Intermediate substance of the spinal cord. Definition and significance of spinal cord nucleus formation. Why is the defeat of white and gray matter dangerous?
Functions and structure
Shell
Vessels
Development
Question 1
spinal cord functions:
1. reflex center all motor reactions of skeletal muscles (except facial), reflexes of blood vessels, genitourinary system, rectum
2. conduction of impulses to the brain and back... The spinal cord is controlled by the brain
3. reflex arc closuretransmitting nerve impulse from the sensitive link to the motor
4. endocrine - ependymoglia of the spinal canal (intraspinal organ) at a young age produces biologically active substances that regulate blood pressure, circadian rhythms, sexual function
ü development of the spinal cord is directly proportional to the development of skeletal muscles and skin, which is due to the large receptor field of the skin and a variety of muscle movements
Spinal cord (medulla spinalis)
cylindrical cord, compressed dorsoventrally and lies in the spinal canal (occupies 2/3 of the volume)
ü front border - large occipital foramen
ü back border - different:
In cattle - up to 4 lumbar vertebrae, in a pig - 6 lumbar, in a dog - 7 lumbar, in a horse - 2 sacral, in a cat - 3 sacral, in humans - up to 2 lumbar
v segment - a section of the spinal cord with a pair of nerves
ü highlight cervical, thoracic, lumbar, sacral and tail segments
ü Due to the advancing growth of the spinal column, the boundaries of the spinal cord segments do not coincide with the boundaries of the vertebrae of the corresponding departments
Spinal cord segment
Spinal cord
has 2 thickenings:
1) cervical - contains neurons, the processes of which form the nerves of the thoracic extremities (brachial plexus)
2) lumbosacral - contains neurons, the processes of which form the nerves of the pelvic extremities (lumbar and sacral plexus). Behind it, the spinal cord narrows - cerebral cone
ü the cone continues in terminal(terminal) a threadreaching the 6th caudal vertebra
ü terminal filament and tail nerves form "Ponytail" - cauda equina
Surface view
ventral surface:
1.ventral median fissure - lies the central spinal cord. and in.
2.two lateral ventral grooves - the exit site of the ventral (motor) roots of the spinal nerves
dorsal surface:
1.small dorsal median sulcus
2.dorsal lateral grooves - the place of entry of the dorsal (sensory) roots of the spinal nerves
Spinal nerves (nervus spinalis)
ü exit in pairs in each segment through the intervertebral foramen
ü each nerve begins with bundles of root filaments that form the dorsal (sensory) and ventral (motor) roots
ü thickening on the dorsal roots - spinal nodes (ganglia) - from sensitive neurons evicted outside the central nervous system
ü in the cervical and thoracic parts of the spinal cord, nerves depart perpendicular to the brain, and in the lumbosacral - obliquely back (associated with the advanced growth of the spine)
Sectional view
gray matter(substantia grisea) - lies in the center, has a shape butterflies (letters H):
1. dorsal horns(pillars) - sensitive
2. ventral horns -motor
3. lateral horns- in the thoracolumbar and sacral regions
4. intermediate- between the dorsal and ventral horns
5. gray adhesion- connects halves of gray matter
6. spinal canal- in the center of the commissure, cranially passes into the 4th cerebral ventricle of the medulla oblongata, caudally - ends blindly. Sent by ependymoglia, filled liquor
Gray matter structure
ü represented by bodies of neurons surrounded by glia
ü core of gray matter- a group of neurons of the same structure and function
ü neurons of the dorsal horns form:
1. gelatinous and spongy substance- axons form their own bundles (intersegmental connections with participation in the response of many segments)
2. dorsal horn core- axons form pathways of pain and temperature sensitivity (Latin dorsal-thalamic path of the opposite side), touch and pressure (vent.spinal-thalamic path)
3. pectoral nucleus (Clarke)- axons form dors. the spinal cord on its side (coordination of movements)
nuclei and pathways of the spinal cord
types of neurons by localization of axons:
1. radicular - axons are involved in the formation of the ventral (motor) roots of the spinal nerves
2. bundle - axons form bundles of white matter connecting the spinal cord segments with each other and with the brain
3. internal - numerous processes do not leave the gray matter, connecting the neurons of the spinal cord nuclei within the segment
white medulla (substantia alba) - along the periphery of the gray matter of the brain
ü represented by processes of neurons
ü horns of gray matter are divided into paired ropes: dorsal, ventral, lateral
