Conducting pathways of proprioceptive sensitivity. Afferent pathways Thin bundle of Gaulle and wedge-shaped burda
The conducting (descending and ascending) paths are located at various points in the vicinity of the nuclei and roots of the cranial nerves. Knowledge of the spatial relationships between the cranial nerves and pathways is of paramount importance for the topical diagnosis of the pathological focus.
ascending paths. Path of deep sensitivity. The bundles of Gaulle and Burdach - conductors of deep sensitivity in the spinal cord, reaching the lower part of the medulla oblongata, are called f. gracilis (gentle bundle) - continuation of Gaulle's bundle and f. cuneatus (wedge-shaped bundle) - continuation of Burdakh's bundle. Here they gradually terminate in the nuclei of these bundles. The axons of the cells of the nuclei, which are the second neuron of deep sensitivity, tractus bulbo-thalamicus, pass to the opposite side (sensitive decussation) in the form of a median loop, reach the thalamus and from there go to the cerebral cortex. The defeat of the area of intersection of these paths can cause a violation of deep sensitivity on both sides, and sometimes, depending on the involvement of certain fibers in the form of cross anesthesia (arm on one side, leg on the other). Involvement in the pathological process of the loop at any of its levels leads to a violation of deep sensitivity on the opposite half of the body.
The path of skin sensitivity is located in the depth of the mesh formation. In the more oral parts of the hindbrain, this bundle is close to the medial loop, with which it merges at the level of the midbrain. In practice, this means that the defeat of these levels already causes a violation of all types of sensitivity in the opposite half of the body.
The posterior direct cerebellar pathway of Phlegsig at the level of the medulla oblongata as part of the inferior cerebellar peduncle ends in the cerebellar vermis. On the periphery of the medulla oblongata, it stands out in the form of a roller and is located above the lower olive. At this level, fibers from the posterior columns and vestibular nuclei join it.
In the depths of the reticular formation lies Govers's cross-cerebellar tract. It is located between the olive and the rope body. Rising up, Govers's bundle through the pons reaches the superior cerebellar peduncle, in which it ends in the cerebellar vermis.
descending paths. The pyramidal pathway in the midbrain is located in a compact bundle in the brain stem, occupying its middle third. At the base of the pons, the pyramidal fibers lie in scattered small bundles, between which are the aforementioned own nuclei of the pons and the cortical-pontocerebellar connections. In the rest of the medulla oblongata, the pyramidal fibers again gather into two compact bundles on either side of the anterior cleft. Finally, at the border with the spinal cord, there is a cross of pyramidal fibers heading to the spinal cord. The defeat of the pyramidal pathways at the level of the entire brain stem above the decussation causes central paralysis on the opposite half of the body with unilateral lesions and bilateral movement disorders with lesions of the pyramids on both sides. Brainstem damage is characterized by early bilateral involvement in the process of pyramids. The defeat of the pyramids at the base of the bridge is distinguished by some features arising from what has been said about their location: here there may be incomplete hemiparesis, the prevalence of the disorder in one of some limbs, and a combination of pyramidal signs with cerebellar disorders.
The presence of a pathological process in the area of the intersection of the pyramids causes various combinations of central paralysis, more often bilateral, sometimes peculiarly located: paralysis of the arm on one side, legs on the other.
Tractus cortico-bulbaris s. cortico-nuclearis - the path from the cerebral cortex (lower sections of the anterior central gyrus) to the nuclei of the motor cranial nerves. Passing through the knee of the internal capsule, the corticobulbar tract is located in the brain stem medially from the main pyramidal bundle and then gradually ends in the nuclei of the motor cranial nerves at different levels of the brain stem.
The cortico-bridge path starts from various parts of the cerebral cortex, mainly from the frontal lobe, passes through the internal capsule and the brain stem. In the latter, the cortico-bridge path is located as follows: the frontal-bridge paths occupy the medial, and the occipital-parietal-temporal-bridge paths occupy its lateral sections.
In the tegmentum of the midbrain, the Monakovic bundle begins in the red nuclei. Upon exiting them, he makes a cross (Trout) and goes through the brain stem to the spinal cord. In the trunk, it is located in the depths of the mesh formation. Impulses from the cerebellum and subcortical nodes are carried along this path to the spinal cord.
