Gamma loop physiology. Lectures: General characteristics of the functions of the spinal cord. Neural organization of the spinal cord. Segmental and intersegmental principles of operation of the spinal cord. spinal group of reflexes
Complex movements can only be carried out if the effector impulses are constantly adjusted to take into account the changes that occur every moment in the muscle during its contraction. Therefore, the muscular system is a source of numerous afferent impulses. The spinal cord constantly receives information about the degree of tension of muscle fibers and their length.
The receptor part of the motion analyzer is muscle spindles and Golgi tendon organs.
Muscle spindles. In muscles, mainly extensors, that perform anti-gravity function is muscle fibers, thin and short others. They are placed in small bundles (from 2 to 12 fibers) in a connective tissue capsule. Due to their shape, such structures are called muscle spindles (Figure 4.8). Muscle fibers located in the capsule, called intrafusal(lat. Fusus- spindle), while ordinary fibers, which account for the bulk of the muscle, called extrafusal, or working fibers. Probably one end is attached to the perimysium of the extrafusal muscle fiber, the other - to the tendon. The central part of the intrafusal fibers is the actual receptor part.
There are two types of intrafusal muscle fibers that differ in the location of their nuclei: nuclear chain fiber nuclei and nuclear bursa fiber nuclei. Obviously, these two types of fibers are functionally different.
Afferent innervation. Each spindle is penetrated by a thick myelinated nerve fiber; it sends a branch to each intrafusal fiber and ends on its middle part, spiraling around it and creating the so-called annulo-spiral endings. These afferents are fibers 1a (Aa), and their endings are called primary sensory endings. An adequate stimulus for them is the change and rate of change in the length of the muscle fiber (Fig. 4.9). Some spindles are innervated afferent fibers of group II (Ab). These sensory fibers “serve” exclusively the intrafusal fibers with the nuclear chain and are called secondary sensory endings; They are located with their processes peripherally from the anulospiral endings. their excitability is lower, and their sensitivity to dynamic parameters is less.
Efferent innervation intrafusal muscle fibers are carried out by nerve fibers groups A-y. The nerve cell from which they arise is γ-motoneuron.
Rice. 4.8. Diagram of the structure of the muscle spindle (according to R. Schmidt, G. Tevs, 1985)
Rice. 4.9. Scheme of the myotatic reflex
Golgi tendon organs - special receptors, which consist of tendon filaments extending from approximately 10 extrafusal muscle fibers and are fixed in the muscle tendons sequentially, in the foredeck chain. An adequate stimulus for them is a change in muscle tension.
Thick myelin fibers of group and b (Αβ) fit into the Golgi organs. In the tendon organ they branch into thinner, numerous branches and lose myelin. Such receptors are common in skeletal muscles Oh.
The nature of excitation of muscle spindles and tendon organs depends on their placement: the muscle spindles are connected in parallel, and the tendon organs are connected in series relative to the extrafusal muscle fibers. So, as a consequence, muscle spindles perceive mainly the length of the muscle, and tendon organs - his tension.
The sensitive endings of muscle spindles can be excited not only under the influence of muscle stretching, but also as a result contraction of intrafusal muscle fibers upon excitation of γ-motoneurons. This mechanism is called γ-loops(Fig. 4.10). When only the intrafusal fibers contract, the length or tension of the muscle does not change, but the central part of these fibers is stretched and therefore the sensory endings are excited.
Thus there is two excitation mechanisms muscle spindles: 1) muscle stretching and 2) contraction of intrafusal fibers; these two mechanisms may act synergistically.
Neural organization of the spinal cord
Neurons of the spinal cord form gray matter in the form of symmetrically located two anterior and two posterior horns in the cervical, lumbar and sacral regions. IN thoracic region The spinal cord has, in addition to those mentioned, also lateral horns.
The posterior horns perform mainly sensory functions and contain neurons that transmit signals to overlying centers, to symmetrical structures on the opposite side, or to the anterior horns of the spinal cord.
The anterior horns contain neurons that send their axons to the muscles. All descending pathways of the central nervous system that cause motor responses end on the neurons of the anterior horns.
The human spinal cord contains about 13 million neurons, of which 3% are motor neurons, and 97% are intercalary neurons. Functionally, spinal cord neurons can be divided into 5 main groups:
1) motor neurons, or motor neurons, are cells of the anterior horns, the axons of which form the anterior roots. Among the motor neurons, there are a-motoneurons, which transmit signals to muscle fibers, and y-motoneurons, which innervate intraspinal muscle fibers;
2) interneurons of the spinal cord include cells that, depending on the course of their processes, are divided into: stial, the processes of which branch within several adjacent segments, and interneurons, the axons of which pass through several segments or even from one part of the spinal cord to another, forming own bundles of the spinal cord;
3) the spinal cord also contains projection interneurons that form the ascending tracts of the spinal cord. Interneurons are neurons that receive information from the genital ganglia and are located in the dorsal horns. These neurons respond to pain, temperature, tactile, vibration, proprioceptive stimulation;
4) sympathetic, parasympathetic neurons are located mainly in the lateral horns. The axons of these neurons exit the spinal cord as part of the ventral roots;
5) associative cells - neurons of the spinal cord’s own apparatus, establishing connections within and between segments.
In the middle zone of the gray matter (between the posterior and anterior horns) and at the apex of the posterior horn of the spinal cord, the so-called gelatinous substance (gelatinous substance of Roland) is formed and performs the functions of the reticular formation of the spinal cord.
Functions of the spinal cord. The first function is reflexive. The spinal cord carries out motor reflexes of skeletal muscles relatively independently. Examples of some motor reflexes of the spinal cord are: 1) elbow reflex - tapping on the tendon of the biceps brachii muscle causes flexion in the elbow joint due to nerve impulses that are transmitted through 5-6 cervical segments; 2) knee reflex - tapping the tendon of the quadriceps femoris muscle causes extension in the knee joint due to nerve impulses that are transmitted through the 2-4 lumbar segments. The spinal cord is involved in many complex coordinated movements - walking, running, labor and sports activities, etc. The spinal cord carries out autonomic reflexes to change the functions of internal organs - cardiovascular, digestive, excretory and other systems.
Thanks to reflexes from proprioceptors in the spinal cord, motor and autonomic reflexes are coordinated. Reflexes are also carried out through the spinal cord from internal organs to skeletal muscles, from internal organs to receptors and other organs of the skin, from an internal organ to another internal organ.
The second function is conductive. Centripetal impulses entering the spinal cord along the dorsal roots are transmitted along short pathways to its other segments, and along long pathways to different parts of the brain.
The main long pathways are the following ascending and descending pathways.
9. PARTICIPATION OF THE SPINAL CORD IN THE REGULATION OF MUSCLE TONE. ROLE OF ALPHA AND GAMA MOTONEURONS IN THIS PROCESS.
The function of maintaining muscle tone is provided by the principle of feedback at various levels of regulation of the body. Peripheral regulation is carried out with the participation of the gamma loop, which includes supraspinal motor pathways, interneurons, the descending reticular system, alpha and gamma neurons.
There are two types of gamma fibers in the anterior horn of the spinal cord. Gamma-1 fibers ensure the maintenance of dynamic muscle tone, i.e. tone necessary for the implementation of the movement process. Gamma-2 fibers regulate the static innervation of muscles, i.e. posture, posture of a person. Central regulation of the functions of the gamma loop is carried out by the reticular formation through the reticulospinal tract. The main role in maintaining and changing muscle tone is given to the functional state of the segmental arc of the stretch reflex (myotatic or proprioceptive reflex). Let's take a closer look at it.
Its receptor element is the encapsulated muscle spindle. Each muscle contains a large number of these receptors. The muscle spindle consists of intrafusal muscle fibers (thin) and a nuclear bursa, braided by a spiral-shaped network of thin nerve fibers, which are the primary sensory endings (anulospinal filament). Some intrafusal fibers also have secondary, grape-shaped sensory endings. When intrafusal muscle fibers are stretched, the primary sensory endings strengthen the impulses emanating from them, which are carried through fast-conducting gamma-1 fibers to the alpha-large motor neurons of the spinal cord. From there, through also fast-conducting alpha-1 efferent fibers, the impulse goes to the extrafusal white muscle fibers, which provide rapid (phasic) muscle contraction. From secondary sensory endings that respond to muscle tone, afferent impulses are carried along thin gamma-2 fibers through a system of interneurons to alpha small motor neurons, which innervate the tonic extrafusal muscle fibers (red), which maintain tone and posture.
Intrafusal fibers are innervated by gamma neurons of the anterior horns of the spinal cord. Excitation of gamma neurons, transmitted along gamma fibers to the muscle spindle, is accompanied by contraction of the polar sections of the intrafusal fibers and stretching of their equatorial part, while the initial sensitivity of the receptors to stretch changes (the threshold of excitability of stretch receptors decreases, and tonic tension of the muscle increases).
Gamma neurons are influenced by central (suprasegmental) influences transmitted along fibers that come from motor neurons of the oral parts of the brain as part of the pyramidal, reticulospinal, and vestibulospinal tracts.
Moreover, if the role of the pyramidal system is primarily to regulate the phasic (i.e. fast, purposeful) components of voluntary movements, then the extrapyramidal system ensures their smoothness, i.e. predominantly regulates the tonic innervation of the muscular system. Thus, according to J. Noth (1991), spasticity develops after supraspinal or spinal damage to the descending motor systems with the obligatory involvement of the corticospinal tract in the process.
Inhibitory mechanisms also take part in the regulation of muscle tone, without which reciprocal interaction of antagonist muscles is impossible, and therefore, purposeful movements are impossible. They are realized with the help of Golgi receptors located in muscle tendons and Renshaw intercalary cells located in the anterior horns of the spinal cord. Golgi tendon receptors, when the muscle is stretched or significantly strained, send afferent impulses along fast-conducting type 1b fibers to the spinal cord and have an inhibitory effect on the motor neurons of the anterior horns. Renshaw intercalary cells are activated through collaterals when alpha motor neurons are excited, and act on the principle of negative feedback, contributing to the inhibition of their activity. Thus, the neurogenic mechanisms of regulation of muscle tone are diverse and complex.
When the pyramidal tract is damaged, the gamma loop is disinhibited, and any irritation by stretching the muscle leads to a constant pathological increase in muscle tone. In this case, damage to the central motor neuron leads to a decrease in inhibitory effects on motor neurons as a whole, which increases their excitability, as well as on interneurons of the spinal cord, which helps to increase the number of impulses reaching alpha motor neurons in response to muscle stretching.
Other causes of spasticity include structural changes at the level of the segmental apparatus of the spinal cord that arise as a result of damage to the central motor neuron: shortening of the dendrites of alpha motor neurons and collateral sprouting (proliferation) of afferent fibers that make up the dorsal roots.
Secondary changes also occur in muscles, tendons and joints. Therefore, the mechanical-elastic characteristics of muscle and connective tissue, which determine muscle tone, suffer, which further enhances movement disorders.
Currently, an increase in muscle tone is considered as a combined lesion of the pyramidal and extrapyramidal structures of the central nervous system, in particular the corticoreticular and vestibulospinal tracts. Moreover, among the fibers that control the activity of the gamma neuron-muscle spindle system, inhibitory fibers usually suffer to a greater extent, while activating fibers retain their influence on the muscle spindles.
The consequence of this is muscle spasticity, hyperreflexia, the appearance of pathological reflexes, as well as the primary loss of the most subtle voluntary movements.
The most significant component of muscle spasm is pain. Painful impulses activate alpha and gamma motor neurons of the anterior horns, which increases the spastic contraction of the muscle innervated by this segment of the spinal cord. In the same time, muscle spasm, which occurs during the sensorimotor reflex, enhances the stimulation of muscle nociceptors. Thus, according to the negative feedback mechanism, a vicious circle is formed: spasm - pain - spasm - pain.
In addition, local ischemia develops in spasmodic muscles, since algogenic chemicals (bradykinin, prostaglandins, serotonin, leukotrienes, etc.) have a pronounced effect on the vessels, causing vasogenic tissue edema. Under these conditions, substance “P” is released from the terminals of type “C” sensory fibers, as well as the release of vasoactive amines and increased microcirculatory disorders.
Data on the central cholinergic mechanisms of muscle tone regulation are also of interest. Renshaw cells have been shown to be activated by acetylcholine through both motor neuron collaterals and the reticulospinal system.
10. REFLECTOR ACTIVITY OF THE MEDULENA, ITS ROLE IN THE REGULATION OF MUSCLE TONE. DECEREBRATORY RIGIDITY. The medulla oblongata, like the spinal cord, performs two functions - reflex and conductive. Eight pairs of cranial nerves (V to XII) emerge from the medulla oblongata and the pons and it, like the spinal cord, has a direct sensory and motor connection with the periphery. Through sensory fibers it receives impulses - information from receptors of the scalp, mucous membranes of the eyes, nose, mouth (including taste buds), from the organ of hearing, the vestibular apparatus (organ of balance), from receptors of the larynx, trachea, lungs, as well as from interoceptors of the heart -vascular system and digestive system. Through the medulla oblongata, many simple and complex reflexes are carried out, covering not individual metameres of the body, but organ systems, for example, the digestive, respiratory, and circulatory systems.
Reflex activity. The following reflexes occur through the medulla oblongata:
· Protective reflexes: coughing, sneezing, blinking, tearing, vomiting.
· Food reflexes: sucking, swallowing, juice production (secretion) of the digestive glands.
· Cardiovascular reflexes that regulate the activity of the heart and blood vessels.
· The medulla oblongata contains an automatically functioning respiratory center that provides ventilation to the lungs.
· The vestibular nuclei are located in the medulla oblongata.
From the vestibular nuclei of the medulla oblongata begins the descending vestibulospinal tract, which is involved in the implementation of posture reflexes, namely in the redistribution of muscle tone. A bulbar cat can neither stand nor walk, but the medulla oblongata and cervical segments of the spinal cord provide those complex reflexes that are elements of standing and walking. All reflexes associated with the standing function are called positioning reflexes. Thanks to them, the animal, despite the forces of gravity, maintains the posture of its body, as a rule, with the crown upward. The special importance of this part of the central nervous system is determined by the fact that the medulla oblongata contains vital centers - respiratory, cardiovascular, therefore not only removal, but even damage to the medulla oblongata results in death.
In addition to the reflex function, the medulla oblongata performs a conductive function. Conducting pathways pass through the medulla oblongata, connecting the cortex, diencephalon, midbrain, cerebellum and spinal cord with a bilateral connection.
The medulla oblongata plays an important role in the implementation of motor acts and in the regulation of skeletal muscle tone. Influences emanating from the vestibular nuclei of the medulla oblongata increase the tone of the extensor muscles, which is important for the organization of posture.
Nonspecific parts of the medulla oblongata, on the contrary, have a depressing effect on the tone of skeletal muscles, reducing it in the extensor muscles. The medulla oblongata is involved in the implementation of reflexes to maintain and restore body posture, the so-called positioning reflexes.
Decerebrate rigidity is a plastic, pronounced increase in the tone of all muscles that function with resistance to gravity (extensor spasticity), and is accompanied by fixation in the position of extension and inward rotation of the arms and legs. and also often opisthotonus. This condition is also called apallic syndrome. It is based on damage to the midbrain, especially herniation into the tentorial foramen due to supratentorial processes, primarily neoplasia in the temporal lobes, cerebral hemorrhage with blood escaping into the ventricles, severe brain contusions, hemorrhage into the brainstem, encephalitis, anoxia, and poisoning. The pathology may initially manifest itself in the form of “cerebral spasms” and be provoked by external stimuli. With the complete cessation of the influence of descending impulses in the spinal cord, spasticity develops in the flexors. Rigidity is a sign of damage to the extrapyramidal system. It is observed in various etiological variants of parkinsonism syndrome (accompanied by akinesia, the “cogwheel” phenomenon and often tremor, which first appear on one side) and in other degenerative diseases accompanied by parkinsonism, for example, olivopontocerebellar atrophy, orthostatic hypotension, Creutzfeldt-Jakob disease, etc. .
