Nervous system. spinal cord

The human central nervous system controls the activities of the body and is divided into several sections. The brain sends and receives signals from the body and, after processing them, has information about the processes. The nervous system is divided into the autonomic and somatic nervous systems.

Differences between the autonomic and somatic nervous systems

Somatic nervous system is regulated by human consciousness and can control the activity of skeletal muscles. All components of a person’s reaction to external factors are under the control of the brain hemispheres. It provides human sensory and motor reactions, controlling their excitation and inhibition.

Autonomic nervous system controls the peripheral activity of the body and is not controlled by consciousness. It is characterized by autonomy and generalized effects on the body in the complete absence of consciousness. Efferent innervation of internal organs allows it to control metabolic processes in the body and provide trophic processes to skeletal muscles, receptors, skin and internal organs.

Structure of the vegetative system

The autonomic nervous system is controlled by the hypothalamus, which is located in the central nervous system. The autonomic nervous system has a metasegmental structure. Its centers are located in the brain, spinal cord and cerebral cortex. The peripheral sections are formed by trunks, ganglia, and plexuses.

The autonomic nervous system is divided into:

• Sympathetic. Its center is located in the thoracolumbar spinal cord. It is characterized by paravertebral and prevertebral ganglia of the ANS.
• Parasympathetic. Its centers are concentrated in the midbrain and medulla oblongata, the sacral part of the spinal cord. mostly intramural.
• Metasympathetic. Innervates the gastrointestinal tract, blood vessels, and internal organs of the body.

It includes:

1. Nuclei of nerve centers located in the brain and spinal cord.
2. Autonomic ganglia, which are located along the periphery.

Reflex arc of the autonomic nervous system

The reflex arc of the autonomic nervous system consists of three parts:

• sensitive or afferent;
• intercalary or associative;
• effector.

Their interaction occurs without the participation of additional interneurons, as in the reflex arc of the central nervous system.

sensitive link

The sensory unit is located in the spinal ganglion. This ganglion has nerve cells formed in groups, and their control is exercised by the nuclei of the central brain, the cerebral hemispheres and their structures.

The sensory link is represented partially by unipolar cells that have one afferent or afferent axon, and they belong to the spinal or cranial ganglia. As well as the nodes of the vagus nerves, which have a structure similar to spinal cells. This link includes type II Dogel cells, which are components of the autonomic ganglia.

insert link

The intercalary link in the autonomic nervous system serves for transmission through the lower nerve centers, which are the autonomic ganglia, and this is done through synapses. It is located in the lateral horns of the spinal cord. There is no direct connection from the afferent link to the preganglionic neurons for their communication; there is a shortest path from the afferent neuron to the associative one and from it to the preganglionic neuron. Signal transmission to and from afferent neurons in different centers occurs with different numbers of interneurons.

For example, in the arc of the spinal autonomic reflex, there are three synapses between the sensory and effector units, two of which are located in and one in the autonomic node, in which the efferent neuron is located.

Efferent link

The efferent link is represented by effector neurons, which are located in the vegetative nodes. Their axons form unmyelinated fibers, which, together with mixed nerve fibers, innervate internal organs.

The arches are located in the lateral horns.

The structure of the nerve node

A ganglion is a collection of nerve cells that look like nodular extensions about 10 mm thick. According to its structure, the autonomic ganglion is covered on top with a connective tissue capsule, which forms a stroma of loose connective tissue inside the organs. Multipolar neurons, which are built from a rounded nucleus and large nucleoli, consist of one efferent neuron and several diverging afferent neurons. These cells are of the same type as brain cells and are motor cells. They are surrounded by a loose membrane - mantle glia, which creates a constant environment for nervous tissue and ensures the full functioning of nerve cells.

The autonomic ganglion has a diffuse arrangement of nerve cells and many processes, dendrites and axons.

The spinal ganglion has nerve cells that are arranged in groups, and their arrangement has a determined order.

Autonomic nerve ganglia are divided into:

• Sensory neurons that are located close to the spinal or central region of the brain. The unipolar neurons that make up this ganglion represent an afferent or afferent process. They serve for afferent transmission of impulses, and their neurons form a bifurcation when the processes branch. These processes transmit information from the periphery to the central afferent neuron - this is the peripheral process, the central one - from the body of the neuron to the brain center.
• consist of efferent neurons, and depending on their position they are called paravertebral, prevertebral.

Sympathetic ganglia

Paravertebral chains of ganglia are located along the spinal column in the sympathetic trunks, which run in a long line from the base of the skull to the coccyx.

The prevertebral nerve plexuses are located closer to the internal organs, and their localization is concentrated in front of the aorta. They form the abdominal plexus, which consists of the solar, inferior and superior mesenteric plexuses. They are represented by motor adrenergic and inhibitory cholinergic neurons. Also, communication between neurons is carried out by preganglionic and postganglionic neurons, which use the mediators acetylcholine and norepinephrine.

