Sense organs. Scheme of the conduction pathways of the nervous system Path of the impulse

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Each sensory system (analyzer, according to Pavlov) includes several departments.

In the peripheral a signal from the external or internal environment turns into an electrical process - a nerve impulse. This happens with the help of special structures - receptor formations.

Impulses from the periphery along the nerve fibers enter the brain and spinal cord, and then to the cerebral cortex, which is central, or cortical, department any sensory system in which final signal processing takes place.

Pathways connecting the receptor and cortical sections are referred to as conductor department sensory system (analyzer).

Irritants and receptors

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Irritants

The stimuli that act on the receptors can be of different modalities:

• light,
• sound,
• mechanical,
• chemical
• etc.

Each modality is perceived by its own type of receptors and is transmitted along strictly defined neural pathways. In this regard, they speak of the presence of certain sensory systems: visual, auditory, vestibular, somatosensory, gustatory, olfactory.

Receptors

Receptors are specialized for the perception of a certain type of cell stimulation or the end of a neuron.

Primary sensory receptors

If the stimulation is perceived by a specialized end of the dendrite of the afferent neuron, such a receptor is called primary sensory. . These are skin receptors that respond to mechanical stimulation.

Secondary sensing receptors

If the receptor is represented by a specialized cell on which the afferent nerve fiber forms a synaptic contact, such a receptor is called a secondary sensory . An example is the receptor cells of the gustatory, auditory, and vestibular sensory systems.

Exteroreceptors

If the receptors perceive irritation from the external environment, they are called exteroreceptors. . Among them, distant (visual, auditory) and contact (gustatory, tactile) receptors are distinguished.

Interoreceptors

Interoreceptors signal the state of internal organs, changes in the chemical composition of blood, tissue fluid, and the composition of the contents of the gastrointestinal tract.

Proprioreceptors

Proprioceptors transmit information about the state of the musculoskeletal system. Thus, receptors have specificity - they are most effectively excited by a stimulus of a certain modality.

receptive field

Each afferent fiber forms contacts with many receptors. The surface from which a given fiber collects information is called its receptive field. . Such fields of neighboring fibers overlap, which ensures greater reliability of the receptor function.

Projection and association areas of the cortex

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The bodies of afferent neurons, as a rule, lie in sensory spinal or cranial ganglia. The exceptions are the visual and olfactory systems, where sensory neurons are located directly in the retina (ganglion cells) or olfactory bulb, respectively. The processes of these neurons enter the spinal cord or brain, where they switch to the neuron of the next order. Further along the network of neurons, the signal propagates in an upward direction. For most sensory systems, except for the olfactory one, the penultimate neuron lies in the specific nuclei of the thalamus. From here, information enters the corresponding projection and association zones of the cortex, where memory processes are included in signal processing. It was noted that impulses from receptors reach the primary, projection zones of the cortex by the shortest route, while the activation of associative zones occurs somewhat later due to the involvement of polysynaptic nerve networks in this process (see Fig. 3.45).

Rice. 3.45.

Rice. 3.45. The system of connections between the fields of the human cerebral cortex (according to Polyakov):
I - primary (central) fields;
II - secondary (peripheral) fields;
III — tertiary (associative) fields (analyzer overlap zones).
Bold lines highlight: the system of projection (cortical-subcortical) connections of the cortex; system of projection-associative connections of the cortex; system of associative connections of the cortex.
1 - receptor;
2 - effector;
3 – sensory ganglion neuron;
4 - motor neuron;
5–6, switching neurons of the spinal cord and brainstem;
7–10 - switching neurons of subcortical formations;
11, 14 - afferent fiber from the subcortex;
13 – pyramid of layer V;
16 and 18 - pyramids of layer III; 12, 15, 17 - stellate cells of the cortex.

Pulse path

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The projections of sensory systems in the brain are topical in nature; a specific body area or group of receptors is associated with a local group of neurons in the CNS.

When the pulse passes along the described path, the modality of the signal is preserved and its partial processing takes place. This path is called specific. When passing through it, information from the receptors is sorted, part of it is inhibited ("filtered"), and only the most important part of the signal reaches the higher centers.

In addition to this, there are many non-specific pathways, passing through which the modality of the signal is lost. Afferent impulses, irrespective of the place of origin, necessarily enter the reticular formation of the brainstem along axon collaterals and cause its activation. Fig. 1. 3.19. Reticular formation of the brain stem:
A - scheme of activating bonds of the reticular formation:
1 - cerebral cortex;
2 - cerebellum;
3 - afferent collaterals;
4 - medulla oblongata;
5 - bridge;
6 - midbrain;
7 - ascending activating reticular system of the brain stem;
8 - hypothalamus;
9 - thalamus;
B – axon ramifications of a separate large reticular neuron of the medulla oblongata (sagittal section of the brain of a 2-day-old rat):
1 - nuclei of the thalamus;
2 - ventromedial nucleus of the hypothalamus;
3 - mastoid body;
4 - midbrain;
5 - bridge;
6 - medulla oblongata;
7 - core of a thin beam;
8 - cerebellum;
9 - central gray matter of the midbrain

Some regularities in the structure of efferent projection pathways

1. The first neuron of all efferent pathways is localized in the cerebral cortex.

2. Efferent projection paths occupy the anterior leg, knee and anterior part of the posterior leg of the internal capsule, pass at the base of the legs of the brain and the bridge.

3. All efferent paths end in the nuclei of the motor cranial nerves and in the anterior horns of the spinal cord, where the last motor neuron is located.

4. Efferent paths form a complete or partial crossover, as a result of which impulses from the cerebral cortex are transmitted to the muscles of the opposite half of the body.

The sense organs carry out the perception of various stimuli acting on the human and animal organism, as well as the primary analysis of these stimuli. Academician IP Pavlov defined sense organs as peripheral zones of analyzers. Their specific perceiving elements are sensitive nerve endings - receptors that convert the energy of an external stimulus into nerve impulses. The latter contain in coded form information about objects and phenomena of the external world. These impulses are transmitted along the afferent nerve pathways to the subcortical and cortical centers, where the final analysis of stimuli takes place. According to the doctrine of analyzers, the afferent paths represent their middle, conductive section, and the perceiving cortex zones are their central ends. The appearance of sensations is associated with the cortical sections of the analyzers.

In protozoa, sensitivity is inherent in the outer layer of the protoplasm of their single cell. In lower animals, whose body consists of endoderm and ectoderm, all cells of the latter respond to external stimuli. Simultaneously with the differentiation of the muscular and nervous systems, individual perceptive cells are isolated in the ectoderm, which are associated with the central nervous system and represent the primary sensory cells: at first (in lower intestinal cavities) they are scattered throughout the body, then they are grouped in certain places, especially around the mouth. Such groups of sensory cells are the simplest in structure and functions of the sense organs. Finally, more perfect forms are observed in higher ones, where the sensory organs include not only perceptive elements, but also special additional (auxiliary) apparatuses: first, indifferent (supporting) epithelial cells, then connective and muscle tissues.

