The central nervous system (CNS) in the human body is represented by two brain elements: the head and the spinal. The human skeleton has a spinal canal, where the spinal cord is located. What functions does it perform?
It performs two vital functions:
- conductor (paths for transmitting impulse signals);
- reflex-segmental.
The conductive function is carried out by the transmission of impulses along the ascending cerebral pathways to the brain and back to the executing organs along the descending cerebral pathways. Long paths for transmitting impulse signals allow them to be transmitted from spinal cord into different functional parts of the head, and short ones provide a connection between adjacent segments of the spinal cord.
The reflex function is reproduced by activating a simple reflex arc (knee reflex, extension and flexion of the arms and legs). Complex reflexes are reproduced with the participation of the brain. The spinal cord is also responsible for the implementation of autonomic reflexes, which control the work of the human internal environment - the digestive, urinary, cardiovascular, reproductive systems. The diagram below illustrates the functions vegetative system in organism. Autonomic and motor reflexes are controlled by proprioceptors in the thickness of the spinal cord. The structure and function of the spinal cord have a number of features in humans.
Let's consider the structure of the spinal cord for a better understanding of what functions it performs.
Anatomical features
The structure of the human spinal cord is not as simple as it might seem at first. Outwardly, the back of the brain resembles a cord with a diameter of up to 1 cm, a length of 40-45 cm. It originates from the oblong part of the brain and ends with a cauda equina to the end of the spinal column. The vertebrae protect the spinal cord from damage.
The spinal cord is a cord, it is formed by the brain tissue. Throughout its length, it has a rounded shape in cross section, the only exceptions are thickening zones, where its flattening is observed. The cervical thickening is located from the third vertebra of the neck to the first thoracic vertebra. Lumbosacral flattening is localized in the region of 10-12 vertebra of the thoracic region.
In front and behind the spinal cord, on its surface, it has grooves that divide the organ into two halves. The brain cord has three sheaths:
- firm - is a white shiny dense fibrous tissue, rich in elastic fibers;
- arachnoid - made of endothelium-coated connective tissue;
- choroid - a membrane of loose connective tissue rich in blood vessels to provide nutrition to the spinal cord.
CSF (cerebrospinal fluid) is located between the two lower layers.
The central sections of the spinal cord are filled with gray matter. On the preparation of an organ cut, this substance resembles a butterfly in outline. This component of the brain consists of the bodies of nerve cells (insertional and motor type). This site nervous system divided into functional zones: front and back horns. The former contain motor-type neurons, the latter have intercalary nerve cells... There are additional lateral horns along the segment of the spinal cord from the 7th cervical segment to the 2nd lumbar segment. It contains the centers responsible for the functioning of the autonomic NS (nervous system).
The hind horns are characterized by their heterogeneous structure. As part of these areas of the spinal cord, there are special nuclei made by intercalary neurons.
The outer part of the spinal cord is formed by a white matter made by the axons of the butterfly neurons. The spinal grooves conditionally divide the white matter into 3 pairs of cords, known as: lateral, posterior and anterior. Axons are combined into several conductive tracts:
- associative fibers (short) - provide a connection between various spinal segments;
- ascending fibers, or sensitive, - transmit nerve signals to the head of the central nervous system;
- descending fibers, or motor, - transmit impulse signals from the cerebral cortex to the anterior horns, which control the executing organs.
The posterior cords contain only ascending conductors, and the remaining two pairs are characterized by the presence of descending and ascending conduction pathways. The number of conductive paths in the cords is different. The table below shows the location of the conduction tracts in the dorsal part of the central nervous system.
Lateral guide wire:
- spinal cord (posterior) - transmits impulse signals of a proprioceptive nature to the cerebellum;
- spinal cord (anterior) - is responsible for communication with the cerebellar cortex, where it transmits impulse signals;
- spinal thalamic tract (external lateral) - is responsible for the transmission of impulse signals to the brain from receptors that respond to pain and temperature changes;
- pyramidal tract (external lateral) - conducts motor impulse signals from the cortex of large hemispheres to the spinal cord;
- red-spinal tract - controls the maintenance of skeletal muscle tone and regulates the performance of subconscious (automatic) motor functions.
