PERIPHERAL NERVOUS SYSTEM - a division of the nervous system that provides communication between the central nervous system and various parts of the body. Includes the cranial and spinal nerves that extend from the brainstem and spinal cord and form the plexus and peripheral nerves. The composition of P. n. from. also include the spinal, cranial and autonomic ganglia, which are clusters of neuronal bodies outside the center of the nervous system. Information from internal and external receptors flows along peripheral nerves to the brain, and signals go in the opposite direction to skeletal muscles, vascular smooth muscles or the gastrointestinal tract and glands. Most peripheral nerve structures contain sensitive, motor and vegetative fibers.

The cranial nerves (12 pairs) leave the medulla at the base of the brain. From the spinal cord there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. Each spinal nerve has an anterior and posterior root, which merge to form the nerve itself. The posterior root contains sensory fibers and is closely associated with the spinal ganglion, which consists of the bodies of neurons from which these fibers extend. The anterior root consists of motor fibers, which are the processes of the motor neurons of the anterior horns of the spinal cord. The lumbar and sacral roots, leaving the spinal cord, follow down to the place of their exit from the spinal canal through the intervertebral foramen, along the way forming the so-called. ponytail. Each spinal nerve is divided into an anterior branch, which innervates the anterior and lateral parts of the body, and a posterior branch, which innervates the posterior parts of the body. The anterior branches of the spinal nerves form plexuses. The upper 4 nerves form the cervical plexus, from which the nerves that innervate the occipital and cervical... The branches of the spinal nerves form the brachial plexus, which runs between the anterior and middle scalene muscles in the direction of the subclavian fossa. From the brachial plexus there are nerves that innervate the shoulder girdle and arm, the largest of which are the median, ulnar and radial. The lumbar plexus is formed by the 4 upper lumbar spinal nerves, from which the nerves that innervate the lower abdomen, pelvic girdle and thigh, in particular the femoral nerve, come out. The sacral plexus is formed by the spinal nerves L5-S4 and is located in the pelvic cavity. Nerves that innervate the lower extremities depart from it; the main one is the sciatic nerve, which divides into the peroneal and tibial nerves.

Each nerve is a collection of fibers, organized in groups and surrounded by connective tissue, in which the vessels that feed the fibers pass. The nerve fiber consists of an axial cylinder - an axon and a sheath formed by Schwann cells. A significant part of the nerve fibers is also covered by the myelin sheath. The myelin sheath is formed from cell membrane Schwann cells, each of which is repeatedly twisted around the axon. The area of \u200b\u200bthe axon where 2 adjacent Schwann cells touch each other is called a Ranvier intercept. The myelin sheath speeds up the conduction of nerve impulses along the axon by about 10 times due to the fact that they "jump" from one interception of Ranvier to another. Proteins and other membrane components necessary to maintain the structure of the fiber are synthesized in the area of \u200b\u200bthe neuron body and are transferred from it to the endings of the nerve using axo-plasma current, which can be slow (1-4 mm / day) or fast (200-400 mm / day). The feedback of the nerve endings and the cell body is carried out using the retrograde axo-plasma current.

P.N.s.'s defeat can be caused by trauma, autoimmune, metabolic and vascular disorders, intoxication, hereditary diseases. Depending on the localization of the process, radiculopathy, plexopathy, neuropathy, gangliopathy, as well as systemic lesions (multiple mononeuropathies, polyradiculopathy, polyneuropathy, etc.) are distinguished. Allocate 3 main. variant of damage to peripheral fibers: 1) Wallerian degeneration, which occurs during the transverse intersection of the axon and is characterized by degeneration of the axon and myelin sheath distal to the injury site, 2) axonal degeneration caused by impaired metabolism in the neuron and suppression of axoplasmic transport and manifested by degeneration of the most distant parts of axons, 3) segmental demyelination with primary damage to Schwann cells and myelin. Unlike the center, the nervous system, for P. of N. from. the ability to regenerate is more characteristic, due to which, when plural. diseases P.N. from. in the case of elimination of the pathogenic factor, a relatively good recovery of functions is noted.

