The structure of the white matter of the spinal cord, its connections with other parts of the central nervous system. The value of the conducting paths. Spinal cord. The spinal cord (medulla spinalis) is located in the spinal canal. The main ascending tracts of the spinal cord.

The spinal cord is an oblong, somewhat flattened cylindrical cord, and therefore its transverse diameter throughout its entire length, 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 curves as the spinal column, cervical and thoracic curves. The upper sections of the spinal cord pass into the brain, the lower ends with a cerebral cone, the top 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 metamerism of the structure of the human body, the spinal cord is divided into segments, or neuromeres. A segment is a section of the spinal cord with the right and left anterior (motor) roots emerging 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 - cross of pyramids;

4 - anterior median fissure;

5 - cervical thickening;

6-anterior roots of the spinal nerves;

7 - lumbosacral thickening;

8 - brain cone;

9 - ponytail;

10 - terminal thread.

B - rear view:

1- rhomboid fossa;

2 - posterior median sulcus;

3 - posterior roots of the spinal nerves.

Throughout the spinal cord, 31 pairs of anterior and posterior roots depart from the spinal cord, which, merging, form 31 pairs of right and left roots. 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 sections of the 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 extremities.

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 a horizontal course; in the thoracic and upper lumbar regions, the roots follow obliquely down and laterally; in the lower lumbar and sacrococcygeal regions, the roots, heading towards the corresponding intervertebral lumbar and sacral foramens, are located almost vertically in the spinal canal. The set of anterior and posterior roots of the lower lumbar and sacrococcygeal nerves surrounds the terminal thread like ponytail .

Along the entire anterior surface of the spinal cord 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 sulcus, two anterior lateral sulci stretch - here the anterior roots come out of the spinal cord on the right and left. On the posterior surface there are posterior lateral grooves - places of penetration from both sides into the spinal cord of the posterior roots.

The spinal cord contains gray and white matter. In the gray matter passes the central canal, the upper end of which communicates with the IV ventricle.

The gray matter along the spinal cord forms two vertical columns located to the right and left of the central canal. In each column there are front and rear poles. At the level of the lower cervical, all thoracic and two upper lumbar segments of the spinal cord, 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 anterior horn and narrow rear horn. In the anterior horns are 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 form their own nucleus, and at the base of the posterior horn it is noticeably well delineated by a layer of white matter thoracic nucleus made up of large nerve cells.

The cells of all nuclei of the posterior 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. In the latter there are centers of the sympathetic part of the autonomic nervous system.

The white matter of the spinal cord is located on the periphery of the gray matter. The sulci 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 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 processes of nerve cells (sensory, intercalary and motor neurons), and the totality of processes of nerve cells in the cords of the spinal cord makes up three systems of bundles - tracts, or pathways of the spinal cord:

1) short bundles of associative fibers connect segments of the spinal cord located at different levels;

2) ascending (afferent, sensory) bundles are sent 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. In the anterior and lateral cords, ascending and descending fiber systems follow.

Anterior cords contain the following pathways

anterior, motor, cortical-spinal (pyramidal) path. This path contains 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 pathway in the middle part of the anterior cord provides impulses of tactile sensitivity (touch and pressure);

located on the border of the anterior funiculus with the lateral vestibulospinal tract, originating from the vestibular nuclei of the VIII pair of 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 funiculi contain the following pathways:

posterior dorsal tract occupies the posterior lateral sections of the lateral cords and is a conductor of reflex proprioceptive impulses heading to the cerebellum;

anterior dorsal tract located in the anterolateral sections of the lateral cords, it follows the cerebellar cortex;

lateral spinothalamic path - the path for conducting 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 the extrapyramidal - red nuclear-spinal path;

lateral corticospinal tract it is represented by fibers of the main motor pyramidal pathway (the path of impulses that causes conscious movements), which lie medially to the posterior spinal cerebellar tract and occupy a significant part of the lateral cord, especially in the upper segments of the spinal cord;

red nuclear-spinal tract located ventral to the lateral cortico-spinal (pyramidal) tract. This path is a reflex motor efferent path.