In the process of evolution, organs are developed that are adapted to the perception of a wide variety of environmental agents - mechanical, physical, chemical. For example, termites perceive a magnetic field, bees and ants perceive ultraviolet rays, cockroaches and squids perceive infrared rays, fish have a lateral line organ that perceives the direction and speed of water movement, and shrews and bats are capable of perceiving ultrasonic vibrations. In higher animals and humans, the sense organs are the organ of smell, the organ of taste, the organ of vision, the vestibulocochlear organ, and the skin, which, together with its appendages, forms the general covering of the body.

Based on the features of development, structure and function, 3 types of sensory organs are distinguished. Type I includes the organs of vision and smell, which are laid down in the embryo as part of the brain. Their structure is based on primary sensory, or neurosensory, cells. These cells have specialized peripheral processes that perceive vibrations of light waves or molecules of volatile substances, and central processes through which excitation is transmitted to afferent neurons.

To type II belong the organ of taste, hearing and balance. They are laid in the embryonic period in the form of a thickening of the ectoderm, placodes. Their main receptor element is secondary-sensing, sensory epithelial cells. Unlike neurosensory cells, they do not have axon-like processes. The excitation arising in them under the influence of flavoring substances, vibrations of air or a liquid medium is transmitted to the endings of the corresponding nerves.

The third type of sense organs is represented by receptor encapsulated or non-encapsulated bodies and formations. These include receptors in the skin and subcutaneous tissue. They are nerve endings surrounded by connective tissue or glial cells. A common feature of all receptive cells is the presence of flagella - kinocilia or microvilli - stereocilia. Molecules of special photo-, chemo- and mechanoreceptor proteins are embedded in the plasma membrane of the flagella and microvilli. These molecules perceive impacts of only one specific type and encode them into specific information of the cell, which is transmitted to the corresponding nerve centers.

The sense organs also differ in the complexity of their anatomical structure. Relatively simple are the organs of taste and skin sensation, which are represented mainly by epithelial formations. The organs of smell, vision, hearing and balance have auxiliary apparatuses that ensure that only those stimuli are supplied to them, to the perception of which these sense organs are adapted. So the auxiliary apparatus of the olfactory organ is the ethmoid labyrinth and the paranasal sinuses, which direct the air stream to the olfactory receptors. The organ of vision is equipped with an optical apparatus that casts an image of external objects onto the retina of the eye. The organ of hearing has a complex apparatus for capturing and conducting sounds.

Auxiliary apparatuses of the sense organs not only ensure the interaction of specific stimuli with receptors, but also block the path of extraneous, inadequate stimuli, and also protect the sense organs from external mechanical influences and damage.

(The data on conducting paths in this edition of the textbook are supplemented and updated with information taken from the latest manuals and monographs by E. P. Kononova (1959), V. N. Chernigovsky (1960), F. A. Poemny and E. P. Semenova (1960). ).)

Conducting paths in terms of the direction of impulse conduction can be divided into two large groups - afferent and efferent. Afferent pathways make up the middle link - the conductor of one or another analyzer; therefore, some of them will be considered together with the corresponding analyzers (see "Sense Organs").

afferent pathways

Since the organism receives irritation both from the external environment and from the internal one, there are pathways that carry impulses from the receptors of external stimuli and from the receptors of internal stimuli.

Pathways from receptors of external stimuli

Receptors that perceive external stimuli are called exteroceptors. In the early stages of evolution, they were laid down mainly in the outer integument of the body, which is necessary for the perception of external stimuli, which is why in humans they develop in embryogenesis from the outer germ layer, the ectoderm. An exception is the organ of taste, which is functionally closely related to the digestive system and therefore develops from the endoderm (epithelium of the pharyngeal pockets). Subsequently, with the complication of the organization of animals and the complication of their way of life, those of the exteroceptors that were of vital importance began to develop intensively and become more complex in their organization, acquiring the structure of special organs that perceive irritations whose sources are at a certain distance from the body and therefore are called distant. . These are the receptors for hearing, sight and smell. The remaining receptors of the outer integument remained embedded in the skin, constituting the peripheral part of the skin analyzer. Conductive pathways from sound, light, taste and smell receptors will be considered when describing the corresponding analyzers in the section of esthesiology. Here the conducting paths of the skin analyzer will be outlined.

Pathways of the skin analyzer

Afferent fibers of the skin analyzer carry tactile stimuli, a sense of stereognosis, pain and temperature stimuli to the cerebral cortex. In this regard, they can be divided into several groups.

Pathways of tactile sensitivity of the skin (sense of touch)(Fig. 348). Trdctus gdnglio-spino-thaldmo-corticlis. The receptor is located in the thickness of the skin. The conductor consists of 3 neurons. cell body first neuron is placed in the spinal node, which is an accumulation of cells of peripheral neurons of all types of sensitivity. The process departing from the cells of this node is divided into two branches, of which the peripheral one goes as part of the cutaneous nerve to the receptor, and the central one, as part of the posterior root, goes to the posterior cords of the spinal cord, where, in turn, it is divided into ascending and descending branches. The terminal branches and collaterals of one part of the fibers end in the posterior horns of the spinal cord in substantia gelatinosa (this part of the tract is called tr. gangliospindlis), the other part of the ascending fibers does not go into the posterior horns, but goes in the posterior cords of the spinal cord and reaches as part of fasciculus gracilis et cuneatus of the similar nuclei of the medulla oblongata, nucleus gracilis et nucleus cuneatus (this part of the tract is called trdctus gangliobulbdris).

The cell body is located in the posterior horns of the spinal cord and in the named nuclei of the medulla oblongata. second neuron. The axons of cells embedded in the posterior horns cross the median plane in the commissura alba and are part of the trdctus spinothaldmicus anterior located in the lateral funiculus of the opposite side, which they form (see Fig. 270).

It is important to keep in mind that the crossing of the fibers of the spinothalamic bundles does not occur at the level of the entry of the corresponding posterior root into the spinal cord, but 2-3 segments higher. This fact is essential for the clinic, since with unilateral damage to this bundle, a disorder of skin sensitivity on the opposite side is observed not at the level of the lesion, but downwards from it (EP Kononova, 1959). This beam through the stem part of the brain reaches the thalamus. Along the way, it establishes a connection with the motor nuclei of the brain stem and head nerves, along which head reflexes occur when the skin is irritated, for example, eye movement when the skin of the hand is irritated. The axons of the cells of the second link, laid down in the nuclei of the medulla oblongata, also reach the visual mound along the tract, called trdctus bulbothaldmicus, which in the medulla oblongata passes to the opposite side, forming a decussation of the medial loop (decussdtlo lemniscorum) (Fig. 349). Thus, for each half of the body in the spinal cord, there are, as it were, two tracts that transmit touch impulses: 1) one, uncrossed, in the posterior cord of the same side and 2) the other, crossed, in the lateral cord of the opposite side. Therefore, with a unilateral spinal cord injury, tactile sensitivity can remain intact, since the corresponding bundle is preserved on the healthy side.