Intramural ganglia have three types of neurons. Their description was made by the Russian scientist A.S. Dogel, who, while studying the histology of neurons of the autonomic nervous system, identified neurons such as long-axonal efferent cells of the first type, equilateral afferent cells of the second type and associative cells of the third type.

Ganglion receptors

Afferent neurons have a highly specialized function, and their role is to perceive stimuli. Such receptors are mechanoreceptors (response to stretching or pressure), photoreceptors, thermoreceptors, chemoreceptors (responsible for reactions in the body, chemical bonds), nociceptors (the body's response to painful stimuli - damage to the skin, and others).

In the sympathetic trunks, these receptors transmit information through a reflex arc to the central nervous system, which serves as a signal about damage or disturbances in the body, as well as its normal functioning.

Functions of the ganglia

Each ganglion has its own location, blood supply, and its functions are determined by these parameters. The spinal ganglion, which has innervation from the nuclei of the brain, provides direct communication between processes in the body through a reflex arc. These structural components of the spinal cord innervate the glands and smooth muscles of the muscles of the internal organs. Signals arriving along the reflex arc travel slower than in the central nervous system, and they are completely regulated by the autonomic system, which also has a trophic, vasomotor function.

Development of the spinal ganglion.

Development of the dorsal ganglia and ganglia of the autonomic nervous system occurs in parallel with the development of the spinal cord from neural crest cells, which in the form of longitudinal rows lie between the neural tube and the superficial ectoderm. Some neural crest cells migrate towards the abdominal cavity, forming the anlage of the sympathetic and parasympathetic ganglia and the adrenal medulla. That part of the nerve cells that remains on both sides of the neural tube forms the ganglion plates. The latter are segmented, their cellular elements differentiate into neuroblasts and glioblastomas, which turn into neurons and gliocytes of the spinal and paravertebral nodes.

General characteristics of the autonomic (autonomic) nervous system.

The autonomic nervous system is a complex of central and peripheral neural structures that regulate the functional level of homeostasis necessary for an adequate response of all systems. We cannot talk only about neurons of the brain and spinal cord and forget about peripheral neurons . Main functions of the ANS- regulation...

metabolism

digestion

blood circulation

discharge

growth

reproduction

In other words, the object of control is the internal processes occurring in the body. While for the somatic system, the object of control is the processes of interaction of the organism with the external environment. The functions controlled by the ANS are traditionally called autonomic, visceral.

The possibility of conditioned reflex regulation of visceral processes means that the higher parts of the brain can regulate the work of organs innervated by the autonomic nervous system, as well as coordinate their activity in accordance with the current needs of the body.

Morphofunctional characteristics of the sympathetic department.

The sympathetic part of the autonomic nervous system is connected with the middle part of the spinal cord, where the bodies of the first neurons are located, the processes of which end in the nerve nodes of the two sympathetic chains located on either side of the front of the spine. The sympathetic nerve ganglia contains the bodies of second neurons, the processes of which directly innervate the working organs.

The sympathetic nervous system enhances metabolism, increases the excitability of most tissues, mobilizes the body's forces for active activity and carries out an adaptive-trophic function. The parasympathetic nervous system helps restore spent energy reserves and regulates the body’s vital functions during sleep.

11. Morphofunctional characteristics of the parasympathetic department.
The parasympathetic part of the autonomic nervous system is formed by several nerves that arise from the medulla oblongata and from the lower part of the spinal cord. The parasympathetic nodes, where the bodies of the second neurons are located, are located in the organs whose activity they influence. Most organs are innervated by both the sympathetic and parasympathetic nervous systems.

Features of reflex arcs of the sympathetic and parasympathetic departments.

The difference between the sympathetic nervous arcs from parasympathetic: from sympathetic nervous arches preganglionary tract short, since the autonomic ganglion lies closer to the spinal cord, and the postganglionic tract is long.

In the parasympathetic arc, the opposite is true: the preganglionic pathway is long, since the ganglion lies close to the organ or in the organ itself, and the postganglionic pathway is short.

Cerebellar cortex, its layers.

The human cerebellar cortex is represented by three layers: the granular layer (deepest), the Purkinje cell layer and the molecular layer (superficial)

The molecular layer on fresh sections is dotted with small dots (which is where its name comes from). It contains three types of neurons - basket cells, stellate cells and Lugaro cells. The direction of the axons of Lugaro cells is unknown; the axons of basket cells end on the body (soma), and the axons of stellate cells end on the dendrites of Purkinje cells.

Stellate and basket cells of the molecular layer are inhibitory interneurons with endings on Purkinje cells. The projections of basket neurons to Purkinje cells are oriented at right angles to the long axis of the cerebellar layers. These axons are called transverse fibers

The middle layer is formed by Purkinje cells, the number of which in humans is 15 million. These are large neurons, their dendrites branch widely in the molecular layer. The axons of Purkinje cells descend to the cerebellar nuclei, and a small number of them end on the vestibular nuclei. These are the only axons that exit the cerebellum. The organization of the cerebellar cortex is usually considered in relation to the Purkinje cells that form its output.

