Pyramid system

Pyramid system (synonym pyramid path) - a set of long efferent projection fibers motor analyzer, originating mainly in the forward Central gyrus of a bark of a brain, ending with motor cells of the anterior horns of the spinal cord and in the cells of motor nuclei of craniocerebral nerves, carrying out arbitrary motion.
Pyramid path goes from the bark, large pyramidal cells Betz layer V field 4 as part of a radiant crown, occupying the front two-thirds of the back of the thigh and knee internal bags brain. Then goes through the middle third of the founding of the leg of a brain in the bridge (varolii). In the medulla pyramid system forms a compact beams (pyramids), part of fibers which are at the level of the border between oblong and spinal cord goes to the opposite side (the decussation of the pyramids). In the brain stem and pyramid system to the nuclei of the front and sublingual nerves and to the motor nuclei of the trigeminal nerve depart fiber, overlapping slightly above or on the level of these nuclei. In the spinal cord crossed fiber pyramid system occupy the rear side of the spermatic cord, neprikrashennaya - front spinal cord. Afferent impulses motor analyzer receives from the muscles, joints and ligaments. These pulses are to the brain via the optic promontory where appropriate to the back Central gyrus.
In the front and rear centre brains are distribution cortical points for individual muscles, coinciding with the distribution of the muscles of the body. Irritation of cortical part of the pyramid system, such as a scar membranes of the brain that causes seizures Jacksonian epilepsy (see). At loss of function pyramid system in the brain (see) appear paralysis or paresis (see Paralysis, paresis)and pyramidal symptoms (increased tendon and the emergence of pathological reflexes, increased muscle tone paralyzed muscles). Defeat kortiko-nuclear ways facial nerve leads to the Central paresis of this nerve. The lesion pyramid system in the field of internal bags leads to hemiplegia (see). Damage pyramid system in the brain stem does the combination of pyramidal symptoms on opposite side with symptoms of nuclei of craniocerebral nerves on the affected side - alternating syndromes (see). The defeat of the pyramid system in spinal cord - see the Spinal cord.

Pyramid system (tractus pyramidalis; synonym pyramid path) - a system of long efferent projection fibers motor analyzer, originating in the forward Central gyrus of a bark of a brain (cytoarchitectonics field 4 in) and partly from other fields and areas. Its name of P.F. received from the so-called pyramid oblong brain formed on its ventral surface taking place there pyramid paths.
In lower vertebrates P.F. missing. It appears only in mammals, and its importance in the evolution of gradually increasing. A person P.F. reaches maximum development, and its fibers in the spinal cord is about 30% of the area of cross-section (the higher apes 21,1%, dogs 6,7%). Representation of P.F. in the cortex of the brain is the core of motor analyzer. In lower mammals kernel motor analyzer spatial not separated from the kernel skin analyzer and IV has a granular layer (sign sensitive bark). These cores are overlapping, as phylogenetic development more oboeblaeser from each other. The most marginalized, they are in humans, although it has the remains of overlap in the form fields and 3/4 5. In ontogenesis cortical the core of motor analyzer differentiated early - at the beginning of the second half of the uterine life. Before birth box 4 saves IV granular layer that is the repetition in ontogenesis signs detected in the early stages of phylogenesis mammals. Facing the myelin sheath of nerve fibers pyramid system is carried out within the 1st year of life.
An adult basic cortical representation of P.F. corresponds cytoarchitectonics fields 4 and 6 front of the Central gyrus of the brain. Field 4 is characterized by the presence of a giant pyramid Betz cells in layer V, granularity (lack of granular layers) and wide crust (about 3.5 mm). Box 6 has a similar structure, but does not have large pyramidal cells Betz. From these fields, from giant pyramid Betz cells and other pyramidal cells layers V and III, and according to current data, and from other fields and areas of the cortex of the brain starts pyramidal tract. It is formed descending fibers caliber from 1 to 8 microns and more that are in the white matter of brain hemispheres, in radiant crown converge towards the inside of the bag, where, forming a compact bundle that occupy the front two-thirds of its rear hip and knee.
Then the fibers pyramid system are in the middle third of the Foundation of the legs of the brain. Entering the bridge, they break up into separate small beams, passing among cross located fibers frontal-cerebellopontine path and own kernels bridge. In the medulla fiber P.F. again gather in compact beam and form of the pyramid. Here the most part of fibers goes in the opposite direction, making the decussation of the pyramids. In the brain stem fiber to the motor cranial nerves (kortiko-nuclear; tractns corticonuclearis) and to the front horns spinal cord (kortiko-spinal; tractus corticospinals lat. et ant.) go together to the bottom of the top of Oliva. Then kortiko-nuclear path gradually gives up its fiber to the motor nuclei front, sublingual, trigeminal and vagus nerves. These fibers cross-level cores or directly over them. Kortiko-spinal fiber descend to the spinal cord (see), where overlapping fiber P.F. focus in the side column, taking his back, and neprekraschayuschayasya are in the front post. Ending on a motor cells of the front horns (or inserted) cells of the spinal cord, fiber P. E., stay relatively sustainable gradually reach of the sacral spinal cord. The number of fibers P.F. exceeds 1 million in Addition to the motor, there are vegetative fibers.
Cortical Department pyramid system, or motor cortex of the brain, is the core of motor analyzer. Analytic, or afferent, the nature of this kernel is confirmed by afferent fibers, coming to him from visual occiput. As installed, fiber P.F. originate from the wider region of the cortex of the brain than the forward Central gyrus and P.F. closely connected with the extrapyramidal system, particularly in the cortical Department (Fig. 1). Therefore, when various localizations brain lesions usually in tone degree or another suffers P.F.
Physiologically P.F. is a system that provides random motion, although the latter is ultimately the result of the activity of the brain. In the forward Central gyrus has somatotroponoe distribution cortical points for individual muscles, electric irritation of which causes of discrete motion of these muscles. Especially widely represented muscles that perform the most delicate work arbitrary motion (Fig. 2).

