PYRAMIDAL SYSTEM [tractus pyramidalis (PNA)] — system of the efferent projective nerve fibrils connecting motoriums of a cerebral cortex with motive kernels of cranial nerves and cells of kernels of front horns of a spinal cord and participating in implementation of autokinesias. Page received the name P. from the pyramids formed by fibers of a cortical and spinal (pyramidal) way and located on a ventral surface myelencephalon (see).
Comparative anatomy. In the course of P.'s phylogenesis by the village for the first time appears at mammals. At the lowest mammals its cortical center is not isolated from originally undifferentiated bark. The upper floor of bark is poorly developed, consists of two narrow layers (II and III). Much more widely the first floor including layers of V and VI. At rodents it is already possible to allocate in bark of the field 4 and 6. At predatory in the field 4 colossal pyramidal cells come to light. In group of primacies there is a further increase in width of a layer of III. At the person structure of bark of the field 4 brains are characterized by the expressed piramidization of neurocytes, the arranged their look, a powerful layer of III, existence of gigantopiramidalny neurocytes (neurocytes, T.) in a layer of V, an agranu-lyarnost (absence clearly the expressed granular layers of II and IV; granular elements in them are replaced with small pyramidal cells), the maximum width of bark (3 — 4 mm). The similar structure is kept by the field 6, but gigantopiramidalny neurocytes in it are absent.
In ontogenesis the cortical center clearly stands apart at the beginning of the second half of pre-natal development and till the birth in it the layer of IV remains. At the adult the pyramidal way occupies apprx. 30% of cross-sectional area of a spinal cord, at the highest monkeys — more than 21%, At dogs — less than 7%.
Anatomy and histology
The efferent projective fibers which are P.'s part of page originate from pyramidal neurocytes of a ganglionic plate of a cerebral cortex (fig. 1); at the same time about 40% of these fibers begin from gigantopiramidalny neurocytes of the field 4 bark of the precentral crinkle and a paracentral segment of a brain (see. Very tectonics of a cerebral cortex ), 20% — from the pyramidal neurocytes located in bark of a postcentral crinkle and 40% — from pyramidal neurocytes of a back third of upper and average frontal crinkles, a front third of an upper parietal segment and a supramarginal crinkle of a brain. These fibers follow further in the descending direction, forming a pyramidal way. A part of fibers of a pyramidal way reaches a limit at cells of motive kernels cherepnomozgovy (cranial, T.) nerves also makes a cortical and nuclear way (tractus corticonuclearis), and other part — at motive cells of kernels of front horns of a spinal cord, making a front and lateral cortical and spinal (pyramidal) way [tractus corticospinales (pyramidales) ant. et lat.]. Going to kernels of cranial nerves and front horns of a spinal cord, fibers of a pyramidal way at first pass in structure of a radiate crown (corona radiata). Then they approach with each other and in the form of a compact bunch go to a brain trunk between a thalamus and a lenticular kernel; at the same time cortical and nuclear fibers, being located medially, occupy a knee, and cortical and spinal fibers — front two thirds of a back hip of the internal capsule. Further the pyramidal way passes through ventral department of a mesencephalon (the basis of a leg of a brain), a front (basilar) part of the bridge and a pyramid of a myelencephalon. In the bridge of fiber of a pyramidal way lose compactness, being divided by fibers of a mostomozzhechkovy way into small bunches. In a myelencephalon of fiber of a pyramidal way approach again and form the pyramids acting on its ventral surface. On the course one part of cortical and nuclear fibers gradually comes over to the opposite side, reaching a limit at cells of motive kernels of cranial nerves: oculomotor, block (on average a brain), trigeminal, taking away, front (in the bridge), glossopalatine, wandering, additional, hypoglossal (in a myelencephalon); other part of these fibers reaches the kernels of the same name on the party. In the bottom of a myelencephalon of 80% of cortical and spinal fibers comes over to the opposite side, forming decussation of pyramids (decussatio pyramidum), and as a part of side cords of a spinal cord, occupying their vnutrennezadny department, goes to front horns of a spinal cord and approaches its sacral segments. The smaller part of cortical and spinal fibers (20%) which is not participating in formation of decussation of pyramids remains on the party, goes down in a front cord of a spinal cord and posegmentno comes over to the opposite side through front white commissure. Thus, all cortical and spinal fibers are crossed. In front horns of gray columns of a spinal cord they come to an end posegmentno or directly at motor neurons, or take up with them through internuncial neurons. It is established that about 55% of all korkovospinnomozgovy fibers reach a limit in cervical segments of a spinal cord, 20% — in chest and 25% - in lumbar segments, and fibers of a front cortical and spinal way do not fall below chest segments. A part of fibers of pyramidal neurocytes of fields 4 would also reach a thalamus, basal kernels, a red kernel, black substance and a cerebellum. There is an interrelation between certain sites of a cerebral cortex and groups of muscles of various areas of a body. At the same time the right cerebral hemisphere provides management of the left half of a body of the movements, and left — right. The upper site of the precentral crinkle and paracentral segment is connected with muscles of the lower extremity, the average site — with muscles of a trunk and an upper extremity, and lower — with muscles of a neck and the head.
