The main pathways of the spinal cord.

Ascending pathways spinal cord

Medial lemniscal tracts formed by two ascending tracts: 1) thin Gaulle bundle; 2) wedge-shaped bundle of Burdach (Fig. 4.14).

Afferent fibers of these pathways transmit information from tactile receptors in the skin and proprioceptors, in particular joint receptors. They enter the gray matter of the posterior horns of the spinal cord, should not be interrupted and pass in the posterior funiculi to the thin and cuneate nuclei (Gaull and Burdach), where information is transmitted to the second neuron. The axons of these neurons cross, pass to the opposite side and, as part of the medial loop, rise to specific switching nuclei of the thalamus, where switching occurs to third neurons, the axons of which transmit information in the posterior central gyrus, which ensures the formation of tactile sensation, sense of body position, passive movements, vibrations.

Spinocerebellar tract They also have 2 tracts: 1) posterior Flexig and 2) anterior Govers. their afferent fibers transmit information from proprioceptors of muscles, tendons, ligaments and tactile pressure receptors on the skin. They are characterized by a switch to the second neuron in the gray matter of the spinal cord and a transition to the opposite side. They then pass through the lateral cords of the spinal cord and carry information to the cerebellar cortex.

Spinothalamic tract(lateral, anterior), their afferent fibers transmit information from skin receptors - cold, heat, pain, tactile - about gross deformation and pressure on the skin. They switch to the second neuron in the gray matter of the dorsal horns of the spinal cord, move to the opposite side and rise in the lateral and anterior cords to the nuclei of the thalamus, where they switch to third neurons that transmit information to the posterior central gyrus.

RICE. 4.14.

Descending tracts of the spinal cord

Receiving information from the ascending conduction system about the state of activity of the effector organs, the brain sends impulses (“instructions”) through descending conductors to the working organs, among which is the spinal cord, and plays a leading-executive role. This happens with the following systems(Fig. 4.15).

Cortinospinal or pyramidal tracts(ventral, lateral) pass through the medulla oblongata, where most intersect at the level of the pyramids, and are called pyramidal. They carry information from the motor centers of the motor cortex to the motor centers of the spinal cord, due to which voluntary movements are carried out. The ventral corticospinal tract runs in the anterior cords of the spinal cord, and the lateral tract runs in the lateral cords.

Rubrospinal tract- its fibers are axons of neurons of the red nucleus of the midbrain, cross and go as part of the lateral cords of the spinal cord and transmit information from the red nuclei to the lateral interneurons of the spinal cord.

Stimulation of the red nuclei leads to activation of flexor motor neurons and inhibition of extensor motor neurons.

Medial retinulospinal tract (pontoretiulospinal) starts from the pons nuclei, goes to the anterior funiculi of the spinal cord and transmits information to the ventromedial parts of the spinal cord. Stimulation of the pontine nuclei leads to the activation of motor neurons in both flexors and extensors, with a predominant effect on the activation of motor neurons in the extensors.

Lateral retinulospinal tract (medulore tinulospinal) starts from the reticular formation medulla oblongata, goes in the anterior funiculi of the spinal cord and transmits information to the interneurons of the spinal cord. Its stimulation causes a general inhibitory effect, mainly on motor neurons in the extensors.

Vestibulospinal tract starts from the Deiters nuclei, goes to the anterior funiculi of the spinal cord, transmits information to interneurons and motor neurons on the same side. Stimulation of Deiters' nuclei leads to activation of extensor motor neurons and inhibition of flexor motor neurons.

RICE. 4.15.

RICE. 4.16.

Tectospinal tract starts from the superior colliculus and quadrigeminal and transmits information to the motor neurons of the cervical spinal cord, providing regulation of the functions of the cervical muscles. The topography of the spinal cord pathways is shown in Fig. 4.16.

Reflex function The spinal cord is that it contains reflex centers. Alpha motor neurons of the anterior horns constitute motor centers skeletal muscles torso, limbs, as well as the diaphragm, and β-motoneurons are tonic, maintaining tension and a certain length of these muscles. Motor neurons of the thoracic and cervical (CIII-CIV) segments that innervate respiratory muscles, constitute the "spinal respiratory center". In the lateral horns of the thoracolumbar part of the spinal cord there are bodies of sympathetic neurons, and in the sacral part - parasympathetic ones. These neurons make up the centers vegetative functions: vasomotor, regulation of cardiac activity (TI-TV), pupil dilation reflex (TI-TII), sweat secretion, heat generation, regulation of contraction of smooth muscles of the pelvic organs (in the lumbar sacral region).