Characteristic posture for decerebrate rigidity
8.1. GENERAL PROVISIONS
In previous chapters (see Chapters 2, 3, 4) the general principles of the structure of the spinal cord and spinal nerves, as well as the manifestations of sensory and motor pathology when they are damaged, were discussed. This chapter focuses mainly on specific issues of morphology, function and some forms of damage to the spinal cord and spinal nerves.
8.2. SPINAL CORD
The spinal cord is a part of the central nervous system that has retained distinct features of segmental structure, characteristic primarily of its gray matter. The spinal cord has numerous mutual connections with the brain. Both of these parts of the central nervous system normally function as a single unit. In mammals, in particular in humans, the segmental activity of the spinal cord is constantly influenced by efferent nerve impulses emanating from various structures of the brain. This influence, depending on many circumstances, can be activating, facilitating or inhibiting.
8.2.1. Gray matter of the spinal cord
Gray matter of the spinal cord make up mainly bodies of nerve and glial cells. The non-identity of their number at different levels of the spinal cord causes variability in the volume and configuration of gray matter. In the cervical region of the spinal cord, the anterior horns are wide; in the thoracic region, the gray matter on a cross section becomes similar to the letter “H”; in the lumbosacral region, the size of both the anterior and posterior horns is especially significant. The gray matter of the spinal cord is fragmented into segments. A segment is a fragment of the spinal cord, anatomically and functionally connected to one pair of spinal nerves. The anterior, posterior and lateral horns can be considered as fragments of vertically located columns - anterior, posterior and lateral, separated from each other by the spinal cord cords consisting of white matter.
The following circumstance plays an important role in the implementation of reflex activity of the spinal cord: almost all axons of the cells of the spinal ganglia entering the spinal cord as part of the dorsal roots have branches - collaterals. Collaterals of sensory fibers contact directly with peripheral motor neurons, located in the anterior horns, or with interneurons, the axons of which also reach the same motor cells. Collaterals of axons extending from the cells of the intervertebral ganglia not only reach the corresponding peripheral motor neurons located in the anterior horns of the nearest segments of the spinal cord, but also penetrate into its neighboring segments, forming the so-called spinal-spinal intersegmental connections, providing irradiation of excitation that came to the spinal cord after irritation of the receptors of deep and superficial sensitivity located on the periphery. This explains a common reflex motor reaction in response to local irritation. This kind of phenomenon is especially typical when the inhibitory influence of pyramidal and extrapyramidal structures on peripheral motor neurons that are part of the segmental apparatus of the spinal cord decreases.
Nerve cells,The components of the gray matter of the spinal cord can be divided into the following groups according to their function:
1. Sensitive cells (T cells of the dorsal horn of the spinal cord) are the bodies of the second neurons of the sensory pathways. Most of the axons of second neurons sensitive pathways within the white commissure goes to the opposite side, where it participates in the formation of the lateral cords of the spinal cord, forming ascending cords in them spinothalamic tracts And Govers' anterior spinocerebellar tract. Axons of second neurons, have not crossed over to the opposite side, are directed to the homolateral lateral cord and form in him Flexig's posterior spinocerebellar tract.
2. Association (intercalated) cells, related to the spinal cord's own apparatus, participate in the formation of its segments. Their axons end in the gray matter of the same or closely located spinal segments.
3. Vegetative cells located in the lateral horns of the spinal cord at the level of C VIII - L II segments (sympathetic cells) and in segments S III -S V (parasympathetic cells). Their axons leave the spinal cord as part of the anterior roots.
4. Motor cells (peripheral motor neurons) constitute the anterior horns of the spinal cord. A large number of nerve impulses coming from various parts of the brain along numerous descending pyramidal and extrapyramidal pathways converge to them. In addition, nerve impulses come to them along the collaterals of the axons of pseudounipolar cells, the bodies of which are located in the spinal ganglia, as well as through the collaterals of the axons of sensory cells of the dorsal horns and associative neurons of the same or other segments of the spinal cord, carrying information mainly from deep sensitivity receptors, and along the axons located in the anterior horns of the spinal cord, Renshaw cells, which send impulses that reduce the level of excitation of alpha motor neurons and, therefore, reduce the tension of the striated muscles.
The cells of the anterior horns of the spinal cord serve as a site for the integration of excitatory and inhibitory impulses coming from various sources. Difficult
the reduction of excitatory and inhibitory biopotentials entering the motor neuron determines it total bioelectric charge and in connection with this, features of the functional state.
Among the peripheral motor neurons located in the anterior horns of the spinal cord, two types of cells are distinguished: a) alpha motor neurons - large motor cells, the axons of which have a thick myelin sheath (A-alpha fibers) and end in the muscle with end plates; they provide the degree of tension of extrafusal muscle fibers, which make up the bulk of striated muscles; b) gamma motor neurons - small motor cells, the axons of which have a thin myelin sheath (A-gamma fibers) and, therefore, a lower speed of nerve impulses. Gamma motor neurons make up approximately 30% of all cells in the anterior horn of the spinal cord; their axons are directed to the intrafusal muscle fibers that are part of the proprioceptors - muscle spindles.
Muscle spindle consists of several thin intrafusal muscle fibers enclosed in a fusiform connective tissue capsule. The axons of gamma motor neurons end on the intrafusal fibers, affecting the degree of their tension. Stretching or contraction of intrafusal fibers leads to changes in the shape of the muscle spindle and irritation of the spiral fiber surrounding the equator of the spindle. In this fiber, which is the beginning of the dendrite of a pseudounipolar cell, a nerve impulse arises, which is directed to the body of this cell, located in the spinal ganglion, and then along the axon of the same cell to the corresponding segment of the spinal cord. The terminal branches of this axon directly or through interneurons reach the alpha motor neuron, exerting an excitatory or inhibitory effect on it.
Thus, with the participation of gamma cells and their fibers, gamma loop, ensuring the maintenance of muscle tone and a fixed position of a certain part of the body or contraction of the corresponding muscles. In addition, the gamma loop ensures the transformation of the reflex arc into a reflex ring and takes part in the formation, in particular, of tendon or myotatic reflexes.
Motor neurons in the anterior horns of the spinal cord form groups, each of which innervates muscles that share a common function. Along the length of the spinal cord there are anterior internal groups of cells of the anterior horns, which provide the function of muscles that influence the position of the spinal column, and anterior external groups of peripheral motor neurons, on which the function of the remaining muscles of the neck and torso depends. In the segments of the spinal cord that provide innervation to the limbs, there are additional groups of cells located mainly behind and outside the already mentioned cellular associations. These additional groups of cells are the main cause of cervical (at the level of C V -Th II segments) and lumbar (at the level of L II -S II segments) thickenings of the spinal cord. They provide mainly innervation to the muscles of the upper and lower extremities.
Motor unit The neuromotor apparatus consists of a neuron, its axon and the group of muscle fibers innervated by it. The sum of peripheral motor neurons participating in the innervation of one muscle is known as its motor pool, while the bodies of motor neurons of one motor
body pool can be located in several adjacent segments of the spinal cord. The possibility of damage to part of the motor units that are part of the muscle pool is the cause of partial damage to the muscle innervated by it, as happens, for example, with epidemic poliomyelitis. Widespread damage to peripheral motor neurons is characteristic of spinal amyotrophies, which are hereditary forms of neuromuscular pathology.
Among other diseases in which the gray matter in the spinal cord is selectively affected, syringomyelia should be noted. Syringomyelia is characterized by expansion of the usually reduced central canal of the spinal cord and the formation of gliosis in its segments, while the dorsal horns are more often affected, and then a dissociated type of sensitivity disorder occurs in the corresponding dermatomes. If degenerative changes also extend to the anterior and lateral horns, manifestations of peripheral muscle paresis and vegetative-trophic disorders are possible in the body metameres of the same name as the affected segments of the spinal cord.
In cases hematomyelia(spinal cord hemorrhage), usually resulting from spinal cord injury, the symptoms are similar to syringomyelitic syndrome. The lesion in traumatic hemorrhage in the spinal cord is predominantly of the gray matter due to the peculiarities of its blood supply.
Gray matter is also the site of predominant formation intramedullary tumors, growing from its glial elements. At the onset of the tumor, symptoms may manifest as damage to certain segments of the spinal cord, but subsequently the medial sections of the adjacent cords of the spinal cord are involved in the process. At this stage of intramedullary tumor growth, conduction-type sensory disturbances appear slightly below the level of its localization, which subsequently gradually descend downwards. Over time, at the level of the intramedullary tumor, a clinical picture of damage to the entire diameter of the spinal cord may develop.
Signs of combined damage to peripheral motor neurons and corticospinal pathways are characteristic of amyotrophic lateral sclerosis (ALS syndrome). In the clinical picture, various combinations of manifestations of peripheral and central paresis or paralysis arise. In such cases, as more and more peripheral motor neurons die, the symptoms of already developed central paralysis are replaced by manifestations of peripheral paralysis, which over time increasingly dominate the clinical picture of the disease.
8.2.2. White matter of the spinal cord
White matter forms cords located along the periphery of the spinal cord, consisting of ascending and descending pathways, most of which have already been discussed in previous chapters (see Chapters 3, 4). Now you can supplement and generalize the information presented there.
nerve fibers, present in the spinal cord can be differentiated into endogenous, which are processes of the spinal cord’s own cells, and exogenous- consisting of nerve processes that penetrate the spinal cord
cells whose bodies are located in the spinal nodes or are part of the structures of the brain.
Endogenous fibers can be short or long. The shorter the fibers, the closer to the gray matter of the spinal cord they are located. Short endogenous fibers form spinospinal connections between the segments of the spinal cord itself (their own bundles of the spinal cord - fasciculi proprii). From long endogenous fibers, which are the axons of second sensory neurons, the bodies of which are located in the dorsal horns of the spinal cord segments, afferent pathways are formed that conduct pain and temperature sensitivity impulses going to the thalamus, and impulses going to the cerebellum (spinothalamic and spinocerebellar tracts).
Exogenous fibers of the spinal cord are axons of cells located outside of it. They can be afferent and efferent. Afferent exogenous fibers make up thin and wedge-shaped bundles that form the posterior funiculi. Among the efferent pathways, consisting of exogenous fibers, the lateral and anterior corticospinal tracts should be noted. Exogenous fibers also consist of the extrapyramidal system of the red nucleus-spinal cord, vestibule-spinal cord, olivo-spinal cord, tectal-spinal cord, vestibulo-spinal cord, reticulospinal cord pathways.
The most important pathways are distributed in the spinal cord cords in the following way(Fig. 8.1):
Posterior funiculi (funiculus posterior seu dorsalis) consist of ascending pathways conducting impulses of proprioceptive sensitivity. At the bottom of the spinal cord, the posterior cord is thin Gaulle bun (fasciculus gracilis). Starting from the mid-thoracic part of the spinal cord and above, lateral to the thin fasciculus, a wedge-shaped bundle of Burdach (fasciculus cuneatus). In the cervical spinal cord, both of these bundles are well defined and separated by a glial septum.
Damage to the posterior cord of the spinal cord leads to impaired proprioception and a possible decrease in tactile sensitivity below the level of the spinal cord lesion. A manifestation of this form of pathology is a violation of reverse afferentation in the corresponding part of the body due to the lack of proper information sent to the brain about the position of body parts in space. As a result, sensory ataxia and afferent paresis occur, while muscle hypotonia and tendon hyporeflexia or areflexia are also characteristic. This form of pathology is characteristic of tabes dorsalis, funicular myelosis, and is part of the symptom complexes characteristic of various forms of spinocerebellar ataxia, in particular Friedreich’s ataxia.
Lateral cords (funiculus lateralis) consist of ascending and descending tracts. The dorsolateral section of the lateral funiculus occupies the posterior spinocerebellar tract of Flexig (tractus spinocerebellaris dorsalis). In the ventrolateral section is the anterior spinocerebellar tract of Govers (tractus spinocerebellaris ventralis). Medial to Govers's path is the path of surface sensitivity impulses - the lateral spinothalamic tract (tractus spinothalamicus lateralis), behind it is the red-spinal tract (tractus rubrospinalis), between it and the dorsal horn is the lateral corticospinal (pyramidal) tract (tractus corticospinalis lateralis). In addition, the lateral cord contains the spinal reticular tract, tegmental-
Rice. 8.1.Pathways on a transverse section of the upper thoracic spinal cord. 1 - posterior median septum; 2 - thin beam; 3 - wedge-shaped bundle; 4 - posterior horn; 5 - spinocerebellar tract, 6 - central canal, 7 - lateral horn; 8 - lateral spinothalamic tract; 9 - anterior spinocerebellar tract; 10 - anterior spinothalamic tract; 11 - front horn; 12 - anterior median fissure; 13 - olivospinal tract; 14 - anterior corticospinal (pyramidal) tract; 15 - anterior reticular-spinal tract; 16 - vestibulospinal tract; 17 - reticular-spinal tract; 18 - anterior white commissure; 19 - gray commissure; 20 - red nucleus-spinal tract; 21 - lateral corticospinal (pyramidal) tract; 22 - posterior white commissure.
spinal tract, olivospinal tract, and autonomic fibers are scattered near the gray matter.
Since in the lateral cord the corticospinal tract is located dorsal to the lateral spinothalamic tract, damage to the posterior segment of the spinal cord can lead to a disorder of deep sensitivity in combination with a pyramidal disorder below the level of localization of the pathological focus while maintaining superficial sensitivity (Roussy-Lhermitte-Schelvin syndrome).
Selective damage to the pyramidal tracts of the lateral cords of the spinal cord is possible, in particular, with familial spastic paraplegia, or Strumpel's disease, in which, by the way, due to the heterogeneity of the fibers that make up the pyramidal tract, a splitting of the pyramidal syndrome is characteristic, which is manifested by lower spastic paraparesis with a predominance of spastic muscle tension over a decrease in their strength.
Anterior cords (funiculus anterior seu ventralis) consist mainly of efferent fibers. Adjacent to the median fissure is the tegmental spinal column.
gov pathway (tractus tectospinalis), belonging to the system of descending extrapyramidal tracts. More lateral are the anterior (uncrossed) corticospinal (pyramidal) tract (tractus corticospinalis anterior), vestibulospinal tract (tractus vestibulospinalis), anterior reticular spinal tract (tractus reticulospinalis anterior) and afferent anterior spinothalamic tract (tractus spinothalamicus anterior). Behind them passes the medial longitudinal fasciculus (fasciculis longitudinalis medialis), carrying impulses from a number of cellular formations of the trunk tire.
At development of ischemia in the anterior spinal artery basin (Preobrazhensky syndrome) blood circulation in the anterior 2/3 of the spinal cord is impaired. At the level of the ischemic zone, flaccid muscle paralysis develops, below this level - spastic paralysis. Disorders of pain and temperature sensitivity of the conduction type and dysfunction of the pelvic organs are also characteristic. Proprioceptive and tactile sensitivity is preserved. This syndrome was described in 1904 by M.A. Preobrazhensky (1864-1913).