Posterior cords contain paths of conscious prioprioceptive sensitivity (conscious joint-muscular feeling), which are sent to the cortex of the cerebral hemispheres 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 thoracic segments, the posterior cords of the spinal cord are divided into two bundles by the posterior and intermediate sulcus: a thin bundle (Gaulle's bundle), which lies more medially, and a wedge-shaped bundle (Burdach's bundle), adjacent to the posterior horn.

CONDUCTING WAYS OF THE SPINAL CORD

There are a number of neurons in the spinal cord that give rise to long ascending pathways to various brain structures. A large number of descending tracts, formed by axons of nerve cells localized in the cerebral cortex, in the midbrain and medulla oblongata, also enter the spinal cord. All these projections, along with the paths that connect the cells of various spinal segments, form a system of pathways formed in the form of white matter, where each tract occupies a well-defined position.

MAIN ASCENDING WAYS OF THE SPINAL CORD

Some of them are continuous fibers of primary afferent (sensory) neurons. These fibers - thin (Gaulle's bundle) and wedge-shaped (Burdach's bundle) bundles go as part of the dorsal funiculi of the white matter and end in the medulla oblongata near the neutron relay nuclei, called the nuclei of the dorsal cord, or the nuclei of Gaulle and Burdach. The fibers of the dorsal cord are conductors of skin-mechanical sensitivity.

The location of the most important pathways of the spinal cord is shown in Fig. 2.8. The diagram shows the relative area of ​​individual paths.

• 1. Posterior cord
• 1) thin beam (Gaulle's beam);
• 2) wedge-shaped bundle (Burdakh's bundle);
• 3) rear own beam;
• 4) radicular zone.

thin beam located in the medial part of the posterior funiculus. It is formed by the central processes of pseudo-unipolar cells of 19 lower sensory nodes of the spinal nerves (coccygeal, all sacral and lumbar, and eight lower thoracic). These fibers enter the spinal cord as part of the posterior roots and, without entering the gray matter, are sent to the posterior funiculus, where they take an upward direction. Nerve fibers of the thin bundle conduct impulses of conscious proprioceptive and partly tactile sensitivity from the lower extremities and lower trunk. Proprioceptive (deep) sensitivity is information from muscles, fascia, tendons and joint bags about the position of body parts in space, muscle tone, a sense of weight, pressure and vibration, the degree of muscle contraction and relaxation.

Rice. 2.8.

1 - lateral cortical-spinal path; 2 - red nuclear-spinal path; 3 - olivospinal path; 4 - pre-door-spinal path; 5 - medial longitudinal bundle; 6 - reticular-spinal path; 7 - anterior cortical-spinal path; 8 - roof-spinal path; 9 - front own beam; 10 - dorsal-reticular path; 11 - anterior spinal-thalamic path; 12 - anterior root of the spinal nerve; 13 - anterior spinal cerebellar path; 14 - lateral own beam; 15 - lateral spinal-thalamic path; 16 - posterior spinal-cerebellar path; 17 - posterior root of the spinal nerve; 18 - rear own beam; 19 - wedge-shaped bundle; 20 - thin beam

wedge-shaped bundle appears in the upper half of the spinal cord and is located lateral to the thin bundle. It is formed by the central processes of the pseudo-unipolar cells of the 12 upper sensory nodes of the spinal nerves (four upper thoracic and all cervical). It conducts nerve impulses of conscious proprioceptive and partially tactile sensitivity from receptors in the muscles of the neck, upper limbs, and upper torso.

Rear own beam represents the axons of intercalary neurons belonging to the segmental apparatus. They are located on the medial side of the posterior horn, oriented in the craniocaudal direction.

root zone formed by the central processes of pseudo-unipolar cells located within the posterior funiculus (from the posterior lateral groove to the posterior horn). It is located in the posterolateral part of the funiculus.

Thus, the posterior funiculus contains sensory nerve fibers.

