Structure of peripheral nerves. The structure of the peripheral section Theme

Any nerve consists of nerve fibers - a conducting apparatus and shells - a supporting connective tissue frame.

Shells

Adventitia. The adventitium is the densest, fibrous outer membrane.

Epinsvriy. The epineurium is an elastic, elastic connective tissue membrane located under the adventitium.

Perineurium. The perineurium is a covering consisting of 3-10 layers of cells of the epithelioid type, very resistant to stretching, but easily torn when stitched together. The perineurium divides the nerve into bundles containing up to 5000-10000 fibers.

Endoneurium. Represents a delicate sheath separating single fibers and small bundles. At the same time, it acts as a blood-brain barrier.

Peripheral nerves can be considered as a kind of axonal cables, delimited by more or less complex sheaths. These cables are outgrowths of living cells, and the axons themselves are continuously renewed by a stream of molecules. The nerve fibers that make up the nerve are processes of various neurons. Motor fibers are processes of motoneurons of the anterior horns of the spinal cord and nuclei of the brain stem, sensitive fibers are dendrites of pseudo-unstolary neurons of the spinal ganglia, autonomic fibers are axons of neurons of the border sympathetic trunk.

A separate nerve fiber consists of the actual process of the neuron - the axial cylinder and the myelin sheath. The myelin sheath is formed by outgrowths of the Schwann cell membrane and has a phospholipid composition. In this, peripheral nerve fibers differ from CNS fibers. where the myelin sheath is formed by outgrowths of oligodendrocytes.

The blood supply to the nerve is carried out possentarno from neighboring tissues or vessels. A longitudinal network of vessels is formed on the surface of the nerve, from which many perforating branches extend to the internal structures of the nerve. With blood, glucose, oxygen, low-molecular energy substrates enter the nerve fibers, and decay products are removed.

To perform the function of conducting the nerve) "fiber, it is necessary to constantly maintain its structure. However, its own structures that carry out biosynthesis are not enough to meet the plastic needs in the processes of the neuron. Therefore, the main synthesis occurs in the body of the neuron, followed by the transport of formed substances along the axon. To a much lesser extent, this the process is carried out by Schwann cells with a further transition of metabolites into the axial cylinder of the nerve fiber.

axonal transport.

There are fast and slow types of movement of substances through the fiber.

Fast orthograde axonal transport occurs at a rate of 200-400 mm per day and is mainly responsible for the transport of membrane components: phospholigas, lipoproteins and membrane enzymes. Retrograde axonal transport ensures the movement of membrane parts in the opposite direction at a speed of up to 150-300 mm per day and their accumulation around the nucleus in close connection with lysosomes. Slow orthograde axonal transport occurs at a rate of 1-4 mm per day and carries soluble proteins and elements of the internal cell scaffold. The volume of substances carried by slow transport is much larger than by fast transport.

Any type of axonal transport is an energy-dependent process performed by contractile proteins analogs of actin and myelin in the presence of macroergs and calcium ions. Energy substrates and ions enter the nerve fiber along with the local blood flow.

Local blood supply to the nerve is an absolutely necessary condition for the implementation of axonal transport.

Neurophysiology of impulse transmission:

Conduction of a nerve impulse along the fiber occurs due to the propagation of a depolarization wave along the sheath of the process. Most peripheral nerves, through their motor and sensory fibers, provide impulse conduction at a speed of up to 50-60 m / s. The actual depolarization process is quite passive, while the restoration of the resting membrane potential and the ability to conduct is carried out by the functioning of the NA / K and Ca pumps. Their work requires ATP, a prerequisite for the formation of which is the presence of segmental blood flow. The cessation of the blood supply to the nerve immediately blocks the conduction of the nerve impulse.

Semiotics of neuropathies

Clinical symptoms developing with damage to peripheral nerves are determined by the functions of the nerve fibers that form the nerve. According to the three groups of fibers, there are also three groups of symptoms of suffering: motor, sensory and vegetative.

Clinical manifestations These disorders may present with symptoms of loss of function, which is more common, and symptoms of irritation, the latter being a rarer variant.

Movement disorders according to the type of prolapse are manifested by plegia and paresis of a peripheral nature with low tone, low reflexes and malnutrition. The symptoms of irritation include convulsive contraction of muscles - cramps. These are paroxysmal, painful contractions of one or more muscles (what we used to call a cramp). Most often, cramps are localized in the maxillohyoid muscle, under the occipital muscle, adductors of the thigh, quadriceps femoris, and triceps calf. The mechanism of occurrence of crumpy is not clear enough, partial morphological or functional denervation is assumed in combination with vegetative irritation. At the same time, vegetative fibers take over part of the somatic functions, and then the striated muscle begins to respond to acetylcholine in a similar way to smooth muscles.

Sensitive disturbances according to the type of prolapse are manifested by hypesthesia, anesthesia. Irritation symptoms are more diverse: hyperesthesia, hyperpathia (a qualitative perversion of sensation with the acquisition of an unpleasant shade), paresthesia (“goosebumps”, burning in the innervation zone), pain along the nerves and roots.

Vegetative disorders are manifested by a violation of sweating, suffering from the motor function of the hollow internal organs, orthostatic hypotension, trophic changes in the skin and nails. The irritative variant is accompanied by pain with an extremely unpleasant cutting, twisting component, which occurs mainly when the median and tibial nerves are damaged, as they are the richest in autonomic fibers.

It is necessary to pay attention to the variability of manifestations of neuropathy. Slow change clinical picture occurring within weeks, months really reflect the dynamics of neuropathy, while changes within hours or one or two days are more often associated with changes in blood flow, temperature, electrolyte balance.

Pathophysiology of neuropathy

What happens to nerve fibers in nerve diseases?
There are four main options for change.