8.3. SPINAL DIVISION OF THE PERIPHERAL NERVOUS SYSTEM AND SIGNS OF ITS DAMAGE
As already noted (see Chapter 2), the spinal part of the peripheral nervous system consists of the anterior and posterior spinal roots, spinal nerves, ganglia, nerve plexuses and peripheral nerves.
8.3.1. Some general issues of clinical manifestations in lesions of the peripheral nervous system
Syndromes of damage to the peripheral nervous system consist of peripheral paresis or paralysis and disorders of superficial and deep sensitivity of various nature and severity, and a significant frequency of pain syndrome should be noted. These phenomena are often accompanied by vegetative-trophic disorders in the corresponding part of the body - pallor, cyanosis, swelling, decreased skin temperature, impaired sweating, and degenerative processes.
When the spinal roots, ganglia or spinal nerves are damaged, the above disorders occur in the corresponding segments (metameres) of the body - their dermatomes, myotomes, sclerotomes. Selective involvement of the posterior or anterior spinal roots (radiculopathy) manifested by pain and sensory disturbances or peripheral paresis in the areas of their innervation. If the plexus is affected (plexopathy)- local pain is possible, radiating along the nerve trunks formed in this plexus, as well as motor, sensory and autonomic disorders in the innervation zone. In case of damage to the peripheral nerve trunk and its branches (neuropathy) characterized by flaccid paresis or paralysis of the muscles they innervate. In the area innervated by the affected nerve, they may
be sensory disturbances and vegetative-trophic disorders, manifesting distal to the level of damage to the nerve trunk and in the area innervated by its branches extending below the location of the main pathological process. At the site of nerve damage, pain and soreness are possible, radiating along the course of the nerve, especially noticeable upon percussion of the affected area (Tinel's symptom).
Multiple symmetrical lesions of the distal parts peripheral nerves, characteristic of polyneuropathy, can cause combinations of movement disorders, sensitivity, as well as autonomic and trophic disorders in the distal parts of the extremities. However, with various forms of neuropathy or polyneuropathy, primary damage to the motor, sensory or autonomic structures of the peripheral nerves is possible. In such cases, we can talk about motor, sensory or autonomic neuropathy.
With damage to the peripheral nerve, motor impairment may be less than expected in accordance with existing schematic concepts. This is due to the fact that some muscles are innervated by two nerves. In such cases, interneural anastomoses may be significant, the nature of which is subject to large individual fluctuations. Anastomoses between nerves can, to some extent, help restore impaired motor functions.
When analyzing lesions of the peripheral nervous system, one must take into account the possibility of the development of compensatory mechanisms, sometimes masking existing muscle paresis. For example, dysfunction of the shoulder abductor deltoid muscle is partially compensated by the pectoral, subscapularis and trapezius muscles. The nature of the active movement can be assessed incorrectly due to the fact that it is performed not due to the contraction of the muscle under study, but as a result of the relaxation of its antagonists. Sometimes active movements are limited due to pain or due to damage to blood vessels, muscles, ligaments, bones and joints. Limitation of active and passive movements may be a consequence of formed contractures, in particular contractures of the antagonist muscles of the affected muscle. Multiple lesions of peripheral nerves, for example, with a nerve plexus injury, can also complicate topical diagnosis.
The diagnosis of peripheral paralysis or paresis, in addition to impaired movement, muscle hypotonia and a decrease or disappearance of certain reflexes, is facilitated by signs of muscle wasting that usually appear a few weeks after damage to a nerve or nerves, as well as a disturbance in the electrical excitability of the corresponding nerves and muscles that accompanies peripheral paresis or paralysis.
In the topical diagnosis of lesions of the peripheral nervous system, information obtained from a careful study of the state of sensitivity may be important. It must be borne in mind that each peripheral nerve corresponds to a certain zone of innervation on the skin, reflected in existing diagrams (Fig. 3.1). When diagnosing lesions of the peripheral nervous system, it should be taken into account that the zone of sensory impairment when individual nerves are damaged is usually smaller than its anatomical territory indicated on such diagrams. This is explained by the fact that the zones innervated by neighboring peripheral nerves, as well as sensitive spinal roots, partially overlap each other and, as a result,
Therefore, the skin areas located on their periphery have additional innervation due to neighboring nerves. Therefore, the boundaries of the zone of impaired sensitivity in case of peripheral nerve damage are often limited to the so-called autonomous zone innervation, the size of which can vary within quite large limits due to the existing individual characteristics of innervation.
Impulses of different types of sensitivity pass through different nerve fibers running as part of the peripheral nerve. In the case of nerve damage in the innervation zone, sensitivity of one type or another may be disrupted, leading to dissociation of sensory disorders. Impulses of pain and temperature sensitivity are transmitted through thin myelinated or unmyelinated fibers (A-gamma fibers or C-fibers). Impulses of proprioceptive and vibration sensitivity are carried along thick myelin fibers. Both thin and thick myelinated fibers are involved in the transmission of tactile sensitivity, while autonomic fibers are always thin and unmyelinated.
Determining the location and extent of damage to the peripheral nerve can be facilitated by the analysis of the sensations described by the patient that arise during palpation of the nerve trunks, their soreness, as well as the irradiation of pain that occurs during percussion of a possible site of nerve damage (Tinel’s symptom).
The causes of damage to peripheral nerves are varied: compression, ischemia, trauma, exogenous and endogenous intoxication, infectious and allergic lesions, metabolic disorders, in particular, due to enzymopathies and associated metabolic disorders caused by certain forms of hereditary pathology.
8.3.2. Spinal nerve roots
Posterior roots (radices posteriores) spinal nerves are sensitive; they are composed of axons of pseudounipolar cells, the bodies of which are located in the spinal ganglia (ganglion spinalie). The axons of these first sensory neurons enter the spinal cord at the location of the posterior lateral sulcus.
Anterior roots (radices anteriores) mainly motor, they consist of axons of motor neurons that are part of the anterior horns of the corresponding segments of the spinal cord; in addition, they include the axons of vegetative Jacobson cells located in the lateral horns of the same spinal segments. The anterior roots exit the spinal cord through the anterior lateral sulcus.
Following from the spinal cord to the intervertebral foramina of the same name in the subarachnoid space, all the roots of the spinal nerves, except the cervical ones, descend down to one or another distance. It is small for the thoracic roots and more significant for the lumbar and sacral roots, which participate in the formation, together with the terminal filament, of the so-called horse tail.
The roots are covered with the pia mater, and at the junction of the anterior and posterior roots into the spinal nerve at the corresponding intervertebral foramen, the arachnoid membrane is also pulled towards it. As a result
Tate around the proximal part of each spinal nerve is filled with cerebrospinal fluid a funnel-shaped vagina, the narrow part directed towards the intervertebral foramen. The concentration of infectious agents in these funnels sometimes explains the significant frequency of damage to the spinal nerve roots during inflammation of the meninges (meningitis) and the development of the clinical picture. meningoradiculitis.
Damage to the anterior roots leads to peripheral paresis or paralysis of the muscle fibers that make up the corresponding myotomes. There may be a violation of the integrity of the corresponding reflex arcs and, in connection with this, the disappearance of certain reflexes. With multiple lesions of the anterior roots, for example with acute demyelinating polyradiculoneuropathy (Guillain-Barré syndrome), Widespread peripheral paralysis may also develop, tendon and skin reflexes decrease and disappear.
Irritation of the dorsal roots due to one reason or another (discogenic radiculitis due to osteochondrosis of the spine, neuroma of the dorsal root, etc.) leads to pain that radiates to the metameres corresponding to the irritated roots. Nerve root pain may be provoked when checking the nerve root Neri's symptom, included in the group of tension symptoms. It is checked on a patient who lies on his back with his legs straightened. The examiner places his palm under the back of the patient's head and sharply bends his head, trying to ensure that the chin touches the chest. With pathology of the dorsal roots of the spinal nerves, the patient experiences pain in the area of the projection of the affected roots.
When the roots are damaged, irritation of the nearby meninges and the appearance of changes in the cerebrospinal fluid are possible, usually of the type of protein-cell dissociation, as is observed, in particular, with Guillain-Barre syndrome. Destructive changes in the dorsal roots lead to a disorder of sensitivity in the dermatomes of the same name as these roots and can cause loss of reflexes, the arcs of which were interrupted.
8.3.3. Spinal nerves
The spinal nerves (Fig. 8.2), formed as a result of the union of the anterior and posterior roots, turn out to be mixed. They penetrate the dura mater, are short in length (about 1 cm) and are located in the intervertebral or sacral foramina. The surrounding connective tissue (epineurium) is connected to the periosteum, which makes their mobility very limited. Damage to the spinal nerves and their roots is often associated with degenerative phenomena in the spine (osteochondrosis) and the resulting posterior or posterolateral herniation of the intervertebral disc, less often with infectious-allergic pathology, trauma, oncological diseases and, in particular, with intravertebral extramedullary tumor, previously just a neuroma, or tumor of the spine. It manifests itself as signs of combined damage to the corresponding anterior and posterior roots of the spinal nerves, with possible pain, sensory disturbances, motor and autonomic disorders in the area of the corresponding dermatomes, myotomes and sclerotomes.
Rice. 8.2.Transverse section of the spinal cord, formation of the spinal nerve and its branches.
1 - posterior horn; 2 - posterior cord; 3 - posterior median groove; 4 - posterior root; 5 - spinal node; 6 - trunk of the spinal nerve; 7 - posterior branch of the spinal nerve; 8 - internal branch of the posterior branch; 9 - external branch of the posterior branch; 10 - anterior branch; 11 - white connecting branches; 12 - shell branch; 13 - gray connecting branches; 14 - node of the sympathetic trunk; 15 - anterior median fissure; 16 - front horn; 17 - anterior cord; 18 - anterior root, 19 - anterior gray commissure; 20 - central channel; 21 - lateral cord; 22 - postganglionic fibers.
Sensory fibers are indicated in blue, motor fibers in red, white connective fibers in green, and gray connective branches in purple.
Exists 31-32 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-2 coccygeal.
The first cervical spinal nerve exits between the occipital bone and the atlas, the fifth sacral and coccygeal nerves exit through the inferior opening of the sacral canal. (hiatus sacralis).
Coming out of the intervertebral or sacral foramen, spinal nerves are divided into front, thicker, and rear branches: mixed in the composition of their constituent nerve fibers.
It immediately arises from the anterior branch of each spinal nerve shell (meningeal) branch (ramus meningeus), also known as Luschka's nerve, returning to the spinal canal and participating in the formation of the meningeal plexus (plexus meningeus), providing sensitive and autonomic innervation of the walls and vessels of the spinal canal, including the posterior longitudinal ligament, and the dura mater. In addition, each anterior branch is connected white connecting branch (ramus communicantes albi) with the nearest node of the border sympathetic trunk.
ribs The anterior branches of the thoracic spinal nerves form intercostal nerves. The anterior branches of the cervical, upper thoracic, lumbar and sacral spinal nerves are involved in the formation nerve plexuses.
There are cervical, brachial, lumbar, sacral, pudendal and coccygeal plexuses. From these plexuses come peripheral nerves, which provide innervation to most of the muscles and integumentary tissues of the human body. Nerve plexuses and the peripheral nerves emerging from them have their own anatomical and functional characteristics, and their damage leads to neurological symptoms that have a certain specificity.
Posterior branches of the spinal nerves relatively thin, bend around the articular processes of the vertebrae, are directed into the spaces between the transverse processes (on the sacrum they pass through the posterior sacral foramina) and, in turn, are divided into internal and external branches. The posterior branches of the spinal nerves innervate the muscles and skin in the paravertebral region throughout the spinal column.
The posterior branch of the first cervical (C I) spinal nerve is the suboccipital nerve (n. suboccipitalis) innervating the group of suboccipital muscles - the anterior rectus capitis muscle (m. rectus capitis anteriores), major and minor posterior rectus capitis muscles (mm. recti capitis posteriores major et minor), superior and inferior oblique muscles of the head (m. obliquus capiti superiores et inferiores), splenius capitis muscle (m. splenius capiti), longus capitis muscle (m. longus capitis), when contracted, the head is extended and tilted back and towards the contracted muscles.
The posterior branch of the second cervical spinal nerve (C p) is directed between the atlas (C I) and axial (C p) vertebrae, goes around the lower edge of the inferior oblique muscle of the capitis and is divided into 3 branches: the ascending (ramus ascendens), downward (ramus descendens) And greater occipital nerve (nervus occipitalis major), which goes upward and, together with the occipital artery, pierces the tendon of the trapezius muscle near the external occipital protuberance and innervates the skin in the medial part of the occipital and parietal regions up to the level of the coronal suture. With damage to the second cervical spinal nerve (C n) or its posterior branch, which usually occurs with pathology of the upper cervical vertebrae (osteochondrosis, spondyloarthritis, discopathy, etc.), the development of neuralgia of the greater occipital nerve, manifested by intense, sometimes sharp, pain in the back of the head on the side of the pathological process. Attacks of pain can be provoked by movements of the head; therefore, patients usually fix their head, slightly tilting it to the side and back towards the affected area. At neuralgia of the greater occipital nerve determined characteristic pain point, located on the border of the middle and inner thirds of the line connecting the mastoid process and the occipital boo-gor. Sometimes there is hypo or hyperesthesia of the skin of the back of the head, and one can observe a forced (due to pain) posture of the head - the head is motionless and slightly tilted back and towards the pathological process.
8.3.4. Cervical plexus and its nerves
Cervical plexus (plexus cervicalis) is formed by the interweaving of nerve fibers passing through the anterior branches of the I-IV cervical spinal nerves. The plexus is located in front of the corresponding cervical vertebrae
on the anterior surface of the middle scalene muscle and the levator scapulae muscle, and is covered top part sternocleidomastoid muscle.
The first cervical spinal nerve (C I) emerges from the spinal canal between the occipital bone and the atlas, being located in the groove of the vertebral artery. Its anterior branch passes between the anterior lateral and lateral rectus capitis muscles (mm. rectus capitis anterioris et lateralis). Damage to this nerve can lead to convulsive contraction of the inferior oblique capitis muscle, which causes the head to jerk in the direction of the lesion.
The remaining cervical nerves enter the anterior surface of the spine, passing between the anterior and posterior intertransverse muscles behind the vertebral artery. Two groups of branches depart from the cervical plexus - muscular and cutaneous.
Muscular branches of the cervical plexus: 1) short segmental branches to the deep muscles of the neck; 2) anastomosis with the descending branch of the hypoglossal nerve, participating in the formation of its loop; 3) branch to the sternocleidomastoid muscle; branch to the trapezius muscle and 4) the phrenic nerve containing sensory fibers.
Deep branches of the cervical plexus participate in the innervation of the muscles that provide movement in the cervical spine and the sublingual muscles. Together with the XI (accessory) cranial nerve, they participate in the innervation of the sternocleidomastoid and trapezius muscles (m. sternocleidomastoideus et m. trapezius), and longus muscle neck (n. longus colli), the contraction of which leads to flexion of the cervical spine, and with unilateral contraction - to flexion of the neck in the same direction.
Phrenic nerve (n.phrenicus)- continuation of the fibers of the anterior branches, mainly IV, partly III and V cervical spinal nerves - goes down, located between the subclavian artery and vein, penetrates the anterior mediastinum. On its way, the nerve of the diaphragm gives off sensory branches to the pleura, pericardium, and diaphragm, but the main part of it is motor and provides innervation to the diaphragm (abdominal barrier), recognized as the most important respiratory muscle.