A characteristic feature of the peripheral nervous system is the absence of a special protective program, which is inherent in the brain, as well as the spinal cord. That is why its components - nerve endings, nodes, fiber as a whole are more often affected by negative external and internal factors. Because of this feature of the peripheral nerve system, they more often manifest themselves various diseases - functional disorders. A neurologist deals with the treatment of such pathologies.

The components of the peripheral nervous system are formed by the ganglia and cranial / spinal nerves as well as plexuses. All of them are located freely in the human body - without protection by dense tissues or aqueous media.

When asked what structures are attributed to the peripheral nervous system in humans, experts traditionally answer - the fibers of the somatic and autonomic nerves, as well as their radicular representation in the central part of the brain - the ganglion.

Thus, the sympathetic system is responsible for collecting complete information from the senses in order to later transmit it to the brain. After its processing, the impulses go in the opposite order - to the motor structures. This, in fact, is a tool for human interaction with the surrounding space.

Whereas the autonomic nerve system makes up a picture of what is happening on the periphery and in the internal organs. It controls the activity of the cardiovascular, respiratory, digestive, and excretory system... A feature of this function of the peripheral nervous control system is its unconsciousness. The person doesn't even make any effort. Everything happens autonomously and automatically - the laying takes place by the embryonic formation of organs and systems.

Briefly, you can imagine that the sense organ - vision, received information about the danger, transmitted it to the brain. From there, the impulse moved through the processes of peripheral nerves to the muscle fibers of the limbs. The man changed his body position and avoided a dangerous situation.

Main characteristics

The advantage, and in some cases, the lack of the autonomic part of the nervous system, experts point out is the fact that the location of most important nuclei is placed outside the cranium. The intercalary neurons are located for the sympathetic section in the prevertebral ganglia, while for the parasympathetic, in the paravertebral ganglia, as well as near the innervated structures.

Therefore, several centers of control of impulse conduction belong to the peripheral nervous system at once - both in the ganglia, on the periphery, and in the central region - the brain. Whereas the fibers from which the peripheral nerves are formed are divided into two subgroups:

• centripetal - capable of transmitting impulses to the structures of the cerebral cortex from organs;
• centrifugal - are responsible for bringing the impulse from the brain to the innervated organ;
• trophic - providing metabolic tissue processes.

In the roots with the spinal ganglion, as a rule, the motor and sensory nerve fibers are connected. Another feature is that large nerves pass near the articular folds, and neurovascular bundles, united by a common sheath, are equipped with almost all organs important for humans.

Functions

Since the peripheral innervation system includes 31 pairs of nerves that emanate from the spinal cord, as well as 12 pairs of cranial leads, the functional responsibilities of the system include:

• coordination of human movements in space;
• sensory definition of the world - visual perception, tactile sensations, as well as recognition of taste, smell;
• response to an impending danger - changes in heart rate, pressure, the production of stress hormones;
• the functioning of each cell of tissues and organs;
• adequate activity of the genitourinary, cardiovascular, respiratory, motor system;
• good rest - relaxation, dilation of blood vessels, pupils, deep breathing.

Most people do not even realize how complex their body is, how everything is interconnected and functions in it. For each external or internal irritation, an immediate response follows - the temperature in the room has changed, the body has adjusted the activity of integumentary tissues, mucous membranes, as well as the center of thermoregulation. Or, when abundant food is received, the stomach provides information to the brain, and from there a signal is sent to the digestive organs to increase the production of enzymes and juices for full assimilation.

System malfunction

The lack of natural protection of the nerve fiber - bones, muscles, fluid, makes it susceptible to various negative influences. The main diseases that arise in the peripheral system:

• neuralgia - an inflammatory focus in cells, but without their destruction or death;
• neuritis - severe inflammation, or a consequence of trauma, in which the structure of the tissue is destroyed.

By the location of the pathological focus - the level of damage to peripheral nerves, it is customary to distinguish:

• mononeuritis - inflammation of one branch of the nerve;
• polyneuritis - damage to several nerve fibers at once;
• mulineuritis - pathology affects almost all nerves;
• plexitis - an inflammatory process in the nerve plexus;
• funiculitis - a disease of the nerve cords;
• radiculitis is a lesion by inflammation of the roots of peripheral nerves, in which there is a violation of the sensitivity and motor activity of a person.

