Single residual lesions of the white matter of the brain. White and gray matter pathways

14.01.2019

Our portal is already more than six months old. During this time, we posted about 700 materials on the site. And almost every one of them mentions either some part of the brain, or a type of nerve cell, or some part of this very cell — that is, everything that relates to the section of anatomy, histology and cytology. In addition, we often mention some molecules that play an important role in the functioning of the brain and the whole nervous system. Therefore, we are starting two large series of materials at once: “How does the brain work?” — about the parts, tissues and cells of the brain and, together with, “Neuromolecules” — about those substances that control all these tissues and cells. And we will start, as usual, with a blank sheet of paper. Sorry, from the white matter of the brain.

White matter brain

When people talk about the brain, they often— almost synonymous— gray matter is mentioned. But if basically everyone is familiar with the gray matter of the convolutions, then how many lay people know about the existence of white matter, or, as anatomists say in Latin,substantia alba? And, by the way, it occupies most of our brain.

If the brain is imagined as the planet Earth, it turns out that earth's crust — this is the cerebral cortex, the mantle (all its layers)— this is exactly the same white substance, and the core of the Earth— basal ganglia of the brain (we will also write about them). Even the ratio of parts is approximately the same.

And the white matter plays a very important role here. It consists of bundles of axons, processes of neurons, covered with a myelin sheath (an insulating layer consisting of oligodendrocytes (in the peripheral nervous system they are called Schwann cells). White matter not only connects various parts of the nervous system, but also coordinates all the work of the human body.

However, substantia alba — not only the head, it is also found in the spinal cord. And what’s most interesting is that only in this part of the nervous system does it seem to “envelop” the gray matter, that is, it is conditionally located outside. Here, its structure is made up of fibers leading from the brain (mainly from the “motor” centers) to the spinal cord, as well as connecting areas of the spinal cord itself. By the way, in the white matter of the spinal cord, anatomists distinguish the anterior cords (funiculus anterior), lateral cords (funiculus lateralis) and posterior cords (funiculus posterior). You see, such a rather unusual type of transport as the funicular is etymologically related to white matter!

Section of the spinal cord

Previously it was believed that white matter— it is only a passive carrier or transporter of information, but increasingly there is evidence of its direct participation in the processes of learning and information processing. In addition, some studies have shown that in people suffering from insomnia, the structure of the white matter, namely the myelin sheaths that electrically insulate the nerve processes, is disrupted.

Damage to the white matter can lead to paralysis (complete immobility of one or all limbs at once), visual field defects, and impaired coordination of movements. It is with the destruction of the myelin sheath of axons and replacement nerve tissue The connective tissue in the white matter of the brain and spinal cord is responsible for such a terrible disease as multiple sclerosis.

However, sometimes doctors deliberately damaged the white matter. Moreover, for this they even awarded the Nobel Prize to the Portuguese Egas Moniz, who proposed dissecting the white matter connecting the frontal lobes to treat mental disorders. "Dissection of the white" is translated as "leucotomy" in Greek. This word was included in the verdict of the Nobel committee, although another name for this procedure sounds much more ominous: lobotomy.

Anastasia Sheshukova

The brain consists of gray and white matter. White matter occupies the entire space between the gray matter of the cerebral cortex and the basal ganglia. The surface of the hemisphere, the cloak (pallium), is formed by a uniform layer of gray matter 1.3 - 4.5 mm thick, containing nerve cells.

First, let's look at white matter.

White matter has four parts:

1) the central substance of the corpus callosum, internal capsule and long associative fibers.

2) radiant crown (corona radiata), formed by radiating fibers entering and leaving the internal capsule (capsula interna);

3) the area of white matter in the outer parts of the hemisphere - the semi-oval center (centrum semiovale);

4) white matter in the gyri between the sulci;

Nerve fibers of white matter are divided into projection, associative and commissural.

The white matter of the hemispheres is formed by nerve fibers connecting the cortex of one gyrus with the cortex of other gyri of its and the opposite hemispheres, as well as with underlying formations.

Two brain commissures, commissura anterior and commissura fornicis, are much smaller in size and relate to the olfactory brain of the rhinencephalon and connect: commissura anterior - olfactory lobes and both parahippocampal gyri, commissura fornicis - hippocampi.

Most of the commissural fibers are part of the corpus callosum, which connects the parts of both hemispheres belonging to the brain.

Commissural fibers, which are part of the cerebral commissures, or commissures, connect not only symmetrical points, but also the cortex belonging to different lobes of the opposite hemispheres.

Association fibers connect different parts of the cortex of the same hemisphere.

Associative fibers are divided into short and long.

Short fibers connect neighboring convolutions in the form of arcuate bundles.

Long association fibers connect areas of the cortex that are more distant from each other.

Projection fibers connect the cerebral cortex big brain with underlying formations, and through them with the periphery. These fibers are divided into centripetal (ascending, corticopetal, afferent).

