The spinal cord is characterized by a pronounced segmental structure, reflecting the segmental structure of the vertebrate body. Two pairs of ventral and dorsal roots depart from each spinal segment. The dorsal roots form the afferent inputs of the spinal cord. They are formed by the central processes of the fibers of the primary afferent neurons, the bodies of which are brought to the periphery and are located in the spinal ganglia. The ventral roots form the efferent outlets of the spinal cord. Axons of a and g-motor neurons, as well as preganglionic neurons of the autonomic nervous system, pass through them. This distribution of afferent and efferent fibers was established at the beginning of the last century and was called the Bell-Magendie law. After transection of the anterior roots on one side, a complete shutdown of motor reactions is observed; but the sensitivity of this side of the body remains. Transection of the posterior roots turns off the sensitivity, but does not lead to the loss of motor reactions of the muscles.
1 - white matter;
2 - gray matter;
3 - back (sensitive) spine;
4 - spinal nerves;
5 - anterior (motor) root;
6 - spinal ganglion
The neurons of the spinal ganglia are simple unipolar, or pseudo-unipolar, neurons. The name "pseudo-unipolar" is explained by the fact that in the embryonic period, the primary afferent neurons originate from bipolar cells, the processes of which then merge. The neurons of the spinal ganglia can be divided into small and large cells. The body of large neurons has a diameter of about 60–120 µm, while in small neurons it ranges from 14 to 30 µm.
Large neurons give rise to thick myelinated fibers. From the small ones, both thin myelinated and unmyelinated fibers begin. After bifurcation, both processes go in opposite directions: the central one enters the dorsal root and, in its composition, enters the spinal cord, the peripheral one enters various somatic and visceral nerves suitable for the receptor formations of the skin, muscles, and internal organs.
Sometimes the central processes of primary afferent neurons extend into the ventral root. This occurs during trifurcation of the axon of the primary afferent neuron, as a result of which its processes are projected into the spinal cord and through the dorsal and ventral roots.
Of the entire population of dorsal ganglion cells, approximately 60–70% are small neurons. This corresponds to the fact that the number of unmyelinated fibers in the dorsal root exceeds the number of myelinated fibers.
The bodies of neurons in the spinal ganglia do not have dendritic processes and do not receive synoptic inputs. Their excitation occurs as a result of the arrival of an action potential along the peripheral process in contact with the receptors.
Spinal ganglion cells contain high concentrations of glutamic acid, one of the putative mediators. Their surface membrane contains receptors specifically sensitive to g-aminobutyric acid, which coincides with the high sensitivity to g-aminobutyric acid of the central endings of the primary afferent fibers. Small ganglion neurons contain substance P or somatostatin. Both of these polypeptides are also likely mediators released by the endings of primary afferent fibers.
Each pair of roots corresponds to one of the vertebrae and leaves the spinal canal through the opening between them. Therefore, segments of the spinal cord are usually designated by the vertebra near which the corresponding roots emerge from the spinal cord. The spinal cord is also usually divided into several sections: cervical, thoracic, lumbar and sacral, each of which contains several segments. In connection with the development of the limbs, the neural apparatus of those segments of the spinal cord that innervate them has received the greatest development. This was reflected in the formation of cervical and lumbar thickenings. In the area of thickening of the spinal cord, the roots contain the largest number of fibers and have the greatest thickness.
On a transverse section of the spinal cord, the centrally located gray matter, formed by an accumulation of nerve cells, and the white matter fringing it, formed by nerve fibers, are clearly distinguished. In the gray matter, ventral and dorsal horns are distinguished, between which lies an intermediate zone. In addition, in the thoracic segments, there is also a lateral protrusion of the gray matter - the lateral horns.
All neuronal elements of the spinal cord can be divided into 4 main groups: efferent neurons, intercalary neurons, ascending tract neurons, and intraspinal fibers of sensory afferent neurons. Motor neurons are concentrated in the anterior horns, where they form specific nuclei, all of whose cells send their axons to a specific muscle. Each motor nucleus usually extends over several segments. Therefore, the axons of motor neurons innervating the same muscle leave the spinal cord as part of several ventral roots.
In addition to the motor nuclei located in the ventral horns, there are large accumulations of nerve cells in the intermediate zone of gray matter. This is the main nucleus of the intercalary neurons of the spinal cord. Axons of intercalary neurons spread both within the segment and into the nearest neighboring segments.