The posterior longitudinal bundle begins in the nucleus of Darkshevich, passes through the entire brain stem to the spinal cord. It contains ascending and descending fibers, connects various levels of the trunk with individual segments of the spinal cord. Through the posterior longitudinal bundle, a connection is made between the nuclei of all oculomotor nerves, between them, the vestibular apparatus and the spinal cord. Involvement in the pathological process of the system of the posterior longitudinal bundle in the brain stem causes a number of vestibular disorders.
Nystagmus. Depending on the level of damage to this system, the nature of nystagmus changes. With the defeat of the caudal parts of the trunk, nystagmus is more often rotatory in nature, with the defeat of its middle parts - horizontal, upper - vertical. Often there is a violation of the act of convergence (insufficiency, and sometimes lack of convergence), varying degrees of gaze paralysis. When the oral parts of the system of the posterior longitudinal fasciculus are involved in the process, vertical strabismus and paresis of the upward gaze are sometimes observed.
Dizziness occurs mainly when moving the eyes. In clinical practice, a symptom known as a static phenomenon is of interest. If you put the patient in a pose with shifted legs and, gradually bringing the researcher's finger closer to the eyes of the researcher, forcing him to convert the eyeballs in this way, then if this symptom is present, the patient develops dizziness, staggering, more often back, sometimes combined with a feeling of Fear and blanching of the face .
Central bundle of Bechterew's tire. This path begins in the diencephalon, passes through the tegmentum of the entire brain stem and ends in the inferior olive of the hindbrain. The axons of the cells of the inferior olive pass to the opposite side and, as part of the inferior cerebellar peduncle, terminate in the cerebellar hemisphere.
The central bundle of the tegmentum is, therefore, one of the most important connections of the extrapyramidal system with the cerebellum. With the defeat of the central bundle of the tire in combination with the defeat of the inferior olive and the dentate nucleus of the cerebellum, in some cases myoclonic twitches of the soft palate, tongue, pharynx, and larynx are noted. Sometimes these myoclonic jerks, which are rhythmic in nature, also affect other muscles (intercostal muscles, neck muscles, etc.).
Afferent nerve pathways can be classified into conscious and unconscious sensory pathways. The paths of conscious sensitivity end in the projection (integration) centers of the cerebral cortex; paths of unconscious sensitivity - in the subcortical integration centers (cerebellum, mounds of the midbrain, thalamus). According to the types of sensitivity, afferent pathways of general and special sensitivity are distinguished (Table 4.1).
Table 4.1
afferent pathways
General sensitivity pathways
1. The path of exteroceptive sensitivity. The path of pain, temperature and tactile sensitivity (ganglio-spinal-thalamo-cortical path) originates from the exteroreceptors of the skin of the trunk, limbs and neck (Fig. 4.2). Due to the fact that the skin makes up the covering of the body, this sensitivity is also called superficial, or exteroceptive.
Exteroceptors for various types of surface sensitivity are specialized and are contact receptors. Pain is perceived by free nerve endings, heat by Ruffini's bodies, cold by Krause's flasks, touch and pressure by Meisner's bodies, Golgi-Mazzoni, Vater-Pacini and Merkel's discs.
From exteroceptors, impulses arrive through the peripheral processes of pseudounipolar neurons to their bodies, which are located in the sensory nodes of the spinal nerves (the bodies of the first neurons). The central processes of pseudo-unipolar cells in the composition of the posterior roots are sent to the spinal cord. The main part of the central processes ends in synapses on the cells of the own nucleus of the posterior horn. The tract from the sensitive node of the spinal nerve to the intercalary neuron can be called ganglio-spinal.
Rice. 4.2.
1 - postcentral gyrus; 2 - thalamus; 3 - own nucleus of the posterior horn; 4 - sensitive node of the spinal nerve; 5 - anterior spinal-thalamic path; 6 - lateral dorsal-thalamic pathway; 7 - dorsal-thalamic path; 8 - thalamo-cortical path
The axons of the neurons of the own nucleus of the posterior horn (second neurons) form bundles of fibers (spinal-thalamic tracts) that conduct nerve impulses to the thalamus.