Rice. 349. Projection of the course of the entire medial loop on the lateral surface of the brain stem. l m - lemniscus medialis; 1, 2, 3 - cross sections of the medulla oblongata, pons and midbrain with the position of the medial loop (l m) in the thickness of these formations; 4 - nucleus lateralis thalami; 5 - paths of the posterior funiculus of the spinal cord (Gaulle and Burdakh); 6 - tractus gangliospinothal amicus; 7 - decussatio lemniscorum

The cell body is located in the thalamus third neuron, whose axons are sent to the cerebral cortex as part of tr. thalamocorticlidis, in posterior central gyrus(fields 1, 2, 3) and superior parietal lobe(fields 5, 7), where the cortical end of the skin analyzer is located (Fig. 350).

Tactile and pain sensitivity have a diffuse localization in the cerebral cortex, which explains their lesser disturbance with limited cortical lesions (EP Kononova, 1959).

Pathways of spatial skin sensitivity - stereognosis (recognition of objects by touch)(Fig. 270). This type of skin sensitivity, like the tactile sensitivity that runs along the fasciculus gracilis et cuneatus, has three links: 1) the spinal ganglia, 2) the nucleus gracilis et cuneatus in the medulla oblongata, 3) the visual tubercle and, finally, the nucleus of the skin analyzer in the superior parietal slice (fields 5, 7).

Pathways for pain and temperature sensation. cell body first neuron lies in the spinal node, the cells of which are connected by peripheral processes with the skin, and by the central processes with the posterior horns of the spinal cord (nuclei proprii), where the cell body of the second neuron (tractus gangliospinalis) is placed. axon second neuron passes to the other side as part of the commissura alba and rises as part of the tractus spinothalamicus lateralis to the thalamus. It should be noted that the tractus spinothalamicus lateralis, in turn, is divided into two parts - anterior and posterior, of which pain sensitivity is transmitted along the anterior, and thermal sensitivity along the posterior. The cell body lies in the thalamus third neuron, the process of which, as part of the tractus thalamocortical, goes to the cerebral cortex, where it ends in posterior central gyrus(cortical end of the skin analyzer).

Some believe that the feeling of pain is perceived not only in the cortex, but also in the thalamus, where various types of sensitivity acquire an emotional coloring. Pain and temperature impulses from the departments or organs of the head come along the corresponding head nerves - V, VII, IX, X pairs.

Due to the intersection of the fibers of the second neuron of the pathways coming from the exteroceptors, impulses of pain, temperature and partially tactile sensitivity are transmitted to the posterior central gyrus from the opposite side of the body. Therefore, it should be remembered that the defeat of the first neuron or the second neuron before the decussation causes a sensitivity disorder on the side of the lesion. If the fibers of the second neuron after the decussation or the third neuron are affected, then the disorder of the same types of sensitivity is observed on the side opposite to the lesion.

Pathways from receptors of internal stimuli

The pathways from the receptors of internal stimuli can be divided into pathways from the apparatus of movement (the body itself), i.e. from the proprioceptors (proprios - own) that make up the conductor motor analyzer, and paths from the receptors of the viscera and blood vessels, i.e., interoceptors; the second group of paths is the conductor interoceptive analyzer.

Pathways of the motor analyzer

The motor analyzer perceives deep proprioceptive sensitivity, which includes the musculo-articular feeling, vibrational sensitivity, the feeling of pressure and weight (gravity). The main type of proprioceptive sensitivity is a muscular-articular feeling, that is, impulses that arise in connection with changes in the degree of tendon tension and muscle tension; thanks to these impulses, a person gets an idea about the position of the body and its parts in space and about the change in this position (which is, in particular, important when flying into space, where a state of weightlessness is created).

The pathways of the motor analyzer are tractus ganglio-bulbo-thalamo-corticalis and tractus spinocerebellaris anterior et posterior.

Tractus ganglio-bulbo-thalamo-corticalis(see fig. 349). Receptors are found in bones, muscles, tendons, joints, that is, in the body itself, which is why they are called proprioceptors (see Fig. 351).

The conductor consists of three neurons. cell body first neuron is placed in the spinal node. The axon of this cell is divided into two branches - the peripheral one, which goes as part of the muscle nerve to the proprioceptor, and the central one, which goes as part of the posterior roots to the posterior cords of the spinal cord, fasciculus gracilis et fasciculus cuneatus, to the medulla oblongata (see Fig. 270, 348, 349). Here they end in the named nuclei of the named cords - nucleus gracilis et nucleus cuneatus (tractus ganglio-bulbaris).

Bodies are placed in these nuclei second neurons. Their axons as part of the tractus bulbothalamicus reach the lateral nuclei of the thalamus, where the third link begins. The axons of the cells of the latter are sent through the capsula interna (see Fig. 297) to the cortex anterior central gyrus, where the cortical end of the motor analyzer is placed (fields 4 and 6). Along the described proprioceptive pathways (passing through the spinal nerves), nerve impulses enter the cerebral cortex: along the fasciculus gracilis - from the muscles of the lower extremities and the lower half of the body and along the fasciculus cuneatus - from the upper half of the body and upper limb. Proprioceptive fibers from the muscles of the head pass along the head nerves: trigeminal (V) - from the muscles of the eye and from the chewing muscles, VII - from the facial muscles, IX, X, XI and XII - from the tongue, from the muscles of the pharynx and other muscles of the former visceral apparatus.

With the loss of deep (proprioceptive) sensitivity, the patient loses the idea of ​​​​the position of parts of his body in space and the change in position; movements lose their clarity, consistency, there is a disorder of coordination of movements - ataxia. Unlike cerebellar (motor) ataxia, it is called sensory (sensitive).

Not all pathways of proprioceptive sensitivity reach the cortex. Subconscious proprioceptive impulses are sent to the cerebellum, which is the most important center of proprioceptive sensitivity.

Proprioceptive pathways to the cerebellum(Fig. 352). Sensitive subconscious impulses from the apparatus of movement (bones, joints, muscles and tendons) reach the cerebellum through spinal, proprioceptive pathways, of which the most important are tractus spinocerebellaris posterior et anterior (see Fig. 270).

