The second neuron of the pyramidal motor pathway is located. motor pyramidal tract
The main efferent structure is the central motor neuron, represented by giant Betz pyramidal cells of the V layer of the projection motor cortex (prerolandic gyrus and paracentral lobule, 4th field). The set of processes of Betz cells is part of the pyramidal pathway. A significant part of its fibers originate from other parts of the cerebral cortex: the secondary motor cortex of the inner surface of the frontal lobe, the superior frontal gyrus, the premotor cortex (6th field), as well as the postcentral gyrus, and not only from the large pyramidal cells of layer V, but also from small pyramidal cells of layer III and from others. Most of the fibers of the pyramidal pathway terminate in the formations of the extrapyramidal system - the striatum, the pale ball, the substantia nigra, the red nucleus, and also in the reticular formation of the brain stem, carrying out the interaction of the pyramidal and extrapyramidal systems. Other fibers, especially the thickly myelinated ones, originate from the giant Betz cells of the projection motor cortex and end on the dendrites of the peripheral motor neuron.
The motor neuron is located in two places - the anterior horns of the spinal cord and in the motor nuclei of the cranial nerves, and therefore the pyramidal path consists of two paths - corticospinal and corticonuclear (Fig. 1.2.1).
The main part of the fibers of the corticospinal tract at the border of the medulla oblongata and spinal cord passes to the other side and there it goes in the lateral cords of the spinal cord, ending segmentally: most of the path is in the anterior horns of the cervical and lumbar thickening, the motor neurons of which innervate the limbs, its other part goes on its side in the anterior canal. Presumably the muscles of the trunk have a bilateral innervation.
The corticonuclear pathway ends in the brain stem on the dendrites of the motor nuclei of the cranial nerves. material from the site
The functional principle of somatotopic localization is implemented in the projection motor cortex: the representation of the muscles that perform the most complex and significant voluntary movements occupies the maximum area. This applies to the facial muscles (facial expression is a means of biocommunication), the muscles of the tongue, pharynx, larynx (articulation is the basis of motor speech), as well as the hands, especially the fingers of the hand and the hand itself, presented respectively in the lower and middle parts of the projection motor cortex. (Fig. 1.2.2). The latter occupies the back of the outer surface of the frontal lobe (precentral gyrus). Anterior to the projection motor cortex is the premotor cortex, which plays an important role in transforming movements into actions, and anterior to the premotor cortex is the prefrontal cortex, which is responsible for the implementation of holistic activities. The premotor cortex is also part of the extrapyramidal system. When complex motor skills are mastered, they are already performed automatically according to programs read from the premotor cortex.
Lesions of the projection motor cortex cause central paralysis, premotor - disturbances in action (praxis), and prefrontal - activity. The prefrontal cortex is also important in upright walking in humans, and its defeat leads to a disorder of standing and walking.
The pyramidal system (synonymous with the pyramidal path) is a collection of long efferent projection fibers of the motor analyzer, originating mainly in the anterior central gyrus of the cerebral cortex, ending on the motor cells of the anterior horns of the spinal cord and on the cells of the motor nuclei that perform voluntary movements.
The pyramidal path goes from the cortex, from the giant pyramidal Betz cells of layer V of field 4 as part of the radiant crown, occupying the anterior two-thirds of the posterior femur and the knee of the internal brain bag. Then it passes through the middle third of the base of the brain stem into the bridge (varoli). In the medulla oblongata, the pyramidal system forms compact bundles (pyramids), some of the fibers of which, at the level of the border between the medulla oblongata and the spinal cord, pass to the opposite side (the cross of the pyramids). In the brainstem from the pyramidal system to the nuclei of the facial and hypoglossal nerves and to the motor nuclei, fibers depart, crossing slightly above or at the level of these nuclei. In the spinal cord, the crossed fibers of the pyramidal system occupy the posterior part of the lateral cords, and the uncrossed fibers occupy the anterior cords of the spinal cord. The motor analyzer receives afferent impulses from muscles, joints and. These impulses pass to the cerebral cortex through the optic tubercle, from where they reach the posterior central gyrus.
In the anterior and posterior central gyri, there are distributions of cortical points for individual muscles, coinciding with the distribution of the corresponding muscles of the body. Irritation of the cortical part of the pyramidal system, for example, by a scar of the meninges, causes Jackson's seizures (see). With the loss of the function of the pyramidal system in the brain (see), paralysis or paresis appears (see), as well as pyramidal symptoms (increased tendon and the appearance of pathological reflexes, increased muscle paralyzed muscles). Damage to the corticonuclear pathways of the facial nerve leads to central paresis of this nerve. The center of defeat of pyramidal system in the field of an internal bag conducts to a hemiplegia (see). Damage to the pyramidal system in the brain stem gives a combination of pyramidal symptoms on the opposite side with symptoms of damage to the nuclei of the cranial nerves on the side of the lesion - alternating syndromes (see). Damage to the pyramidal system in the spinal cord - see.
The pyramidal system (tractus pyramidalis; synonymous with the pyramidal path) is a system of long efferent projection fibers of the motor analyzer, originating in the anterior central gyrus of the cerebral cortex (cytoarchitectonic fields 4 and c) and partially from other fields and areas. The pyramidal system got its name from the so-called pyramids of the medulla oblongata, formed on its ventral surface by the pyramidal tracts passing there.
In lower vertebrates, the pyramidal system is absent. It appears only in mammals, and its importance in evolution is gradually increasing. In humans, the pyramidal system reaches its maximum development, and its fibers in the spinal cord occupy about 30% of the area of the diameter (in higher monkeys 21.1%, in dogs 6.7%). The representation of the pyramidal system in the cerebral cortex is the core of the motor analyzer. In lower mammals, the nucleus of the motor analyzer is not spatially separated from the nucleus of the skin analyzer and has a granular layer IV (a sign of the sensitive cortex). These nuclei mutually overlap, becoming more and more isolated from each other as phylogenetic development proceeds. They are most isolated in humans, although they also have remnants of overlap in the form of fields 3/4 and 5. In ontogenesis, the cortical nucleus of the motor analyzer differentiates early - at the beginning of the second half of uterine life. Until birth, area 4 retains granular layer IV, which is a repetition in ontogeny of features found in the early stages of mammalian phylogenesis. The myelin lining of the nerve fibers of the pyramidal system is carried out during the 1st year of life.
In an adult, the main cortical representation of the pyramidal system corresponds to the cytoarchitectonic fields 4 and 6 of the anterior central gyrus of the brain. Field 4 is characterized by the presence of giant pyramidal Betz cells in layer V, agranularity (absence of granular layers) and a large cortex width (about 3.5 mm). Field 6 has a similar structure, but does not have Betz's giant pyramidal cells. From these fields, from Betz's giant pyramidal cells and from other pyramidal cells of layers V and III, and according to modern data, from other fields and areas of the cerebral cortex, the pyramidal tract originates. It is formed by descending fibers of caliber from 1 to 8 microns and more, which, in the white matter of the cerebral hemispheres, converge in the radiant crown towards the inner bag, where, forming a compact bundle, they occupy the anterior two-thirds of her hind thigh and knee.