According to the etiological factor, experts classify all neuritis as infectious - due to the activity of pathogens, traumatic, as well as toxic and dysmetabolic. The doctor will make a full diagnosis after evaluating all the information - neurological examination, laboratory and instrumental studies.

Diagnostics

The complexity of the structure and features of the functioning of peripheral nerve fibers and their centers determine their own characteristics of diagnosing diseases. A huge role is played by the professionalism of the doctor - far from everyone will be able, on the basis of the patient's complaints, to assume a disorder in a distant part of the autonomic plexus. For example, the posterior branches are divided into medial, as well as lateral - each innervate its own part of the body, which will determine the localization of unpleasant sensations in the patient.

To recognize that the peripheral nervous system is affected, modern diagnostic procedures help specialists:

• electroneuromyography - graphic registration of impulse conduction along a nerve fiber;
• immunological tests and PCR diagnostics of cerebrospinal fluid - identification of the causative agent of infectious diseases;
• x-ray of the spine - injuries, fractures, degenerative processes in the vertebrae;
• computed / magnetic resonance imaging of the brain, spinal cord, internal organs - maximum information about masses, hemorrhages, infringements and inflammations of a different etiology in the nervous structures.

In some cases, consultation of doctors of related specialties is required - oncologists, infectious disease specialists, rheumatologists, endocrinologists, since the symptoms of peripheral nerve damage are similar to the course of diseases of internal organs.

Drug therapy

Focusing on the structure of peripheral nerves and information from diagnostic examinations. The doctor individually selects the optimal treatment regimen. The main emphasis is on eliminating the cause of the disorder - infringement in the vertebral structures, a tumor process, or inflammation due to infection.

There is no universal scheme of drug action on peripheral nerves. With the help of pharmacy preparations, specialists have a symptomatic effect - to eliminate pain, stop muscle spasm, reduce inflammation in tissues, and improve the conduction of impulses along the nerve fiber.

In the case of diagnosing an infectious process, the doctor will select antibacterial drugs - as a rule, from subgroups of the second or third generation, with a wide spectrum of activity. Their name, doses, course of treatment directly depend on the identified pathogenic microorganism.

With a severe nature of peripheral nerve injuries, or if the negative effect is due to a tumor, specialists decide on surgical intervention. Subsequently, medications are prescribed during the rehabilitation period to restore the functional activity of the nervous system.

Drug-free system

In addition to synthetic drugs, there are other methods of treatment in the arsenal of doctors to help patients with peripheral nerve damage. Many thin collagen fibers form a thin network directly under the integumentary tissues, innervating and regulating their activity.

For the purpose of non-drug exposure, doctors are actively resorting to physiotherapy. Ultrasound and magnetotherapy, electrophoresis and darsonvalization have proven their worth. In each clinic, physiotherapy devices are presented in a wide range. Their competent use significantly improves the well-being of people, without even requiring medication in mild cases of autonomic disorders.

Various options for medical massage - vacuum, acupressure, cupping, are also able to restore nerve conduction in the periphery. The doctor will determine the optimal option and the number of massage sessions on an individual basis. In addition, exercise therapy is mandatory. The set of exercises is selected for the identified disease. The tasks of exercise therapy are to stimulate blood circulation, improve tissue nutrition, stretch spasmodic muscles, and restore the full value of movements in the joints.

Spa treatment is another way to improve health in case of disorders in the peripheral nervous system. Climatotherapy and diet therapy, hydrotherapy and the intake of decoctions and infusions of medicinal herbs, mud therapy and inhalations will allow, with their competent combination, to eliminate various problems with the innervation of organs and systems.

The peripheral nervous system is that part of the nervous system that lies outside the brain and spinal cord. Through the peripheral nervous system, the brain and spinal cord regulates the functions of all systems, apparatus, organs and tissues.