1. Wallerian degeneration.

2. Atrophy and degeneration of the axon (axonopathy).

3. Segaentary demyelination (myelinopathy).

4. Primary damage to the bodies of nerve cells (neuronopathy).

Wallerian degeneration occurs as a result of gross local damage to the nerve fiber, more often due to mechanical and ischemic factors, The function of conduction along this section of the fiber is completely and immediately disrupted. After 12-24 hours, the structure of the axoplasm changes in the distal part of the fiber, but the impulse conduction persists for another 5-6 days. On the 3-5th day, the destruction of the nerve endings occurs, and by the 9th day - their disappearance. From the 3rd to the 8th day, the myslin membranes are progressively destroyed. In the second week, the division of Schwann cells begins, and by the 10-12th day they form longitudinally oriented nerve processes. From 4 to 14 days, multiple growth flasks appear on the proximal sections of the fibers. The rate of fiber germination through the s/t at the site of injury can be extremely low, but distally, in undamaged parts of the nerve, the rate of regeneration can reach 3-4 mm per day. With this type of lesion, a good recovery is possible.

Axonal degeneration occurs as a result of metabolic disturbances in the bodies of neurons, which then causes process disease. The cause of this condition is systemic metabolic diseases and the action of exogenous toxins. Axonal necrosis is accompanied by the uptake of myelin and remnants of the axial cylinder by Schwann cells and macrophages. The possibility of restoring nerve function with this suffering is extremely low.

Segmental demyelination is manifested by a primary lesion of the myelin sheaths with the preservation of the axial cylinder of the fiber. The severity of the development of disorders may resemble that of a mechanical injury to the nerve, but the dysfunction is easily reversible, sometimes within a few weeks. Pathologically, disproportionately thin myelin sheaths, accumulation of mononuclear phagocytes in the endoneural space, proliferation of processes of Schwann cells around the processes of neurons are determined. Restoration of function occurs quickly and in full upon termination of the damaging factor.

Lecture #11

nervous tissue. Embryonic histogenesis. The structure of the neural tube. Sources of development of the components of the nervous tissue. Neurons. Structure. Neurofibrils of granular ER. Their meaning. Morphological and functional classification. Neuroglia. Varieties. Sources of development. Morphofunctional characteristic. Localization. Nerve fibres. Definition. Varieties. Features of formation, structure and functions. Nerve endings. Definition. Classification: morphological and functional. Morphofunctional characteristics. peripheral nerve. Structure.

Nervous tissue is the main structural and functional component nervous system which provides reception, excitation and transmission of nerve impulses.

Textile- a set of cells and their derivatives.

Components of the nervous tissue:

Cells (neurons)

Intercellular substance (represented by cells)

Formation of the neural tube, neural crest, neural placodes.

neural tube is a source of development of the central nervous system: spinal cord and brain.

neural crest- accumulation of cells of the neural plate, localized between the ectoderm and the neural tube.

The neural crest is the source of development:

· Neurons, glial cells (spinal ganglia or nodes or spinal cord).

Ganglia of cranial nerves

Melanocytes (pigmentocytes)

Calcium tonitocytes (cells thyroid gland)

Chromoffinocytes (adrenal medulla) and single hormone-producing cells

The endothelium of the cornea of ​​the eye

Neural placodes- thickening of the ectoderm on both sides of the neural tube in the head section of the embryo.

They form:

The neurons of the olfactory organ

Neurons of the vestibular and auditory ganglia

Neurons 5,6,9,10 pairs of cranial nerves

The structure of the neural tube

Consists of three layers.

1. Internal (clearance ) ependymal - represented by a single layer, the prismatic shape of cells, in the future, ependymocytes will develop from this layer of cells

2. Medium - cloak or mantle zone- multilayer, cubic and prismatic cells. Among the cells, 2 varieties are distinguished: 1 - neuroblasts, neurons develop from them, 2 - spongioblasts, sharp cells and oligodendrocytes develop from these cells. This layer forms the gray matter of the spinal cord and brain.

3. Outdoor - edge veil- represented by processes of cells of 1.2 layers. The marginal veil is the source of development of the white matter of the brain and spinal cord.

Function and structure of a neuron (shape, size, organelles)

Functions:

Reception of nervous excitement

Processing of nervous excitement

transmission of nervous excitement

The structure of a neuron.

Outgrowth form of the cell. It has the following parts:

1 - body (soma or perikaryon) -

2 - processes:

Dendrite - impulse goes To perikaryon

Axon (neuritis) - the impulse goes from perikarya, covered with plasmalemma on the outside, rounded or oval nucleus located in the center. Organelles: mitochondria, Golgi complex, granular ER, neurofibrils.

neurofibrils is a complex of neurofilaments and neurotubules. Neurofilaments 10 nm in diameter, neurotubules 24 nm (in the form of thin filaments). In the perikaryon, neurofibrils form a network. In the processes will be localized parallel to each other.

Nissel's tigroid substance, Nissl's chromotaphilic station, Nissl's basophilic substance - accumulation of granular EPS. Localized in the perikaryon.

Absent in the axon and axonal hillock.

The axonal hillock is where the axon exits.

Morphological classification of neurons (according to the number of processes)

Unipolar neuron - one process (axon) - after birth there are no such neurons, during embryonic development it is localized in the neuroblast

Bipolar - two processes of a dendrite and an axon, found in the retina, in the spiral ganglion of the organ of hearing

Multipolar neuron - several processes, one axon, the rest are dendrites. Localized in the gray matter of the brain, spinal cord, cerebellum, autonomic ganglia.

Pseudo-unipolar (false) - has a cytoplasmic outgrowth, two processes come from the outgrowth, one axon, the other dendrite. Location: spinal ganglion.

Functional classification of neurons (by function)

Afferent, sensory, receptor

Efferent (motor, effector)

Associative (insert)

Morphofunctional characteristics of neuroglial cells

Ependymocytes

They have a prismatic shape, the nuclei are oval elongated, line the spinal canal and the ventricles of the brain, and have mobile cilia (kinocilia), microvilli.

