerve impulses cause flexion of one and straightening of the other.
Psychological Encyclopedia

Dictionary of medical terms

innervation (innervatio; in- + nerve)

providing nerves and, therefore, communication with the central nervous system of organs, areas and parts of the body.

New explanatory dictionary of the Russian language, T. F. Efremova.

innervation

and. Connection of organs and tissues with the central nervous system through nerves (in anatomy).

Encyclopedic Dictionary, 1998

innervation

INNERVATION (from Latin in - in, inside and nerves) connection of organs and tissues with the central nervous system using nerves. A distinction is made between afferent, or centripetal innervation (from organs and tissues to the central nervous system), and efferent, or centrifugal (from the central nervous system to organs and tissues).

Innervation

(from Latin in ≈ in, inside and nerves), supplying organs and tissues with nerves, which ensures their connection with the central nervous system (CNS). I. are distinguished between afferent (centripetal) and efferent (centrifugal). Signals about the state of the organ and the processes occurring in it are perceived by sensitive nerve endings (receptors) and transmitted to the central nervous system via centripetal fibers. The centrifugal nerves transmit response signals that regulate the functioning of organs, thanks to which the central nervous system constantly monitors and changes the activity of organs and tissues in accordance with the needs of the body. The role of the central nervous system in regulating the functions of different organs is different. In some organs (for example, in skeletal muscle or the salivary gland), signals coming from the central nervous system determine all their vital functions; therefore, complete disconnection from the central nervous system (denervation) leads to organ atrophy. Some other organs (for example, the heart, intestines) have the ability to function under the influence of impulses arising in the organ itself (see Automatism). In such cases, denervation does not lead to atrophy, but only limits adaptive reactions to one degree or another, which, however, are preserved not only due to humoral regulation, but also due to the presence of the intraorgan nervous system. See also Nervous regulation.

G. I. Kositsky, I. N. Dyakova.

Wikipedia

Innervation

Innervation(from Latin in - in, inside and nerves) - supplying organs and tissues with nerves, which ensures their connection with the central nervous system.

Examples of the use of the word innervation in literature.

Innervation The thyroid gland is carried out by sympathetic and parasympathetic nerves.

Since it was written before the discovery of the important role of estrogen and progesterone and even before the understanding of the role of acetylcholine, norepinephrine and epinephine, not to mention oxytocin and prostaglandins, one cannot help but be amazed by the brilliant conclusions about the importance of a balanced innervation uterus.

There is a discrepancy here: the final common path is really narrow, and in order to get through to the executive organ, it is necessary to suppress, crush the rival, the antagonist, but it was precisely Ukhtomsky’s idea that brought the excitation currents to a wide expanse of innumerable neurons of the brain, and for this reason alone a fundamentally new one is needed model of antagonism as purely functional, a new model of reciprocal innervation as the operating principle of not only effectors, but also the reflex arc itself in its central part.

Let individual data about this reciprocal innervation the work of the muscles is even disputed, the matter is immediately transferred to the next instance: after all, many organs of the body, a wide variety of peripheral apparatuses can perform opposite antagonistic works.

Russian physiologists, in turn, paid a lot of attention to reciprocal innervation antagonistic muscles, since they rightly saw in this one of the simple apparatuses on which it is possible to study the complex problem of the relationship between excitation and inhibition in the activity of the nervous system.

Sacral autonomic innervation limited to small localized interference of certain superior ganglionic fibers.

We need to know that innervation the muscles involved in this act may be influenced by emotional stress.

It is worth recalling that there is also a local innervation uterus, which allows the longitudinal muscles to continue to contract, even if the vegetative innervation will be completely turned off by the prevailing irritation of the sympathetic system.

This ensures innervation, with the help of which the prosthesis will be controlled in the future.

However, here he also covered other, higher levels of reciprocal innervation, taking especially into account Sherrington's ideas.

Ukhtomsky on the issue of reciprocal innervation antagonists rises one step above Sherrington: not only in the sense of the floor of the central nervous system, entrusting this work of simultaneous excitation and inhibition to the higher neurostructures of the brain, including the cortex, but also in the sense of replacing the anatomical antagonism of muscles with the physiological antagonism of functions.

As in the question of reciprocal innervation, we can trace the hierarchy from simpler mechanisms of inhibition and excitation, which are of an anatomical nature, to more complex physicochemical ones, to higher functional ones.

About this second half of the matter in phenomena innervation There have been speculations for a long time.

Referring to the principle of reciprocal innervation in the central nervous system, developed by Vvedensky, Sherrington and Hering, based on the research of D.

Thus the sensation found its way to the somatic innervation and through this brought to the fore its complex of associations.

Distinguish between innervation afferent(sensitive) and efferent(motor). Signals about the state of the organ and the processes occurring in it are perceived by sensitive nerve endings (receptors) and transmitted to the central nervous system via centripetal fibers. The centrifugal nerves transmit response signals that regulate the functioning of organs, thanks to which the central nervous system constantly monitors and changes the activity of organs and tissues in accordance with the needs of the body.

Role of the central nervous system

The role of the central nervous system in regulating the functions of different organs is different. In some organs (for example, in skeletal muscle or the salivary gland), signals coming from the central nervous system determine all their vital functions; therefore, complete disconnection from the central nervous system - denervation- leads to organ atrophy. Some other organs (for example, heart, intestines) have the ability to function under the influence of impulses arising in the organ itself (see automatism). In such cases, denervation does not lead to atrophy, but only limits adaptive reactions to one degree or another, which, however, are preserved not only due to humoral regulation, but also due to the presence of the intraorgan nervous system. Renal nerve denervation is used in cardiovascular diseases