A characteristic accumulation of nerve cells also occupies the dorsal part of the dorsal horn. These cells form dense interlacings, and the indicated zone is called Roland's gelatinous substance.
The most accurate and systematic idea of the topography of the nerve cells of the gray matter of the spinal cord is given by dividing it into successive layers, or plates, in each of which mainly neurons of the same type are grouped.
Although the layered gray matter typography was initially identified in the cat spinal cord, it turned out to be quite universal and quite applicable to the spinal cord of both other vertebrates and humans.
According to these data, all gray matter can be divided into 10 plates. The very first dorsal plate contains mainly the so-called marginal neurons. Their axons project rostrally, giving rise to the spinothalamic tract. On the edge neurons, the fibers of the Lissauer tract terminate, which is formed by a mixture of primary afferent fibers and axons of propriospinal neurons.
The second and third plates form a gelatinous substance. Two main types of neurons are localized here: smaller and relatively large neurons. Although the bodies of neurons in the second plate have a small diameter, their dendritic ramifications are very numerous. The axons of the second plate neurons project to the Lissauer tract and the spinal cord's own dorsolateral bundle, but many remain within the gelatinous substance. On the cells of the second and third plates, the fibers of the primary afferent neurons terminate, mainly skin and pain sensitivity.
The fourth plate occupies approximately the center of the dorsal horn. The dendrites of layer IV neurons penetrate the gelatinous substance, and their axons project into the thalamus and lateral cervical nucleus. They receive synaptic inputs from the neurons of the gelatinous substance, and their axons are projected to the thalamus and the lateral cervical nucleus. They receive synaptic inputs from neurons of the gelatinous substance and primary afferent neurons.
In general, the nerve cells of the first-fourth plates capture the entire top of the dorsal horn and form the primary sensory area of the spinal cord. The fibers of most of the dorsal-radicular afferents from exteroreceptors are projected here, including skin and pain sensitivity. In the same zone, nerve cells are localized, giving rise to several ascending tracts.
The fifth and sixth plates contain numerous types of intercalary neurons that receive synaptic inputs from the fibers of the dorsal root and descending tracts, especially the corticospinal and rubrospinal tracts.
In the seventh and eighth plates, propriospinal intercalary neurons are localized, giving rise to long axons reaching the neurons of distant segments. Afferent fibers from proprioreceptors, fibers of the vestibulospinal and reticulospinal tracts, axons of propriospinal neurons end here.
The bodies of a- and g-motor neurons are located in the ninth plate. This area is also reached by presynaptic endings of primary afferent fibers from muscle stretch receptors, endings of fibers of descending tracts, cortico-spinal fibers, and axon terminals of excitatory and inhibitory interneurons.
The tenth plate surrounds the spinal canal and contains, along with neurons, a significant amount of glial cells and commissural fibers.
Spinal neuroglial cells cover the surface of neurons for a considerable extent, and the processes of the glial cell are directed, on the one hand, to the bodies of neurons, and on the other hand, often contact with blood capillaries, being intermediaries between nerve elements and their food sources.
The spinal cord transmits signals along the ascending pathways to the suprasegmental levels of the brain, and along the descending pathways it receives commands for action from there. Ascending pathways transmit impulses from proprioceptors along the fibers of the spinobulbar bundles of Gaulle and Burdach and the spinal cerebellar tracts of Govers and Flexigo, from pain and temperature receptors along the lateral spinothalamic tract, from tactile receptors along the ventral spinothalamic tract and partially through the Gaull and Burdach bundles.
Descending paths pass as part of the corticospinal, or pyramidal, tracts and extracorticospinal, or extrapyramidal.
According to the morphofunctional characteristics, 3 main types of neurons are distinguished.
Afferent (sensory, receptor) neurons conduct impulses to the CNS, i.e. centripetally. The bodies of these neurons always lie outside the brain or spinal cord in the nodes (ganglia) of the peripheral nervous system. motor, secretory, effector) neurons conduct impulses along their axons to the working organs (muscles, glands). The bodies of these neurons are located in the central nervous system or on the periphery - in the sympathetic and parasympathetic nodes.
The main form of nervous activity is the reflex. Reflex (lat. reflexus - reflection) - a causal reaction of the body to irritation, carried out with the obligatory participation of the central nervous system. The structural basis of reflex activity is made up of neural circuits of receptor, intercalary and effector neurons. They form the path along which nerve impulses pass from the receptors to the executive organ, called the reflex arc. It includes: receptor -> afferent nerve path -> reflex center -> efferent path -> effector.