In case of defeat phrenic nerve arises paradoxical type of breathing: when inhaling, the epigastric region sinks, when exhaling, it protrudes - the opposite phenomenon to what is usually observed normally; In addition, coughing movements are difficult. Fluoroscopy reveals prolapse of the dome of the diaphragm and limitation of its mobility on the side of the affected nerve. Irritation of the nerve causes a spasm of the diaphragm, manifested by persistent hiccups, shortness of breath and pain in the chest, radiating to the shoulder girdle and shoulder joint area.
The following are formed in the cervical plexus: cutaneous nerves.
Lesser occipital nerve (n. occipitalis minor).It is formed by the fibers of the anterior branches of the cervical (C II - C III) spinal nerves, emerges from under the posterior edge of the sternocleidomastoid muscle at the level of its upper third and penetrates the skin of the outer part of the occipital region and the mastoid process. When the lesser occipital nerve is irritated, pain occurs in the innervation zone, often of a paroxysmal nature. (neuralgia of the lesser occipital nerve), in this case, a painful point is identified behind the sternocleidomastoid muscle, at the level of its upper third.
Greater auricular nerve (n. auricularis magnus, C III) innervates most of the skin auricle, parotid region and inferolateral surface of the face.
Cutaneous cervical nerve (n. cutaneus colli, C III) innervates the skin of the anterior and lateral surfaces of the neck.
Supraclavicular nerves (nn. supraclaviculares, C III -C IV) innervate the skin of the supraclavicular region, the upper outer part of the shoulder, as well as the upper parts of the chest - in front to the first rib, in the back - in the upper scapular region.
Irritation of the cervical plexus can cause spasm of the longus colli muscle and diaphragm. With tonic tension of the neck muscles, the head tilts back and to the affected side; with a bilateral spasm, the head leans back, which creates the impression of stiff neck muscles. With bilateral paralysis of the cervical muscles, the head hangs helplessly forward, as happens in some cases of myasthenia gravis, poliomyelitis or tick-borne encephalitis.
Isolated lesions of the cervical plexus may be caused by trauma or tumor at the upper cervical level.
8.3.5. Brachial plexus and its nerves
Brachial plexus (plexus brachialis) formed from the anterior branches of the C V - Th I spinal nerves (Fig. 8.3).
The spinal nerves, from which the brachial plexus is formed, leave the spinal canal through the corresponding intervertebral foramina, passing between the anterior and posterior intertransverse muscles. The anterior branches of the spinal nerves, connecting with each other, first form 3 trunks (primary bundles) of the brachial plexus that make it up
Rice. 8.3.Brachial plexus. I - primary upper beam; II - primary middle bundle; III - primary lower beam; P - secondary posterior bundle; L - secondary outer beam; M - secondary internal beam; 1 - musculocutaneous nerve; 2 - axillary nerve; 3 - radial nerve; 4 - median nerve; 5 - ulnar nerve; 6 - internal cutaneous nerve; 7 - internal cutaneous nerve of the forearm.
supraclavicular part, each of which is connected by means of white connecting branches to the middle or lower cervical vegetative nodes.
1. Upper trunk arises as a result of the connection of the anterior branches of the C V and C VI spinal nerves.
2. Medium trunk is a continuation of the anterior branch of the C VII spinal nerve.
3. Lower trunk consists of the anterior branches of the C VIII, Th I and Th II spinal nerves.
The trunks of the brachial plexus descend between the anterior and middle scalene muscles above and behind the subclavian artery and pass into the subclavian part of the brachial plexus, located in the area of the subclavian and axillary fossae.
At the subclavian level each of the trunks (primary bundles) of the brachial plexus is divided into anterior and posterior branches, from which 3 bundles (secondary bundles) are formed, constituting the infraclavicular part of the brachial plexus and named depending on their location relative to the axillary artery (a. axillaris), which they surround.
1. Posterior bun formed by the fusion of all three posterior branches of the trunks of the supraclavicular part of the plexus. It starts from him axillary and radial nerves.
2. Lateral bundle constitute the connected anterior branches of the upper and partially middle trunks (CV, C VI, C VII). From this bunch they originate musculocutaneous nerve and part (outer leg - C VII) median nerve.
3. Medial bundle is a continuation of the anterior branch of the lower primary bundle; from it are formed ulnar nerve, cutaneous medial nerves of the shoulder and forearm, and part of the median nerve (internal leg - C VIII), which connects to the external leg (in front of the axillary artery), together they form a single trunk of the median nerve.
The nerves formed in the brachial plexus belong to the nerves of the neck, shoulder girdle and hands.
Nerves of the neck.Short muscle branches participate in the innervation of the neck (rr. musculares), innervating deep muscles: intertransverse muscles (mm. intertrasversarii); longus colli muscle(m. longus colli), tilting the head in one direction, and when both muscles contract, tilting it forward; front, middle and back scalene muscles (mm. scaleni anterior, medius, posterior), which, with a fixed chest, tilt the cervical spine in their direction, and with bilateral contraction, tilt it forward; if the neck is fixed, then the scalene muscles, contracting, raise the 1st and 2nd ribs.
Nerves of the shoulder girdle. The nerves of the brachial girdle begin from the supraclavicular part of the brachial plexus and are primarily motor in function.
1. Subclavian nerve (n. subclavius, C V -C VI) innervates the subclavian muscle (m. subclavius), which, when contracted, moves the clavicle down and medially.
2. Anterior thoracic nerves (nn. thoracales anteriores, C V -Th I) innervate the major and minor pectoral muscles(mm. pectorales major et minor). The contraction of the first of them causes adduction and internal rotation of the shoulder, the contraction of the second causes the scapula to shift forward and downward.
3. Suprascapular nerve (n. suprascapularis, C V -C YI) innervates the supraspinatus and infraspinatus muscles (m. supraspinatus et m. infraspinatus); the first one contributes
abduction of the shoulder, the second - rotates it outward. The sensory branches of this nerve innervate the shoulder joint.
4. Subscapular nerves (nn. subscapulares, C Y -C YII) innervate the subscapularis muscle (m. subscapularis), internally rotating shoulder, and teres major muscle (m. teres major), which rotates the shoulder inward (pronation), takes it back and leads it to the body.
5. Posterior thoracic nerves (nn. toracales posteriores): dorsal nerve of the scapula (n. dorsalis scapulae) and long thoracic nerve (n. thoracalis longus, C Y -C YII) innervate muscles, the contraction of which ensures mobility of the scapula (m. levator scapulae, m. rhomboideus, m. serratus anterior). The last of them helps to raise the arm above the horizontal level. Damage to the posterior thoracic nerves leads to scapular asymmetry. When moving the shoulder joint, winging of the scapula on the affected side is characteristic.
6. Thoracospinal nerve (n. thoracodorsalis, C VII -C VIII I) innervates the latissimus dorsi muscle (m. latissimus dorsi), which brings the shoulder to the body, pulls it back to the midline and rotates it inward.
Nerves of the hand.The nerves of the arm are formed from secondary bundles of the brachial plexus. The axillary and radial nerves are formed from the posterior longitudinal fascicle, and the musculocutaneous nerve and the external peduncle of the median nerve are formed from the external secondary fascicle; from the secondary internal bundle - the ulnar nerve, the internal leg of the median nerve and the medial cutaneous nerves of the shoulder and forearm.
1. Axillary nerve (n. axillaris, C Y -C YII)- mixed; innervates the deltoid muscle (m. deltoideus), which, when contracted, abducts the shoulder to a horizontal level and pulls it back or forward, as well as the teres minor muscle (m. teres minor), externally rotating the shoulder.
Sensory branch of the axillary nerve - superior external cutaneous nerve of the shoulder (n. cutaneus brachii lateralis superior)- innervates the skin over deltoid muscle, as well as external skin and partly back surface the upper part of the shoulder (Fig. 8.4).
When the axillary nerve is damaged, the arm hangs like a whip, and it is impossible to move the shoulder forward or backward.
2. Radial nerve (n. radialis, C YII, partly C YI, C YIII, Th I)- mixed; but predominantly motor, innervates mainly the extensor muscles of the forearm - the triceps brachii muscle (m. triceps brachii) and elbow muscle (m. apponens), extensors of the hand and fingers - long and short extensor carpi radialis (mm. extensor carpi radialis longus et brevis) and extensor digitorum (m. extensor digitorum), forearm instep support (m. supinator), brachioradialis muscle (m. brachioradialis), taking part in flexion and pronation of the forearm, as well as the muscles that abduct the thumb (mm. abductor pollicis longus et brevis), extensor pollicis brevis and longus (mm. extensor pollicis brevis et longus), extensor index finger (m. extensor indicis).
Sensitive fibers radial nerve constitute the posterior cutaneous branch of the shoulder (n. cutaneus brachii posteriores), providing sensitivity to the back of the shoulder; inferior lateral cutaneous nerve of the shoulder (n. cutaneus brachii lateralis inferior), innervating the skin of the lower outer part of the shoulder, and the posterior cutaneous nerve of the forearm (n. cutaneus antebrachii posterior), determining the sensitivity of the posterior surface of the forearm, as well as the superficial branch (ramus superficialis), participating in the innervation of the dorsum of the hand, as well as the posterior surface of the I, II and half of the III fingers (Fig. 8.4, Fig. 8.5).
Rice. 8.4.Innervation of the skin of the surface of the hand (a - dorsal, b - ventral). 1 - axillary nerve (its branch is the external cutaneous nerve of the shoulder); 2 - radial nerve (posterior cutaneous nerve of the shoulder and posterior cutaneous nerve of the forearm); 3 - musculocutaneous nerve (external cutaneous nerve of the forearm); 4 - internal cutaneous nerve of the forearm; 5 - internal cutaneous nerve of the shoulder; 6 - supraclavicular nerves.
Rice. 8.5.Innervation of the skin of the hand.
1 - radial nerve, 2 - median nerve; 3 - ulnar nerve; 4 - external nerve of the forearm (branch of the musculocutaneous nerve); 5 - internal cutaneous nerve of the forearm.
Rice. 8.6.Drooping hand due to damage to the radial nerve.
Rice. 8.7.Palm and finger spread test for lesions of the right radial nerve. On the affected side, the bent fingers “slide” along the palm of the healthy hand.
A characteristic sign of damage to the radial nerve is a drooping hand in a pronated position (Fig. 8.6). Due to paresis or paralysis of the corresponding muscles, extension of the hand, fingers and thumb, as well as supination of the hand with the extended forearm are impossible; the carporadial periosteal reflex is reduced or not evoked. In the case of high damage to the radial nerve, the extension of the forearm is also impaired due to paralysis of the triceps brachii muscle, while the tendon reflex from the triceps brachii muscle is not evoked.
If you put your palms next to each other and then try to separate them, then on the side of the lesion of the radial nerve the fingers do not straighten, sliding along the palmar surface of the healthy hand (Fig. 8.7).
The radial nerve is very vulnerable; in terms of the frequency of traumatic lesions, it ranks first among all peripheral nerves. Damage to the radial nerve occurs especially often with fractures of the shoulder. Often the cause of damage to the radial nerve is also infection or intoxication, including chronic alcohol intoxication.
3. Musculocutaneous nerve (n. musculocutaneus, C V -C VI) - mixed; motor fibers innervate biceps muscle shoulder (m. biceps brachii), bending the arm at the elbow joint and supinating the bent forearm, as well as brachialis muscle (m. brachialis), involved in flexion of the forearm, and the coracobrachialis muscle (m. coracobrachialis), promoting anterior elevation of the shoulder.
Sensitive fibers of the muscle cutaneous nerve form its branch - the external cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis), providing sensitivity to the skin of the radial side of the forearm up to the eminence of the thumb.
When the musculocutaneous nerve is damaged, flexion of the forearm is impaired. This is revealed especially clearly with a supinated forearm, since flexion of the pronated forearm is possible due to the brachioradialis muscle innervated by the radial nerve (m. brachioradialis). Loss is also typical
tendon reflex from the biceps brachii muscle, raising the shoulder anteriorly. Sensory disturbances can be detected on the outer side of the forearm (Fig. 8.4).
4. Median nerve (n. medianus)- mixed; formed from part of the fibers of the medial and lateral bundle of the brachial plexus. At the level of the shoulder, the median nerve does not give branches. Muscular branches extending from it to the forearm and hand (rami musculares) innervate the pronator teres (m. pronator teres), pronates the forearm and promotes its flexion. Flexor radialis wrists (m. flexor carpi radialis) along with flexion of the wrist, it abducts the hand to the radial side and participates in flexion of the forearm. Palmaris longus muscle (m. palmaris longus) stretches the palmar aponeurosis and participates in flexion of the hand and forearm. Flexor digitorum superficialis (m. digitorum superficialis) bends the middle phalanges of the II-V fingers, participates in flexion of the hand. In the upper third of the forearm, the palmar branch of the median nerve departs from the median nerve (ramus palmaris n. mediani). It passes in front of the interosseous septum between the flexor pollicis longus and the flexor digitorum profundus and innervates flexor longus thumb (m. flexor pollicis longus), flexing the nail phalanx of the thumb; part of the deep flexor digitorum (m. flexor digitorum profundus), flexing the nail and middle phalanges of the II-III fingers and hand; pronator quadratus (m. pronator quadratus), pronating the forearm and hand.
At the level of the wrist, the median nerve divides into 3 common palmar digital nerves (nn. digitales palmares communes) and the own palmar digital nerves arising from them (nn. digitales palmares proprii). They innervate the abductor pollicis brevis muscle (m. abductor pollicis brevis), muscle that opposes the thumb (m. opponens policis), flexor pollicis brevis (m. flexor pollicis brevis) and I-II lumbrical muscles (mm. lumbricales).
Sensitive fibers of the median nerve innervate the skin in the area of the wrist joint (its anterior surface), the eminence of the thumb (thenar), I, II, III fingers and the radial side of the IV finger, as well as the dorsal surface of the middle and distal phalanges of the II and III fingers (Fig. 8.5).
Damage to the median nerve is characterized by a violation of the ability to oppose the thumb to the rest, while the muscles of the eminence of the thumb atrophy over time. The thumb in such cases ends up in the same plane as the rest. As a result, the palm takes on the typical shape of the median nerve lesion, known as the “monkey hand” (Fig. 8.8a). If the median nerve is affected at the level of the shoulder, a disorder occurs in all functions depending on its condition.
To identify impaired functions of the median nerve, the following tests can be performed: a) when trying to clench the hand into a fist, fingers I, II and partly III remain extended (Fig. 8.8b); if the palm is pressed to the table, then the scratching movement with the nail of the index finger is not possible; c) to hold a strip of paper between the thumb and index finger, due to the inability to bend the thumb, the patient brings the straightened thumb to the index finger - thumb test.
Due to the fact that the median nerve contains a large number of autonomic fibers, when it is damaged, trophic disorders are usually pronounced and more often than when any other nerve is damaged, causalgia develops, manifested in the form of a sharp, burning, diffuse pain.
Rice. 8.8.Damage to the median nerve.
a - “monkey hand”; b - when the hand is clenched into a fist, fingers I and II do not bend.
5. Ulnar nerve (n. ulnaris, C VIII -Th I)- mixed; it begins in the axillary fossa from the medial fascicle of the brachial plexus, descends parallel to the axillary and then the brachial artery and goes to the internal condyle of the humerus and at the level of the distal part of the shoulder passes along the groove of the ulnar nerve (sulcus nervi ulnaris). In the upper third of the forearm, branches depart from the ulnar nerve to the following muscles: flexor carpi ulnaris (m. flexor carpi ulnaris), flexor and adductor wrist; medial part of the deep flexor digitorum (m. flexor digitorum profundus), flexing the nail phalanx of the IV and V fingers. In the middle third of the forearm, the cutaneous palmar branch departs from the ulnar nerve (ramus cutaneus palmaris), innervating the skin of the medial side of the palm in the area of the eminence of the little finger (hypotenar).
