The spinal cord (medulla spinalis) is located in the spinal canal. Level I cervical vertebra And occipital bone the spinal cord passes into the oblong, and downwards stretches to the level of I-II of the lumbar vertebra, where it becomes thinner and turns into a thin terminal thread. Length spinal cord 40–45 cm, thickness 1 cm. The spinal cord has cervical and lumbosacral thickenings, where nerve cells are located that provide innervation of the upper and lower extremities.
The spinal cord consists of 31–32 segments. A segment is a section of the spinal cord that contains one pair of spinal roots (anterior and posterior).
The anterior root of the spinal cord contains motor fibers, the posterior root contains sensory fibers. Connecting in the region of the intervertebral node, they form a mixed spinal nerve.
The spinal cord is divided into five parts:
cervical (8 segments);
Thoracic (12 segments);
Lumbar (5 segments);
sacral (5 segments);
Coccygeal (1-2 rudimentary segments).
The spinal cord is somewhat shorter than the spinal canal. In this regard, in the upper parts of the spinal cord, its roots run horizontally. Then, starting from the thoracic region, they descend somewhat downward before exiting the corresponding intervertebral foramina. In the lower sections, the roots go straight down, forming the so-called ponytail.
Anterior median fissure, posterior median sulcus, symmetrically located anterior and posterior lateral sulci are visible on the surface of the spinal cord. Between the anterior median fissure and the anterior lateral sulcus is the anterior funiculus (funiculus anterior), between the anterior and posterior lateral sulci is the lateral cord (funiculus lateralis), between the posterior lateral sulcus and the posterior median sulcus is the posterior cord (funiculus posterior), which is in the cervical part the spinal cord is divided by a shallow intermediate groove into a thin bundle (fasciculus gracilis). adjacent to the posterior median sulcus, and located outward from it, a wedge-shaped bundle (fasciculus cuneatus). The cords contain pathways.
The anterior roots emerge from the anterior lateral sulcus, and the posterior roots enter the spinal cord in the region of the posterior lateral sulcus.
On a transverse section in the spinal cord, gray matter is clearly distinguished, located in the central parts of the spinal cord, and white matter, lying on its periphery. The gray matter in the transverse section resembles a butterfly with open wings or the letter "H" in shape. In the gray matter of the spinal cord, more massive ones are isolated. wide and short anterior horns and thinner, elongated posterior horns B thoracic regions a lateral horn is revealed, which is also less pronounced in the lumbar and cervical sections of the spinal cord. The right and left halves of the spinal cord are symmetrical and connected by spikes of gray and white matter. Anterior to the central canal is the anterior gray commissure (comissura grisea anterior), then the anterior white commissure (comissura alba anterior); posterior to the central canal are the posterior gray commissure and the posterior white commissure in succession.
In the anterior horns of the spinal cord, large motor nerve cells are localized, the axons of which go to the anterior roots and innervate the striated muscles of the neck, trunk and limbs. The motor cells of the anterior horns are the final authority in the implementation of any motor act, and also have trophic effects on the striated muscles.
Primary sensory cells are located in the spinal (intervertebral) nodes. Such a nerve cell has one process, which, moving away from it, is divided into two branches. One of them goes to the periphery, where it receives irritation from the skin, muscles, tendons or internal organs. and on the other branch, these impulses are transmitted to the spinal cord. Depending on the type of irritation and, therefore, the pathway along which it is transmitted, the fibers entering the spinal cord through the posterior root may terminate on the cells of the posterior or lateral horns, or pass directly into the white matter of the spinal cord. Thus, the cells of the anterior horns perform motor functions, the cells of the posterior horns perform the function of sensitivity, and the spinal vegetative centers are localized in the lateral horns.
The white matter of the spinal cord consists of fibers of pathways that interconnect both different levels of the spinal cord with each other, and all overlying parts of the central nervous system with the spinal cord.
In the anterior cords of the spinal cord, there are mainly pathways involved in the implementation motor functions:
1) anterior cortical-spinal (pyramidal) path (non-crossed) going mainly from the motor area of the cerebral cortex and ending on the cells of the anterior horns;
2) pre-door-spinal (vestibulospinal) path, coming from the lateral vestibular nucleus of the same side and ending on the cells of the anterior horns;
3) the occlusal-spinal tract, starting in the upper colliculus of the quadrigemina of the opposite side and ending on the cells of the anterior horns;
4) the anterior reticular-spinal tract, coming from the cells of the reticular formation of the brain stem of the same side and ending on the cells of the anterior horn.
