Neurology is one of the most exact sciences of medicine. With the help of topical diagnostics, a neurologist, using a hammer, questioning and examination, as well as samples and various tests, can in some cases localize the lesion with high accuracy. This lesion may be located in the spinal cord or head. Previously, this was an applied science, and before that it was a descriptive science (anatomy also always belonged to a descriptive science).

Basic Prerequisites

In neurology, such concepts as “putamen”, “cerebellar peduncles”, “plumbing” running deep in the brain, “fence”, “temmel quadrigeminal tubercles” and many other formations are used. Their functionality for a long time remained a mystery. The only understanding was that the components of the brain and spinal cord are gray and white matter, but this, perhaps, was the only difference. Analysis of the internal structure was not performed because there were no dyes yet that could image neurons and prove the cellular structure of the central nervous system. These cells consist of the longest processes (about 1 meter long).

Neuroanatomy as a science did not yet exist. What a nerve fiber was was not known. Then Virchow's cell theory was invented, according to which the functionality of an organ depends directly on what cells it consists of. Physiology also appeared, studying neurons, their functions and differences. The nerve cell and the integrity of its work became accessible to understanding. Scientists Sechenov and Pavlov took the next steps.

Pyramid path - general concept

The pyramidal system is referred to as the “internal formation” of the central nervous system. It contributes to all motor conscious acts of a person. In the absence of the pyramid system, we would not have the opportunity to move, and this would lead to the impossibility of developing civilization. The human brain and hands created civilization, but this is all thanks to the pyramidal path, which provides intermediary services (bringing brain impulses for movement to the muscles).

The pyramidal system is considered to be a system of efferent neurons; they are located in the cerebral cortex. Their endings are located in the motor nuclei of the nerves of the skull and the gray matter of the spinal cord. The pyramidal tract consists of corticonuclear and corticospinal fibers. These are the axons of nerve cells in the cerebral cortex.

In this article we will consider the pyramid system, its functionality, as well as the diagram of the pyramid path.

What is a pyramid system?

The pyramidal tracts (or system) are called the corticospinal, efferent, or descending tracts. They originate in the place where the precentral gyrus is located, or more precisely, in the gray matter of this gyrus. The neural bodies are located there. They produce impulses that give commands to the striated (skeletal) muscles. These are conscious impulses; the pyramidal system is easy to subordinate to the will of the mind.

The function of the pyramidal tract is to perceive the program of voluntary movement and conduct the impulses of the program to the brain stem and spinal cord. The pyramidal and extrapyramidal (unconscious) systems are united into a single system, which is responsible for movement, coordination of balance and muscle tone.

Beginning and ending of pyramid paths

Let's figure out where the pyramid path begins? Its origin is located in the precentral gyrus. To be more precise, in this gyrus there is a special field projected along it in the direction from bottom to top.

This band is called Brodmann's cytoarchitectonic area No. 4. The location of Betz's giant pyramidal cells is available here. (Vladimir Betse - Russian histologist and anatomist, discovered these cells in 1874). They generate impulses with the help of which precise and targeted movements are made.

Where does the pyramid system end? The end of the pyramidal tracts is located in the spinal cord (in its anterior horns), the levels are different - starting from the neck and ending with the sacrum. Here there is a switch to large motor neurons, the endings of which are located in the neuromuscular junction. The neurotransmitter acetylcholine signals the muscles to contract. This is the essence of how the pyramid path works. Next, the anatomy and organization of the structures of the corticospinal tract will be discussed in detail, and the different levels will be described.

Neurons

Neurons of the pyramidal tract, which are located in the lower sections, are responsible for the movement of the pharynx and the production of sounds. Somewhat higher are the cells that innervate facial expressions, muscles of the arms, torso and legs.

There is such a thing as a “motor homunculus”. Nerve cells are responsible for the hands and fingers (those subtle movements that they make), as well as for vocal and facial muscles. A small number of cells are responsible for the innervation of the legs, which perform mainly stereotypical movements.

The task of cortical impulses born large cells Betsa - get to the muscle as quickly as possible. This is not like the autonomic nervous system, which works smoothly internally human body. The better and faster the movements of the hands and fingers are, the better a person will be able to, for example, get food. The isolation of the axons of these neurons occurs “to the highest class.” Their fibers have a thick myelin sheath. This is the best of all pathways; it includes only a small number of axons from the total volume of the pyramidal system. In another part of the cerebral cortex zone, the rest of the small neurons - sources of impulses - are located.

There are also fields, in addition to the Brodmann field, which are called prematory. They also give back their impulses. This is already the corticospinal tract. All movements performed on the opposite side of the body are performed by the cortical structures we mentioned. What does this mean? Left neurons generate movements of the right side of the body, right ones generate movements of the left side. The fibers create a certain crossover, moving to the other half of the body. This is the structure of the pyramidal path.

Nerves and their functions

Everyone knows that there are muscles in the arms, legs and torso, but in addition to this, it is necessary to mention the muscles of the face and head. The innervation of the limbs and torso is created by one bundle of fibers, and a smaller bundle switches the impulses of the motor nuclei, with the help of which voluntary and conscious movements are made.

The pyramidal tract is the first bundle, the second is the corticonuclear or corticonuclear tract. Let's take a closer look at the nerves and their work that receive impulses from the pyramidal tract:

The oculomotor nerve (3rd pair) moves the eyes and eyelids.

The trochlear nerve (4th pair) also moves the eyes, only to the side.

The trigeminal nerve (5th pair) carries out chewing movements.

The abducens nerve (6th pair) makes eye movements.

The facial nerve (7th pair) creates facial movements.

The glossopharyngeal nerve (9th pair) controls the stylopharyngeal muscle and pharyngeal constrictors.

The vagus nerve (10th pair) creates movements of the muscles of the pharynx and larynx.

The accessory nerve (11th pair) carries out the work of the trapezius and sternocleidomastoid muscles.

The hypoglossal nerve (12th pair) moves the tongue muscle.