ü the cords of the opposite sides are connected white soldering
ü in the ropes - pathways between spinal cord segments, spinal cord and brain:
1) associative - connect segments of the spinal cord at different levels - own bundles all the cords
2) ascending (sensitive) - to the centers in the brain
3) downstream (motor) - from the brain to the neurons of the ventral horns of the spinal cord
cords of the white medulla:
1. dorsal - ascending ways,contains 2 bundles:
1) thin (Gaulle) - from the back of the body and hind legs
2) wedge-shaped (Burdakha) - from the front of the body and forelimbs
ü formed by the axons of the neurons of the spinal nodes
ü entering the medulla oblongata are combined into the medulla oblongata (tractus spinobulbaris)
ü conduct impulses from proprioceptors into the medulla oblongata, and then into the cerebral cortex about the position of the body and its parts in space
2. lateral - ascending and descending paths:
ascending:
1) dorsal dorsal cerebellar / Flexiga / (from the thoracic nucleus)
2) dorsal-cerebellar ventral / Goversa / (from the intermediate med. Nucleus)
3) dorsal-thalamic (from the own nucleus of the dorsal horn of the opposite side)
downstream:
1) cortical-spinal (pyramidal) lateral - provides the implementation of conscious movements
2) red-nuclear-spinal - formed by the axons of the cells of the red nucleus of the midbrain (control of muscle tone)
3. ventral -ascending and descending paths:
ascending:
dorsal-thalamic ventral (from the own nucleus of the dorsal horn of the opposite side) - the path of touch and pressure
downstream:
1) vestibulo-spinal - formed by the axons of neurons of the vestibular nuclei of the medulla oblongata (Deiters, Roller) - equilibrium reflexes
2) cortical-spinal (pyramidal) ventral - the path of voluntary motor reactions
3) tecto-spinal - from the roof of the midbrain from the cells of the visual and auditory hills
segmental (own) apparatus of the spinal cord:
The site of the closure of unconditioned (innate) reflexes from skin receptors to muscles and blood vessels
More ancient in development
relate:
1) gray matter of the spinal cord
2) own beams (associative pathways)
3) spinal nodes
4) the roots of the spinal nerves
spinal cord conduction apparatus:
Associated with different parts of the brain
Conditioned and unconditioned reflexes pass from various analyzers (olfactory, visual, auditory, vestibular)
Later origin, arose as a result of the development of muscles and parts of the brain
relate:
Gray matter of the spinal cord
Ascending and descending pathways connecting the spinal cord with different parts of the brain
Ventral (motor) roots of the spinal nerves
Question 2
Spinal cord membranes
dura mater spinalis:
ü consists of PST, expelled from the inside by endothelium
ü external, covers the spinal cord with a sheath and hangs it in the spinal canal
ü between the hard shell and the periosteum of the spinal canal - epidural space filled with fat and vein plexus (shockproof + mobility in the spinal canal)
ü passes to the spinal nerves, forming vaginas on them
arachnoid - arachnoidea spinalis:
ü thin translucent, consists of PCT, covered with endothelium on both sides
ü closely adheres to the hard shell, separating with a slit subdural space filled with PCT
ü will connect to the hard shell: vessels, dentate ligaments of the soft shell and the nerves to which it passes
ü separated from the soft shell subarachnoid space filled with CSF (cerebrospinal fluid)
soft (vascular) membrane - pia mater spinalis:
ü firmly grows together with the brain, since, accompanying the vessels, it is introduced with them into the medulla
ü covered with endothelium from the subarachnoid space
ü on the lateral surfaces of the spinal cord forms left and right lateral ligaments ... From them between the segments of the brain to the hard shell depart dentate ligaments perforating the arachnoid
ü soft + spider web - leptomeninx (their inflammation is leptomeningitis)
spinal cord fixation apparatus:
1. dura mater- fixed on the ventral arch of the atlas, the epistropheus tooth, along the edges of the intervertebral foramen and in the caudal vertebrae
2. dentate ligaments- attach the spinal cord in the soft membrane to the arachnoid and hard membranes
3. numerous threads, partitionsfrom connective tissue, connecting the soft membrane with arachnoid
4. spinal nerve roots- leaving through the intervertebral foramen, the brain is suspended "on stretchers"
ü membranes, the contents of the intershell spaces, the fixation apparatus hold the spinal cord, protect against compression during spinal movements
Question 3
spinal cord vessels:
spinal arteriesare spinal branches:
1) vertebral and deep cervical a. (cervical)
2) dorsal intercostal aa. (thoracic region)
3) lumbar aa. (lumbosacral region)
ü these branches penetrate into the spinal canal along the roots of the spinal nerves and form on the spinal cord 3 longitudinal arterial lines
3 arterial highways of the spinal cord:
1. unpaired ventral spinal cord.- lies with the vein of the same name in the ventral median fissure, gives off branches to the gray medulla
2. paired spinal dorsal aa.- lie along the dorsal nerve roots, and the corresponding veins - along the ventral roots
ü 3 lines anastomose among themselves in each segment, forming vascular crown ... Branches depart from it into the white medulla, connecting with a. gray matter
ü blood flows from the veins into the internal vertebral venous plexus and the paired vertebral ventral sinus (in the epidural space and connects to the segmental veins)
Question 4
Spinal cord development
phylogenesis:
Development is associated with the evolution of skeletal muscle
First found in chordates
at the lanceletprimitive, in the form of a tube. Nerve cells are scattered throughout the brain. Nerve fibers are myelin-free - gray... Nerves leave the brain asymmetrically, because peristaltic movements. The nerve roots are not divided into sensory and motor roots. From shells - primitive soft
in fish- the concentration of neurons and the formation of the gray medulla. The ventral columns are developed, the dorsal columns are not developed, because weak skin sensitivity. The roots of the spinal nerves are divided into motor and sensory
in amphibians and reptilesa dura mater appears
with access to landand the appearance of limbs in the spinal cord, 2 thickenings are formed, the gray matter becomes in the form of H, sensitive cells are moved to the spinal nodes. With the reduction of the tail as an organ of movement, the spinal cord is shortened
in mammalsa spider web appears
ontogenesis:
Is developing from ectoderm→1. neural plate→ 2. nerve groovelimited by nerve ridges → 3. neural tube, when closing the edges of the groove
ü if the neural plate is divided into 2 - 2 spinal cords - diplomacy
ü if the ectoderm above the neural tube does not close, then the spinal cord remains open - raskhis
The cells of the monolayer neural tube are divided into glioblasts (neuroglia) and neuroblasts (neurons)
The neural tube becomes three-layered
Nervous system
The nervous system unites parts of the body (integration), ensures the regulation of various processes, the coordination of the work of organs and the interaction of the body with the external environment. She perceives a variety of information coming from the external environment and internal organs, processes it and generates signals that determine adequate responses.
Anatomically, the nervous system is subdivided into central (brain and spinal cord) and peripheral (peripheral nerve nodes, nerve trunks and nerve endings). From a physiological point of view, an autonomous (autonomic) nervous system is distinguished, which innervates the internal organs, glands, blood vessels, and the somatic (cerebrospinal) nervous system, which regulates the activity of the rest of the body (skeletal muscle tissue).
Development nervous system
The development of the nervous system occurs from the neuroectoderm (neural plate), which forms the neural tube, neural crest, and neurogenic placodes. The spinal cord and brain develops from the neural tube, in which the following layers differentiate:
Inner boundary membrane;
Ependymal layer;
Cloak layer;
Edge veil;
Outer pororganic membrane.
The source of all cells CNS are the matrix (ventricular) cells of the inner layer. They are concentrated near the inner boundary membrane, actively multiply and move. Cells that have finished proliferating - neuroblasts, as well as glioblasts capable of proliferation, are moved into the mantle layer. Part of the ventricular cells remains in situ, and later on, this is the future ependyma.
Neuroblasts give rise to all neurons in the central nervous system, after migration they lose their ability to proliferate. Glioblasts become precursors of macroglia, they are capable of proliferation.
The rigidity of brain organization is determined by two factors: targeted cell migration and directed growth of processes. The mechanism of directed movements is due to chemotropism, which is carried out along a pre-marked path. At certain stages of ontogenesis, programmed cell death occurs. The volume of the subpopulation of dying neurons is estimated in the range of 25-75%. At the same time, the cellular elements of the ganglionic plate form the spinal and vegetative nodes.