In addition, near the gray matter there are fibers that connect different segments of the spinal cord with each other.
Both motor and sensory pathways are located in the lateral cords of the spinal cord. Movement paths include:
Lateral cortical-spinal (pyramidal) path (crossed) going mainly from the motor area of the cerebral cortex and ending on the cells of the anterior horns of the opposite side;
The spinal tract, coming from the red nucleus and ending on the cells of the anterior horns of the opposite side;
Reticular-spinal tracts, coming mainly from the giant cell nucleus of the reticular formation of the opposite side and ending on the cells of the anterior horns;
Olivospinal tract, connecting the lower olives with the motor neuron of the anterior horn.
The afferent, ascending conductors include the following paths of the lateral cord:
1) posterior (dorsal uncrossed) dorsal-cerebellar path, coming from the cells of the posterior horn and ending in the cortex of the superior cerebellar vermis;
2) anterior (crossed) dorsal-cerebellar path, coming from the cells of the posterior horns and ending in the cerebellar vermis;
3) the lateral dorsal-thalamic pathway, coming from the cells of the posterior horns and ending in the thalamus.
In addition, the lateral funiculus contains the dorsal-opercular path, the dorsal-reticular path, the spinal-olive path, and some other conductor systems.
In the posterior funiculi of the spinal cord are afferent thin and wedge-shaped bundles. The fibers included in them begin in the intervertebral nodes and end, respectively, in the nuclei of the thin and wedge-shaped bundles located in the lower part of the medulla oblongata.
Thus, part of the reflex arcs is closed in the spinal cord and the excitation coming through the fibers of the posterior roots is subjected to a certain analysis, and then transmitted to the cells of the anterior horn; the spinal cord transmits impulses to all overlying parts of the central nervous system up to the cerebral cortex.
The reflex can be carried out in the presence of three consecutive links: 1) the afferent part, which includes receptors and pathways that transmit excitation to nerve centers; 2) central part reflex arc where the analysis and synthesis of incoming stimuli take place and a response to them is developed; 3) the effector part of the reflex arc, where the response occurs through the skeletal muscles, smooth muscles and glands. The spinal cord, therefore, is one of the first stages at which the analysis and synthesis of stimuli are carried out both from the internal organs and from the receptors of the skin and muscles.
The spinal cord carries out trophic influences, i.e. damage nerve cells of the anterior horns leads to a violation of not only movements, but also the trophism of the corresponding muscles, which leads to their degeneration.
One of important functions spinal cord is the regulation of the activity of the pelvic organs. The defeat of the spinal centers of these organs or the corresponding roots and nerves leads to persistent disorders of urination and defecation.
- (f. anterior) see Anterior cord ... Big Medical Dictionary
anterior cord Big Medical Dictionary
Anterior cord- (funiculus anterior, PNA, BNA; fasciculus ventralis, JNA; syn. anterior cord of the spinal cord) a paired bundle of nerve fibers located in the white matter of the spinal cord between the anterior median fissure and the anterior lateral sulcus; contains ... ... Medical Encyclopedia
Spinal cord- (medulla spinalis) (Fig. 254, 258, 260, 275) is a strand of brain tissue located in the spinal canal. Its length in an adult reaches 41 45 cm, and its width is 1 1.5 cm. Upper section the spinal cord smoothly passes into ... ... Atlas of human anatomy
spinal cord- (medulla spinalis) department of the central nervous system, from the point of view of evolution, its most ancient part, which has preserved a segmental structure. It is a white cord 40-45 cm long, located in the spinal canal (from the large ... ... Glossary of terms and concepts on human anatomy
Pyramid system- a system of efferent neurons, whose bodies are located in the cerebral cortex, terminate in the motor nuclei cranial nerves and gray matter of the spinal cord. As part of the pyramidal path (tractus pyramidalis), cortical nuclear fibers are isolated ... ... Medical Encyclopedia
lateral furrow anterior Big Medical Dictionary
Lateral furrow anterior- (sulcus lateralis anterior, PNA, BNA; sulcus lateralis ventralis, JNA) a paired longitudinal depression on the anterior surface of the spinal cord and medulla oblongata, limiting the anterior funiculus of the spinal cord and the pyramid from the outside; place… … Medical Encyclopedia
tectospinal tract Big Medical Dictionary
Tire-spinal tract- (tractus tectospinalis, PNA, BNA, JNA; syn. tectospinal path) projection descending nerve path, starting in the upper mounds of the roof of the midbrain, passing through the brainstem and anterior cord of the spinal cord, ending in its ... ... Medical Encyclopedia
Spinal cord- (medulla spinalis) part of the central nervous system located in the spinal canal. S. m. has the appearance of a strand white color, somewhat flattened from front to back in the area of thickenings and almost round in other departments. In the spinal canal ... ... Medical Encyclopedia
Fresh sections of the brain show that some structures are darker - this is the gray matter of the nervous system, while other structures are lighter - the white matter of the nervous system. The white matter of the nervous system is formed by myelinated nerve fibers, the gray matter is formed by unmyelinated parts of the neuron - soma and dendrites.