• 2. Lateral cord contains the following pathways:
• 1) posterior dorsal cerebellar path (Flxig's bundle);
• 2) anterior dorsal cerebellar path (Govers bundle);
• 3) lateral dorsal-thalamic pathway;
• 4) lateral corticospinal tract;
• 5) red nuclear-spinal tract (Monakov's bundle);
• 6) olivo-spinal tract;
• 7) lateral proper bundle.

Posterior dorsal tract located in the posterolateral part of the lateral funiculus. It is formed by the axons of the cells of the thoracic nucleus only on its side. The tract provides for the conduction of impulses of unconscious proprioceptive sensitivity from the trunk, limbs and neck.

Anterior dorsal tract located in the anterolateral part of the lateral funiculus. It is formed by the axons of the cells of the intermediate-medial nucleus partly on its side and partly on the opposite side. Nerve fibers from the opposite side are part of the anterior white commissure. The anterior dorsal cerebellar pathway performs the same role as the posterior one.

Lateral dorsal thalamic pathway located medial to the anterior spinal tract. It is formed by the axons of the cells of the own nucleus of the posterior horn. They pass to the opposite side as part of the anterior white commissure, rising obliquely by 2–3 segments. The lateral spinal-thalamic pathway conducts impulses of pain and temperature sensitivity from the trunk, limbs and neck.

Lateral corticospinal tract located in the medial-posterior part of the lateral funiculus. By area, it occupies about 40% of the lateral funiculus. The nerve fibers of the lateral cortical-spinal tract are axons of the pyramidal cells of the cortex of the cerebral hemispheres of the opposite side, therefore it is also called the pyramidal tract. In the spinal cord, these fibers end in segments with synapses on the motor cells of the own nuclei of the anterior horns. The role of this tract is manifested in the performance of conscious (voluntary) movements and in the inhibitory effect on the neurons of the own nuclei of the anterior horns of the spinal cord.

Red nuclear-spinal tract located in the middle of the anterior part of the lateral funiculus. It is formed by the axons of the cells of the red nucleus of the midbrain of the opposite side. Axons pass to the opposite side in the midbrain. The fibers in the spinal cord end on the neurons of the own nuclei of the anterior horns. The function of the tract is to ensure long-term maintenance of skeletal muscle tone (in a comfortable position) and to perform complex automatic conditioned reflex movements (running, walking).

Olivo-spinal tract located in the anteromedial part of the lateral funiculus. The olivo-spinal tract is formed by the axons of the nuclei of the olive medulla oblongata of its side. The nerve fibers of these pathways end on the motor cells of the own nuclei of the anterior horns of the spinal cord. The function of this pathway is to provide unconditioned reflex regulation of muscle tone and unconditioned reflex movements with changes in body position in space (with vestibular loads).

Lateral own bundle - this is a thin bundle of axons of intercalary neurons belonging to the segmental apparatus. It is located in close proximity to the gray matter. These fibers provide the transmission of nerve impulses to the neurons of the own nuclei of the anterior horns of the higher and lower segments.

Thus, the lateral cord contains ascending (afferent), descending (efferent) and own bundles, i.e. in terms of the composition of the pathways, it is mixed.

• 3. Anterior funiculus contains the following paths:
• 1) roof-spinal tract;
• 2) anterior cortical-spinal tract;
• 3) reticular-spinal path;
• 4) anterior spinal thalamic pathway;
• 5) medial longitudinal bundle;
• 6) pre-door-spinal path;
• 7) front own beam.

Roof-spinal tract located in the medial part of the anterior cord, adjacent to the anterior median fissure. It is formed by the axons of the neurons of the upper colliculus of the midbrain of the opposite side. Crossing of fibers is carried out in the midbrain. The fibers in the spinal cord end on the motor cells of the own nuclei of the anterior horns. The role of the tract is to perform unconditioned reflex movements in response to strong light, sound, olfactory and tactile stimuli - protective reflexes.