On a frontal section of the brain, the internal capsule looks like an oblique white stripe that continues into the cerebral peduncle.

In the internal capsule, the anterior leg (crus anterius) is distinguished - between the caudate nucleus and the anterior half inner surface lenticular nucleus, hind leg(crus posterius), - between the thalamus and the posterior half of the lenticular nucleus and genu (genu), lying at the inflection point between both parts of the internal capsule. Projection fibers can be divided according to their length into the following three systems, starting with the longest:

1. Fibrae thalamocorticalis et corticothalamici - fibers from the thalamus to the cortex and back from the cortex to the thalamus. Conducting excitation towards the cortex, and centrifugal (descending, corticofugal, efferent).

2. Tractus corticonuclearis - pathways to the motor nuclei of the cranial nerves. Since all motor fibers are collected in a small space in the internal capsule (the knee and the anterior two-thirds of its posterior leg), if they are damaged in this place, unilateral paralysis of the opposite side of the body is observed.

3. Tractus corticospinalis (pyramidalis) conducts motor volitional impulses to the muscles of the trunk and limbs.

4. Tractus corticopontini - paths from the cerebral cortex to the pontine nuclei. Using these pathways, the cerebral cortex has an inhibitory and regulatory effect on the activity of the cerebellum.

Projection fibers in the white matter of the hemisphere closer to the cortex form the corona radiata, and then the main part of them converges into the internal capsule, which is a layer of white matter between the lentiform nucleus (nucleus lentiformis) on one side, and the caudate nucleus (nucleus caudatus) and thalamus ( thalamus) - on the other.

Now let's look at the gray matter.

The surface of the cloak has a very complex drawing, consisting of alternating various directions grooves and ridges between them, called convolutions, gyri.

Deep permanent grooves are used to divide each hemisphere into large areas called lobes, lobi; the latter, in turn, are divided into lobules and convolutions.

The size and shape of the grooves are subject to significant individual fluctuations, as a result of which not only the brains of different people, but even the hemispheres of the same individual are not quite similar in the pattern of the grooves.

There are five lobes of the hemisphere: frontal (lobus frontalis), parietal (lobus parietalis), temporal (lobus temporalis), occipital (lobus occipitalis) and a lobe hidden at the bottom of the lateral sulcus, the so-called insula.

The central sulcus (sulcus cenrtalis) begins at the upper edge of the hemisphere and goes forward and down. The area of the hemisphere located in front of the central sulcus. Refers to the frontal lobe. The part of the brain surface lying posterior to the central sulcus constitutes the parietal lobe. The posterior border of the parietal lobe is the end of the parieto-occipital sulcus (sulcus parietooccipitalis), located on the medial surface of the hemisphere.

Frontal lobe. In the posterior region outer surface This lobe runs sulcus precentralis almost parallel to the direction of sulcus centralis. Two grooves run from it in the longitudinal direction: sulcus frontalis superior et sulcus frontalis inferior. Thanks to this frontal lobe is divided into four convolutions.

The vertical gyrus, gyrus precentralis, is located between the central and precentral sulci. The superior lateral surface of the hemisphere is delimited into lobes by three sulci: the lateral, central and the upper end of the parieto-occipital sulcus.

The lateral groove (sulcus cerebri lateralis) begins on the basal surface of the hemisphere from the lateral fossa and then passes to the superolateral surface

The lobe consists of a number of convolutions, called in some places lobules, which are limited by the grooves of the brain surface.

The horizontal convolutions of the frontal lobe are: superior frontal (gyrus frontalis superior), middle frontal (gyrus frontalis medius) and inferior frontal (gyrus frontalis inferior).

Temporal lobe. The lateral surface of this lobe has three longitudinal convolutions, delimited from each other by sulcus temporalis superior and sulcus temporalis inferior. The gyrus temporalis medius extends between the superior and inferior temporal grooves. Below it runs the gyrus temporalis inferior.

Occipital lobe. The grooves on the lateral surface of this lobe are variable and inconsistent. Of these, the transversely running sulcus occipitalis transversus is distinguished, usually connecting to the end of the interparietal sulcus.

Parietal lobe. On it, approximately parallel to the central groove, there is a sulcus postcentralis, usually merging with the sulcus intraparietalis, which runs in a horizontal direction. Depending on the location of these grooves, the parietal lobe is divided into three gyri.

The vertical gyrus, gyrus postcentralis, runs behind the central sulcus in the same direction as the precentral gyrus. Above the interparietal sulcus is the superior parietal gyrus, or lobule (lobulus parietalis superior), below - lobulus parietalis inferior.

Island. This lobe has the shape of a triangle. The surface of the insula is covered with short convolutions.

The lower surface of the hemisphere in that part that lies anterior to the lateral fossa belongs to the frontal lobe.