Then the fibers of the pyramidal system go to the middle third of the base of the brain stem. Entering the bridge, they break up into separate small bundles passing among the transversely located fibers of the frontal-bridge-cerebellar pathway and the own nuclei of the bridge. In the medulla oblongata, the fibers of the pyramidal system are again assembled into a compact bundle and form pyramids. Here, most of the fibers pass to the opposite side, making up the intersection of the pyramids. In the brainstem, fibers to the motor cranial nerves (corticonuclear; tractns corticonuclearis) and to the anterior horns of the spinal cord (corticospinal; tractus corticospinals lat. et ant.) run together to the lower edge of the superior olive. Then the corticonuclear pathway gradually gives its fibers to the motor nuclei of the facial, hypoglossal, trigeminal and vagus nerves. These fibers cross at the level of the nuclei or directly above them. Cortico-spinal fibers descend into the spinal cord (see), where the crossing fibers of the pyramidal system are concentrated in the lateral column, occupying its back, and the non-crossing fibers pass in the anterior column. Terminating on the motor cells of the anterior horns (or intercalary cells) of the spinal cord, the fibers of the pyramidal system, gradually exhausted, reach the sacral spinal cord. The number of fibers of the pyramidal system exceeds 1 million. In addition to motor, there are also vegetative fibers.
The cortical section of the pyramidal system, or the motor zone of the cerebral cortex, is the core of the motor analyzer. The analyzer, or afferent, nature of this nucleus is confirmed by afferent fibers coming to it from the thalamus. It has been established that the fibers of the pyramidal system originate from a wider area of the cerebral cortex than the anterior central gyrus and the pyramidal system is closely connected with the extrapyramidal system, especially in the cortical region (Fig. 1). Therefore, with a variety of localizations of brain lesions, the pyramidal system usually suffers to one degree or another.
Physiologically, the pyramidal system is a system that performs voluntary movements, although the latter are ultimately the result of the activity of the entire brain. In the anterior central gyrus, there is a somatotopic distribution of cortical points for individual muscles, electrical stimulation of which causes discrete movements of these muscles. Especially widely represented are the muscles that perform the most subtle working voluntary movements (Fig. 2).
Rice. 1. Scheme of the pyramidal tract and the distribution of its places of origin in the cerebral cortex: 1 - limbic region; 2 - parietal region; 3 - precentral area; 4 - frontal area; 5 - island region; 6 - temporal region; 7 - visual tubercle; 8 - inner bag. 
Rice. 2. Scheme of the somatotopic distribution of the muscles of the limbs, trunk and face in the cortex of the anterior central gyrus (according to Penfield and Baldry).
Lesions of the pyramidal system in lower mammals do not cause significant impairment of motor functions. The higher the mammal is organized, the more significant these violations. Pathological processes in the cortical part of the pyramidal system, especially in the anterior central gyrus, irritating the cerebral cortex, cause partial (partial), or Jacksonian, epilepsy, manifested mainly by clonic convulsions of the muscles of the opposite half of the face, trunk and limbs on the opposite side. Loss of functions of the pyramidal system are manifested by paralysis, paresis.
Lesions of the pyramidal system are detected by neurological examination of voluntary (active) movements, their volume in various joints, muscle strength, muscle tone and reflexes in combination with other neurological symptoms. Electroencephalography and electromyography are gaining more and more diagnostic value. With a unilateral lesion of the cerebral cortex in the zone of the anterior central gyrus, monoplegia and monoparesis of the arm or leg of the opposite side of the body are most often observed. Damage to the corticonuclear pathways of the facial nerve is usually expressed by central paresis of the lower and middle branches of this nerve. The upper branch is usually less affected due to its bilateral innervation, although its defeat can often be detected (the patient cannot close his eye on the side of the lesion in isolation). A focal lesion of the pyramidal system in the region of the internal bag usually leads to hemiplegia (or hemiparesis), and with bilateral damage to tetraplegia.
Lesions of the pyramidal system in the region of the brain stem are determined by the combination of pyramidal symptoms on the opposite side with damage to the nuclei of the cranial nerves or their roots on the side of the lesion, that is, by the presence of alternating syndromes (see).
With pyramidal hemiplegia and hemiparesis, the distal extremities usually suffer the most.
Hemiplegia and hemiparesis in the defeat of the pyramidal system are usually characterized by an increase in tendon reflexes, an increase in muscle tone, loss of skin reflexes, especially plantar reflexes, the appearance of pathological reflexes - extensor (Babinsky, Oppenheim, Gordon, etc.) and flexor (Rossolimo, Mendel - Bekhterev, etc.). ), as well as protective reflexes. Tendon and periosteal reflexes are evoked from the extended zone. There are cross reflexes and friendly movements - the so-called synkinesis (see). In the initial stages of pyramidal hemiplegia, muscle tone (and sometimes reflexes) is reduced due to diaschism (see). An increase in muscle tone is detected later - after 3-4 weeks from the onset of the lesion. Most often, especially with capsular lesions, an increase in muscle tone predominates in the flexors of the forearm and extensors of the lower leg. Such a distribution of muscle hypertension leads to the appearance of contractures of the Wernicke-Mann type (see Wernicke-Mann type of contractures).
Neurology and neurosurgery Evgeny Ivanovich Gusev
3.1. pyramid system
3.1. pyramid system
There are two main types of movements: involuntary and arbitrary.
Involuntary include simple automatic movements carried out by the segmental apparatus of the spinal cord and brain stem in the form of a simple reflex act. Arbitrary purposeful movements are acts of human motor behavior. Special voluntary movements (behavioral, labor, etc.) are carried out with the leading participation of the cerebral cortex, as well as the extrapyramidal system and the segmental apparatus of the spinal cord. In humans and higher animals, the implementation of voluntary movements is associated with the pyramidal system. In this case, the conduction of an impulse from the cerebral cortex to the muscle occurs along a chain consisting of two neurons: central and peripheral.
Central motor neuron. Voluntary muscle movements occur due to impulses traveling along long nerve fibers from the cerebral cortex to the cells of the anterior horns of the spinal cord. These fibers form the motor ( cortical-spinal), or pyramidal, path. They are axons of neurons located in the precentral gyrus, in cytoarchitectonic field 4. This zone is a narrow field that stretches along the central fissure from the lateral (or Sylvian) groove to the anterior part of the paracentral lobule on the medial surface of the hemisphere, parallel to the sensory area of the postcentral gyrus cortex .
The neurons that innervate the pharynx and larynx are located in the lower part of the precentral gyrus. Next in ascending order are the neurons that innervate the face, arm, torso, and leg. Thus, all parts of the human body are projected in the precentral gyrus, as it were, upside down. Motor neurons are located not only in field 4, they are also found in neighboring cortical fields. At the same time, the vast majority of them are occupied by the 5th cortical layer of the 4th field. They are "responsible" for precise, targeted single movements. These neurons also include Betz giant pyramidal cells, which have axons with a thick myelin sheath. These fast-conducting fibers make up only 3.4-4% of all fibers of the pyramidal tract. Most of the fibers of the pyramidal tract originate from small pyramidal, or fusiform (fusiform) cells in motor fields 4 and 6. The cells of field 4 give about 40% of the fibers of the pyramidal tract, the rest originate from cells of other fields of the sensorimotor zone.
Field 4 motoneurons control fine voluntary movements of the skeletal muscles of the opposite half of the body, since most of the pyramidal fibers pass to the opposite side in the lower part of the medulla oblongata.
