The main pathways of the spinal cord. Descending pathways of the spinal cord

The CNS pathways are built from functionally homogeneous groups of nerve fibers; they represent internal connections between the nuclei and cortical centers located in different parts and departments of the brain, and serve for their functional association (integration). The pathways, as a rule, pass through the white matter of the spinal cord and brain, but can also be localized in the tegmentum of the brainstem, where there are no clear boundaries between the white and gray matter.

The main conducting link in the system of transmitting information from one center of the brain to another is nerve fibers - the axons of neurons that transmit information in the form of a nerve impulse in a strictly defined direction, namely from the cell body. Among the pathways, depending on their structure and functional significance, various groups of nerve fibers are distinguished: fibers, bundles, tracts, radiances, adhesions (commissures).

Projection pathways consist of neurons and their fibers that provide connections between the spinal cord and the brain. Projection paths also connect the nuclei of the trunk with the basal nuclei and the cerebral cortex, as well as the nuclei of the trunk with the cortex and nuclei of the cerebellum. Projection paths can be ascending and descending.

Ascending (sensory, sensitive, afferent) projection pathways conduct nerve impulses from extero-, proprio- and interoreceptors (sensory nerve endings in the skin, organs of the musculoskeletal system, internal organs), as well as from the sense organs in an upward direction to the brain, predominantly to the cerebral cortex, where they mainly end at the level of the IV cytoarchitectonic layer.

A distinctive feature of the ascending pathways is the multi-stage, sequential transmission of sensory information to the cerebral cortex through a number of intermediate nerve centers.

In addition to the cerebral cortex, sensory information is also sent to the cerebellum, the midbrain, and the reticular formation.

Descending (efferent or centrifugal) projection pathways conduct nerve impulses from the cerebral cortex, where they originate from the pyramidal neurons of the V cytoarchitectonic layer, to the basal and stem nuclei of the brain and further to the motor nuclei of the spinal cord and brain stem.

They transmit information related to the programming of body movements in specific situations, therefore they are motor pathways.

A common feature of the descending motor pathways is that they necessarily pass through the internal capsule - a layer of white matter in the cerebral hemispheres that separates the thalamus from the basal ganglia. In the brainstem, most of the descending pathways to the spinal cord and cerebellum go at its base.

35. Pyramidal and extrapyramidal systems

The pyramidal system is a combination of motor centers of the cerebral cortex, motor centers of cranial nerves located in the brain stem, and motor centers in the anterior horns of the spinal cord, as well as efferent projection nerve fibers that connect them together.

Pyramidal pathways provide the conduction of impulses in the process of conscious regulation of movements.

Pyramidal pathways are formed from giant pyramidal neurons (Betz cells), as well as large pyramidal neurons localized in layer V of the cerebral cortex. Approximately 40% of the fibers originate from pyramidal neurons in the precentral gyrus, where the cortical center of the motor analyzer is located; about 20% - from the postcentral gyrus, and the remaining 40% - from the posterior sections of the upper and middle lobar gyrus, and from the supramarginal gyrus of the lower parietal lobule, in which the center of praxia is located, which controls complex coordinated purposeful movements.

Pyramidal pathways are divided into corticospinal and cortical-nuclear. Their common feature is that, starting in the cortex of the right and left hemispheres, they move to the opposite side of the brain (i.e., cross) and ultimately regulate the movements of the contralateral half of the body.

The extrapyramidal system combines phylogenetically more ancient mechanisms for controlling human movements than the pyramidal system. It carries out predominantly involuntary, automatic regulation of complex motor manifestations of emotions. A distinctive feature of the extrapyramidal system is a multi-stage, with many switches, transmission of nerve influences from various parts of the brain to the executive centers - the motor nuclei of the spinal cord and cranial nerves.

Through the extrapyramidal pathways, motor commands are transmitted during protective motor reflexes that occur unconsciously. For example, thanks to the extrapyramidal pathways, information is transmitted when the vertical position of the body is restored as a result of a loss of balance (vestibular reflexes) or during motor reactions to a sudden light or sound effect (protective reflexes that close in the roof of the midbrain), etc.

The extrapyramidal system is formed by the nuclear centers of the hemispheres (basal nuclei: caudate and lenticular), diencephalon (medial nuclei of the thalamus, subthalamic nucleus) and the brain stem (red nucleus, black matter), as well as pathways connecting it with the cerebral cortex, with the cerebellum , with the reticular formation and, finally, with the executive centers lying in the motor nuclei of the cranial nerves and in the anterior horns of the spinal cord.

There is also a somewhat extended interpretation, when to E.S. they include the cerebellum, the nuclei of the quadrigemina of the midbrain, the nuclei of the reticular formation, etc.

Cortical pathways originate from the precentral gyrus, as well as other parts of the cerebral cortex; these pathways project the influence of the cortex to the basal ganglia. The basal nuclei themselves are closely connected with each other by numerous internal connections, as well as with the nuclei of the thalamus and with the red nucleus of the midbrain. The motor commands formed here are transmitted to the executive motor centers of the spinal cord mainly in two ways: through the red nuclear-spinal (rubrospinal) tract and through the nuclei of the reticular formation (reticulospinal tract). Also, through the red nucleus, the influence of the cerebellum on the work of the spinal motor centers is transmitted.