On the posterior portion of the basal surface of the hemisphere, two grooves are visible: the sulcus occipitotemporalis, running in the direction from the occipital pole to the temporal and limiting the gyrus occipitotemporalis lateralis, and the sulcus collateralis running parallel to it. Here the sulcus olfactorius runs parallel to the medial edge of the hemisphere. Parallel to and above this groove, the sulcus cinguli runs along the medial surface of the hemisphere. Between them is the gyrus occipitotemporalis medialis.

Medial to the collateral sulcus there are two gyri: between the posterior part of this sulcus and the sulcus calcarinus lies the gyrus lingualis; between the anterior section of this groove and the deep sulcus hippocampi lies the gyrus parahippocampalis.

The gyrus adjacent to the brain stem is already located on the medial surface of the hemisphere.

Behind the precuneus lies a separate area of the cortex belonging to the occipital lobe - the cuneus. Between the lingual sulcus and the sulcus of the corpus callosum stretches the cingulate gyrus (gyrus cinguli), which, through the isthmus (isthmus), continues into the parahippocampal gyrus, ending with the hook (uncus). Gyrus cinguli, isthmus and gyrus parahippocampalis form together a vaulted gyrus (gyrus fornicatus), which describes an almost complete circle, open only below and in front.

On the medial surface of the hemisphere there is a groove of the corpus callosum (sulcus corpori callosi), running directly above the corpus callosum and continuing with its posterior end into the deep sulcus hippocampi, which is directed forward and downward.

The paracentral lobule (lobulus paracentralis) is a small area above the lingual sulcus. From the paracentral lobule there is quadrangular surface(the so-called precuneus, precuneus). It belongs to the parietal lobe. The vaulted gyrus is not related to any of the lobes of the cloak. It belongs to the limbic region. The limbic region is part of the neocortex of the cerebral hemispheres, occupying the cingulate and parahippocampal gyri; part of the limbic system.

Pulling apart the edge of the sulcus hippocampi, one can see a narrow jagged gray stripe, which is a rudimentary gyrus of the gyrus dentatus.

References

1. M.G. Prives, N.K. Lysenkov, V.I. Bushkovich. Human anatomy. M., 1985

2. Great medical encyclopedia. vol. 11, M., 1979

3. Great medical encyclopedia. vol. 6, M., 1977

Gray and white matter of the brain Abstract. How to treat the disease?
Gray and white matter of the brain Abstract. Traditional methods of treatment and healing.
Unique healing video sessions.

The white matter of the cerebral hemispheres consists of three types of fibers - association fibers, connecting individual areas of the cerebral cortex within one hemisphere, commissural fibers - connecting the cerebral hemispheres with each other, and projection - conducting pathways of the analyzers, providing two-way communication between the cerebral cortex and the underlying ones. formations.

Internal capsule and semioval center. The internal capsule is a compact cluster of pathways going to the cortex and from the cortex to the underlying parts of the central nervous system. From the outside it borders on the lenticular nucleus, and from the inside on the optic tubercle and the caudate body.

The pathways are located in the internal capsule in a certain order. In its anterior thigh there are pathways connecting the frontal lobe of the brain with the cerebellum and with the optic thalamus. In the knee of the internal capsule there are corticonuclear pathways to the nuclei of the motor cranial nerves. The most anterior sections of this segment are occupied by fibers for combined eye movements.

In the posterior thigh of the internal capsule, the pathways lie in the following order. Its anterior sections are occupied by the pyramidal fasciculus. In the segment of the pyramidal tract passing through the internal capsule, the fibers are located in such a way that in front, directly adjacent to the corticobulbar tracts, lie the pyramidal fibers for the neck and arm, and more posteriorly for the trunk and legs. In both the foot and hand bundles, the finger conductors are behind the others, but the boundary between the groups of conductors is usually blurred and the fibers are partially mixed. Here, in addition to the pyramidal fibers, there are cortico-rubral and thalapallidal connections. This should be kept in mind because any pathological focus in this place, in addition to the pyramidal ones, usually affects these connections. Posterior to the pyramidal conductors are sensory pathways running from the thalamus optic to the cerebral cortex.

Further, posteriorly, the visual pathways are located and, finally, in the pars sublenticularis there are the auditory pathway and the pathway connecting the temporal and occipital regions of the cortex with the cerebellum through the pons. As can be seen from the above, in the internal capsule the pathways are located in a certain sequence: connections of the frontal lobe with the underlying formations are located more orally, connections of the parietal lobe with the underlying formations are located posterior to them, and, finally, the caudal parts of the capsule are occupied by connections of the occipital and temporal lobes with the underlying formations. formations. Knowledge of the topography of the conductive pathways located in the capsule is necessary for topical diagnosis of its lesions. In this case, we must keep in mind the following circumstance. In the internal capsule, all conductors lie compactly in a rather limited space, as a result of which a pathological focus in the internal capsule (for example, hemorrhage) simultaneously affects a number of conducting systems. This explains the massiveness of symptoms in capsular localizations of the process.