Function of the corticonuclear pathway

The corticonuclear or corticonuclear pyramidal tract serves almost all nerves. The exception is the particularly sensitive nerves - olfactory and visual. The bundles, which have already separated, go around the inner capsule with tightly lying conductors. Here is concentrated highest concentration networks of brain cables. The internal capsule is a small strip that is located in the white matter. The basal ganglia surround it. It has the so-called “thigh” and “knee”. The “hips” first deviate, then they connect. This is the “knee”. Having passed its way to the nuclei of the cranial nerves, the impulse moves further and, with the help of individual nerves, is directed to the muscles. Here the beams also cross, and movements are carried out on the opposite side. But only part of them passes in a contralateral way, and the other part - in an ipsilateral way.

The anatomy of the pyramidal tracts is unique. The main beam produces movements of the arms and legs. It exits through the occipital foramen, and its density and thickness increases. The axons leave the internal capsule, then enter the middle of the cerebral peduncles, after which they descend into the pons. Here they are surrounded by pontine nuclei, fibers of the reticular formation and other formations.

After which they leave the pons and enter the medulla oblongata. This is how the pyramidal tracts become visible. These are elongated and inverted pyramids located symmetrically from the center. Hence the name - pyramidal tracts of the brain.

Main ascending paths

• The ascending hindbrain includes the posterior spinocerebellar tract of Flexig and the anterior spinocerebellar tract of Govers. Both spinocerebellar tracts conduct unconscious impulses.
• The ascending midbrain includes the lateral spinal midbrain tract.
• To the diencephalon - the lateral spinothalamic tract. It carries out irritations from temperature and pain. Also included here is the anterior spinothalamic tract, which carries impulses of touch and touch.

Place of transition to the spinal cord

Resting against the medulla oblongata, the axons intersect. A side beam is formed. The part that did not twist is called the anterior corticospinal tract.

The transition of axons to the other mirror side still occurs, but in the part where innervation occurs. The end of this bundle is located in the sacral region, where it becomes very thin.

Most of the fibers switch not to motor neurons in the spinal cord, but to interneurons. They form synapses in which there are large motor neurons. Their functions are different. Interneurons make contact with sensory and motor nerve cells; they are autonomous. Each segment has its own polysynaptic “relay substation”. It's a kind of motor system. The pyramidal tract and the extrapyramidal pathway for movement regulation are different from each other.

An extrapyramidal system operating in a completely autonomous mode does not require as many two-way communications because it does not require voluntary control.

Structure of the extrapyramidal system

The extrapyramidal system is distinguished by the following brain structures:

Basal ganglia;

Red core;

Interstitial nucleus;

Tectum;

Black substance;

Reticular formation of the pons and medulla oblongata;

The nucleus of the vestibular complex;

Cerebellum;

Premotor cortex area;

Striped body.

Conclusion

What happens if an obstacle appears in the path of the pyramidal beam? If the axons are interrupted due to injury, tumor, or hemorrhage, muscle paralysis will occur. After all, the command to move was gone. With a partial break, partial paralysis or paresis appears. The muscle becomes weak and hypertrophied. The central neuron dies, but the second neuron may remain unharmed.

This also happens when there is a break in the path. The second neuron is located in the anterior horns of the spinal cord, it is close to the muscle directly. It’s just that nothing from above controls him anymore. This is called central paralysis. This situation is very unpleasant, so you need to take care of your health and try to avoid injuries and other damage.

We looked at the pyramidal system, its structure, and found out what a nerve fiber is.

Efferent pathways are classified into pyramidal and extrapyramidal. Lower vertebrates do not have pyramidal tracts - they appear only in mammals and reach their greatest development in humans.

The pyramidal tracts begin in the fifth layer of the cortex from giant pyramidal cells (Betz cells), located in the precentral gyrus and paracentral lobule. These tracts end on the neurons of the motor nuclei of the cranial nerves and the motor nuclei of the anterior horns of the spinal cord. In the brain stem, the pyramidal tracts are localized in zone I - the base of the brain stem, and in the medulla oblongata they pass as part of the pyramids.

The extrapyramidal tracts begin from the gray matter nuclei located in the brain stem. They conduct impulses that provide unconscious (involuntary) movements and maintain muscle tone. These tracts pass in zone II of the brain stem - the tegmentum.

Pyramid paths

The main efferent pyramidal tracts are the corticospinal and corticonuclear tracts.

1. Corticospinal tract conducts conscious (volitional) motor nerve impulses that provide control of the skeletal muscles of the trunk and limbs, and the execution of precise, highly differentiated movements. In addition, this pathway conducts inhibitory impulses from the cerebral cortex big brain to the neurons of the motor nuclei of the anterior horns of the spinal cord (Fig. 4.9), i.e. it has an inhibitory effect on the segmental apparatus of the spinal cord.

The corticospinal tract is formed by the axons of the pyramidal cells of the cortex of the precentral gyrus and the pericentral lobule. Some axons are directed from the postcentral gyrus.

Rice. 4.9.

1 – intersection of pyramids; 2 – lateral corticospinal tract; 3 – lateral funiculus; 4 – anterior root of the spinal nerve; 5 – motor nuclei of the anterior horns of the spinal cord; 6 – anterior cord; 7 – anterior horn; 8 – anterior corticospinal tract; 9 – medulla oblongata; 10 – corticospinal tract; 11 – internal capsule; 12 – Betz cells

In the cortex of the precentral gyrus, pyramidal neurons are localized according to the “Penfield motor homunculus” rule. In the uppermost parts of the precentral gyrus there are neurons that begin the efferent pathways for the innervation of the muscles of the lower limb, and in the paracentral lobule there is a somatotopic projection of the muscles of the foot, and laterally - the muscles of the lower leg and thigh. Next are the neurons that give rise to the efferent nerve pathways to the muscles of the trunk. The middle third of the precentral gyrus is occupied by neurons that provide muscle innervation upper limb(above for the shoulder muscles, below for the forearm and hand). It should be noted that the area of ​​somatotopic projection zones in the cerebral cortex is proportional to the complexity of movements performed by a particular muscle group. The muscles of the hand have the largest area of ​​somatotopic projection (see Fig. 3.26).