Anterior cord of the conductors:
- pyramidal tract (anterior) - transmits a motor signal from the cortex of the upper parts of the central nervous system to the lower;
- dorsal thalamic tract (anterior) - transmits impulse signals from tactile receptors;
- vestibular-spinal - carries out the coordination of conscious movements and balance, and is also characterized by the presence of a connection with the medulla oblongata.
The posterior cord of the conductors:
- Gaulle's thin fiber bundle - responsible for the transmission of impulse signals from proprioceptors, interoreceptors and skin receptors of the lower parts of the trunk and legs to the brain;
- wedge-shaped bundle of Burdakh fibers - responsible for the transmission of the same receptors to the brain from the arms and upper torso.
The human spinal cord in its structure belongs to the segmental organs. How many segments does it have in the human body? In total, the cord cord contains 31 segments, corresponding to the sections of the spine:
- in the cervical - eight segments;
- in the chest - twelve;
- in the lumbar - five;
- in the sacrum - five;
- in the tailbone - one.
The cord cord segments each have four roots that form the spinal nerves. The dorsal roots are formed from the axons of sensory neurons, they enter the dorsal horns. The dorsal roots have sensitive ganglia (one on each). Then, in this place, a synapse is formed between the sensory and motor cells of the NS. The axons of the latter form the anterior roots. This diagram shows the structure of the spinal cord and its roots.
In the center of the spinal cord along its entire length, the canal is localized, it is filled with cerebrospinal fluid. To the head, arms, lungs and heart muscle, conductive fibers extend from the cervical and upper chest segments. Segments of the lumbar and thoracic region of the brain give off nerve endings to the muscles of the trunk and abdominal cavity with its contents. The lower lumbar and sacral segments of a person give off nerve fibers to the legs and muscles of the lower press.
The spinal cord is an oblong, somewhat flattened cylindrical cord, and therefore its transverse diameter throughout, as a rule, is larger than the anterior one. Located in the spinal canal from the level of the base of the skull to the I-II lumbar vertebrae, the spinal cord has the same bends as the spinal column, cervical and thoracic bends. The upper parts of the spinal cord pass into the brain, the lower ones end in the cerebral cone, the apex of which continues into a thin terminal thread. The length of the spinal cord in an adult is on average 43 cm, weight is about 34-38 g. Due to the metameric structure of the human body, the spinal cord is subdivided into segments, or neuromeres. A segment is a section of the spinal cord with the right and left anterior (motor) roots extending from it and the right and left posterior (sensory) roots penetrating into it.
Fig 1. Spinal cord.
A, B - front view:
2- medulla oblongata;
3 - the cross of the pyramids;
4 - anterior median fissure;
5-cervical thickening;
6-anterior roots of the spinal nerves;
7 - lumbosacral thickening;
8 - cerebral cone;
9 - ponytail;
10 - terminal thread.
B - rear view:
1- rhomboid fossa;
2 - posterior median groove;
3 - posterior roots of the spinal nerves.
Along the entire length on each side of the spinal cord, 31 pairs of anterior and posterior roots depart, which, merging, form 31 pairs of right and left spinal nerves... each segment of the spinal cord corresponds to a certain part of the body that receives innervation from this segment.
In the cervical and lumbar spinal cord, cervical and lumbosacral thickenings are found, the appearance of which is explained by the fact that these sections provide innervation, respectively, of the upper and lower limbs.