Anterior corticospinal tract located in the anterior part of the cord, lateral to the roof-spinal tract. The tract is formed by the axons of the pyramidal cells of the cerebral cortex, therefore this tract is called the same as the lateral cortical-spinal tract - pyramidal. In the spinal cord, its fibers terminate at the neurons of the own nuclei of the anterior horns. The function of this tract is the same as that of the lateral corticospinal tract.

Reticular-spinal tract located lateral to the anterior corticospinal tract. This tract is a collection of axons of neurons of the reticular formation of the brain (descending fibers). It plays an important role in maintaining muscle tone, in addition, it differentiates impulses (amplification or weakening) passing through other tracts.

Anterior dorsal thalamic pathway located lateral to the previous one. It is formed, like the lateral spinothalamic pathway, by the axons of the cells of the own nucleus of the posterior horn of the opposite side. Its function is to conduct impulses of predominantly tactile sensitivity.

Medial longitudinal bundle located in the posterior part of the anterior funiculus. It is formed by the axons of the cells of the Cajal and Darkshevich nuclei located in the midbrain. Axons terminate in the spinal cord on the cells of the own nuclei of the anterior horns of the cervical segments. The function of the beam is to provide a combined (simultaneous) turn of the head and eyes.

Vestibulo-spinal tract located on the border of the anterior and lateral cords. The path is formed by the axons of the vestibular nuclei of the bridge of its side. It ends on the motor cells of the own nuclei of the anterior horns of the spinal cord. The function of this pathway is to provide unconditioned reflex regulation of muscle tone and unconditioned reflex movements with changes in body position in space (with vestibular loads).

Front own beam located in the anterior funiculus on the medial side of the anterior horn. This bundle is formed by axons of intercalary neurons belonging to the segmental apparatus. It provides the transmission of nerve impulses to the neurons of the own nuclei of the anterior horns of the higher and lower segments.

Thus, the anterior funiculus contains predominantly efferent fibers.

LECTURE #15

ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD

The spinal cord (medulla spinalis) is a complex of the nucleus of the gray matter and the nerve fibers of the white matter, forming 31 pairs of segments. The spinal cord is about 43-45 cm long, about 1 cm in diameter, and weighs about 30-32 g. Each segment includes a corresponding sensory root that enters from the dorsal side and a motor (motor) root that exits from the ventral side.

The spinal cord (SC) is located in the spinal canal from C1 to L2, surrounded by membranes, between which cerebrospinal fluid (CSF) circulates. From above, the SM is connected to the brain. In the lower part, the SM has a cerebral cone (conus medullaris), from which the final thread (filum terminale) begins, at the level of the 2nd coccygeal vertebra, attached to the dura mater. With flexion and extension of the spine, there is a slight displacement in the spinal canal.

The diameter of the SM along its length is uneven. At the level of C 4-7 and Th 1, as well as in the lumbar and sacral regions, there are thickenings ( cervical enlargement and lumbosacral thickening), which are determined by the quantitative content of gray matter nerve cells involved in the innervation of the upper and lower extremities.

The SM consists of two symmetrical halves (right and left), separated in front - deep anterior median fissure, and behind - deep posterior median fissure. On the right and left halves there are anterior and posterior lateral grooves, in which, respectively, motor and sensory roots are located. There are 124 roots in total: 62 anterior (motor) and 62 posterior (sensory). The anterior roots are the axons of the effector cells located in the spinal cord. The posterior roots are the central processes of pseudo-unipolar cells located in the spinal nodes.

The CM consists of 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). Segment - a section of the spinal cord located in the horizontal plane, anatomically and functionally associated with 4 roots of the spinal nerves. The segments are responsible for the innervation of the skin and muscles of the corresponding parts of the body: cervical - neck, upper limbs, diaphragm; chest - chest, back and abdomen; lumbar, sacral and coccygeal - lower torso and lower extremities. Innervation on the trunk is presented in the form of annular bands, on the extremities - longitudinal.