The peripheral nervous system (pars peripherica) includes the cranial and spinal nerves, sensory nodes of the cranial and spinal nerves, nodes and nerves of the autonomic (autonomic) nervous system. This also includes sensitive apparatuses (nerve endings - receptors) embedded in tissues and organs that perceive external and internal stimuli (influences), as well as nerve endings - effectors that transmit impulses to muscles, glands and other organs (tissues) that respond to the adaptive reactions of the body ...

Nervesformed by the processes of nerve cells, whose bodies lie within the brain and spinal cord, as well as in the nerve nodes of the peripheral nervous system. Outside, the nerves and their branches are covered with a loose fibrous connective tissue sheath - epineurium. In the epineurium, fat cells are found, blood vessels, lymph vessels and thin bundles of nerve fibers pass. In turn, the nerve consists of bundles of nerve fibers surrounded by a thin sheath - perineurium (perineurium). Between the nerve fibers there are thin layers of connective tissue - endoneurium.

Nerves come in a variety of lengths and thicknesses. Longer nerves are located in the tissues of the limbs, especially the lower ones. The longest cranial nerve is the vagus nerve. Nerves of large diameter are called nerve trunks (trunci), branches of nerves are called branches (rami). The thickness of the nerve and the size of the innervated area depend on the number of nerve fibers in the nerves. For example, in the middle of the shoulder, the ulnar nerve contains 13,000-18,000 nerve fibers, the median - 19,000-32,000, and the musculocutaneous - 3000-12,000 nerve fibers. In large nerves, fibers along the course of a nerve can pass from one bundle to another, therefore, the thickness of the bundles, the number of nerve fibers in them are not the same throughout.

The nerve fibers that make up a nerve do not always run in a straight line. Often they have a zigzag course, which protects them from overstretching during movements of the trunk and limbs. Nerve fibers can be myelinated,thickness from 1 to 22 microns and myelin-free,1-4 microns thick. Among the myelin fibers, thick (3-22 microns), medium and thin (1-3 microns) are distinguished. The content of myelinated and nonmyelinated fibers in nerves is different. So, in the ulnar nerve the number of medium and thin myelin fibers is from 9 to 37%, in the radial - from 10 to 27%; in cutaneous nerves - from 60 to 80%, in muscle - from 18 to 40%.

Nerves are supplied with blood by numerous vessels, widely anastomosed with each other. Arterial branches to the nerve go from the vessels that accompany the nerves. In the endoneurium, there are blood capillaries, which have a predominantly longitudinal direction in relation to the nerve fibers. The innervation of the nerve sheaths is carried out by branches extending from this nerve.

The nerve fibers that form the nerves of the peripheral nervous system can be divided into centripetal and centrifugal. Centripetal fibers(sensitive, afferent) transmit a nerve impulse from receptors to the spinal cord and brain. Sensory fibers are found in all nerves of the peripheral nervous system.

Centrifugal fibers(efferent, effector, efferent) conduct impulses from the brain to the innervated organs and tissues. Among this group of fibers, the so-called motor and secretory fibers are distinguished. Motor fibers innervate skeletal muscles, secretory fibers - glands. Also, trophic fibers are isolated, which provide metabolic processes in tissues. The motor nerves are formed by the axons of neurons, the bodies of which form the nuclei of the anterior horns of the spinal cord and the motor nuclei of the cranial nerves. The processes of cells located in these nuclei are directed to the skeletal muscles. Sensory nerves are represented by processes of nerve cells, the bodies of which lie in the sensory nodes of the cranial nerves and in the spinal (sensory) nodes. The mixed nerve contains sensory and motor nerve fibers.

The cranial and spinal nerves are isolated as part of the peripheral nerves. The cranial nerves (nervi craniales) originate from the brain and the spinal nerves (nervi spinales) from the spinal cord.