Functions:

o Secretory - participation in the formation of cerebrospinal fluid

o Barrier - the formation of a hemato-liquor barrier

o Transport

ASTROCYTES are:

1 - short-beam (protoplasmic) - are found in the gray matter in the central nervous system

2 - long beam (fibrous)

Functions:

o Reference

o Barrier - take part in the blood-brain barrier

o Transport

o Exchange

o Regulatory - neuron growth factor

OLIGODENDROCYTES

In dense adjacent to the neuron, surrounds the perikareon or any of the processes. The names are different:

1. Surrounds the perikareons - a cell - a satellite or a mantle cell - a satellite cell.

2. Surrounds processes - neuroleimocyte or leukocyte, Schwann cell

o Trophic

o Barrier

o Electrical insulation

nerve fiber

nerve fiber is a process of a nerve cell surrounded by a glial sheath.

The outgrowth of a nerve cell in a nerve fiber is called axle cylinder.

The membrane covering the axial cylinder is called - axolemma.

Types of nerve fibers:

1. Non-myelinated nerve fiber (non-myelinated)

2. Myelinated nerve fiber (pulpy)

Unmyelinated nerve fiber (non-myelinated) found in the autonomic nervous system . The fibers are constructed according to the cable type. Slow fiber, impulse conduction speed 1-2 meters per second.

Mesaxon– duplication of the plasmalemma of the lemmocyte

Components of fiber:

Multiple axle cylinders

Lemmocyte

Myelinated nerve fiber (pulpy) found in the CNS . The fiber is fast 5-120 meters per second. The section of the pulpy fiber in which the myelin layer is absent is called nodal interception of Ranvier. The myelin layer conducts electricity, so the fiber is fast.

myelin layer- mesaxon twist around the axial cylinder, rich in lipids.

Components of fiber:

One axle cylinder

myelin layer

Neurilemma (nucleus and cytoplasm displaced to the periphery of the Schwan cell)

nerve ending

A nerve ending is a terminal or terminal apparatus of a nerve fiber.

Functional classification nerve endings

Affector (receptors - dendrite of a sensitive neuron)

Effector (effectors - axons)

Interneuronal synapses

Classification of receptor nerve endings

1. By origin

Exteroreceptors

· Interoreceptors

2. By nature

· Temperature

pressure, etc.

Morphological classification of receptor nerve endings

1. Free - nerve ending, not accompanied by a glial cell (many among the cells of the epidermis, dermis, react to pain and temperature).

2. Non-free - the nerve ending is accompanied by a glial cell

o Unencapsulated - not surrounded by a connective tissue capsule

o Encapsulated - surrounded by a connective tissue capsule

Nerve endings:

Meissner's tactile body localized in the papillae of the papillary dermis.

Lamellar body of Vater-Pochinni(baroreceptor) is localized in the dermis, the stroma of the internal abdominal organs. The capsule is presented in the form of plates, between the plates there is liquid. connective tissue surface outer bulb, inner capsule flask.

Synapse- a specialized contact between two neurons or a neuron and a working organ, providing one-sided conduction of nervous excitation with the help of a neurotransmitter.

In the synapse there are:

1. Presynaptic part - in which the neurotransmitter is stored, synthesized and secreted in the form of a bubble.

2. Postsynaptic part - there are receptors for the mediator, mediators bind to receptors and cause a change in the membrane potential.

3. Synoptic gap - between parts 1 and 2.

Types of synapses:

1. Axosomatic

2. Axodendritic

3. Axo-axonal

4. Axo-vasal

The structure of the peripheral nerve

Nerve- accumulation of myelinated or unmyelinated fibers.

Endoneurium - loose connective tissue surrounding each fiber.

Perinerium - a layer, several fibers.

The epineurium is the outer connective tissue (outside the nerve).

The human nervous system is the most important organ that makes us us in every sense of the word. This is a collection of various tissues and cells (the nervous system consists not only of neurons, as many people think, but also of other special specialized bodies), which are responsible for our sensitivity, emotions, thoughts, and also for the work of every cell in our body.

Its function as a whole is to collect information about the body or environment with the help of a huge number of receptors, transferring this information to special analytical or command centers, analyzing the information received on a conscious or subconscious level, as well as developing decisions, transmitting these decisions to internal organs or muscles with control over their execution using receptors.

All functions can be conditionally divided into command or executive. Commands include information analysis, body control, and thinking. Auxiliary functions, such as control, collection and transmission of information, as well as command signals to internal organs, are the purpose of the peripheral nervous system.

Although the entire human nervous system is usually conceptually divided into two parts, the central and peripheral nervous systems are one whole, since one is impossible without the other, and a violation of the work of one immediately leads to pathological malfunctions in the work of the second, as a result, as a result, to a violation of the body or motor activity.

How the PNS works and its functions

The peripheral nervous system consists of all the plexuses and nerve endings that are outside the spinal cord, as well as the brain, which are the organs of the central nervous system.

Simply put, the peripheral nervous system is the nerves that are located on the periphery of the body outside the organs of the central nervous system, which occupy a central place.

The structure of the PNS is represented by cranial and spinal nerves, which are a kind of main conductive nerve cables that collect information from smaller, but very numerous nerves located throughout the human body, directly connecting the CNS to the organs of the body, as well as the nerves of the autonomic and somatic nervous system.

The division of the PNS into autonomic and somatic is also a bit arbitrary, it occurs in accordance with the functions performed by the nerves:

The somatic system consists of nerve fibers or endings, the task of which is to collect and deliver sensory information from receptors or sensory organs to the central nervous system, as well as the implementation of motor activity, according to the signals of the central nervous system. It is represented by two types of neurons: sensory or afferent and motor - efferent. Afferent neurons are responsible for sensitivity and deliver information to the central nervous system about the environment around a person, as well as about the state of his body. Efferent, on the contrary, deliver information from the central nervous system to muscle fibers.

The autonomic nervous system regulates the activity of internal organs, exercising control over them with the help of receptors, transmitting excitatory or inhibitory signals from the central nervous system to the organ, forcing it to work or rest. It is the vegetative system, in close cooperation with the central nervous system, that provides homeostasis by regulating internal secretion, blood vessels, and many processes in the body.

The device of the vegetative department is also quite complicated and is represented by three nervous subsystems:

• The sympathetic nervous system is a collection of nerves responsible for the excitation of organs and, as a result, an increase in their activity.
• Parasympathetic - on the contrary, it is represented by neurons, whose function is to inhibit or calm the organs or glands to reduce their performance.
• Metasympathetic consists of neurons that can stimulate contractile activity, which are located in organs such as the heart, lungs, bladder, intestines and other hollow organs capable of contraction to perform their functions.