At the border between the middle and lower third of the forearm, the dorsal branch of the hand is separated from the ulnar nerve (ramus dorsalis manus) and palmar branch of the hand (ramus volaris manus). The first of these branches is sensitive; it extends to the back of the hand, where it branches into the dorsal nerves of the fingers (nn. digitales dorsales), which end in the skin of the dorsal surface of the V and IV fingers and the ulnar side of the III finger, while the nerve of the V finger reaches its nail phalanx, and the rest reach only the middle phalanges. The second branch is mixed; its motor part is directed to the palmar surface of the hand and at the level of the pisiform bone is divided into superficial and deep branches. The superficial branch innervates the palmaris brevis muscle, which pulls the skin to the palmar aponeurosis; it is further divided into common and proper palmar digital nerves (nn. digitales palmares communis et proprii). The common digital nerve innervates the palmar surface of the fourth finger and the medial side of its middle and terminal phalanges, as well as the dorsum of the nail phalanx of the fifth finger. The deep branch penetrates deep into the palm, goes to the radial side of the hand and innervates the following muscles: the adductor pollicis muscle (m. adductor policis), adductor V finger (m. abductor
digiti minimi),flexor main phalanx of the fifth finger, muscle opposing the fifth finger (m. opponens digiti minimi)- she brings the little finger to the midline of the hand and opposes it; deep head of the short flexor pollicis (m. flexor pollicis brevis); vermiform muscles (mm. lumbricales), muscles that flex the main and extend the middle and nail phalanges of the II and IV fingers; palmar and dorsal interosseous muscles (mm. interossei palmales et dorsales), flexing the main phalanges and simultaneously extending the other phalanges of the II-V fingers, as well as abducting the II and IV fingers from the middle (III) finger and adducting the II, IV and V fingers to the middle one.
Sensitive fibers of the ulnar nerve innervate the skin of the ulnar edge of the hand, the dorsum of the fifth and partly fourth fingers, and the palmar surface of the fifth, fourth and partly third fingers (Fig. 8.4, 8.5).
In cases of damage to the ulnar nerve, due to developing atrophy of the interosseous muscles, as well as hyperextension of the main and flexion of the remaining phalanges of the fingers, a claw-shaped hand is formed, reminiscent of a bird's paw (Fig. 8.9a).
To identify signs of damage to the ulnar nerve, the following tests can be performed: a) when trying to clench the hand into a fist, fingers V, IV and partly III are not bent enough (Fig. 8.9b); b) scratching movements with the nail of the little finger with the palm pressed tightly to the table are not successful; c) if the palm lies on the table, then spreading and bringing the fingers together fails; d) the patient cannot hold a strip of paper between the index finger and straightened thumb. To hold it, the patient needs to sharply bend the terminal phalanx of the thumb (Fig. 8.10).
6. Cutaneous internal nerve of the shoulder (n. cutaneus brachii medialis, C YIII -Th I)- sensitive, originates from the medial bundle of the brachial plexus, at the level axillary fossa has connections with external cutaneous branches (rr. cutani laterales) II and III thoracic nerves (nn. thoracales) and innervates the skin of the medial surface of the shoulder to the elbow joint (Fig. 8.4).
Rice. 8.9.Signs of damage to the ulnar nerve: a claw-shaped hand (a), when the hand is clenched into a fist, the fifth and fourth fingers do not bend (b).
Rice. 8.10.Thumb test.
In the right hand, pressing a strip of paper is only possible with a straightened thumb due to its adductor muscle, innervated by the ulnar nerve (a sign of damage to the median nerve). On the left, pressing the strip of paper is carried out due to the long muscle flexor of the thumb innervated by the median nerve (a sign of damage to the ulnar nerve).
7. Cutaneous internal nerve of the forearm (n. cutaneus antebrachii medialis, C VIII - Th II)- sensitive, originates from the medial bundle of the brachial plexus, is located in the axillary fossa next to the ulnar nerve, descends along the shoulder to medial sulcus its biceps muscle innervates the skin of the inner surface of the forearm (Fig. 8.4).
Brachial plexus lesion syndromes. Along with isolated damage to individual nerves emerging from the brachial plexus, damage to the plexus itself is possible. Plexus damage is called plexopathy.
The etiological factors of damage to the brachial plexus are gunshot wounds of the supra- and subclavian areas, fracture of the clavicle, first rib, periostitis of the first rib, dislocation of the humerus. Sometimes the plexus is affected due to its overstretching, when the arm is quickly and strongly pulled back. Damage to the plexus is also possible in a position where the head is turned in the opposite direction and the hand is placed behind the head. Brachial plexopathy can be observed in newborns due to traumatic injury during complicated childbirth. Damage to the brachial plexus can also be caused by carrying heavy weights on the shoulders or on the back, especially with general intoxication with alcohol, lead, etc. The cause of compression of the plexus can be an aneurysm of the subclavian artery, additional cervical ribs, hematomas, abscesses and tumors of the supra- and subclavian region.
Total brachial plexopathy leads to flaccid paralysis of all muscles of the shoulder girdle and arm, while only the ability to “raise the shoulder girdle” may be preserved due to the preserved function of the trapezius muscle, innervated by the accessory cranial nerve and the posterior branches of the cervical and thoracic nerves.
In accordance with the anatomical structure of the brachial plexus, syndromes of damage to its trunks (primary bundles) and bundles (secondary bundles) are distinguished.
Syndromes of damage to the trunks (primary bundles) of the brachial plexus occur when the supraclavicular part is damaged, and syndromes of damage to the upper, middle and lower trunks can be distinguished.
1. Syndrome of damage to the upper trunk of the brachial plexus (the so-called upper Erb-Duchenne brachial plexopathy) occurs when there is damage (usually traumatic) to the anterior branches of the V and VI cervical spinal nerves or
part of the plexus in which these nerves unite, forming the superior trunk after passing between the scalene muscles. This place is located 2-4 cm above the collarbone, approximately a finger's width behind the sternocleidomastoid muscle and is called Erb's supraclavicular point.
Superior brachial Erb-Duchenne plexopathy is characterized by a combination of signs of damage to the axillary nerve, long thoracic nerve, anterior thoracic nerves, subscapular nerve, dorsal scapular nerve, musculocutaneous and part of the radial nerve. Characterized by paralysis of the muscles of the shoulder girdle and proximal parts of the arm (deltoid, biceps, brachialis, brachioradialis and supinator muscles), shoulder abduction, flexion and supination of the forearm are impaired. As a result, the arm hangs like a whip, is adducted and pronated, the patient cannot raise his arm or bring his hand to his mouth. If you passively supinate your arm, it will immediately turn inward again. The reflex from the biceps muscle and the radiocarpal (carporadial) reflex are not evoked; in this case, radicular type hypalgesia usually occurs on the outer side of the shoulder and forearm in the zone of dermatomes C V - C VI. Palpation reveals pain in the area of Erb's supraclavicular point. A few weeks after the plexus is damaged, increasing wasting of the paralyzed muscles appears.
Erb-Duchenne brachial plexopathy most often occurs due to injuries, it is possible, in particular, when falling on an outstretched arm, and may be a consequence of compression of the plexus during a long stay with the arms placed under the head. Sometimes it appears in newborns during pathological births.
2. Middle trunk brachial plexus syndrome occurs when the anterior branch of the VII cervical spinal nerve is damaged. In this case, violations of the extension of the shoulder, hand and fingers are characteristic. However, the triceps brachii muscle, the extensor pollicis muscle and the abductor pollicis longus muscle are not completely affected, since, along with the fibers of the VII cervical spinal nerve, fibers that came into the plexus along the anterior branches of the V and VI cervical spinal nerves also participate in their innervation. This circumstance is an important sign in the differential diagnosis of the syndrome of damage to the middle trunk of the brachial plexus and selective damage to the radial nerve. The reflex from the triceps tendon and the radiocarpal (carporadial) reflex are not evoked. Sensory disturbances are limited to a narrow strip of hypalgesia on the dorsum of the forearm and the radial part of the dorsum of the hand.
3. Syndrome of the lower trunk of the brachial plexus(inferior brachial plexopathy Dejerine-Klumpke) occurs when nerve fibers entering the plexus are damaged along the VIII cervical and I thoracic spinal nerves, with characteristic signs of damage to the ulnar nerve and cutaneous internal nerves of the shoulder and forearm, as well as part of the median nerve (its internal leg). In this regard, with Dejerine-Klumke paralysis, paralysis or paresis of the muscles occurs mainly in the distal part of the arm. The ulnar part of the forearm and hand suffers mainly, where sensory disturbances and vasomotor disorders are detected. Extension and abduction of the thumb are impossible or difficult due to paresis of the extensor pollicis brevis and the abductor pollicis muscle, innervated by the radial nerve, since the impulses going to these muscles are
pass through the fibers that are part of the VIII cervical and I thoracic spinal nerves and the lower trunk of the brachial plexus. Sensation in the arm is impaired on the medial side of the shoulder, forearm and hand. If, simultaneously with the damage to the brachial plexus, the white connecting branches going to the stellate ganglion are also affected (ganglion stellatum), That possible manifestations of Horner's syndrome (constriction of the pupil, palpebral fissure and mild enophthalmos. In contrast to combined paralysis of the median and ulnar nerves, the function of the muscles innervated by the external leg of the median nerve is preserved in the syndrome of the lower trunk of the brachial plexus.
Dejerine-Klumke palsy most often occurs as a result of traumatic damage to the brachial plexus, but it can also be a consequence of compression by a cervical rib or a Pancoast tumor.
Syndromes of damage to the bundles (secondary bundles) of the brachial plexus arise from pathological processes and injuries in the subclavian region and, in turn, are divided into lateral, medial and posterior fascicular syndromes. These syndromes practically correspond to the clinical picture of combined lesions of peripheral nerves formed from the corresponding bundles of the brachial plexus. Lateral fascicle syndrome is manifested by dysfunction of the musculocutaneous nerve and the superior peduncle of the median nerve, posterior fascicle syndrome is characterized by dysfunction of the axillary and radial nerve, and medial fascicle syndrome is expressed by dysfunction of the ulnar nerve, medial peduncle of the median nerve, medial cutaneous nerves of the shoulder and forearm. When two or three (all) bundles of the brachial plexus are affected, a corresponding summation of clinical signs occurs, characteristic of syndromes in which individual bundles are affected.
8.3.6. Thoracic nerves
Thoracic nerves (nn. thoracalis) It is customary to call the spinal nerves of the thoracic level. Like other spinal nerves, the thoracic nerves are divided into posterior and anterior branches. Posterior branches (rami posteriores) bend around the articular processes of the vertebrae and are directed between the transverse processes to the back, where they are in turn divided into internal and lateral branches, providing innervation to paravertebral tissues, in particular longus dorsi muscle (m. longissimus dorsi), semispinalis muscle(m. semispinalis), sacrospinous muscle(m. sacrospinalis), and multipartite , rotating, interspinous And intertransverse muscles. All these long and short muscles the backs support the torso in an upright position, extend or bend the spine, and when they contract on one side, the spine bends or rotates in that direction.
Part of the fibers of the anterior branches of the first and second thoracic spinal nerves takes part in the formation of the brachial plexus, part of the anterior branch of the XII thoracic spinal nerve is part of lumbar plexus. The parts not involved in the formation of plexuses (Th I - Th II and Th XII) and the anterior branches of the thoracic spinal nerves (Th III - Th XI) form intercostal nerves (nn. intercostales). The six superior intercostal nerves pass to the edge of the sternum and end as the anterior cutaneous thoracic branches; the six inferior intercostal nerves pass behind the angles of the costal cartilages
into the thickness of the abdominal muscles and are located there first between the transverse and internal oblique muscles, approach the rectus abdominis muscle and end as the cutaneous anterior abdominal nerves.
The intercostal nerves are mixed and play an important role in the innervation of the muscles of the chest and abdomen involved in the act of breathing.
At irritation of intercostal nerves (in a pathological process) there is a girdle pain, aggravated by breathing movements, especially by coughing and sneezing. Pain on palpation of certain intercostal spaces is common, possible pain points: posterior - in the paravertebral region, lateral - along the axillary line and anterior - along the line of connection of the sternum with the costal cartilages; a decrease in the amplitude of respiratory movements is possible. Damage to the lower intercostal nerves causes paresis of the abdominal wall muscles, accompanied by loss of the corresponding abdominal reflexes, the arcs of which pass through the VII-XII segments of the spinal cord, and exhalation, coughing, and sneezing are especially difficult. Difficulty urinating and defecating is common. In addition, the lordosis of the lumbar spine becomes excessive with the pelvis moving forward; when walking, he leans back, a duck's gait appears.
Sensitivity when the thoracic nerves are damaged can be impaired in the chest, abdomen, armpits and on the inner surface of the shoulder due to the lesion n. intercostobrachialis.
Damage to the thoracic nerves can be a consequence of spinal pathology, ganglioneuropathy due to herpes zoster, rib fractures, inflammatory and oncological diseases of the chest organs, and intravertebral tumors, in particular neuroma.
The lumbar spinal roots depart from the corresponding segments of the spinal cord at the level of the X-XII thoracic vertebrae and go down to the intervertebral foramina of the same name, each of which is located below the vertebra of the same name. Here, the corresponding spinal nerves are formed from the anterior and posterior roots. After passing through the intervertebral foramina, they are divided into branches. The posterior and anterior branches of the spinal nerves, as at other levels of the spine, are mixed in composition.
The posterior branches of the lumbar spinal nerves are divided into medial and lateral branches. The medial branches innervate the lower parts of the deep back muscles and provide skin sensitivity in the paravertebral zone of the lumbar region. The lateral branches innervate the lumbar intertransverse and multifidus muscles. The superior gluteal nerves arise from the three superior lateral rami (nn. cunium superiores), running through the iliac crest to the skin of the upper half of the gluteal region, i.e. to the skin over the gluteus maximus and medius muscles up to the greater trochanter of the thigh.
8.3.7. Lumbar plexus and its nerves
The anterior branches of the lumbar spinal nerves take part in the formation of the lumbar plexus (plexus lumbalis).This plexus (Fig. 8.11) consists of loops formed by the anterior branches of the L I -L III and partially the Th XII and L IV spinal nerves. The lumbar plexus is located in front of the transverse processes of the lumbar vertebrae on the anterior surface of the quadrate
muscles of the lower back between the bundles of the large psoas muscle. The lumbar plexus has numerous connections with the underlying sacral plexus. Therefore, they are often combined under the name lumbosacral plexus. Most of the peripheral nerves emerging from the lumbar plexus are mixed in composition. However, there are also muscle branches (rami musculares), innervating, in particular, internal muscles pelvis: iliopsoas muscle (m. iliopsoas) and psoas minor muscle (m. psoas minor), hip flexors hip joint, as well as the quadratus lumborum muscle, which rotates the thigh outward.
Iliohypogastric nerve (n. iliohypogastricus, Th XII -L I) goes obliquely down parallel to the XII intercostal nerve, penetrates the transverse abdominal muscle, passes between it and the internal oblique abdominal muscle. At the level of the inguinal (pupart) ligament, the nerve passes through the internal oblique muscle of the abdomen and is located between it and the aponeurosis of the external oblique muscle. Along the route, branches depart from the iliohypogastric nerve to the muscles of the lower abdomen and the external cutaneous branch, which separates in the area of the middle part of the iliac crest, perforates the oblique muscles of the abdomen and innervates the area of skin above the middle gluteal muscle and the tensor fascia muscle. In addition, an anterior cutaneous branch arises from the iliohypogastric nerve, which pierces the anterior wall of the inguinal canal and innervates the skin above and medial to the external opening of the inguinal canal.
