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Structure and function of the spinal ganglion. Characteristics of pseudounipolar neurocytes

(with the participation of a number of other tissues) forms the nervous system, which ensures the regulation of all life processes in the body and its interaction with the external environment.

Anatomically, the nervous system is divided into central and peripheral. The central includes the brain and spinal cord, the peripheral unites nerve nodes, nerves and nerve endings.

The nervous system develops from neural tube And ganglionic plate. The brain and sensory organs differentiate from the cranial part of the neural tube. From the trunk part of the neural tube - the spinal cord, from the ganglion plate the spinal and vegetative nodes and chromaffin tissue of the body are formed.

Nerve nodes (ganglia)

Nerve ganglia, or ganglia, are collections of neurons outside the central nervous system. Highlight sensitive And vegetative nerve nodes.

Sensitive nerve ganglia lie along the dorsal roots of the spinal cord and along the cranial nerves. Afferent neurons in the spiral and vestibular ganglion are bipolar, in the remaining sensory ganglia - pseudounipolar.

Spinal ganglion (spinal ganglion)

The spinal ganglion has a fusiform shape, surrounded by a capsule of dense connective tissue. From the capsule, thin layers of connective tissue penetrate into the parenchyma of the node, in which blood vessels are located.

Neurons The spinal ganglion is characterized by a large spherical body and a light nucleus with a clearly visible nucleolus. Cells are located in groups, mainly along the periphery of the organ. The center of the spinal ganglion consists mainly of neuronal processes and thin layers of endoneurium bearing vessels. The dendrites of nerve cells go as part of the sensitive part of the mixed spinal nerves to the periphery and end there with receptors. The axons collectively form the dorsal roots, which carry nerve impulses to the spinal cord or medulla oblongata.

In the spinal ganglia of higher vertebrates and humans, bipolar neurons become pseudounipolar. One process extends from the body of the pseudounipolar neuron, which wraps around the cell many times and often forms a ball. This process divides in a T-shape into afferent (dendritic) and efferent (axonal) branches.

The dendrites and axons of cells in the node and beyond are covered with myelin sheaths made of neurolemmocytes. The body of each nerve cell in the spinal ganglion is surrounded by a layer of flattened oligodendroglial cells, which are called mantle gliocytes, or ganglion gliocytes, or satellite cells. They are located around the body of the neuron and have small round nuclei. On the outside, the glial membrane of the neuron is covered with a thin fibrous connective tissue membrane. The cells of this membrane are distinguished by the oval shape of their nuclei.

Neurons of the spinal ganglia contain neurotransmitters such as acetylcholine, glutamic acid, substance P.

Autonomous (vegetative) nodes

Autonomic nerve nodes are located:

  • along the spine (paravertebral ganglia);
  • in front of the spine (prevertebral ganglia);
  • in the wall of organs - the heart, bronchi, digestive tract, bladder (intramural ganglia);
  • near the surface of these organs.

Myelinated preganglionic fibers containing processes of neurons of the central nervous system approach the vegetative nodes.

According to their functional characteristics and localization, the autonomic nerve ganglia are divided into sympathetic And parasympathetic.

Most internal organs have double autonomic innervation, i.e. receives postganglionic fibers from cells located in both the sympathetic and parasympathetic nodes. The reactions mediated by their neurons often have opposite directions (for example, sympathetic stimulation increases cardiac activity, and parasympathetic stimulation inhibits it).

General plan of the building vegetative nodes are similar. On the outside, the node is covered with a thin connective tissue capsule. Autonomic ganglia contain multipolar neurons, which are characterized by an irregularly shaped, eccentrically located nucleus. Multinucleated and polyploid neurons are common.

Each neuron and its processes are surrounded by a shell of glial satellite cells - mantle gliocytes. The outer surface of the glial membrane is covered with a basement membrane, outside of which there is a thin connective tissue membrane.

Intramural nerve ganglia internal organs and associated pathways, due to their high autonomy, complexity of organization and characteristics of mediator exchange, are sometimes distinguished as independent metasympathetic department of the autonomic nervous system.