In the spinal cord, the spinal-thalamic tracts have a number of characteristic features: all 100% of the fibers pass to the opposite side; the transition to the opposite side is carried out in the area of the white adhesion, while the fibers rise obliquely 2-3 segments above the initial level. The fibers that conduct pain and temperature sensitivity form the lateral spinothalamic tract, and the fibers that conduct tactile sensitivity form predominantly the anterior spinothalamic tract.
In the area of the medulla oblongata, the lateral and anterior spinal thalamic tracts are combined into a single spinal thalamic tract. At this level, the tract receives a second name - the spinal loop. Gradually, the dorsal-thalamic tract deviates in a dorsolateral direction, passing through the tegmentum of the pons and midbrain. The spinal-thalamic tract ends with synapses on the neurons of the ventrolateral nuclei of the thalamus (third neurons). The tract formed by the axons of these nuclei of the thalamus is called the thalamo-cortical tract.
The main part of the axons of the third neurons is directed through the middle part of the posterior pedicle of the internal capsule to the postcentral gyrus - the projection center of general sensitivity. Here they end on the neurons of the fourth layer of the cortex (fourth neuron), distributing along the gyrus, respectively, of the somatotopic projection (Penfield's sensory homunculus). A small part of the fibers (5–10%) ends on the neurons of the fourth layer of the cortex in the region of the intraparietal sulcus (the center of the body scheme).
Thus, the path of exteroceptive sensitivity consists of three successive tracts - ganglio-spinal, spinal-thalamic, thalamo-cortical.
Given the peculiarities of the location of the pathways, it is possible to determine the level of damage to the nervous structures. If the sensory nodes of the spinal nerves, the posterior roots, or the nucleus of the posterior horn are damaged, surface sensitivity disorders are noted on the side of the same name. In case of damage to the fibers of the spinal-thalamic tract, cells of the veitrolateral nuclei of the thalamus and fibers of the thalamo-cortical bundle, upset
Sensory properties are noted on the opposite side of the body.
2. The path of conscious proprioceptive sensitivity (deep sensitivity)(ganglio-bulbar-thalamo-cortical path) conducts nerve impulses from proprioceptors (Fig. 4.3).
Proprioceptive sensitivity is information about the state of the proprioceptors of muscles, tendons, ligaments, joint capsules and periosteum, i.e. information about the functional state of the musculoskeletal system. It allows you to judge muscle tone, the position of body parts in space, a sense of pressure, weight and vibration. Proprioceptors constitute the most extensive group of receptor structures, represented by muscle spindles and encapsulated receptors. They also perceive tactile sensitivity, so the conscious proprioceptive sensitivity pathway partially conducts tactile impulses as well.
From the proprioceptors, the nerve impulse enters through the peripheral processes of pseudo-unipolar cells to their bodies, which are located in the sensitive nodes of the spinal nerves (the bodies of the first neurons). The central processes of pseudo-unipolar cells as part of the posterior roots of the spinal nerves enter the spinal cord. In the spinal cord, they give off collaterals to the segmental apparatus. The main part of the fibers, bypassing the gray matter, is sent to the posterior funiculus.
In the posterior funiculus of the spinal cord, the central processes of pseudounipolar cells form two bundles: medially located - a thin bundle (Gaulle's bundle), and laterally located - a wedge-shaped bundle (Burdach's bundle).
Gaulle's bundle conducts impulses of conscious proprioceptive sensitivity from the lower extremities and lower half of the body - from 19 lower sensory nodes of the spinal nerves of its side (1 coccygeal, 5 sacral, 5 lumbar and 8 thoracic). The Burdach bundle includes fibers from 12 upper sensory nodes of the spinal nerves, i.e. it conducts proprioceptive sensory impulses from the upper torso, upper limbs, and neck. Consequently, a thin bundle runs throughout the entire spinal cord, and the wedge-shaped one appears only from the level of the fourth thoracic segment. The area of each of the beams gradually increases in the cranial direction.
Rice. 4.3.
1 - nuclei of thin and wedge-shaped bundles; 2 - medulla oblongata; 3 - wedge-shaped bundle; 4 - sensitive node of the spinal nerve; 5 - thin beam; 6 - internal arcuate fibers; 7 - bulbar-thalamic path; 8 - inner capsule; 9 - thalamo-cortical path; 10 - precentral gyrus; 11 - thalamus
As part of the posterior funiculi of the spinal cord, the bundle of Gaulle and the bundle of Burdach rise to the nuclei of the thin and sphenoid tubercles of the medulla oblongata, where the bodies of the second neurons are located. The bundles of Gaulle and Burdach, formed by the central processes of the pseudo-unipolar cells of the sensitive nodes of the spinal nerves, can be called the ganglion-bulbar tract.