Ilioinguinal nerve (n. ilioinguinalis, L I) runs parallel to and below the iliohypogastric nerve, pierces the transverse abdominal muscle and goes further between it and the internal oblique abdominal muscle, passes over the Pupart ligament and exits under the skin through the external inguinal ring, then it is located medially and in front of the spermatic cord and is divided into terminal sensory branches.
Along the path of the ilioinguinal nerve, muscle branches depart from it to the external and internal oblique muscles of the abdomen and the transverse abdominal muscle, cutaneous branches providing sensitivity in groin area and in the upper part of the inner
Rice. 8.11.Lumbar and sacral plexus.
1 - iliohypogastric nerve; 2 - ilioinguinal nerve; 3 - femoral-genital nerve; 4 - lateral cutaneous nerve of the thigh; 5 - obturator nerve; 6 - femoral nerve, 7 - sciatic nerve; 8 - genital nerve.
surface of the thigh, as well as the anterior scrotal branches, innervating the skin of the pubic area, the root of the penis and the anterior scrotum (in women - the skin of the labia majora) and the upper part of the medial thigh.
Femorogenital nerve (n. genitofemoralis, L I -L III) passes between the transverse processes of the lumbar vertebrae and the psoas major muscle. It then passes down through the thickness of this muscle and appears on its anterior surface at the level of the L III vertebra. Here he is divided into femoral and genital branches.
Femoral branch passes downward laterally from the femoral vessels under the Pupart ligament, where it branches: part of the branches passes through the foramen ovale, the other part is lateral from it; the last group of branches is distributed in the skin below the inguinal fold along the anterior surface of the thigh (Fig. 8.12).
Sexual branch goes down along the inner edge of the psoas major muscle, penetrates the inguinal canal through its posterior wall, approaches the posterior surface of the spermatic cord (in women, the round uterine ligament) and reaches the scrotum (labia majora). On its way, this nerve gives off branches to m. cremaster and cutaneous branches.
Rice. 8.12.Innervation of the skin of the posterior (a) and anterior (b) surface of the leg. 1 - superior gluteal nerve; 2 - posterior sacral nerves; 3 - middle gluteal nerve; 4 - posterior cutaneous nerve of the thigh; 5 - external cutaneous nerve of the thigh; 6 - obturator nerve;
7 - external cutaneous sural nerve (branch of the peroneal nerve);
8 - nervus saphenus (branch of the femoral nerve); 9 - internal cutaneous sural nerve (branch of the tibial nerve); 10 - calcaneal branch of the tibial nerve; 11 - external plantar nerves (branches of the tibial nerve); 12 - internal plantar nerves; 13 - sural nerve (branch of the tibial and peroneal nerves); 14 - deep peroneal nerve; 15 - superficial peroneal nerve; 16 - external cutaneous nerve of the thigh; 17 - inguinal nerve; 18 - genital femoral nerve.
When the genitofemoral nerve is damaged, the cutaneous cremasteric reflex disappears. Sensitive nerve fibers innervate the skin of the groin area and the upper part of the inner thigh.
Obturator nerve (n. obturatorius, L II -L IV innervates the pectineus muscle (m. pectineus), involved in adduction and flexion of the hip, the adductor major muscle (m. adductor longus), which flexes the thigh and rotates it outward; and adductor brevis (m. adductor brevis), adductor of the thigh and involved in its flexion, as well as the adductor magnus muscle (m. adductorius magnus), which adducts the thigh and is involved in its extension, the obturator externus muscle (n. obturatorius externus), contraction of which leads to outward rotation of the thigh, as well as the gracilis muscle (m. gracilis), adducting the thigh, flexing the tibia and simultaneously rotating it inward. Sensory fibers of the obturator nerve (rr. cutanei n. obturatorii) innervate the skin of the lower part of the inner thigh. When the obturator nerve is damaged, hip adduction and, to a lesser extent, hip abduction and rotation are weakened. When walking, some excess hip abduction may be noted. It is difficult for a patient sitting on a chair to place the sore leg on the healthy one.
External cutaneous nerve of the thigh (n. cutaneus femoris lateralis, L II -L III) passes under the Poupart ligament and 3-5 cm below it divides into branches that innervate the skin of the outer surface of the thigh. Isolated damage to the external cutaneous nerve of the thigh occurs quite often and leads to the development of Roth's disease, which has a different etiology (usually compression of the nerve) and is manifested by paresthesia and hypalgesia with elements of hyperpathy on the anterior outer surface of the thigh.
Femoral nerve (n. femoralis, L nII -L IV)- the largest nerve of the lumbar plexus. It innervates the quadriceps femoris muscle (m. quadriceps femoris), including the rectus muscle, as well as the lateral, intermediate and medial muscles. broad muscles hips. The quadriceps femoris muscle is primarily a powerful extensor of the tibia at the knee joint. In addition, the femoral nerve innervates the sartorius muscle (m. sartorius), taking part in flexing the leg at the hip and knee joints and rotating the thigh outward.
Anterior cutaneous nerves (rr. cutanei anteriores) And saphenous nerve (n. saphenus), being the terminal branch of the femoral nerve, passing to the lower leg, it provides innervation to the skin of the anterior inner surface of the thigh and lower leg and the medial side of the foot to the big toe.
With damage to the femoral nerve below the Poupart ligament, the extension of the leg is impaired, the knee reflex decreases or disappears, and a sensitivity disorder occurs in the area innervated by n. saphenus. If the femoral nerve is damaged above the Pupart ligament, then at the same time the sensitivity on the anterior inner surface of the thigh is impaired and the ability to actively flex it is difficult. It is difficult for a patient lying on his back with straightened legs to sit up without the help of his hands, and with bilateral damage to the femoral nerves this becomes impossible.
Damage to the femoral nerve makes walking, running, and especially climbing stairs very difficult. When walking on level ground, the patient tries not to bend the leg at the knee joint. When walking, the patient's leg, bent at the knee joint, is thrown forward and at the same time the heel hits the floor.
When the femoral nerve is damaged due to decreased tone and then hypotrophy of the quadriceps muscle, the anterior surface of the thigh becomes flattened
and a depression appears above the patella, revealed when examining the patient lying on his back (Flatau-Sterling symptom).
If there is a lesion of the femoral nerve, then in a standing patient, when he transfers the center of gravity and relies only on the extended sore leg, free passive displacement of the patella to the sides is possible (symptom of a dangling patella, Froman's symptom).
If the femoral nerve is irritated, pain and tenderness may occur in the area of the ligament and on the front side of the thigh. In such cases, the symptoms of Wasserman, Matskevich, related to the symptoms of tension, and the Seletsky phenomenon are positive.
Wasserman's sign is checked with the patient lying on his stomach. The examiner strives to extend the leg at the hip joint as much as possible, while at the same time fixing his pelvis at the bedside. In case of irritation of the femoral nerve, the patient experiences pain in the groin area, radiating along the anterior surface of the thigh.
Matskevich's symptom is caused in the same position of the patient by sharply bending the lower leg and bringing it closer to the thigh. As a result, the patient experiences the same reactions as when checking Wasserman's symptom. The protective reaction that occurs when these tension symptoms are caused - raising the pelvis - is known as Seletsky phenomenon.
8.3.8. Sacral plexus and its nerves
The sacral spinal nerves arise from the sacral segments of the spinal cord at the level of the body of the first lumbar vertebra and descend down into the sacral canal, at the level of which the sacral spinal nerves are formed in the area of the intervertebral foramina of the sacrum due to the fusion of the anterior and posterior spinal roots. These nerves are divided into anterior and posterior branches, leaving the sacral canal through the intervertebral foramina of the sacrum, with the anterior branches exiting onto the pelvic surface of the sacrum (into the pelvic cavity), and the posterior branches onto its dorsal surface. The branches of the fifth sacral spinal nerve exit the sacral canal through the sacral fissure (hiatus sacralis).
The posterior branches, in turn, are divided into internal and external. The internal branches innervate the lower segments of the deep muscles of the back and end with cutaneous branches in the sacrum, closer to the midline. The external branches of the I-III sacral spinal nerves are directed downward and are called the middle cutaneous nerves of the buttocks (nn. clunium medii), innervating the skin of the middle parts of the gluteal region.
The anterior branches of the sacral nerves, emerging through the anterior sacral foramina onto the pelvic surface of the sacral bone, form the sacral plexus.
Sacral plexus (plexus sacralis) consists of loops formed by the anterior branches of the lumbar and sacral spinal nerves (L V -S II and partially L IV and S III). The sacral plexus, which has numerous connections with the lumbar plexus, is located in front of the sacrum, on the anterior surface of the piriformis and partly coccygeal muscles on the sides of the rectum and goes down to the greater sciatic notch (incisura ischiadica major), through which the peripheral nerves formed in the sacral plexus leave the pelvic cavity.
The muscular branches of the sacral plexus innervate the following muscles: a) piriformis muscle (m. piriformis), which is located between the anterior surface of the sacrum and the inner surface of the greater trochanter of the femur. Crossing the greater sciatic foramen, this muscle divides it into supra- and infrapiriform parts, through which vessels and nerves pass; b) obturator internus muscle (m. obturatorius internus), located inside the pelvis; c) upper and outer twin muscles (mm. gemelles superior et inferior); G) quadratus femoris muscle (m. quadratus femoris). All of these muscles externally rotate the hip. To determine their strength, the following tests can be performed: 1) the patient, lying on his stomach with the lower leg bent at a right angle, is asked to move the lower leg inward, while the examiner resists this movement; 2) the patient lying on his back is asked to rotate his legs outward, while the examiner resists this movement.
Superior gluteal nerve (n. gluteus superior, L IV -S I) - motor, it innervates gluteus medius and minimus muscles (mm. glutei medius et minimus), tensor fascia lata (m. tensor fasciae latae), the contraction of which leads to hip abduction. Damage to the nerve causes difficulty in hip abduction, flexion and internal rotation. With bilateral damage to the superior gluteal nerve, the patient's gait becomes like a duck's - the patient seems to waddle from one foot to the other when walking.
Inferior gluteal nerve (n. gluteus inferior, L V -S II) is motor, innervates gluteus maximus muscle (m. gluteus maximus), extending the hip, and with a fixed hip, tilting the pelvis backward. If the inferior gluteal nerve is damaged, hip extension is difficult. If a standing patient bends over, then it is difficult for him to straighten his torso. The pelvis in such patients is fixed tilted forward, as a result of which compensated lordosis develops. lumbar region spine. Patients find it difficult to climb stairs, jump, or get out of a chair.
Posterior cutaneous nerve of the thigh (n. cutaneus femoris posterior, S I -S III - sensitive. It exits through the infrapiriform foramen behind the sciatic nerve, with which it has anastomoses. Then it passes between the ischial tuberosity and the greater trochanter, goes down and innervates the skin of the back of the thigh, including the popliteal fossa. The inferior cutaneous nerves of the buttock arise from the posterior cutaneous nerve of the thigh. (nn. clinium inferiores), perineal nerves (rr. perineales), which provide sensitivity to the corresponding skin areas.
Sciatic nerve(n. ischiadicus, L IV -S III) - mixed; the largest of the peripheral nerves. Its motor part innervates most of the muscles of the leg, in particular all the muscles of the lower leg and foot. Even before exiting the thigh, the sciatic nerve gives off motor branches to biceps femoris muscle (m. biceps femoris), semitendinosus muscle(m. semitendinosus) And semimembranosus muscle (m. semimembranosus), bending the lower leg at the knee joint and rotating it inward. In addition, the sciatic nerve innervates adductor magnus muscle (m. adductor magnus), which flexes the lower leg, rotating it outward.
Having reached the level of the thigh, the sciatic nerve passes along its posterior side and, approaching the popliteal fossa, divides into two branches - the tibial and peroneal nerves.
Tibial nerve (n. tibialis, L IV -S III is a direct continuation of the sciatic nerve. It runs down the middle of the popliteal fossa along the back of the shin to the inner ankle. Motor branches are larger
tibial nerve innervate the triceps surae muscle (m. triceps surae), consisting of the soleus muscle (m. soleus) and calf muscle. The triceps surae muscle flexes the lower leg at the knee joint and the foot at the ankle. In addition, the tibial nerve innervates popliteus muscle (m. popliteus), involved in flexing the tibia at the knee joint and rotating it inward; tibialis posterior muscle (m. tibialis posterior), adducting and elevating the inner edge of the foot; flexor digitorum longus (m. flexor digitorum longus), bending the nail phalanges of the II-V fingers; flexor pollicis longus (m. flexor hallucis longus), the contraction of which causes flexion of the first toe.
At the level of the popliteal fossa, it departs from the tibial nerve medial cutaneous nerve of the leg (n. cutaneus surae medialis), the branches of which innervate the skin of the posterior surface of the leg (Fig. 8.12). In the lower third of the leg, this cutaneous nerve anastomoses with the branch of the lateral cutaneous nerve of the leg, which arises from the peroneal nerve, and is then called sural nerve (n.suralis) descends along the lateral edge of the calcaneal (Achilles) tendon, wraps around the back of the outer ankle. Here it departs from the sural nerve lateral calcaneal branches (rr. calcanei laterales), innervating the skin of the lateral part of the heel. Next, the sural nerve goes forward to the lateral surface of the foot called lateral dorsal cutaneous nerve (n. cutaneus dorsalis lateralis) and innervates the skin of the dorsolateral surface of the foot and little toe.
Slightly above the level of the medial malleolus, they extend from the tibial nerve medial calcaneal branches (rr. rami calcanei mediales).
Going down to the ankle joint, tibial nerve passes at the posterior edge of the inner ankle onto the sole. On inside he calcaneus divided by final branches: medial and lateral plantar nerves.
Medial plantar nerve (n. plantaris medialis)passes under the abductor pollicis muscle, and then goes forward and divides into muscular and cutaneous branches. The muscular branches of the medial plantar nerve innervate the short flexor of the fingers (m. flexor digitorum brevis), which flexes the middle phalanges of the II-V fingers; flexor pollicis brevis (m. flexor hallucis brevis), involved in ensuring flexion of the thumb; abductor pollicis muscle (m. adductor hallucis), involved in flexion of the thumb and ensuring its abduction. In addition, the own plantar digital nerves arise from the medial plantar nerve. innervating the skin of the medial and plantar surface of the big toe, as well as the common plantar digital nerves innervating the skin of the first three interdigital spaces and the plantar surface of I-III, as well as the medial side of the IV fingers. From the I and II common plantar nerves, muscle branches also extend to the I and II lumbrical muscles, flexing the main and extending the remaining phalanges of the I, II and partly III toes.
Lateral plantar nerve (n. plantaris lateralis)directed along the plantar side of the foot forward and outward, gives off branches innervating the quadratus plantar muscle (m. quadratus plantae), promoting finger flexion; flexor digitorum brevis (m. abductor digiti minimi), abductor and flexor of the little finger. After these branches depart, the lateral plantar nerve is divided into deep and superficial branches.
deep branch (r. profundus)penetrates deep into the plantar surface of the foot and innervates the muscle that adducts the big toe (m. adductor hallucis) and short flexor of the fifth finger (m. flexor digiti minimi brevis) and III-IV lumbrical muscles (mm. lumbricales), flexing the main and extensor middle and nail phalanges of the IV, V and partly III toes, as well as the plantar and dorsal interosseous muscles (mm. inercostales plantares et dorsales), flexing the main and extending the remaining phalanges of the fingers, as well as abductor and adductor toes.