A different picture is observed with damage to the white matter, located under the cerebral cortex, down to the level of the subcortical nodes and known as centrum semiovale and corona radiata. Here, the sensitive conductors on the way from the capsule to the cortex begin to fan out, and even more so the closer to the cortex. On the contrary, the pyramidal pathways along the path from the cortex to the capsule begin to converge in a fan-shaped manner, and the closer to the capsule, the more so. This creates conditions under which pathological foci in the centrum semiovale, other things being equal, simultaneously affect fewer conductors and cause less massive syndromes than with capsular lesions. The most commonly affected areas are the posterior hip and knee of the internal capsule. When the knee of the internal capsule is damaged, the corticobulbar pathways that send motor impulses to the nuclei of the motor cranial nerves are affected. But since most of these nerves receive bilateral corticonuclear innervation, only those that are connected to one opposite hemisphere of the brain are affected. The patient will experience central palsy of the XII and VII nerves on the side opposite to the lesion. With bilateral damage to the knee of the internal capsule, the patient develops pseudobulbar palsy. Isolated damage to the conductors located in the knee of the internal capsule is rare. In most cases, it is combined with damage to the pyramidal fasciculus, and often to other conductors located in the posterior thigh of the internal capsule. In these cases, the patient, in addition to disruption of the supranuclear innervation of the VII and XII nerves, experiences spastic (central) hemiplegia on the opposite side. Capsular hemiplegia is characterized by a more or less uniform distribution of paralysis in the arm and leg, as well as a peculiar posture of the affected limbs. With it, the arm is abducted from the body and bent at the elbow joint, the hand is drained and bent. The fingers are also bent. The leg is extended at the hip and knee joint and brought. The foot is flexed and slightly supinated. When walking, the patient, due to the “lengthening” of the leg, abducts it, describing it in a semicircle. This position, due to the selective distribution of muscle hypertension, is called the Wernicke-Mann position.

In paralyzed limbs, the distal parts suffer more. Movements of the trunk with unilateral lesions of the capsule are not noticeably impaired due to the double pyramidal innervation of the trunk muscles. Synkinesis, or pathological conjugate movements, are observed in paralyzed limbs.

If the pathological process, in addition to the pyramidal tract, also involves sensitive conductors, then the patient’s paralyzed limbs also suffer from sensitivity. Sensory impairment is more or less evenly distributed over the entire half of the body, with the arm being affected somewhat more than the leg, and the distal sections being more affected than the proximal ones. Of all types of sensitivity, deep sensitivity is most affected. Typically, with capsular localizations of the process, sensory disorders are less constant and less persistent than motor disorders.

When the visual pathways lying behind the conductors of general sensitivity are involved in the process, the patient develops homonymous hemianopsia - the halves of the visual fields opposite to the lesion are lost. Most often, hemianopia in these cases occurs as a negative scotoma (the patient does not notice the visual defect). When the “blind” halves are illuminated, the reaction of the pupils is preserved.

The section of the internal capsule, where the central auditory tract is located, is rarely affected. Only more subtle methods can detect bilateral hearing loss, more on the side opposite to the lesion.

It should be borne in mind that with capsular localizations of the process, only symptoms of prolapse are observed; There are no symptoms of irritation (motor, sensory, visual, etc.). Damage to the centrum semiovale, like damage to the internal capsule, is accompanied by disturbances in movement, sensitivity, etc. due to damage to pathways running in a centrifugal and centripetal direction relative to the cortex. However, the clinical symptoms are distinguished by a certain originality and consist in the fact that the symptoms of damage to the semi-oval center contain both capsular and cortical features, depending on the degree of damage. Thus, when the center semiovale is affected, a combination of symptoms of prolapse and symptoms of irritation (motor or sensory) is often encountered. In contrast to capsular localizations, uneven hemiplegia is observed, often approaching the type of cortical monoplegia. Sensitivity disorders are of the same nature: the area of distribution of these disorders is smaller than with capsular disorders, sensitivity suffers much more in the arm (more often) or in the leg. Here there are conditions under which dissociation of motor, sensory and other disorders occurs more often than simultaneous damage to the motor, sensory and visual pathways, as well as supranuclear innervation of the cranial nerves, as with damage to the internal capsule. Damage to the parts of the centrum semiovale closest to the cortex can affect not only the projection pathways, but also the commissural and association fibers lying directly under the cortex. And then the clinical picture can be supplemented by symptoms of a violation of higher cortical functions (speech disorders, apraxia, etc.).

Commissural fibers. Commissural fibers, concentrated mainly in the corpus callosum, connect the frontal, parietal, temporal and occipital lobes of both hemispheres. Therefore, syndromes of lesions of the corpus callosum include, depending on the location of its lesion, to varying degrees, symptoms of damage to these areas of the brain. Often, when the corpus callosum is damaged, apraxia is observed in the clinic, limited only to the left hand. This selectivity of apractical disorders is explained by the fact that when the corpus callosum is damaged, the connection between the left parietal region and the right hemisphere, associated with the motor functions of the left hand, is disrupted.