The axons of the nuclei of the thin and sphenoid tubercles of the medulla oblongata form two groups of fibers. The first group is internal arcuate fibers that intersect with the same fibers of the opposite side, bend in the form of a loop and go up.
The bundle of these fibers is called the bulbar-thalamic tract, or medial loop. A smaller part of the axons of the second neurons, constituting the second group (external arcuate fibers), is sent to the cerebellum through its lower pedicle, forming the bulbar-cerebellar tract. The fibers of this tract terminate on the neurons of the middle part of the cortex of the cerebellar vermis.
The bulbar-thalamic tract runs along the brainstem in the tegmentum, next to the spinal-thalamic tract and ends on the neurons of the ventrolateral nuclei of the thalamus (the body of the third neurons).
The axons of the neurons of the ventrolateral nuclei of the thalamus are sent to the projection centers of the cerebral cortex (fourth neuron). Basically, they end on the neurons of the fourth layer of the cortex of the precentral gyrus (60%) - in the center of motor functions. A smaller part of the fibers goes to the cortex of the postcentral gyrus (30%) - the center of general sensitivity, and an even smaller part - to the interparietal sulcus (10%) - the center of the body schema. The somatotopic projection to these convolutions is carried out from the opposite side of the body, since the bulbar-thalamic tracts cross in the medulla oblongata.
The path from the ventrolateral nuclei of the thalamus to the projection centers of the cerebral cortex is called the thalamo-cortical tract. It passes through the internal capsule in the middle section of the hind leg.
The pathway of conscious proprioceptive sensitivity is phylogenetically more recent than other afferent pathways. When it is damaged, the perception of the position of body parts in space, the perception of posture, and the sensation of movements are disturbed. With closed eyes, the patient cannot determine the direction of movement in the joint, the position of body parts. The coordination of movements is also disturbed, the gait becomes uncertain, the movements are awkward, disproportionate.
3. The path of general sensitivity from the face area(ganglio-nuclear-thalamo-cortical path) conducts nerve impulses of pain, temperature, tactile and proprioceptive sensitivity from the face along the sensitive branches of the trigeminal nerve. From the proprioceptors of the mimic muscles, nerve impulses are conducted along the branches of the trigeminal nerve, and from the chewing muscles - along the mandibular seal. In addition to the facial area, the trigeminal nerve provides sensitive innervation (pain, temperature and tactile) of the mucous membranes, lips, gums, nasal cavity, paranasal sinuses, lacrimal sac, lacrimal gland and eyeball, as well as the teeth of the upper and lower jaws.
All three branches of the trigeminal nerve go to the trigeminal node (Gasser node), which is composed of pseudo-unipolar cells (the bodies of the first neurons).
The central processes of pseudounipolar cells enter the bridge as part of the sensory root of the trigeminal nerve and then go to the sensory nuclei (the bodies of the second neurons). Fibers are sent to the bridge nucleus, conducting impulses of tactile sensitivity from the skin of the face, impulses of pain, temperature and tactile sensitivity from deep tissues and organs of the head; to the nucleus of the spinal tract of the trigeminal nerve - fibers that conduct impulses of pain and temperature sensitivity from the skin of the face; to the midbrain nucleus - fibers that conduct impulses of proprioceptive sensitivity from the masticatory and facial muscles.
The axons of the second neurons pass to the opposite side and form the nuclear-thalamic tract, which ends in the ventrolateral nuclei of the thalamus. In the brainstem, this tract runs adjacent to the spinothalamic tract and is known as the trigeminal loop.
The axons of the third neurons located in the ventrolateral nuclei of the thalamus are sent through the posterior thigh of the internal capsule to the neurons of the cerebral cortex to the centers of general sensitivity, motor functions and body schema. They pass as part of the thalamo-cortical tract and end on the neurons of these centers in those areas of the cortex (the bodies of the fourth neurons) where the head area is projected.