The impulses of the pyramidal cells of the motor cortex follow two paths. One - the cortical-nuclear pathway - ends in the nuclei of the cranial nerves, the second, more powerful, cortical-spinal - switches in the anterior horn of the spinal cord on the intercalary neurons, which in turn terminate in the large motor neurons of the anterior horns. These cells transmit impulses through the anterior roots and peripheral nerves to the motor end plates of the skeletal muscles.
When the fibers of the pyramidal tract leave the motor cortex, they pass through the corona radiata of the white matter of the brain and converge towards the posterior leg of the internal capsule. In somatotopic order, they pass through the internal capsule (its knee and the anterior two-thirds of the posterior thigh) and go to the middle part of the legs of the brain, descend through each half of the base of the bridge, being surrounded by numerous nerve cells of the nuclei of the bridge and fibers of various systems. At the level of the pontomedullary articulation, the pyramidal pathway becomes visible from the outside, its fibers forming elongated pyramids on either side of the midline of the medulla oblongata (hence its name). In the lower part of the medulla oblongata, 80-85% of the fibers of each pyramidal tract pass to the opposite side at the intersection of the pyramids and form lateral pyramidal tract. The remaining fibers continue to descend uncrossed in the anterior cords as anterior pyramidal tract. These fibers cross at the segmental level through the anterior commissure of the spinal cord. In the cervical and thoracic parts of the spinal cord, some fibers connect with the cells of the anterior horn of their side, so that the muscles of the neck and trunk receive cortical innervation from both sides.
Crossed fibers descend as part of the lateral pyramidal tract in the lateral cords. About 90% of the fibers form synapses with interneurons, which in turn connect with large alpha and gamma neurons of the anterior horn of the spinal cord.
The fibers that form cortical-nuclear pathway, are sent to the motor nuclei (V, VII, IX, X, XI, XII) of the cranial nerves and provide voluntary innervation of the facial and oral muscles.
Noteworthy is another bundle of fibers, starting in the "eye" field 8, and not in the precentral gyrus. The impulses going along this bundle provide friendly movements of the eyeballs in the opposite direction. The fibers of this bundle at the level of the radiant crown join the pyramidal pathway. Then they pass more ventrally in the posterior crus of the internal capsule, turn caudally and go to the nuclei of the III, IV, VI cranial nerves.
Peripheral motor neuron. Fibers of the pyramidal tract and various extrapyramidal tracts (reticular, tegmental, vestibulo, red nuclear-spinal, etc.) and afferent fibers entering the spinal cord through the posterior roots terminate on the bodies or dendrites of large and small alpha and gamma cells (directly or through intercalary, associative or commissural neurons of the internal neuronal apparatus of the spinal cord) In contrast to the pseudo-unipolar neurons of the spinal nodes, the neurons of the anterior horns are multipolar. Their dendrites have multiple synaptic connections with various afferent and efferent systems. Some of them are facilitating, others are inhibitory in their action. In the anterior horns, motor neurons form groups organized in columns and not divided into segments. There is a certain somatotopic order in these columns. In the cervical part, the lateral motor neurons of the anterior horn innervate the hand and arm, and the motor neurons of the medial columns innervate the muscles of the neck and chest. In the lumbar region, the neurons innervating the foot and leg are also located laterally in the anterior horn, while those innervating the trunk are medial. The axons of the anterior horn cells exit the spinal cord ventrally as radicular fibers, which gather in segments to form the anterior roots. Each anterior root connects to the posterior root distally to the spinal nodes and together they form the spinal nerve. Thus, each segment of the spinal cord has its own pair of spinal nerves.
The composition of the nerves also includes efferent and afferent fibers emanating from the lateral horns of the spinal gray matter.
Well myelinated, fast-conducting axons of large alpha cells run directly to the striated muscle.
In addition to large and small alpha motor neurons, the anterior horns contain numerous gamma motor neurons. Among the intercalary neurons of the anterior horns, Renshaw cells, which inhibit the action of large motor neurons, should be noted. Large alpha cells with a thick and fast-conducting axon carry out rapid muscle contractions. Small alpha cells with a thinner axon perform a tonic function. Gamma cells with a thin and slow-conducting axon innervate the proprioceptors of the muscle spindle. Large alpha cells are associated with giant cells in the cerebral cortex. Small alpha cells have a connection with the extrapyramidal system. Through gamma cells, the state of muscle proprioceptors is regulated. Among the various muscle receptors, the neuromuscular spindles are the most important.
afferent fibers called ring-spiral, or primary, endings, have a fairly thick myelin coating and are fast-conducting fibers.
Many muscle spindles have not only primary but also secondary endings. These endings also respond to stretch stimuli. Their action potential propagates in the central direction along thin fibers communicating with intercalary neurons responsible for the reciprocal actions of the corresponding antagonist muscles. Only a small number of proprioceptive impulses reach the cerebral cortex, most are transmitted through feedback loops and do not reach the cortical level. These are the elements of reflexes that serve as the basis for voluntary and other movements, as well as static reflexes that oppose gravity.
Extrafusal fibers in a relaxed state have a constant length. When the muscle is stretched, the spindle is stretched. The ring-spiral endings respond to stretching by generating an action potential, which is transmitted to the large motor neuron along fast-conducting afferent fibers, and then again along fast-conducting thick efferent fibers - extrafusal muscles. The muscle contracts, its original length is restored. Any stretching of the muscle activates this mechanism. Percussion along the tendon of a muscle causes stretching of this muscle. The spindles react immediately. When the impulse reaches the motor neurons of the anterior horn of the spinal cord, they react by causing a short contraction. This monosynaptic transmission is the basis for all proprioceptive reflexes. The reflex arc covers no more than 1-2 segments of the spinal cord, which is of great importance in determining the localization of the lesion.
Gamma neurons are under the influence of fibers descending from the motor neurons of the CNS as part of such pathways as pyramidal, reticular-spinal, vestibulo-spinal. The efferent influences of gamma fibers make it possible to finely regulate voluntary movements and provide the ability to regulate the strength of the response of receptors to stretch. This is called the gamma-neuron-spindle system.
Research methodology. Inspection, palpation and measurement of muscle volume are carried out, the volume of active and passive movements, muscle strength, muscle tone, rhythm of active movements and reflexes are determined. Electrophysiological methods are used to identify the nature and localization of movement disorders, as well as clinically insignificant symptoms.
The study of motor function begins with an examination of the muscles. Attention is drawn to the presence of atrophy or hypertrophy. By measuring the volume of the muscles of the limb with a centimeter, it is possible to identify the severity of trophic disorders. When examining some patients, fibrillar and fascicular twitches are noted. With the help of palpation, you can determine the configuration of the muscles, their tension.
active movements are checked sequentially in all joints and performed by the subject. They may be absent or limited in scope and weakened in strength. The complete absence of active movements is called paralysis, the restriction of movements or the weakening of their strength is called paresis. Paralysis or paresis of one limb is called monoplegia or monoparesis. Paralysis or paresis of both arms is called upper paraplegia or paraparesis, paralysis or paraparesis of the legs is called lower paraplegia or paraparesis. Paralysis or paresis of two limbs of the same name is called hemiplegia or hemiparesis, paralysis of three limbs - triplegia, paralysis of four limbs - quadriplegia or tetraplegia.
Passive movements are determined with complete relaxation of the muscles of the subject, which makes it possible to exclude a local process (for example, changes in the joints), which limits active movements. Along with this, the definition of passive movements is the main method for studying muscle tone.