Association fibers. Damage to association fibers causes symptoms of dysfunction of the cerebral cortex.

The human brain contains white and gray matter of the hemispheres, which are necessary for the functioning of brain activity. We will look at what each of them is responsible for and what they are.

"Substantia grisea", the gray matter of the brain is one of the main components of the central nervous system, which includes capillaries different sizes and neurons. In terms of its functional characteristics and structure, the gray matter is quite different from the white matter, which consists of bundles of myelin nerve fibers. The difference in color between substances is due to the fact that white gives myelin, from which the fibers are made. "Substantia grisea" actually has a gray-brown color, since numerous vessels and capillaries give it this shade. On average, the amount of substantia grisea and substantia alba in the human brain is approximately the same.

"Substantia alba" or white matter is the fluid that occupies the cavity between the basal ganglia and the "substantia grisea". White matter consists of many nerve fibers, which are conductors that diverge into different directions. Its main functions include not only its conduction of nerve impulses, but also creates a safe environment for the functioning of the nuclei and other parts of the cerebrum (translated from Latin as “brain”). White matter is fully formed in humans in the first six years of their life.

In medical science, it is customary to divide nerve fibers into three groups:

Associative fibers, which, in turn, are also different types- short and long, they are all concentrated in one hemisphere, but perform different functions. The short ones connect neighboring convolutions, and the long ones, accordingly, maintain the connection of more distant areas. The paths of associative fibers are as follows - the superior oblong fasciculus of the frontal lobe to the temporal, parietal and occipital cortex; hook-shaped bun and belt; inferior longitudinal fasciculus from the frontal lobe to the occipital cortex.
Commissural fibers are responsible for the function of connecting the two hemispheres, as well as for the compatibility of their functions in brain activity. This group fibers are represented by the anterior commissure, the commissure of the fornix and the corpus callosum.
Projection fibers connect the cortex with other centers of the central nervous system, up to the spinal cord. There are several such types of fibers: some are responsible for motor impulses sent to the muscles of the human body, others lead to the nuclei of the cranial nerves, others lead from the thalamus to the cortex and back, and the last from the cortex to the nuclei of the bridge.

Functions of white matter of the brain

The white matter of the cerebral hemispheres “Substantia alba” is generally responsible for coordinating all human life activities, since it is this part that provides communication to all parts of the nerve chain. White matter:

connects together the work of both hemispheres;
plays an important role in transmitting data from the cortex cerebral hemispheres to areas of the nervous system;
ensures contact of the visual thalamus with the cerebrum cortex;
connects the convolutions in both parts of the hemispheres.

Damage to the “substantia alba”

Against the background of changes in the condition of this department, the following diseases may develop:

Hemiplegia – paralysis of one part of the body;
“Three hemi syndrome” - loss of sensitivity in half of the face, torso or limb - hemianesthesia; destruction of sensory perception - hemiataxia; visual field defect - hemianopsia;
Mental illnesses – lack of recognition of objects and phenomena, untargeted actions, pseudobulbar syndrome;
Disorders and disorders of the swallowing reflex.

White matter function and brain health

The speed of conduction of human nervous reactions directly depends on the health and integrity of the “substantia alba”. His normal functioning is, first of all, his health. Absent-mindedness, Alzheimer's disease and other mental disorders - this is what threatens the destruction of the microstructure of this part of our brain.

Physical activity

According to the latest research by scientists from the USA physical activity capable in a positive way affect the structure of white matter, and therefore the health of the entire brain as a whole. Firstly, physical exercise help increase blood supply to myelin fibers. Secondly, exercise makes your brain matter denser, which allows it to quickly transmit signals from one part of the brain to another. In addition, it has been scientifically proven that both children and older people should perform physical activity to preserve it.

Relationship between age and white matter status

Neuroscientists from the USA conducted an experiment: in scientific research group included people aged 7 to 85 years. Using diffusion tomography, more than a hundred participants were examined in the brain and in particular the volume of the “substantia alba”.

The conclusions are: greatest number qualitative connections were observed in subjects aged from 30 to 50 years. Peak activity of thinking and highest degree Learning ability develops to its maximum in the middle of life, and then declines.

White matter and lobotomy

And if until recently it was believed that white matter is a passive transmitter of information, now this opinion is changing in the geometrically opposite direction.

This may seem surprising, but at one time experiments were carried out on white matter. The Portuguese Egashu Monizo at the beginning of the 20th century received Nobel Prize for proposing to dissect the white matter of the brain to treat mental disorders. This particular procedure is known in medicine as leucotomy or lobotomy, one of the most terrible and inhumane procedures known to the world.

