The pyramidal system , the pyramidal path ( lat. Tractus pyramidalis , PNA) - a system of nervous structures. It supports complex and subtle coordination of movements [1] [2] .
The pyramidal system is one of the late acquisitions of evolution . The lower vertebrates have no pyramidal system, it appears only in mammals , and reaches its greatest development in monkeys and especially in humans [1] . The pyramidal system plays a special role in upright posture [2] .
Content
Pyramid path
The cerebral cortex in the V layer contains Betz cells (or giant pyramidal cells) [3] .
In 1874, scientist Vladimir Alekseevich Betz discovered and described giant pyramidal cells of the cerebral cortex (Betz cells).
The pyramidal pathway is carried out by nerve fibers that emanate from Betz cells and descend into the spinal cord without interruption. The pyramidal path passes through the inner capsule, the brain stem, giving off branches (collaterals) with the extrapyramidal system , as well as with the subcortical nuclei (motor nuclei of the cranial nerves) in its path [2] [3] .
The fibers cross at the border of the brain and spinal cord (most of them are in the medulla oblongata, and the smaller part is in the spinal cord). Then they pass through the spinal cord (front and side pillars of the spinal cord). In each segment of the spinal cord, these fibers form synaptic endings (see. Synapse ), which are responsible for a certain part of the body (cervical spinal cord - for innervation of the arms, chest - for the trunk, and lumbar - for the legs) [3] . Impulses from the cerebral cortex transmit these fibers either directly or through intercalary neurons [1] .
Motor Bark
Direct irritation of certain parts of the cerebral cortex leads to muscle cramps corresponding to the part of the cortex - the projective motor zone. With irritation of the upper third of the anterior central gyrus, a cramp in the muscles of the leg, middle - arm, lower - face occurs, and, on the side opposite the focus of irritation in the hemisphere. These convulsions are called partial (Jackson). They were discovered by the English neurologist D.H. Jackson (1835-1911). In the motor parts of the cortex of each hemisphere of the brain, all muscles of the opposite half of the body are represented [2] .
Types of Nerve Fibers
The human pyramidal system contains about 1 million nerve fibers. The following types of fibers are distinguished [1] :
| Type of nerve fibers | Diameter | Speed | Function |
|---|---|---|---|
| Thick, fast-conducting | 16 microns | up to 80 m / s | provide fast phase motion |
| Thin, slow conducting | 4 microns | from 25 to 7 m / s | responsible for the tonic state of the muscles |
The largest number of pyramidal cells (Betz cells) innervates the small muscles responsible for the thin differentiated movements of the hand, facial expressions and speech act. A significantly smaller number of them innervates the muscles of the trunk and lower extremities [2] .
Pathology
Damage to the pyramidal system is manifested by paralysis, paresis , pathological reflexes [1] .
The defeat of the pyramidal system can be caused by inflammation (see Encephalitis ), impaired cerebral circulation (see Stroke ), a tumor, traumatic brain injury and other causes [2] .
Depending on the localization of the pathological process, the following manifestations are distinguished [2] .
| Localization of the pathological process of the pyramidal path | Symptoms |
|---|---|
| projection zones of the cerebral cortex | central paralysis (or paresis ), see below. |
| in the area of ββthe inner capsule | hemiplegia - paralysis of the arm and leg on the side opposite to the localization of the focus. |
| in the brain stem | Alternating syndromes - a combination of hemiplegia on the side opposite to the focus, with signs of impaired cranial nerve function on the affected side. |
| in the spinal cord | Hemiplegia or paralysis of the leg on the side of the injury - the fiber cross remains higher. |
Central (spastic) paralysis , or paresis
Also called - pyramidal insufficiency, spastic ataxia , Pierre Marie's disease. Occurs with damage to the projection area of ββthe cerebral cortex. If Betz cells in the cerebral cortex (or their axons ) are affected, then spastic paralysis occurs (from the word spasm , that is, when muscle tone is increased). In this case, the Betz cell begins to send an excessive amount of nerve impulses to the muscles. This leads to an increase in muscle tone and reflexes , and trembling occurs. This condition is called central paralysis (with incomplete loss of voluntary movements - central paresis ). With central paralysis (paresis), nutritional disorders of the limb (malnutrition, atrophy) do not occur [3] .
Peripheral (flaccid) paralysis, or paresis
If peripheral nerves or plexuses are affected, then flaccid, or peripheral paralysis occurs (and with incomplete loss of function - paresis) - a decrease in muscle tone, up to complete paralysis of the muscle [3] .
Diagnostic methods for pyramidal insufficiency
- Magnetic resonance imaging (MRI) is a mandatory examination method for epilepsy and seizures.
- Computed tomography of the brain (on the recommendation of the International League Against Epilepsy, CT is performed as an additional method of examination, or when it is impossible to do an MRI).
- Electromyography is a method of studying the neuromuscular system by registering the electrical potentials of muscles.
- Electroencephalography (EEG study) - allows you to identify seizures. More than 65% of seizures occur in a dream, therefore, recording of the eeg during physiological, natural sleep is necessary. Due to the inconsistent nature of seizures, continuous monitoring (video or Holter) is carried out. The study reveals the appearance of diffuse delta waves , as well as the synchronization of theta waves. The appearance of epileptiform activity is possible.
- Ultrasound examination (ultrasound) of the brain - reveals signs of increased pressure in the brain, which creates an irritating effect and can cause central paralysis. Reflexes decrease or completely disappear, and hypotrophy of the innervated area occurs [3] .
- Clinical and neurological tests for the detection of pyramidal insufficiency.
Pyramidal insufficiency treatment
Treatment is aimed at the underlying disease, as well as at the restoration of motor functions in paralysis [2] .
In treatment, adhere to the principle of increased physical activity [3] .
See also
- Extrapyramidal system
Notes
- β 1 2 3 4 5 Pyramid system - article from the Great Soviet Encyclopedia .
- β 1 2 3 4 5 6 7 8 Brief medical encyclopedia . - 2nd ed .. - M .: Soviet Encyclopedia, 1989.
- β 1 2 3 4 5 6 7 Ivan Sitnikov. The pyramidal system, symptoms arising from its insufficiency and research methods for this pathology . SVS clinic named after Savinov V.M. Date of appeal April 18, 2017.