Investigate the volume of passive movements in the joints of the upper limb: shoulder, elbow, wrist (flexion and extension, pronation and supination), finger movements (flexion, extension, abduction, adduction, opposition of the first finger to the little finger), passive movements in the joints of the lower extremities: hip, knee, ankle (flexion and extension, rotation outward and inward), flexion and extension of the fingers.
muscle strength is determined consistently in all groups with active resistance of the patient. For example, when examining the strength of the muscles of the shoulder girdle, the patient is asked to raise his arm to a horizontal level, resisting the examiner's attempt to lower his arm; then they offer to raise both hands above the horizontal line and hold them, offering resistance. To determine the strength of the shoulder muscles, the patient is asked to bend the arm at the elbow joint, and the examiner tries to straighten it; the strength of the abductors and adductors of the shoulder is also examined. To study the strength of the muscles of the forearm, the patient is given the task to perform pronation, and then supination, flexion and extension of the hand with resistance during the movement. To determine the strength of the muscles of the fingers, the patient is offered to make a “ring” of the first finger and each of the others, and the examiner tries to break it. They check the strength when the V finger is abducted from the IV and the other fingers are brought together, when the hands are clenched into a fist. The strength of the muscles of the pelvic girdle and thigh is examined when asked to raise, lower, adduct and abduct the thigh, while providing resistance. The strength of the thigh muscles is examined, inviting the patient to bend and straighten the leg at the knee joint. The strength of the calf muscles is checked as follows: the patient is asked to bend the foot, and the examiner keeps it extended; then the task is given to unbend the foot bent at the ankle joint, overcoming the resistance of the examiner. The strength of the muscles of the toes is also examined when the examiner tries to bend and unbend the fingers and separately bend and unbend the first finger.
To identify paresis of the extremities, a Barre test is performed: the paretic arm, extended forward or raised up, gradually lowers, the leg raised above the bed also gradually lowers, while the healthy one is held in the given position. With mild paresis, one has to resort to a test for the rhythm of active movements; pronate and supinate hands, clench hands into fists and unclench them, move legs like on a bicycle; the insufficiency of the strength of the limb is manifested in the fact that it is more likely to get tired, the movements are performed not so quickly and less dexterously than with a healthy limb. The strength of the hands is measured with a dynamometer.
Muscle tone- reflex muscle tension, which provides preparation for movement, maintaining balance and posture, the ability of the muscle to resist stretching. There are two components of muscle tone: own muscle tone, which depends on the characteristics of the metabolic processes occurring in it, and neuromuscular tone (reflex), reflex tone is more often caused by muscle stretching, i.e. irritation of proprioreceptors, determined by the nature of the nerve impulses that reach this muscle. It is this tone that underlies various tonic reactions, including antigravitational ones, carried out under conditions of maintaining the connection of muscles with the central nervous system.
The basis of tonic reactions is the stretch reflex, the closure of which occurs in the spinal cord.
Muscle tone is influenced by the spinal (segmental) reflex apparatus, afferent innervation, reticular formation, as well as cervical tonic, including vestibular centers, cerebellum, red nucleus system, basal nuclei, etc.
The state of muscle tone is assessed during examination and palpation of the muscles: with a decrease in muscle tone, the muscle is flabby, soft, pasty. with increased tone, it has a denser texture. However, the determining factor is the study of muscle tone through passive movements (flexors and extensors, adductors and abductors, pronators and supinators). Hypotension is a decrease in muscle tone, atony is its absence. A decrease in muscle tone can be detected when examining Orshansky's symptom: when lifting up (in a patient lying on his back) a leg unbent at the knee joint, its overextension in this joint is revealed. Hypotension and muscle atony occur with peripheral paralysis or paresis (violation of the efferent section of the reflex arc with damage to the nerve, root, cells of the anterior horn of the spinal cord), damage to the cerebellum, brain stem, striatum and posterior cords of the spinal cord. Muscle hypertension is the tension felt by the examiner during passive movements. There are spastic and plastic hypertension. Spastic hypertension - an increase in the tone of the flexors and pronators of the arm and extensor and adductors of the leg (with damage to the pyramidal tract). With spastic hypertension, there is a symptom of a “penknife” (an obstacle to passive movement in the initial phase of the study), with plastic hypertension, a symptom of a “cog wheel” (feeling of tremors during the study of muscle tone in the limbs). Plastic hypertension is a uniform increase in the tone of muscles, flexors, extensors, pronators and supinators, which occurs when the pallidonigral system is damaged.
reflexes. A reflex is a reaction that occurs in response to irritation of receptors in the reflexogenic zone: muscle tendons, skin of a certain part of the body, mucous membrane, pupil. By the nature of the reflexes, the state of various parts of the nervous system is judged. In the study of reflexes, their level, uniformity, asymmetry are determined: at an increased level, a reflexogenic zone is noted. When describing reflexes, the following gradations are used: 1) live reflexes; 2) hyporeflexia; 3) hyperreflexia (with an extended reflex zone); 4) areflexia (absence of reflexes). Reflexes can be deep, or proprioceptive (tendon, periosteal, articular), and superficial (skin, mucous membranes).
Tendon and periosteal reflexes are evoked by percussion with a hammer on the tendon or periosteum: the response is manifested by the motor reaction of the corresponding muscles. To obtain tendon and periosteal reflexes on the upper and lower extremities, it is necessary to call them in an appropriate position favorable for the reflex reaction (lack of muscle tension, average physiological position).
Upper limbs. Biceps tendon reflex caused by a hammer blow on the tendon of this muscle (the patient's arm should be bent at the elbow joint at an angle of about 120 °, without tension). In response, the forearm flexes. Reflex arc: sensory and motor fibers of the musculocutaneous nerve, CV-CVI. Triceps tendon reflex caused by a blow of the hammer on the tendon of this muscle above the olecranon (the patient's arm should be bent at the elbow joint almost at an angle of 90 °). In response, the forearm extends. Reflex arc: radial nerve, СVI-СVII. Beam reflex caused by percussion of the styloid process of the radius (the patient's arm should be bent at the elbow joint at an angle of 90 ° and be in a position between pronation and supination). In response, flexion and pronation of the forearm and flexion of the fingers occur. Reflex arc: fibers of the median, radial and musculocutaneous nerves, CV-CVIII.
lower limbs. knee jerk caused by hammer blow on the tendon of the quadriceps muscle. In response, the leg is extended. Reflex arc: femoral nerve, LII-LIV. When examining the reflex in a horizontal position, the patient's legs should be bent at the knee joints at an obtuse angle (about 120 °) and lie freely on the examiner's left forearm; when examining the reflex in the sitting position, the patient's legs should be at an angle of 120 ° to the hips or, if the patient does not rest with his feet on the floor, freely hang over the edge of the seat at an angle of 90 ° to the hips or one leg of the patient is thrown over the other. If the reflex cannot be evoked, then the Endrashik method is used: the reflex is evoked at the time when the patient pulls towards the hand with tightly clasped fingers. Calcaneal (Achilles) reflex caused by percussion on the calcaneal tendon. In response, plantar flexion of the foot occurs as a result of contraction of the calf muscles. Reflex arc: tibial nerve, SI-SII. In a lying patient, the leg should be bent at the hip and knee joints, the foot at the ankle joint at an angle of 90 °. The examiner holds the foot with the left hand, and the calcaneal tendon is percussed with the right hand. In the position of the patient on the stomach, both legs are bent at the knee and ankle joints at an angle of 90 °. The examiner holds the foot or sole with one hand, and strikes with a hammer with the other. The reflex is caused by a short blow to the heel tendon or sole. The study of the heel reflex can be done by placing the patient on his knees on the couch so that the feet are bent at an angle of 90 °. In a patient sitting on a chair, you can bend the leg at the knee and ankle joints and cause a reflex by percussing the calcaneal tendon.