The white matter of the nervous system is represented by central tracts and peripheral nerves. The function of white matter is the transmission of information from receptors to the central nervous system and from one part of the nervous system to another.
In the white matter directly adjacent to the top of the posterior horn, a border zone is distinguished.
White matter, substantia alba, as noted, is localized around the gray matter, along the periphery of the spinal cord. The white matter of one half of the spinal cord is connected with the white matter of the other half by a very thin white commissure, commissura alba, running transversely in front of the central canal.
The sulci of the spinal cord divide the white matter of each half into three cords. The anterior cord, funiculus ventralis, is located between the anterior median fissure and the anterior lateral groove. The posterior cord, funiculus dorsalis, is located between the posterior median and posterior lateral grooves. The lateral cord, funiculus lateralis, is located between the anterolateral and posterolateral grooves.
The white matter of the spinal cord is represented by processes of nerve cells that have myelin sheaths. The totality of these processes in the cords of the spinal cord form three systems of the pathways of the spinal cord.
1. Own associative bundles (anterior, lateral and posterior) that carry out connections between segments at various levels within the spinal cord (refer to the segmental apparatus). As a result, irritation coming from a certain area of the body is transmitted not only to the corresponding segment of the spinal cord, but also captures other segments. As a result, a simple reflex can involve an entire muscle group in response, providing a complex coordinated movement.
2. Ascending (afferent, sensory) bundles heading to the centers of the brain and cerebellum.
3. Descending (efferent, motor) paths from the brain to the cells of the anterior horns of the spinal cord.
The last two systems of bundles form a new young suprasegmental conductor apparatus of bilateral connections of the spinal cord and brain. It arose only when the brain appeared. And as the brain developed, the pathways of the spinal cord grew outward from the gray matter, forming its white matter. This explains the fact that white matter surrounds gray matter on all sides.
In the white matter of the anterior cords there are predominantly descending pathways, in the lateral cords - both ascending and descending pathways, in the posterior cords there are ascending pathways.
The anterior cord, funiculus ventralis, includes the following pathways:
1. Anterior cortical-spinal (pyramidal) path, tractus corticospinalis anterior (pyramidalis) - motor, located near the anterior median fissure, occupies the medial sections of the anterior cord. Transmits impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord.
2. The reticular-spinal tract, tractus reticulospinalis, conducts impulses from the reticular formation of the brain to the motor nuclei of the anterior horns of the spinal cord. It is located in the central part of the anterior funiculus, lateral to the pyramidal tract. Participates in the regulation of muscle tone.
3. The operculo-spinal tract, tractus tectospinalis, is located anterior to the pyramidal tract, connects the subcortical centers of vision (upper colliculus) and hearing (lower colliculi) with motor nuclei anterior horns of the spinal cord. The presence of this tract allows for reflex defensive reactions with sharp visual and auditory stimuli.
4. The anterior spinothalamic path, tractus spinothalamicus anterior, is somewhat anterior to the reticulospinal path. Conducts impulses of tactile sensitivity (touch and pressure).
5. The vestibulo-spinal tract, tractus vestibulospinalis, is located in the anterior sections of the anterior cord and extends to the border of the anterior cord with the lateral cord, i.e. to the anterolateral groove. The fibers of this path go from the vestibular nuclei of the VIII pair of cranial nerves located in the medulla oblongata, to motor neurons anterior horns of the spinal cord. Participates in maintaining the balance of the body.