No. p / p	Path name	Path characteristic
descending	Ascending
Anterior cords
	Anterior corticospinalis tract, tractus corticospinalis ventralis (anterior)	Efferent (pyramidal)
	Covering-spinal tract, tractus tectospinalis
	Vestibulospinalis, tractus vestibulospinalis	Efferent (extrapyramidal)
	Reticular-spinal tract, tractus reticulospinalis	Efferent (extrapyramidal)
	Posterior longitudinal bundle, fasciculus longitudinalis dorsalis (posterior)	Included in the structure of efferent pathways
	Anterior spinothalamic tract, tractus spinothalamicus ventralis (anterior)		Afferent
Posterior cords
	Thin bundle, fasciculus gracilis (Gaul's bundle)		Afferent
	Wedge-shaped bundle, fasciculus cuneatus (Burdach's bundle)		Afferent
Lateral cords
	Lateral spinothalamic tract, tractus spinothalamicus lateralis		Afferent
	Anterior dorsal tract, tractus spinocerebellaris ventralis (anterior), Gowers bundle		Afferent
	Posterior spinocerebellar tract, tractus spinocerebellaris ventralis (posterior), Flexig's bundle		Afferent
	Lateral corticospinal tract, tractus corticospinalis lateralis	Efferent (pyramidal)
	Red nuclear-spinal tract, tractus rubrospinalis	Efferent (extrapyramidal)

Rice. 6. Conducting pathways of the spinal cord: 1 - thin bundle (Gaulle's bundle); 2 - wedge-shaped bundle (Burdakh's bundle); 3 - posterior dorsal-cerebellar path (Flexig's bundle); 4 - lateral cortical-spinal path; 5 - red nuclear-spinal path; 6 - lateral dorsal-thalamic path; 7 - posterior vestibular tract; 8 - anterior spinal-cerebellar path (Govers bundle); 9 - reticular-spinal path; 10 - pre-door-spinal path; 11 - anterior spinal-thalamic path; 12 - anterior cortical-spinal path; 13 - occlusal-spinal path; 14 - posterior longitudinal bundle.

In the white matter of the spinal cord, at the level of the cervical segments between the anterior and posterior columns, and at the level of the upper thoracic segments between the lateral and posterior columns, there is a reticular formation, formatio reticularis, consisting of sparsely located neurons with a large number anastomosing processes.

SM structures include roots (front and back). Each segment has one pair of anterior and posterior roots (Fig. 1). The anterior root, radix anterior, represents a collection of axons of motor neurons, the bodies of which are located in the anterior columns of the spinal cord. At the level of segments C 8 - L 1-2 and S 2-4, the anterior roots also include axons of autonomic neurons, the bodies of which are localized in the lateral columns.

Each posterior root, radix posterior, is represented by a collection of axons (central processes) of pseudo-unipolar cells, whose bodies are located in the spinal ganglia, ganglia spinales. Ganglia are located at the junction of the posterior root with the anterior. Within the intervertebral foramen, the nerve fibers of the anterior spinal nerve roots begin to be located together with the peripheral processes of the pseudounipolar cells of the spinal nodes. The combination of these two types of fibers forms spinal nerve, nervus spinalis. The number of pairs of spinal nerves corresponds to the number of SC segments, i.e. there are 31 pairs of them - 8 pairs of cervical spinal nerves, 12 - thoracic, 5 - lumbar, 5 - sacral and 1-3 - coccygeal. Their length is equal to the length of the intervertebral foramens in which they lie.

The roots of the lumbar, sacral and coccygeal segments, before reaching the intervertebral foramina, pass some distance within the vertebral and then the sacral canals. The combination of these roots forms the cauda equina, inside which are the brain cone, conus medullaris, and the terminal thread, filum terminale.

Sheaths of the spinal cord. The SM is covered with three membranes, meninges, (Fig. 7). The outer one is the dura mater spinalis, under it is the arachnoid membrane, arachnoidea spinalis, and the inner one is the soft (vascular) membrane, pia mater spinalis.

The dura mater is covered with endothelium from the inner surface and is connected by numerous bridges to the arachnoid membrane. Between these membranes is the subdural slit-like cavity, cavum subdurale, filled with cerebrospinal fluid and connective tissue fibers.

Between the dura mater and the periosteum of the vertebrae is the epidural space, cavum epidurale. It houses fatty tissue and the internal vertebral venous plexus.

Rice. 7. Shells of the spinal cord: 1 - dura mater spinalis; 2 - cavitas epiduralis; 3 - arachnoidea mater spinalis; 4 - cavitas subarachnoidalis; 5 - pia mater spinalis; 6 - ganglion spinale; 7 - ligamentum denticulatum

The arachnoid is covered with endothelium on both sides. Numerous jumpers connect it to the vascular and dura mater. Serrated ligaments, ligamenta denticulata, depart from the arachnoid in the frontal plane. In the region of the intervertebral foramina, these ligaments fuse with both membranes. Bars and dentate ligaments are absent within the cauda equina.

The choroid adjoins directly to the SC, enters the anterior median fissure and all its furrows. Outside, it is covered with endothelium. Between the vascular and arachnoid membranes is the subarachnoid space, cavitas subarachnoidalis, which is somewhat expanded around the cauda equina, which is called the terminal cistern, cisterna terminalis. The subarachnoid space contains 120-140 ml of cerebrospinal fluid.

The membranes of the SM and intershell spaces with cerebrospinal fluid provide mechanical protection for the organ, and the choroid also performs a trophic function in relation to the SC.

Spinal Cord Functions They consist in conducting nerve impulses and ensuring unconditional reflex activity of the muscles of the trunk and limbs.