The structure of the sympathetic and parasympathetic systems is quite similar. They both obey special nuclei (sympathetic and parasympathetic, respectively) located in the spinal cord or brain, which, analyzing the information received, are activated and regulate the activity of the internal organs, which are mostly responsible for processing or secretion.

Metasympathetic, however, does not have such nuclei and functions as separate complexes of microganglionic formations, the nerves that connect them, and individual nerve cells with their processes, which are completely located in the controlled organ, therefore it acts somewhat autonomously from the central nervous system. Its control points are represented by special intramural ganglia - nerve nodes that are responsible for rhythmic muscle contractions and can be regulated with the help of hormones produced by the endocrine glands.

All the nerves of the sympathetic or parasympathetic autonomic subsystem, together with the somatic ones, are connected into large main nerve fibers that lead to the spinal cord, and through it to the brain, or directly to the organs of the brain.

Diseases that affect the human peripheral nervous system:

Peripheral nerves, like all human organs, are subject to certain diseases or pathologies. Diseases of the PNS are divided into neuralgia and neuritis, which are complexes of various ailments that differ in the severity of nerve damage:

• Neuralgia is a nerve disease that causes inflammation without destroying its structure or cell death.
• Neuritis - inflammation or injury with the destruction of the structure of the nervous tissue of varying severity.

Neuritis can occur immediately due to a negative effect on the nerve of any origin or develop from neglected neuralgia when, due to lack of treatment inflammatory process caused neuronal death.

Also, all the ailments that can affect the peripheral nerves are divided according to the topographic-anatomical feature, or, more simply, according to the place of occurrence:

• Mononeuritis is a disease of one nerve.
• Polyneuritis is a disease of several.
• Multineuritis is a disease of many nerves.
• Plexitis is an inflammation of the nerve plexuses.
• Funiculitis - inflammation of the nerve cords - conducting nerve impulses channels of the spinal cord, through which information moves from the peripheral nerves to the central nervous system and vice versa.
• Radiculitis is an inflammation of the roots of peripheral nerves, with the help of which they are attached to the spinal cord.

They are also distinguished by etiology - the reason that caused neuralgia or neuritis:

• Infectious (viral or bacterial).
• Allergic.
• Infectious-allergic.
• Toxic
• Traumatic.
• Compression-ischemic - diseases due to compression of the nerve (various pinchings).
• Dysmetabolic nature, when they are caused by a metabolic disorder (vitamin deficiency. Production of some substance, etc.)
• Discirculatory - due to circulatory disorders.
• Idiopathic character - i.e. hereditary.

Disorders of the peripheral nervous system

When the organs of the central nervous system are affected, people feel a change in mental activity or a disruption in the functioning of internal organs, as the controlling or command centers send the wrong signals.

When a breakdown of peripheral nerves occurs, the person's consciousness usually does not suffer. It can only be noted possible incorrect sensations from the senses, when a person seems to have a different taste, smell, or tactile touches, goosebumps, etc. way. Also, problems can arise with problems with the vestibular nerve, with a bilateral lesion of which a person can lose orientation in space.

Usually, lesions of peripheral neurons lead, first of all, to pain or loss of sensation (tactile, gustatory, visual, etc.). Then there is a cessation of the organs for which they were responsible (muscle paralysis, cardiac arrest, inability to swallow, etc.) or a malfunction due to incorrect signals that were distorted during passage through the damaged tissue (paresis, when muscle tone is lost , sweating, increased salivation).

Serious damage to the peripheral nervous system can lead to disability or even death. But can the PNS recover?

Everyone knows that the central nervous system is not able to regenerate its tissues through cell division, since neurons in humans stop dividing after reaching a certain age. The same applies to the peripheral nervous system: its neurons are also unable to multiply, but can be replenished to a small extent by stem cells.

However, people who underwent surgery, and temporarily lost sensitivity of the skin of the incision area, noticed that after some long time it was restored. Many people think that new nerves have sprouted instead of cut old ones, but in fact this is not the case. It is not new nerves that grow, but old nerve cells form new processes, and then throw them into an uncontrolled area. These processes can be with receptors at the ends or intertwined, forming new nerve connections, and, consequently, new nerves.

The restoration of the nerves of the peripheral system occurs in the same way as the restoration of the central nervous system through the formation of new nerves. nerve connections and redistribution of responsibilities between neurons. Such restoration replenishes the lost functions often only partially, and also does not do without incidents. With severe damage to any nerves, one neuron may not belong to one muscle, as it should, but to several with the help of new processes. Sometimes these processes penetrate rather illogically, when, with an arbitrary contraction of one muscle, an involuntary contraction of another occurs. Such a phenomenon quite often occurs with advanced neuritis of the trigeminal nerve, when, while eating, a person begins to involuntarily cry (crocodile tears syndrome) or his facial expressions are disturbed.

As an option for restoring peripheral fibers, a neurosurgical intervention is possible, when they are simply sutured. In addition, a new method is being developed using foreign stem cells.

Each peripheral nerve consists of a large number of nerve fibers united by connective tissue sheaths (Fig. 265- A). In the nerve fiber, regardless of its nature and functional purpose, there are axle cylinder- cylindroaxis, covered with its own shell - axolemma and nerve sheath - neurolemma. If there is a fat-like substance in the latter - myelin, the nerve fiber is called pulpy or myelin neurofibra myelinate, and in its absence - bezmyelnoy or amyelin- neurofibra amyelinata (naked nerve fibers - neurofibria nuda).

The significance of the pulpy membrane lies in the fact that it contributes to a better conduction of nervous excitation. In the non-fleshy nerve fibers, excitation is carried out at a speed 0,5-2 m / s, while in the pulp fibers - 60-120 m / s ". According to the diameter, individual nerve fibers are divided into thick pulpy (from 16-26 µm in a horse, ruminants up to 10-22" microns in a dog) "- efferent somatic; medium pulpy (from 8-15 µm in a horse, ruminants up to 6-8 microns in a dog) - afferent somatic; thin (4--8 μm) ^ -y efferent vegetative (Fig. 265- B).