The reflex function of the spinal cord is studied experimentally after its isolation from the higher parts of the brain. To preserve breathing due to the diaphragm, cuts are made between the V and VI cervical segments. Immediately after cutting, all functions are suppressed. A state of areflexia occurs, which is called spinal shock.

The main pathways of the spinal cord

Without setting ourselves the task of listing all the pathways of the central nervous system, let us consider the basic principles of the organization of these pathways using the example of the most important of them (Fig. 30). The pathways in the central nervous system are divided into:

ascending- are formed by the axons of cells whose bodies are located in the gray matter of the spinal cord. These axons are composed of white matter heading to upper sections spinal cord, brain stem and cortex cerebral hemispheres.

descending– are formed by the axons of cells whose bodies are located in various nuclei of the brain. These axons descend through the white matter to various spinal segments, enter the gray matter and leave their endings on certain of its cells.

A separate group is formed propriospinal conducting paths. They can be either ascending or descending, but they do not extend beyond the spinal cord. After passing through several segments, they return to the gray matter of the spinal cord. These paths are located in the deepest part lateral And ventral cords, they connect various nerve centers spinal cord. For example, the centers of the lower and upper limbs.

Ascending pathways.

Gaulle's (thin fasciculus) and Burdach's (wedge-shaped fasciculus) tracts. The main ascending tracts pass through the dorsal funiculi of the spinal cord and represent the axons of afferent neurons dorsal ganglia. They run along the entire spinal cord and end in the area oblong brain in the nuclei of the dorsal funiculus, which are called the nuclei of Gaulle and Burdach. That's why they are called Gaulle's tract And Burdach tract.

1. The first link of neurons:

a. Fibers located medially in the cord carry afferent signals from the lower part of the body, mainly from lower limbs.

b. Fibers located laterally go to Burdach's nucleus and transmit afferent signals from receptors in the upper torso and forelimbs.

2. Second link of neurons:

In turn, the axons of the cells of the Gaulle and Burdach nuclei in the brain stem intersect and rise in the form of a dense bundle to intermediate brain This bundle of fibers, already formed by the axons of the cells of the Gaulle and Burdach nuclei, is called medial lemniscus.

3. The third link of neurons:

Cell nuclei diencephalon give off axons that go to the cerebral cortex.

All other ascending paths begin not from the neurons of the spinal ganglia, but from neurons located in gray matter of the spinal cord. Consequently, their fibers are not first-order, but second-order fibers.

1. The first link Neurons of the spinal ganglia also serve in these pathways, but in the gray matter they leave their endings on cells of a sort of “second link.”

The cells of this "second link" send their axons to the nuclei of the brain stem and the cerebral cortex. The bulk of the fibers of these pathways pass in the lateral funiculus.

Spino-thalamic tracts (ventral and lateral).

2. Second link of neurons:

Begins at the base of the dorsal horn of the spinal cord. The axons of the neurons forming this path move to the contralateral (opposite) side, enter the white matter of the opposite lateral or ventral cord and rise through the entire spinal cord And brain stem right down to the kernels intermediate brain

2. The third link of neurons:

Neurons of the nuclei of the diencephalon transfer impulses to the cerebral cortex.

All of the pathways described above (Gaull, Burdach and spinothalamic) connect the receptive areas of each side of the body with cortical neurons the opposite hemispheres.

Spinocerebellar tracts. Two more pathways passing through the lateral funiculi connect the spinal cord with cerebellar cortex.

Flexing Path - located more dorsally and contains fibers that do not pass to the opposite side of the brain. This pathway in the spinal cord starts from the neurons of Clarke's nucleus, the axons of which reach the medulla oblongata and enter the cerebellum through the inferior cerebellar peduncle.

Govers way - located more ventrally, it contains fibers that rise up the lateral funiculus of the opposite side of the body, but in the brain stem these fibers cross again and enter the cerebellar cortex from the side on which this path began. In the spinal cord, it starts from the nuclei of the intermediate zone, the axons enter the cerebellum through the superior cerebellar peduncle.