Starting from the 4th month of fetal development, the spinal cord lags behind the growth of the spine. In this regard, there is a change in the direction of the roots. In an adult, the roots of the cranial segments still retain their horizontal course; in the thoracic and upper lumbar regions, the roots follow obliquely - downward and laterally; in the lower lumbar and sacrococcygeal regions, the roots, heading to the corresponding intervertebral lumbar and sacral foramen, are located almost vertically in the spinal canal. The set of the anterior and posterior roots of the lower lumbar and sacrococcygeal nerves surrounds a terminal thread like horse tail .
Along the entire front surface of the spinal cord in median fissure, and along the back surface - posterior median sulcus... They serve as boundaries dividing the spinal cord into two symmetrical halves.
On the anterior surface, somewhat lateral to the median groove, there are two anterior lateral grooves - the anterior roots extend here from the spinal cord to the right and left. On the posterior surface there are posterior lateral grooves - the places of penetration from both sides into the spinal cord of the posterior roots.
In the spinal cord, gray and white matter is secreted. The central canal passes through the gray matter, the upper end of which communicates with the IV ventricle.
The gray matter along the length of the spinal cord forms two vertical columns located to the right and left of the central canal. Each column is distinguished front and rear pillars... At the level of the lower cervical, all thoracic and two upper lumbar segments of the spinal cord, the gray matter is isolated side post, which is absent in other parts of the spinal cord.
On a transverse section of the spinal cord, the gray matter has the shape of a butterfly or the letter "H", a wider front horn and narrow rear horn... The anterior horns contain large nerve cells - motor neurons.
The gray matter of the posterior horns of the spinal cord is heterogeneous. The bulk of the nerve cells of the posterior horn forms its own nucleus, and at the base of the posterior horn it is noticeably well outlined by a layer of white matter pectoral nucleus composed of large nerve cells.
The cells of all nuclei of the dorsal horns of the gray matter are, as a rule, intercalary, intermediate, neurons, the processes of which go in the white matter of the spinal cord to the brain.
The intermediate zone, located between the anterior and posterior horns, is represented by the lateral horn. The latter contains the centers of the sympathetic part of the autonomic nervous system.
The white matter of the spinal cord is located along the periphery of the gray matter. The grooves of the spinal cord divide it into septenary: anterior, middle and posterior cords. The anterior cord is located between the anterior median fissure and the anterior lateral groove, the posterior cord is located between the posterior middle and posterior lateral grooves, the lateral cord is between the anterior and posterior lateral grooves.
The white matter of the spinal cord is represented by the processes of nerve cells (sensitive, intercalated and motor neurons), and the totality of the processes of nerve cells in the cords of the spinal cord is three systems of bundles - tracts, or pathways of the spinal cord:
1) short bundles of associative fibers connect spinal cord segments located at different levels;
2) ascending (afferent, sensory) beams are directed to the centers of the brain or to the cerebellum;
3) descending (motor, efferent) bundles go from the brain to the cells of the anterior horns of the spinal cord. The ascending tracts are located in the white matter of the posterior cords. Ascending and descending fiber systems follow in the anterior and lateral cords.
Front cords contain the following pathways
anterior, motor, cortical-spinal (pyramidal) path... This pathway contains the processes of pyramidal cells of the cortex of the anterior central gyrus, which end on the motor cells of the anterior horn of the opposite side, transmits impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord;
anterior dorsal thalamic tract in the middle part of the anterior cord provides the conduction of impulses of tactile sensitivity (touch and pressure);
on the border of the anterior cord with the lateral predoor-spinocerebral pathway originating from the vestibular nuclei of the VIII pair cranial nerves located in the medulla oblongata, and heading to the motor cells of the anterior horns. The presence of the tract allows you to maintain balance and coordinate movements.