The corticospinal tract runs in a descending direction into the internal capsule, in which it occupies the anterior part of the posterior peduncle. The location of the fibers of this tract in the internal capsule has characteristic features: in close proximity to the knee of the internal capsule there are fibers that conduct nerve impulses for the muscles of the upper limb, behind them there are fibers for the muscles of the trunk and, finally, fibers for the muscles of the lower limb.

Next, the corticospinal tract passes along the ventral surface of the brain stem. In the bridge, it disintegrates into a large number of small bundles, separated from each other by the nuclei of the bridge. In the region of the medulla oblongata, scattered bundles of fibers are reassembled into one large bundle, which runs as part of the pyramid. At the border between the medulla oblongata and the spinal cord, most of the fibers of each pyramid pass to the opposite side (80%), forming a pyramidal decussation with similar fibers of the opposite side. Of the pyramid, 20% of the fibers remain on their side and continue into the anterior cord of the spinal cord. They make up the anterior corticospinal tract. The crossed fibers are sent to the lateral cord of the spinal cord. IN lateral funiculus This is the largest bundle of fibers and is called the lateral corticospinal tract. Thus, the corticospinal tract in the spinal cord, which is uniform throughout the brain stem, is divided into two independent ones.

The lateral corticospinal tract gradually becomes thinner in the caudal direction. The largest number of fibers are separated from it in the area of ​​spinal cord thickenings, the segments of which contain effector neurons responsible for the innervation of the muscles of the upper and lower extremities. Having reached their segment, the fibers leave the tract and end on the cells of the motor nuclei of the anterior horns of the spinal cord on their side.

The anterior corticospinal tract is located in the anterior funiculus of the spinal cord. It is a relatively small bundle of fibers, the main part of which passes segment by segment in the area of ​​the anterior white commissure to the opposite side and ends on the neurons of the motor nuclei of the anterior horns.

Axons of second neurons (motoneurons) located in the motor nuclei of the anterior horns of the spinal cord leave the spinal cord as part of the ventral roots spinal nerves. They then pass through the spinal nerves and their branches to the skeletal muscles.

When pyramidal neurons and corticospinal tracts are damaged, central paralysis occurs (loss of motor functions) or paresis (weakening of motor functions). Central paralysis is characterized by increased tone of paralyzed muscles (hypertonicity), increased tendon reflexes (hyperreflexia), and the appearance of pathological reflexes. These manifestations are due to the lack of an inhibitory effect on the segmental apparatus of the spinal cord.

If the lesion of the corticospinal tract is localized at the level of the upper cervical segments, paralysis of the upper and lower extremities occurs on the same side. If the pathological focus of the lesion is in the precentral gyrus or in the brain stem, paralysis of the limbs occurs on the opposite side, as the fibers of the corticospinal tract cross.

When a peripheral motor neuron or its axon is damaged, peripheral paralysis occurs, which is characterized by atony, areflexia and atrophy. In this case, movements are completely absent, and the muscles atrophy over time and are replaced by fatty and connective tissue.

2. Corticonuclear pathway belongs to the group of motor pyramidal tracts. It conducts conscious (volitional) motor nerve impulses that provide control of the muscles of the head and partly the neck, performing precise and highly differentiated movements. In addition, this pathway conducts inhibitory impulses from the cerebral cortex to the neurons of the motor nuclei of cranial nerves III, IV, V, VI, VII, IX, X, XI and XII pairs, i.e. it has an inhibitory effect on the segmental apparatus of the brain stem.

The corticonuclear tract is formed by the axons of the pyramidal cells of the fifth layer of the cerebral cortex. Most of the axons originate from the cells of the inferolateral third of the precentral gyrus, a smaller part - from the cells of the lower third of the postcentral gyrus. Participation in the formation of the corticonuclear pathway of the axons of the cells of the lower third of the postcentral gyrus is due to the somatotopic projection onto the cortex of the masticatory and facial muscles, muscles soft palate, pharynx and larynx.

The axons of the pyramidal cells fan out into a bundle that passes through the knee of the internal capsule. Next, the cortical-nuclear tract passes along the ventral surface of the brain stem - in the middle part of the base of the cerebral peduncle, the base of the pons and the pyramids of the medulla oblongata.

In the region of the midbrain, a part of the fibers is separated from the cortical-nuclear tract, which ends with synapses on the cells of the motor nuclei of the oculomotor (III pair) and trochlear (IV pair) cranial nerves, which innervate the muscles eyeball.

In the area of ​​the bridge, fibers are again separated from the cortical-nuclear path, which go in the dorsal direction and end on the neurons of the motor nuclei of the V, VI and VII pairs of cranial nerves. Axons of motor neurons of the motor nucleus trigeminal nerve innervate masticatory muscles; mylohyoid and anterior belly of the digastric muscle; the muscle that strains the soft palate, as well as the muscle that strains the eardrum. The axons of the cells of the motor nucleus of the abducens nerve are directed to the lateral rectus muscle of the eyeball. The axons of the motor neurons of the motor nucleus of the VII pair innervate the facial muscles, the stapedius muscle, the posterior belly of the digastric muscle, the stylohyoid and subcutaneous muscles.

A relatively small part of the fibers of the corticonuclear tract reaches the medulla oblongata and the upper cervical segments of the spinal cord. These fibers also deviate in the dorsal direction and end on the neurons of the motor nuclei of the IX, X, XI and XII pairs of cranial nerves. The axons of the motor neurons of the double nucleus, common to the IX and X pairs of cranial nerves, innervate the muscles of the pharynx, soft palate, larynx and upper esophagus. The axons of the motor neurons of the motor nucleus of the XI pair go to the trapezius and sternocleidomastoid muscles, and the axons of the motor neurons of the motor nucleus of the XII pair go to the muscles of the tongue.