The spinal cord (medulla spinalis) is the initial section of the CNS. It is located in the spinal canal and is a cylindrical, flattened from front to back strand 40-45 cm long, 1 to 1.5 cm wide, weighing 34-38 g (2% of the mass of the brain). At the top, it passes into the medulla oblongata, and below it ends with a sharpening - a cerebral cone at the level of I - II lumbar vertebrae, where a thin terminal (terminal) thread departs from it (a vestige of the caudal (tail) end of the spinal cord). The diameter of the spinal cord in different parts is not the same. In the cervical and lumbar regions, it forms thickenings (innervation of the upper and lower extremities). On the anterior surface of the spinal cord there is an anterior median fissure, on the posterior surface there is a posterior median sulcus, they divide the spinal cord into interconnected right and left symmetrical halves. On each half, weakly expressed anterior lateral and posterior lateral furrows are distinguished. The first is the exit point of the anterior motor roots from the spinal cord, the second is the point of entry into the brain of the posterior sensory roots of the spinal nerves. These lateral grooves also serve as the boundary between the anterior, lateral, and posterior cords of the spinal cord. Inside the spinal cord there is a narrow cavity - the central canal, filled with cerebrospinal fluid (in an adult, in various departments, and sometimes overgrows throughout).
The spinal cord is divided into parts: cervical, thoracic, lumbar, sacral and coccygeal, and the parts are divided into segments. A segment (structural and functional unit of the spinal cord) is a section corresponding to two pairs of roots (two anterior and two posterior). Throughout the spinal cord, 31 pairs of roots depart from each side. Accordingly, 31 pairs of spinal nerves in the spinal cord are divided into 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal.
The spinal cord is made up of gray and white matter. Gray matter - neurons (13 million), forming 3 gray columns in each half of the spinal cord: anterior, posterior and lateral. On a transverse section of the spinal cord, columns of gray matter on each side look like horns. The wider anterior horn and the narrow posterior horn correspond to the anterior and posterior gray pillars. The lateral horn corresponds to the intermediate column (vegetative) of the gray matter. In the gray matter of the anterior horns there are motor neurons (motor neurons), the posterior horns contain intercalary sensory neurons, and the lateral horns contain intercalary autonomic neurons. The white matter of the spinal cord is localized outward from the gray and forms the anterior, lateral and posterior cords. It consists mainly of longitudinally running nerve fibers, combined into bundles - pathways. In the white matter of the anterior cords there are descending pathways, in the lateral cords - ascending and descending pathways, in the posterior cords - ascending pathways.
The connection of the spinal cord with the periphery is carried out through nerve fibers passing in the spinal roots. The anterior roots contain centrifugal motor fibers, and the posterior roots contain centripetal sensory fibers (therefore, with bilateral transection of the posterior roots of the spinal cord in a dog, sensitivity disappears, anterior roots remain, but muscle tone of the limbs disappears).
The spinal cord consists of two symmetrical halves, separated from each other in front by a deep median fissure, and behind by a median sulcus. The spinal cord is characterized by a segmental (metameric) structure (31-33 segments); each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots.
In the spinal cord there are Gray matter located in the central part, and white matter lying on the periphery.
The outer border of the white matter of the spinal cord forms glial border membrane, consisting of fused flattened processes of astrocytes. This membrane is permeated by nerve fibers that make up the anterior and posterior roots.
Throughout the entire spinal cord in the center of the gray matter runs the central canal of the spinal cord, which communicates with the ventricles of the brain.
The gray matter on the transverse section has the appearance of a butterfly and includes front, or ventral, rear, or dorsal, and lateral, or lateral, horns. The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. The main component of gray matter, which distinguishes it from white, are multipolar neurons. Between the bodies of neurons is neuropil- a network formed by nerve fibers and processes of glial cells.
Among all the neurons of the spinal cord, three types of cells can be distinguished:
radicular,
internal,
beam.
axons radicular cells leave the spinal cord as part of its anterior roots, these are cells of the lateral and anterior horns. offshoots internal cells end in synapses within the gray matter of the spinal cord (mainly neurons of the posterior horns). axons beam cells pass in the white matter in separate bundles of fibers that carry nerve impulses from certain nuclei of the spinal cord to its other segments or to the corresponding parts of the brain, forming pathways.