The lower layer of the cerebellar cortex is called granular because it has a granular appearance in sections. This layer is made up of small granule cells (about 1,000-10,000 million), the axons of which go into the molecular layer. There, the axons divide in a T-shape, sending a branch (parallel fiber) 1-2 mm long in each direction along the surface of the cortex. These branches pass through the dendritic branching areas of other types of cerebellar neurons and form synapses on them. The granular layer also contains larger Golgi cells, the dendrites of which extend over relatively long distances in the molecular layer, and the axons go to the granular cells.

The granular layer is adjacent to the white matter of the cerebellum and contains a large number of interneurons (including Golgi cells and granule cells) about half of all neurons in the brain. Mossy fibers form excitatory synaptic endings in the cerebellar cortex on the dendrites of granule cells (granular cells). Many similar fibers converge on each granular cell. Synaptic endings are collected in the so-called cerebellar glomeruli (glomeruli). They receive inhibitory projections from Golgi cells.

Vitreous body.

The vitreous body is transparent, colorless, elastic, jelly-like. Located behind the lens. Structure. On the anterior surface of the vitreous body there is a depression - the vitreous fossa, corresponding to the lens. The vitreous body is fixed in the region of the posterior pole of the lens, in the flat part of the ciliary body and near the optic nerve head. Throughout the rest of its length it is only adjacent to the internal limiting membrane of the retina. Between the optic disc and the center of the posterior surface of the lens there passes a narrow, downwardly curved vitreous canal, the walls of which are formed by a layer of compacted fibers. In embryos, the vitreous artery passes through this canal.

Functions:

Supportive function (support for other eye structures).

Transmission of light rays to the retina.

Passively participates in accommodation.

Creates favorable conditions for constant intraocular pressure and a stable shape of the eyeball.

Protective function - protects the inner membranes of the eye (retina, ciliary body, lens) from displacement due to injury.

TOPIC: Spinal cord system. Spinal ganglion. Autonomic (autonomic) nervous system

The nervous system is divided into central and peripheral. The central nervous system includes the brain and spinal cord, the peripheral nervous system includes the peripheral nerve ganglia, nerve trunks and nerve endings. Based on functional characteristics, the nervous system is divided into somatic and autonomic. The somatic nervous system innervates the entire body, except for the internal organs, exocrine and endocrine glands and the cardiovascular system. The autonomic nervous system innervates everything except the body.

NERVE TRUNKS consist of nerve myelinated and unmyelinated afferent and efferent fibers; nerves may contain individual neurons and individual nerve ganglia. Nerves contain layers of connective tissue. The layer of loose connective tissue surrounding each nerve fiber is called the endoneurium; surrounding the bundle of nerve fibers is the perineurium, which consists of 5-6 layers of collagen fibers; between the layers there are slit-like cavities lined with neuroepithelium; fluid circulates in these cavities. The entire nerve is surrounded by a layer of connective tissue called the epineurium. The perineurium and epineurium contain blood vessels and nerve nerves.

SENSITIVE NERVE GANGLIA are present in the head region and sensory spinal (ganglion spinalis), or spinal ganglia. SPINAL GANGLIA are located along the dorsal roots of the spinal cord. Anatomically and functionally, the spinal ganglia are closely related to the dorsal and anterior roots and the spinal nerve.

On the outside, the ganglia are covered with a capsule (capsula fibrosa), which consists of dense connective tissue, from which connective tissue layers extend deep into the node, forming its stroma. The dorsal ganglia include sensitive pseudounipolar neurons, from which one common process emerges, which entwines the round body of the neuron several times, then divides into an axon and a dendrite.

The cell bodies of neurons are located along the periphery of the ganglion. They are surrounded by glial cells (gliocyti ganglii), which form a glial sheath around the neuron. Outside the glial sheath, there is a connective tissue sheath around the body of each neuron.

The processes of pseudounipolar neurons are located closer to the center of the ganglion. DENDRITS of neurons are directed as part of the spinal nerves to the periphery and end with receptors. SPINAL

NERVES consist of dendrites of pseudounipolar neurons of the spinal ganglion (sensitive nerve fibers) and the anterior roots of the spinal cord (motor nerve fibers) attached to them. Thus, the spinal nerve is mixed. Most of the nerves in the human body are branches of the spinal nerves.

Axons of PSEUDOUNIPOLAR NEURONS as part of the dorsal roots are directed to the spinal cord. Some of these axons enter the gray matter of the spinal cord and end at synapses on its neurons. Some of them form thin fibers carrying substance P and glutamic acid, i.e. mediators. Thin fibers conduct sensory impulses from the skin (cutaneous sensitivity) and internal organs (visceral sensitivity). Other thicker fibers carry impulses from tendons, joints and skeletal muscles (proprioception). The second part of the axons of the pseudounipolar neurospinal ganglia enters the white matter and forms the gentle (thin) and wedge-shaped fasciculi, within which they are sent to the medulla oblongata and end on the neurons of the nucleus of the gentle fasciculus and the nucleus of the wedge-shaped fasciculus, respectively.