1. Tractus spinocerebellaris posterior(Flechsig). cell body first neuron lies in the spinal node, the axon is divided into two branches, of which the peripheral one goes as part of the muscular nerve to the receptor embedded in one or another part of the movement apparatus, and the central one, as part of the posterior root, penetrates into the posterior columns of the spinal cord and with the help of its terminal branches and collaterals branches around the nucleus thoracicus of the posterior horns of the spinal cord. In the nucleus thoracicus lie the cells of the second neuron, the axons of which form the tractus spinocerebellaris posterior. Nucleus thoracicus, as the name suggests, is best expressed in the thoracic region at the level from the last cervical segment to the second lumbar. Having reached the oblong on its side as part of the lateral funiculus of the spinal cord, this tract, as part of the lower cerebellar peduncles, reaches the vermis cortex. On its way in the spinal cord and medulla oblongata, it does not cross, which is why it is called the direct cerebellar tract. However, having entered the cerebellum, it for the most part crosses over in the vermis.

2. Tractus spinocerebellaris anterior(Gowers). First neuron the same as in the posterior tract. cells in the posterior horn second neurons, whose axons, forming tractus spinocerebellaris anterior, which enters the anterior sections of the lateral funiculus of its and the opposite side through the commissura alba, cross in it. The tract rises through the medulla oblongata and the pons to the superior medullary velum, where the decussation occurs again. After that, the fibers enter the cerebellum through its upper legs, where they end in the cortex of the worm. As a result, this whole path turns out to be crossed twice; as a result, proprioceptive sensitivity is transferred to the same side from which it came.

Thus, both cerebellar pathways connect the same halves of the spinal cord and cerebellum (F. A. Poemny and E. P. Semenova).

In addition to these pathways, the cerebellum also receives proprioceptive impulses from the nucleus gracilis and nucleus cuneatus located in the medulla oblongata. The processes of cells embedded in these nuclei go to the cerebellum through its lower legs.

All paths of deep (subconscious) sensitivity end in the worm, that is, in the old part of the cerebellum, the paleocerebellum.

Interoceptive analyzer

The interoceptive analyzer, unlike others, does not have a compact and morphologically strictly defined conductor part, although it retains specificity throughout its entire length.

Its receptors, called interoceptors, are scattered in all organs of plant life (the viscera, blood vessels, smooth muscles and glands of the skin, etc.).

The conductor consists of afferent fibers of the autonomic nervous system, which run as part of the sympathetic, parasympathetic and animal nerves and further in the spinal cord and brain to the cortex. Part of the conductor of the interoceptive analyzer is made up of afferent fibers that go as part of the head nerves (V, VII, IX, X) and carry impulses from the organs of plant life located in the distribution area of ​​\u200b\u200bthe innervation of each of these nerves. The afferent path formed by them is divided into 3 links: cells first link lie in the nodes of these nerves (ganglion trigeminale, ganglion geniculi, ganglion inferius); cells second neuron are located in the nuclei of these nerves (nucleus tractus spinalis n. trigemini, nucleus tractus solitarii nn. VII, IX, X). The fibers emanating from these nuclei pass to the other side, heading towards the thalamus. Finally, cells 3rd link laid in the optic tubercle.

A significant part of the conductor of the interoceptive analyzer is formed by the vagus nerve, which is the main component of parasympathetic innervation. The afferent path running along it is also divided into 3 links: cells first neurons lie in ganglion inferius n. vagi; cells second neurons- in the nucleus tractus solitarii.

The fibers of the vagus nerve emanating from this nucleus, together with the processes of the second neurons of the glossopharyngeal nerve, pass to the opposite side, crossing with the fibers of the opposite side, and rise along the brain stem. At the level of the superior tubercles of the quadrigemina, they join the second neurons of the skin analyzer (lemniscus medialis) and reach the thalamus where the cells lie. third neurons. The processes of the latter pass through the posterior third of the posterior femur of the internal capsule to the lower part of the posterior central gyrus.

Here is one of the parts cortical end interoceptive analyzer associated with the head parasympathetic nerves and the area of ​​their innervation.

Afferent paths from the organs of plant life also go as part of the posterior roots of the spinal nerves. The cells of the first neurons in this case lie in the spinal nodes. A powerful collector of the afferent path from the organs of plant life passes through the celiac nerves (nn. splanchnici major et minor). Various groups of nerve fibers of the splanchnic nerves ascend in the spinal cord as part of its posterior and lateral cords. Afferent fibers of the posterior cords transmit interoceptive impulses that reach through the visual tubercles of the cerebral cortex.

Afferent fibers of the lateral cords terminate in the nuclei of the brainstem, cerebellum and thalamus (nucleus ventralis posterior). Thus, cells of the third neurons of the entire conductor of the interoceptive analyzer, associated with both sympathetic and parasympathetic innervation, lie in the thalamus opticus. Therefore, in the thalamus, interoceptive reflex arcs are closed and an "exit" to the efferent pathways is possible.

Closure for individual reflexes can also occur at other, lower levels. This explains the automatic, subconscious activity of organs controlled by the autonomic nervous system. Cortical end The interoceptive analyzer, in addition to the posterior central gyrus, as mentioned above, is located in the premotor zone, where the afferent fibers coming from the thalamus terminate. Interoceptive impulses coming through the celiac nerves also reach the cortex of the anterior and posterior central gyri in the areas of musculocutaneous sensitivity.

It is possible that these zones are the first cortical neurons of the efferent pathways of the autonomic nervous system, which carry out cortical regulation of autonomic functions. From this point of view, these first cortical neurons can be considered as a kind of analogue of Betz's pyramidal cells, which are the first neurons of the pyramidal pathways.

As can be seen from the above, the interoceptive analyzer is structurally and functionally similar to the exteroceptive analyzers, however, the area of ​​the cortical end of the interoceptive analyzer is much smaller compared to the exteroceptive ones. This explains its "roughness", i.e., the lower subtlety, the accuracy of differentiations in relation to consciousness.

At all levels of the central nervous system - in the spinal cord, cerebellum, visual tubercles and cerebral cortex - there is a very close overlap of the paths and zones of representation of animal and vegetative organs. Visceral and somatic afferent impulses can be addressed to the same neuron, "serving" both vegetative and somatic functions (V. N. Chernigovsky). All this ensures the interaction of the animal and vegetative parts of a single nervous system. The highest integration of animal and vegetative functions is carried out in the cerebral cortex, especially in the premotor zone.

So far, we have considered afferent pathways associated with a certain specialization of neurons, conducting certain specific impulses (tactile, proprioceptive, interoceptive). Together with the pathways from the organs of vision, hearing, taste, smell, they constitute the so-called specific afferent system. Along with this, there is afferent system represented by the so-called reticular formation related to non-specific structures. The reticular formation perceives all impulses without exception - pain, light, sound, etc. But while specific impulses from each sense organ arrive through special conductor systems in the cortex of the corresponding analyzers, there is no specialization of neurons in the reticular formation; the same neurons receive different impulses and transmit them to all layers of the cortex. Thus, the reticular formation constitutes the second afferent system.

The second afferent system of the brain is the mesh formation, formatio reticularis

(It is presented mainly according to I. N. Filimonov (an article in the BME) with the addition of special works in this direction, the authors of which are indicated.)