The distribution of fibers of the thalamo-cortical bundle, which conducts impulses of general sensitivity from the head region, is as follows: 60% is sent to the postcentral gyrus, 30% to the precentral gyrus, and 10% to the interparietal sulcus.
A small part of the axons of the third neurons goes to the medial nuclei of the thalamus (the subcortical sensory center of the extrapyramidal system).
(Flexig's bundle) provides impulses of unconscious proprioceptive sensitivity (Fig. 4.4). From the proprioceptors, along the fibers of the spinal nerves, impulses arrive at the pseudo-unipolar cells of the sensory nodes (the bodies of the first neurons). Their central processes, as part of the posterior roots, enter the spinal cord and penetrate into the gray matter, reaching the neurons of the thoracic nucleus. They pass as part of the gaiglio-spialial tract.
Rice. 4.4.
1 - lower cerebellar peduncle; 2 - thoracic nucleus; 3 - sensitive node of the spinal nerve; 4 - sacral segment; 5 - lumbar segment; 6 - cervical segment; 7 - posterior spinal-cerebellar path
The axons of the neurons of the thoracic nucleus (second neurons) are sent to the lateral funiculus of their side. In the posterolateral part of the lateral funiculus, they form the posterior spinal cerebellar tract. This tract, receiving fibers segment by segment, increases to the level of the seventh cervical segment; above this level, the area of the bundle does not change. In the region of the medulla oblongata, the posterior spinal cerebellar tract is located in the dorsal region and penetrates the cerebellum as part of its lower leg. In the cerebellum, this path ends on the neurons of the cortex of the lower part of the vermis (the third neuron).
(Govers bundle) also conducts impulses of unconscious proprioceptive sensitivity (Fig. 4.5).
The first link in the reflex arc of the Gowers and Flexig bundles is represented by similar nerve structures. The bodies of receptor neurons (pseudo-unipolar cells) are located in the sensory nodes of the spinal nerves (the first neuron). Their peripheral processes as part of the spinal nerves and their branches reach the proprioceptors. The central processes as part of the posterior roots of the spinal nerves penetrate the spinal cord, enter the gray matter and end on the neurons of the intermediate medial nucleus (second neuron). Most of its axons (90%) are sent to the opposite side through the anterior white commissure. A smaller part of the axons (10%) goes to the anterolateral part of the lateral funiculus of its side. Thus, in the lateral funiculus, the anterior spinal cerebellar path is formed, formed by the axons of the cells of the intermediate-medial nuclei of the predominantly opposite, in a small number of their sides. It should be noted that fibers from the lower segments of the spinal cord occupy the medial part of the tract, from each overlying segment they join from the lateral side.
In the medulla oblongata, the anterior spinal cerebellar tract is located in the dorsal region between the olive and the lower cerebellar peduncles. Then it rises into the tire of the bridge. At the level of the border of the bridge and the midbrain, the anterior spinal cerebellar tract turns sharply in the dorsal direction. In the region of the superior medullary sail, the fibers that crossed in the spinal cord return to their side and then, as part of the superior cerebellar peduncles, reach the upper cortex of the cerebellar vermis (third neuron).
Rice. 4.5.
1 - superior cerebellar peduncle; 2 - sensitive node of the spinal nerve; 3 - intermediate-medial nucleus; 4 - sacral segment; 5 - lumbar segment; 6 - cervical segment; 7 - anterior spinal cerebellar path
Due to the fact that the nerve fibers that make up the Gowers bundle form decussations twice (in the anterior white commissure of the spinal cord and in the superior medullary velum), impulses of unconscious proprioceptive sensitivity are transmitted to the cerebellum from the same side of the body.
The bundles of Gaulle and Burdach are fast-conducting pathways of spatial skin sensitivity (the sense of touch, touch, pressure, vibration, body mass) and the sense of position and movement (articular-muscular (kinesthetic) sense).
The first neurons of the thin and wedge-shaped bundles are represented by pseudo-unipolar cells, the bodies of which are located in the spinal nodes. Dendrites pass through the spinal nerves, beginning with rapidly adapting receptors in the scalp (Meissner bodies, Vater-Pacini bodies) and articular capsule receptors. Recently, the possibility of participation of proprioceptors of muscles and tendons in the formation of a conscious proprioceptive feeling has been shown.