Articular reflexes are caused by irritation of the receptors of the joints and ligaments on the hands. 1. Mayer - opposition and flexion in the metacarpophalangeal and extension in the interphalangeal articulation of the first finger with forced flexion in the main phalanx of the III and IV fingers. Reflex arc: ulnar and median nerves, СVII-ThI. 2. Leri - flexion of the forearm with forced flexion of the fingers and the hand in the supination position, reflex arc: ulnar and median nerves, CVI-ThI.
Skin reflexes are caused by stroke stimulation with the handle of the neurological malleus in the corresponding skin zone in the position of the patient on his back with slightly bent legs. Abdominal reflexes: upper (epigastric) is caused by irritation of the abdominal skin along the lower edge of the costal arch. Reflex arc: intercostal nerves, ThVII-ThVIII; medium (mesogastric) - with irritation of the skin of the abdomen at the level of the navel. Reflex arc: intercostal nerves, ThIX-ThX; lower (hypogastric) - with skin irritation parallel to the inguinal fold. Reflex arc: ilio-hypogastric and ilio-inguinal nerves, ThXI-ThXII; there is a contraction of the abdominal muscles at the appropriate level and the deviation of the navel in the direction of irritation. The cremaster reflex is triggered by stimulation of the inner thigh. In response, the testicle is pulled up due to the contraction of the muscle that lifts the testicle, the reflex arc: the femoral-genital nerve, LI-LII. Plantar reflex - plantar flexion of the foot and fingers with dashed irritation of the outer edge of the sole. Reflex arc: tibial nerve, LV-SII. Anal reflex - contraction of the external sphincter of the anus with tingling or dashed irritation of the skin around it. Called in the position of the subject on the side with the legs brought to the stomach. Reflex arc: pudendal nerve, SIII-SV.
Pathological reflexes . Pathological reflexes appear when the pyramidal tract is damaged, when spinal automatisms are disturbed. Pathological reflexes, depending on the reflex response, are divided into extensor and flexion.
Pathological extensor reflexes on the lower extremities. The Babinsky reflex is of the greatest importance - extension of the first toe with dashed irritation of the skin of the outer edge of the sole, in children under 2-2.5 years old - a physiological reflex. Oppenheim reflex - extension of the first toe in response to running fingers along the tibial crest down to the ankle joint. Gordon's reflex - slow extension of the first toe and fan-shaped divergence of other fingers during compression of the calf muscles. Schaefer's reflex - extension of the first toe with compression of the calcaneal tendon.
Flexion pathological reflexes on the lower extremities. The most important is the Rossolimo reflex - flexion of the toes with a quick tangential blow to the balls of the fingers. Bekhterev-Mendel reflex - flexion of the toes when hit with a hammer on its back surface. Zhukovsky reflex - flexion of the toes when struck with a hammer on its plantar surface directly under the fingers. Ankylosing spondylitis reflex - flexion of the toes when struck with a hammer on the plantar surface of the heel. It should be borne in mind that the Babinski reflex appears with an acute lesion of the pyramidal system, for example, with hemiplegia in the case of a cerebral stroke, and the Rossolimo reflex is a late manifestation of spastic paralysis or paresis.
Flexion pathological reflexes on the upper limbs. Tremner reflex - flexion of the fingers in response to quick tangential irritations by the fingers of the examiner of the palmar surface of the terminal phalanges of the II-IV fingers of the patient. Jacobson's reflex - Weasel - combined flexion of the forearm and fingers in response to a hammer blow on the styloid process of the radius. Zhukovsky reflex - flexion of the fingers of the hand when struck with a hammer on its palmar surface. Bekhterev's carpal-finger reflex - flexion of the fingers of the hand during percussion with the hammer of the back of the hand.
Pathological protective, or spinal automatism, reflexes on the upper and lower extremities- involuntary shortening or lengthening of a paralyzed limb during a prick, pinch, cooling with ether or proprioceptive irritation according to the Bekhterev-Marie-Foy method, when the examiner makes a sharp active flexion of the toes. Protective reflexes are often flexion in nature (involuntary flexion of the leg in the ankle, knee and hip joints). The extensor protective reflex is characterized by involuntary extension of the leg in the hip and knee joints and plantar flexion of the foot. Cross-protective reflexes - flexion of the irritated leg and extension of the other are usually noted with a combined lesion of the pyramidal and extrapyramidal tracts, mainly at the level of the spinal cord. When describing protective reflexes, the form of the reflex response, the reflexogenic zone, is noted. the reflex evoking area and the intensity of the stimulus.
Neck tonic reflexes arise in response to irritations associated with a change in the position of the head in relation to the body. Magnus-Klein reflex - increased extensor tone in the muscles of the arm and leg, towards which the head is turned with the chin, flexor tone in the muscles of opposite limbs when turning the head; flexion of the head causes an increase in flexor, and extension of the head - extensor tone in the muscles of the limbs.
Gordon reflex- delay of the lower leg in the extension position when inducing a knee jerk. Foot phenomenon (Westphalian)- "freezing" of the foot with its passive dorsiflexion. Foix-Thevenard's Shin Phenomenon- incomplete extension of the lower leg in the knee joint in a patient lying on his stomach, after the lower leg was kept in the position of extreme flexion for some time; manifestation of extrapyramidal rigidity.
Yaniszewski's grasping reflex on the upper limbs - involuntary grasping of objects in contact with the palm; on the lower extremities - increased flexion of the fingers and feet during movement or other irritation of the sole. Distant grasping reflex - an attempt to capture an object shown at a distance. It is observed with damage to the frontal lobe.
An expression of a sharp increase in tendon reflexes are clonuses, manifested by a series of rapid rhythmic contractions of a muscle or group of muscles in response to their stretching. Foot clonus is caused in a patient lying on his back. The examiner flexes the patient's leg in the hip and knee joints, holds it with one hand, and with the other hand grabs the foot and, after maximum plantar flexion, jerks the foot dorsiflexion. In response, rhythmic clonic movements of the foot occur during the time of stretching the calcaneal tendon. Clonus of the patella is caused in a patient lying on his back with straightened legs: fingers I and II grab the top of the patella, pull it up, then sharply shift it in the distal direction and hold it in this position; in response, a series of rhythmic contractions and relaxations of the quadriceps femoris muscle and a twitching of the patella appear.
Synkinesia- reflex friendly movement of a limb or other part of the body, accompanying the voluntary movement of another limb (part of the body). Pathological synkinesis is divided into global, imitation and coordinating.