If the cerebral cortex is always connected with afferent fibers of the opposite side of the body, then the cerebellar cortex receives fibers mainly from neural structures of the same name sides.

Descending pathways. Downstream fibers are also divided into several paths. The names of these pathways are based on the names of the parts of the brain in which they originate.

Corticospinal (lateral and ventral) tracts formed by axons pyramidal cells lower layers of the motor zone of the cerebral cortex. These paths are often called pyramidal. The fibers pass through white matter of the cerebral hemispheres, base of the midbrain peduncles, along the ventral sections Varoliev Bridge And oblong brain in dorsal brain.

o Lateral the path crosses at the bottom of the pyramids of the medulla oblongata and ends at the neurons of the base of the dorsal horn.

o Ventral the path crosses the pyramids of the medulla oblongata without crossing. Before entering the anterior horn gray matter of the corresponding segment of the spinal cord, the fibers of this pathway pass to the opposite side and end on the motor neurons of the anterior horns of the contralateral side.

Thus, one way or another, the motor area of the cerebral cortex is always associated with neurons opposite sides of the spinal cord.

Rubrospinal tract – main descending path midbrain, starts at red core. The axons of the neurons of the red nucleus intersect immediately below it and, as part of the white matter of the lateral funiculus, descend to the segments of the spinal cord, ending on the cells intermediate area gray matter. This is due to the fact that the rubrospinal system, along with the pyramidal system, is the main system for controlling the activity of the spinal cord.

Tectospinal tract – Originates from neurons midbrain quadrigeminal and reaches the motor neurons of the anterior horns.

Pathways starting in the medulla oblongata:

Vestibulospinal– starts from the vestibular nuclei, mainly from the cells of the Deiters nucleus.

Reticulospinal– begins from a vast accumulation nerve cells reticular formation occupying central part brain stem. The fibers of each of these pathways end on neurons in the medial part of the anterior horn of the gray matter of the spinal cord. The main part of the endings are located on intercalary cells.

Olive-spinal- formed by the axons of the olive cells of the medulla oblongata, ends on the motor neurons of the anterior horns of the spinal cord.

Section 4

BRAIN

Ascending (afferent) pathways starting in the spinal cord

The bodies of the first neurons - conductors of all types of sensitivity to the spinal cord - lie in the spinal ganglia. Cell axons spinal nodes as part of the dorsal roots they enter the spinal cord and are divided into two groups: the medial group, consisting of thick, more myelinated fibers, and the lateral group, formed by thin, less myelinated fibers.

Medial fiber group dorsal root is sent to the posterior cord of the white matter, where each fiber divides in a T-shape into ascending and descending branches. The ascending branches, following upward, come into contact with the cells of the gray matter of the spinal cord in the gelatinous substance and in the dorsal horn, and some of them reach the medulla oblongata, forming thin and wedge-shaped bundles, fasciculi gracilis et cuneatus(see Fig. , , ), spinal cord.

The descending branches of the fibers are directed downward and come into contact with the cells of the gray matter of the posterior columns over six to seven underlying segments. Some of these fibers form in the chest and cervical regions spinal cord bundle, which has the appearance of a comma on the cross section of the spinal cord and is located between the wedge-shaped and thin bundles; V lumbar region– type of medial cord; in the sacral region - type of oval fascicle posterior funiculus adjacent to the medial surface thin beam.

The lateral group of fibers of the dorsal root is directed to the marginal zone, and then to the posterior column of the gray matter, where it comes into contact with the cells of the dorsal horn located in it.

The fibers extending from the cells of the spinal cord nuclei are directed upward partly along the lateral cord on their side, and partly pass as part of the white commissure to the opposite side of the spinal cord and are also directed upward in the lateral cord.