BRAIN

CEREBRUM, Greek. ENCEPHALON

The brain (GM) with its surrounding membranes is located in the cavity brain department skulls. The mass of GM in an adult varies from 1100 to 2000 g, on average 1320 g: for men - 1394 g, for women - 1245 g. After 60 years, the mass of GM decreases somewhat. In the structure of the GM (Fig. 8) there are: telencephalon, telencephalon; intermediate - diencephalon; middle - mesencephalon; posterior - metencephalon; oblong - medulla oblongata, Greek. myelencephalon.

Medulla

Myelencephalon

The medulla oblongata is located between the spinal cord and hindbrain. Its average length is 25 mm. The border with the SM is drawn along the exit line of the 1st pair of spinal nerves or along the lower edge of the foramen magnum. The border with the hindbrain runs from the ventral surface along the lower edge of the pons (Fig. 9a), and on the dorsal surface, along the brain strips, stria medullaris of the IV ventricle (Fig. 9b). In shape, the medulla oblongata resembles a truncated cone or bulb, which in the past gave rise to its name as the bulb of the brain, bulbus cerebri (BNA), therefore clinical symptoms associated with damage to the nuclear structures of the medulla oblongata are called bulbar disorders.

Rice. 9. Medulla oblongata: a - ventral, b - dorsal surfaces; 1 - olive; 2 - pyramis; 3 - sulcus anterolateralis; 4 - fissura mediana anterior; 5 - decussatio pyramidum; 6 - funiculus lateralis; 7 - tuberculum gracile; 8 - tuberculum cuneatum; 9 - fasciculus cuneatus; 10 - fasciculus gracilis; 11 - sulcus medianus posterior; 12 - pons; 13 - sulcus posterolateralis; 14 - pedunculus cerebellaris inferior; 15 - stria medullaris

Rice. 10. Hind brain: 1 - pons; 2 - cerebellum; 3 - medulla oblongata; 4 - sulcus basillaris; 5 - pedunculus cerebellaris medius; 6 - pedunculus cerebri

In the medulla oblongata, there are anterior, posterior and two lateral surfaces, as well as the anterior median fissure, fissura mediana ventralis (anterior) and five sulci: unpaired - posterior median sulcus, sulcus medianus dorsalis (posterior), and paired - anterior and posterior lateral sulci, sulci ventrolaterales (anterolaterales), sulci dorsolaterales (posterolaterales), which are a continuation of the furrows of the CM.

On the anterior surface of the medulla oblongata between the anterior median fissure and the anterior lateral sulci are pyramids, pyramis, most of whose fibers are in lower section PM pass to the opposite side and are part of the lateral cords of the SM. Non-crossed fibers enter the anterior cords of the SM. The indicated intersection of fibers was called the intersection of the pyramids, decussatio pyramidum. Motor (pyramidal) pathways pass through the pyramids.

Lateral to the pyramids, it is located along the olive, oliva, inside which the olive nuclei, nuclei olivarii, are localized. These nuclei have multiple connections with the cerebellum and spinal cord, which determines their participation in maintaining balance. Between the pyramid and the olive, the roots of the XII pair of cranial nerves, nervi hypoglossi, emerge from the anterolateral groove.

On rear surface medulla oblongata between the posterior median and posterior lateral sulci are the posterior cords coming from the SM. Each funiculus is divided into two bundles by means of an intermediate furrow, sulcus intermedius - thin, lying medially, and wedge-shaped, located laterally. From above, the bundles end on both sides with tubercles of the same name - tubercles of thin and wedge-shaped nuclei, tubercula nucleorum gracile et cuneatum. Dorsal to the olive, cranial nerves emerge from the posterolateral groove: glossopharyngeal, vagus, and accessory (IX, X, and XI pairs). Part of the fibers extending from the neurons of the thin and sphenoid nuclei form the lower cerebellar peduncles, connecting the cerebellum with the medulla oblongata. These legs from below and laterally limit the lower triangle of the rhomboid fossa, within which the nuclei of the IX-XII pairs of cranial nerves are located. The other part of the fibers forms the medial loop, lemniscus medialis. The fibers of the right and left medial loops pass to the opposite side, forming a decussation of the medial loops, decussatio lemniscorum medialium. Above this intersection is the posterior longitudinal bundle, fasciculus longitudinalis dorsalis (posterior).

The fibers of the thin and sphenoid tracts, as well as the medial loop, are the structures of the analyzer of proprioceptive sensitivity. The paths in the lower cerebellar peduncles also belong to the paths of proprioceptive sensitivity.

Within the medulla oblongata there is a part of the reticular formation, in which vital centers are localized: cardiovascular (blood circulation) and respiration.

Functions of the medulla oblongata. Due to the location in the medulla oblongata of the nuclei of the IX-XII pairs of cranial nerves and the reticular formation, it ensures the implementation of the following types of unconditioned vital reflexes:

1) protective, associated with coughing, blinking, sneezing, vomiting, lacrimation;

2) food associated with sucking, swallowing, secretion of juice in the digestive tract;

3) cardiovascular and respiratory, providing regulation of the work of the heart, blood vessels and respiratory muscles;

4) adjusting, associated with the redistribution of the tone of the striated muscles;

5) emotional, providing reflection through facial expressions mental state person.