Unilateral destruction of pyramidal neurons in the lower part of the precentral gyrus or damage to the corticonuclear tract causes not paralysis, but paresis (limitation of voluntary movements and reduction in muscle contractile force), since motor neurons of the motor nuclei of the cranial nerves in most cases receive nerve impulses from both hemispheres. The exceptions are the muscles of the tongue and facial muscles. Only crossed fibers of the cortical-nuclear tract go to the neurons of the motor nucleus of the hypoglossal nerve, so their defeat causes paralysis of the muscles of the tongue on the opposite side. Motor neurons of the motor nucleus facial nerve, associated with the innervation of the lower half of the face, receive only crossed fibers.

Motor neurons associated with the innervation of the muscles of the upper half of the face receive fibers from the corticonuclear tracts of their own and opposite sides. In this regard, complete muscle paralysis develops only in the lower half of the face on the side opposite to the lesion. In the upper half of the face, only paresis of the facial muscles is noted. Only bilateral damage to the cortical centers or corticonuclear tracts leads to the development of central paralysis.

When all motor neurons of the motor nuclei of cranial nerves are destroyed or their axons are damaged, peripheral paralysis occurs, which leads to the disappearance of reflexes (areflexia), loss of muscle tone (atony) and their atrophy.

Movement - a universal manifestation of life activity, providing the opportunity active interaction How components the body and the whole organism with the environment by moving in space. There are two types of movements:

1) involuntary- simple automated movements that are carried out due to the segmental apparatus of the spinal cord, brain stem according to the type of simple reflex motor act;

2) arbitrary (targeted)- arising as a result of the implementation of programs formed in the motor functional segments of the central nervous system.

In humans, the existence of voluntary movements is associated with the pyramidal system. Complex acts of human motor behavior are controlled by the cerebral cortex (middle parts frontal lobes), the commands of which are transmitted through the pyramidal tract system to the cells of the anterior horns of the spinal cord, and from them through the peripheral motor neuron system to the executive organs.

The movement program is formed on the basis of sensory perception and postural reactions from the subcortical ganglia. Correction of movements occurs through a feedback system with the participation of a gamma loop, starting from the spindle-shaped receptors of intramuscular fibers and closing on the gamma motor neurons of the anterior horns, which, in turn, are under the control of the overlying structures of the cerebellum, subcortical ganglia and cortex. The motor sphere of a person is so completely developed that a person is able to carry out creative activities.

3.1. Neurons and pathways

Motor tracts of the pyramidal system (Fig. 3.1) consist of two neurons:

1st central neuron - cell of the cerebral cortex;

2nd peripheral neuron - motor cell of the anterior horn of the spinal cord or motor nucleus of the cranial nerve.

1st central neuron located in layers III and V of the cerebral cortex (Betz cells, medium and small pyramidal

Rice. 3.1.Pyramid system (diagram):

A)pyramidal tract: 1 - cerebral cortex; 2 - internal capsule;

3 - cerebral peduncle; 4 - bridge; 5 - intersection of pyramids; 6 - lateral corticospinal (pyramidal) tract; 7 - spinal cord; 8 - anterior corticospinal tract; 9 - peripheral nerve; III, VI, VII, IX, X, XI, XII - cranial nerves; b) convexital surface of the cerebral cortex (fields

4 and 6); topographic projection of motor functions: 1 - leg; 2 - torso; 3 - hand; 4 - brush; 5 - face; V) horizontal section through the internal capsule, location of the main pathways: 6 - visual and auditory radiation; 7 - temporopontine fibers and parieto-occipital-pontine fascicle; 8 - thalamic fibers; 9 - corticospinal fibers to the lower limb; 10 - corticospinal fibers to the muscles of the trunk; 11 - corticospinal fibers to the upper limb; 12 - cortical-nuclear pathway; 13 - frontal-pontine tract; 14 - corticothalamic tract; 15 - anterior leg of the internal capsule; 16 - elbow of the internal capsule; 17 - posterior leg of the internal capsule; G) anterior surface of the brain stem: 18 - decussation of pyramids

cells) in the area anterior central gyrus, posterior parts of the superior and middle frontal gyri and paracentral lobule(4, 6, 8 cytoarchitectonic fields according to Brodmann).

The motor sphere has a somatotopic localization in the anterior central gyrus of the cerebral hemisphere cortex: the centers of movement of the lower extremities are located in the upper and medial sections; the upper limb - in its middle section; head, face, tongue, pharynx, larynx - in the lower middle. The projection of body movements is presented in the posterior section of the superior frontal gyrus, the rotation of the head and eyes is represented in the posterior section of the middle frontal gyrus (see Fig. 3.1 a). The distribution of motor centers in the anterior central gyrus is uneven. In accordance with the principle of “functional significance”, the greatest representation in the cortex are those of the body that perform the most complex, differentiated movements (centers that provide movement of the hand, fingers, and face).

The axons of the first neuron, going down, converge like a fan, forming the corona radiata, then pass through the internal capsule in a compact bundle. From the lower third of the anterior central gyrus, the fibers involved in the innervation of the muscles of the face, pharynx, larynx, and tongue pass through the knee of the internal capsule, in the trunk they approach the motor nuclei of the cranial nerves, and therefore this path is called corticonuclear. The fibers that form the corticonuclear tract are directed to the motor nuclei of the cranial nerves (III, IV, V, VI, VII, IX, X, XI) of both their own and the opposite side. The exception is the corticonuclear fibers that go to the lower part of the nucleus of the VII and to the nucleus of the XII cranial nerves and carry out unilateral voluntary innervation of the lower third of the facial muscles and half of the tongue on the opposite side.

Fibers from the upper 2/3 of the anterior central gyrus, involved in the innervation of the muscles of the trunk and limbs, pass into anterior 2/3 posterior limbs of the internal capsule and in the brain stem (corticospinal or actually pyramid path) (see Fig. 3.1 c), and the fibers are located outside to the muscles of the legs, and inside - to the muscles of the arms and face. At the border of the medulla oblongata and the spinal cord, most of the fibers of the pyramidal tract form a cross and then pass as part of the lateral cords of the spinal cord, forming lateral (lateral) pyramidal tract. The smaller, uncrossed part of the fibers forms the anterior funiculi of the spinal cord (anterior pyramidal

path). The crossover is carried out in such a way that the fibers externally located in the crossover zone, innervating the leg muscles, are located inside after the crossover, and, conversely, the fibers to the arm muscles, located medially before the crossover, become lateral after moving to the other side (see Fig. 3.1 d ).