Superficial branch (ramus superficialis)lateral plantar nerve divides into common plantar digital nerves (nn. digitales plantares communis), from which the 3 own plantar digital nerves arise (nn. digitales plantares proprii), innervating the skin of the fifth and lateral side of the fourth fingers, as well as the lateral part of the foot.
If the tibial nerve is damaged, it becomes impossible to flex the foot and its toes. As a result, the foot becomes fixed in the extension position (Fig. 8.13a), and therefore the so-called calcaneal foot (pes calcaneus)- the patient steps primarily on the heel while walking; he cannot rise on his toes. Atrophy small muscles feet leads to a claw-like position of the toes (to the development claw-shaped foot). In this case, spreading and bringing the toes together is difficult. Sensation on the lateral and plantar side of the foot is impaired.
If the sciatic or tibial nerves are damaged, the heel (Achilles) reflex decreases or disappears.
Common peroneal nerve (n. peroneus communis, L IV -S I) - the second of the main branches of the sciatic nerve. The cutaneous external nerve of the calf arises from the common peroneal nerve (n. cutaneus surae lateralis), branching on the lateral and posterior surfaces of the leg. On the lower third of the leg, this nerve anastomoses with the cutaneous medial nerve of the leg, which is a branch of the tibial nerve, thereby forming the sural nerve (n. suralis).
Rice. 8.13.“Heel” foot with damage to the tibial nerve (a); “dropping” foot with damage to the peroneal nerve (b).
Behind the head fibula The common peroneal nerve is divided into two parts: the superficial and deep peroneal nerves (n. peroneus profundus).
Superficial peroneal nerve (n. peroneus superficialis)goes down the anterior outer surface of the leg, gives branches to the long and short peroneal muscles (mm. peronei longus et brevis), abducting and lifting the outer edge of the foot and at the same time flexing it. In the middle third of the leg, this nerve exits under the skin and divides into the medial and intermediate dorsal cutaneous nerves.
Medial dorsal cutaneous nerve (nervus cutaneus dorsalis medialis) is divided into two branches: medial and lateral. The first of them is directed to the medial edge of the foot and big toe, the second - to the skin of the dorsal surface of the halves of the second and third fingers facing each other.
Intermediate dorsal cutaneous nerve (a. cutaneus dorsalis intermedius) gives off sensory branches to the skin of the knees and dorsum of the foot and is divided into medial and lateral branches. The medial branch is directed to the dorsal surface of the halves of the third and fourth fingers facing each other.
Deep peroneal nerve (a. peroneus profundus)innervates the tibialis anterior muscle (m. tibialis anterior), which extends the foot and elevates its inner edge; extensor longus fingers (m. extensor digitorum longus), extensor foot, II-V fingers, as well as abductor and pronating foot; extensor pollicis brevis (m. extensor hallucis longus), extending and supinating the foot, as well as extending the big toe; extensor pollicis brevis (m. extensor digitorum brevis), extending the thumb and deflecting it to the lateral side.
If the peroneal nerve is damaged, it becomes impossible to extend the foot and toes and turn the foot outward. As a result, the foot hangs down, being slightly turned inward, its toes bent at the joints of the main phalanges (Fig. 8.13b). Leaving the foot in this position for a long time can lead to contracture. Then they talk about development equine foot (pes equinus). When the peroneal nerve is damaged, a characteristic gait develops. Avoiding contact of the back surface of the fingers with the floor, the patient raises his leg high when walking, bending it at the hip and knee joints more than usual. The foot touches the floor first with the toe, and then with the main surface of the sole. This gait is called peroneal, equine, cockerel and is often denoted by the French word steppage (steppage). A patient with damage to the peroneal nerve cannot stand on his heels, straighten the foot and toes, or turn the foot outward.
With total damage to the sciatic nerve, naturally, the function of the tibial and peroneal nerves simultaneously suffers, which is manifested by paralysis of the foot muscles, loss of the reflex from the heel tendon (calcaneal or Achilles reflex). In addition, flexion of the lower leg is impaired. Sensitivity in the lower leg remains intact only along the anterior internal surface in the zone of innervation of the saphenous nerve n. saphenus. With high damage to the sciatic nerve, sensory impairment also manifests itself on the back of the thigh.
If the pathological process irritates the sciatic nerve, then this is primarily manifested by severe pain, as well as pain on palpation along the nerve, especially distinct in the so-called Valle points:
Rice. 8.14.Lasègue's symptom (first and second phases). Explanation in the text.
between the ischial tuberosity and the greater trochanter, in the popliteal fossa, behind the head of the fibula.
It has important diagnostic value in cases of damage to the sciatic nerve. Lasègue's symptom (Fig. 8.14), belonging to the group of tension symptoms. It is checked with the patient lying on his back with his legs straightened. If you try to bend the patient’s leg, which is extended at the knee joint, at the hip joint, then tension in the sciatic nerve will occur, accompanied by pain that limits the possible range of movement performed, and this can be measured in angular degrees and thus objectify the angle at which it is possible to raise the leg above the horizontal flat. After bending the leg at the knee joint, the tension on the sciatic nerve decreases, and at the same time the pain reaction decreases or disappears.
With damage to the sciatic nerve containing a large number of autonomic fibers and its branch - the tibial nerve, as well as with damage to the median nerve on the arm, the pain often has a causal tinge; Severe tissue trophic disorders are also possible, in particular trophic ulcers (Fig. 8.15).
Rice. 8.15.Trophic ulcer on the foot due to damage to the sciatic nerve.
8.3.9. Pudendal plexus
Pudendal plexus (plexus pudendus) is formed mainly from the anterior branches of the III-IV and parts of the I-II sacral spinal nerves. It is located on the anterior surface of the sacrum at the lower edge of the piriformis muscle, below the sacral plexus. The pudendal plexus has connections with the coccygeal plexus and the sympathetic trunk. Muscular branches that innervate the levator ani muscle arise from the pudendal plexus. (m. levator ani), coccygeus muscle (m. coccygeus) and the dorsal nerve of the penis or clitoris. The largest branch of the pudendal plexus is pudendal nerve (n.pudendus)- exits the pelvic cavity above piriformis muscle, goes around the ischial tubercle and through the lesser sciatic foramen reaches the lateral wall of the ischiorectal fossa, in which the lower rectal nerves, the nerves of the perineum, depart from the pudendal nerve.
8.3.10. Coccygeal plexus
The coccygeal plexus is formed by part of the anterior branches of the V sacral (S V) and I-II coccygeal (Co I -Co II) nerves. The plexus is located on both sides of the sacrum, in front of the coccygeus muscle. It has connections with the lower part of the sympathetic trunk. Muscular branches depart from it to the pelvic organs and pelvic floor muscles, to the coccygeus muscle and to the levator ani muscle, as well as the anal-coccygeal nerves (nn. anococcygei), innervating the skin between the coccyx and the anus.
The clinical picture of damage to the pudendal and coccygeal plexus is manifested by a disorder of urination, defecation, genital function, loss of the anal reflex, and sensitivity disorder in the anogenital zone.
4. The cerebellum in ensuring motor activity. 5. Functions of the basal ganglia in the regulation of movements. 6. Motor cortex in ensuring motor action. 8.1. General plan of central regulation of motor activity. A person actively interacts with the external environment and actively influences it through movements. They can be aimed at maintaining posture, moving the body in space, moving body parts, and thermoregulation. A fundamentally important function of the motor system is its role in the implementation of genetically determined programs of growth and development. Movements can be voluntary or involuntary. Motor activity is not only the result of reflex reactions, but also an external manifestation of motor programs embedded in the central nervous system. The structural organization of movement regulation involves the division of functions between different structures of the central nervous system. The higher ones (motivational zones of the cortex, subcortex and associative zones of the cortex) determine the plan of movements, which includes the motivation to action and the intention of the action. The command to plan an action is addressed to the structures of the software of movements (the basal ganglia system and the cerebellum). They contain genetically determined (basal ganglia) and acquired (cerebellum) programs for the interaction of different muscle groups in the process of performing movements (Fig. 37). The executive structures of the central nervous system are the motor cortex, brainstem and spinal cord with motor units. At the level of the cortex, the movement pattern program turns into commands for certain muscle groups to carry out elements of movement. The brain stem provides regulation of posture and the tonic component of movements. The spinal cord carries out the simplest reflexes of maintaining the length and limiting muscle tension, and executing commands from structures located above. Violations in this hierarchical system at any level lead to impaired motor activity. Due to the plasticity of the nerve centers, some of the disturbances can be compensated. The more highly organized the motor center, the more opportunities there are to compensate for violations. Motor paralysis associated with disorders of associative and motivational zones goes away most quickly. The dysfunction of spinal neurons is much worse compensated for. 61 STRUCTURE FUNCTION ROLE IN MOVEMENT Motivational Inducement to cortical zones and sub-actions Cortex PLAN E N Associative Intent of daison of self-interest C Basal-Cerebellum Ganglia P Pattern of action PROGRAM N Thalamus E Motor cortex PU Trunk brain TI Regulation of posture Spinal cord EXECUTION neuro- Mono- and poly synaptic Motor neuron reflexes Muscle length, spinal cord tension Fig. 37. The role of parts of the nervous system in the organization of movements 8.2. The spinal cord in the regulation of movements is an executive structure in relation to the higher motor centers. The independent activity of the spinal motor systems provides the simplest, but very important motor reactions. These are reflexes for maintaining constancy of the length of skeletal muscles, reflexes for limiting tension in skeletal muscles, and polysynaptic reflexes. In its pure form, the spinal cord's own reflexes can be studied in a spinal animal. Spinal shock. Occurs when the spinal cord is ruptured. It manifests itself in a pronounced impairment of reflexes, the centers of which are localized below the site of injury. The main cause of shock is disruption of connections with higher located nerve centers. In the spinal cord, the regulation of motor activity is provided by interneurons, alpha motor neurons and gamma motor neurons. Efferent innervation of skeletal muscles is provided by alpha motor neurons. Their axons form thick A-alpha fibers. The receptive apparatus of skeletal muscles is represented by muscle spindles and Golgi bodies. The muscle spindles are located parallel to the extrafusal muscle fibers. Each muscle spindle consists of a connective tissue capsule that includes intrafusal muscle fibers. Sensory fibers of afferent neurons wrap around the middle part of the intrafusal fiber, forming an annulospiral ending. These fibers are called primary afferents. Intrafusal endings with a nuclear chain are also innervated by secondary sensory endings (secondary afferents) located on the periphery of the fiber. Afferent impulses from muscle fibers with the nuclear bursa are triggering reflexes for maintaining the length of skeletal muscles. Afferent impulses from muscle fibers with a nuclear chain activate neuronal groups involved in ensuring the movement of the entire limb. Afferent impulses from muscle spindles are constant (background impulses), increasing when muscles are stretched and decreasing when they are shortened. Efferent innervation of intrafusal fibers is provided by gamma motor neurons. An increase in impulses from them causes contraction of the intrafusal fiber, irritation of sensory fibers and increased afferent impulses. According to the modality of stimulation, muscle spindles are stretch receptors. When a muscle is stretched corresponding to the resting length, the frequency of action potentials traveling along the afferent fibers is small. With further stretching of the muscle, the impulse increases. A similar increase in afferentation can be obtained with constant muscle length but an increase in gamma neuron tone. Thus, there are two mechanisms leading to 63 excitation of muscle spindles: 1) stretching of the muscle, and 2) contraction of the intrafusal fiber. Golgi bodies. They are formed by tendon filaments extending from ten extrafusal muscle fibers and surrounded by a connective tissue capsule. The Golgi tendon bodies are approached by thick myelinated fibers that form sensitive endings around the tendon filaments. Unlike muscle spindles, they are not located parallel to extrafusal muscle fibers, but in series. There is no background afferentation from Golgi bodies. It occurs only when muscle tension increases. Reflexes for maintaining the length of skeletal muscles. They consist of a reflex shortening or relaxation of skeletal muscles with an increase or decrease in afferentation from muscle spindles. These reflexes have great importance to maintain constant tone of skeletal muscles, ensuring the preservation of posture. An example is the monosynaptic knee reflex, which occurs when the extensor tendon of a limb is struck with a neurological hammer. Short-term stretching of the extensor muscles increases afferentation from the muscle spindles, which leads to increased excitation of the neurons innervating these muscles. Muscle contraction and limb extension occur. At the same time, through intercalary inhibitory neurons, reciprocal (conjugate) inhibition of antagonist muscles occurs. When performing complex motor acts, simultaneous activation occurs - coactivation of alpha and gamma motor neurons. It consists in the fact that alpha neurons are simultaneously activated (the movement itself is ensured) and gamma neurons (the excitation of alpha neurons is supported). The activation of alpha motor neurons through gamma motor neurons is called the gamma loop. Reflexes limiting tension in skeletal muscles (inhibitory tendon reflexes). Carried out by increasing muscle tension. Increasing mechanical tension in the tendons is an irritant for the Golgi bodies. The resulting excitation enters the spinal cord and, through the system of inhibitory intercalary neurons, ensures inhibition of its motor neurons with simultaneous activation of antagonist muscle motor neurons through excitatory cells. These reflexes are mirror images of the reflexes for maintaining muscle length. Inhibitory tendon reflexes, in contrast to reflexes for maintaining the length of skeletal muscles, are addressed not to one muscle, but to a group of agonist muscles, and are polysynaptic. Thus, two feedback systems are involved in the regulation of the activity of each muscle: the length regulation system and the tension regulation system. Polysynaptic motor reflexes. They are carried out by irritating skin receptors, joint receptors, pressure and pain receptors of skeletal muscles. An example of this group of reflexes is the defensive flexion reflex. It consists of a reflex increase in the tone of the flexor muscles in response to painful stimulation while simultaneously decreasing the tone of the extensor muscles of one limb. Simultaneously with the implementation of this reflex, the same neural circuit is involved in providing the crossed extensor reflex. Painful stimulation leads to the implementation of 4 reflex reactions: - activation of the flexor of the limb, - inhibition of the extensor of the limb, - activation of the extensor of the opposite limb, - inhibition of the flexor of the opposite limb. This nature of reflex reactions is necessary to shift the center of gravity in the process of implementing the protective reflex. All the reflexes described above are intrasegmental (implemented within one segment of the spinal cord). Intersegmental motor systems are provided by proprespinal interneurons. They make up the bulk of the neurons in the spinal cord. They ensure the coordinated activity of neural ensembles regulating the upper and lower extremities. These reflexes are triggered by secondary afferents of muscle spindles with a nuclear chain, irritation of receptors that initiate the flexion reflex. Thanks to these reflexes, the spinal cord can provide complex motor acts that are triggered both by primary afferentation from the periphery and by incoming signals from higher motor centers of the brain. 