The lateral cords contain the following pathways:
posterior spinal cord occupies the posterior lateral sections of the lateral cords and is a conductor of reflex proprioceptive impulses heading to the cerebellum;
anterior spinal cord located in the anterolateral sections of the lateral cords, it follows into the cerebellar cortex;
lateral dorsal thalamic path - the pathway for the impulses of pain and temperature sensitivity, located in the anterior sections of the lateral cord. From the descending tracts in the lateral cords are the lateral cortical-spinal (pyramidal) path and extrapyramidal - the red-nuclear-spinal path;
lateral cortical-spinal pathway It is represented by the fibers of the main motor pyramidal pathway (a pathway for conducting impulses that causes conscious movements), which lie medial to the posterior spinal pathway and occupy a significant part of the lateral cord, especially in the upper segments of the spinal cord;
red-spinal tract located ventral to the lateral cortical-spinal (pyramidal) pathway. This pathway is a reflex motor efferent pathway.
Rear cords contain pathways of conscious prioceptive sensitivity (conscious joint-muscular feeling), which are directed to the cerebral cortex and deliver information about the position of the body and its parts in space to the cortical analyzers. At the level of the cervical and upper chest segments posterior cords of the spinal cord by the posterior and intermediate sulcus are divided into two bundles: a thin bundle (Gaul's bundle), lying more medially, and a wedge-shaped bundle (Burdach bundle), adjacent to the posterior horn.
SPINAL CORD TRACKS
The spinal cord contains a number of neurons that give rise to long ascending pathways to various structures in the brain. The spinal cord enters and a large number of descending tracts formed by the axons of nerve cells localized in the cortex large hemispheres, in the middle and medulla oblongata. All these projections, along with the pathways connecting the cells of various spinal segments, form a system of pathways formed in the form of a white matter, where each tract occupies a completely definite position.
MAIN ASCENDING TRAINS OF THE SPINAL CORD
Pathways |
Spinal Cord Columns | Physiological significance | |
| Ascending (sensitive) paths | |||
| 1 | Thin beam (Gaulle beam) | Rear | Tactile sensitivity, feelings of body position, passive body movements, vibration |
| 2 | Wedge-shaped bundle (Burdakh bundle) | >> | Also |
| 3 | Dorsolateral | Side | Pathways of pain and temperature sensitivity |
| 4 | Dorsal spinocerebellar Flexig | >> | Impulses from proprioceptors of muscles, tendons, ligaments; feeling of pressure and touch from the skin |
| 5 | Ventral spinocerebellar (Goversa) | >> | Also |
| 6 | Dorsal spinothalamic | >> | Pain and temperature sensitivity |
| 7 | Spinotectal | >> | Sensory pathways of visual-motor reflexes (?) And pain sensitivity (?) |
| 8 | Ventral spinothalamic | Front | Tactile sensitivity |
Some of them are fibers of primary afferent (sensory) neurons running without interruption. These fibers - thin (Gaul's bundle) and wedge-shaped (Burdach bundle) bundles go as part of the dorsal cords of the white matter and end in the medulla oblongata near neutron relay nuclei, called the nuclei of the dorsal cord, or Gaulle and Burdach nuclei. The fibers of the dorsal cord are conductors of skin-mechanical sensitivity.
Spinal cord structure
Spinal cord, medulla spinalis (Greek myelos), lies in the spinal canal and in adults it 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 (cranially) directly passes into the medulla oblongata , and below (caudally) ends in a conical sharpening, 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 the syringe needle between the spinous processes of the III and IV lumbar vertebrae).
From the conus medullaris, the so-called end thread , filum terminale, representing the atrophied lower part of the spinal cord, which at the bottom consists of an extension 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 nerve roots of the upper and lower extremities: the upper one is called cervical thickening , intumescentia cervicalis, and the lower one is lumbosacral , intumescentia lumbosacralis. Of these thickenings, the lumbosacral is more extensive, but the cervical is more differentiated, which is associated with the more complex innervation of the hand as an organ of labor. Formed as a result of thickening of the side walls of the spinal tube and passing along the midline anterior and posterior longitudinal furrows : 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 weakly 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 back of the medulla oblongata.