6. The posterior longitudinal bundle, fasciculus longitudinalis dorsalis, stretches from the brain stem to the upper segments of the spinal cord. Conducts nerve impulses that coordinate muscle activity eyeball and neck muscles, due to which a friendly turn of the head and eyes in the right direction is carried out.
The lateral cord, funiculus lateralis, contains the following pathways:
1. The posterior spinocerebellar path, tractus spinocerebellaris posterior, (Flexig's bundle), conducts impulses of proprioceptive sensitivity.
2. Anterior spinocerebellar path, tractus spinocerebellaris anterior, (Govers bundle), which also carries unconscious proprioceptive impulses to the cerebellum (unconscious coordination of movements).
3. The lateral spinal thalamic pathway, tractus spinothalamicus lateralis, conducts impulses of pain and temperature sensitivity.
The descending tracts of the lateral funiculus include:
4. The lateral cortical-spinal tract, tractus corticospinalis lateralis (pyramidalis), conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord.
5. The red nuclear-spinal tract, tractus rubrospinalis, is a conductor of impulses for automatic (subconscious) control of movements and skeletal muscle tone.
6. Olivospinal tract, tr. olivospinalis,
The posterior cord, funiculus dorsalis, is divided into two bundles at the level of the cervical and upper thoracic segments of the spinal cord by the posterior intermediate groove, sulcus intermedius dorsalis. The medial is directly adjacent to the posterior median sulcus - this is a thin bundle (Gaul's bundle), fasciculus gracilis. Slightly more lateral is the wedge-shaped bundle, fasciculus cuneatus (Burdach's bundle).
thin beam consists of longer conductors running from the lower parts of the trunk and lower extremities of the corresponding side to the medulla oblongata. Moreover, these conductors enter the spinal cord as part of the posterior roots of the 19 lower segments of the spinal cord and occupy a medial position in the posterior cord.
wedge-shaped bundle includes shorter conductors coming from upper limbs and upper body also to the medulla oblongata. These conductors enter the spinal cord as part of the posterior roots of the 12 upper segments of the spinal cord and occupy a lateral position in the posterior funiculus.
Gaulle and Burdach beams- these are conductors of conscious proprioceptive sensitivity (joint-muscular feeling) of the cortical direction. In addition, they are conductors of skin stereognostic sense. Thus, they carry information about the position of the body and its parts in space and relative to each other to the cerebral cortex.
The structure of the spinal cord
Spinal cord, medulla spinalis (Greek myelos), lies in the spinal canal and in adults is a long (45 cm in men and 41-42 cm in women), somewhat flattened from front to back, cylindrical cord, which at the top (cranial) directly passes into the medulla oblongata , and below (caudally) ends with a conical point, conus medullaris, at level II of the lumbar vertebra. Knowledge of this fact is of practical importance (in order not to damage the spinal cord during a lumbar puncture for the purpose of taking cerebrospinal fluid or for the purpose of spinal anesthesia, it is necessary to insert a syringe needle between the spinous processes of the III and IV lumbar vertebrae).
From the conus medullaris, the so-called terminal thread , filum terminale, representing the atrophied lower part of the spinal cord, which below consists of a continuation of the membranes of the spinal cord and is attached to the II coccygeal vertebra.
The spinal cord along its length has two thickenings corresponding to the roots of the nerves of the upper and lower limbs: the top one is called cervical enlargement , intumescentia cervicalis, and the lower one - lumbosacral , intumescentia lumbosacralis. Of these thickenings, the lumbosacral is more extensive, but the cervical is more differentiated, which is associated with a more complex innervation of the hand as a labor organ. Formed as a result of thickening of the side walls of the spinal tube and passing along the midline anterior and posterior longitudinal grooves : deep fissura mediana anterior, and superficial, sulcus medianus posterior, the spinal cord is divided into two symmetrical halves - right and left; each of them, in turn, has a slightly pronounced longitudinal groove running along the line of entry of the posterior roots (sulcus posterolateralis) and along the line of exit of the anterior roots (sulcus anterolateralis).
These grooves divide each half of the white matter of the spinal cord into three longitudinal cords: front - funiculus anterior, side - funiculus lateralis and rear - funiculus posterior. The posterior cord in the cervical and upper thoracic regions is also divided by an intermediate groove, sulcus intermedius posterior, into two bundles: fasciculus gracilis and fasciculus cuneatus . Both of these bundles, under the same names, pass at the top to the posterior side of the medulla oblongata.