In the spinal cord, the pyramidal tract (anterior and lateral) gives off segmental fibers to alpha major neurons of the anterior horn (second neuron), directly communicating with the working striated muscle. Due to the fact that the segmental zone of the upper extremities is the cervical enlargement, and the segmental zone of the lower extremities is the lumbar enlargement, fibers from the middle third of the anterior central gyrus end predominantly in the cervical enlargement, and from the upper third - in the lumbar enlargement.

Motor cells of the anterior horn (2nd, peripheral neuron) located in groups responsible for contracting the muscles of the trunk or limbs. In the upper cervical and thoracic regions spinal cord there are three groups of cells: anterior and posterior medial, providing contraction of the trunk muscles (flexion and extension), and central, innervating the diaphragm muscle, shoulder girdle. In the area of ​​the cervical and lumbar thickenings, these groups are joined by the anterior and posterior lateral, innervating the flexor and extensor muscles of the limbs. Thus, in the anterior horns at the level of the cervical and lumbar thickenings there are 5 groups of motor neurons (Fig. 3.2).

In each of the groups of cells in the anterior horn of the spinal cord and in each motor nucleus of the cranial nerves, there are three types of neurons that perform different functions.

1. Alpha large cells conducting motor impulses at high speed (60-100 m/s), providing the possibility of rapid movements, are associated primarily with the pyramidal system.

2. Alpha small neurons receive impulses from the extrapyramidal system and exert postural influences, providing postural (tonic) contraction of muscle fibers, and perform a tonic function.

3. Gamma neurons receive impulses from the reticular formation and their axons are directed not to the muscle itself, but to the proprioceptor contained in it - the neuromuscular spindle, affecting its excitability.

Rice. 3.2.Topography of motor nuclei in the anterior horns of the spinal cord at the level of the cervical segment (diagram). On the left is the general distribution of anterior horn cells; on the right - nuclei: 1 - posteromedial; 2 - anteromedial; 3 - front; 4 - central; 5 - anterolateral; 6 - posterolateral;

7 - posterolateral; I - gamma efferent fibers from small cells of the anterior horns to the neuromuscular spindles; II - somatic efferent fibers giving collaterals to medially located Renshaw cells; III - gelatinous substanceRice. 3.3.

Cross section of the spine and spinal cord (diagram):

1 - spinous process of the vertebra;

2 - synapse; 3 - skin receptor; 4 - afferent (sensitive) fibers;

5 - muscle; 6 - efferent (motor) fibers; 7 - vertebral body; 8 - node of the sympathetic trunk; 9 - spinal (sensitive) node; 10 - gray matter of the spinal cord; 11 - white matter of the spinal cord The neurons of the anterior horns are multipolar: their dendrites have multiple connections with various afferent and efferent systems. The axon of a peripheral motor neuron leaves the spinal cord as part of anterior root goes into

3.2. Movement disorder syndromes (paresis and paralysis)

The complete absence of voluntary movements and a decrease in muscle strength to 0 points, caused by damage to the cortico-muscular pathway, is called paralysis (plegia); limitation of range of motion and decrease in muscle strength to 1-4 points - paresis. Depending on the distribution of paresis or paralysis, they are distinguished.

1. Tetraplegia/tetraparesis (paralysis/paresis of all four limbs).

2. Monoplegia/monoparesis (paralysis/paresis of one limb).

3. Triplegia/triparesis (paralysis/paresis of three limbs).

4. Hemiplegia/hemiparesis (unilateral paralysis/paresis of the arms and legs).

5. Upper paraplegia/paraparesis (paralysis/paresis of the arms).

6. Lower paraplegia/paraparesis (paralysis/paresis of the legs).

7. Cross hemiplegia/hemiparesis (paralysis/paresis of the arm on one side and the leg on the opposite).

There are 2 types of paralysis - central and peripheral.

3.3. Central paralysis. Topography of central motor neuron lesion Central paralysis occurs when the central motor neuron is damaged, i.e. with damage to Betz cells (layers III and V) in the motor zone of the cortex or pyramidal tract all the way from the cortex to the anterior horns of the spinal cord or the motor nuclei of the cranial nerves in the brain stem. The following symptoms are characteristic:

1. Muscular spastic hypertension, upon palpation, the muscles are tense, compacted, "jackknife" symptom contractures.

2. Hyperreflexia and expansion of the reflexogenic zone.

3. Clonus of the feet, kneecaps, lower jaw, hands.

4. Pathological reflexes.

5. Defensive reflexes(reflexes of spinal automatism).

6. Decreased skin (abdominal) reflexes on the side of paralysis.

7. Pathological synkinesis.

Synkinesias are involuntary movements that occur during active movements. They are divided into physiological(for example, swinging your arms while walking) and pathological. Pathological synkinesias occur in a paralyzed limb when the pyramidal tracts are damaged and are caused by the loss of inhibitory influences from the cerebral cortex on intraspinal automatisms. Global synkinesis- contraction of the muscles of paralyzed limbs, which occurs when muscle groups are tensed healthy side. For example, when a patient tries to rise from a lying position or stand up from a sitting position on the paretic side, the arm is bent at the elbow and brought to the body, and the leg is extended. Coordinating synkinesis- when trying to make any movement with a paretic limb involuntarily

another movement appears, for example, when trying to flex the lower leg, dorsiflexion of the foot and big toe occurs (tibial synkinesis or tibial Strumpel phenomenon). Imitative synkinesis- involuntary repetition by a paretic limb of those movements that are performed by a healthy limb. Topography of central motor neuron lesions at different levels

Anterior central gyrus irritation syndrome - clonic convulsions, motor Jacksonian seizures.

Syndrome of damage to the cortex, corona radiata - hemi/monoparesis or hemi/monoplegia on the opposite side.