Global, or spastic, is called pathological synkinesis in the form of an increase in flexion contracture in a paralyzed arm and extensor contracture in a paralyzed leg when trying to move paralyzed limbs or when actively moving healthy limbs, tensing the muscles of the trunk and neck, coughing or sneezing. Imitative synkinesis is an involuntary repetition by paralyzed limbs of voluntary movements of healthy limbs on the other side of the body. Coordinator synkinesis manifests itself in the form of additional movements performed by paretic limbs in the process of a complex purposeful motor act.
contractures. Persistent tonic muscle tension, causing limitation of movement in the joint, is called contracture. Distinguish in shape flexion, extensor, pronator; by localization - contractures of the hand, foot; monoparaplegic, tri- and quadriplegic; according to the method of manifestation - persistent and unstable in the form of tonic spasms; by the time of occurrence after the development of the pathological process - early and late; in connection with pain - protective-reflex, antalgic; depending on the damage to various parts of the nervous system - pyramidal (hemiplegic), extrapyramidal, spinal (paraplegic), meningeal, with damage to peripheral nerves, such as the facial one. Early contracture - hormetonia. It is characterized by periodic tonic spasms in all limbs, the appearance of pronounced protective reflexes, dependence on intero- and exteroceptive stimuli. Late hemiplegic contracture (Wernicke-Mann posture) - bringing the shoulder to the body, flexion of the forearm, flexion and pronation of the hand, extension of the thigh, lower leg and plantar flexion of the foot; when walking, the foot describes a semicircle.
Semiotics of movement disorders. Having revealed, on the basis of a study of the volume of active movements and their strength, the presence of paralysis or paresis caused by a disease of the nervous system, determine its nature: whether it occurs due to damage to the central or peripheral motor neurons. The defeat of the central motor neurons at any level of the cortical-spinal tract causes the occurrence central, or spastic, paralysis. With the defeat of peripheral motor neurons in any area (anterior horn, root, plexus and peripheral nerve), peripheral, or sluggish, paralysis.
Central motor neuron : damage to the motor area of the cerebral cortex or the pyramidal pathway leads to the cessation of the transmission of all impulses for the implementation of voluntary movements from this part of the cortex to the anterior horns of the spinal cord. The result is paralysis of the corresponding muscles. If the interruption of the pyramidal tract occurs suddenly, the stretch reflex is suppressed. This means that the paralysis is initially flaccid. It may take days or weeks for this reflex to recover.
When this happens, the muscle spindles will become more sensitive to stretch than before. This is especially evident in the flexors of the arm and extensors of the leg. Hypersensitivity of stretch receptors is caused by damage to the extrapyramidal pathways that terminate in the cells of the anterior horns and activate gamma motor neurons that innervate intrafusal muscle fibers. As a result of this phenomenon, the impulses along the feedback rings that regulate the length of the muscles change so that the flexors of the arm and the extensors of the leg are fixed in the shortest possible state (the position of the minimum length). The patient loses the ability to voluntarily inhibit hyperactive muscles.
Spastic paralysis always indicates damage to the central nervous system, i.e. brain or spinal cord. The result of damage to the pyramidal tract is the loss of the most subtle voluntary movements, which is best seen in the hands, fingers, and face.
The main symptoms of central paralysis are: 1) a decrease in strength combined with a loss of fine movements; 2) spastic increase in tone (hypertonicity); 3) increased proprioceptive reflexes with or without clonus; 4) decrease or loss of exteroceptive reflexes (abdominal, cremasteric, plantar); 5) the appearance of pathological reflexes (Babinsky, Rossolimo, etc.); 6) protective reflexes; 7) pathological friendly movements; 8) the absence of the reaction of rebirth.
Symptoms vary depending on the location of the lesion in the central motor neuron. The defeat of the precentral gyrus is characterized by two symptoms: focal epileptic seizures (Jacksonian epilepsy) in the form of clonic convulsions and central paresis (or paralysis) of the limb on the opposite side. Paresis of the leg indicates a lesion of the upper third of the gyrus, the hand - its middle third, half of the face and tongue - its lower third. It is diagnostically important to determine where clonic convulsions begin. Often, convulsions, starting in one limb, then move to other parts of the same half of the body. This transition is made in the order in which the centers are located in the precentral gyrus. Subcortical (radiant crown) lesion, contralateral hemiparesis in the arm or leg, depending on which part of the precentral gyrus the focus is closer to: if to the lower half, then the arm will suffer more, to the upper - the leg. Damage to the internal capsule: contralateral hemiplegia. Due to the involvement of corticonuclear fibers, there is a violation of innervation in the area of the contralateral facial and hypoglossal nerves. Most cranial motor nuclei receive pyramidal innervation from both sides in whole or in part. Rapid damage to the pyramidal tract causes contralateral paralysis, initially flaccid, as the lesion has a shock-like effect on peripheral neurons. It becomes spastic after a few hours or days.
Damage to the brain stem (brain stem, pons, medulla oblongata) is accompanied by damage to the cranial nerves on the side of the focus and hemiplegia on the opposite side. Cerebral peduncle: A lesion in this area results in contralateral spastic hemiplegia or hemiparesis, which may be associated with ipsilateral (on the side of the lesion) oculomotor nerve lesion (Weber's syndrome). Brain pons: If affected in this area, contralateral and possibly bilateral hemiplegia develops. Often not all pyramidal fibers are affected.
Since the fibers descending to the nuclei of the VII and XII nerves are located more dorsally, these nerves may be intact. Possible ipsilateral involvement of the abducens or trigeminal nerve. The defeat of the pyramids of the medulla oblongata: contralateral hemiparesis. Hemiplegia does not develop, since only the pyramidal fibers are damaged. The extrapyramidal pathways are located dorsally in the medulla oblongata and remain intact. If the chiasm of the pyramids is damaged, a rare syndrome of cruciant (or alternating) hemiplegia develops (right arm and left leg and vice versa).
For the recognition of focal lesions of the brain in patients in a coma, the symptom of a rotated outward foot is important. On the side opposite the lesion, the foot is turned outward, as a result of which it rests not on the heel, but on the outer surface. In order to determine this symptom, you can use the method of maximum turn of the feet outward - Bogolepov's symptom. On the healthy side, the foot immediately returns to its original position, and the foot on the side of hemiparesis remains turned outward.
If the pyramidal tract is damaged below the decussation in the brainstem or upper cervical segments of the spinal cord, hemiplegia occurs involving the ipsilateral limbs or, in the case of bilateral damage, tetraplegia. Damage to the thoracic spinal cord (involvement of the lateral pyramidal tract) causes spastic ipsilateral monoplegia of the leg; bilateral involvement leads to lower spastic paraplegia.
Peripheral motor neuron : damage can capture the anterior horns, anterior roots, peripheral nerves. In the affected muscles, neither voluntary nor reflex activity is detected. Muscles are not only paralyzed, but also hypotonic; there is an areflexia due to interruption of the monosynaptic arc of the stretch reflex. After a few weeks, atrophy sets in, as well as the reaction of the degeneration of paralyzed muscles. This indicates that the cells of the anterior horns have a trophic effect on muscle fibers, which is the basis for normal muscle function.