Hind brain

Metencephalon

The hindbrain borders caudally on the oblong, and cranially on the middle brain. The border with the midbrain runs on the ventral surface along the anterior edge of the pons, and on the dorsal surface, along the lower colliculi and their handles; on the border with the medulla oblongata, see above. The hindbrain includes the pons and the cerebellum (Fig. 10). The medulla oblongata and hindbrain are formed from the rhomboid brain, the cavity of which is the IV ventricle, ventriculus quartus.

Bridge, pons (varolian bridge). It is adjacent to the slope of the occipital bone. On the ventral surface of the bridge in the middle is the main groove, sulcus basillaris, in which the artery of the same name is located. The frontal section of the bridge (Fig. 11) shows its internal structure.

In the central part there is a powerful bundle of transversely arranged fibers - the trapezoid body, corpus trapezoideum. Between its fibers are paired ventral and dorsal nuclei, nuclei trapezoidei ventrales et dorsales. The fibers and nuclei of the trapezoid body belong to the pathways of the auditory analyzer.

The trapezoid body divides the bridge into the ventral (basilar) part, pars ventralis (basillaris) pontis, and the dorsal part (tire) of the bridge, pars dorsalis (tegmentum) pontis. In the tire of the bridge over the trapezoid body, on the right and left, there are fibers of the medial loops, lemniscus medialis, and laterally and above them - lateral loops, lemniscus lateralis. Closer to the middle above the trapezoid body are the structures of the reticular formation, and even higher - the posterior longitudinal bundle, fasciculus longitudinalis dorsalis.

Rice. 11. Cross section of the bridge: 1 - vellum medullare superius; 2 - pedunculus cerebellaris superior; 3 - corpus trapezoideum; 4 - sulcus basillaris; 5 - fasciculus longitudinalis dorsalis; 6 - lemniscus medialis; 7 - lemniscus lateralis; 8 - fibrae pontis longitudinales; 9-n. trigeminus; 10 - n. abducens; 11 - n. facialis; 12 - ventriculus quartus

Rice. 12. Cerebellum, a - top view: 1 - hemispheria cerebelli; 2 - vermis; 3, fissura cerebelli; 4 - fissura horizontalis; 5 - folia cerebelli; b - horizontal section of the cerebellum: 1 - nucleus dentatus; 2 - nucleus emboliformis; 3 - nucleus globusus; 4 - nucleus fastigii; 5 - cortex cerebellaris; 6 - arbor vitae cerebelli; 7-vermis

In addition to these structures, the nuclei of 4 pairs of cranial nerves - V, VI, VII and VIII (nn. trigeminus, abducens, facialis et vestibulocochlearis) are localized in the pontine cover within the boundaries of the upper triangle of the rhomboid fossa. In the basilar part of the bridge are the own nuclei of the bridge, nuclei pontis. The processes of the neurons of these nuclei form bundles of transverse fibers of the bridge, fibrae pontis transversae, which enter the cerebellum, forming its middle legs. The boundary between these legs and the bridge is the place where the root passes, n. trigeminus. The efferent pyramidal and extrapyramidal pathways pass through the basilar part of the pons.

Cerebellum (small brain), cerebellum, is located above the medulla oblongata and the bridge, occupying the cavity of the posterior cranial fossa. From above, it borders on the occipital lobes of the cerebral hemispheres, from which it is separated by a transverse fissure of the brain, fissura transversa cerebri.

In the cerebellum, the upper and lower surfaces are distinguished, separated by a horizontal fissure, fissura horizontalis. On the lower surface there is a recess - the valley of the cerebellum, vallecula cerebelli, to which the medulla oblongata adjoins.

The cerebellum consists of 2 hemispheres, hemispheria cerebelli, connected by an unpaired formation - a worm, vermis cerebelli (Fig. 12 a). The surface of the hemispheres of the cerebellum and the vermis is indented with many transverse fissures, between which there are sheets (gyrus) of the cerebellum, folia cerebelli. Deeper furrows of the hemispheres and the worm separate their lobules from each other. The oldest lobule of the hemispheres, adjacent to the ventral surface of the middle peduncles of the cerebellum, is a piece, flocculus, which, through its legs, pedunculi flocculi, connects to a lobule of the worm, which is called a nodule, nodulus. Between the nodule and the legs of the shred are the lobules of the hemispheres - the tonsil of the cerebellum, tonsila cerebelli.

In the hemispheres and in the vermis of the cerebellum, it is located outside Gray matter- cortex cerebelli, and under it - white matter, in which the paired nuclei of the cerebellum are localized (Fig. 12 b). In the center of the hemispheres is the largest dentate nucleus, the nucleus dentatus. On a horizontal section of the hemispheres, it looks like a thin winding strip, which is not closed in the medial direction. This place is called the gates of the dentate nucleus, hilum nuclei dentati, through which the fibers of the upper cerebellar peduncles enter. In the medial direction from the dentate nucleus are the corky and spherical nuclei, nuclei emboliformis et globusus, and the most medial in the worm above the fourth ventricle is the core of the tent, nucleus fastigii.

On sections of the cerebellum and especially on the sagittal median section of the worm, its gray and white matter create the appearance of a thuja leaf, an evergreen “living” tree, which prompted ancient anatomists to give the drawing a mythical name - the tree of life, arbor vitae.

The cerebellum is connected to other parts of the brain through three pairs of legs - upper, lower and middle (Fig. 13). The superior cerebellar peduncles, pedunculi cerebellaris superiores, connect the cerebellum to the midbrain. They pass through the pathways of proprioceptive sensitivity, tractus spinocerebellaris anterior and fibers associated with the extrapyramidal pathway, tractus rubrospinalis.