Knee internal capsule syndrome (damage to the corticonuclear pathways from the lower third of the anterior central gyrus to the nuclei of the VII and XII nerves) - weakness of the lower third of the facial muscles and half of the tongue.

Syndrome of damage to the anterior 2/3 of the posterior thigh of the internal capsule - uniform hemiplegia on the opposite side, Wernicke-Mann position with a predominance of spastic tone in the arm flexors and leg extensors (“the hand asks, the leg squints”) [Fig. 3.4].

Rice. 3.4.Wernicke-Mann pose: A- on right; b- left

Brain stem pyramidal tract syndrome - damage to the cranial nerves on the side of the lesion, on the opposite side hemiparesis or hemiplegia (alternating syndromes).

Pyramidal tract lesion syndrome in the decussation area at the border of the medulla oblongata and spinal cord - cross hemiplegia or hemiparesis (affecting the arm on the side of the lesion, the leg on the contralateral side).

Pyramidal tract lesion syndrome in the lateral cord of the spinal cord - central paralysis below the level of the lesion homolaterally.

3.4. Peripheral paralysis. Topography of peripheral motor neuron lesions

Peripheral (flaccid) paralysis develops when a peripheral motor neuron is damaged (cells of the anterior horns or motor nuclei of the brain stem, roots, motor fibers in the plexuses and peripheral nerves, neuromuscular synapse and muscle). It manifests itself with the following main symptoms.

1. Muscle atony or hypotension.

2. Areflexia or hyporeflexia.

3. Muscular atrophy (hypotrophy), which develops as a result of damage to the segmental reflex apparatus after some time (at least a month).

4. Electromyographic signs of damage to peripheral motor neurons, roots, plexuses, peripheral nerves.

5. Fascicular muscle twitching, resulting from pathological impulses of a nerve fiber that has lost control. Fascicular twitching usually accompanies atrophic paresis and paralysis during a progressive process in the cells of the anterior horn of the spinal cord or the motor nuclei of the cranial nerves, or in the anterior roots of the spinal cord. Much less often, fasciculations are observed with generalized damage to peripheral nerves (chronic demyelinating polyneuropathy, multifocal motor neuropathy).

Topography of peripheral motor neuron lesions

Anterior horn syndrome characterized by atony and muscle atrophy, areflexia, electromyographic signs of damage to the peripheral motor neuron (at the level of the horns)

ENMG data. Asymmetry and mosaic of the lesion are typical (due to possible isolated lesion separate groups cells), early onset of atrophy, fibrillary twitching in the muscles. According to stimulation electroneurography (ENG): the appearance of giant and repeated late responses, a decrease in the amplitude of the M-response with a normal or slightly slower rate of propagation of excitation, no disruption of conduction along sensory nerve fibers. According to needle electromyography (EMG): denervation activity in the form of fibrillation potentials, positive sharp waves, fasciculation potentials, “neuronal” type motor unit potentials in the muscles innervated by the affected segment of the spinal cord or brain stem.

Anterior root syndrome characterized by atony and muscle atrophy mainly in the proximal parts, areflexia, electromyographic signs of damage to the peripheral motor neuron (at the level of the roots) according to ENMG. Typically combined damage to the anterior and posterior roots (radiculopathy). Signs radicular syndrome: according to stimulation ENG (impaired late responses, in the case of secondary damage to the axons of nerve fibers - a decrease in the amplitude of the M-response) and needle EMG (denervation activity in the form of fibrillation potentials and positive sharp waves in the muscles innervated by the affected root, potentials are rarely recorded fasciculations).

Peripheral nerve syndrome includes a triad of symptoms - motor, sensory and autonomic disorders (depending on the type of peripheral nerve affected).

1. Motor disorders characterized by atony and muscle atrophy (usually in the distal parts of the limbs, after some time), areflexia, signs of peripheral nerve damage according to ENMG.

2. Sensory disorders in the area of ​​nerve innervation.

3. Autonomic (vegetative-vascular and vegetative-trophic) disorders.

Signs of impairment of the conductive function of motor and/or sensory nerve fibers, according to stimulation ENG data, appear in the form of a slowdown in the speed of propagation of excitation, the appearance of chronodispersion of the M-response, and conduction blocks

excitement. In the case of axonal damage to the motor nerve, denervation activity is recorded in the form of fibrillation potentials and positive sharp waves. Fasciculation potentials are rarely recorded.

Symptom complexes of lesions of various nerves and plexuses

Radial nerve: paralysis or paresis of the extensors of the forearm, hand and fingers, and with high damage - the abductor pollicis longus muscle, the “dangling hand” pose, loss of sensitivity on the dorsal surface of the shoulder, forearm, part of the hand and fingers (dorsal surface of I, II and half of III ); loss of the reflex from the triceps tendon, inhibition of the carporadial reflex (Fig. 3.5, 3.8).

Ulnar nerve: a typical “clawed paw” is the impossibility of clenching the hand into a fist, limitation of palmar flexion of the hand, adduction and extension of the fingers, extension contracture in the main phalanges and flexion contracture in the terminal phalanges, especially the fourth and fifth fingers. Atrophy of the interosseous muscles of the hand, lumbrical muscles going to the 4th and 5th fingers, hypothenar muscles, partial atrophy of the forearm muscles. Impaired sensitivity in the innervation zone, on the palmar surface of the fifth finger, back surface V and IV fingers, ulnar part of the hand and III finger. Sometimes trophic disorders and pain radiating to the little finger are observed (Fig. 3.6, 3.8).

Median nerve: violation of palmar flexion of the hand, I, II, III fingers, difficulty in opposition of the thumb, extension of the middle and terminal phalanges of the II and III fingers, pronation, atrophy of the muscles of the forearm and thenar (“monkey hand” - the hand is flattened, all fingers are extended, the thumb is close brought to the index). Loss of sensitivity on the hand, palmar surface of the 1st, 2nd, 3rd fingers, radial surface of the 4th finger. Vegetative-trophic disorders in the innervation zone. In case of injuries to the median nerve - causalgia syndrome (Fig. 3.7, 3.8).