First, let's look at white matter.

White matter has four parts:

Central substance of the corpus callosum, internal capsule and long association fibers;

Radiant crown (corona radiata), formed by radiating fibers entering and leaving the internal capsule (capsula interna);

The area of white matter in the outer parts of the hemisphere is the semioval center (centrum semiovale);

White matter in the gyri between the sulci.

Nerve fibers of white matter are divided into projection, associative and commissural.

Two brain commissures, commissura anterior and commissura fornicis, are much smaller in size and relate to the olfactory brain of rhinencephalon and connect: commissura anterior - olfactory lobes and both parahippocampal gyri, commissura fornicis - hippocampi.

Commissural fibers, which are part of the cerebral commissures, or commissures, connect not only symmetrical points, but also the cortex belonging to different lobes of the opposite hemispheres.

Association fibers connect different parts of the cortex of the same hemisphere.

Associative fibers are divided into short and long.

Short fibers connect neighboring convolutions in the form of arcuate bundles.

Long association fibers connect areas that are more distant from each other

Projection fibers connect the cerebral cortex with the underlying formations, and through them with the periphery.

On a frontal section of the brain, the internal capsule looks like an oblique white stripe that continues into the cerebral peduncle.

In the internal capsule, the anterior leg (crus anterius) is distinguished - between the caudate nucleus and the anterior half of the inner surface of the lentiform nucleus, as well as the posterior leg (crus posterius) - between the thalamus and the posterior half of the lenticular nucleus and the knee (genu). Projection fibers according to their length can be divided into the following three systems:

Fibrae thalamocorticalis et corticothalamici - fibers from the thalamus to the cortex and back from the cortex to the thalamus; conducting excitation towards the cortex and centrifugal (descending, corticofugal, efferent).

Tractus corticonuclearis - pathways to the motor nuclei of the cranial nerves. Since all motor fibers are collected in a small space in the internal capsule (the knee and the anterior two-thirds of its posterior leg), if they are damaged in this place, unilateral paralysis of the opposite side of the body is observed.

Tractus corticospinalis (pyramidalis) conducts motor volitional impulses to the muscles of the trunk and limbs.

Tractus corticopontini - pathways from the cerebral cortex to the pontine nuclei. Using these pathways, the cerebral cortex has an inhibitory and regulatory effect on the activity of the cerebellum.

Projection fibers in the white matter of the hemisphere closer to the cortex form the corona radiata, and then the main part of them converges into the internal capsule, which is a layer of white matter between the lentiform nucleus (nucleus lentiformis), the caudate nucleus (nucleus caudatus) and the thalamus (thalamus).

Now let's look at the gray matter.

The surface of the cloak has a very complex pattern, consisting of grooves alternating in different directions and ridges between them, called convolutions.

Deep, permanent grooves are used to divide each hemisphere into large areas called lobes; the latter, in turn, are divided into lobules and convolutions.

The central sulcus (sulcus cenrtalis) begins at the upper edge of the hemisphere and goes forward and down. The part of the hemisphere located in front of the central sulcus belongs to the frontal lobe. The part of the brain surface lying posterior to the central sulcus constitutes the parietal lobe. The posterior border of the parietal lobe is the end of the parieto-occipital sulcus (sulcus parietooccipitalis), located on the medial surface of the hemisphere.

Frontal lobe. In the posterior part of the outer surface of this lobe the sulcus precentralis runs almost parallel to the direction of the sulcus centralis. Two grooves run from it in the longitudinal direction: sulcus frontalis superior et sulcus frontalis inferior. Due to this, the frontal lobe is divided into four convolutions.

The lateral groove (sulcus cerebri lateralis) begins on the basal surface of the hemisphere from the lateral fossa and then passes to the superolateral surface

The lobe consists of a number of convolutions, called in some places lobules, which are limited by the grooves of the brain surface.

The horizontal convolutions of the frontal lobe are: superior frontal (gyrus frontalis superior), middle frontal (gyrus frontalis medius) and inferior frontal (gyrus frontalis inferior).

Island. This lobe has the shape of a triangle. The surface of the insula is covered with short convolutions.

The lower surface of the hemisphere in that part that lies in front of the lateral fossa belongs to the frontal lobe.

The gyrus adjacent to the brain stem is already located on the medial surface of the hemisphere.

The paracentral lobule (lobulus paracentralis) is a small area above the lingual sulcus. From the paracentral lobule there is a quadrangular surface (the so-called precuneus, precuneus). It belongs to the parietal lobe. The vaulted gyrus is not related to any of the lobes of the cloak. It belongs to the limbic region. The limbic region is part of the neocortex of the cerebral hemispheres, occupying the cingulate and parahippocampal gyri; part of the limbic system.

Pulling apart the edge of the sulcus hippocampi, one can see a narrow jagged gray stripe, which is a rudimentary gyrus of the gyrus dentatus.