The inferior cerebellar peduncles, pedunculi cerebellares inferiores, connect the cerebellum to the medulla oblongata. They pass through the pathways of proprioceptive sensitivity, tractus spinocerebellaris posterior, and fibers associated with the extrapyramidal pathway, tractus vestibulospinalis, as well as fibrae arcuatae externi (tr. bulbothalamicus, uncrossed part).

The middle peduncles of the cerebellum, pedunculi cerebellares medii, are the most powerful peduncles. Their fibers, called "cerebellar pontine pathways", connect the nuclei of the bridge with the cerebellar cortex and are part of the cortical-bridge pathways.

From the position of phylogenesis, three parts are morphologically and functionally distinguished in the cerebellum.

1. The ancient one, archicerebellum, is the scrap and core of the tent. They provide the spatial orientation of the body and its parts, as well as the balance of the body.

2. Old, paleocerebellum, - worm, corky and spherical nuclei. They provide regulation of muscle tone and coordination of body movements.

3. New, neocerebellum, - dentate nucleus and hemispheres as a whole. This part of the cerebellum provides coordination of voluntary movements of the limbs.

Functions of the hindbrain. Due to the location in the hindbrain of the nuclei of the V-VIII pairs of cranial nerves, the reticular formation and the nuclei of the cerebellum, it performs the following functions.

1. Regulation muscle tone and ensuring the coordination of movements of parts of the human body, making them smooth, accurate, proportionate.

2. Coordination of fast (phasic) and slow (tonic) components of motor acts, providing balance of the body and maintaining the posture.

3. Maintaining the stability of a number of vegetative functions associated with blood constants, the work of the digestive system, regulation vascular tone and metabolic processes.

Fig.13. Cerebellum, side view: 1 - pedunculus cerebri; 2 - lemniscus medialis; 3 - lemniscus lateralis; 4, pons; 5 - pedunculus cerebellaris superior; 6 - pedunculus cerebellaris inferior

Rice. 14. Rhomboid fossa. 1 - obex; 2 - recessus lateralis; 3 - sulcus medianus; 4 - eminentia medialis; 5 – sulcus limitans; 6 - colluculus facialis; 7 - trigonum nervi hypoglossi; 8 - trigonum nervi vagi; 9 - stria medullaris; 10 - area vestibularis; 11, 12, 13 - pedunculi cerebellares superior, medius et inferior

Similar information.

The nerve cell has a large number of processes. The processes removed from the cell body are called nerve fibers. Nerve fibers that do not extend beyond the central nervous system form conductors of the brain and spinal cord. Fibers that travel outside the central nervous system gather into bundles and form peripheral nerves.

Nerve fibers passing inside the brain and spinal cord have different lengths - some of them come into contact with neurons located close, others with neurons located at a greater distance, and still others are far removed from the body of their cell. In this regard, three types of conductors can be distinguished that carry out the transmission of impulses within the central nervous system.

1. Projection conductors communicate with the overlying sections of the central nervous system with the sections located below. (Fig. 4). Among them, there are two types of paths. Descending conduct impulses from the overlying parts of the brain down and are called centrifugal. They are motor in nature. The paths that direct from the periphery the conductive impulses from the skin, muscles, joints, ligaments, bones to the center have an upward direction and are called centripetal. They are sensitive in nature.

Rice. 4.

I - posterior spinal bundle; II - fibers of the posterior cord; III - spinal tuberous bundle; IV - anterior cortical-spinal bundle; V - lateral cortical-spinal bundle; VI - vestibulo-spinal bundle

2. Commissural, or adhesive, conductors connect the hemispheres of the brain. Examples of such compounds are corpus callosum, connecting the right and left hemispheres, the anterior commissure, the uncinate gyrus commissure, and the gray commissure thalamus connecting both halves of the thalamus.

3. Associative, or associative, conductors connect parts of the brain within the same hemisphere. Short fibers connect various convolutions in one or closely spaced lobes, and long ones stretch from one lobe of the hemisphere to another. For example, the arcuate bundle connects the lower and middle sections of the frontal lobe, the lower longitudinal connects the temporal lobe with the occipital lobe. Allocate the fronto-occipital, frontal-parietal bundles, etc. (Fig. 5).

Rice. 5.

I - upper longitudinal (or arcuate) bundle; II - fronto-occipital bundle; III - lower longitudinal beam; IV - waist bun; V - hook-shaped bundle; VI - arcuate fiber; VII - large commissure (corpus callosum)

Consider the course of the main projection conductors of the brain and spinal cord.

centrifugal ways

The pyramidal path starts from large and giant pyramidal cells (Betz cells) located in the fifth layer of the anterior central gyrus and the paracentral lobule. In the upper sections there are paths for the legs, in the middle sections of the anterior central gyrus - for the trunk, below - for the arms, neck and head. Thus, the projection of human body parts in the brain is presented inverted. From the total amount of fibers a powerful bundle is formed, which passes through the inner bag. Then the pyramidal bundle passes through the base of the brain stem, the pons, entering the medulla oblongata, and then into the spinal cord.

At the level of the pons and medulla, part of the fibers of the pyramidal pathway ends in the nuclei of the cranial nerves (trigeminal, abducens, facial, glossopharyngeal, vagus, accessory, hypoglossal). This short bundle of fibers is called the cortical-bulbar pathway. It starts from the lower sections of the anterior central gyrus. Before entering the nuclei, the nerve fibers of the short pyramidal pathway cross over. Another, longer bundle of pyramidal nerve fibers, starting from the upper sections of the anterior central gyrus, descends down into the spinal cord and is called the cortical-spinal path. The latter, on the border of the medulla oblongata with the spinal cord, forms an incomplete decussation, and most of the nerve fibers (subjected to decussation) continue their way in the lateral columns of the spinal cord, and a smaller part (not crossed) goes as part of the anterior columns of the spinal cord of its side. Both segments end in motor cells anterior horn spinal cord.