In intramural nodes by Russian histologist A.S. Dogel. Three types of neurons have been described:

  1. long axonal efferent cells type I;
  2. equiprocess afferent cells type II;
  3. association cells type III.

Long axon efferent neurons ( Dogel cells type I) - numerous and large neurons with short dendrites and a long axon, which is directed beyond the node to the working organ, where it forms motor or secretory endings.

Equilateral afferent neurons ( Dogel cells type II) have long dendrites and an axon extending beyond a given node to neighboring ones. These cells are included as a receptor link in the local reflex arcs, which close without the nerve impulse entering the central nervous system.

Association neurons ( Dogel cells type III) are local interneurons that connect several type I and II cells with their processes.

The neurons of the autonomic nerve ganglia, like the spinal ganglia, are of ectodermal origin and develop from neural crest cells.

Peripheral nerves

Nerves, or nerve trunks, connect the nerve centers of the brain and spinal cord with receptors and working organs, or with nerve ganglia. Nerves are formed by bundles of nerve fibers, which are united by connective tissue membranes.

Most nerves are mixed, i.e. include afferent and efferent nerve fibers.

Nerve fiber bundles contain both myelinated and unmyelinated fibers. The diameter of the fibers and the ratio between myelinated and unmyelinated nerve fibers are not the same in different nerves.

A cross section of a nerve shows sections of the axial cylinders of nerve fibers and the glial sheaths covering them. Some nerves contain single nerve cells and small ganglia.

Between the nerve fibers in the nerve bundle there are thin layers of loose fibrous tissue - endoneurium. There are few cells in it, reticular fibers predominate, and small blood vessels pass through.

Individual bundles of nerve fibers are surrounded perineurium. The perineurium consists of alternating layers of densely arranged cells and thin collagen fibers oriented along the nerve.

Outer sheath of the nerve trunk - epineurium- is a dense fibrous tissue, rich in fibroblasts, macrophages and fat cells. Contains blood and lymphatic vessels, sensory nerve endings.

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

Development. The source of development of the nervous system is the neural tube and the neural crest (ganglionic plate). The brain and cephalic ganglia develop from the cephalic end of the neural tube and the neural crest, and the spinal cord develops from the caudal end. Neurons and neuroglia of the spinal ganglia and peripheral ganglia of the autonomic nervous system are formed from the neural crest.

As a result of the proliferation of neural tube cells, its lateral surfaces thicken, in which 3 layers are formed: 1) ependymal, 2) mantle (mantle), 3) marginal veil. At this time, the neural tube distinguishes between dorsal (wing) and ventral plates and anterior, posterior and lateral columns.

From ependymal layer ependymoglial epithelium lining the central canal develops from raincoat- gray matter, from edge veil- white matter of the spinal cord.

Neuroblasts of the anterior columns differentiate into motor neurons, the axons of which form the anterior roots. Neuroblasts of the dorsal columns differentiate into associative efferent neurons, the axons of which extend into the white matter and go to the brain.

Neural crest neuroblasts migrate to the localization of the autonomic nerve and spinal ganglia and differentiate into neurocytes of these structures. The axons of sensory neurons of the spinal ganglia form the dorsal roots of the spinal cord, which are directed into its gray and white matter.

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

Sensitive nerve nodes. There are sensitive spinal (ganglion spinalis), or spinal, ganglia in the head region.


Spinal ganglia. They are located along the dorsal roots of the spinal cord. Anatomically and functionally closely related to the posterior 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 arises, which several times entwines the round body of the neuron, which is then divided 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. Dendrites neurons are sent 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 sent 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 (proprioceptive sensation).

The second part of the axons of pseudounipolar neurons of the spinal ganglia enters the white matter and forms the gentle (thin) and wedge-shaped fascicles, 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). The spinal cord 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 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. Gray matter(substantia grisea) is located in the central part and resembles the shape of a butterfly or the letter H. The gray matter contains 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 sheathed processes, 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, the space around the central canal - X plate.