Non-fleshy nerve fibers are part of both somatic and visceral nerves, but in quantitative terms there are more of them in the autonomic nerves. They differ both in diameter and in the shape of the nuclei of the neurolemma: 1) low-pulp, or non-pulp, fibers with a rounded shape of the nuclei (fiber diameter 4-2,5 µm, core size 8X4",6µm, distance between nuclei 226-345 µm); 2) low-pulp or non-pulp fibers with an oval-elongated shape of the nuclei of the neurolemma (fiber diameter 1-2,5 µm, core size 12,8 X 4 µm, distance between nuclei 85- 180 µm); 3) non-fleshy fibers with spindle-shaped nuclei of the neurolemma (fiber diameter 0,5-1,5 µm, core size 12,8 X 1,2 µm, dis-

A .56

Rice. 265. Structure of the peripheral nerve? A - nerve on a transverse section: / - epineurium; 2 - perineurium; 3 - endoneurium! 4 - neurofibra myelinata; 5 - cylindraxis; 5 - composition of nerve fibers in the somatic nerve of a sheep; 1, 2, 3 - neurofibra myelinata; 4 - neurofibra amyelinata; 5i6, 7 - neurofibra nuda; a - temmocytus; e. incisio myelini; With - isthmus nodi.

standing between fibers 60-120 microns). In animals of different species, these indicators may not be the same.

Sheaths of the nerve. Nerve fibers extending from the brain, through the connective tissue, are combined into bundles that form the basis of the peripheral nerves. In each nerve, connective tissue elements participate in the formation of: a) inside the bundle base - endoneurium, located in the form of loose connective tissue between individual nerve fibers; b) a connective tissue sheath covering individual groups of nerve fibers, or perineurium- perineurium. In this shell, a double layer of squamous epithelial cells of an "ependy-moglial nature" is distinguished from the outside, which form a perineural sheath around the nerve bundle, or perineural space- spatium peri-neurii. Connective tissue fibers depart from the basilar inner layer of the lining of the perineural sheath into the depths of the nerve bundle, forming bundle fibers inside perineural septa- septum peri-neurii; the latter serve as a place! passage of blood vessels, and also participate in the formation of the endoneurium. ^

The perineural sheaths accompany bundles of nerve fibers along their entire length and divide as the nerve divides into smaller branches. The cavity of the perineural sheath is reported by the subarachnoid and subdural spaces of the spinal cord or brain and. contains a small amount of cerebrospinal fluid (a neurogenic pathway for the rabies virus to enter the central parts of the nervous system).

Groups of primary nerve bundles through dense unformed connective tissue are combined into larger secondary and tertiary bundles of nerve trunks and make up the outer connective tissue sheath in them, or epineurium- epineurium. In comparison with the endoneurium, larger blood and lymphatic vessels - vasa nervorum - pass into the epineurium. Around the nerve trunks there is one or another amount (depending on the place of passage) of loose connective tissue, which forms an additional near-nervous (protective) sheath - paraneural m., along the periphery of the nerve trunk. In close proximity to the nerve bundles, it is transformed into the epineural sheath.

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REGULARITIES OF THE TRAVEL AND BRANCHING OF THE NERVES

The topography and branching of the peripheral nerves have much in common with topo graphics and branching of blood vessels, with which they often pass together, forming neurovascular bundles. Their joint passage is due to the peculiarities of the development of the organs for which they are intended, the area of ​​​​distribution and the conditions of functioning. Located in one, common connective tissue case, blood vessels ensure the creation of an optimal temperature regime. For conduction of nerve impulses, as well as for the nutrition of nerve trunks. In addition, some other features are characteristic of peripheral nerves.

]. "The spinal nerves depart from the spinal cord metamerically in accordance with the division of the bone base and are divided into cervical, thoracic, lumbar, sacral and tail. The cranial nerves depart from the oblongata (from XII By V pair) and midbrain (IV and III pairs). I and II cranial pairs of nerves occupy a special position in this regard, being the nerve tracts of the most important sense organs.

2. Each spinal nerve has two root - dorsal and ventral- radix dorsalis et ventralis. On the dorsal root is spinal ganglion- ganglion spinale. Both roots at the exit from the spinal canal are connected into a common nerve stvbl- spinal nerve - n. spinalis, "containing sensory, motor and sympathetic fibers. The cranial nerves depart mainly with one root, corresponding to the dorsal or ventral root of the spinal nerve.

3: All efferent (motor) nerve fibers come out of the ventral columns of the gray medulla of the spinal cord and from the "corresponding motor nuclei of the medulla oblongata and midbrain (III, IV, VI, XI, XII). On the spinal cord they form ventral motor roots.

All afferent (sensory) nerve fibers consist of neurite cells of the spinal nodes and, accordingly, the ganglia of the cranial nerves (V, VII, VIII, IX and X pairs). Consequently, all bodies of receptor (sensitive) neurons lie outside the spinal cord and brain.

Each spinal nerve, upon exiting the spinal canal, gives off a white connecting branch - ramus (r) communicans albus - into the sympathetic trunk, "branch into the membranes of the spinal cord" -r. meningeus, then receives a gray connecting branch - g. communicans griseus - from the sympathetic trunk and is divided into dorsal and ventral branches - g. dorsalis et ventralis - according to the delimitation of the trunk muscles into dorsal and ventral muscle cords with their vessels. Each of the mentioned branches, in turn, is divided into medial and lateral branches - rnedialis et lateralis - for muscles and skin, which is also due to the division of muscle strands into lateral and medial layers. The totality of the branches of each segmental nerve

together with the corresponding part of the spinal cord forms a nerve segment - neurotome- neurotom. Neurotomes are more clearly expressed where there is a clear segmentation in the skeleton and muscles, for example, in the thoracic region of the body.