On both sides of the spinal cord, the roots of the spinal nerves emerge in two longitudinal rows. Anterior spine , radix ventral is s. anterior, exiting through the sulcus anterolateralis, consists of neurites motor (centrifugal, or efferent) neurons whose cell bodies lie in the spinal cord, while posterior root , radix dorsalis s. posterior, included in the sulcus posterolateralis, contains processes sensitive (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 sensitive and together they form the trunk of the spinal nerve, truncus n. spinalis, which neuropathologists distinguish under the name of the cord, funiculus. With inflammation of the cord (funiculitis), segmental disorders of both motor and sensory
spheres; with root disease (radiculitis), segmental disorders of one sphere are observed - either sensory or motor, and with inflammation of the branches of the nerve (neuritis), the disorders correspond to the zone of distribution of this nerve. The trunk of the nerve is usually very short, since when it leaves the intervertebral foramen, the nerve splits into its main branches.
In the intervertebral foramen near the junction of both roots, the posterior root has a thickening - spinal cord , ganglion spinale, containing pseudo-unipolar nerve cells (afferent neurons) with one process, which then divides into two branches: one of them, the central one, goes as part of the dorsal root into the spinal cord, the other, peripheral, continues into the spinal nerve. Thus, there are no synapses in the spinal nodes, since the cellular bodies of only afferent neurons lie here. In this, the named nodes differ from the autonomic nodes of the peripheral nervous system, since in the latter, intercalary and efferent neurons enter into contacts. The spinal nodes of the sacral roots lie inside the sacral canal, and the coccygeal root node 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 site of the nerve roots does not correspond to the level of the intervertebral foramen. To get into the latter, the roots are directed not only to the sides of the brain, but also downward, and the more steep the lower they go from the spinal cord. In the lumbar part of the latter, the nerve roots descend to the corresponding intervertebral foramen parallel to the filum terminate, wrapping it and the conus medullaris with a thick bundle, which is called horse tail , cauda equina.
I. Dorsal (posterior) cords... These ascending (afferent) pathways are formed by collateral axons of sensory neurons of the spinal ganglia. There are two bundles of them:
· Thin (delicate) bundle (Gaulle bundle)... It starts from the lower segments of the spinal cord and is located more medially. Carries information from receptors of the musculoskeletal system and tactile receptors of the skin of the lower extremities and lower half of the body.
· Wedge-shaped bundle (Burdakh bundle)... Appears at the level of 11-12 thoracic segments. Located more laterally. Carries information from the same receptors in the upper half of the body and upper extremities.
II. Lateral (lateral cords)... There are ascending and descending paths:
· Ascending paths (afferent, sensory):
Ø Dorsal cerebellar tract(Govers path) (these are the axons of the interneurons of the dorsal horns). They transmit signals from receptors of the musculoskeletal system and tactile receptors of the skin to the cerebellum.
Ø Dorsal thalamic tract... Axons of dorsal horn interneurons transmit signals from pain receptors, thermoreceptors, skin, as well as from all receptors internal organs(transmitted to the thalamus and further to the cerebral cortex (our sensations))
· Descending (efferent) pathways (motor tracts):
Ø Rubrospinal tract- axons of neurons of the red nucleus (Nucleus ruber) of the midbrain, which are directed to the interneurons of the intermediate zone. Functions: about nor control flexor muscles.
Ø Corticospinal (pyramidal) tract... There is a motor zone in the cortex (in the frontal lobe). These are the axons of the pyramidal neurons of the motor (motor) zone of the cerebral cortex, which pass through the entire brain stem to interneurons to the intermediate zone of the spinal cord. In humans, 8% of the fibers of this tract end directly on the motor neurons of the anterior horns. Path function: voluntary regulation of fine and precise movements, mainly of the limbs.
III. Ventral (anterior) cords. There are ascending and descending paths.
· Descending tracts:
Ø Vestibulo-spinal tract. These are the axons of the neurons of the vestibular nuclei of the brainstem, which end on the neurons of the anterior horns. Functions: to They control the extension of the limbs.
