Motor innervation of muscle fibers of skeletal muscles. Structure, innervation and functions of skeletal muscles What are innervated organs

Motor and sensory somatic innervation of muscle fibers of skeletal muscles carried out respectively by alpha and gamma motor neurons of the anterior horns spinal cord and motor nuclei 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 a 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 nerve ending membrane 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. Abs 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 development 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

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 thyroid gland 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 general 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 it is fundamentally necessary new model 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, very 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 covered other, more high levels 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.

(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 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

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.

see also

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Excerpt characterizing innervation

Muscle structure. The muscle consists of bundles of striated muscle fibers connected by loose connective tissue into first-order bundles. They, in turn, are combined into bundles of the second order, etc. As a result, muscle bundles of all orders are united by a connective membrane, forming a muscle belly. The connective tissue layers present between the muscle bundles at the ends of the abdomen pass into the tendon Part muscle that attaches to bone. In During contraction, the muscle belly shortens and its ends come closer together. In this case, the contracted muscle, with the help of a tendon, pulls the bone, which acts as a lever. This is how various movements are performed

Muscle functions. Muscles- these are the organs of the body consisting of muscle tissue, capable of contracting under the influence of nerve impulses. They are an active element of the musculoskeletal system, as they provide a variety of movements when a person moves in space, maintaining balance, breathing movements, contractions of the walls internal organs, voice formation, etc.

Innervation of muscles. Skeletal muscles receive motor, sensory and trophic (vegetative) innervation.

The skeletal muscles of the trunk and limbs receive motor (efferent) innervation from motor neurons of the anterior horns of the spinal cord, and the muscles of the face and head - from motor neurons of certain cranial nerves. In this case, either a branch from the axon of the motor neuron or the entire axon approaches each muscle fiber. In muscles that provide fine coordinated movements (muscles of the hands, forearms, neck), each muscle fiber is innervated by one motor neuron. In muscles that primarily maintain posture, tens and even hundreds of muscle fibers receive motor innervation from one motor neuron through the branching of its axon.

The motor nerve fiber, approaching the muscle fiber, penetrates under the endomysium and basal plate and breaks up into terminals, which, together with the adjacent specific area of ​​the myosymplast, form an axo-muscular synapse or motor plaque. Under the influence of a nerve impulse, a wave of depolarization from the nerve ending is transmitted to the plasmalemma of the myosymplast, spreads further along the T-tubules and in the region of the triads is transmitted to the terminal tanks of the sarcoplasmic reticulum, causing the release of calcium ions and the beginning of the process of muscle fiber contraction.

Sensitive (afferent) innervation of skeletal muscles is carried out by pseudounipolar neurons of the spinal ganglia, through various receptor endings of the dendrites of these cells.

Structure, innervation and functions of visceral muscles.

Visceral muscles acting involuntarily and devoid of transverse stripes, they are located primarily in the walls of the digestive tube. They are responsible for the peristaltic movements that push food through the digestive tract.

Visceral smooth muscle has a double innervation- sympathetic and parasympathetic, the function of which is to change activity smooth muscle. Stimulation of one of the autonomic nerves usually increases smooth muscle activity, while stimulation of the other decreases it.

The doctrine of bones and their joints.

Bone structure

The skeleton, as a support, carries a large load: on average 60-70 kg (body weight of an adult). Therefore, bones must be strong. Bones can withstand tension almost as well as cast iron, and their resistance to compression is twice that of granite.

The soft parts of a bone do not make it any less strong. Cells bone tissue They live as if they were one family, connecting to each other with shoots, like bridges. Blood vessels, piercing the bone and delivering nutrients and oxygen to bone cells, do not reduce the reliable hardness of the bone.

In tubular bones, differences in structure from the center to the ends also increase their strength. The tubular bone in the center is more hard and less elastic than at the ends. Towards the articular surface, the structure of the tubular bone changes from compact to dense. This change in structure ensures the main transfer of stress from the bone through the cartilage to the surface of the joint.

On the outside, the bone is covered with periosteum, which is pierced by blood vessels that feed the bone. The periosteum contains many sensitive nerve endings, but the bone itself is insensitive.

The cavity of the tubular bones is filled with red bone marrow, which is replaced by yellow marrow (adipose tissue) throughout life.

Bone shapes.

Bone Shape

Bones differ from each other in shape and structure. There are tubular, flat, mixed and air-bearing bones. Among the tubular bones, there are long (humerus, femur, bones of the forearm, tibia) and short (carpal bones, metatarsals, phalanges of the fingers). Spongy bones consist of a spongy substance covered with a thin layer of compact substance. They have the shape of an irregular cube or polyhedron and are located in places where a large load is combined with mobility (for example, the patella).

Flat bones participate in the formation of cavities, limb girdles and perform a protective function (bones of the skull roof, sternum).

Mixed dice have a complex shape and consist of several parts of different origins. Mixed bones include vertebrae and bones of the base of the skull.

Airborne bones have a cavity in their body lined with mucous membrane and filled with air. These are, for example, some parts of the skull: frontal, sphenoid, upper jaw and some others.

The shape and relief of the bones depend on the nature of the muscles attached to them. If a muscle is attached to a bone with the help of a tendon, then a tubercle, process or ridge is formed at this place. If the muscle is directly combined with the periosteum, then a depression is formed.