6. When the myotomes are displaced in the process of evolution, the branches of the corresponding neurotomes innervating them are displaced after them. So, the phrenic nerve - p. phrenicus, originating from the 5th-7th cervical neurotomes, approaches the diaphragm through the entire chest cavity; or, for example, an accessory nerve - n. accessorius - exits the spinal canal through a torn hole in the skull, and goes to the cervical region to innervate the brachiocephalic, trapezius and sternomaxillary muscles.

In the area where the nerves originate in the limb, the brachial and

Fig 266. Zones of distribution of skin nerves: / - infraorbital n.; G - subblock n.; 2 - frontal n.; 2 1

1 - zygomatic n.; 3 - dorsal branches of the cervical n.; 4 - dorsal branches of thoracic n.; 5 - ilio-hypogastric n.; 6 - ileo-inguinal n.; 7 - cranial skin gluteal n.; 8 - medium skin gluteal n.; - 9 - tail n.; 10 - perineal n.; 11 - caudal skin gluteal n.; 12 - tibial n.; 13 - plantar cutaneous nerves of the foot; 14 - low-borium surface n.; 15 - cutaneous lateral nerve of the leg; 16 - cutaneous lateral nerve of the thigh; 17 - external shameful n.; 18 - n. safenus; 19 - cutaneous medial n. feet; 20 - ventral branches of thoracic * ny n.; 21 - ulnar n.;, 22 - median n.; 23 - musculocutaneous n.; 24 - radial superficial n,; 25 - axillary n.; 26 - ventral cervical n.; 27 -

mandibular n.

lumbosacral nerve plexuses - plexus brachialis et lumbosacral, and nerves heading to certain muscle groups already originate from them. Usually, both nerves and muscles of the limbs are multisegmented. Nerve plexuses are also found in the neck, which is also explained by the complex origin of the neck muscles. Connecting branches between individual nerves -rr. communicantes - indicate the origin of individual nerves from several neurotomes.

7. Sensory nerves, although they basically correspond to skin segments - dermatomes, innervate not only the area of ​​\u200b\u200bits segment, but also go into adjacent dermatomes. Therefore, anesthesia of any skin segment. (dermatome) is possible only when three adjacent neurotomes are turned off (Fig. 266).

SPINAL NERVES

Spinal nerves - nervi spinales - are divided into cervical (C), thoracic (Th), lumbar (L), sacral (S) and caudal (Co) (corresponding to the division of the spinal column).

NERVES OF THE NECK

Neck nerves - nn. cervicales - in the amount of 8 pairs exit through the intervertebral foramina [the first pair (C I) exits through the intervertebral foramen of the atlas, the second pair (C II) - through the intervertebral foramen behind the atlas, and the eighth pair (C VIII) - behind the 7th cervical vertebra ]. Each cervical nerve receives gray branch- g. griseus, including C VIII-VII - from the stellate node, C VI-III (II) -j-ot of the vertebral nerve and C I (II) - from the cranial cervical sympathetic node. Having received the gray branch and given shell branch- g. meningeus, the spinal nerve is divided into dorsal and ventral branches- rr. dorsales and ventrales. The dorsal medial branches go along the medial surface of the subcostal "muscle of the head and neck, and the lateral ones - along the medial surface of the muscles of the neck - patch-like and longest. The dorsal medial branch of the first cervical nerve is called the large occipital nerve - n. occipitalis major, which branches into short muscles of the occipito-atlant and osatlant joints, as well as in the skin of the occipital region and caudal muscles of the ear.

Separate ventral branches of the cervical nerves are characterized by a special course and, accordingly, receive special names. The ventral branch of the first "cervical nerve connects with the hypoglossal and ventral branches of the second cervical nerve, branches in the muscles of the neck. The ventral branch of the second cervical nerve has connections with C I, C III, the accessory nerve. From it beret Start great ear nerve - n. auricularis magnus, which branches in the skin of the base of the head, muscles * auricle and here It has connection with branches of n. facialis. The continuation of the ventral branch C II is transverse nerve of the neck- n. transversus colli; having received a connecting branch from C III, it branches in the skin of the cabbage soup, having connections with the skin branches of the neck - P. facialis.

Phrenic nerve - p. phrenicus - comes from C (V), VI and VII. Medially" from the scalene muscle and subclavian artery, it goes into the chest cavity and branches in the diaphragm.

supraclavicular nerve- n. supraclavicular is - comes from C VI, branches in the skin of the area shoulder joint, shoulder and dewlap. The ventral branches of the 3 (4) last: cervical nerves take part in the formation of the brachial plexus, from which the nerves for the shoulder girdle and the free section of the thoracic limb emerge.

SHOULDER! PLEXUS

The brachial plexus - plexus brachialis - is formed by two trunks - trunci plexus - from the ventral branches C VI, VII And C VIII, Th I (II). It lies ventrally from the scalene muscle and medially from the scapula. The nerves that innervate the region of the shoulder girdle, the muscles of the scapula come out of it And free Department of the limb (Fig. 267).

Dorsal nerve shoulder blades dorsalis scapulae (15) -double, -departs from C V And VI. Both nerves go to the rhomboid muscle - one along the medial surface, and the other in the thickness of the cervical part of the ventral dentate muscle, to which they send branches. It has connecting branches with a long thoracic nerve.

Long thoracic nerve- n. thoracicus longus - originates in two branches from C VII-VIII, which, having united, go caudally and branch out in the ventral dentate Muscle.

suprascapular nerve- n. suprascapularis (1) - formed from C VI and VIi ,iHfleT together with the suprascapular artery into the supraspinatus and infraspinatus muscles and into the scapula.

Subscapular nerves- nn. subscapulars (b) - in the amount of 2-4

start from C VI and go to the muscle of the same name, giving branches to the large round muscle and the periosteum of the medial surface of the scapula. . I..

The thoracic nerve - n. thoracodorsal (7) - originates along with the subscapular or axillary nerves from C VI ^-VII (in ungulates C VII-VIII) and goes to the latissimus dorsi muscle, giving branches to the large round muscle along its course.