Autonomic (autonomic) fibers emerging from the spinal cord and brain as part of the roots of the spinal and cranial nerves, and then their branches, are formed by the processes of the neurons of the lateral horns of the spinal cord and the autonomic nuclei of the cranial nerves. The axons of the neurons of these cells are directed to the periphery to the nodes of the autonomic nerve plexus, on the cells of which these fibers end. The processes of cells located in peripheral vegetative nodes are directed to the organs. The path of autonomic innervation from the brain to the working organ consists of two neurons. The first neuron, whose processes extend from the autonomic nucleus in the brain to the autonomic node in the periphery, was called the prenodal (preganglionic) neuron. A neuron, the body of which is located in peripheral autonomic (autonomous) nodes, and the process is directed to the working organ, is called postnodal (postganglionic) neuron.Autonomic nerve fibers are found in most of the cranial and all spinal nerves and their branches.

There are patterns of topography and features of nerve branching. On their way to organs and tissues, nerves have much in common with blood vessels. In the walls of the trunk, nerves, like blood vessels, run segmental (intercostal nerves and arteries). Large nerves are located mainly on the flexor surfaces of the joints.

Nerves combine with arteries and veins into neurovascular bundles, which have a common connective tissue sheath for the vessels and nerves - the fibrous vagina. This ensures greater protection of the nerves.

Distinguish between cutaneous (superficial), articular and muscular (deep) nerves and their branches. The order in which the muscle branches leave the nerve usually corresponds to the order in which the arteries enter the muscle.

The place of entry of nerves into the muscle is often the middle third of the muscular abdomen. The nerves enter the muscle from its inner side.

Variants of peripheral innervation are associated with the distribution of nerves and their branches belonging to different segments of the spinal cord. A significant role is played by the connections of adjacent nerves with each other, with the formation of nerve plexuses. Peripheral nerve connections can be of several varieties. A simple transition of fibers from one nerve to another is possible. There are interconnections in which nerves exchange fibers. Sometimes the detachable fibers of one nerve enter into the composition of another nerve, go in it for a certain length, and then return back to the nerve from which they came out. At the joints, the nerve can receive fibers of other functional purposes. In some cases, a group of nerve fibers leaves the nerve trunk, passes separately in the perivascular tissue and returns to its nerve trunk. Connections are found between both the spinal and cranial nerves, between the visceral and somatic nerves, between the adjacent spinal nerves. Connections can be located outside and intraorgan.

The main instrument that is responsible for human consciousness and feelings is the nervous system. It regulates the entire higher nervous activity of a person and, in turn, is conditionally subdivided into two sections: the central nervous system and the peripheral. Each has its own structure and performs its own specific functions. Let us examine what the peripheral nervous system is.

General information

PNS is a part of the nervous system of the body, carried outside the brain and spinal cord, and consisting of nerve cells distributed along the periphery of the body (hence the name): on the skin, in the sensory organs, mucous membranes and internal tissues. This structure is responsible for collecting information from the internal and external environment, and transmitting this information to the central parts of the nervous system.

If we imagine that our body is a kind of building, then PNS is its video surveillance system. Its neurons receive and record information about everything that happens inside and outside the building (organism), and transmit this information in real time to the central apparatus (brain), where it is processed and on its basis significant parameters of the environment are regulated (the most optimal behavior strategy).

Just as the sensors of a "smart" house themselves monitor the humidity, air temperature in the room and change the operation of the climate system accordingly, notify about the absence of any products based on information from the refrigerator, etc., so the PNS constantly scans the state of the external and the internal environment and transfers this data to the central nervous system so that the brain can build a model of behavior that is most suitable for the current situation.

Composition of the peripheral nervous system

There is a division of the structure into somatic and vegetative. regulates the functioning of the sense organs and the coordinated activity of the locomotor system, thereby ensuring the accuracy of response and the ability to move. Morphologically, it is represented by motor nerves that connect the central nervous system with muscles and sensory organs.

The PNS is responsible for the functioning of internal organs, endocrine glands, blood vessels and some muscle groups. It includes neurons that go from the central nervous system to the internal systems of the body. Depending on which nerve fibers are involved in building the reaction of the central nervous system in response to any impact, the sympathetic and parasympathetic autonomic systems can be distinguished. The sympathetic is represented by neurons involved in the regulation of pulse, breathing, stomach contraction, and is activated mainly in a state of stress (wakefulness), responsible for the mobilization of the whole organism. The parasympathetic autonomic system, on the contrary, works in a state of rest and is regulated by those neurons that provide, for example, relaxation of the muscles, constriction of the pupil, slowing down of breathing, etc. and serves energy storage and regeneration processes. Thus, both parts of the autonomic PNS work alternately and cyclically.