The central processes of pseudo-unipolar cells as part of the posterior roots enter segmentally into the spinal cord in the region of the posterior lateral sulcus and, having given collaterals to the II-IV plates, go in an ascending direction as part of the posterior funiculi of the spinal cord, forming a medially located thin Gaulle's fascicle and laterally - a wedge-shaped Burdakh's bundle (Fig. 5).
Gaulle's bundle
conducts proprioceptive sensitivity from the lower extremities and lower half of the body: from 19 lower spinal nodes, including 8 lower thoracic, 5 lumbar, 5 sacral and 1 coccygeal, and Burdach bundle
- from the upper body, upper limbs and neck, corresponding to 12 upper spinal nodes (8 cervical and 4 upper thoracic).
The bundles of Gaulle and Burdach, without interrupting or crossing in the spinal cord, reach the nuclei of the same name (thin and wedge-shaped) located in the dorsal sections of the medulla oblongata, and here they switch to the second neurons. The axons of the second neurons go to the opposite side, making up the internal arcuate fibers (fibrae arcuatae internae) and, crossing the median plane, intersect with the same fibers of the opposite side, forming a cross in the medulla oblongata between the olives. medial loop (decussatio lemniscorum)
External arcuate fibers (fibrae arcuatae externae) through the lower legs of the cerebellum connect the loop system with the cerebellar cortex.
Next, the fibers follow through the pons operculum, the operculum of the legs of the brain and reach the lateral nuclei of the thalamus (ventrobasal complex), where they switch to third neurons. In the bridge, the spinal-thalamic tract (paths of skin sensitivity of the neck, trunk and limbs) and the loop of the trigeminal nerve, which conduct skin and proprioceptive sensitivity from the face, join the medial loop from the outside.
Through the lower third of the posterior femur of the internal capsule, the loop system reaches the superior parietal lobule (5th, 7th cytoarchitectonic fields) and the postcentral gyrus of the cerebral cortex (SI).
Receptors are embedded in the subcutaneous tissue (exteroceptors), muscles, tendons, articular surfaces,
ligaments, fascia, periosteum (proprioceptors). Pulses are transmitted along sensitive fibers
spinal nerves to cells of the spinal ganglia, representing
is the 1st neuron. The central processes of the axons of these cells enter the spinal cord as part of the posterior
roots and enter the posterior funiculus, forming
thin beam (Goll)(fasciculus gracilis) And wedge-shaped bundle (Burdaha)(fasciculus cuneatus). axons
enter the posterior cord, starting from the lower segments of the spinal cord. Each next bundle of axons
adjoins from the lateral side to the existing ones. Thus, the outer sections of the posterior funiculus
(wedge-shaped bundle) are occupied by axons of cells that carry out proprioceptive innervation of the chest,
neck and upper limbs. Axons that occupy the inside of the posterior cord (thin bundle)
carry proprioceptive impulses from
lower limbs and lower half of the body. bundles of axons ascend to the medulla oblongata and
terminate in thin and wedge-shaped nuclei (nucleus gracilis et nucleus cuneatus), where the 2nd neuron is laid
conducting path. The axons of the cells of the thin and wedge-shaped nuclei arcuate forward and
medially at the level of the lower angle of the rhomboid fossa and in the interolive layer they pass to the opposite
side, forming a decussation of the medial loops (decussatio lemniscorum medialium). fiber bundle,
facing in the medial direction is called the internal arcuate fibers
(fibrae arcuatae internae), which are the beginning of the medial loop (lemniscus medialis). They
rise through the tire of the bridge and the midbrain to the thalamus, ending in its dorso-lateral
cores. In the nuclei of the thalamus, the 3rd neuron of the pathway is localized; the processes of the neurons of these nuclei pass
in the thalamo-cortical tract (fibrae thalamocorticales) through the posterior third of the posterior leg of the inner
capsules and end in the inner granular layer of the cortex of the postcentral gyrus (primary
cortical fields 1, 2, 3 - the core of the analyzer of general sensitivity) and the upper parietal lobule (secondary
cortical field 5). The described path is associated with the so-called epicritical sensitivity, that is,
the ability to accurately localize irritations and their qualitative and quantitative assessment.