The pathways of the central nervous system (tractus sistematis nervosi centralis) are groups of nerve fibers that are characterized by common structure and functions and connect various parts of the brain and spinal cord.

All nerve fibers of one path begin from homogeneous neurocytes and end on neurocytes that perform the same function. In the process of phylogenesis c.n.s. As a result of the development of the brain, the simple reflex arc underlying the functions of the nervous system becomes more complex, and in each part of it, instead of one neurocyte, chains of neurocytes are formed, the axons of which are grouped into pathways. Some pathways of the central nervous system, uniting phylogenetically earlier nuclei located in the brain stem, provide motor reflex responses to external stimuli, maintain muscle tone, body balance, etc. Others transmit impulses to the higher parts of the central nervous system, to the cerebral cortex or from it to the subcortical nuclei and spinal cord.

There are associative (combinative) nerve fibers or bundles of fibers that carry out one-way connections; commissural (commissural) fibers, providing bilateral connections between functionally homogeneous parts of the brain or spinal cord, and projection fibers connecting the cerebral cortex with the underlying parts of the brain and spinal cord. Depending on the size, shape and direction, groups of nerve fibers are called tracts, fascicles, fibers, commissures, loops and radiates.

Associative are intracortical fibers located within the cerebral cortex and extracortical short fibers connecting areas of the cortex of adjacent convolutions of the cerebral hemispheres and are called arcuate fibers. Long fibers form bundles connecting the lobes within one hemisphere. These include the upper and lower longitudinal and uncinate fascicles, etc. In the spinal cord, associative fibers make intersegmental connections and form the anterior, lateral and posterior fascicles of their own.

The commissural fibers of the cerebral hemispheres form the anterior commissure, which connects the parts of the olfactory brain of the right and left sides; the fornix commissure, which connects the cortex of the medial surfaces of both cerebral hemispheres and the hippocampus; corpus callosum, the fibers of which form the radiance of the corpus callosum and connect parts of the neocortex of the right and left hemispheres. Within the diencephalon and mesencephalon, functionally homogeneous formations of the right and left sides are connected by the epithalamic (posterior) commissure, leash commissure, dorsal and ventral supraoptic commissures. In the spinal cord, the white commissure is formed by fibers passing from one side of the spinal cord to the other (fibers of the spinothalamic fascicle, etc.).

Projection fibers in the brain and spinal cord form centripetal (ascending, afferent, sensory) pathways that transmit impulses from receptors that perceive information from the external world and the internal environment of the body to the brain, and centrifugal (descending, efferent, motor) pathways that transmit impulses from brain structures to cells of motor nuclei of cranial nerves and anterior horns of the spinal cord

Afferent pathways, depending on the types of sensitivity, are divided into the paths of extero-, proprio- and interoceptive sensitivity (see Autonomic nervous system).

The pathways of exteroceptive sensitivity include the lateral and anterior spinothalamic tracts, the pathways of the sensory organs. The lateral spinothalamic pathway (pain and temperature sensitivity) begins from the false unipolar cells of the spinal ganglia (the first neuron). Their peripheral processes are part of the spinal nerves and end with receptors in the skin and mucous membranes. The central processes form the dorsal roots and go into the spinal cord, ending on the dorsal horn cells (second neuron). The processes of the second neurons pass through the white commissure of the spinal cord to the opposite side (form a decussation), become part of the spinothalamic fascicle and ascend into the medulla oblongata as part of the lateral cord. There they are adjacent from the lateral wall to the medial lemniscus, forming a spinal lemniscus, and go through the medulla oblongata, the tegmentum of the pons and the cerebral peduncles to the cells of the ventrolateral nucleus of the thalamus (third neuron). The processes of the cells of the thalamic nucleus constitute the thalamocortical bundle, passing through the posterior leg of the internal capsule to the cortex of the postcentral gyrus, where the cortical end of the general sensitivity analyzer is located. The anterior spinothalamic tract is a pathway for touch and pressure, the receptors of which are located in the skin, and the first neurons are in the spinal ganglia. Their central shoots, as part of the dorsal roots, enter the spinal cord and end on the cells of the dorsal horn (second neuron). The processes of the second neurons pass through the white commissure of the spinal cord into the anterior cord of the opposite side, forming a decussation, and join the spinothalamic fascicle, within which they go to the medulla oblongata. In the brain, this pathway runs along with the lateral spinal tract as part of the lateral part of the medial lemniscus called the spinal lemniscus. The third neuron of this type is the cells of the ventrolateral nucleus of the thalamus. Some of the fibers conducting tactile sensitivity do not form a decussation and follow to the brain in the posterior cord along with the thin and wedge-shaped bundles. The anterior and lateral spinothalamic tracts are often combined into one spinothalamic fascicle, in which fibers coming from pressure receptors pass in the anterior cord closer to midline. More lateral are the fibers that conduct the sense of touch, and then the sensation of pain and temperature. This group also includes the pathways of the sense organs.