Spinal cord
The spinal cord is a part of the central nervous system that is located in the spinal canal and looks like a round cord, slightly flattened in the dorsal-abdominal direction. In the center of the spinal cord is the central spinal canal lined with ependymal glia.
The spinal cord, like the brain, is covered by three meninges:
Inner - the pia mater with blood vessels and nerves in its loose connective tissue. It is directly adjacent to the spinal cord.
This is followed by a thin layer of loose connective tissue - the arachnoid membrane. Between these membranes is the subarachnoid (subarachnoid) space with thin connective tissue fibers connecting the two membranes. This space with cerebrospinal fluid communicates with the ventricles of the brain.
The outer shell is a dura mater, consisting of dense connective tissue, fused with the periosteum in the cranial cavity. In the spinal cord there is an epidural space between the periosteum of the vertebrae and the dura mater, filled with loose fibrous connective tissue, which gives some mobility to the membrane. Between the dura mater and the arachnoid there is a subdural space with a small amount of fluid. The subdural and subarachnoid spaces are covered from the inside with a layer of flat glial cells.
The spinal cord consists of two symmetrical halves, delimited from each other in front by a median fissure, and behind by a median groove.
On the cross-section, gray and white substances are easily distinguished.
Gray matter located in the central part, surrounded by white matter.
The gray matter in cross-section has the shape of butterfly wings. The protrusions of the gray matter are called horns: there are front, rear and lateral horns. There is an intermediate zone between the anterior and posterior horns. In reality, the horns are pillars that run along the spinal cord.
The gray matter of both symmetrical halves is connected to each other in the region of the spinal canal by a central gray commissure (formed by commissures).
Gray matter is formed by bodies nerve cells, their dendrites and partly axons, as well as glial cells.
Nerve cells are located in the gray matter in the form of not always sharply demarcated clusters - nuclei. Based on the location of neurons, the nature of their connections and the function of B. Rexed in the gray matter of the spinal cord, 10 plates were identified. The topography of the nuclei corresponds to the topography of the plates, although they do not always coincide.
Depending on from axonal topography spinal cord neurons are subdivided as follows:
♦ Internal - neurons whose axons end within the gray matter of a given segment of the spinal cord.
♦ Beam - their axons form bundles of fibers in the white matter of the spinal cord.
♦ Root - their axons leave the ich of the spinal cord as part of the anterior roots.
The rear horns are distinguished: spongy layer, gelatinous substance, own nucleus of the posterior horn and pectoral nucleus.
Spongy layer stretches continuously along the spinal cord, forming the dorsal lobe of the posterior horn, which corresponds to the I plate, is characterized by a glial skeleton, which contains a large number of small intercalary neurons. These neurons respond to pain and temperature stimuli and release fibers to the spinal thalamic pathway on the opposite side. Among these neurons are cells containing substance P and enkephalin.
In gelatinous substance, or Roland gelatinous substance (plate II, III), glial elements predominate. Nerve cells here are small, few of them. They are approached by axons coming from the posterior cord, and fibers of pain and tactile sensitivity. The axons of the neurons of this layer either end within a given segment of the spinal cord (enter the Lissauer's marginal belt, which forms transverse and longitudinal connections on the surface of the gelatinous substance), or go into their own bundles or to the thalamus, cerebellum, lower olives. The neurons in this layer produce enkephalin, an opioid-type peptide that inhibits pain effects.
The main significance of the gelatinous substance is the implementation of an inhibitory effect on the functions of the spinal cord by controlling the sensory information entering it: skin, partially visceral and proprioceptive.
Own core consists of intercalary neurons that receive afferent impulses from the spinal nodes and descending fibers of the brain. Their axons pass through the anterior white commissure to the opposite side and ascend to the thalamus, just as the gelatinous substance is responsible for exteroceptive sensitivity.
The thoracic nucleus of the posterior horn (Clark's nucleus) is located in the VII plates. It is formed by neurons, to which there are thick myelinated collaterals of sensory neurons, delivering proprioceptive sensory sensitivity from joints, tendons and muscles. The axons of the Clarke nucleus cells form the posterior spinal cord.
In the intermediate zone VI and partially in the VII plates, the outer and inner basilar nuclei are located. They process the bulk of information coming from the brain and transmit it to motoneurons. On the cells of the outer nucleus, thick, fast-conducting axons are interrupted, originating from the largest and most gigantic pyramids of the motor cortex. Thin, slow-conducting fibers are projected onto the neurons of the inner nucleus. In humans, about 90% of the fibers of the cortico-spinal tract ends on the neurons of the basilar nuclei.