The pyramidal way consists of pulpy and amyelenic fibers to dia. 1 — 8 microns which number slightly above decussation of pyramids fluctuates from 700 000 to 1 300 000 on one party; fibers preferential thin, poorly myelinized (only apprx. 3% from them has a thick myelin cover), are axons of gigantopiramidalny neurocytes.
P. of page is the general for many motor reflex arcs. By means of microelectrode technics (see. Microelectrode method of a research ) it is established that gigantopiramidalny neurocytes of a cerebral cortex from which a part of fibers P. of page begins can become more active not only somatic, but also optical, acoustic, flavoring and other irritations. In this regard gigantopiramidalny neurocytes call polytouch, i.e. reacting to many types of touch irritants.
It is known that in pyramids of a myelencephalon there passes only the pyramidal way and it gives the chance in vitro to make the isolated P.'s damage by page at animals. Section of pyramids of a myelencephalon at dogs, e.g., leads to insignificant disturbances of motive functions. In the first days after operation disorder of gait is found in them, a cut in the next days disappears. The conditioned motive reflexes developed at dogs before operation remain also after it, and in a stage of compensation of motive frustration accurate bending conditioned reflexes are developed. The bilateral pyramidotomy at cats also does not interfere with recovery earlier developed and to formation of new conditioned motive and food reflexes. The isolated P.'s damage by page does not cause those disturbances, to-rye describe as a syndrome of pyramidal defeat. The clinical syndrome of pyramidal defeat, apparently, is caused by the combined damage of conductors of pyramidal system and the descending ways accompanying them extrapyramidal that leads to a disinhibition of vnu-trisegmentarny phasic and topical reflex activity. These data are confirmed a wedge, the observations which showed that a pedunkulotomiya (the isolated section of a pyramidal way in a leg of a brain) at various forms of motive disturbances (a hemiballism, a tremor, etc.) does not lead to spastic paralysis with increase in tendon jerks, and causes the opposite phenomena, such as decrease in a tone of muscles, lengthening of stage of latency of motor conditional reactions, their astenich-nost, etc. All this gave the grounds to some researchers to conclude that P. the page has tonic effect on spinal motor functions. The similar hypothesis was stated by Ch. Sherrington (1906) observing the phenomena of spinal shock (see. Spinal cord ) as a result of a pyramidotomy. However this mechanism is not universal. So, in particular, the pyramidotomy causes spinal shock only in the highest animals. Elektrofiziol, by researches it is established also that P. the page, making impact on the spinal motor centers, increases their functional activity, strengthens monosinaptichesky answers of fleksorny motor-neurons and suppresses answers of motor-neurons extensors. Pyramidal influences lead to braking of the muscles participating in tonic anti-gravitational reflexes and to activation of those muscles, to-rye participate in phase bending reflexes.
The item of page consists of two main components: fast-carrying out and medlennoprovodyashchy. The first provides bystry (phase) motor reactions of an organism. It consists of the thick nerve fibrils originating from gigantopiramidalny neurocytes of bark. The second component provides regulation of tonic reactions of any muscles and is presented by fine fibers.
The pyramidal system, thus, is an efferent link by means of which cortical regulation of activity of spinal motor-neurons is carried out. Loss of function P. of page can lead to a certain disturbance of this regulation. Rather bystry compensation of pyramidal disturbances at animals allows to assume that the impulsation going from cells of bark of big hemispheres reaches final motor-neuron not only through pyramidal, but also other ways, including in krasnoyaderno-spinal, preddverno-medullispinal, reticular and spinal and pokryshechno-spinal ways.