The pathways of proprioceptive sensitivity (muscular-articular sense) are directed to the cerebral cortex and to the cerebellum, which regulates the coordination of movements. The pathway of proprioceptive sensitivity, going to the cerebral cortex, received in its different parts different names. In the spinal cord, it passes through the posterior funiculus, where it forms a thin bundle (bundle of Gaulle). which transmits impulses from the lower extremities and the lower half of the torso, and the laterally located wedge-shaped bundle (Burdach's bundle), which carries impulses from the upper half of the torso and upper extremities. Both pathways end on the cells of the nuclei of the same name in the medulla oblongata, where the second neurons are located. The processes of the second neurons in the medulla oblongata form the decussation of the medial lemniscus, and then within the brain stem form the bulbothalamic tract, called the medial lemniscus. Part of the fibers of the second neuron, upon exiting the thin and cuneate nuclei, bends outward and forms external dorsal and ventral arcuate fibers, which follow through the inferior cerebellar peduncles to the cortex of the cerebellar vermis. The medial loop passes in the tegmentum (posterior part) of the pons and midbrain, its fibers end in the thalamus on the cells of the ventrolateral nucleus of the thalamus (third neuron), the processes of the third neurons (thalamoparietal fibers) pass in the posterior leg of the internal capsule and are sent to the cerebral cortex in the postcentral gyrus.

Proprioceptive pathways leading to the cerebellum transmit information about the state of the musculoskeletal system, which ensures the regulation of body movements and balance. They are represented by the posterior (uncrossed) and anterior (double crossed) spinocerebellar tracts.

The central processes of the first neurons of the posterior spinocerebellar tract (Flexig's bundle), lying in the spinal ganglia, in the spinal cord approach the cells of the thoracic nucleus (Clark's column), located at the base of the dorsal horn (second neuron). The axons of the second neurons exit into the posterior part of the lateral funiculus and rise to the medulla oblongata, from where they go through the inferior cerebellar peduncle to the cells of the cerebellar vermis cortex.

The central process of the first neuron of the anterior spinocerebellar tract (Gowers' bundle) ends on the cells of the central intermediate substance adjacent to the thoracic nucleus (second neuron). The processes of the second neurons pass through the white commissure into the anterior part of the lateral funiculus of the opposite side and rise into the brain to the level of the isthmus of the rhombencephalon. In the area of the superior medullary velum, most of the fibers return to their side and go through the superior cerebellar peduncle to the cortex of the cerebellar vermis.

Association fibers connect the cortex of the vermis and the cerebellar hemispheres and, through the dentate nucleus, with the red nucleus (one of the centers of the extrapyramidal system), and through the thalamus with the cerebral cortex. From the cortex of the cerebellar hemispheres, the impulse is transmitted to the dentate nucleus, from the cells of which the dentate-red-nuclear fibers begin, passing through the superior cerebellar peduncle to the red nucleus of the opposite side. In addition to the connections listed above, the cerebellum has numerous afferent and efferent pathways connecting it with the vestibular nuclei, reticular formation, olive, roof and tegmentum of the midbrain, etc. Among them, the afferent pathway going to the cerebellar hemispheres from the cerebral cortex - cortico- cerebellopontine tract.

Motor P. items are represented by two groups. The first group includes the main motor (pyramidal) pathway, or pyramidal system. It originates from the giant pyramidal neurocytes (Betz cells) of the cortex of the precentral gyrus and pericentral lobule and ends on the cells of the motor nuclei of the cranial nerves (corticonuclear tract) and the cells of the anterior horns of the spinal cord (lateral and anterior corticospinal tracts). The second group consists of extrapyramidal, reflex motor pathways included in the extrapyramidal system. The descending pathways that descend into the spinal cord include the red nucleus-spinal cord tract, which originates from the cells of the red nucleus; vestibular cord, starting from the cells of the vestibular nuclei; tegmental-bulbar and tegnospinal tracts, coming from the superior and inferior colliculi of the roof of the midbrain. All of them end on the cells of the motor nuclei of the cranial nerves or the cells of the anterior horn-spinal cord.

Most motor pathways intersect, so when a section of the cortex or motor center is damaged on one side, motor function is impaired on the other. The lateral corticospinal tract can be traced to the sacral part of the spinal cord and often contains uncrossed fibers. The anterior corticospinal tract crosses segmentally and often ends in the thoracic region. That. connections are made with the motor cortex on both the opposite and the same side.

Conducting pathways of the central nervous system connect the centers of the brain with each other and with the spinal cord in both directions. Thus, the textospinal, vestibulospinal, reticulospinal, olivospinal and other descending tracts descend into the spinal cord, and the spinotectal, spinovestibular, spinoreticular, spinolivar and other ascending tracts ascend from the spinal cord to the brain.