In the lower sections of the spine, the length of the roots of the spinal nerves (SN) is greater than in the upper ones (in the lumbar and sacral - 3-12 cm, in the cervical 1-1.5 cm). The roots of the 10 lower segments of the spine (L 2-5, S 1-5, Co 1) are ponytail, located in the sac of the dura mater and containing 40 roots (20 anterior + 20 posterior).

On a transverse section, the CM consists of both gray matter located inside in the form of a butterfly and white matter surrounding it. Gray matter is a collection of nerve cells, permeated with nerve fibers. White matter is represented by processes of nerve cells that form nerve fibers.

AT gray matter distinguish the following departments:

1) Hind horns.

They contain sensitive nuclei that receive information from the sensitive (receptor) cells of the spinal nodes, accumulate it and transmit it to the integration centers of the brain.

2) Front horns (wider).

3) Lateral horns.

They contain vegetative sympathetic nuclei that receive information from the sensitive cells of the spinal nodes, analyze it and provide sympathetic innervation of the internal organs.

4) Intermediate zone.

It contains a large number of intercalary neurons (about 90% of all gray matter cells).

The white matter on the right and left sides is divided by the roots of the spinal nerves into 3 cords (posterior, lateral and anterior), in which bundles of nerve fibers pass - tracts that provide two-way communication between the nuclei of the spinal cord and certain centers of the brain. A tract is a collection of axons of neurons that are identical in function and ensure the conduction of nerve impulses in a strictly defined direction.

The paths going from the sensory nuclei of the SM to the nuclei of the brain are called ascending (afferent); going from the centers of the brain to the SM - descending (afferent).

SPINAL TRACTS

I . Posterior cord

At the level of the cervical and upper thoracic segments of the spinal cord, the posterior intermediate sulcus is divided into two bundles.

1. thin beam (face. gracillis, Gaulle beam)

It is formed from the central processes of the nerve cells of the spinal nodes (SMU), from Th 9 and below.

2. wedge-shaped bundle (face. cuneatus, Burdach beam)

It is located laterally than the previous one. It consists of processes of cells of the thoracic and cervical SMU. The fibers of the thin and wedge-shaped bundles end in the nuclei of the medulla oblongata and provide conscious proprioceptive sensitivity.

3. Beam for holding tactile feeling.

Located between the two previous ones. It starts from the nuclei of the posterior columns and ends in the thalamus.

II . Lateral cord

A. Ascending paths:

1. Posterior spinal tract (tr. spinocerebelaris posterior, the Flexig sheaf).

Conducts proprioceptive impulses

2. Anterior dorsal tract (tr. spinocerebelaris anterior, the Gowers beam).

Conducts proprioceptive impulses to the cerebellum. It is located anterior to the Flexig's bundle.

The anterior and posterior spinal cerebellar tracts provide unconscious and proprioceptive sensation.

3. Lateral spinothalamic tract (tr. spinothalamicus lateralis)

It represents the fibers of the ascending pathway, which begin in the posterior column of the spinal cord, cross in the SM and end in the thalamus. Provides pain, temperature, tactile sensitivity from the opposite side.

B. Descending paths:

1. Lateral cortical-spinal tract (lateral-pyramidal) -tr. corticospinalis.

Conducts motor impulses from the cerebral cortex to the anterior horns of the spinal cord. The fibers of this path are processes of giant pyramidal cells. Its fibers in each segment of the SM on their side form synapses with the motor cells of the anterior column. Provides conscious movement.

2. Red nuclear-spinal tract (tr. rubrospinalis)

It is a conductor of impulses of automatic (subconscious) control of movements and tone of skeletal muscles to the anterior horns of the spinal cord.

3. Olivo-spinal and vestibular-spinal tract (tr. olivospinalis et vestibulospinalis).

Responsible for coordinating movements and maintaining balance.

III . Anterior funiculus

1. Medial longitudinal bundle

Responsible for the combined rotation of the head and eyes.

2. tectospinal tract (tr. tectospinalis).

It connects the subcortical centers of vision (upper mounds of the roof of the midbrain) and hearing (lower mounds) with the motor nuclei of the anterior horns of the spinal cord. Provides response protective reactions to visual and auditory stimuli.