As the spinal cord develops from the neural tube, neurons are isogenetically grouped into 10 layers, or Rexeda plates. At the same time, plates I-V correspond to the posterior horns, plates VI-VII correspond to the intermediate zone, plates VIII-IX correspond to the anterior horns, plate X corresponds to the zone near the central canal. On transverse sections, nuclear groups of neurons are more clearly visible, and on sagittal sections, the lamellar structure is better seen, where neurons are grouped into Rexed columns.
Cells similar in size, structure and functional significance lie in gray matter in groups called nuclei.
AT posterior horns distinguish between a spongy layer, a gelatinous substance, the own nucleus of the posterior horn and the thoracic nucleus of Clark, Roland's nucleus with inhibitory neurons, Lissauer's zone.
Neurons spongy zone and gelatinous substance carry out a connection between the sensitive cells of the spinal ganglia and the motor cells of the anterior horns, closing the local reflex arcs.
Neurons clarke nuclei receive information from the receptors of muscles, tendons and joints (proprioceptive sensitivity) along the thickest radicular fibers and transmit it to the cerebellum, these are large multipolar neurons.
Neurons own core the posterior horn is intercalated small multipolar cells, the axons of which terminate within the gray matter of the spinal cord of the same side (associative cells) or the opposite side (commissural cells).
Between the posterior and lateral horns, the gray matter juts into the white as strands, as a result of which its mesh-like loosening is formed, called the mesh formation, or the reticular formation of the spinal cord.
In the intermediate zone (lateral horns) the centers of the autonomic (autonomous) nervous system are located - preganglionic cholinergic neurons of its sympathetic and parasympathetic divisions.
AT anterior horns are the largest neurons in the spinal cord. These are radicular cells, since their axons make up the bulk of the fibers of the anterior roots. In the anterior horns there are 3 types of neurons that form 5 groups of nuclei that are significant in volume (lateral - anterior and posterior groups, medial - anterior and posterior groups and the central or intermediate nucleus).
Alpha motor neurons- large neurons 100-140 microns. By function, they are motor and their axons, as part of the anterior roots, exit the spinal cord and go to the striated muscles.
Gamma motor neurons- smaller, are cells that control the strength and speed of contraction.
Renshaw cells - inhibitory cells carry out mutual inhibition of flexor and extensor motoneurons, and also carry out recurrent inhibition.
white matter The horns of the brain are divided into columns: anterior (descending), middle (mixed) and posterior (ascending). The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated nerve fibers. Bundles of nerve fibers that communicate between different parts of the nervous system are called tracts, or pathways, of the spinal cord.
4. Reflex apparatus of the spinal cord (somatic reflex arcs)
The elementary reflex arc of the intrinsic apparatus of the spinal cord is represented by two neurons. The body of the first afferent neuron located in the spinal ganglion. Its dendrite goes to the periphery and ends with a receptor. The axon of the afferent neuron, as part of the posterior roots, enters the spinal cord, its posterior horns, and transits to the cells of the anterior horns of the spinal cord. Bodies in the anterior horns motor efferent cells- large alpha motor neurons, on which the axon of the sensitive cell ends with an axosomatic synapse. The axon of the efferent neuron leaves the spinal cord, enters into the anterior roots, then into the spinal nerve, plexus, and finally, as part of the somatic nerve, reaches effector organ(muscles, glands).
When irritation is applied (prick of a finger), the receptor apparatus (noceceptors of the skin) is irritated and a nerve impulse is generated, which is centripetally through the dendrite, the body of the afferent neuron and its axon is carried through the synaptic connection to the body of the second efferent neuron. From there, the nerve impulse centrifugally leaves the spinal cord, anterior root, nerve through the cell axon and causes excitation in the effector organ (biceps brachii), which, in turn, leads to the expected effect - pulling the hand away.
The principle of the structure and operation of vegetative reflex arcs is disassembled independently.
The spinal cord is the most ancient and primitive formation of the central nervous system of vertebrates, retaining its morphological and functional segmentation in the most highly organized animals. A characteristic feature of the organization of the spinal cord is the periodicity of its structure in the form of segments with inputs in the form of posterior roots, a cell mass of neurons (gray matter) and outputs in the form of anterior roots.