Femoral nerve: with a high lesion in the pelvic cavity - impaired flexion of the hip and extension of the leg, atrophy of the muscles of the anterior surface of the thigh, inability to walk up stairs, run, jump. Sensitivity disorder on the lower 2/3 of the anterior surface of the thigh and the anterior inner surface of the leg (Fig. 3.9). Loss of knee reflex positive symptoms Wasserman, Matskevich. At low level

Rice. 3.5.Symptom of “dangling hand” with damage to the radial nerve (a, b)

Rice. 3.6.Symptom of “clawed paw” with damage to the ulnar nerve (a-c)

Rice. 3.7.Symptoms of the “monkey hand” with damage to the median nerve (“obstetrician’s hand”) [a, b]

Rice. 3.8.Innervation of cutaneous sensitivity of the upper limb (peripheral type)

Rice. 3.9.

lesions - isolated lesion of the quadriceps femoris muscle.

Obturator nerve: violation of hip adduction, leg crossing, hip outward rotation, atrophy of the hip adductors. Sensitivity disorder on the inner surface of the thigh (Fig. 3.9).

External cutaneous nerve of the thigh: sensitivity disorder on the outer surface of the thigh, paresthesia, sometimes severe neuralgic paroxysmal pain.

Sciatic nerve: with a high complete lesion - loss of function of its main branches, the entire group of leg flexor muscles, inability to flex the leg, paralysis of the foot and fingers, foot drop, difficulty in

walking, atrophy of the muscles of the back of the thigh, all muscles of the lower leg and foot. Sensitivity disorder on the anterior, outer and posterior surfaces of the lower leg, dorsal and plantar surfaces of the foot, fingers, decreased or loss of the Achilles reflex, severe pain along the sciatic nerve, soreness of Walle's points, positive symptoms of tension, antalgic scoliosis, vasomotor-trophic disorders, in case of injury to the sciatic nerve - causalgia syndrome.

Gluteal nerves: violation of hip extension and pelvic fixation, “duck walk”, atrophy of the gluteal muscles.

Posterior cutaneous nerve of the thigh: sensitivity disorder on the back of the thigh and lower buttocks.

Tibial nerve: impaired plantar flexion of the foot and toes, outward rotation of the foot, inability to stand on toes, atrophy of the calf muscles, atrophy of the foot muscles,

Rice. 3.10.Innervation of cutaneous sensitivity of the lower limb (peripheral type)

Rice. 3.11.Symptom of “equine foot” with damage to the peroneal nerve

retraction of the interosseous spaces, a peculiar type of foot - “heel foot” (Fig. 3.10), sensitivity disorder on the back surface of the leg, on the sole, plantar surface of the fingers, decrease or loss of the Achilles reflex, vegetative-trophic disorders in the innervation zone, causalgia.

Peroneal nerve: limitation of dorsiflexion of the foot and toes, inability to stand on the heels, drooping of the foot downward and rotation inward (“horse foot”), a kind of “cock’s gait” (when walking, the patient raises his leg high so as not to touch the floor with his foot); atrophy of the muscles of the anterior outer surface of the leg, sensitivity disorder along the outer surface of the leg and dorsum of the foot; the pain is not pronounced (Fig. 3.11).

When the plexuses are damaged motor, sensory and autonomic disorders occur in the area of ​​innervation of this plexus.

Brachial plexus(C 5 -Th 1): persistent pain radiating throughout the arm, aggravated by movements, atrophic paralysis of the muscles of the entire arm, loss of tendon and periosteal reflexes. Impairment of all types of sensitivity in the area of ​​innervation of the plexus.

- Superior brachial plexus(C 5 -C 6) - Duchenne-Erb palsy: predominant damage to the muscles of the proximal arm,

sensitivity disorder along the outer edge of the entire arm, loss of the reflex from the biceps brachii muscle. - Inferior brachial plexus(From 7 - Th 1)- Dejerine-Klumpke palsy: disorder of movements in the forearm, hand and fingers while maintaining the function of the muscles of the shoulder girdle, impaired sensitivity on the inner surface of the hand, forearm and shoulder, vasomotor and trophic disorders in the distal parts of the hand, loss of the carporadial reflex, Bernard-Horner syndrome.

Lumbar plexus (Th 12 -L 4): the clinical picture is due to high damage to three nerves arising from the lumbar plexus: the femoral, obturator and external cutaneous nerve of the thigh.

Sacral plexus (L 4 -S 4): loss of function of the peripheral nerves of the plexus: the sciatic with its main branches - the tibial and peroneal nerves, the superior and inferior gluteal nerves and the posterior cutaneous nerve of the thigh.

Differential diagnosis of central and peripheral paralysis presented in table. 1.

Table 1.Symptoms of central and peripheral paralysis

In practice, we encounter diseases (for example, amyotrophic lateral sclerosis) in which symptoms characteristic of both central and peripheral paralysis are revealed: a combination of atrophy and grossly expressed hyperreflexia, clonus, and pathological reflexes. This is explained by the fact that a progressive degenerative or acute inflammatory process mosaically, selectively affects the pyramidal tract and cells of the anterior horn of the spinal cord, as a result of which both the central motor neuron is affected (central paralysis develops) and the peripheral motor neuron (peripheral paralysis develops). With further progression of the process, the motor neurons of the anterior horn are increasingly affected. With the death of more than 50% of the anterior horn cells, hyperreflexia and pathological reflexes gradually disappear, giving way to symptoms of peripheral paralysis (despite the ongoing destruction of the pyramidal fibers).

3.5. Half-spinal cord lesion (Brown-Séquard syndrome)

The clinical picture of Brown-Séquard syndrome is presented in Table. 2.

Table 2.Clinical symptoms of Brown-Séquard syndrome

Complete transverse spinal cord lesion characterized by development

The pyramidal system (synonymous with the pyramidal path) is a set 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 carry out voluntary movements.