The pyramidal pathway (cortical-spinal and cortical-bulbar) is the central segment of the path that transmits motor impulses from the cells of the cerebral cortex to the nuclei of the cranial nerves and cells of the spinal cord. It does not go beyond the central nervous system.

From the motor nuclei of the cranial nerves and from the cells of the anterior horns of the spinal cord, the peripheral segment of the path along which the impulse is directed to the muscles begins. Consequently, the transmission of a motor impulse is carried out through two neurons. One conducts impulses from the cells of the cortex of the motor analyzer to the cells of the anterior horns of the spinal cord and to the nuclei of the cranial nerves, the other - to the muscles of the face, neck, trunk and limbs (Fig. 6).

When the pyramidal tract is damaged, there is a violation of movements on the side opposite to the lesion, which can be expressed total absence movements in the muscles (paralysis) or their partial weakening (paresis). Depending on the location of the lesion, central and peripheral paralysis or paresis are distinguished.

Rice. 6.

I - cortical-spinal bundle; II - cortical-bulbar bundle; III - the crossed part of the cortical-spinal bundle; IV - uncrossed part of the cortical-spinal bundle; V - cross of pyramids; VI - caudate nucleus; VII - hillock; VIII - lentil kernel; IX - pale ball; X - leg of the brain; XI - varolian bridge; XII - medulla oblongata; K. VII - the nucleus of the facial nerve; K. XII - the nucleus of the hypoglossal nerve

The Monakovic bundle begins in the midbrain from the red nuclei. Immediately upon exiting the red nucleus, the fibers cross and, having passed the hindbrain, descend into the spinal cord. In the spinal cord, this bundle of nerve fibers is located in the lateral columns near the bundle of the crossed pyramidal pathway and gradually ends, like the pyramidal pathway, in the cells of the anterior horns of the spinal cord.

Monakov's bundle conducts motor impulses that regulate muscle tone.

The roof-spinal bundle connects the anterior colliculus of the midbrain with the anterior and partly lateral columns of the spinal cord. Participates in the implementation of visual and auditory orienting reflexes.

The vestibulo-spinal bundle begins in the nuclei of the vestibular apparatus (in the nucleus of Deiters). The fibers descend into the spinal cord and pass in the anterior and partly lateral columns. The fibers end in the cells of the anterior horns. Since the nucleus of Deiters is connected with the cerebellum, impulses from the vestibular system and the cerebellum to the spinal cord follow this path; participates in the balance function.

The reticular-spinal bundle starts from the reticular formation of the medulla oblongata, passes in different bundles in the anterior and lateral columns of the spinal cord. It ends in the cells of the anterior horn; conducts vital impulses from the coordinating center of the hindbrain.

The posterior longitudinal bundle consists of ascending and descending fibers. It travels through the brainstem to the anterior columns of the spinal cord. Impulses from the brain stem and segments of the spinal cord, from the vestibular apparatus and nuclei of the eye muscles, as well as from the cerebellum pass along this path.

To control the work of the whole organism or each individual organ, the motor apparatus, the pathways of the spinal cord are required. Their main task is to deliver impulses sent by the human "computer" to the body and limbs. Any failure in the process of sending or receiving impulses of a reflex or sympathetic nature is fraught with serious pathologies of health and all life activity.

What are pathways in the spinal cord and brain?

The pathways of the brain and spinal cord act as a complex of neural structures. In the course of their work, impulse impulses are sent to specific areas of gray matter. In essence, impulses are signals that prompt the body to act on the call of the brain. Several groups, different in accordance with functional characteristics, represent the pathways of the spinal cord. These include:

• projection nerve endings;
• associative paths;
• commissural connecting roots.

In addition, the performance of the spinal conductors necessitates the selection of the following classification, according to which they can be:

• motor;
• sensory.

Sensitive perception and human motor activity

Sensory or sensory pathways of the spinal cord and brain serve as an indispensable element of contact between these two most complex systems in the body. They also send an impulsive message to every organ, muscle fiber, arms and legs. The instantaneous sending of an impulse signal is a fundamental moment in the implementation by a person of coordinated coordinated body movements performed without the application of any conscious effort. Impulses sent by the brain can be recognized by nerve fibers through touch, pain, body temperature, and joint-muscular motility.

The motor pathways of the spinal cord predetermine the quality of a person's reflex reaction. Providing the sending of impulse signals from the head to the reflex endings of the ridge and the muscular apparatus, they endow a person with the ability to self-control motor skills - coordination. Also, these pathways are responsible for the transmission of stimulating impulses towards the visual and auditory organs.

Where are the pathways located?

Having become acquainted with the anatomical distinguishing features of the spinal cord, it is necessary to figure out where the very pathways of the spinal cord are located, because this term implies a lot of nerve matter and fibers. They are located in specific vital substances: gray and white. Connecting the spinal horns and the cortex of the left and right hemispheres, the pathways through neural connections provide contact between these two departments.