The lateral horns contain: the medial and lateral nuclei.
The lateral nucleus (Th I - L II) contains the neurons of the autonomic reflex arc - the center sympathetic division... The sympathetic nucleus includes the axons of the pseudo-unipolar spinal ganglion, which carry visceral sensitivity. The second group of axons comes from the medial nucleus of the lateral horn. The axons of neurons in the lateral nucleus give rise to preganglionic fibers that emerge from the spinal cord through the anterior roots.
The medial nucleus (S II - Co III) is located in the intermediate zone, where the lateral horns are absent - it receives impulses from the sensitive neurons of the autonomic reflex arc.
In addition, the Onufrovich nucleus is located in the lateral horns of the sacral segments (S2 - S4) of the spinal cord. It contains neurons in the parasympathetic autonomic nervous system, which are involved in the innervation of the pelvic organs.
In the VII plate, Renshaw's interoneurons are concentrated, which are necessary for the implementation of motor function. They receive an excitatory impulse from the collagerals of the axon of motor neurons and inhibit their function. It has essential for the coordinated work of motoneurons and muscles innervated by them for alternate flexion and extension of the limbs.
In the VIII plate, the interstitial nucleus of Cajal is localized. Its interoneurons switch information from afferent neurons to motoneurons. The axons of the neurons of this nucleus are part of their own bundles and form collateral connections on several segments.
The periependymal gray matter corresponds to the X plate, is located throughout the spinal cord and is formed by intercalary neurons of the autonomic nervous system.
The anterior horns contain multipolar motoneurons (plate IX), which are the only executive cells of the spinal cord that send information to skeletal muscles. They combine into nuclei, each of which usually stretches over several segments. Motor neurons end in:
♦ Collaterals of axons of pseudo-unipolar cells, forming with them two-neuronal reflex arcs.
♦ Axons of intercalary neurons, whose bodies lie in the posterior horns of the spinal cord.
♦ Axons of Renshaw cells that form inhibitory axosomatic synapses. The bodies of these small cells are located in the middle of the anterior horn and are innervated by collateral axons of motor neurons.
♦ Fibers of the descending pathways of the pyramidal and extrapyramidal systems, carrying impulses from the cerebral cortex and brain stem nuclei.
According to the classical concepts, motor neurons in the spinal cord are distributed over 5 motor nuclei.
Medial - anterior and posterior - are present throughout the spinal cord, innervate the muscles of the trunk.
Lateral - anterior and posterior - localized in the cervical and lumbar thickenings, innervate the flexors and extensors of the limbs.
Central nucleus - located in the lumbar and cervical regions, innervates the muscles of the girdles of the limbs.
White matter - is divided by the anterior and posterior roots into symmetrical ventral, lateral and dorsal cords. It consists of longitudinal nerve fibers (mainly myelin), which form the descending and ascending paths (tracts), and astrocytes. Each tract is characterized by a predominance of fibers formed by the same type of neurons.
The pathways include 2 groups: propriospinal and supraspinal.
Propriospinal pathways - the spinal cord's own apparatus, formed by the axons of intercalary neurons, which carry out communication between the segments of the spinal cord. These paths pass mainly on the border of white and gray matter in the composition of the lateral and ventral cords.
Supraspinal pathways - provide a connection between the spinal cord and the brain and include the ascending and descending spinal-cerebral pathways.
Pain, temperature, deep and tactile sensitivity is carried out along the ascending pathways. These are the dorsal-thalamic tract, the dorsal and ventral spinal-cerebellar tracts, the tender and wedge-shaped bundles.
The spinal tracts provide the transmission of impulses to the brain. Some of them (there are 20 of them in total) are formed by the axons of the cells of the spinal cord nodes, while the majority are represented by the axons of various intercalary neurons, the bodies of which are located on the same or on the opposite side of the spinal cord.
Cerebrospinal tracts include pyramidal and extra-rapyramidal systems.
The pyramidal system is formed by long axons of the pyramidal cells of the cerebral cortex, which at the level of the medulla oblongata for the most part pass to the opposite side and form the lateral and ventral cortico-spinal tracts. The pyramidal system controls the precise voluntary movements of the skeletal muscles, especially the limbs.