Axillary nerve - n. axillaris (4) - starts from C VII-VIII, "together with the brachial circumferential lateral artery, penetrates between the subscapular and large round muscles deep into and, giving the muscle branches V small round and deltoid muscles (in dogs and horses also in the capsular), goes to the lateral surface of the shoulder. Here, the cranial lateral cutaneous nerve of the shoulder departs from it - n. cutaneus brachii lateralis cranialis - and continues on the forearm, where it is called the cranial cutaneous nerve of the forearm - n. cutaneus antebrachii cranialis, here it branches, reaching the wrist (V. I. Troshin ).

Radial nerve - n. radialis (10) - the largest nerve of the extensor surface of the thoracic limb. It begins with nerve bundles from C VII - C VIII and Th I, passes between the heads of the triceps muscle of the shoulder, where it gives them muscle branches. bending around humerus from the caudal surface in the laterodistal direction, radial nerve V areas elbow joint gives back caudal lateral cutaneous nerve of the shoulder

h. cutaneus brachii lateralis caudalis - and is divided into superficial and deep branches. deep branch- g. profundus - is divided into muscle branches that branch out in the extensors of the forearm. Surface branch - g. superficialis (Fig. 268- 10), giving the lateral cutaneous nerve of the forearm -P. cutaneus antebrachii lateralis, and in carnivores and pigs also the lateral and medial branches, continues distally and is divided into common dorsal digital nerves- nn. digitales dorsales commu-

Rice. 268. Nerves of the hand: A - dogs; B - pigs; IN - cows (from the dorsal surface); G - horses; D - dogs; E - pigs; W - cows (from the palmar surface); 3 - n. muscu-locutaneus; 5 - n. medianus; 10 - g. superficialis n. radialis; 11 - n. ulnaris; 11" - d. dorsalis n. ulnaris; 13 - n. digitales palmares communes; 13" - r. communicants; 14- n. digitalis palmaris proprius (horse - lateralis); 15 - nn. digitales dorsales proprii; 16 - nn. digitales dorsales communes; /- V - fingers.

hes (I-IV - in carnivores, II-IV - in pigs, II-III - in ruminants; the horse does not have them), which continue into the dorsal digital nerves proper. In carnivores, along with the common dorsal digital nerves, the superficial branch departs first non-axial dorsal digital nerve- n. digitalis dorsalis I abaxialis.

Musculocutaneous nerve- n. musculocutaneus (3) - originates from C VI-VII and, having given the proximal branch - g. proximalis - into the coracoid-brachial and biceps muscles, together with the median nerve in ungulates forms axillary loop- ansa axillaris.

In carnivores, the musculocutaneous nerve passes along the medial surface of the shoulder along the biceps muscle (in ungulates, it passes along with the median nerve from the axillary loop to the distal third of the forearm, where it regains its independence). Having given the distal muscular branch to the shoulder muscle and exchanging connecting branches with the median nerve (in carnivores), the musculocutaneous nerve continues as a medial cutaneous nerve of the forearm- n. cutaneus? antebrachii medialis. "

median nerve- n. medianus (5) - originates from C VII-VIII, Th I, passes along the medial surface of the shoulder (in ungulates together with the musculocutaneous nerve) and in the area of ​​the elbow joint gives muscle branches to the round pronator and superficial digital flexor ( in carnivores), into the flexors of the wrist and the deep digital flexor, in which it has intramuscular connections with the branches of the ulnar nerve. Then, giving the interosseous forearm nerve- n. interosseus antebrachii, descends to the distal end of the forearm and is divided into common palmar digital nerves - nn. digitales palmares communes I-III (carnivores), II-III (pigs, ruminants), and in the horse on the medial and lateral palmar nerves - nn. .palmares medialis et lateralis, which correspond to the second and third common palmar digital nerves (13). The common palmar digital nerves from the bones of the metacarpus pass into the corresponding proper palmar digital nerves - n. digitalis palmaris proprius I-IV (carnivorous), II-IV (pig, ruminant) and in the horse to the lateral and medial palmar digital nerves - nn. digitales palmares lateralis et medialis (14).

Ulnar nerve- n. ulnaris (11) - formed due to C VIII and Th I (in a horse and a dog and Th II), passes along the medial surface of the shoulder towards the ulnar tubercle, giving along its course caudal cutaneous nerve of the forearm- n. cutaneus antebrachii caudalis, which reaches the palmar surface of the wrist, and muscle branches into the caudal muscles of the forearm. Above the wrist, the ulnar nerve divides into dorsal and palmar branches.

Dorsal branch.- g. dorsalis "-divides; into the common dorsal digital nerve - n. digitalis dorsalis communis" IV (carnivores, pigs, ruminants) and V non-axial dorsal digital nerve - n. digitalis dorsalis V abaxialis (carnivores, pigs), which continue distally and de-; pour on their own dorsal digital nerves - nn. digitales dorsales proprii IV-V (cat, pig, ruminants). In the horse, the dorsal branch branches in the skin of the dorsolateral surface of the carpus and metacarpus. ,

palmar branch- Mr. palmaris, in turn, is divided on superficial and deep branches.

surface branch- g. superficialis - is divided into two branches. One goes as a common dorsal digital nerve - n. digitalis palmaris communis IV (carnivores, pigs, ruminants), and in a horse III, or a lateral digital nerve - n. palmaris lateralis, in the formation of which the palmar lateral branch of the median nerve also takes part. In the middle of the metacarpal "bone, the lateral palmar nerve in the horse receives a connecting branch from the medial palmar nerve. In the area of ​​the metacarpopetal joint, the common palmar digital nerve divides into the digital nerves proper, axial to V (carnivorous, pig," ruminant), non-axial to IV ( carnivores, pigs, ruminants) and lateral digital in a horse, a dorsal branch departs from it (15) for the laterodorsal surface of the finger. The second branch, departing from, g. superficialis, is found in carnivores and pigs And innervates their fifth finger: n. digitalis palmaris V abaxialis.

deep branch- g. profundus, extending from the palmar branch of the ulnar nerve, is divided into palmar metacarpal "nerves - nn. metacarpei palmares (dog, horse), branching in the interosseous and worm-like muscles, reaching the distal end of the metacarpus. In other animals, it is short and branches in the area wrist.