Jelly-like substance localized in plates I-IV. Enkephalin (a pain mediator) is produced in the neurons of this substance. Neurons of plates I and III 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 plate IV produce GABA (a mediator that inhibits the passage of an impulse through the synapse). The neurocytes of the gelatinous substance suppress sensory impulses coming from the skin (cutaneous sensitivity) and partly from the internal organs (visceral sensitivity), and also partly from the 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 Clark'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 (neurocytes 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.

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

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).

Gelatinous substance of the dorsal 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.

Cores The nervous system is a collection 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).

Nuclei consisting of bundled neurons: 1) own nucleus of the posterior horn (nucleus proprius cornu posterior); 2) thoracic nucleus (nucleus thoracicus); 3) medial intermediate nucleus (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.

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

Thoracic nucleus, or Clark's nucleus, located in the medial part of the base of the posterior 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.

Medial intermediate nucleus 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, the medial intermediate nucleus contains neurons containing cholecystokinin, vasoactive intestinal peptide (VIP) and somatostatin; their axons go to the lateral intermediate nucleus. Thin radicular fibers (axons of spinal ganglia neurons) approach the neurons of the medial intermediate nucleus and 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 root fibers carrying proprioceptive sensitivity approach the medial nucleus of the intermediate zone.

Thus, the axons of the tufted neurons of all 3 nuclei are directed to the cerebellar cortex, and from the nucleus of the dorsal horn proper they are directed to the optic thalamus.

From radicular neurons are formed: 1) nuclei of the anterior horn, including 5 nuclei; 2) lateral intermediate nucleus (nucleus intermediolateralis).

Lateral intermediate nucleus belongs to the autonomic nervous system and is associative-efferent in function, consisting of large radicular neurons. The part of the nucleus located at the level of the 1st thoracic (Th 1) to the 2nd lumbar (L 2) segments, inclusive, belongs to the sympathetic nervous system. The part of the nucleus located cranial to Th l and caudal to the 1st sacral (S 1) 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 them 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 breakdown of neurotransmitters.

These neurons are called radicular because their axons leave the spinal cord as part of the anterior roots in the form of preganglionic myelinated cholinergic nerve fibers. The lateral nucleus of the intermediate zone is approached by thin root fibers (axons of spinal ganglion neurons), carrying glutamic acid as a mediator, volunae from the medial nucleus of the intermediate zone, and volunae from internal neurons of the spinal cord.

Root neurons The anterior horn is 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 root neurons of the anterior horn are the largest in the spinal cord. 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. 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. Medial nuclei innervate the muscles of the trunk.

Thus, in the gray matter of the spinal cord, 9 main nuclei are distinguished, 3 of which consist of fasciculate neurons (the nucleus of the dorsal horn proper, the thoracic nucleus and the medial intermediate nucleus), 6 - of radicular neurons (5 nuclei of the anterior horn and 1 lateral intermediate nucleus). core).

Small (scattered) tufted neurons 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 horns at different levels of the spinal cord. Thus, if an impulse hits only one small tuft cell, it immediately spreads to many motor neurons located in different segments of the spinal cord.

White matter of the spinal cord(substantia alba). It is represented by myelinated and unmyelinated nerve fibers that form pathways. 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 cords there are descending tracts connecting the brain to the spinal cord; in the posterior cords - ascending tracts connecting the spinal cord to the brain; in the lateral funiculi- both descending and ascending paths.

There are 5 main ascending paths:

1) a gentle bundle (fasciculus gracilis) and 2) a wedge-shaped bundle (fasciculus cuneatus) are formed by the 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) anterior spinocerebellar tract (tractus spinocerebellaris ventralis),

4) the posterior spinocerebellar tract (tractus spinocerebellaris dorsalis) and 5) the spinothalamic tract (tractus spinothalamicus) pass in the lateral cord.

Anterior spinocerebellar tract formed by the axons of nerve cells of the nucleus of the dorsal horn and the medial nucleus of the intermediate zone, located in the lateral cord of the white matter of the spinal cord.

Posterior spinocerebellar tract formed by the axons of neurocytes of the thoracic nucleus, located in the lateral cord of the same half of the spinal cord.