Part of the fibers of the 2nd neuron, upon exiting the thin and wedge-shaped nuclei, bends outward and is divided
into two bundles. One bundle - posterior outer arcuate fibers (fibrae arcuatae externae posteriores)
It goes to the lower cerebellar peduncle of its side and ends in the cortex of the cerebellar vermis.
Fibers of another bundle - anterior external arcuate fibers (fibrae arcuatae externae anteriores)–
go ahead,
pass to the opposite side, go around the olive core from the lateral side and also through
the lower cerebellar peduncle is sent to the cortex of the cerebellar vermis. Front and rear outer
arcuate fibers carry proprioceptive impulses to the cerebellum.
Transmission of stimuli coming along the conductors of proprioceptive and skin sensitivity to
efferent pathways occur at the spinal and cortical levels. impulses in the spinal cord
switch from the afferent fibers of the posterior roots to the motor cells of the anterior horn
directly or through intercalary neurons located in the central intermediate substance and
in the anterior horn. Along the fibers of their own bundles (fasciculi proprii) is spreading
irritations on the gray matter of other segments, due to which the response can capture
many muscles.
In the cerebral cortex, the analysis and synthesis of incoming signals takes place and programs are formed
actions that are transmitted from the posterior hemisphere (parietal lobes) to the anterior (frontal)
lobe), where motor pyramidal and extrapyramidal pathways originate.
The paths of Gaulle and Burdakh are conductors of conscious muscular-articular feeling from the proprioreceptors of the apparatus of movement. The first neurons are represented by pseudo-unipolar cells, the bodies of which lie in the spinal nodes. Cell dendrites are sent to the periphery, where they end with receptors in muscles, tendons, ligaments and joint capsules, bones and periosteum. The axons of the cells in the posterior roots enter the spinal cord segment by segment and, without entering the gray matter, go in an ascending direction as part of the posterior cords, forming a thin Gaulle's bundle and a wedge-shaped Burdach's bundle. Gaull's path occupies an internal position, while Burdakh's path occupies an external position. Gaulle's bundle conducts a deep muscular-articular feeling from the lower extremities and lower half of the trunk of the corresponding side, including fibers of 19 lower spinal nodes, and Burdach's bundle - from the upper trunk, neck and upper limbs. The bundles of Gaulle and Burdach reach the nuclei of the same name located in the dorsal parts of the medulla oblongata and here they switch to the second neurons. In general, the first neurons make up the path -tractus gangliobulbaris.
The axons of the second neurons are combined into a single bundle - tractus bulbothalamicus. First, the nerve fibers run in a venro-medial direction along an arcuate trajectory, receiving the name internal arcuate fibers. Then, they pass to the opposite side and form a compact bundle, which makes a sharp bend, which gave reason to call it the medial loop. On the midline there is a crossover of the medial loops of the right and left sides. It is located farther than the pyramids, between the olives and forms the inter-olive layer. Then, through the dorsal part of the bridge and the cover of the legs of the brain, the fibers reach the thalamus, where they switch to the third neurons in the posterolateral ventral nucleus.
In the bridge, the paths of skin sensitivity of the neck, trunk and extremities and the trigeminal loop formed by the fibers of the trigeminal nerve, which conduct conscious skin and proprioceptive impulses from the facial muscles, capsule and ligaments of the temporomandibular joint, join the medial loop. Part of the fibers of the second neurons from the cells of the thin and sphenoid nuclei goes through the inferior cerebellar peduncle to the cerebellar cortex of the same side, the other part - to the cerebellar cortex of the opposite side. Thanks to these connections, the cerebellum is involved in the mechanism of coordination of movements.
The axons of the third neurons in the tractuss thalamocorticalis are sent to the postcentral gyrus of the cerebral hemisphere, where they end in synapses on the cells of the cortex. The fibers pass through the middle section of the posterior pedicle of the internal capsule, and then, spreading like a fan, continue their way as part of the radiant crown. From the lower limb and the half of the body of the same name, conscious proprioceptive impulses enter the upper third of the postcentral gyrus, from the upper limb to the middle, from the head to the lower. The right half of the body corresponds to the convolutions of the left hemisphere of the brain, and the left - to the right. With the loss of deep proprioceptive sensitivity, the idea of the position of one's body and its parts in space, the perception of posture, the sensation of active and passive movements are disturbed. The coordination of movements is disturbed, their dexterity and consistency are lost.