This name means a set of structures located in the central parts of the brain stem and differing in the following morphological features:

1. Neurons of the reticular formation have a structure that distinguishes them from other neurons - their dendrites branch very weakly, neurites, on the contrary, are divided into ascending and descending branches, which release numerous collaterals from themselves, due to which the axon can contact a huge number of nerve cells (with a length in 2 cm - from 27500).

2. Nerve fibers go in a variety of directions, resembling a network under a microscope, which served as the basis for Deiters to call it 100 years ago a mesh, or reticular, formation.

3. The cells of the reticular formation are scattered in some places, and in some places they form nuclei, the beginning of the isolation of which was laid by V. M. Bekhterev, who described the reticular nucleus of the pontine tire (nucleus reticularis tegmenti pontis).

So far, 96 individual nuclei have been described.

Area of ​​distribution of the reticular formation definitely not yet established. Based on physiological data, it is located along the entire length of the brain stem and occupies a central position in the medulla oblongata, pons, midbrain, in the sub- and hypothalamic region, and even in the medial part of the visual tubercles. Here it narrows, ending in a keel - the rostral end.

Connections of the reticular formation. The reticular formation is connected with all parts of the central nervous system, due to which they differ:

1) reticulo-petal connections coming from all parts of the brain;

2) reticulo-fugal connections going to the gray matter and nuclei of the brain and spinal cord;

3) reticulo-reticular connections (ascending and descending) between the various nuclei of the reticular formation itself.

Function. At present, it is believed that the reticular formation is an "energy generator" and regulates the processes occurring in other parts of the central nervous system, including the cerebral cortex. It is especially important that the reticular formation has a general (generalized) non-specific activating effect on the entire cerebral cortex (P. K. Anokhin), which is ensured by the presence of ascending pathways from the mesh formation to all lobes of the cerebral hemispheres. Therefore, it is also called the ascending reticular activating system (Moruzzi and Megun). Being connected by the collaterals of the axons of its cells with all specific afferent pathways passing through the brainstem, it receives impulses from them and carries nonspecific information to the cerebral cortex.

As a result, two afferent systems pass through the brain stem into the cerebral cortex: one is specific - these are all specific sensitive pathways that carry impulses from all receptors (extro-, intero- and proprioceptors) and end on the cell bodies of mainly the 4th layer of the cortex; the other is nonspecific, formed by the reticular formation and ending on the dendrites of all layers of the cortex. The interaction of both these systems determines the final response of the cortical neurons. This is the modern idea of ​​the two afferent systems of the brain.

Considering such a great importance of the mesh formation and its influence on the cerebral cortex, some bourgeois scientists (Penfield, Jasper, etc.) exaggerate its role, believing that it, located in the central parts of the brain, constitutes a special "centrencephalic" system that performs the function of consciousness and integration. The desire to lower the highest level of integration from the cerebral cortex to the subcortex has no factual grounds and is anti-evolutionary, since in the process of evolution the highest part of the brain reaches the greatest development, i.e. its cloak, and not the trunk. This desire is contrary to the materialistic idea of ​​nervism and reflects Freudianism - the idealistic doctrine of the leading role not of the cortex, but of the subcortex. The structure and function of the reticular formation have not yet been fully disclosed and are the subject of further research.

Descending motor pathways

Descending motor pathways come from the cerebral cortex - tractus corticonuclearis et corticospinalis (pyramidal system), from the subcortical nuclei of the forebrain - the extrapyramidal system and from the cerebellum.

Tractus corticospinalis (pyramidalis) or pyramidal system

cell body first neuron lies in the anterior central gyrus of the cerebral cortex (Betz's pyramidal cells). The axons of these cells descend through the corona radiata into the internal capsule (the knee and the anterior two-thirds of the back), then into the crus cerebri (its middle section), and then into the pars basilaris of the pons and the medulla oblongata. Here, part of the fibers of the pyramidal system enters into communication with the nuclei of the head nerves. This part of the pyramidal system, passing through the knee of the internal bag and connecting the cerebral cortex with the nuclei of the head nerves, is called tractus corticonuclearis*. The fibers of this tract partly pass to the other side, partly remain on their side. The axons of cells embedded in the nuclei of the head nerves (cell bodies of the second neurons), as part of the corresponding nerves, end in the striated muscles innervated by these nerves.

* (The fibers of the tractus corticonuclearis are connected with the nuclei of the head nerves not directly, but with the help of intercalary neurons.)

Another part of the pyramidal system, passing in the anterior two-thirds of the back of the inner bag, serves to communicate with the nuclei of the spinal nerves, descends to the anterior horns of the spinal cord and is therefore called tractus corticospinalis. This tract, having passed in the brain stem to the medulla oblongata, forms pyramids in it. In the latter, part of the fibers of the tractus corticospinalis (decussatio pyramidum) crosses, which, descending into the spinal cord, lies in its lateral funiculus, forming tractus corticospinalis(pyramidalis) lateralis. The remaining uncrossed part of the tractus corticospinalis descends in the anterior funiculus of the spinal cord, forming it tractus corticospinalis(pyramidadis) anterior, (see Fig. 270).

The fibers of this bundle gradually along the length of the spinal cord also pass to the other side as part of the commissura alba, as a result of which the entire tractus corticospinalis is crossed. Due to this, the cortex of each hemisphere innervates the muscles of the opposite side of the body.

The motor and sensory intersections occurring in various parts of the brain (decussatio pyramidum, commissura alba, decussatio lemniscorum, etc.) represent, according to I. P. Pavlov, an adaptation of the nervous system aimed at preserving innervation in case of damage to the brain in any place of one his side. The axons that make up the tractus corticospinalis (pyramidalis) connect with the motor cells of the anterior horns of the spinal cord, where second link*. The axons of the cells lying here go as part of the anterior roots and then the muscle nerves to the striated muscles of the trunk and extremities, innervated by the spinal nerves. Thus, tractus corticonuclearis et tractus corticospinalis together make up a single pyramidal system that serves to consciously control the entire skeletal muscles (see Fig. 353).

* (The fibers of the tractus corticospinalis are connected with the cells of the anterior horns not directly, but with the help of intercalary neurons.)

This system is especially developed in man in connection with upright posture and conscious use of his apparatus of movement in the process of labor activity associated with a special kind of movement.

Descending pathways of the subcortical nuclei of the forebrain - extrapyramidal system

Rice. 354. Connections of the striopallidary system and the extrapyramidal system. 6 - 4S - fields of the premotor and motor areas of the cerebral cortex; 1 - fibers ascending from the thalamus to the cortex; 2 - path from the "inhibitory" areas of field 4 to the caudate nucleus (N. caud.); gl. pall. - pale ball; C. L. - Lewis body; N. ruber - red core; S. n. - black substance; F. r. - formatio reticularis of the medulla oblongata. The arrows indicate the direction and "destination station" of the impulses.