Main functions

The peripheral system provides unconscious processes in the body associated primarily with physiological conditions and needs. The most important functions are:

1. Ensuring the perception of the surrounding world (the work of the sense organs, namely their receptors: the retina of the eye, taste papillae of the tongue, olfactory nerves of the nasal mucosa, skin and auditory receptors).
2. The production of hormones that regulate the physical and mental state of the body. Due to this, it is possible to respond quickly to a changing situation and mobilize all the forces of the body.
3. Ensuring coordination of the body in space due to the "muscular feeling". It is for the most part unconscious (we are not aware of how our muscles, ligaments and tendons stretch and contract during running or walking), but it is thanks to this feeling that we can carry out motor activity. Once it is lost (for example, as a result of a spinal cord injury), we can no longer regulate the movement of our limbs.
4. Ensuring the functioning of the urinary, cardiovascular, circulatory, and respiratory systems of the body. All these systems work without our conscious regulation, and in an ordinary healthy state we do not think about how everything works for us: how the blood vessels pump blood, how the lungs are enriched with oxygen, how the intestinal walls contract, etc. But as soon as our PNS fails, such natural and imperceptible things become very tangible. When the mysterious diagnosis of “Vegeto-vascular dystonia” is made, the patient complains of such common symptoms as: shortness of breath, feeling of lack of oxygen, muscle weakness, trembling in the limbs, sweating, rapid or slow heartbeat, etc.

Characteristics

Unlike the central nervous system, the peripheral system, due to the fact that it is located outside the skeleton and is not protected by the blood-brain barrier, is more vulnerable and can be damaged as a result of trauma or intoxication. So, with a high degree burn, certain tissues in which the peripheral nerves were located can die off, as a result of which the burned part of the body loses sensitivity and even some motor functions.

Features of PNS are in its anatomical and physiological structure. Since it is represented mainly by nerve fibers, the ability to transmit impulses to / from the central nervous system is provided by the conduction of neurons.

Thus, myelinated nerve fibers, which are mainly part of the somatic PNS, conduct impulses at a speed of up to 50 m / s. This explains the high speed of the motor reaction, when, for example, our eye immediately closes if a foreign body enters it. Myelin-free fibers and fibers with a thin myelin sheath, of which the vegetative system mainly consists, conduct impulses at a much lower speed: 1-10 m / s. They are responsible for different kinds sensory sensitivity (temperature, gustatory, vibration).

Nerve fibers are woven into bundles, the thickness of which depends both on the number of neurons in their composition and on the morphological characteristics of these neurons (with or without a sheath). This makes it possible to transfer immediately a large number information in different structures of the central nervous system. The same feature explains the fact that when some nerves are damaged, irradiation of electrical impulses can be observed, and adjacent, nearby and closely contacting fibers are also excited. So, with inflammation of the trigeminal nerve, a person experiences diffuse pain, as if the throat, ear, and head ache, although only the structures of the trigeminal nerve are damaged. It is with this feature that the difficulties in making a differential diagnosis for violations and difficulties with its treatment are associated.

Age and sex differences in PNS

As you know, a child is born with an incompletely formed nervous system: he cannot independently hold his head, move and think. All these skills are formed in vivo due to the fact that the nervous system is very actively developing and differentiating during the first years of life. Of the innate reflexes, the newborn has only the swallowing, sucking, orienting and grasping reflex. All of them are partly regulated by the PNS and spinal cord structures. The obvious imperfection of the peripheral system of an infant is manifested in the features of thermoregulation and increased sensitivity of the skin.

Gradually, by 3-5 years, myelin-free nerve fibers are converted into myelin ones, the thickness of neurons and their number increase, they become more branched and begin to conduct impulses more localized. The child no longer cries because it is hot or cold everywhere, but can purposefully warm his hands under water or take off a warm scarf.