SPINAL CORD (medulla spinalis) is located in the canal of the spinal column. The cross section shows that the spinal cord consists of 2 symmetrical halves (right and left). The boundary between these two halves passes through the posterior connective tissue septum (commissure), the central canal and the anterior notch of the spinal cord. The cross section also shows that the spinal cord consists of gray and white matter. The gray matter (substantia grisea) is located in the central part and resembles the shape of a butterfly or the letter H. The gray matter has posterior horns (cornu posterior), anterior horns (cornu anterior) and lateral horns (cornu lateralis). Between the anterior and posterior horns there is an intermediate zone (zona intermedia). In the center of the gray matter is the central canal of the spinal cord. From a histological point of view, GRAY MATTER consists of neurons, their processes, covered with a membrane, i.e. nerve fibers and neuroglia. All gray matter neurons are multipolar. Among them, cells with weakly branched dendrites (isodendritic neurons), with highly branched dendrites (idiodendritic neurons) and intermediate cells with moderately branched dendrites are distinguished. Conventionally, the gray matter is divided into 10 Rexed plates. The posterior horns are represented by I-V plates, the intermediate zone - VI-VII plates, the anterior horns - VIII-IX plates and the space around the central canal - X plate.

JELLIFICAL SUBSTANCE of the posterior horn (I-IV pl.). In the neurons of this

substance, enkephalin (pain mediator) is produced. Neurons of the I and III plates synthesize metenkephalin and neurotensin, which are capable of inhibiting pain impulses arriving with thin radicular fibers (axons of spinal ganglia neurons) carrying substance P. Neurons of the IV plate produce gamma-aminobutyric acid ( a mediator that inhibits the passage of an impulse through a synapse). Neurons of the gelatinous substance suppress sensory impulses coming from the skin (cutaneous sensitivity) and partly from internal organs (visceral sensitivity), and also partly from joints, muscles and tendons (proprioceptive sensitivity). Neurons associated with the conduction of various sensory impulses are concentrated in certain plates of the spinal cord. Skin and visceral sensitivity are associated with the gelatinous substance (I-IV plates). Partially sensitive, partly proprioceptive impulses pass through the nucleus of the dorsal horn proper (plate IV), and proprioceptive impulses pass through the thoracic nucleus, or Clarke’s nucleus (plate V) and the medial intermediate nucleus (plate VI-VII).

NEURONS OF THE GRAY MATTER OF THE SPINAL CORD are represented by 1) tufted neurons (neurocytus fasciculatus); 2) root neurons (neurocytus radiculatus); 3) internal neurons (neurocytus internus). Tuft and root neurons are formed into nuclei. In addition, some tufted neurons are diffusely scattered in the gray matter.

INTERNAL NEURONS are concentrated in the spongy and gelatinous substance of the dorsal horns and in the nucleus of Cajal, located in the anterior horns (plate VIII), and are diffusely scattered in the dorsal horns and the intermediate zone. On internal neurons, the axons of pseudounipolar cells of the spinal ganglia end in synapses.

The spongy substance of the posterior horn (substantia spongiosa cornu posterior) consists mainly of an interweaving of glial fibers, in the loops of which internal neurons are located. Some scientists call the spongy substance of the dorsal horn the dorsomarginal nucleus (nucleus dorsomarginalis) and believe that the axons of some part of this nucleus join the spinothalamic tract. At the same time, it is generally accepted that the axons of the internal cells of the spongy substance connect the axons of pseudounipolar neurons of the spinal ganglia with neurons of their own half of the spinal cord (associative neurons) or with neurons of the opposite half (commissural neurons).

The gelatinous substance of the posterior horn (substantia gelatinosa cornu posterior) is represented by glial fibers, between which internal neurons are located. All neurons, concentrated in the spongy and gelatinous substance and diffusely scattered, are associative or intercalary in function. These neurons are divided into associative and commissural. Associative neurons are those that connect the axons of the sensory neurons of the spinal ganglia with the dendrites of the neurons of their half of the spinal cord. Commissurals are neurons that connect the axons of neurons in the spinal ganglia with the dendrites of neurons in the opposite half of the spinal cord. Intrinsic neurons of the nucleus of Cajal connect the axons of the pseudounipolar cells of the spinal ganglia with the neurons of the motor nuclei of the anterior horns.

NUCLEI of the nervous system are clusters of nerve cells similar in structure and function. Almost every nucleus of the spinal cord begins in the brain and ends at the caudal end of the spinal cord (stretches in the form of a column).