The extrapyramidal system is formed by neurons whose bodies lie in the nuclei of the medulla and medulla oblongata and the pons, and the axons end on motor neurons and interneurons. This system mainly controls the contraction of tonic muscles responsible for maintaining posture and body balance.
Extrapyramidal descending pathways are represented by the rubrospinal pathway originating from the red nucleus and conducting an impulse from the nuclei of the cerebellum, as well as the tecto-spinal pathway, starting from the tectum and conducting impulses from the visual and auditory pathways, as well as the vestibulo-spinal pathway originating from the nuclei of the vestibular nerve and carrying impulses of a static nature.
Spinal cord - an organ of the central nervous system of vertebrates, located in the spinal canal.
The spinal cord looks like a cord whitesomewhat flattened from front to back in the area of \u200b\u200bthickenings and almost round in other sections. In the spinal canal, it extends from the level of the lower edge of the foramen magnum to the intervertebral disc between the I and II lumbar vertebrae. Above, the spinal cord passes into the brain stem, and below, gradually decreasing in diameter, it ends in a cerebral cone. In adults, the spinal cord is much shorter than the spinal canal, its length varies from 40 to 45 cm, weight is about 34-38 g, which is about 2% of the brain weight. The cervical thickening of the spinal cord is located at the level of the III cervical and I thoracic vertebra; The lumbosacral thickening is located at the level of the X-XII thoracic vertebra. The anterior median fissure and the posterior median sulcus divide the spinal cord into symmetrical halves. On the surface of the spinal cord at the exit sites of the ventral (anterior) and dorsal (posterior) roots, two less deep grooves are revealed: anterior lateral and posterior lateral. The segment of the spinal cord corresponding to two pairs of roots (two anterior and two posterior) is called segment... The anterior and posterior roots emerging from the segments of the spinal cord are combined into 31 pairs of spinal nerves. The anterior root is formed by the processes of motor neurons of the nuclei of the anterior columns of the gray matter. The anterior roots of the VIII cervical, XII thoracic, two upper lumbar segments, along with the axons of the motor somatic neurons, include neurites of the cells of the sympathetic nuclei of the lateral columns, and the processes of the neurons of the parasympathetic nuclei of the lateral intermediate substance of the spinal cord are included in the anterior roots of the II-IV sacral segments. The posterior root is represented by the central processes of pseudo-unipolar (sensitive) cells located in the spinal node. The central canal passes through the gray matter of S. of m along its entire length, which, expanding cranially, passes into the IV ventricle of the brain, and forms a terminal ventricle in the caudal part of the cerebral cone.
The spinal cord carries 31 pairs of spinal nerves symmetrically located on both sides: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and one coccygeal.
White and gray matter of the spinal cord
The cross-sections of the spinal cord show the ratio of the location of the white and gray matter. The gray matter occupies the central part and has the shape of a butterfly with spread wings, or the letter "H". The white matter is located around the gray matter, occupying the periphery of the spinal cord. The white matter of the spinal cord is basically a complex system of varying lengths and thicknesses of pulp and partially non-pulp nerve fibers and supporting nervous tissue - neuroglia, as well as blood vessels surrounded by a small amount of connective tissue. The white matter of one half of the spinal cord is connected with the white matter of the other half by a thin white commissure that runs transversely in front of the central canal. Nerve fibers in the white matter are collected in bundles. These three grooves running along the slit on each half of the spinal cord delimit the white matter of each half into three so-called spinal cord cords. There are anterior, lateral and posterior cords. In the upper parts of the thoracic and the entire cervical parts of the spinal cord, the posterior cord is divided into two bundles - thin and wedge-shaped. These cords continue into the initial section of the brain - the medulla oblongata. In the lower parts of the spinal cord, the listed cords merge and become indistinguishable.
The spinal cord has a segmental, bilateral structure. Its inner core is formed by a gray matter consisting of neuronal cells, unmyelinated axons, glial cells, and blood vessels. The outer white matter consists of bundles of myelinated axons that transmit impulses to and from the spinal cord.
The gray matter is the pillars, and in the cut, the horns ( cornu anterius, posterius). The anterior and posterior horns are connected by an intermediate zone of gray matter (Fig. 1), which forms the lateral horns - cornu laterale (from Ⅰ thoracic to Ⅱ - Ⅲ lumbar vertebrae).