The pyramidal tract comes from the cortex, from the giant pyramidal cells of Betz layer V field 4 in the corona radiata, occupying the anterior two-thirds of the posterior femur and the knee of the internal bursa of the brain. Then it passes through the middle third of the base of the cerebral peduncle into the pons (varolii). 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 (pyramid decussation). In the brain stem, fibers extend from the pyramidal system to the nuclei of the facial and hypoglossal nerves and to the motor nuclei, crossing slightly above or at the level of these nuclei. In the spinal cord, the crossed fibers of the pyramidal system occupy back lateral cords, uncrossed - anterior cords of the spinal cord. The motor analyzer receives afferent impulses from muscles, joints, etc. These impulses pass to the cerebral cortex through the optic thalamus, from where they approach the posterior central gyrus.

In the anterior and posterior central gyri there are distributions of cortical points for individual muscles that coincide with the distribution of the corresponding muscles of the body. Irritation of the cortical part of the pyramidal system, for example, by a scar on the lining of the brain, causes Jacksonian seizures (see). When the function of the pyramidal system in the brain (see) is lost, paralysis or paresis appears (see), as well as pyramidal symptoms (increased tendon and the appearance of pathological reflexes, increased muscle paralysis). Damage to the corticonuclear tracts of the facial nerve leads to central paresis of this nerve. The lesion of the pyramidal system in the area of ​​the internal bursa leads to hemiplegia (see). Damage to the pyramidal system in the brainstem results in a combination pyramidal symptoms on the opposite side with symptoms of damage to the nuclei of the cranial nerves on the affected side - 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 partly from other fields and areas. The pyramidal system received its name from the so-called pyramids of the medulla oblongata, formed on its ventral surface by pyramidal tracts passing there.

In lower vertebrates there is no pyramidal system. It appears only in mammals, and its importance in evolution gradually increases. In humans, the pyramidal system reaches its maximum development, and its fibers in the spinal cord occupy about 30% of the diameter area (in great apes 21.1%, in dogs 6.7%). The representation of the pyramidal system in the cerebral cortex is the motor analyzer nucleus. In lower mammals, the nucleus of the motor analyzer is not spatially separated from the nucleus skin analyzer and has a granular layer IV (a sign of the sensitive cortex). These nuclei mutually overlap, becoming increasingly isolated from each other as phylogenetic development progresses. 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, field 4 retains the IV granular layer, which represents a repetition in ontogenesis of the features found on early stages phylogeny of mammals. Myelin covers the nerve fibers of the pyramidal system during the 1st year of life.

In an adult, the main cortical representation of the pyramidal system corresponds to cytoarchitectonic fields 4 and 6 of the anterior central gyrus of the brain. Area 4 is characterized by the presence of Betz giant pyramidal cells in layer V, agranularity (absence of granular layers) and a large cortical width (about 3.5 mm). Area 6 has a similar structure, but does not have Betz 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, in the corona radiata, converge towards the internal bursa, where, forming a compact bundle, they occupy the anterior two-thirds of its posterior thigh and knee.

Then the fibers of the pyramidal system go to the middle third of the base of the cerebral peduncle. Entering the pons, they break up into separate small bundles that pass among the transversely located fibers of the frontal-pontine-cerebellar tract and the pons' own nuclei. In the medulla oblongata, the fibers of the pyramidal system again gather into a compact bundle and form pyramids. Here most of the fibers pass to the opposite side, forming a cross 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.) go together to the lower edge of the superior olive. Then the corticonuclear pathway gradually gives off 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. Corticospinal fibers descend into the spinal cord (see), where the intersecting fibers of the pyramidal system are concentrated in the lateral column, occupying its posterior part, and the non-intersecting fibers pass in the anterior column. Ending on the motor cells of the anterior horns (or on the intercalary cells) of the spinal cord, the fibers of the pyramidal system, gradually depleting, reach sacral region spinal cord. The number of fibers of the pyramidal system exceeds 1 million. In addition to motor fibers, there are also autonomic 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 the afferent fibers coming to it from the optic thalamus. As has been established, 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, at the most various localizations In brain lesions, the pyramidal system is usually affected to one degree or another.

Physiologically, the pyramidal system is a system that carries out 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. The muscles performing the most subtle working voluntary movements are especially widely represented (Fig. 2).

Rice. 1. Diagram of the pyramidal tract and the distribution of places of its origin in the cerebral cortex: 1 - limbic region; 2 - parietal region; 3 - precentral region; 4 - frontal region; 5 - insular region; 6 - temporal region; 7 - visual thalamus; 8 - inner bag.

Rice. 2. Scheme of somatotopic distribution of 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 disturbances are. 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 spasms of the muscles of the opposite half of the face, trunk and limbs on the opposite side. Loss of functions of the pyramidal system is manifested by paralysis and 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 increasing diagnostic importance. With unilateral damage to the cerebral cortex in the area 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 tracts 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 lesion can often be identified (the patient cannot close the eye on the affected side in isolation). A focal lesion of the pyramidal system in the area of ​​the internal bursa usually leads to hemiplegia (or hemiparesis), and with bilateral lesions to tetraplegia.

Lesions of the pyramidal system in the area 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 affected side, that is, by the presence of alternating syndromes (see).

With pyramidal hemiplegia and hemiparesis, the distal parts of the limbs are usually most affected.

Hemiplegia and hemiparesis with damage to the pyramidal system are usually characterized by increased tendon reflexes, increased muscle tone, loss of skin reflexes, especially plantar reflexes, the emergence of pathological reflexes - extensor (Babinsky, Oppenheim, Gordon, etc.) and flexor (Rossolimo, Mendel - Bekhterev, etc. ), and protective reflexes. Tendon and periosteal reflexes are evoked from the expanded zone. Cross reflexes and friendly movements appear - so-called synkinesis (see). In the initial stages of pyramidal hemiplegia, muscle tone (and sometimes reflexes) is reduced due to diaschisis (see). An increase in muscle tone is detected later - 3-4 weeks after the onset of the lesion. Most often, especially with capsular lesions, increased muscle tone predominates in the forearm flexors and leg extensors. This distribution of muscle hypertension leads to the appearance of Wernicke-Mann type contracture (see Wernicke-Mann type of contracture).