NUCLEUS CONSISTING OF BUNCHED NEURONS: 1) proper nucleus of the posterior horn (nucleus proprius cornu posterior); 2) thoracic nucleus (nucleus thoracicus); medial nucleus of the intermediate zone (nucleus intermediomedialis). All neurons of these nuclei are multipolar. They are called bundled because their axons, leaving the gray matter of the spinal cord, form bundles (ascending tracts) connecting the spinal cord to the brain. By function, these neurons are associative afferent.

THE OWN NUCLEUS OF THE REAR HORN is located in its middle part. Part of the axons from this nucleus goes to the anterior gray commissure, passes to the opposite half, enters the white matter and forms the anterior (ventral) spinocerebellar tract (tractus spinocerrebillaris ventralis). As part of this pathway, axons in the form of climbing nerve fibers enter the cerebellar cortex. The second part of the axons of the neurons of the nucleus proper forms the spinothalamic tract (tractus spinothalamicus), carrying impulses to the visual thalamus. Thick radicular

fibers (axons of dorsal ganglia neurons) transmitting proprioceptive sensitivity (impulses from muscles, tendons, joints) and thin root fibers carrying impulses from the skin (cutaneous sensitivity) and internal organs (visceral sensitivity).

THE THORACIC NUCLEUS, OR CLARK'S NUCLEUS, is located in the medial part of the base of the dorsal horn. The thickest nerve fibers formed by the axons of neurons of the spinal ganglia approach the nerve cells of Clark's nucleus. Through these fibers, proprioceptive sensitivity (impulses from tendons, joints, skeletal muscles) is transmitted to the thoracic core. The axons of the neurons of this nucleus extend into the white matter of their half and form the posterior, or dorsal spinocerebellar tract (tractus spinocerebellaris dorsalis). The axons of the neurons of the thoracic nucleus in the form of climbing fibers reach the cerebellar cortex.

The MEDIAL INTERMEDIATE NUCLEUS is located in the intermediate zone near the central canal of the spinal cord. The axons of the tufted neurons of this nucleus join the spinocerebellar tract of their half of the spinal cord. In addition, in the medial intermediate nucleus there are neurons containing cholecystokinin, VIP and somatostatin, their axons are directed to the lateral intermediate nucleus. The neurons of the medial intermediate nucleus are approached by thin root fibers (axons of spinal ganglia neurons) that carry mediators: glutamic acid and substance P. Through these fibers, sensitive impulses from internal organs (visceral sensitivity) are transmitted to the neurons of the medial intermediate nucleus. In addition, thick radicular fibers carrying proprioceptive sensitivity approach the medial nucleus of the intermediate zone. Thus, the axons of the tufted neurons of all three nuclei are directed to the cerebellar cortex, and from the nucleus of the dorsal horn proper they are directed to the optic thalamus. From the radicular neurons, the following are formed: 1) the nuclei of the anterior horn, including 5 nuclei; 2) laterally intermediate nucleus (nucleus intermediolateralis).

THE LATERAL INTERMEDIATE NUCLEUS belongs to the autonomic nervous system and is associative-efferent in function and consists of large radicular neurons. The part of the nucleus located at the level of the 1st thoracic (Th1) to the 2nd lumbar (L2) segments, inclusive, belongs to the sympathetic nervous system. The part of the nucleus located caudal to the 1st sacral (S1) segments belongs to the parasympathetic nervous system. The axons of the neurons of the sympathetic division of the lateral intermediate nucleus leave the spinal cord as part of the anterior roots, then separate from these roots and go to the peripheral sympathetic ganglia. The axons of the neurons that make up the parasympathetic division are directed to the intramural ganglia. Neurons of the lateral intermediate nucleus are characterized by high activity of acetylcholinesterase and choline acetyltransferase, which cause the cleavage of neurotransmitters. These neurons are called radicular because their axons leave the spinal cord in the anterior roots in the form of preganglionic myelinated cholinergic nerve fibers. Thin radicular fibers (axons of dorsal ganglia neurons) approach the lateral nucleus of the intermediate zone, carrying glutamic acid as a mediator, fibers from the medial nucleus of the intermediate zone, fibers from internal neurons of the spinal cord.

ROOT NEURONS of the anterior horn are located in 5 nuclei: lateral anterior, lateral posterior, medial anterior, medial posterior and central. The axons of the radicular neurons of these nuclei leave the spinal cord as part of the anterior roots of the spinal cord, which connect with the dendrites of the sensory neurons of the spinal ganglia, resulting in the formation of the spinal nerve. As part of this nerve, the axons of the radicular neurons of the anterior horn are directed to the fibers of skeletal muscle tissue and end in neuromuscular endings (motor plaques). All 5 nuclei of the anterior horns are motor. The radicular neurons of the anterior horn are the largest in the dorsal

brain. They are called radicular because their axons take part in the formation of the anterior roots of the spinal cord. These neurons belong to the somatic nervous system. The axons of internal neurons of the spongy substance, gelatinous substance, nucleus of Cajal, neurons diffusely scattered in the gray matter of the spinal cord, pseudounipolar cells of the spinal ganglia, scattered fasciculate neurons and fibers of descending tracts coming from the brain approach them. Due to this, about 1000 synapses are formed on the body and dendrites of motor neurons.