The human spinal cord has 31-33 segments: 8 cervical, 12 thoracic, 5 lumbar. 5 sacral, 1-3 coccygeal.
There are no morphological boundaries between segments of the spinal cord; therefore, the division into segments is functional and is determined by the zone of distribution of the fibers of the posterior root in it and the zone of cells that form the exit of the anterior roots. Each segment innervates three metameres of the body through its roots and also receives information from three metameres of the body. As a result of overlap, each metamere of the body is innervated by three segments and transmits signals to three segments of the spinal cord.
The human spinal cord has two thickenings: cervical and lumbar - they contain a larger number of neurons than in its other parts. The fibers entering the posterior roots of the spinal cord perform functions that are determined by where and on which neurons these fibers end. The posterior roots are afferent, sensory, centripetal. Anterior - efferent, motor, centrifugal.
Afferent inputs to the spinal cord are organized by the axons of the spinal ganglia that lie outside the spinal cord, the axons of the extra- and intramural ganglia of the sympathetic and parasympathetic divisions of the autonomic nervous system.
The first group of afferent inputs of the spinal cord is formed by sensory fibers coming from muscle receptors, tendon receptors, periosteum, and joint membranes. This group of receptors forms the beginning of proprioceptive sensitivity.
The second group of afferent inputs of the spinal cord starts from skin receptors: pain, temperature, tactile, pressure - and represents the skin receptor system.
The third group of afferent inputs of the spinal cord is represented by receptive inputs from visceral organs; it is the visceroreceptor system.
Efferent (motor) neurons are located in the anterior horns of the spinal cord, their fibers innervate all skeletal muscles.
The spinal cord has two functions: conduction and reflex.
The spinal cord performs a conductive function due to the ascending and descending pathways passing through the white matter of the spinal cord. These pathways connect individual segments of the spinal cord to each other. The spinal cord connects the periphery with the brain through long ascending and descending pathways. Afferent impulses along the pathways of the spinal cord are carried to the brain, carrying information about changes in the external and internal environment of the body. Downward pathways impulses from the brain are transmitted to the effector neurons of the spinal cord and cause or regulate their activity.
As a reflex center, the spinal cord is able to carry out complex motor and autonomic reflexes. Afferent - sensitive - ways it is connected with receptors, and efferent - with skeletal muscles and all internal organs.
The gray matter of the spinal cord, the posterior and anterior roots of the spinal nerves, and their own white matter bundles form the segmental apparatus of the spinal cord. It provides a reflex (segmental) function of the spinal cord.
The nerve centers of the spinal cord are segmental or working centers. Their neurons are directly connected with receptors and working organs. The functional diversity of spinal cord neurons, the presence in it of afferent neurons, interneurons, motor neurons and neurons of the autonomic nervous system, as well as numerous direct and reverse, segmental, intersegmental connections and connections with brain structures - all this creates conditions for the reflex activity of the spinal cord with the participation , both their own structures and the brain.
Such an organization allows the implementation of all motor reflexes of the body, diaphragm, genitourinary system and rectum, thermoregulation, vascular reflexes, etc.
The nervous system functions according to reflex principles. The reflex is a response of the body to external or internal influences and spreads along the reflex arc, i.e. own reflex activity of the spinal cord is carried out by segmental reflex arcs. Reflex arcs are circuits made up of nerve cells.
There are five links in the reflex arc:
receptor;
sensitive fiber conducting excitation to the centers;
the nerve center, where the excitation switches from sensory cells to motor cells;
motor fiber carrying nerve impulses to the periphery;
the active organ is a muscle or a gland.
The simplest reflex arc includes sensitive and efferent neurons, along which the nerve impulse moves from the place of origin (receptor) to the working organ (effector). The body of the first sensitive (pseudo-unipolar) neuron is located in the spinal ganglion. The dendrite begins with a receptor that perceives external or internal irritation (mechanical, chemical, etc.) and converts it into a nerve impulse that reaches the body of the nerve cell. From the body of the neuron along the axon, the nerve impulse through the sensory roots of the spinal nerves is sent to the spinal cord, where synapses are formed with the bodies of effector neurons. In each interneuronal synapse, with the help of biologically active substances (mediators), an impulse is transmitted. The axon of the effector neuron exits the spinal cord as part of the anterior roots of the spinal nerves (motor or secretory nerve fibers) and goes to the working organ, causing muscle contraction, increased (inhibition) of gland secretion.