By the age of 12-14, the PNS nerve ganglia can be considered formed: they are sufficiently differentiated in terms of functionality and morphologically developed.

By the age of 18-20, the PNS is considered fully formed and no longer develops in terms of the complexity of the structure.

In old age, the number of neurons in the central nervous system and PNS begins to gradually decrease, a number of them completely atrophy and cease to transmit impulses: hence the senile frostiness, numbness of the extremities, and frequent radiated pain syndromes.

Since PNS is susceptible to toxic and chemical influences active substances (this also includes hormones), women are more prone to peripheral system disorders than men. They often have disorders of the vegetative-vascular system, various etiologies of neuritis, neuralgia and pinched nerves. At the same time, men are more often characterized by lesions of the PNS associated with trauma and non-physiological loads: radiculitis, lumbago, intoxication against the background of alcoholism, etc.

The complexity of the PNS structure explains the difficulties in making the correct diagnosis for any of its violations, therefore, doctors often recommend general procedures aimed at maintaining health and maintaining immunity: hardening, proper nutrition, full physical activity and rest, massage and water procedures.

It is also important to remember that the peripheral structure is part of the central nervous system, therefore, respect for the body as a whole is a guarantee of health and a quality life until old age.

LECTURE No. 18

PERIPHERAL NERVOUS SYSTEM.

CRANIAL NERVES.

SPINAL NERVES.

The peripheral nervous system is a collection of nerve structures located outside the spinal cord and brain. Peripheral nerves carry out the function of conducting impulses from the sense organs in the central nervous system and from the brain and spinal cord to the working organs (muscles, glands). Typically, nerves are mixed (i.e., contain motor, sensory and autonomic conductors).

The peripheral nervous system includes the cranial nerves and the spinal nerves; nodes and nerves of the autonomic nervous system, sensory (receptors) and motor (effectors) endings.

Nerves are formed by the processes of nerve cells, whose bodies lie within the brain and spinal cord, as well as in the nerve nodes of the peripheral nervous system. Outside, the nerves and their branches are covered with a loose connective tissue sheath - epineurium (in which the blood and lymph vessels pass, there are fat cells). The nerve consists of bundles of nerve fibers surrounded by a thin sheath - perineurium... There are thin layers of connective tissue between the nerve fibers - endoneurium.

Nerves come in various lengths and thicknesses, depending on the number of nerve fibers. The larger nerves are called nerve trunks, branches of nerves - branches... For example, in the middle of the shoulder, the ulnar nerve contains 13,000-18,000 nerve fibers; median nerve - 19000-32000 nerve fibers; musculocutaneous - 3000-12000 fibers. In large nerves, fibers can pass from one bundle to another, which explains the different thickness of the nerves at different levels.

Spinal nerves

According to the number of spinal cord segments, 31 pairs of spinal nerves (SMN) are distinguished: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.

SMN leaves the spinal cord in the form of two roots: anterior (motor fibers) and posterior (sensory fibers). In the area of \u200b\u200bthe intervertebral foramen, they are connected to one mixed spinal nerve. At the junction, the posterior root forms a node (ganglion), which is an accumulation of sensory neurons of the somatic nervous system. The number of neurons that make up the spinal cord is large. The cervical and lumbar nodes contain about 50,000 neurons (in each node); in the chest - 20,000, in the sacral - 35,000. Each node is surrounded by a spinal capsule, from which thin bundles of connective tissue fibers penetrate into the parenchyma of the node, which make up the skeleton of the node and contain blood vessels. Each spinal nerve contains both sensory and motor fibers. In addition, the composition of the anterior roots extending from C7, Th 1-12 and L1-2 always contains vegetative fibers (sympathetic) coming from the neurons of the lateral horns of the spinal cord.

After leaving the spinal foramen, the spinal nerve divides into 4 branches:

1) Anterior branch - innervates the front half of the body, upper and lower limbs (only muscles and skin);

2) Posterior branch - innervates the posterior half of the body (only muscles and skin);

3) Connecting branch - goes to the node of the sympathetic trunk of the sympathetic NA;

4) The meningeal branch - goes to the membrane of the spinal cord, innervates the vessels and the entire membrane of the spinal cord.