Ø Reticulospinal tract. These are the axons of neurons of the reticular nuclei of the trunk, which end on the interneurons of the intermediate zone. Functions: control the movement of the trunk and ensure the start of locomotion (rhythmic movements, for example, running).
General principle brain work:
Reflex arc. The activity of the nervous system is carried out by reflex principle... Reflex - the body's response to a stimulus, carried out with the participation and control of the nervous system. RD - it is a chain of neurons, the path along which signals pass during the implementation of a reflex. The simplest RD consists of two neurons, between which the synapse is called a two-neuron RD or monosynaptic RD... Of such RD not much in the body.
V reflex arc always 5 functional links:
1. Receptor- a specialized cell that perceives the stimulus and transforms it into a nervous process.
Myelinated nerve fibers are grouped into tracts according to a specific direction - to or from the brain - and the type of impulse they receive or transmit. The ascending tracts transmit nerve impulses about all sensations that arise in the body, up to. Descending tracts transmit impulses from the brain to skeletal muscles, causing voluntary and involuntary movement.
Paths of the posterior cord:
1. Thin beam ( fasciculus gracilis) is located medially, in it pass the fibers going from the lower half of the body, lower limbs through 19 lower spinal nodes and further to the medulla oblongata.
2. Wedge-shaped bundle ( fasciculus cuneatus) is located laterally, in it fibers pass from the upper body through the upper 12 spinal nodes to the medulla oblongata. Both beams conduct conscious tactile, proprioceptive sensitivity and a sense of stereognosis.
3. Rear own beam ( fasciculus proprius posterior).
Lateral cord paths:
4. Lateral own beam ( fasciculus proprius lateralis).
5. Anterior spinal cord ( tr. spinocerebellaris anterior).
6. Posterior spinal cord ( tr. spinocerebellaris posterior).
Both conduct unconscious proprioceptive sensitivity.
7. Spinal path ( tr. spinotectalis).
8. Lateral spinnothalamic pathway ( tr. spinothalamicus lateralis) - conducts conscious temperature and pain sensitivity.
9. Lateral cortical-spinal path ( tr. corticospinalis lateralis) - a conscious motor, pyramidal path.
10. Red-spinal cord ( tr. rubrospinalis).
11. Olive-spinal fibers ( fibrae olivospinales).
12. Thalamo-cerebrospinal ( tr. thalamospinalis).
Paths 10 - 12 are unconscious, motor, extrapyramidal.
Anterior cord pathways:
14. Anterior proper beam ( fasciculus proprius anterior).
15. Anterior cortical-spinal path ( tr. corticospinalis anterior) - a conscious, motor pyramidal path.
16. Roof-spinal path ( tr. tectospinalis).
17. Reticulospinal fibers ( fibrae reticulospinalis).
18. Predoor-spinal path ( tr. vestibulospinalis).
Paths 16-18 are unconscious, motor, extrapyramidal.
19. Anterior spinothalamic pathway ( tr. spinothalamicus anterior) - conducts conscious tactile sensitivity.
20. Medial longitudinal bundle ( fasciculus longitudinalis medialis) is present only in the cervical segments.
Segmental apparatus of the spinal cord- a set of nerve structures that ensure the implementation of innate reflexes, it includes: dorsal root fibers, own bundles, nuclei of the anterior horns, scattered cells, cells of the gelatinous substance, spongy and terminal zones.
The conductive apparatus of the spinal cord provides a two-way connection of the spinal cord with the integration centers of the brain (cerebellar cortex, cerebral cortex, upper hillocks of the quadruple). This apparatus is represented by sensory and motor pathways.
The integration (suprasegmental) apparatus of the spinal cord includes the ascending and descending pathways, as well as the nuclei: own, thoracic and medial intermediate.