The functions of conductors of the main human organs are to implement the intended tasks with the help of specific departments. In particular, the pathways of the spinal cord are located within the upper vertebrae and head, which can be described in more detail as follows:

1. Associative connections are a kind of "bridges" that connect the areas between the cortex of the hemispheres and the nuclei of the spinal substance. In their structure there are fibers of various sizes. Relatively short ones do not go beyond the hemisphere or its brain lobe. Longer neurons transmit impulses that travel some distance to the gray matter.
2. The commissural tracts are a body with a calloused structure and perform the task of connecting the newly formed sections in the head and spinal cord. The fibers from the main lobe bloom in a ray-like manner, they are placed in the white spinal substance.
3. Projection nerve fibers are located directly in the spinal cord. Their performance makes it possible for impulses to arise in the hemispheres in a short time and establish communication with internal organs. The division into ascending and descending pathways of the spinal cord concerns precisely fibers of this type.

System of ascending and descending conductors

The ascending pathways of the spinal cord fill the human need for vision, hearing, motor functions and their contact with important systems organism. The receptors for these connections are located in the space between the hypothalamus and the first segments of the spinal column. The ascending pathways of the spinal cord are able to receive and send further impulses coming from the surface of the upper layers of the epidermis and mucous membranes, life-support organs.

In turn, the descending pathways of the spinal cord include the following elements in their system:

• The neuron is pyramidal (originates in the cortex of the hemispheres, then rushes down, bypassing the brain stem; each of its bundles is located on the spinal horns).
• The neuron is central (it is motor, connecting the anterior horns and the cortex of the hemispheres with the reflex roots; together with the axons, elements of the peripheral nervous system also enter the chain).
• Spinal fibers (conductors lower extremities and column of the spinal cord, including the sphenoid and thin ligaments).

It is rather difficult for an ordinary person who does not specialize in the field of neurosurgery to understand the system represented by the complex pathways of the spinal cord. The anatomy of this department is indeed an intricate structure consisting of neural impulse transmissions. But it is thanks to her that the human body exists as a whole. Due to the double direction in which the conductive pathways of the spinal cord operate, instantaneous transmission of impulses is ensured, which carry information from the controlled organs.

Deep sensory conductors

The structure of the nerve cords, acting in an upward direction, is multi-component. These pathways of the spinal cord are formed by several elements:

• Burdach's bundle and Gaull's bundle (they are paths of deep sensitivity located on the back of the spinal column);
• spinothalamic bundle (located on the side of the spinal column);
• Govers' bundle and Flexig's bundle (cerebellar pathways located on the sides of the column).

Inside the intervertebral nodes are located a deep degree of sensitivity. The processes localized in the peripheral areas end in the most suitable muscle tissue, tendons, bone and cartilage fibers and their receptors.

In turn, the central processes of the cells, located behind, keep the direction towards the spinal cord. Conducting deep sensitivity, rear nerve roots do not go deep into the gray matter, forming only the posterior spinal columns.

Where such fibers enter the spinal cord, they are divided into short and long. Further, the pathways of the spinal cord and brain are sent to the hemispheres, where their cardinal redistribution takes place. Their main part remains in the zones of the anterior and posterior central gyri, as well as in the region of the crown.

It follows that these paths conduct sensitivity, thanks to which a person can feel how his muscular-articular apparatus works, feel any vibrational movement or tactile touch. Gaulle's bundle, located right in the center of the spinal cord, distributes sensation from the lower torso. Burdach's bundle is located above and serves as a conductor of sensitivity upper limbs and the corresponding part of the body.

How to find out about the degree of sensory?

To determine the degree of deep sensitivity, you can use a few simple tests. For their implementation, the patient's eyes are closed. Its task is to determine the specific direction in which the doctor or researcher makes movements of a passive nature in the joints of the fingers, hands or feet. It is also desirable to describe in detail the posture of the body or the position that its limbs have assumed.

With the help of a tuning fork for vibration sensitivity, it is possible to examine the pathways of the spinal cord. The functions of this device will help to accurately determine the time during which the patient clearly feels the vibration. To do this, take the device and click on it to make a sound. At this point, it is necessary to put on any bony protrusion on the body. In the case when this sensitivity drops out earlier than in other cases, it can be assumed that the posterior pillars are affected.

The test for the sense of localization implies that the patient, by closing his eyes, accurately points to the place where the researcher touched him a few seconds before. A satisfactory indicator is considered if the patient made an error within one centimeter.

Sensory sensitivity of the skin

The structure of the pathways of the spinal cord allows you to determine the degree of skin sensitivity at the peripheral level. The fact is that the nerve processes of the protoneuron are involved in skin receptors. The processes located in the center as part of the posterior processes rush directly to the spinal cord, as a result of which the Lisauer zone is formed there.

Just like the path of deep sensitivity, the skin one consists of several successively combined nerve cells. In comparison with the spinothalamic bundle of nerve fibers, information impulses transmitted from the lower extremities or lower body are slightly higher and in the middle.

Skin sensitivity varies according to criteria based on the nature of the irritant. She happens:

• temperature;
• thermal;
• painful;
• tactile.

In this case, the last type of skin sensitivity, as a rule, is transmitted by conductors of deep sensitivity.

How to find out about pain threshold and temperature difference?

To determine the level of pain, doctors use the injection method. In the most unexpected places for the patient, the doctor inflicts several light injections with a pin. The patient's eyes should be closed, because. he must not see what is happening.

The temperature sensitivity threshold is easy to determine. At normal condition a person experiences different sensations at temperatures, the difference of which was about 1-2 °. To detect a pathological defect in the form of a violation of skin sensitivity, doctors use a special apparatus - a thermoesthesiometer. If not, you can test for warm and hot water.