It is important to determine exactly where the pathological process is localized - in the anterior horns, roots, plexuses or in peripheral nerves. When the anterior horn is affected, the muscles innervated from this segment suffer. Often in atrophying muscles, rapid contractions of individual muscle fibers and their bundles are observed - fibrillar and fascicular twitches, which are the result of irritation by the pathological process of neurons that have not yet died. Since the innervation of the muscles is polysegmental, complete paralysis requires the defeat of several neighboring segments. Involvement of all the muscles of the limb is rarely observed, since the cells of the anterior horn, supplying various muscles, are grouped in columns located at some distance from each other. The anterior horns can be involved in the pathological process in acute poliomyelitis, amyotrophic lateral sclerosis, progressive spinal muscular atrophy, syringomyelia, hematomyelia, myelitis, and circulatory disorders of the spinal cord. With damage to the anterior roots, almost the same picture is observed as with the defeat of the anterior horns, because the occurrence of paralysis here is also segmental. Paralysis of the radicular character develops only with the defeat of several neighboring roots.
Each motor root at the same time has its own “indicator” muscle, which makes it possible to diagnose its lesion by fasciculations in this muscle on an electromyogram, especially if the cervical or lumbar region is involved in the process. Since the defeat of the anterior roots is often caused by pathological processes in the membranes or vertebrae, simultaneously involving the posterior roots, movement disorders are often combined with sensory disturbances and pain. Damage to the nerve plexus is characterized by peripheral paralysis of one limb in combination with pain and anesthesia, as well as autonomic disorders in this limb, since the plexus trunks contain motor, sensory and autonomic nerve fibers. Often there are partial lesions of the plexuses. When a mixed peripheral nerve is damaged, peripheral paralysis of the muscles innervated by this nerve occurs, in combination with sensory disturbances caused by a break in the afferent fibers. Damage to a single nerve can usually be explained by mechanical causes (chronic compression, trauma). Depending on whether the nerve is completely sensory, motor or mixed, sensory, motor or autonomic disturbances occur, respectively. The damaged axon does not regenerate in the CNS, but can regenerate in the peripheral nerves, which is ensured by the preservation of the nerve sheath, which can guide the growing axon. Even if the nerve is completely severed, bringing its ends together with a suture can lead to complete regeneration. The defeat of many peripheral nerves leads to widespread sensory, motor and autonomic disorders, most often bilateral, mainly in the distal segments of the extremities. Patients complain of paresthesia and pain. Sensitive disorders such as "socks" or "gloves", flaccid muscle paralysis with atrophy, and trophic skin lesions are revealed. Polyneuritis or polyneuropathy is noted, arising from many reasons: intoxication (lead, arsenic, etc.), alimentary deficiency (alcoholism, cachexia, cancer of internal organs, etc.), infectious (diphtheria, typhoid, etc.), metabolic ( diabetes mellitus, porphyria, pellagra, uremia, etc.). Sometimes it is not possible to establish the cause and this condition is regarded as idiopathic polyneuropathy.
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- this is two-neuron path (2 neurons central and peripheral) , connecting the cerebral cortex with the skeletal (striated) muscles (cortical-muscular path). The pyramidal path is a pyramidal system, the system that provides arbitrary movements.
Central neuron
Central the neuron is located in the Y layer (a layer of large Betz pyramidal cells) of the anterior central gyrus, in the posterior sections of the superior and middle frontal gyri, and in the paracentral lobule. There is a clear somatic distribution of these cells. The cells located in the upper part of the precentral gyrus and in the paracentral lobule innervate the lower limb and trunk, located in its middle part - the upper limb. In the lower part of this gyrus, there are neurons that send impulses to the face, tongue, pharynx, larynx, chewing muscles.
The axons of these cells are in the form of two conductors:
1) cortico-spinal path (otherwise called the pyramidal tract) - from the upper two-thirds of the anterior central gyrus
2) cortico-bulbar tract - from the lower part of the anterior central gyrus) go from the cortex deep into the hemispheres, pass through the internal capsule (the cortico-bulbar path - in the knee area, and the cortico-spinal path through the anterior two-thirds of the posterior thigh of the internal capsule).
Then the legs of the brain, the bridge, the medulla oblongata pass, and at the border of the medulla oblongata and the spinal cord, the cortico-spinal tract undergoes an incomplete decussation. A large, crossed part of the path passes into the lateral column of the spinal cord and is called the main, or lateral, pyramidal bundle. The smaller uncrossed part passes into the anterior column of the spinal cord and is called the direct uncrossed bundle.
The fibers of the cortico-bulbar tract terminate at motor nuclei cranial nerves (Y, YII, IX, X, XI, XII ), and the fibers of the cortico-spinal tract - in anterior horns of the spinal cord . Moreover, the fibers of the cortico-bulbar tract undergo a decussation sequentially, as they approach the corresponding nuclei of the cranial nerves (“supranuclear” decussation). For the oculomotor, masticatory muscles, muscles of the pharynx, larynx, neck, trunk and perineum, there is a bilateral cortical innervation, i.e., to some of the motor nuclei of the cranial nerves and to some levels of the anterior horns of the spinal cord, the fibers of the central motor neurons approach not only from the opposite side, but also with his own, thus ensuring the approach of impulses from the cortex not only of the opposite, but also of his own hemisphere. Unilateral (only from the opposite hemisphere) innervation have limbs, tongue, lower facial muscles. The axons of the motor neurons of the spinal cord are sent to the corresponding muscles as part of the anterior roots, then the spinal nerves, plexuses, and finally the peripheral nerve trunks.
peripheral neuron
peripheral neuron starts from the places where the first one ended: the fibers of the dagger-bulbar path ended on the nuclei of the cranial nerves, which means they go as part of the cranial nerves, and the cortico-spinal path ended in the anterior horns of the spinal cord, which means it goes as part of the anterior roots of the spinal nerves, then peripheral nerves, reaching the synapse.
Central and peripheral paralysis develop with the homonymous lesion of a neuron.
pyramid system- a system of efferent neurons, whose bodies are located in the cerebral cortex, terminate in the motor nuclei of the cranial nerves and the gray matter of the spinal cord. As part of the pyramidal tract (tractus pyramidalis), cortical-nuclear fibers (fibrae corticonucleares) and cortical-spinal fibers (fibrae corticospinales) are isolated. Both those and others are axons of nerve cells of the inner, pyramidal, layer cerebral cortex . They are located in the precentral gyrus and adjacent fields of the frontal and parietal lobes. In the precentral gyrus, the primary motor field is localized, where pyramidal neurons are located that control individual muscles and muscle groups. In this gyrus there is a somatotopic representation of the musculature. The neurons that control the muscles of the pharynx, tongue and head occupy the lower part of the gyrus; above are areas associated with the muscles of the upper limb and trunk; the projection of the muscles of the lower limb is located in the upper part of the precentral gyrus and passes to the medial surface of the hemisphere.
The pyramidal pathway is formed mainly by thin nerve fibers that pass through the white matter of the hemisphere and converge to the internal capsule ( rice. 1 ). Cortical-nuclear fibers form the knee, and cortical-spinal fibers form the anterior 2/3 of the posterior leg of the internal capsule. From here, the pyramidal pathway continues to the base of the brain stem and further to the anterior part of the pons (see Fig. Brain ). Throughout the brainstem, cortical-nuclear fibers pass to the opposite side to the dorsolateral areas of the reticular formation, where they switch to motor nuclei III, IV, V, VI, VII, IX, X, XI, XII cranial nerves ; only uncrossed fibers go to the upper third of the nucleus of the facial nerve. Part of the fibers of the pyramidal pathway passes from the brain stem to the cerebellum.