On both sides, the roots of the spinal nerves emerge from the spinal cord in two longitudinal rows. front spine , radix ventral is s. anterior, exiting through sulcus anterolateralis, consists of neurites motor (centrifugal, or efferent) neurons, whose cell bodies lie in the spinal cord, while back spine , radix dorsalis s. posterior, included in sulcus posterolateralis, contains processes sensory (centripetal, or afferent) neurons whose bodies lie in the spinal nodes.
At some distance from the spinal cord, the motor root is adjacent to the sensory and together they form the trunk of the spinal nerve, truncus n. spinalis, which neuropathologists distinguish under the name of the funiculus, funiculus. Inflammation of the cord (funiculitis) causes segmental disorders of both motor and sensory
spheres; with root disease (sciatica), segmental disorders of one sphere are observed - either sensitive or motor, and with inflammation of the nerve branches (neuritis), the disorders correspond to the distribution zone of this nerve. The trunk of the nerve is usually very short, because after exiting the intervertebral foramen, the nerve splits into its main branches.
In the intervertebral foramina near the junction of both roots, the posterior root has a thickening - spinal ganglion , ganglion spinale containing false unipolar nerve cells (afferent neurons) with one process, which is then divided into two branches: one of them, the central one, goes as part of the posterior root to the spinal cord, the other, peripheral, continues into the spinal nerve. Thus, there are no synapses in the spinal nodes, since only the cell bodies of afferent neurons lie here. In this way, these nodes differ from the autonomic nodes of the peripheral nervous system, since in the latter intercalary and efferent neurons come into contact. The spinal nodes of the sacral roots lie inside the sacral canal, and the node of the coccygeal root lies inside the sac of the dura mater of the spinal cord.
Due to the fact that the spinal cord is shorter than the spinal canal, the exit point of the nerve roots does not correspond to the level of the intervertebral foramina. To get into the latter, the roots are directed not only to the sides of the brain, but also down, and the more sheer, the lower they depart from the spinal cord. In the lumbar part of the latter, the nerve roots descend to the corresponding intervertebral foramens parallel to the filum terminate, enveloping it and the conus medullaris in a thick bundle, which is called ponytail , cauda equina.
Conductor function the spinal cord is that ascending and descending paths pass through it.
TO ascending paths relate:
- the system of the posterior cords (gentle and wedge-shaped bundles), which are conductors of skin-mechanical sensitivity in;
- spinothalamic pathways, along which impulses from receptors arrive to;
- spinocerebellar pathways (dorsal and ventral) are involved in the conduction of impulses coming from skin receptors and proprioreceptors in.
TO descending paths relate:
- pyramidal, or corticospinal, path;
- extrapyramidal pathways, including rubrospinal, reticulospinal, vestibulospinal tracts. These descending pathways provide the influence of the higher parts of the central nervous system on the function of skeletal muscles.
|
Name |
Characteristic |
|
Thin Gaulle beam |
Tendon and muscle proprioceptors, part of the skin tactile receptors, from the lower body |
|
Wedge-shaped bundle of Burdakh |
Tendon and muscle proproceptors, part of the tactile skin receptors from the upper body |
|
Lateral spinothalamic tract |
Pain and temperature sensitivity |
|
Ventral spinothalamic tract |
Tactile sensitivity |
|
Dorsal dorsal tract of Flexig |
Not crossed - proprioception |
|
Ventral dorsal tract of Gowers |
doubly crossed proprioception |
Classification of the descending tracts of the spinal cord
|
Name |
Characteristic |
|
Lateral corticospinal pyramidal |
|
|
Direct anterior corticospinal pyramidal |
|
|
Rubrospinal (Monakova) |
|
|
Vestibulospinal |
|
|
Reticulospinal |
|
|
Tectospinal |
|
Functions for conducting signals
Nerve fibers of the spinal cord form its white matter and are used to conduct a variety of signals from sensory receptors in the CNS, signals between neurons of the spinal cord itself and between neurons of the spinal cord and other parts of the CNS, as well as from spinal cord neurons to effector organs. A significant part of the pathways of the spinal cord are the axons of the so-called propriospinal neurons. The fibers of these neurons create connections between the spinal segments and do not extend beyond the spinal cord.