The hind branches give off the lateral and medial branches, which innervate the deep (own) muscles of the back, the muscles of the occiput, and the skin of the back of the head and trunk. There are branches of the cervical, thoracic, lumbar, sacral and coccygeal nerves.

FRONT BRANCHES, intertwining together, form nerve plexuses:

1. Cervical plexus(plexus cervicales)

Formed by the anterior branches of the CMN, extending from the segments C1-C4. In front, this plexus is covered by the sternocleidomastoid muscle. It is located on the side of the transverse processes between the beginning of the anterior scalene muscle and the long muscle of the neck (medially), the middle scalene muscle, the muscle lifting the scapula and the belt muscle laterally. The largest nerve - the phrenic nerve (n.phrenicus), runs in the anterior mediastinum and reaches the diaphragm; its motor fibers innervate the muscles of the diaphragm, and the sensitive ones - the pleura and pericardium.

2. Brachial plexus (plexus brachialis)

Formed by the anterior branches of the C4-C7 segments of the spinal cord and the anterior branch of the first thoracic segment; located in the lower neck behind the sternocleidomastoid muscle.

In the brachial plexus, 2 parts are distinguished: the supraclavicular part and the subclavian part.

The largest nerves of the brachial plexus:

Musculocutaneous nerve (n.musculocutaneus);

Median nerve (n.medianus);

Ulnar nerve (n.ulnaris);

Radial nerve (n.radialis);

Medial nerves of the shoulder and forearm (n.cutaneus brachii medialis et n.cutaneus antebrachii medialis).

The largest branch of the brachial plexus - radial nerve... Consists of fibers of the anterior branches of the C5-Th1 spinal nerves. It begins at the lower edge of the pectoralis minor muscle. First, it goes behind the axillary artery, then between the lateral and medial heads of the triceps brachii muscle (m.triceps brachii) it passes into the brachial canal. Before entering this channel, the radial nerve departs posterior cutaneous nerve of the forearm (n.cutaneus antebrachii posterior). This nerve extends to the back of the forearm and innervates the skin of the back of the forearm up to the wrist joint. On the shoulder, the radial nerve innervates the triceps brachii and ulnar muscles. Coming out of the brachomuscular canal, the radial nerve descends between the brachial and the beginning of the brachiocephalic muscles, and at the level of the elbow joint it is divided into two branches: superficial and deep.

3. THE CHEST FOREQUARTERS OF PLEXES DO NOT FORM

After leaving the spinal canal, the thoracic branches form intercostal nerves (11 superior branches), the 12th intercostal branch is called the subcostal nerve.

These nerves innervate the respiratory muscles of the chest, parietal pleura, peritoneum and mammary gland.

4. Lumbar plexus (plexus lumbalis)

Formed by the anterior branches of the three lumbar segments and partially by the anterior branches of the 12th thoracic and 4th lumbar segments. Located anterior to the transverse processes of the lumbar vertebrae and on the anterior surface of the quadratus lumbar muscle, in the thickness of the psoas major muscle. The largest nerves are the femoral nerve and the obturator nerve.

Femoral nerve (n.femoralis)

The largest, thickest nerve of the lumbar plexus. Consists of fibers of the anterior branches L2-L4 of the spinal nerves, which are combined into a nerve in the thickness of the fibers of the psoas major and iliac muscles. Through the muscle lacuna, the nerve leaves the pelvic cavity to the thigh. In the femoral triangle, the nerve is located lateral to the vessels and is covered by a deep leaf of the fascia lata of the thigh. 3-4 cm below the inguinal ligament, immediately or gradually, the femoral nerve divides into muscle, cutaneous branches and the saphenous nerve. Muscular branches go to the iliac muscle, quadriceps femoris, sartorius and comb muscles, to the capsule of the hip joint. The cutaneous branches innervate the skin of the anterior thigh to the level of the patella. The saphenous nerve descends along the medial surface of the lower leg to the medial surface thumb feet, giving up the patellar branch and the medial cutaneous branches of the lower leg.