The ascending tracts (see Fig. , , ), starting in the spinal cord, include the following:

Posterior spinocerebellar tract, tractus spinocerebellaris dorsalis, - direct cerebellar pathway, conducts impulses from muscle and tendon receptors to the cerebellum. The bodies of the first neurons lie in the spinal ganglion, the bodies of the second neurons lie throughout the entire length of the spinal cord in the thoracic column (thoracic nucleus) of the dorsal horn. The long processes of the second neurons extend outward; Having reached the posterolateral part of the spinal cord on the same side, they turn upward and rise along the lateral cord of the spinal cord, and then follow the inferior cerebellar peduncle to the cortex of the cerebellar vermis.
Anterior spinocerebellar tract, tractus spinocerebellaris ventralis, conducts impulses from muscle and tendon receptors to the cerebellum. The bodies of the first neurons lie in the spinal ganglion, and the bodies of the second neurons - in the medial nucleus of the intermediate zone and send part of their fibers through the white commissure to the lateral cords of the opposite side, and part - to the lateral cords of their own side. These fibers reach the anterior outer sections of the lateral funiculi, located anterior to the posterior spinocerebellar tract. Here the fibers turn upward, go along the spinal cord, and then along the medulla oblongata and, having passed the bridge, along the superior cerebellar peduncles, making a second decussation, they reach the cerebellar vermis.
Spinoolivarius tract, originates from the cells of the dorsal horns of the gray matter. The axons of these cells cross and rise near the surface of the spinal cord at the border of the lateral and anterior funiculi, ending in the olive nuclei. The fibers of this pathway carry information from skin, muscle and tendon receptors.
Anterior and lateral spinothalamic tracts, tractus spinothalamici ventralis et lateralis(see Fig.), conduct pain and temperature impulses ( lateral path) and tactile (anterior path) sensitivity. The cell bodies of the first neurons lie in spinal ganglia. The processes of the second neurons from the cells of the nucleus of the dorsal horn are directed through the white commissure to the anterior and lateral funiculi of the opposite side. Rising upward, the fibers of these paths pass into posterior regions medulla oblongata, pons and cerebral peduncles and reach the thalamus as part of spinal loop, lemniscus spinalis. The bodies of the third neurons of these pathways lie in the thalamus, and their processes are directed to the cerebral cortex as part of the central thalamic radiations through the posterior leg of the internal capsule (Fig.,).
Spinal reticular tract, tractus spinoreticularis, constitute fibers that pass as part of the spinothalamic tracts, do not intersect and form bilateral projections to all parts of the stem reticular formation.
Spinal tegmental tract, tractus spinotectalis, together with the spinothalamic tract, passes through the lateral cords of the spinal cord and ends in the lamina of the midbrain roof.
Thin tuft, fasciculus gracilis, And wedge-shaped fasciculus, fasciculus cuneatus(see Fig.), conduct impulses from muscles, joints and tactile sensitivity receptors. The bodies of the first neurons of these pathways are localized in the corresponding spinal ganglia. The axons travel as part of the dorsal roots and, having entered the posterior columns of the spinal cord, take an ascending direction, reaching the nuclei of the medulla oblongata.

The thin bundle occupies a medial position and conducts corresponding impulses from the lower extremities and lower parts torso - below the 4th thoracic segment.

The wedge-shaped bundle is formed by fibers starting from the cells of all spinal nodes lying above the 4th thoracic segment.

Having reached the medulla oblongata, the fibers of the thin bundle come into contact with the cells of the nucleus of this bundle, which lies in the tubercle of the thin nucleus; fibers wedge-shaped bundle end in the sphenoid tubercle. The cells of both tubercles are the bodies of the second neurons of the described pathways. Their axons are internal arcuate fibers, fibrae arcuatae internae, - are directed forward and upward, move to the opposite side and, forming decussation of the medial loops (sensitive decussation), decussatio lemniscorum medialium (decussatio sensoria), with fibers of the opposite side, are included in medial loop, lemniscus medialis.

Having reached the thalamus, these fibers come into contact with its cells - the bodies of the third neurons of the pathway, which send their processes through the internal capsule to the cerebral cortex.

Ascending (afferent) pathways starting in the brain stem

The medial lemniscus, trigeminal lemniscus, and ascending tract begin in the brain stem auditory analyzer, optic radiance, thalamic radiance.

1. Medial loop as a continuation of the thin and wedge-shaped fascicles described earlier.

2. Trigeminal loop, lemniscus trigeminalis, formed by processes of nerve cells that make up the sensory nuclei trigeminal nerve(V pair), facial nerve(VII pair), glossopharyngeal nerve(IX pair) and vagus nerve(X pair).