3. Reticular-spinal tract (tr. reticulospinalis).

Conducts impulses from the reticular formation of the brain to the motor nuclei of the anterior horns of the spinal cord. Provides a connection between the structures of the reticular formation. It is located in the central part of the anterior funiculus.

4. anterior corticospinal tract (tr. corticospinalis anterior).

It starts from the pyramidal cells of the anterior central gyrus of the cerebral cortex, reaches the spinal cord, where in each segment it passes to the opposite side. Responsible for conscious movements, conducting impulses of motor reactions from the cerebral cortex to the anterior horns of the spinal cord.

5. Anterior dorsal thalamic tract (tr. spinothalamicus ventralis).

It is located anterior to the reticular-spinal tract. Conducts impulses of tactile sensitivity (pressure and touch).

6. Rear longitudinal beam(fasciculus longitudinalis dorsalis).

It stretches from the brain stem to the upper segments of the spinal cord. The fibers of the bundle conduct nerve impulses that coordinate the work of the muscles of the eyeball and neck.

7. The vestibular tract (tractus vestibulospinalis).

It is located on the border of the anterior funiculus with the lateral one. Localized in the superficial layers of the white matter of the anterior funiculus of the spinal cord. The fibers of this path go from the vestibular nuclei of the VIII pair of cranial nerves located in the medulla oblongata to the motor cells of the anterior horns of the spinal cord.

The posterior cord contains sensory tracts, the lateral cord contains sensory and motor tracts, and the anterior cord contains predominantly motor tracts.

In functional terms, two apparatuses are distinguished in the SM: segmental and conductive.

SEGMENTAL APPARATUS OF THE SPINAL CORD

Designed to provide unconditional simple protective reflexes (pulling the hand when pricked, etc.). This device works on the principle of the simplest reflex arcs (that is, without the participation of the brain). At the same time, the first sensitive neurons are pseudounipolar SMU cells; the second - intercalary neurons of the SM; the third are the effector neurons of the anterior horns of the spinal cord, which send impulses to the muscles. In humans, all reflex acts are polysegmental (i.e., capturing several segments).

CONDUCTION APPARATUS OF THE SPINAL CORD

Designed for the implementation of complex reflexes involving the nerve centers of the brain. Information enters the nuclei of the posterior horns of the spinal cord, where it accumulates and reaches the corresponding nerve centers of the brain through sensory pathways. After analysis in these centers, it is transmitted downstream to the motor cells of the anterior horns of the spinal cord and from them to the muscles.

The spinal cord (medulla spinalis) is located in the spinal canal. At the level of the I cervical vertebra and the occipital bone, the spinal cord passes into the oblong, and downwards stretches to the level of the I-II lumbar vertebra, where it becomes thinner and turns into a thin terminal thread. The spinal cord is 40–45 cm long and 1 cm thick. The spinal cord has cervical and lumbosacral thickenings, where nerve cells are located that provide innervation to 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 - the lateral cord (funiculus lateralis), between the posterior lateral sulcus and the posterior median sulcus - 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. In the thoracic regions, a lateral horn is revealed, which is also less pronounced in the lumbar and cervical regions 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 of 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, in the lateral funiculus, the dorsal-cover way, dorsal-reticular way, spinal-olive way and some other conductor systems pass.

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 the nerve centers; 2) the central part of the 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 to the 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 the important functions of the 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.