Figure: 1.: 1 - posterior horn; 2 - lateral horn; 3 - front horn; 4 - posterior cord; 5 - lateral cord; 6 - anterior cord.
In the hind horns, nerve cells receive information from sensory nerve cells in the body about parameters such as touch, temperature, muscle activity, and body balance. The nerve cells of the lateral horns, located only in the central part of the spinal cord, monitor and regulate the work of internal organs. The anterior horns contain nerve cells that transmit impulses along nerve fibers to the muscles of the skeleton, causing them to contract and move.
In the posterior horn there is a spongy zone and a gelatinous substance (their processes form their own bundles of the spinal cord, providing a connection between the segments), their own and thoracic nuclei, and between the posterior and lateral horns there is a reticular formation of the spinal cord.
The lateral horn contains the medial intermediate nucleus (sensory) and the lateral intermediate nucleus (vegetative, sympathetic) (Fig. 2). Between the anterior and posterior horns in the sacral segments (S II - S IV) there are parasympathetic nuclei.
Figure: 2. White matter pathways (1-12) and the location of the gray matter nuclei (13-17) in the spinal cord; cross section (diagram): 1 - thin beam; 2 - wedge-shaped bundle; 3 - lateral cortical-spinal path; 4 - red-nuclear-spinal path; 5 - lateral spinal thalamic path; 6 - roof-spinal path; 7 - anterior spinothalamic path; 8 - posterior spinal path; 9 - anterior spinal path; 10 - reticulospinal fibers; 11 - predoor-spinal path; 12 - anterior cortical-spinal path; 13 - own core; 14 - thoracic nucleus; 15 - medial intermediate nucleus; 16 - lateral intermediate nucleus; 17 - motor nuclei of the anterior horn.
The anterior horn contains 5 motor nuclei (anteromedial, anterolateral, posteromedial, posterolateral, central), as well as motor nuclei of the accessory and phrenic nerves. One segment contains about 3 thousand motoneurons.
In the motor nuclei there are: large motor neurons for the pyramidal pathways, small ones for the extrapyramidal pathways and gamma motor neurons for the reticular pathways.
Thanks to the connections between the motor nuclei, the following are established:
- the center of gravity;
- consistency of movements of the trunk and limbs;
- coordination of movements of the right and left extremities when walking and running.
The bulk of the gray matter is scattered cells ( cellulae disseminatae) related to the spinal cord's own apparatus.
Gray matter of the spinal cord, substantia grisea (see fig.,), consists mainly of the bodies of nerve cells with their processes that do not have a myelin sheath. In addition to them, in the gray matter there are processes of those nerve cells that are located in other parts of the spinal cord and brain, neuroglia, as well as blood vessels and the accompanying connective tissue.
In the gray matter, two lateral parts are distinguished, located in both halves of the spinal cord, and the transverse part connecting them in the form of a narrow bridge - ... It continues into the lateral parts, occupying their middle, as lateral intermediate (gray) substance, substantia (grisea) intermedia lateralis.
In the middle sections of the central intermediate gray matter, there is a very narrow cavity - central canal, canalis centralis... At different levels of the spinal cord, its lumen on a horizontal section has a different size and shape: in the region of the cervical and lumbar thickenings - oval, and in the chest - round with a diameter of up to 0.1 mm. In adults, the canal cavity can be overgrown in some areas. The central canal stretches throughout the entire spinal cord, passing at the top into the cavity of the IV ventricle. Below, in the region of the cerebral cone, the central canal is expanded and its diameter reaches 1 mm on average; this section of the central channel was named end ventricle, ventriculus terminalis.
The tissue surrounding the central canal of the spinal cord and consisting mainly of neuroglia and a small number of neurons with their fibers is called central gelatinous substance, substantia gelatinosa centralis.
The central intermediate (gray) substance surrounding the central channel is divided into two parts. One part is located in front of the canal and is adjacent to the white commissure that connects the anterior cords of both halves of the spinal cord. Another part lies behind the canal. Posterior to the central intermediate (gray) substance, directly adjacent to the posterior median septum, is located .
Each of the lateral parts of the gray matter forms three protrusions: a more thickened anterior, narrower posterior, and between them a small lateral protrusion, which is not expressed at all levels of the spinal cord. The lateral protrusion is particularly clearly visible in the lower cervical segments and in the upper thoracic segments of the spinal cord.