The axons of afferent neurons located in the trigeminal ganglion approach the sensory nuclei of the trigeminal nerve. The common sensory nucleus of the other three nerves - the nucleus of the solitary tract - is approached by axons of afferent neurons located in the genu node (VII pair) and in the upper and lower nodes of the IX and X pairs of nerves. The bodies of the first neurons are localized in the listed nodes, and the bodies of the second neurons of the path along which impulses from the head receptors are transmitted are located in the sensitive nuclei.

The fibers of the trigeminal lemniscus pass to the opposite side (some of the fibers follow on their side) and reach the thalamus, where they end in its nuclei.

Nerve cells of the thalamus are the cell bodies of the third neurons of the ascending pathways cranial nerves, the axons of which, as part of the central thalamic radiations, through the internal capsule are directed to the cerebral cortex (postcentral gyrus).

3. The ascending path of the auditory analyzer has as its first neurons cells located in the node of the cochlear part of the vestibulocochlear nerve. The axons of these cells approach the cells of the anterior and posterior cochlear nuclei (second neurons). The processes of the second neurons, moving to the opposite side, form a trapezoidal body, and then take an ascending direction and are called lateral loop, lemniscus lateralis. These fibers end on the bodies of the third neurons of the auditory pathway, located in the lateral geniculate body. The processes of third neurons form auditory radiance, radiatio acustica, which goes from the medial geniculate body through the posterior limb of the internal capsule to the middle part of the superior temporal gyrus.

4. Visual radiance, radiatio optica(see Fig.) connects the subcortical centers of vision with the cortex of the calcarine sulcus.

The optic radiance includes two systems of ascending fibers:

geniculate-cortical optic tract, which starts from the cells of the lateral geniculate body;
cushion-cortical tract, starting from the cells of the nucleus located in the thalamic cushion; in humans it is poorly developed.

The totality of these fibers is designated as posterior thalamic radiations, radiationes thalamicae posteriores.

Ascending to the cerebral cortex, both systems pass through the posterior limb of the internal capsule.

5. Thalamic radiations, radiationes thalamicae(see Fig.) are formed by processes of thalamic cells and constitute the final sections of the ascending pathways of the cortical direction.

The thalamic radiations include:

anterior thalamic radiations, radiationes thalamicae anteriores, - radially running fibers of the white matter of the cerebral hemispheres. They begin from the superior medial nucleus of the thalamus and are directed through the anterior limb of the internal capsule to the lateral and lateral cortex. bottom surfaces frontal lobe. Part of the fibers of the anterior thalamic radiates connects the anterior group of thalamic nuclei with the cortex of the medial surface frontal lobes and the anterior part of the cingulate cortex;
central thalamic radiations, radiationes thalamicae centrales, - radial fibers connecting the ventrolateral group of thalamic nuclei with the cortex of the pre- and postcentral gyrus, as well as with the adjacent parts of the cortex of the frontal and parietal lobes. They pass as part of the posterior limb of the internal capsule;
inferior peduncle of the thalamus, pedunculus thalami inferior, contains radial fibers connecting the thalamic cushion and medial geniculate bodies with areas of the temporal chora;
posterior thalamic radiates(see earlier).

In the white matter of the brain stem and spinal cord there are conductors of ascending and descending directions Descending Paths conduct motor impulses from the cerebral cortex (pyramidal tract) to the reflex apparatus of the spinal cord, as well as impulses that promote motor act(extrapyramidal tracts) from various parts of the subcortical formations and the brain stem. Descending motor conductors end on peripheral motor neurons of the spinal cord segment by segment. The overlying departments of the central nervous system have a significant impact on reflex activity spinal cord. They're congesting reflex mechanisms own apparatus of the spinal cord. Thus, with pathological switching off of the pyramidal tracts, the spinal cord’s own reflex mechanisms are disinhibited. At the same time, spinal cord reflexes and muscle tone are enhanced. In addition, it is revealed defensive reflexes and those that are normally observed only in newborns and children in the first months of life.

The ascending pathways transmit sensitive impulses from the spinal cord from the periphery (from the skin, mucous membranes, mice, joints, etc.) to the overlying parts of the brain. Eventually these impulses reach the cerebral cortex. From the periphery, impulses come to the cerebral cortex in two ways: through the so-called specific conductor systems (through the ascending conductor and the visual thalamus) and through nonspecific system- through the reticular formation (network formation) of the brain stem. All sensory conductors give off collaterals to the reticular formation. The reticular formation activates the cerebral cortex, spreading impulses throughout different departments bark. Its influence on the cortex is diffuse, while specific conductors send impulses only to certain projection zones. In addition, the reticular formation is involved in the regulation of various vegetative-visceral and sensorimotor functions of the body. Thus, the overlying parts of the brain are influenced by the spinal cord.