The pyramidal system, as mentioned above, begins in the cerebral cortex (layer 5, Betz's pyramidal cells). Extrapyramidal system composed of subcortical formations. It consists of corpus striatum, thalamus, corpus subthalamicum Luysi, nucleus ruber, substantia nigra and white matter conductors that connect them. The extrapyramidal system differs from the pyramidal system in its development, structure and function. It is the phylogenetically oldest motor-tonic apparatus, which is already found in fish, where there is still only a pale ball, pallidum (paleostriatum); amphibians already have a shell, putdmen (neostriatum). At this stage of development, when the pyramidal system is still absent, the extrapyramidal system is the highest part of the brain, which perceives irritation from the receptor organs and sends impulses to the muscles through the automatic mechanisms of the spinal cord. The result is relatively simple movements (automated). In mammals, as the forebrain and its cortex develop, a new kinetic system is formed - a pyramidal one, corresponding to a new form of motor acts (M.I. Astvatsaturov), associated with an increasing specialization of small muscle groups. As a result, a person fully develops two systems:

1. The pyramidal system is phylogenetically younger, represented by the screen centers of the cortex, which are in charge of the conscious movements of a person, in which certain small muscle groups can participate. (When the pyramidal system is affected, paralysis is observed). Through the pyramidal system, cortical activity is also carried out in movements, based on conditioned reflexes.

2. Extrapyramidal system - phylogenetically older, consisting of subcortical nuclei. In humans, it plays a subordinate role and carries out higher unconditioned reflexes, maintaining muscle tone and automatically regulating its work (involuntary automatic innervation of the bodily muscles). This automatic regulation of the muscles is carried out due to the connections of all components of the extrapyramidal system with each other and with the nucleus ruber, from which the descending motor path goes to the anterior horns of the gray matter of the spinal cord, tractus rubrospinalis. This tract begins in the cells of the red nucleus, passes through the median plane at the level of the anterior tubercles of the quadrigemina, forming the ventral chiasm (decussatio ventralis tegmenti Foreli), and descends through the brain stem into the lateral cords of the spinal cord, after which it ends among the motor neurons of the anterior horns of the gray matter. Thus, the extrapyramidal system acts on the spinal cord through the red nucleus, which is the most important part of this system. The descending cerebellar pathways are closely related to the work of the extrapyramidal system.

Descending motor pathways of the cerebellum

The cerebellum is involved in the control of motor neurons in the spinal cord (muscular coordination, balance, maintaining muscle tone, and overcoming inertia and gravity). This is done using tractus cerebellorubrospinalis. cell body first link This path lies in the cerebellar cortex (Purkinje cells). Their axons end in the nucleus dentatus cerebelli and, possibly, in other nuclei of the cerebellum, where second link. The axons of the second neurons go through the upper legs of the cerebellum to the midbrain and end in the nucleus ruber. Here are the cells third tier, the axons of which are part of the tractus rubrospinal (Monakov), switching in the anterior horns of the spinal cord ( fourth link) reach the skeletal muscles.

Descending tracts of the cerebral cortex to the cerebellum

The cerebral cortex, which is in charge of all the processes of the body, also keeps the cerebellum under its control as the most important proprioceptive center associated with the movements of the body. This is achieved by the presence of a special descending path from the cerebral cortex to the cerebellar cortex - tractus corticopontocerebellaris.

First link this path consists of neurons, the cell bodies of which are laid down in the cerebral cortex, and the axons descend to the nuclei of the bridge, nuclei (proprii) pontis. These neurons make up separate bundles, which are called tractus frontopontinus, occipitopontinus, temporopontinus et pdrietopontinus, according to different lobes of the brain. In the cores of the bridge begin second neurons, the axons of which form the tractus pontocerebelldris, going to the opposite side of the bridge and, as part of the middle cerebellar peduncles, reach the cortex of the cerebellar hemispheres (neocerebellum).

Thus, a connection is established between the cerebral cortex and the cerebellar hemispheres. (The hemispheres of the brain are connected to the opposite hemispheres of the cerebellum). Both of these parts of the brain are younger and are interconnected in their development. The more developed the cerebral cortex and hemispheres, the more developed the cortex and the cerebellar hemisphere. Since the connection between these parts of the brain is carried out through the bridge, the degree of development of the latter is determined by the development of the cerebral cortex.

Consequently, three pairs of cerebellar peduncles provide its multilateral connections: through the lower peduncles, it receives impulses from the spinal cord and medulla oblongata, through the middle ones - from the cerebral cortex; as part of the upper legs, the main efferent path of the cerebellum passes, along which cerebellar impulses are transmitted to the cells of the anterior horns of the spinal cord. The connection of the hemispheres of the brain with the hemispheres of the cerebellum, i.e., with its new part (neocerebellum), is cross, while the connection of the worm, i.e., the old part of the cerebellum (paleocerebellum), with the spinal cord is mainly direct, homolateral.

Pathways n Pathways are bundles of nerve fibers combined on the basis of a common structure, topography, and function into a single anatomical formation that provides functional two-way communication between gray matter sections of various parts of the brain and spinal cord with effector organs.

Pathways n n Within the CNS, pathways consist of tracts. The tracts are single-neuronal and are represented by axons of nerve cells. The structure of the conducting path may include one, two or several serially connected neurons. There are three groups of nerve pathways: associative, commissural, projection.

Pathways n n Associative nerve fibers connect areas of gray matter within one half of the brain, various functional centers. Allocate short and long associative fibers. In the spinal cord, association fibers connect the gray matter of different segments and form the anterior, lateral, and posterior spinal cord own bundles, located along the periphery of the gray matter.

Pathways n Commissural nerve fibers connect the gray matter of the right and left hemispheres in order to coordinate their function. Commissural fibers pass from one hemisphere to another, form commissures (corpus callosum, commissure fornix, anterior commissure).

Conducting pathways n Projective nerve fibers are systems of nerve conductors that connect the cerebral cortex and cerebellum with the subcortical nuclei, brain stem, spinal cord and through them with the periphery: they project the cortex to the periphery and the periphery to the cortex. Accordingly, the projection pathways are divided into afferent (ascending) and efferent (descending).

Conducting pathways n Ascending projection pathways (afferent, sensory) carry impulses to the brain resulting from exposure to environmental factors, as well as impulses from the organs of movement, from internal organs, blood vessels.

Afferent pathways n n According to the nature of the conducted impulses, ascending projection pathways: Exteroceptive pathways, carry impulses from exteroceptors (pain, temperature, tactile, pressure); Proprioceptive pathways - from the proprioceptors of the elements of the musculoskeletal system, carry information about the position of body parts in space; Interoceptive - from the interoceptors of internal organs, vessels, which perceive the state of the internal environment of the body, the intensity of metabolism, the chemistry of blood and lymph, pressure in the vessels.