Thoracic cranial nerves- nn. pectorales craniales (2) - in the amount of 3-4 branches are formed from the medial surface of the brachial plexus from C VI-VIII and are sent to the superficial pectoral muscles, V which branch out.

Thoracic caudal nerve-t n. pectoralis caudalis (8) - originates from the medial surface of the brachial plexus from C VIII-Th I (in dogs and horses and from Th II) giving a muscular branch to the caudal superficial pectoral muscle, continues as lateral thoracic nerve-P. thoracicus lateralis (8) - for innervation of the lateral wall of the chest. In the horse, the ventral branch separates from it, running along the superficial pectoral muscle in the caudal direction, getting lost in the skin of the lateroventral surface of the chest wall.

1. What refers to the peripheral nervous system? How and where do the spinal nerves form and what branches do they divide into?

The peripheral nervous system is that part of the NS that connects the GM and SM with sensitive apparatuses - affectors, as well as with those organs and apparatuses that respond to external and internal stimulation with adaptive reactions (movement, secretion of glands) - effectors.

The PNS consists of:

Nerves (trunks, plexuses, roots)

Nerve ganglions

Peripheral endings

The spinal nerves are formed by the fusion of the posterior and anterior branches, which are anatomically and functionally connected to their spinal cord segments through these branches. Therefore, there are 31 pairs of s/m nerves.

The s/m nerve trunk is divided into branches:

Anterior branch

posterior branch

The meningeal branch

· White connector

2. Posterior branches of s/m nerves: their zone of innervation and peculiarities of distribution?

The posterior branch has a segmental structure. Therefore, it innervates parts of the body that have retained segmentation: deep muscles of the back, neck, skin over these areas.

The posterior branches are mixed, divided into lateral and medial branches, their diameter is less than the anterior branches. The exception is: 1). posterior branch of the I cervical s / m nerve (suboccipital nerve) - motor; 2). The posterior branch of the II cervical s / m nerve is sensitive, larger than the anterior.

3. Anterior branches of the s/m nerves: their zone of innervation and difference from the posterior ones?

The anterior branches are not segmented, they innervate parts of the body that have lost segmentation, form plexuses, the branch is mixed.

4. Why do the anterior branches of the s/m nerves form plexuses? Anterior branches of what nerves do not form them? Why?

ANSWER: plexuses are formed because the anterior branches of the s / m nerves innervate non-segmented areas. Metamerism is retained only by the anterior branches of the s/m nerves of Th2-Th11 segments, they have a segmental structure, they are called intercostal nerves.

5. What plexuses do you know? Their zone of innervation?

Plexus:

· Neck. From the anterior branches of the 4 upper cervical s/m nerves. Innervates the skin in the neck, diaphragm, neck muscles.

· Shoulder. Anterior branches of the 4 lower cervical s/m nerves. Innervates the muscles, skin of the upper extremities, superficial muscles of the chest and back.

· Lumbar plexus. Anterior branches of the lumbar nerves. Innervates the skin, muscles of the lower abdomen, thighs.

The sacral plexus. Formed by sacral nerves

6. cranial nerves: how do they differ from the spinal cord and into what groups according to the composition of the fibers are they divided?

CN - nerves extending from the brain. Differences from s / m nerves:

· They do not have a segmental structure, they are different in function, shape, exit points.

· Different composition of fibers.

According to the composition of the fibers, 4 groups are distinguished:

ü Sensitive (1,2,8 pairs of ChN)

ü Motor (3,4,6,11,12 pairs of ChN)

ü Mixed (5,7,9,10 pairs of CHN)

ü Having plus vegetative fibers (3,7,9,10 pairs of CHN)

7. What are peripheral nerves made of? What connective tissue membranes do they have? What is the perineural space and what is its significance?

A nerve is a part of the nervous system, which is an elongated cord formed by bundles of nerve fibers and connective tissue membranes.

They have three types of connective tissue membranes:

Endoneural - m / y with individual nerve fibers, forms separate bundles of nerve fibers;

Perineurium - surrounds several bundles of nerve fibers, is formed by two plates:

ü Visceral

ü Parietal

Epineurium - present in the largest nerves, rich in blood vessels- nourishes the nerve, provides collateral circulation.

There is a perineural space between the plates, all CNs have it, SMN is debatable, it communicates with the subarachnoid space, contains cerebrospinal fluid. Of clinical importance is the advancement of the rabies pathogen in this space to the GM and SM.

8. What is a nerve fiber? Their classification according to the caliber and speed of impulses.

A nerve fiber is a process of a nerve cell surrounded by a sheath of lemmocytes.

According to the caliber and speed of their conduct, they are divided into:

· Gr.A: thick myelin fibers up to 100 microns, v=10-120 m/s, form somatic nerves.

· Gr.B: thin myelin fibers 1-3mkm, v=3-14m/s, form pregangliol autonomic nerves.

· Gr.S: non-myelinated fibers 0.4-1.2 µm, v=0.6-2.4 m/s, form postgangliol autonomic nerves (to organs).

9. Intra-stem structure of nerves.

In addition to the fact that the composition of the nerve may include nerve fibers of different functions, surrounded by connective tissue membranes, and having a perineural space, bundles of nerve fibers can be located in different ways. According to Sinelnikov, they distinguish:

Cable type (vegetative) - all nerve fibers run in parallel;

· Network type (somatic) - adaptive function, a special form of connections m / y with bundles of nerve fibers.

10. Patterns of location of extraorganic nerves.

The nerves are paired and diverge symmetrically with respect to the central nervous system;

Nerves reach the organs along the shortest path, with the exception of the nerves of those organs that move in the process of their development, while the nerves lengthen and change their path;

Nerves innervate the muscles from those segments that correspond to the myotomes of the muscle anlage, if the muscles move, the nerves lengthen.

The nerves accompany large arteries, veins, forming neurovascular bundles, they are located in protected places.

11. What do the types of branching of intraorgan nerves depend on? What types of them do you know in muscles with different structure and function?

Options for muscle innervation:

Main type - small branches from one large nerve;