DESCENT ROUTES

The corticospinal (pyramidal) tract conducts impulses voluntary movements from the motor cortex to the spinal cord. In the internal capsule it is located in the anterior 2/3 of the posterior thigh and in the knee (fibers pyramid path to the motor nuclei of the cranial nerves). At the border with the spinal cord, the pyramidal tract undergoes incomplete decussation. A more powerful crossed tract descends into the spinal cord along the lateral funiculus; the uncrossed tract passes into the anterior column of the spinal cord. The fibers of the crossed tract innervate the upper and lower extremities, the fibers of the uncrossed tract innervate the muscles of the neck, trunk, and perineum. The fibers of both bundles end segment by segment in the spinal cord, coming into contact with the motor neurons of the anterior horns of the spinal cord. The fibers of the pyramidal tract to the motor nuclei of the cranial nerves intersect when approaching the nuclei directly (Fig. 31).

The rubrospinal tract runs from the red nuclei of the midbrain to the motor neurons of the spinal cord. Under the red nuclei it crosses, passes through the brain stem, and descends along the spinal cord (next to the pyramidal tract) in the lateral cords. It has important for extrapyramidal movement.

The cortical-pontocerebellar tracts (frontal-pontocerebellar and occipitotemporal-pontocerebellar) pass from the cerebral cortex to the pons proper nuclei through the internal capsule. From the pontine nuclei, bundles of fibers are directed to the cerebellar cortex of the opposite side. They conduct impulses from the cerebral cortex after processing all the affective information entering it. These impulses correct the activity of the extrapyramidal system (in particular, the cerebellum).

The posterior longitudinal fasciculus begins from the cells of the Darkshevich nucleus, which lies anterior to the nuclei of the oculomotor nerve. It ends segment by segment at the motor neurons of the spinal cord. Has connections with all cores oculomotor nerves and with the nuclei of the vestibular nerve. In the brain stem it is located close to the midline, in the spinal cord it runs in the anterior columns.

1 - anterior central gyrus of the cerebral cortex; 2 - visual thalamus (thalamus); 3 - back thigh internal capsule; 4 - elbow of the internal capsule; 5 - anterior thigh of the internal capsule; 6 - head of the caudate nucleus; 7 - pyramidal (corticospinal) tract; 8 - midbrain; 9 - cortical-nuclear pathway; 10 - bridge; 11 - medulla oblongata; 12 - lateral (crossed) corticospinal tract; 13 - anterior (uncrossed) corticospinal tract; 14 - motor nuclei anterior horns of the spinal cord; 15 - muscle; 16 - intersection of pyramids; 17 - pyramid; 18 - lenticular core; 19 - fence

Using the rear longitudinal beam simultaneous rotation is determined eyeballs and head, concordance and simultaneity of movements of the eyeballs. Connection of the posterior longitudinal fasciculus with vestibular apparatus, with the striopallidal system and with the spinal cord makes it an important conductor of extrapyramidal influence on the spinal cord.

The tectospinal tract begins from the nuclei of the quadrigeminal roof and ends at the cells of the anterior horns of the cervical segments.

Provides connections between the extrapyramidal system, as well as the subcortical centers of vision and hearing with the cervical muscles. It has great importance in the formation of orientation reflexes.

The vestibulospinal tract comes from the nuclei of the vestibular nerve.

It ends at the motor neurons of the anterior horns of the spinal cord.

Passes in the anterior sections of the lateral cord of the spinal cord.

The reticulospinal tract runs from the reticular formation of the brain stem to the motor neurons of the spinal cord.

The vestibulospinal and reticulospinal tracts are conductors of extrapyramidal influence on the spinal cord.

RISING PATHS

The ascending pathways of the spinal cord and brain stem include sensory (afferent) pathways (Fig. 32).