In the anterior horn, medial and lateral groups of nuclei are distinguished. The lateral nuclei, consisting of radicular neurons, are located only in the region of the cervical and lumbosacral thickenings of the spinal cord. From the neurons of these nuclei, axons are directed to the muscles of the upper and lower extremities. The medial group of nuclei innervates the muscles of the trunk.

Thus, in the gray matter of the spinal cord, 9 main nuclei are distinguished, 3 of them consist of fasciculate neurons (the nucleus of the dorsal horn proper, the thoracic nucleus and the medial intermediate nucleus), 6 consist of radicular neurons (5 nuclei of the anterior horn and the lateral intermediate nucleus). core).

SMALL (SCISSED) BUNCHED NEURONS are scattered in the gray matter of the spinal cord. Their axons leave the gray matter of the spinal cord and form its own tracts. Leaving the gray matter, the axons of these neurons divide into descending and ascending branches, which come into contact with motor neurons of the anterior horn at different levels of the spinal cord. Thus, if an impulse hits only 1 small tufted cell, then it spreads immediately to many motor neurons located in different segments of the spinal cord.

THE WHITE SUBSTANCE OF THE SPINAL CORD (substantia alba) is represented by myelinated and unmyelinated nerve fibers that form the conductive tracts. The white matter of each half of the spinal cord is divided into 3 cords: 1) anterior cord (funiculus anterior), limited by the anterior notch and anterior roots; 2) lateral cord (funiculus lateralis), limited by the anterior and posterior roots of the spinal cord; 3) posterior cord (funiculus dorsalis), limited by the posterior connective tissue septum and dorsal roots.

IN THE ANTERIOR CANDLES there are descending tracts connecting the brain with the spinal cord; in the POSTERIOR CORDS - ascending tracts connecting the spinal cord to the brain; in the LATERAL CANDLES - both descending and ascending paths.

MAIN ASCENDING WAYS 5: 1) gentle bundle (fasciculus gracilis) and 2) wedge-shaped bundle (fasciculus cuneatus) are formed by axons of sensory neurons of the spinal ganglia, pass in the posterior cord and end in the medulla oblongata on the nuclei of the same name (nucleus gracilis and nucleus cuneatus); 3) the anterior spinal cerebellar path (tractus spinocerebellaris ventralis), 4) the posterior spinal cerebellar path (tractus spinocerebellaris dorsalis) and 5) the spinothalamic path (tractus spinothalamicus) pass through the lateral funiculus.

The anterior spinal cerebellar tract is formed by the axons of the nerve cells of the nucleus proper of the posterior horn and the medial nucleus of the intermediate zone, located in the lateral funiculus of the white matter of the spinal cord.

The posterior spinal cerebellar tract is formed by the axons of the neurocytes of the thoracic nucleus, located in the lateral funiculus of the same half of the spinal cord.

The spinothalamic pathway is formed by the axons of the nerve cells of the nucleus proper of the posterior horn, located in the lateral funiculus.

PYRAMID WAYS are the main downward paths. There are two of them: the anterior pyramidal tract and the lateral pyramidal tract. The pyramidal tracts branch off from the great pyramids of the cerebral cortex. Part of the axons of the large pyramids do not cross and form the anterior (ventral) pyramidal pathways. Part of the axons of the pyramidal neurons cross in the medulla oblongata and form the lateral pyramidal pathways. The pyramidal pathways terminate at the motor nuclei of the anterior horns of the gray matter of the spinal cord.

Spinal ganglion of the rabbit (Fig. 112)

On the preparation, rounded nerve cells of the spinal ganglion and the neuroglial cells surrounding them - satellites (satellites) are clearly visible.

To prepare the drug, the material must be taken from young small mammals: guinea pigs, rats, cats,

1 - nucleus of a nerve cell 2 -cytoplasm, 3 - satellite cells, 4 - cells of the connective tissue capsule, 5 - connective tissue cells 6 - sheath of the spinal ganglion

a rabbit. Material taken from a rabbit gives the best results.

A freshly killed animal is opened from the dorsal side. The skin is pushed back and the muscles are removed in such a way as to free the spine. Then a transverse incision is made through the spinal column in the lumbar region. With the left hand, lift the head of the spine and release the spine from the muscles located along the spinal column. Scissors with pointed ends, making two longitudinal

incision, carefully remove the vertebral arches. As a result, the spinal cord opens with the roots extending from it and the paired ganglia associated with the latter. The ganglia should be isolated by cutting the spinal roots. The spinal ganglia isolated in this way are fixed in Zenker's mixture, embedded in paraffin, and sections 5-6 μ thick are made. Sections are stained with alum or iron hematoxylin.