Pathologies associated with impaired conduction pathways

In the ascending direction, the pathways of the spinal cord are formed in a position due to which a person can feel tactile touch. For the study, it is necessary to take something soft, gentle and in a rhythmic manner conduct a subtle examination to identify the degree of sensitivity, as well as check the reaction of hairs, bristles, etc.

Disorders caused by skin sensitivity, currently considered as follows:

1. Anesthesia is the complete loss of sensation of the skin on a specific superficial area of ​​the body. In case of violation of pain sensitivity, analgesia occurs, in case of temperature - termanesthesia.
2. Hyperesthesia is the opposite of anesthesia, a phenomenon that occurs when the threshold of excitation decreases, and when it increases, hypalgesia appears.
3. Misperception of irritants (for example, the patient confuses cold and warm) is called dysesthesia.
4. Paresthesia is a violation, the manifestations of which can be a huge variety, ranging from crawling goosebumps, a feeling of electric shock and its passage through the entire body.
5. Hyperpathy is the most pronounced. It is also characterized by damage to the thalamus, an increase in the threshold of excitability, the inability to locally determine the stimulus, a severe psycho-emotional coloring of everything that happens, and too sharp a motor reaction.

Features of the structure of descending conductors

The descending pathways of the brain and spinal cord include several ligaments, including:

• pyramidal;
• rubro-spinal;
• vestibulo-spinal;
• reticulo-spinal;
• back longitudinal.

All of the above elements are the motor pathways of the spinal cord, which are components of the nerve cords in a downward direction.

The so-called pyramidal path starts from the largest cells of the same name located in the upper layer of the cerebral hemisphere, mainly in the zone of the central gyrus. The pathway of the anterior cord of the spinal cord is also located here - this important element of the system is directed downward and passes through several sections of the posterior femoral capsule. At the point of intersection of the medulla oblongata and spinal cord, an incomplete decussation can be found, forming a straight pyramidal bundle.

In the tegmentum of the midbrain there is a conducting rubro-spinal tract. It starts from the red nuclei. Upon exiting, its fibers cross and pass into the spinal cord through the varoli and medulla oblongata. Rubro-spinal path allows you to conduct impulses from the cerebellum and subcortical nodes.

The pathways of the spinal cord begin in Deiters' nucleus. Located in the brainstem, the vestibulo-spinal path continues in the spinal cord and ends in its anterior horns. The passage of impulses from the vestibular apparatus to the peripheral system depends on this conductor.

In the cells of the reticular formation of the hindbrain, the reticulo-spinal path begins, which is scattered in separate bundles in the white matter of the spinal cord, mainly from the side and front. In fact, this is the main connecting element between the reflex brain center and the musculoskeletal system.

The posterior longitudinal ligament is also involved in connecting motor structures to the brainstem. The work of the oculomotor nuclei and the vestibular apparatus as a whole depends on it. The posterior longitudinal bundle is located in the cervical spine.

Consequences of diseases of the spinal cord

Thus, the pathways of the spinal cord are vital connecting elements that provide a person with the ability to move and feel. The neurophysiology of these pathways is associated with the structural features of the spine. It is known that the structure of the spinal cord surrounded by muscle fibers, has a cylindrical shape. Within the substances of the spinal cord, associative and motor reflex pathways control the functionality of all body systems.

When there is a disease of the spinal cord, mechanical damage or malformations, the conductivity between the two main centers may be significantly reduced. Violations of the pathways threaten a person with a complete cessation of motor activity and loss of sensory perception.

The main reason for the lack of impulse conduction is the death of nerve endings. The most difficult degree of conduction disturbance between the brain and spinal cord is paralysis and lack of sensation in the limbs. Then there may be performance problems. internal organs associated with the brain damaged neuronal bundle. For example, disorders in the lower part of the spinal cord lead to uncontrolled urination and defecation processes.

Are diseases of the spinal cord and pathways treated?

Just appeared degenerative changes almost instantly affect the conduction activity of the spinal cord. Inhibition of reflexes leads to pronounced pathological changes due to the death of neuronal fibers. It is impossible to completely restore the disturbed conduction areas. The disease comes on rapidly and progresses at lightning speed, so avoid gross violations conductivity is possible only if timely start drug treatment. The sooner this is done, the greater the chances of stopping pathological development.

The impermeability of the passing tracts of the spinal cord needs treatment, the primary task of which will be to stop the processes of the death of nerve endings. This can be achieved only if the factors that influenced the onset of the disease are suppressed. Only then can therapy be started in order to maximize possible recovery sensation and motor function.

Drug treatment is aimed at stopping the process of dying of brain cells. Their task is also to restore the disturbed blood supply to the damaged area of ​​the spinal cord. During treatment, doctors consider age features, the nature and severity of damage and progression of the disease. In pathway therapy, it is important to maintain constant stimulation of nerve fibers with electrical impulses. This will help maintain satisfactory muscle tone.

Surgical intervention is carried out in order to restore the conductivity of the spinal cord, therefore, it is carried out in two directions:

1. Suppression of the causes of paralysis of the activity of neural connections.
2. Stimulation of the spinal cord for the speedy acquisition of lost functions.

The operation should be preceded by a complete medical examination of the whole body. This will allow to determine the localization of the processes of degeneration of nerve fibers. In the case of severe spinal injuries, the causes of compression must first be eliminated.