the scheme of the pyramidal tract
Fig. 1. The scheme of the pyramidal tract and distribution of the places of its origin in the cortex of the brain: 1 - limbic areas; 2 - parietal area; 3 - region; 4 - frontal region; 5 - islet area; 6 - the temporal area; 7 - eye hump; 8 - inner bag.
the scheme somatotroponogo distribution muscles
Fig. 2. The scheme somatotroponogo distribution of muscles of the limbs, trunk, and facial in the cortex and the anterior Central gyrus (Penfillb, Badri).

The defeat of P.F. in lower mammals do not cause significant mobility impairments. The higher organized mammal, the more significant of these violations. Pathological processes in the cortical Department of P.F., especially in the forward Central gyrus, irritating the cortex of the brain, causing partial (partial), or Jacksonian, epilepsy, manifested mainly clonic spasms of the muscles of the opposite half of the face, body and extremities on the opposite side. Loss of functions of P.F. apparent paralysis, paresis.
The defeat of P.F. identified neurological examination arbitrary (active) movements, their volume in the various joints, muscle strength, muscle tone and reflexes in combination with other neurological symptoms. Increasing diagnostic significance electroencephalography and electromyography. In the case of unilateral lesion of the cerebral cortex in the front area of the Central gyrus most often observed monoplegia and monoparty arm or leg opposite side of the body. Defeat kortiko-nuclear ways facial nerve is usually expressed by the Central paresis of the lower and middle branches of the nerve. Less affected is usually the upper branch because of its bilateral innervation, although the disease is often possible to detect (the patient can not isolated to a close eye on the affected side). Focal lesion of P.F. in the field of internal bags usually leads to hemiplegia (hemiparesis), and with bilateral lesions to tetraplegia.
The defeat of the pyramid system in the area of the brain stem are determined by the combination of the pyramid of symptoms on opposite side with the defeat of the nuclei of the cranial nerves, or their roots on the affected side, i.e. the presence of alternating syndromes (see).
With pyramid hemiplegia and hemiparesis usually suffer most distal extremities.
Hemiplegia and hemiparesis with the defeat of P.F. usually characterized by the increase of tendon reflexes, increased muscle tone, loss of reflexes cutaneous, especially plantar, pathological reflexes - extensor (Babinski, Oppenheim, Gordon and others) and flexor (Rossolimo, Mendel - Bekhterev and others), as well as protective reflexes. Tendon and periosteal reflexes are invoked with extended zone. Appear cross-reflexes and friendly movement - so-called synkinesia (see). In the initial stages of the pyramid hemiplegia muscle tone (and sometimes reflexes) is reduced in power deschisa (see). Increased muscle tone is detected later 3-4 weeks from the beginning of defeat. Most often, especially when capsular lesions, increased muscle tone prevails in the flexor tendons of the forearm and the extensor tibia. This distribution muscle hypertension leads to contraction of the type Wernicke - Mann (see Wernicke-Mann type contractures).