The spinal ganglion consists of sensory nerve cells with processes, neuroglia and connective tissue.

Nerve cells are very large, round in shape; They are usually located in groups. Their protoplasm is fine-grained and homogeneous. The round light nucleus is, as a rule, not in the center of the cell, but somewhat shifted to the edge. It contains little chromatin in the form of individual dark grains scattered throughout the nucleus. The core shell is clearly visible. The nucleus has a round, regular-shaped nucleolus, which stains very intensely.

Around each nerve cell, small round or oval nuclei with a clearly visible nucleolus are visible. These are the nuclei of satellites, i.e., neuroglial cells accompanying the nervous one. In addition, outside the satellites, you can see a thin layer of connective tissue, which, together with the satellites, forms a capsule around each nerve cell. In the connective tissue layer, thin bundles of collagen fibers and spindle-shaped fibroblasts lying between them are visible. Very often, on the preparation, between the nerve cell, on the one hand, and the capsule, on the other, there is an empty space, which is formed due to the fact that the cells are somewhat compressed under the influence of the fixative.

A process extends from each nerve cell, which, writhing repeatedly, forms a complex glomerulus near or around the nerve cell. At some distance from the cell body, the process branches in a T-shape. One of its branches, the dendrite, goes to the periphery of the body, where it is part of various sensory endings. Another branch - the neurite - enters the spinal cord through the posterior spinal root and transmits excitation from the periphery of the body to the central nervous system. The nerve cells of the spinal ganglion belong to pseudounipolar ones, because only one process extends from the cell body, but it very quickly divides into two, one of which functionally corresponds to a neurite, and the other to a dendrite. In a preparation processed in the manner just described, processes extending directly from the nerve cell are not visible, but their branches, especially neurites, are clearly visible. They pass in bundles between groups of nerve cells. On the longitudinal

in section they appear as narrow fibers of a light purple color after staining with alum hematoxylin or light gray after staining with iron hematoxylin. Between them there are elongated neuroglial nuclei of Schwann syncytium, which forms the pulpy shell of the neurite.

Connective tissue surrounds the entire spinal ganglion in the form of a sheath. It consists of densely lying collagen fibers, between which there are fibroblasts (only their elongated nuclei are visible on the preparation). The same connective tissue penetrates the ganglion and forms its stroma; it contains nerve cells. The stroma consists of loose connective tissue, in which process fibroblasts with small round or oval nuclei can be distinguished, as well as thin collagen fibers running in different directions.

You can prepare a preparation specifically to show the convoluted process surrounding the cell. To do this, the spinal ganglion, isolated in the method just described, is treated with silver according to the Lavrentiev method. With this treatment, nerve cells are painted yellow-brown, satellites and connective tissue elements are not visible; Near each cell there is, sometimes repeatedly cut, an unpaired black process extending from the cell body.

Located along the spinal column. Covered with a connective tissue capsule. Partitions go inward from it. Vessels penetrate through them into the spinal node. Nerve fibers are located in the middle part of the node. Myelin fibers predominate.

In the peripheral part of the node, as a rule, pseudo-unipolar sensory nerve cells are located in groups. They constitute 1 sensitive link of the somatic reflex arc. They have a round body, a large nucleus, wide cytoplasm, and well-developed organelles. Around the body there is a layer of glial cells - mantle gliocytes. They constantly support the vital activity of cells. Around them is a thin connective tissue sheath, which contains blood and lymphatic capillaries. This shell performs protective and trophic functions.

The dendrite is part of the peripheral nerve. On the periphery, it forms a sensitive nerve fiber, where it begins with a receptor. Another neuritic process, the axon, runs towards the spinal cord, forming the posterior root, which enters the spinal cord and terminates in the gray matter of the spinal cord. If you delete a node. Sensitivity will suffer if the posterior root is crossed - the same result.

Spinal cord

Meninges of the brain and spinal cord. The brain and spinal cord are covered by three membranes: soft, directly adjacent to the brain tissue, arachnoid and hard, which borders the bone tissue of the skull and spine.

Pia mater directly adjacent to the brain tissue and delimited from it by the marginal glial membrane. In the loose fibrous connective tissue of the membrane there are a large number of blood vessels that feed the brain, numerous nerve fibers, terminal apparatuses and single nerve cells.

Arachnoid represented by a thin layer of loose fibrous connective tissue. Between it and the pia mater lies a network of crossbars, consisting of thin bundles of collagen and thin elastic fibers. This network connects the shells with each other. Between the pia mater, which repeats the relief of the brain tissue, and the arachnoid, passing through the elevated areas without going into the recesses, there is a subarachnoid (subarachnoid) space, permeated with thin collagen and elastic fibers that connect the membranes with each other. The subarachnoid space communicates with the ventricles of the brain and contains cerebrospinal fluid.