In the medulla oblongata, the pyramidal path is located in the pyramids, which form a cross (decussatio pyramidum) on the border with the spinal cord. Above the decussation, the pyramidal pathway contains 700,000 to 1,300,000 nerve fibers on one side. As a result of crossing, 80% of the fibers pass to the opposite side and form in the lateral funiculus spinal cord lateral cortical-spinal (pyramidal) path. Non-crossed fibers from the medulla oblongata continue into the anterior funiculus of the spinal cord in the form of an anterior cortical-spinal (pyramidal) path. The fibers of this path pass to the opposite side throughout the spinal cord in its white commissure (segmentally). Most of the cortical-spinal fibers terminate in the intermediate gray matter of the spinal cord on its intercalary neurons, only a part of them form synapses directly with the motor neurons of the anterior horns, which give rise to the motor fibers of the spinal cord. nerves . About 55% of the cortical-spinal fibers terminate in the cervical segments of the spinal cord, 20% in the thoracic segments, and 25% in the lumbar segments. The anterior corticospinal tract continues only to the middle thoracic segments. Due to the intersection of fibers in P. s. the left hemisphere of the brain controls the movements of the right half of the body, and the right hemisphere controls the movements of the left half of the body, however, the muscles of the trunk and upper third of the face receive fibers of the pyramidal pathway from both hemispheres.
P.'s function with. consists in the perception of a program of voluntary movement and the conduction of impulses from this program to the segmental apparatus of the brain stem and spinal cord.
In clinical practice, P.'s condition with. determined by the nature of arbitrary movements. The range of motion and the force of contraction of the striated muscles are assessed according to a six-point system (full muscle strength - 5 points, "compliance" of muscle strength - 4 points, a moderate decrease in strength with a full range of active movements - 3 points, the possibility of a full range of movements only after the relative elimination of gravity limbs - 2 points, the safety of movement with a barely noticeable muscle contraction - 1 point and the absence of voluntary movement - 0). The strength of muscle contraction can be quantitatively assessed using a dynamometer. To assess the safety of the pyramidal cortical-nuclear pathway to the motor nuclei of the cranial nerves, tests are used that determine the function of the muscles of the head and neck innervated by these nuclei, the corticospinal tract - in the study of the muscles of the trunk and limbs. The defeat of the pyramidal system is also judged by the state of muscle tone and muscle trophism.
Pathology. Violations of P.'s function with. observed in many pathological processes. In P.'s neurons with and their long axons, metabolic disturbances often occur, which lead to degenerative-dystrophic changes in these structures. Violations are genetically determined or are the result of intoxication (endogenous, exogenous), as well as viral damage to the genetic apparatus of neurons. Degeneration is characterized by a gradual, symmetrical and progressive dysfunction of pyramidal neurons, primarily those with the longest axons, i.e. ending at the peripheral motor neurons of the lumbar thickening. Therefore, the pyramidal in such cases is first detected in the lower extremities. Strumpell's family spastic paraplegia belongs to this group of diseases (see. Paraplegia ), portocaval encephalomyelopathy, funicular myelosis , as well as Mills syndrome - unilateral ascending of unclear etiology. It usually begins at the age of 35-40 to 60 years with a central thorax of the distal parts of the lower limb,
which gradually spreads to the proximal parts of the lower, and then to the entire upper limb and turns into spastic hemiplegia with autonomic and trophic disorders in the paralyzed limbs. P. s. often affected by slow viral infections, such as amyotrophic lateral , scattered and others. Almost always in the clinical picture of focal lesions of the brain and spinal cord there are signs of dysfunction of the pyramidal system. With vascular lesions of the brain (hemorrhage,) pyramidal disorders develop acutely or subacutely with progression in chronic cerebrovascular insufficiency. P. s. may be involved in the pathological process encephalitis and myelitis , at traumatic brain injury and spinal cord injury , with tumors of the central nervous system, etc.At P.'s defeat with. central s and paralysis with characteristic disorders of voluntary movements. Muscle tone increases according to the spastic type (muscle trophism usually does not change) and deep reflexes on the limbs, skin reflexes (abdominal, cremasteric) decrease or disappear, pathological reflexes appear on the hands - Rossolimo - Venderovich, Yakobson - Lask, Bekhterev, Zhukovsky, Hoffmann, on the feet - Babinsky, Oppenheim, Chaddock, Rossolimo, Bekhterev, etc. (see. reflexes ). Juster's symptom is characteristic of pyramidal insufficiency: a pin prick of the skin in the area of the eminence of the thumb causes the thumb to flex and bring it to the index finger while simultaneously extending the remaining fingers and dorsiflexing the hand and forearm. Quite often, a symptom of a folding knife is revealed: with passive extension of the spastic upper limb and flexion of the lower limb, the examiner first experiences a sharp springy resistance, which then suddenly weakens. At P.'s defeat with. global, coordinating and imitation synkinesis .
P.'s defeat diagnosis with. established on the basis of a study of the patient's movements and the identification of signs of pyramidal insufficiency (the presence of a or a, increased muscle tone, increased deep reflexes, clonuses, pathological hand and foot signs), clinical course and the results of special studies (electroneuromyography, electroencephalography, tomography, etc.). ).
The differential diagnosis of pyramidal paralysis is carried out with peripheral ami and ami,
that develop with damage to peripheral motor neurons. The latter are also characterized by paretic muscles, a decrease in muscle tone (hypo- and atony), a weakening or absence of deep reflexes, changes in the electrical excitability of muscles and nerves (rebirth reaction). At acute development of P.'s defeat of page. in the first few hours or days, there is often a decrease in muscle tone and deep reflexes in paralyzed limbs. It is related to the state diaschiza , after the elimination of which there is an increase in muscle tone and deep reflexes. At the same time, pyramidal signs (Babinski's symptom, etc.) are also detected against the background of signs of diaschisis.Treatment of P.'s defeats with. directed at the underlying disease. Drugs are used that improve metabolism in nerve cells (nootropil, cerebrolysin, encephabol, glutamic acid, aminalon), nerve impulse conduction (prozerin, dibazol), microcirculation (vasoactive drugs), normalizing muscle tone (mydocalm, baclofen, lioresal), vitamins of the group C, E. Exercise therapy, massage (point) and reflexotherapy are widely used to reduce muscle tone; physio- and balneotherapy, orthopedic measures. Neurosurgical treatment is performed for tumors and injuries of the brain and spinal cord, as well as for a number of acute cerebrovascular accidents (with e or e extracerebral arteries, intracerebral hematoma, malformations of cerebral vessels, etc.).
Bibliography: Blinkov S.M. and Glezer I.I. The human brain in figures and tables, p. 82, L., 1964; Diseases of the nervous system, ed. P.V. Melnichuk, vol. 1, p. 39, M., 1982; Granite R. Fundamentals of regulation of movements, translated from English, M., 1973; Gusev E.I., Grechko V.E. and Burd G.S. Nervous diseases, p. 66, M., 1988; Dzugaeva S.B. Pathways of the human brain (in ontogeny), p. 92, M., 1975; Kostyuk P.K. Structure and function of the descending systems of the spinal cord, L. 1973; Lunev D.K. Violation of muscle tone in cerebral e, M. 1974; Multi-volume guide to neurology, ed. N.I. Grashchenkova, vol. 1, book. 2, p. 182, Moscow, 1960; Skoromets D.D. Topical diagnosis of diseases of the nervous system, p. 47, L., 1989; Turygin V.V. Pathways of the brain and spinal cord, Omsk. 1977.