As the best known examples of the simplest neural networks for conducting signals in the spinal cord and using them to control the work of effector organs are neural networks of somatic and autonomic reflexes . The sensory neuron and its fibers, intercalary and motor neurons take part in the conduction of the signal (nerve impulse) that initially occurs in the receptor nerve ending.
The signal is not only conducted by neurons within the segment in which they are located, but is processed and used to implement a reflex reaction to receptor stimulation.
Signals arising in the receptors of the body surface, muscles, tendons, internal organs are also conducted to the overlying structures of the central nervous system along the fibers of the cords (pillars) of the spinal cord, called ascending (sensitive) pathways(Table 1). These pathways are formed by fibers (axons) of sensory neurons, whose bodies are located in the spinal ganglia, and intercalary neurons, whose bodies are located in the dorsal horns of the spinal cord.
Table 1. Main ascending sensory pathways of the CNS
|
Name |
Beginning, 1st neuron |
Localization in the spinal cord |
Ending |
Function |
|
Medial and posterior cords |
Somatosensory cortex of the opposite hemisphere. fields 1. 2. 3 |
|||
|
wedge-shaped |
Axons of sensory neurons |
Lateral and posterior cords |
Somatosensory cortex of the opposite hemisphere, fields 1, 2,3 |
Proprioceptive signals (conscious) |
|
Dorsal spinocerebellar |
Clark's ipsilateral nucleus |
Lateral cord |
Cortex of the inenlateral hemisphere of the cerebellum |
Proprioceptive signals (unconscious) |
|
Ventral spinocerebellar |
Contralateral posterior horn |
Lateral cord |
The cortex of the contralateral hemisphere of the cerebellum |
Proirnoceptive signals (unconscious) |
|
Lateral spinothalamic |
Contralateral posterior horn |
Lateral cord |
thalamus, somatosensory cortex |
Pain temperature sensitivity signals |
|
Anterior spinothalamic |
Contralateral posterior horn |
thalamus, somatosensory cortex |
Touch |
The course of the fibers that conduct signals from receptors of different sensitivity (modality) is not the same. For example, pathways from proprioreceptors conduct signals about the state of muscles, tendons, and joints to the cerebellum and cerebral cortex. The fibers of this pathway are the axons of the sensory neurons of the spinal ganglia. Having entered the spinal cord through the posterior roots, they, along the same side of the spinal cord (without crossing), as part of thin and wedge-shaped bundles, ascend to the neurons of the medulla oblongata, where they end with the formation of a synapse and transmit information to the second afferent neuron of the pathway (Fig. 1 ).
This neuron conducts the processed information along the axon passing to the opposite side to the neurons of the thalamic nuclei. After switching on the neurons of the thalamus, information about the state of the motor apparatus is transmitted to the neurons of the postcentral region of the cerebral cortex and is used to form sensations about the degree of muscle tension, the position of the limbs, the angle of flexion in the joints, passive movement, and vibration.
As part of a thin bundle, there is also a part of the fibers from the skin receptors that conduct information used to form conscious tactile sensitivity in the form of touch, pressure, vibration.
Other spinal sensory pathways are formed by the axons of the second afferent (intercalary) neurons, the bodies of which are located in the posterior horns of the spinal cord. The axons of these neurons within their segment make a cross and on the opposite side of the spinal cord as part of the lateral spinothalamic pathway go to the neurons of the thalamus.
Rice. 1. Scheme of the pathways from proprioceptors, tactile, temperature and pain receptors to the brain stem and cortex
This pathway contains fibers that conduct signals for pain and temperature sensitivity, as well as part of the fibers that conduct signals for tactile sensitivity (see Fig. 1).
The anterior and posterior spinocerebellar tracts also pass through the lateral cords. They conduct signals from proprioreceptors to the cerebellum.
Signals along ascending sensory pathways are also conducted to the centers of the ANS, the reticular formation of the brain stem and other structures of the CNS.
The neurons of the spinal cord receive signals from the neurons of the higher structures of the brain. They follow the axons of nerve cells that form descending(mainly motor) pathways used to control muscle tone, form posture and organize movements. The most important among them are the corticospinal (pyramidal), rubrospinal, reticulospinal, vestibulospinal, and tectospinal pathways (Table 2).