1. Cords of the spinal cord, funiculi medullae spinalis. Three columns of white matter, separated by anterior and posterior horns of gray matter, as well as the corresponding radicular filaments.
2. Anterior cord, funiculus anterior. It lies between the anterior median fissure on one side, the anterior horn and its radicular filaments on the other. Rice. BUT.
3. Lateral cord, funiculus lateralis. It is located outside the gray matter between the anterior and posterior roots. Rice. BUT.
4. Posterior cord, funiculus posterior. It is located between the posterior horn and its radicular threads on the one hand, the posterior median septum on the other. Rice. BUT.
5. Segments of the spinal cord, segmenta medullae spinalis. Areas of the brain, the radicular threads of which form one pair of spinal nerves passing through the corresponding intervertebral foramens. There are no boundaries between segments on an isolated spinal cord.
6. Neck segments - cervical part, segmenta cervicalia l - 57 - pars cervicalis. The radicular filaments of segments 1-7 emerge from the spinal canal above the vertebra corresponding to them by number, and the radicular filaments of the eighth segment go below the C7 body. The cervical part of the spinal cord extends from the atlas to the middle of C7. AT.
7. Thoracic segments = thoracic part, segmenta thoracica = pars thoracica. They are located along the length from the middle of C 7 to the middle of T 11. Fig. AT.
8. Lumbar segments - lumbar part, segmenta lumbalia - pars lumbalis. They are projected from the middle of T 11 to the upper edge of the body L 1. Fig. AT.
9. Sacral segments - sacral part, segmenta sacralia - pars sacralia Lie behind the body L 1. Fig. AT.
10. Coccygeal segments - coccygeal part, segmenta coccygea - pars coccygea. Three small segments of the spinal cord. Rice. AT.
11. Sections of the spinal cord, sectiones medullae spinalis. They are used to describe the internal structure of the spinal cord.
12. Central canal, canalis centralis. Obliterated remnant of the neural tube cavity. Located within the central intermediate. Rice. Ah, G.
13. Gray matter, substantia grisea. It is located medially from the white matter and consists of multipolar ganglion cells that form symmetrical solid columns interconnected throughout the spinal cord. On transverse sections, they correspond to the horns of gray matter, the shape and size of which vary in different parts of the spinal cord. Rice. BUT.
14. White matter, substantia alba. It is formed by myelinated nerve fibers, which are grouped into pathways and are part of the three cords. Rice. BUT.
15. Central gelatinous substance, substantia gelatinosa centralis. A narrow area around the central canal, which consists of processes of ependymal cells.
16. Gray pillars, columnae griseae. There are three columns of gray matter in the spinal cord. Rice. B.
17. Front column, columna anterior. Consists mainly of motor neurons. Rice. B.
18. Anterior horn, cornu anterius. Corresponds to the front pillar. Rice. G.
19. Anterolateral nucleus, nucleus anterolateralis. It is located in the anterolateral part of the anterior horn of the fourth - eighth cervical (C4 - 8) and second lumbar - first sacral (L2 - S1) segments of the spinal cord. The neurons of this nucleus innervate the muscles of the limbs. Rice. G.
20. Anterior medial nucleus, nucleus anteromedialis. It is located in the anteromedial section of the anterior horn throughout the spinal cord. Rice. G.
21. The posterolateral nucleus, nucleus posterolateralis. It is located behind the anterolateral nucleus in the fifth cervical - first thoracic (C5 - T1) and second lumbar - second sacral (L2 - S2) segments of the spinal cord. Its neurons innervate the muscles of the limbs. Rice. G.
22. The posterolateral nucleus, nucleus retroposterolateralis. It lies behind the posterolateral nucleus in the eighth cervical - first thoracic (C8 - T1) and first - third sacral (S1 - 3) segments of the spinal cord. Rice. G.
23. Posterior medial nucleus, nucleus posteromedialis. It is located next to the white commissure along the first thoracic - third lumbar (T1 - L3) segments of the spinal cord. The neurons of this nucleus probably innervate the muscles of the trunk. Rice. G.
24. Central nucleus, nucleus centralis. Small in size, without clear boundaries, a group of neurons in some cervical and lumbar segments. Rice. G.
25. Accessory nerve core, nucleus nervi accessorii (nuc. accessorius). Located in the upper six cervical segments (C1 - b) near the anterolateral nucleus. The processes of the neurons of the nucleus form the spinal part of the accessory nerve. Rice. G.
26. The nucleus of the phrenic nerve, nucleus nervi phrenici (nuc. phrenicus). Lies in the middle of the anterior horn along the fourth - seventh cervical segments (C4 - 7). Rice. G.