Dysfunction of P. of page of this or that degree of manifestation is observed at organic diseases and defeats of c. N of page. The symptom complex of defeat of P. of page is noted at many degenerative diseases of a nervous system, napr, at a side amyotrophic sclerosis, especially its form with preferential pyramidal insufficiency (see. Amyotrophic side sclerosis ), and a family spastic paraplegia of Shtryumpell (see. Paraplegia ). Carry Mills's syndrome to the same group of diseases — the unilateral ascending paralysis of not clear etiology beginning usually at the age of 40 — 60 years with the paresis of distal departments of the lower extremity extending gradually to proximal departments lower and upper extremities and passing then in full spastic hemiplegia (see) with vegetative, and sometimes and trophic disturbances on the paralyzed extremities. P.'s defeat by the village is often observed at disturbances of blood circulation in a head or spinal cord (see. Stroke , Crises ). At cerebral vascular crises signs of defeat of P. of page, as well as other focal symptoms, often have passing character and rather quickly disappear. Tumors of a head and spinal cord, infectious, intoksikatsionny and traumatic defeats of c quite often are followed by symptoms of pyramidal insufficiency. N of page. Disturbances of autokinesias, the central paresis and paralyzes with increase in a muscle tone on spastic type are characteristic of a pyramidal syndrome (see. Paralyses, paresis ), high tendon and periosteal jerks, absence or decrease in cutaneous reflexes — belly, a cremaster reflex (see. Belly reflexes , Reflex ), patol, reflexes, especially standing — Babinski's reflexes, Oppengeym, Gordon, Schäffer, Rossolimo, Mendel — Bekhtereva, etc. (see. Babinsky reflex , Gordon reflexes , Rossolima reflex , Reflexes pathological ); on hands reflexes of fleksorny group prevail. A characteristic pyramidal symptom is Zhyuster's symptom — the prick a pin of skin in the field of the tenor (an eminence of a thumb of a brush) causes bending of a thumb and its reduction to index at simultaneous extension of other fingers and a dorsiflexion of a brush and a forearm. The symptom of a penknife is quite often noted — at passive bending of a spastichny lower extremity and extension upper the hand investigating tests the sharp springing resistance, a cut then suddenly weakens. At P.'s defeat by the village come to light global, koordinatorny and imitating synkineses (see).
The wedge, options of defeat of P. of page are very various. Kapsulyarny is most often observed hemiplegia (see). It is characterized by spastic paralysis of extremities on the party opposite patol, to the center, with deeper damage of a hand, than leg, a typical pose of Vernike — Mann (fig. 2) and so naz> «gait of the mower».
Spasticity and then and a contracture of the paralyzed muscles arise owing to simultaneous defeat in the internal capsule of fibers of pyramidal: and extrapyramidal systems. At bilateral damage of a spinal cord below cervical, but above a lumbosacral thickening the spastic lower paraplegia is observed, and at localization patol, process above a cervical thickening — a tetraplegia (quadriplegia) or more rare trinlegiya.
Defeats of the cortical centers P. of page Due to the wide spatial somatotoppchesky relationship of cortical structures of these centers in cerebral hemispheres of their defeat most often differ in a big originality are shown as a monollegiya: paralysis of one hand or yoga, brush or foot and even separate fingers. Perhaps also defeat separate a skull-yaykh of nerves, is more often front and hypoglossal. Insufficiency of a facial nerve is shown by paralysis or paresis of muscles of the lower half of the face since they unlike an upper half of the face have a unilateral nadjyaderny innervation; at the same time the patient cannot sometimes close eyes (to close eyelids) on the paralyzed party (Reviyo's symptom).
P.'s defeat by the village is established on the basis of a research of a physical activity of the patient and identification of pyramidal symptoms, data of the anamnesis, features by a wedge, currents and results of special researches.
Differential diagnosis pyramidal paralyzes carry out with the flaccid paralyzes and paresis arising owing to damages of a peripheral motor neuron and which are characterized by a low muscle tone, decrease or lack of tendon and periosteal jerks, the expressed atrophy of muscles with change of their electroexcitability — reactions of degeneration (see. Paralyses, paresis ). It is necessary to consider that the decrease in a muscle tone noted sometimes at pyramidal paralyzes, tendon and periosteal jerks is, as a rule, connected with a state diaschisis (see) after which elimination there occurs increase in a tone and reflexes.
Treatment of defeats of pyramidal system is more often conservative, sometimes operational also is directed first of all to a basic disease. During the performing conservative treatment apply the pharmaceuticals improving metabolism in nervous tissue and carrying out nervous impulse, normalizing a muscle tone, etc. LFK, massage, a fiziobalneoterapiya, orthopedic treatment is widely used. Operational treatment is carried more often out at P.'s damages of page caused by tumors and injuries of a head and spinal cord, and also an acute disorder of cerebral circulation.
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