The protrusions throughout the spinal cord form gray pillars, columnae griseae... Each of them on a cross section of the spinal cord is named horns, cornu(see fig.,). Distinguish front pillar, columna ventralis, in cross section - front horn, cornu ventrale, back pillar, columna dorsalis (back horn, cornu dorsale)and lateral pillar, columna lateralis (lateral horn, cornu laterale).
The anterior horn is much wider but shorter than the posterior one and does not reach the periphery of the spinal cord, while the posterior horn, which is narrower and longer, reaches the outer surface of the brain.
In the hind horn, one can discern the top of the rear horn, apex cornus dorsalis, - the narrowest part of the dorsal part of the posterior horn, surrounding the head of the posterior horn, caputcornusdorsaliswhich goes into neck of the posterior horn, cervix cornus dorsalis, and that, in turn, into the widest part of the rear horn - base of the posterior horn, basiscornusdorsalis (see fig.).
The apex of the posterior horn is bordered by an area rich in neuroglia, with a large number of nerve cells, which is called gelatinous substance, substantia gelatinosa.
Nerve cells in the gray matter form clusters - nuclei, or centers, of the spinal cord, which have their own constant topography (Fig. 883).
1.In front pillar motor nuclei lie, whose cells send their axons to the anterior roots of the spinal cord:
- anterolateral nucleus, nucleus ventrolateralis, which has two parts: the upper, lying in the segments C IV –C VIII, and the lower, located in the segments L II –S I;
- anterior medial nucleus, nucleus ventromedialis, often also represented by two parts: upper in С II –L IV and lower in S II –Со I; less often these parts do not have a break in the segments (L V –S I);
- posterolateral nucleus, nucleus dorsolateralis, is divided into two parts: the larger upper one in С V –С VIII and the lower one in L III –S II;
- posterolateral nucleus, nucleus retrodorsolateralis, lies posterior to the previous one. It is represented by two small clusters of cells in C VIII –Th I and S I –S III;
- posteromedial nucleus, nucleusdorsomedialis, represented by a small upper part lying in the upper cervical segment C I, and the lower one - in the segments Th I –S II;
- central nucleus, nucleuscentralis, more often located in the segments Th I –L III, but may have an additional part in S I –S V;
- the nucleus of the accessory nerve, nucleusn. accessorii, usually limited to segments C I –C VI;
- phrenic nerve nucleus,nucleus n. phrenici, occurs in segments C IV –C VII;
- lumbar dorsal nucleus,nucleus lumbodorsalis, lies in segments L III - S I.
2.In back post sensitive cores lie:
- gelatinous substance, substantia gelatinosa, has, in cross-section, the form of a half moon, bordering the apex of the posterior horn;
- own nucleus of the posterior horn, nucleus proprius cornus posterioris(BNA), located in its central part, occupies almost the entire area and extends along the entire posterior column (C I –Co I);
- secondary visceral substance, substantia visceralis secundaria, lies somewhat dorsal to the central intermediate (gray) substance.
3. Side post contains the following kernels:
- chest column [chest nucleus], \u200b\u200bcolumna thoracica, is limited by the segments Th I –L II and is located on the medial side of the base of the posterior horn, therefore some authors attribute it to the nuclei of the latter;
- central intermediate (gray) substance, substantia (grisea) intermedia centralis, localized in the segments Th I –L III, in the central part of the lateral horn, almost reaching the central canal;
- lateral intermediate (gray) substance, substantia (grisea) intermedialateralis, lies lateral to the previous nucleus, occupying the protrusion of the lateral horn and extending to the segments Th I –L III;
- sacral parasympathetic nuclei,nuclei parasympathici sacrales, occupy segments S II –S IV, located somewhat ahead of the previous one.
In the lower cervical and upper thoracic segments of the spinal cord, in the angle between the lateral horn and the lateral edge of the posterior horn, the gray matter in the form of processes penetrates into the white matter, forming a reticular structure - reticular formation, formatio reticularis, the spinal cord, in the loops of which the white matter is located.
The location of the anterior and posterior horns corresponds to the anterior and posterior lateral grooves of the spinal cord. This correspondence between the horns and grooves determines the topography of the white matter in cross sections: its division into anterior, posterior, and lateral white matter cords.