The reflex centers and spinal reflexes in functional terms are the nuclei of the spinal cord. In the cervical region of the spinal cord is the center of the phrenic nerve, the center of pupil constriction. In the cervical and thoracic regions there are motor centers of the muscles of the upper limbs, chest, abdomen and back. In the lumbar region there are centers of the muscles of the lower extremities. In the sacral region there are centers for urination, defecation and sexual activity. In the lateral horns of the thoracic and lumbar regions lie sweat centers and vasomotor centers.
The spinal cord has a segmental structure. A segment is a segment that gives rise to two pairs of roots. If the frog's back roots are cut on one side and the front roots on the other, then the paws on the side where the back roots are cut lose sensitivity, and on the opposite side, where the front roots are cut, they will be paralyzed. Consequently, the posterior roots of the spinal cord are sensitive, and the anterior roots are motor.
The reflex reactions of the spinal cord depend on the location, strength of stimulation, the area of the irritated reflex zone, the speed of conduction along the afferent and efferent fibers, and, finally, on the influence of the brain. The strength and duration of spinal cord reflexes increase with repeated stimulation. Each spinal reflex has its own receptive field and its own localization (location), its own level. So, for example, the center of the skin reflex is in the II-IV lumbar segment; Achilles - in the V lumbar and I-II sacral segments; plantar - in the I-II sacral, the center of the abdominal muscles - in the VIII-XII thoracic segments. The most important vital center of the spinal cord is the motor center of the diaphragm, located in the III-IV cervical segments. Damage to it leads to death due to respiratory arrest.
The spinal cord consists of two symmetrical halves, separated from each other in front by a deep median fissure, and behind by a median sulcus. The spinal cord is characterized by a segmental structure; each segment is associated with a pair of anterior (ventral) and a pair of posterior (dorsal) roots.
In the spinal cord, gray matter located in the central part and white matter lying along the periphery are distinguished.
The white matter of the spinal cord is a collection of longitudinally oriented predominantly myelinated nerve fibers. Bundles of nerve fibers that communicate between different parts of the nervous system are called tracts, or pathways, of the spinal cord.
The gray matter in cross section is butterfly-shaped and includes anterior or ventral, posterior or dorsal, and lateral or lateral horns. The gray matter contains the bodies, dendrites and (partly) axons of neurons, as well as glial cells. The main component of the gray matter are multipolar neurons.
Cells similar in size, fine structure and functional significance lie in gray matter in groups called nuclei.
Axons of radicular cells leave the spinal cord as part of its anterior roots. The processes of internal cells end in synapses within the gray matter of the spinal cord. The axons of the beam cells pass through the white matter as separate bundles of fibers that carry nerve impulses from certain nuclei of the spinal cord to its other segments or to the corresponding parts of the brain, forming pathways. Separate areas of the gray matter of the spinal cord differ significantly from each other in the composition of neurons, nerve fibers and neuroglia.
In the posterior horns, a spongy layer, a gelatinous substance, a proper nucleus of the posterior horn, and Clark's thoracic nucleus are distinguished. Between the posterior and lateral horns, the gray matter juts into the white as strands, as a result of which its mesh-like loosening is formed, which is called the mesh formation, or reticular formation, of the spinal cord.
The posterior horns are rich in diffusely located intercalary cells. These are small multipolar associative and commissural cells, the axons of which terminate within the gray matter of the spinal cord of the same side (associative cells) or the opposite side (commissural cells).
The neurons of the spongy zone and the gelatinous substance communicate between the sensitive cells of the spinal ganglia and the motor cells of the anterior horns, closing the local reflex arcs.
Clark's nucleus neurons receive information from muscle, tendon, and joint receptors (proprioceptive sensitivity) along the thickest radicular fibers and transmit it to the cerebellum.
In the intermediate zone, there are centers of the autonomic (autonomous) nervous system - preganglionic cholinergic neurons of its sympathetic and parasympathetic divisions.
The largest neurons of the spinal cord are located in the anterior horns, which form nuclei of considerable volume. This is the same as the neurons of the nuclei of the lateral horns, radicular cells, since their neurites make up the bulk of the fibers of the anterior roots. As part of the mixed spinal nerves, they enter the periphery and form motor endings in the skeletal muscles. Thus, the nuclei of the anterior horns are motor somatic centers.