Dura mater formed by dense fibrous connective tissue containing many elastic fibers. In the cranial cavity, it is tightly fused with the periosteum. In the spinal canal, the dura mater is delimited from the vertebral periosteum by the epidural space, filled with a layer of loose fibrous connective tissue, which provides it with some mobility. Between the dura mater and the arachnoid membrane is the subdural space. The subdural space contains a small amount of fluid. The membranes on the side of the subdural and subarachnoid space are covered with a layer of flat cells of glial nature.

In the anterior part of the spinal cord, white matter is located and contains nerve fibers that form the spinal cord pathways. The middle part contains gray matter. The halves of the spinal cord are separated in front the median anterior fissure, and behind the posterior connective tissue septum.

In the center of the gray matter is the central canal of the spinal cord. It connects to the ventricles of the brain, is lined with ependyma and is filled with cerebrospinal fluid, which is constantly circulating and being produced.

In gray matter contains nerve cells and their processes (myelinated and unmyelinated nerve fibers) and glial cells. Most nerve cells are located diffusely in the gray matter. They are intercalary and can be associative, commissural, or projection. Some nerve cells are grouped into clusters that are similar in origin and function. They are designated cores gray matter. In the dorsal horns, intermediate zone, medial horns, the neurons of these nuclei are intercalary.

Neurocytes. Cells similar in size, fine structure and functional significance lie in the gray matter in groups called nuclei. Among the neurons of the spinal cord, the following types of cells can be distinguished: radicular cells(neurocytus radiculatus), the neurites of which leave the spinal cord as part of its anterior roots, internal cells(neurocytus interims), the processes of which end in synapses within the gray matter of the spinal cord, and tuft cells(neurocytus funicularis), the axons of which pass through the white matter in separate bundles of fibers, carrying nerve impulses from certain nuclei of the spinal cord to its other segments or to the corresponding parts of the brain, forming pathways. Individual areas of the gray matter of the spinal cord differ significantly from each other in the composition of neurons, nerve fibers and neuroglia.

There are anterior horns, posterior horns, intermediate zone, lateral horns.

In the hind horns allocate spongy layer. It contains a large number of small intercalary neurons. Gelatinous layer(substance) contains glial cells and a small number of intercalated internal neurons. In the middle part of the posterior horns is located own nucleus of the posterior horn, which contains tufted neurons (multipolar). Tufted neurons are cells whose axons extend into the gray matter of the opposite half, penetrate it and enter the lateral cords of the white matter of the spinal cord. They form ascending sensory pathways. At the base of the posterior horn in the inner part is located dorsal or thoracic nucleus (Clark's nucleus). Contains tufted neurons, the axons of which extend into the white matter of the same half of the spinal cord.

In the intermediate zone allocate medial nucleus. Contains fascicle neurons, the axons of which also extend into the lateral cords of the white matter, the same halves of the spinal cord, and form ascending pathways that carry afferent information from the periphery to the center. Lateral nucleus contains radicular neurons. These nuclei are the spinal centers of autonomic reflex arcs, mainly sympathetic. The axons of these cells emerge from the gray matter of the spinal cord and participate in the formation of the anterior roots of the spinal cord.

In the dorsal horns and the medial part of the intermediate zone there are intercalary neurons that constitute the second intercalary link of the somatic reflex arc.

Front horns contain large nuclei in which large multipolar root neurons are located. They form medial nuclei, which are equally well developed throughout the spinal cord. These cells and nuclei innervate the skeletal muscle tissue of the body. Lateral nuclei better developed in the cervical and lumbar regions. They innervate the muscles of the limbs. The axons of motor neurons extend from the anterior horns beyond the spinal cord and form the anterior roots of the spinal cord. They are part of a mixed peripheral nerve and end at a neuromuscular synapse on a skeletal muscle fiber. The motor neurons of the anterior horns constitute the third effector link of the somatic reflex arc.

Own apparatus of the spinal cord. In the gray matter, especially in the dorsal horns and intermediate zone, a large number of tufted neurons are located diffusely. The axons of these cells extend into the white matter and immediately at the border with the gray matter they divide into 2 processes in a T-shape. One goes up. And the other one is down. They then return back to the gray matter in the anterior horns and end in the motor neuron nuclei. These cells form their own apparatus of the spinal cord. They provide communication, the ability to transmit information within the adjacent 4 segments of the spinal cord. This explains the synchronous response of the muscle group.

White matter contains mainly myelinated nerve fibers. They go in bundles and form the pathways of the spinal cord. They provide a link between the spinal cord and the brain. The bundles are separated by glial septa. At the same time, they distinguish ascending paths that carry afferent information from the spinal cord to the brain. These pathways are located in the posterior cords of the white matter and the peripheral parts of the lateral cords. Descending pathways these are effector pathways, they carry information from the brain to the periphery. They are located in the anterior cords of the white matter and in the inner part of the lateral cords.

Regeneration.

Gray matter regenerates very poorly. White matter is able to regenerate, but this process is very long. If the body of the nerve cell is preserved. Then the fibers regenerate.