The spinothalamic pathway conducts pain, temperature and partially tactile sensitivity. The receptor apparatus (exteroceptors) is located in the skin and mucous membranes. Impulses from receptors travel along spinal nerves into the body of the first one located in the intervertebral node sensory neuron. The central processes from the node cells enter the posterior horn of the spinal cord, where the second neuron lies. Nerve fibers from the cells of the posterior horn through the anterior gray commissure of the spinal cord they pass to the opposite side and along the lateral column of the spinal cord they rise into the medulla oblongata, then, without interruption, they pass through the pons and cerebral peduncles to the optic thalamus, where the third neuron is located. From the optic thalamus, fibers go through the internal capsule into the cerebral cortex - into its posterior central gyrus and into parietal lobe. The bulbothalamic pathway is a conductor of articular-muscular, tactile, vibration sensitivity, feelings of pressure, heaviness. Receptors (proprioceptors) are located in muscles, joints, ligaments, etc. Along the spinal nerves, impulses from the receptors are transmitted to the body of the first neuron (in the intervertebral node). Fibers from the first neurons enter the dorsal funiculi of the spinal cord through the dorsal root. They form Gaulle's bundles (fibers from the lower extremities) and Burdach's bundles (fibers from the upper extremities). The fibers of these conductors end in special nuclei of the medulla oblongata. Upon exiting the nuclei, these fibers cross and connect with the fibers of the spinothalamic tract. Their common path called the medial (internal) loop (the common path of all types of sensitivity).

1 - anterior spinothalamic tract; 2 - medial (internal) loop; 3 - lateral spinothalamic tract; 4- visual thalamus (thalamus); 5- cerebellum; 6 - posterior spinocerebellar tract (Flexig's bundle); 7 - anterior spinocerebellar tract (Gowers bundle); 8-nuclei of the thin and wedge-shaped bundles; 9 - receptors: A - deep sensitivity (receptors of muscles, tendons, joints); B - vibration, tactile sensitivity, feelings, position; B - touch and pressure; G - pain and temperature sensitivity; 10 - intervertebral node; 11 - posterior horns of the spinal cord

The medial loop ends at the optic thalamus.

The trigeminal loop joins the internal loop, approaching it from the other side.

Lateral or lateral loop - auditory pathway brain stem.

It ends in the internal geniculate body and in the posterior tubercle of the quadrigeminal.

The spinocerebellar tracts (anterior and posterior) carry proprioceptive information to the cerebellum.

The anterior spinocerebellar tract (Gowers bundle) begins in the periphery in the proprioceptors. The first neuron, as usual, is located in the intervertebral ganglion. Fibers from it, as part of the dorsal root, enter the dorsal horn. There is a second neuron there. Fibers from the second neurons exit into the lateral column of their side, are directed upward and, as part of the lower cerebellar peduncles, reach the cerebellar vermis.

The posterior spinocerebellar tract (Flexig's bundle) has the same origin. Fibers from the dorsal horn cells of the second neurons are located in the lateral column of the spinal cord and reach the cerebellar vermis through the superior cerebellar peduncles.

These are the main conductors of the spinal cord, medulla oblongata, pons and cerebral peduncles. They provide communication various departments brain with spinal cord (see Fig. 32).

Ascending (afferent) pathways starting in the spinal cord
Cell bodies of the first neurons- conductors of all types of sensitivity to the spinal cord - lie in the spinal ganglia. The axons of the cells of the spinal ganglia as part of the dorsal roots enter the spinal cord and are divided into two groups: medial, consisting of thick, more myelinated fibers, and lateral, formed by thin, less myelinated fibers.

The medial group of dorsal root fibers is sent to the posterior cord of the white matter, where each fiber divides in a T-shape into ascending and descending branches. The ascending branches, following upward, come into contact with the cells of the gray matter of the spinal cord in the substantia pulposum and in the dorsal horn, and some of them reach the medulla oblongata, forming a thin and wedge-shaped fascicle, fasciculi gracilis et cuneatus, spinal cord.

Spinal cord, medulla spinalis; front, right and top views (semi-schematic).

Descending fiber branches are directed downwards and come into contact with the cells of the gray matter of the posterior columns along six to seven underlying segments. Some of these fibers form a bundle in the thoracic and cervical sections of the spinal cord, which has the appearance of a comma on the cross section of the spinal cord and is located between the wedge-shaped and thin bundles; in the lumbar region - the type of medial cord; in the sacral region - a view of the oval bundle of the posterior cord adjacent to the medial surface of the thin bundle.