8.3. Motor systems of the brainstem. The structures of the brain stem provide a higher level of regulation of movements and are classified as structures of direct action. Their activity consists not only in the implementation of action programs launched by higher motor centers. They are characterized by their own complex reflexes of coordination of the tone of different groups of skeletal muscles. Thus, the structures of the brain stem are involved in the regulation of posture and various motor acts. The stem centers include: the red nucleus, the vestibular nucleus (Deiters nucleus), the nuclei of the reticular formation of the pons and the medulla oblongata (Fig. 38). Rice. 38. Motor nuclei of the brainstem The nuclei of the brainstem regulate the tone of antagonistic muscle groups through pathways. The red nucleus forms the descending rubrospinal tract, activates alpha and gamma flexor neurons, and inhibits extensors. Deiters' nucleus forms the vestibulospinal tract and excites alpha and gamma extensor neurons. The reticular formation of the pons activates alpha and gamma neurons of the extensors and inhibits the flexors. The reticular formation of the medulla oblongata activates alpha and gamma flexor motor neurons and inhibits extensors. Decerebrate rigidity demonstrates the role of brainstem centers in the regulation of tone and posture. It occurs when the central nervous system is cut below the red nucleus. It consists of an increase in extensor tone, which is manifested in the characteristic posture of the animal. This phenomenon is explained by the predominance of the tonic influence of the Deiters nucleus on extensor motor neurons. The proof is the elimination of rigidity after transection of the central nervous system below the medulla oblongata. In the occurrence of decerebrate rigidity, the gamma loop is of significant importance, since deafferentation of the limb eliminates it. Tonic reflexes of the brain stem are divided into static and statokinetic; static ones, in turn, are divided into posnotonic and installation ones. Posnotonic reflexes are provided mainly by the bulbar region. Associated with a certain redistribution of flexor and extensor tone in the process of maintaining a pose. For the implementation of this group of reflexes, afferentation from skeletal muscles is important. Setting reflexes are closed at the level of the midbrain. They are more complex and consist of a dynamic redistribution of antagonist muscle tone in the process of taking a pose. Their implementation is very difficult in the absence or disruption of afferent impulses from the receptors of the vestibular apparatus, proprioceptors, and exteroceptors of the skin. The sequence of chain reflex reactions of the attitudinal reflex is as follows: irritation of the receptors of the vestibular apparatus - turning the head upward - irritation of the proprioceptors of the neck - rotation of the body - irritation of the exteroceptors of the body - taking a position that is comfortable for the animal. Statokinetic reflexes arise during linear or angular acceleration. These are the most complex reflexes of the brain stem. They are carried out with the participation of all its structures. Thus, motor reflexes of the brain stem ensure the coordinated work of many muscle groups in the process of maintaining a posture and changing it. These reflexes are necessarily used during complex motor acts (walking) due to the connections of the brain stem with the cerebellum and basal ganglia. The stem centers are the highest subcortical centers providing direct action. Complex motor acts are associated with the implementation of action programs laid down at the level of higher motor centers. 8.4. The cerebellum in ensuring motor activity. It is neither a sensory, nor a motor, nor an integrative formation of the central nervous system in the reflex sense. It stands apart from the main inputs and outputs of the central nervous system and serves as a structure that directs and coordinates the activity of other centers of the brain. It is most developed in animals with an active lifestyle. 67 Anatomically, the cerebellum consists of the vermis and two hemispheres. There are three layers in the cortex: 1 - superficial or molecular, 2 - layer of Purkinje cells, - 3 - granular layer. The white matter contains the cerebellar nuclei. Cerebellar afferent connections can be divided into three categories: 1) pathways from the vestibular nerves and their nuclei, 2) somatosensory pathways from the spinal cord, 3) descending pathways from the cerebral cortex. Efferent connections are addressed through the thalamus to the motor cortex, as well as to the subcortical motor centers. Basic functions of the cerebellum. 1 - regulation of posture, muscle tone, balance, supporting movements. The cerebellar vermis is responsible for its implementation, which, receiving impulses from the somatosensory system, regulates the brain stem centers responsible for maintaining skeletal muscle tone and posture (Deiters nucleus and the reticular formation of the medulla oblongata). When it is violated, atony and de-equilibration develop. 2 - correction of slow, purposeful movements during their execution. and coordinating them with the reflexes of maintaining a posture. Provided by the pars intermedius of the cerebellum. It receives incoming information from the motor and somatosensory areas about the upcoming movement and the position of the body in space. Outgoing impulses addressed to the motor cortex and brainstem centers provide correction of motor acts during their execution. Outgoing impulses to the brainstem centers ensure that the posture corresponds to the purposeful motor act being performed. 3 - ensuring highly coordinated fast movements. Software function. Provided by the cerebellar hemispheres. At their level, information about the intention of action coming from the associative zones of the cortex activates neural circuits that store information about action programs. Programs are addressed through the motor nucleus of the thalamus to the motor cortex and brain stem centers for tonic support of movements. This function is compensated last. Thus, the cerebellum not only modulates already begun motor acts, but also ensures the creation and storage of individual programs for fast, highly coordinated movements. 8.5. Functions of the basal ganglia in the regulation of movements. 68 Perform the function of software for stereotypical, slow, ("worm-like") movements. These motor programs are specific and genetically determined. Destruction of the structures of the basal ganglia or disruption of connections between them leads to akinesia (the beginning and end of movement are disrupted), rigidity (like general muscle hypertonicity), and resting tremor (disappears after the start of movement). Dysfunction of the substantia nigra leads to impairment of small highly coordinated movements and resting tremor (Parkinson's disease). Functionally, the basal ganglia are synergistic with the cerebellum. These functionally equivalent centers provide different motor programs. The cerebellum - fast movements, the basal ganglia - slow. The programs of the basal ganglia are genetically fixed, while those of the cerebellum are acquired. Differences in the function performed are reflected in the consequences of lesions of these structures. Removal of the cerebellum causes action tremor, destruction of the basal ganglia causes rest tremor. Removal of the cerebellum leads to muscle atony; damage to the basal ganglia causes their hypertonicity. The striopallidal system (basal ganglia system) includes the following brain structures: striatum (striatum), globus pallidus (pallidum), substantia nigra, subthalamic nucleus, amygdala. Afferents of the striatum come from all areas of the cortex, thalamus, and substantia nigra. Its efferents are addressed to the substantia nigra, globus pallidus, and ultimately through the thalamus to the motor cortex. In this case, the cortical intention of the action turns into a specific program, which is implemented by the action through the activation of the motor cortex and brain stem centers. 8.6. Motor cortex in providing motor action. Functionally, it is the lowest level of the organization of the action program and highest level its implementation directly into action. In the structure of the motor cortex, two patterns revealed in experiments with electrical stimulation of its different areas can be traced. 1 - somatotopic organization involves a certain projection of certain movements onto the precentral gyrus. The area of these projections is proportional to the complexity of the movements performed, but not to the proportions of the body (the area of the tongue is proportional to the representation of the torso). 69 2 - the multiplicity of representation is that in the cortex, in addition to the precentral gyrus (primary motor zone M1), there is a secondary motor zone located in the interhemispheric fissure (M11). Somatosensory areas S1 and S11 also have motor projections. Thus, we can talk about the existence of 4 motor areas of the cortex M1, M11, S1, S11. Their significance decreases from M1 to S11. Functional organization. The efferent pathways are formed by the axons of Betz's giant pyramidal cells. These neurons form functional cortical columns with a diameter of about 1 mm, located perpendicular to the surface of the cortex. They feature specific movements. Morphological motor columns have a smaller diameter (about 80 µm). They represent specific muscle groups. Since any motor act is associated with coordinated excitation and inhibition of certain groups of neurons, it is believed that the motor cortex represents not individual muscle groups, but certain movements. In this case, the cortical representation of skeletal muscles is preserved, but becomes multiple. The same muscle group can be represented in different columns and participate in different movements. Efferent connections of the motor cortex are provided by the corticospinal tract, which consists of axons of motor cortex neurons that form monosynaptic contacts on spinal motor neurons. It also contains efferents to the cranial nerves (corticobulbar tract). 90% of the fibers of the corticospinal tract decussate in the region of the pyramids and form the lateral corticospinal tract. These tracts form pyramidal tracts, and the system of connections between the motor cortex and the motor neurons of the spinal cord is called the pyramidal system. Descending to the spinal cord, the pyramidal tracts give collaterals to the thalamus, red nucleus, pons, cerebellum, and reticular formation of the medulla oblongata. Functionally, the pyramidal system provides targeted motor acts. Movements that are carried out with its participation are considered voluntary, although this is not entirely true. From the motor cortex there are conductive pathways to the subcortical motor centers - the red nucleus, the reticular formation of the pons and the medulla oblongata (corticorubral tracts, rubrospinal tracts, corticoreticular tracts, reticulospinal tracts). Together they form the extrapyramidal pathways, and the system of connections between the motor cortex and the subcortical nuclei - the extrapyramidal system. 70
The function of maintaining muscle tone is provided by the principle of feedback at various levels of regulation of the body. Peripheral regulation is carried out with the participation of the gamma loop, which includes supraspinal motor pathways, interneurons, the descending reticular system, alpha and gamma neurons.
There are two types of gamma fibers in the anterior horn of the spinal cord. Gamma-1 fibers ensure the maintenance of dynamic muscle tone, i.e. tone necessary for the implementation of the movement process. Gamma-2 fibers regulate the static innervation of muscles, i.e. posture, posture of a person. Central regulation of the functions of the gamma loop is carried out by the reticular formation through the reticulospinal tract. The main role in maintaining and changing muscle tone is given to the functional state of the segmental arc of the stretch reflex (myotatic or proprioceptive reflex). Let's take a closer look at it.
Its receptor element is the encapsulated muscle spindle. Each muscle contains a large number of these receptors. The muscle spindle consists of intrafusal muscle fibers (thin) and a nuclear bursa, braided by a spiral-shaped network of thin nerve fibers, which are the primary sensory endings (anulospinal filament). Some intrafusal fibers also have secondary, grape-shaped sensory endings. When intrafusal muscle fibers are stretched, the primary sensory endings strengthen the impulses emanating from them, which are carried through fast-conducting gamma-1 fibers to the alpha-large motor neurons of the spinal cord. From there, through also fast-conducting alpha-1 efferent fibers, the impulse goes to the extrafusal white muscle fibers, which provide rapid (phasic) muscle contraction. From secondary sensory endings that respond to muscle tone, afferent impulses are carried along thin gamma-2 fibers through a system of interneurons to alpha small motor neurons, which innervate the tonic extrafusal muscle fibers (red), which maintain tone and posture.
Intrafusal fibers are innervated by gamma neurons of the anterior horns of the spinal cord. Excitation of gamma neurons, transmitted along gamma fibers to the muscle spindle, is accompanied by contraction of the polar sections of the intrafusal fibers and stretching of their equatorial part, while the initial sensitivity of the receptors to stretch changes (the threshold of excitability of stretch receptors decreases, and tonic tension of the muscle increases).
Gamma neurons are influenced by central (suprasegmental) influences transmitted along fibers that come from motor neurons of the oral parts of the brain as part of the pyramidal, reticulospinal, and vestibulospinal tracts.
Moreover, if the role of the pyramidal system is primarily to regulate the phasic (i.e. fast, purposeful) components of voluntary movements, then the extrapyramidal system ensures their smoothness, i.e. predominantly regulates the tonic innervation of the muscular system. Thus, according to J. Noth (1991), spasticity develops after supraspinal or spinal damage to the descending motor systems with the obligatory involvement of the corticospinal tract in the process.
Inhibitory mechanisms also take part in the regulation of muscle tone, without which reciprocal interaction of antagonist muscles is impossible, and therefore, purposeful movements are impossible. They are realized with the help of Golgi receptors located in muscle tendons and Renshaw intercalary cells located in the anterior horns of the spinal cord. Golgi tendon receptors, when the muscle is stretched or significantly strained, send afferent impulses along fast-conducting type 1b fibers to the spinal cord and have an inhibitory effect on the motor neurons of the anterior horns. Renshaw intercalary cells are activated through collaterals when alpha motor neurons are excited, and act on the principle of negative feedback, contributing to the inhibition of their activity. Thus, the neurogenic mechanisms of regulation of muscle tone are diverse and complex.
When the pyramidal tract is damaged, the gamma loop is disinhibited, and any irritation by stretching the muscle leads to a constant pathological increase in muscle tone. In this case, damage to the central motor neuron leads to a decrease in inhibitory effects on motor neurons as a whole, which increases their excitability, as well as on interneurons of the spinal cord, which helps to increase the number of impulses reaching alpha motor neurons in response to muscle stretching.
Other causes of spasticity include structural changes at the level of the segmental apparatus of the spinal cord that arise as a result of damage to the central motor neuron: shortening of the dendrites of alpha motor neurons and collateral sprouting (proliferation) of afferent fibers that make up the dorsal roots.
Secondary changes also occur in muscles, tendons and joints. Therefore, the mechanical-elastic characteristics of muscle and connective tissue, which determine muscle tone, suffer, which further enhances movement disorders.
Currently, an increase in muscle tone is considered as a combined lesion of the pyramidal and extrapyramidal structures of the central nervous system, in particular the corticoreticular and vestibulospinal tracts. Moreover, among the fibers that control the activity of the gamma neuron-muscle spindle system, inhibitory fibers usually suffer to a greater extent, while activating fibers retain their influence on the muscle spindles.
The consequence of this is muscle spasticity, hyperreflexia, the appearance of pathological reflexes, as well as the primary loss of the most subtle voluntary movements.
The most significant component of muscle spasm is pain. Painful impulses activate alpha and gamma motor neurons of the anterior horns, which increases the spastic contraction of the muscle innervated by this segment of the spinal cord. At the same time, muscle spasm that occurs during the sensorimotor reflex increases the stimulation of the muscle's nociceptors. Thus, according to the negative feedback mechanism, a vicious circle is formed: spasm - pain - spasm - pain.
In addition, local ischemia develops in spasmodic muscles, since algogenic chemicals (bradykinin, prostaglandins, serotonin, leukotrienes, etc.) have a pronounced effect on the vessels, causing vasogenic tissue edema. Under these conditions, substance “P” is released from the terminals of type “C” sensory fibers, as well as the release of vasoactive amines and increased microcirculatory disorders.
Data on the central cholinergic mechanisms of muscle tone regulation are also of interest. Renshaw cells have been shown to be activated by acetylcholine through both motor neuron collaterals and the reticulospinal system.
M. Schieppati et al., (1989) found that pharmacological activation of central cholinergic systems significantly reduces the excitability of alpha motor neurons by increasing the activity of Renshaw cells.
IN last years researchers in the regulation of muscle tone attach great importance to the role of descending adrenergic supraspinal pathways starting in the locus coeruleus. Anatomically, these formations are closely related to the spinal structures, especially to the anterior horns of the spinal cord. Norepinephrine, released from the bulbospinal fiber terminals, activates adrenergic receptors located in interneurons, primary afferent terminals and motor neurons and simultaneously acts on alpha and beta adrenergic receptors in the spinal cord (D. Jones et al., 1982). Numerous axons of pain sensitivity approach the nuclear formations of the reticular formation of the trunk. Based on information entering the reticular formation of the brain stem, somatic and visceral reflexes are built. From the nuclear formations of the reticular formation, connections are formed with the thalamus, hypothalamus, basal ganglia and limbic system, which ensure the implementation of neuroendocrine and affective manifestations of pain, which is especially important in chronic pain syndromes.
As a result, the resulting vicious circle includes muscle spasm, pain, local ischemia, and degenerative changes, which self-support each other, reinforcing the root cause of pathological changes.
It should be borne in mind that the more components of this vicious circle that are targeted in treatment, the higher the likelihood of its success. Therefore, modern requirements for muscle relaxant therapy are: the power of the muscle relaxant effect, its selectivity, the presence of anticonvulsant and anticlonic effects, the power of the analgesic effect, as well as the safety and availability of a wide therapeutic range of doses of the drug.
According to modern concepts, most muscle relaxants act on transmitters or neuromodulators of the central nervous system. The effects may include suppression of excitatory mediators (aspartate and glutamate) and/or enhancement of inhibitory processes (GABA, glycine).