Table 2. Main descending efferent pathways of the CNS
|
Path name |
Beginning, 1st neuron |
Localization in the spinal cord |
Ending |
Function |
|
Lateral corticospinal |
Contralateral cortex |
Lateral cord |
Inelateral ventral and dorsal horns |
|
|
Anterior corticospinal |
ipsilatral cortex |
Anterior funiculus |
Contralateral ventral and dorsal horns |
Movement control and sensitivity modulation |
|
Rubrospinal |
Contralateral red nucleus of the midbrain |
Lateral cord |
Movement control |
|
|
Lateral vestibulospinal |
Ipsilateral, lateral vestibular nucleus |
Lateral cord |
Ipsilateral ventral horn |
Control of the muscles that maintain posture and body balance |
|
Medial westernbulospinal |
Ipsi- and contralateral medial vestibular nuclei |
Anterior funiculus |
Ipsilateral ventral horn |
Head position for vestibular signals |
|
Regulospinal |
Reticular formation of the bridge and medulla oblongata |
Lateral and anterior cords |
Ipsilateral ventral horn and intermediate zone |
Movement and posture control, sensitivity modulation |
|
Tectospinal |
Contralateral superior colliculus |
Anterior funiculus |
Ipsilateral ventral horn |
Head position associated with eye movements |
As part of the corticospinal tract, the lateral one is distinguished, the fibers of which go in the lateral cords of the white matter of the spinal cord, and the anterior one - in the anterior cords. The corticospinal tract is formed by axons of pyramidal neurons in motor areas of the cortex. hemispheres, which end in synapses mainly on the interneurons of the spinal cord. small part fibers of the lateral corticospinal tract ends with synapses directly on the a-motoneurons of the spinal cord, innervating the muscles of the hand and distal muscles of the extremities.
Rubrospinal, reticulospinal, vestibulospinal and tectospinal paths are formed by axons of neurons of the corresponding nuclei of the brainstem and they are also called extrapyramidal. Through these pathways, efferent nerve impulses are carried mainly to the intercalary neurons and y-motor neurons of the spinal cord, which are used to maintain muscle tone, posture and exercise. arbitrary movements performed due to congenital or acquired reflexes. Through these pathways, conditions are formed for the effective execution of voluntary movements initiated by the cerebral cortex.
Signals are conducted through the spinal cord from the higher centers of the ANS to the preganglionic neurons of the sympathetic nervous system located in the lateral horns of its thoracolumbar region and to the neurons of the parasympathetic nervous system located in the sacral region of the spinal cord. Through these pathways of the spinal cord, the tone of the sympathetic nervous system and its influence on the work of the heart, the state of the lumen of the vessels, the work of the gastrointestinal tract and other internal organs, as well as the parasympathetic nervous system and its influence on the functions of the pelvic organs are maintained.
Starting from the level of motor fiber decussation of the corticospinal tract of the medulla oblongata to the level of C3 cervical spinal cord contains the spinal nucleus trigeminal nerve, to the neurons of which the axons of sensitive neurons located in the trigeminal ganglion descend through the medulla oblongata. Through them, signals of pain sensitivity of teeth, other tissues of the jaws and oral mucosa, pain, temperature and touch signals from the surface of the face, tissues of the eye and orbit enter the nucleus.
The axons of the neurons of the spinal nucleus of the trigeminal nerve cross and follow in the form of a diffuse bundle to the neurons of the thalamus and to the neurons of the reticular formation of the brain stem. With damage to the afferent fibers of the trigeminal tract and the spinal nucleus of the trigeminal nerve, there may be a decrease or loss of pain and temperature sensitivity on the ipsilateral side of the face.
In case of violation of the integrity of the pathways for conducting afferent and (or) efferent signals at the level of the spinal cord or other levels of the central nervous system in a person, the certain kind sensation and/or movement. Knowing the morphological features of the structure of the decussation of the fibers of the pathways, it is possible, taking into account the nature of the violation of sensitivity and (or) movements, to establish the level of damage to the central nervous system that caused these disorders.
Signals from the neurons of the locus coeruleus and the raphe nucleus of the brainstem are carried to the intercalary and motor tracts along the descending pathways. They are used to control muscle activity associated with sleep and wake states. Signals from the neurons of the periaqueductal gray matter are carried down descending pathways to the intercalary neurons of the spinal cord. These signals and the neurotransmitters released from the axons of these neurons are used to control pain sensitivity.