Afferent pathways Patterns of the structure of the afferent projection pathways. n n The beginning of each pathway is represented by receptors located in the skin, subcutaneous tissue or deep parts of the body. The first neuron in all afferent pathways is located outside the central nervous system, in the spinal ganglia. The second neuron is localized in the nuclei of the spinal or medulla oblongata. All ascending pathways run in the dorsal part of the brain stem.

Afferent pathways n n The third neuron in the pathways leading to the cortex of the cerebral hemispheres is located in the nuclei of the thalamus, and in the cerebellar pathways in the cerebellar cortex. The paths that bring impulses to the cerebral cortex have one decussation made by the processes of the 2nd neuron; due to this, each half of the body is projected onto the opposite hemisphere of the large brain. The cerebellar pathways either do not have a single decussation, or they decussate twice, so that each half of the body is projected onto the cortex of the same half of the cerebellum. The paths connecting the cerebellum with the cerebral cortex are crossed.

Efferent pathways n Descending (efferent) projection pathways conduct impulses from the cortex, subcortical centers to the underlying sections, to the nuclei of the brain stem and to the motor nuclei of the spinal cord. These paths are subdivided: pyramidal, extrapyramidal.

Efferent pathways n The pyramidal pathway connects the neurons of the 5th layer of the motor cortex directly with the motor nuclei of the spinal cord and cranial nerves. It transmits signals to the muscles of voluntary movements regulated by the cerebral cortex. Pyramidal pathways serve for conscious (volitional) control of skeletal muscles.

Efferent pathways n n Extrapyramidal pathways are represented by multilink descending pathways, carry impulses from the cortex through the subcortical centers to the motor nuclei of the cranial nerves or anterior horns of the spinal cord, and then to the skeletal muscles. Through the extrapyramidal system, regulation of involuntary movements, automatic motor acts, muscle tone, as well as movements that express emotions (smile, laugh, cry, etc.) is carried out.

Efferent pathways n n n Structure patterns of efferent pathways The first neuron of all efferent pathways is located in the cerebral cortex. Efferent projection pathways occupy the anterior leg, knee and anterior part of the posterior leg of the internal capsule, pass at the base of the legs of the brain and the bridge. All efferent pathways end in the nuclei of the motor cranial nerves and in the anterior horns of the spinal cord, where the last motor neuron is located. Efferent pathways form a complete or partial intersection, as a result of which impulses from the cerebral cortex are transmitted to the muscles of the opposite half of the body.

ROSZDRAV

State educational institution of higher professional education

FAR EASTERN STATE MEDICAL UNIVERSITY

FEDERAL AGENCY FOR HEALTH AND SOCIAL DEVELOPMENT

DEPARTMENT OF HUMAN ANATOMY

PATHWAYS OF THE BRAIN AND SPINAL CORD

Educational and methodical manual for students of medical and pediatric

faculties

Khabarovsk

UDC 611.81 + 611.82 (075.8) LBC 28.706ya 73 P 782

COMPILERS:

Associate Professor G.A. Ivanenko, associate professor A.V. Kuznetsov

REVIEWERS:

Doctor of Medical Sciences, Professor B.Ya. Ryzhavsky Doctor of Medical Sciences, Professor A.M. Helimsky

Approved at the meeting of the CMS University 23.01.07.

Foreword ……………………………………………………………………4

Classification of pathways …………………………………………5

Projection pathways …………………………………………...6

Afferent pathways ………………………………………...6

Proprioceptive pathways (deep)

sensitivity …………………………………………………………..7

Conductive path of the skin analyzer ……………………………….11

Conductive path of tactile sensitivity …………………….14

Proprioceptive pathways to the cerebellum …………………………………...17

Conductive path of the interoceptive analyzer ………………….24

Efferent pathways ……………………………………….26

Pyramidal pathways ……………………………………………………………………………………………………………………………………………………………………………………………………27

Extrapyramidal nervous system …………………………………….36

Reticulo-spinal tract ………………………………………...41

Predverno-spinal path …………………………………….41

Descending pathways of the cerebellum ……………………………………………..42

Commissural pathways ……………………………………….46

Associative pathways ……………………………………………48

FOREWORD

The section "Anatomy of the central nervous system" is one of the most difficult in the course of human anatomy studied by students -

doctors. Its significance is determined by the role it plays in shaping the students' dialectical materialistic worldview.

vision, correct understanding of simple and complex forms of behavior,

the whole system of consciousness and reason in human behavior, his thinking, memory and creative work.

Lesson on the topic "Conducting pathways of the central nervous system"

is the final, summing up the work of students in the study

Research Institute of CNS Anatomy. In the various activities of the nervous system,

pathways are the morphological substrate that provides connections between various brain structures and functional

development of the nervous system as a whole, they differ in the complexity of the structure

and high operational reliability.

The study of the anatomy of the pathways of the brain and spinal cord is a difficult task. Textbooks on human anatomy present only their classical description without the clinical aspects of the structure. For future pediatricians, in addition, it is necessary to know the age-related features of the pathways, since this is of great importance in clinical practice.

The proposed teaching aid is addressed to students

there I-II courses of medical and pediatric faculties as an additional

material for studying the topic "Anatomy of the pathways of the central nervous system." In the manual, the conducting paths are considered

are taken from a clinical standpoint, so it will be useful for senior students in preparation for classes on nervous diseases.

yum. We think that this manual will be useful to doctors - inter-

us and clinical residents who want to become neuropathologists and neurologists.

CLASSIFICATION OF PATHWAYS

The pathways of the central nervous system are a system of nerve fibers that connects various parts of the brain and spinal cord, both among themselves and within either only the brain or only the spinal cord, providing a functional bilateral

communication between different brain structures. Thanks to the

pathways, the integrative activity of the central nervous system is achieved

system, the unity of the organism and its connection with the external environment.

Sections of complex multi-neuron reflex arcs, represented by

chains of neurons along which a nerve impulse follows a strictly defined direction are considered as pathways of the central nervous system.

Conducting paths are usually divided into three groups: projection, which

missural and associative.

Depending on the direction of the impulse, the projection

paths are divided into afferent (centripetal) and efferent

nye (centrifugal). Afferent pathways conduct nerve impulses from receptors to the centers of the brain and spinal cord. Efferent pu-

ti - conduct impulses from the centers of the brain and spinal cord to the work

which organs.

Commissural pathways connect parts of the cortex of the right

th and left cerebral hemispheres.

Associative paths can be defined as chains of intercalated neu-

rons (within one hemisphere of the brain) connecting various centers of the nervous system and thus uniting

afferent and efferent pathways into the reflex arc.

In ontogenesis, projection pathways initially develop, yes

The next - commissural and the most recent - associative paths.

In this order, we will consider them in this tutorial.

PROJECTION PATHWAYS

These pathways provide a two-way connection of the cerebral cortex with the nuclei of the brain stem and the nuclei of the spinal cord.