Spinal cord, medulla spinalis

TO upward paths, starting in the spinal cord, include the following:

1. Posterior spinocerebellar tract, tractus spinocerebellaris dorsalis (posterior),- direct cerebellar pathway, conducts impulses from muscle and tendon receptors to the cerebellum. The cell bodies of the first neurons lie in spinal node, bodies of second neurons - throughout the spinal cord in the thoracic column ( thoracic nucleus) posterior horn. The long processes of the second neurons extend outward; Having reached the posterolateral part of the spinal cord on the same side, they turn upward and rise along the lateral cord of the spinal cord, and then follow the inferior cerebellar peduncle to cerebellar vermis cortex.

2. Anterior spinocerebellar tract, tractus spinocerebellaris ventralis (anterior), conducts impulses from muscle and tendon receptors to the cerebellum. The cell bodies of the first neurons lie in spinal node, and the second neurons - in medial nucleus intermediate zone and send part of their fibers through the white commissure to the lateral cords of the opposite side, and part - to the lateral cords of their own side. These fibers reach the anterior outer sections of the lateral funiculi, located anterior to the posterior spinocerebellar tract. Here the fibers turn upward, go along the spinal cord, and then along the medulla oblongata and, having passed the bridge, along the superior cerebellar peduncles, having made a second decussation, they reach cerebellar vermis.

3. Spino-olive tract, tractus spinoolivaris, originates from the cells of the dorsal horns of the gray matter. The axons of these cells cross and rise near the surface of the spinal cord at the border of the lateral and anterior cords, ending at olive kernels. The fibers of this pathway carry information from skin, muscle and tendon receptors.

4. Anterior and lateral spinothalamic tracts, tractus spinothalamici ventralis (anterior) et lateralis, conduct impulses of pain, temperature (lateral path) and tactile (anterior path) sensitivity. The cell bodies of the first neurons lie in the spinal ganglia. The processes of the second neurons from the cells of the nucleus of the dorsal horn are directed through the white commissure to the anterior and lateral funiculi of the opposite side. Rising upward, the fibers of these pathways pass in the posterior parts of the medulla oblongata, pons and cerebral peduncles and reach the thalamus as part of the spinal lemniscus, lemniscus spinalis The bodies of the third neurons of these pathways lie in the thalamus, and their processes are directed to the cerebral cortex as part of the central thalamic radiations through the posterior leg of the internal capsule.

Capsules and the course of pathways through the internal capsule (semi-schematic).

5. Spinoreticular tract, tractus spinoreticularis, consist of fibers that pass as part of the spinothalamic tracts, do not intersect and form bilateral projections to all parts of the stem reticular formation.

6. Spinal-tegmental tract, tractus spinotectalis, together with the spinothalamic tract, passes through the lateral cords of the spinal cord and ends in the lamina of the midbrain roof.

7. Thin bun, fasciculus gracilis, and wedge-shaped bundle, fasciculus cuneatus, conduct impulses from muscles, joints and tactile sensitivity receptors. The bodies of the first neurons of these pathways are localized in the corresponding spinal ganglia. The axons travel as part of the dorsal roots and, having entered the posterior columns of the spinal cord, take an ascending direction, reaching the nuclei of the medulla oblongata.

Ascending tracts of the spinal cord and brain;

right hemisphere (semi-schematic).

Thin Bun occupies a medial position and conducts corresponding impulses from the lower extremities and lower parts of the torso - below the 4th thoracic segment.

Wedge-shaped bundle is formed by fibers starting from the cells of all spinal nodes lying above the 4th thoracic segment.

Having reached the medulla oblongata, the fibers of the thin bundle come into contact with the cells of the nucleus of this bundle, which lies in the tubercle of the thin nucleus; the fibers of the sphenoid fasciculus end in the sphenoid tubercle. The cells of both tubercles are the bodies of the second neurons of the described pathways. Their axons are internal arcuate fibers, fibrae arcuatae internae, - are directed forward and upward, move to the opposite side and, forming a cross of the medial loops (sensitive cross), decussatio lemniscorum medialium(decussatio sensoria), with fibers of the opposite side, are part of the medial loop, lemniscus medialis.