Projection pathways are divided into afferent (sensory) and

efferent (motor). Functionally, they pre-

constitute a single whole, as they are links of a complex ref-

lecture arc. But due to the complexity of the structure, these links are considered

separately as afferent and efferent pathways.

AFFERENT PATHWAYS

These are sensitive paths through which the projection of the surface of the body, internal organs, muscles, joints is carried out into the senses.

stimulating and motor centers of the cortex.

By the nature of the impulses conducted, the afferent pathways

are divided into three groups.

I. Exteroceptive pathways - carry impulses (pain, temperature-

nye, tactile, pressure), resulting from the impact

external environment on the skin.

II. Proprioceptive pathways - conduct impulses from the organs of movement

nia (muscles, tendons, joint capsules, ligaments), carry information

theory about the position of body parts in space.

III. Interoceptive pathways - conduct impulses from internal organs

new vessels, where chemo-, baro- and mechanoreceptors perceive the state of the internal environment of the body, the intensity of metabolism, the chemistry of blood and lymph, and the pressure in the vessels.

Some regularities in the structure of afferent projection pathways.

 The beginning of each pathway is represented by receptors located in the skin, subcutaneous tissue, or deep parts of the body.

 The first neuron in all afferent pathways is outside the center

tral nervous system, in the spinal ganglia.

 The second neuron is localized in the nuclei of the spinal or stem part of the brain.

 All ascending pathways pass through the tegmentum of the brainstem.

 The third neuron in the paths leading to the cortex of the hemispheres of the pain

brain, is located in the nuclei of the thalamus, and in the cerebellar

tei - in the cerebellar cortex.

 The paths that bring impulses to the cerebral cortex have one decussation made by processes 2nd neuron; thanks to this-

mu each half of the body is projected onto the opposite

brain louse.

 The cerebellar pathways either do not have a single decussation, or

are baptized twice, so that each half of the body is projected onto the cortex of the same half of the cerebellum.

 Pathways connecting the cerebellum with the cerebral cortex

are crossed.

The conductive path of the proprioceptive (deep) sensitive

ness (Tractus ganglio-bulbo-thalamo-corticalis)

This path conducts conscious muscular-articular feeling from the proprioreceptors of the movement apparatus. Phylogenetically, it is the youngest. With loss of joint-muscular feeling -

the patient loses an idea of ​​the position of body parts in space

ve, cannot determine the direction of movement of the limbs; in pain-

th there is a violation of coordination of movements: disproportionate, disproportionate

coordinated movements, unsteady gait.

The path of conscious proprioceptive impulses is three-neuron-

ny (Fig. 1). It is represented by three consecutive tracts: tractus gangliobulbaris, tractus bulbothalamicus, tractus thalamocorticalis.

Rice. 1. Pathways of proprioceptive sensitivity

cortical direction.

The first neurons are represented by pseudo-unipolar cells,

whose bodies are located in the spinal nodes. Cell dendrites are sent to the periphery as part of the spinal nerves and end

proprioreceptors in the bones, periosteum, ligaments and capsule of the joints, tendons and muscles. Axons - the central processes of the pseudo-

pre-unipolar cells, as part of the posterior roots, enter the spinal cord segment by segment, without entering the gray matter, go up - to

the composition of the posterior cords of the spinal cord, forming bundles of the posterior cords

kov: medially located thin bundle of Gaulle (fasciculus gracilis) and

laterally - wedge-shaped bundle of Burdakh (fasciculus cuneatus). Gaulle's bundle conducts conscious proprioceptive impulses from the lower extremities and lower half of the trunk of the corresponding side, to

it is suitable for fibers from 19 spinal nodes: 1 coccygeal, 5

sacral, 5 lumbar, 8 lower thoracic. Burdakh's bundle conducts a deep joint-muscular feeling from the upper torso, neck,

upper limbs. It includes fibers of 12 spinal nodes: 4 upper thoracic and 8 cervical.

The fibers of the posterior cords are arranged in layers. The most me-

dially (closer to the posterior median sulcus) are adjacent fibers coming from the sacral spinal nodes. Gaulle's and Burdach's bundles reach the medulla oblongata without interrupting in the spinal cord.

In the medulla oblongata, the fibers of the posterior cords approach the poison

frames: nucleus gracilis et nucleus cuneatus, located in the tubercles of the same name, and here they switch to the second neurons. The first neurons make up the path - tractus gangliobulbaris.

The axons of the second neurons, whose bodies are located in the nucleus gracilis et nucleus cuneatus of the medulla oblongata, pass to the counter-

the opposite side, forming a dorsal sensitive decussation or decussation of the medial loop - decussatio lemniscorum. These fibers are

Being an integral part of the medial loop - lemniscus medialis, they pass in the medulla oblongata dorsal to the pyramids, then through the dorsal part of the bridge and the midbrain tegmentum. Fibers of the second neurons, dos-

thalamus, approach the ventrolateral nuclei of the visual bu-

gra, where they switch to the bodies of third neurons. In the region of the bridge, a spinal loop joins these fibers (paths of the skin senses)

limbs, trunk and neck), as well as the trigeminal loop

(skin and proprioceptive sensitivity from the face, which conducts

fibers of the trigeminal nerve). The second neurons make up the path

tractus bulbothalamicus.

Part of the axons of the second neurons (cells of the thin and wedge-shaped nuclei) through the lower legs of the cerebellum reach the cortex of its hemispheres on their own and opposite sides. Thus, the cerebellum receives proprioceptive impulses, due to which it participates in the coordination of movements.

The fibers of the third neurons, whose bodies are located in the ventro-

lateral nuclei of the thalamus pass through the middle section of the posterior leg of the internal capsule, then, as part of the radiant crown, they approach the precentral gyrus of the cerebral hemisphere, where they end

are located on the cells of the fourth layer of the cortex. The third neurons make up the path tractus thalamocorticalis. In the upper third of the precentral gyrus of the

yut conscious proprioceptive impulses from the lower limb and the same half of the body; in the middle third of the gyrus - from the upper limb; in the lower third - from the head. Since the fibers are

th tract in the region of the medulla oblongata make a cross (re-

cross of the medial loop), then into the precentral gyrus of the right

the lusaria of the large brain receives impulses from the left half of the body;

from the right half of the body - to the precentral gyrus of the left hemisphere -

From the muscles of the head, capsule and ligaments of the temporomandibular joint

tava conscious proprioceptive impulses are carried out along the fibers

us the trigeminal and glossopharyngeal nerves. These pathways are three-neural.

The bodies of the first neurons are located in the sensitive nodes indicated

cranial nerves. The bodies of the second neurons are sensory cells

cranial nerve nuclei in the region of the brainstem. Axons are auto-

ry neurons pass to the opposite side and, as part of the tractus nucleothalamicus, reach the ventrolateral nuclei of the thalamus, where the bodies of third neurons lie. From the bodies of the third neurons of the thalamo-

cortical tract (tractus thalamocorticalis) is directed through the middle