Spinothalamic tract formed by the axons of nerve cells of the nucleus of the dorsal horn, located in the lateral cord.

Pyramid paths- these are the main descending paths. There are 2 such pathways: anterior pyramidal and lateral pyramidal. The pyramidal tracts arise from the greater pyramids of the cerebral cortex. Some of the axons of the large pyramids go without crossing and form the anterior (ventral) pyramidal muti. Some of the axons of pyramidal neurons cross in the medulla oblongata and form the lateral pyramidal tracts. The pyramidal tracts end at the motor nuclei of the anterior horns of the gray matter of the spinal cord.


Concept of the peripheral nervous system. Ganglia and nerves. General principles of the course and branching of nerves. Spinal ganglia and nerves. Cervical, thoracic, lumbar, sacral and caudal nerves. Cranial ganglia and nerves.

The peripheral nervous system is the part of the nervous system that lies outside the brain and spinal cord. Its main functions are:

1. Conduction of nerve impulses from all receptors into the central nervous system (segmental apparatus of the spinal cord and into the corresponding formations of the brain).

2. Discharge of nerve impulses from the central structures of the brain and spinal cord (regulating and controlling) to all organs and tissues.

The peripheral nervous system includes ganglia and nerves with their roots, plexuses and endings.

A ganglion (ganglion, nerve ganglion) is a cluster of neuron bodies on the periphery, which is surrounded by a connective tissue sheath. In lower animals they form the central part of the nervous system. Ganglia can strengthen or weaken the conduction of nerve impulses, as well as distribute nerve impulses to a large number of neurons. They are located along the nerves.

Classification of ganglia. Depending on their function, they are divided into affector (sensitive) and effector (motor), and depending on topography - into spinal, cranial and autonomic.

A nerve (nervus) is a group of nerve fibers that are enclosed in a common connective tissue frame. In the nerve there are epineurium, dressing the nerve from the surface, perineurium, dressing bundles of fibers, and endoneurium, dressing each nerve fiber individually. Blood and lymphatic vessels pass through the epineurium, arterioles and capillaries pass through the perineurium, and blood capillaries of a predominantly longitudinal direction pass through the endoneurium. In addition, under the peri- and endoneurium there are perineural lymphatic spaces that communicate with the subdural and subarachnoid spaces of the brain. As for the innervation of the nerve sheaths, it is carried out by branches extending from this nerve.

Biomechanical properties of the nerve determined by its connective tissue components. For small deformations, the main factors determining the strength of the nerve are the elastic and collagen fibers of the epineurium, which act as shock absorbers and take on most of the deforming load. In case of large deformations and rupture, the main factors determining its strength are the perineurium and endoneurium.

Shape of nerves. Nerves come in different thicknesses and lengths. Large diameter nerves are called nerve trunks(trunci), and of small diameter - nerve branches(rami). In large nerves, fibers along the course of the nerve can pass from one bundle to another, therefore the thickness of the bundles and the number of nerve fibers in them are not the same throughout. The nerve fibers that form a nerve do not always run straight through it; they often have a zigzag course, which is a structural reserve of extensibility when moving the torso and limbs. In addition, there are also species features passage of nerve fibers. For example, the axillary nerve, in a dog- the nerve has plexuses along its entire length, and at the cat's only in the proximal part.

Classification of nerves. Depending on the function performed, the nerves are sensitive, motor and mixed, and depending on the topography - spinal, cranial and autonomic. Mostly nerves are mixed, i.e. they contain both sensory and motor fibers. Afferent fibers are divided into pain, tactile, thermal, and efferent fibers are divided into motor, secretory and trophic

Age-related changes in nerves. With age, the number of nerve fibers in the nerves decreases, their diameter decreases, especially myelin fibers, and connective tissue sheaths grow. The epineurium increases most strongly, mainly due to the proliferation of lipocytes. The perineurium and endoneurium thicken due to predominantly collagen fibers, which is also associated with aging, but of connective tissue (Slutsky L.I., 1969). The decrease in the number of nerve fibers is also associated with age-related changes in the blood supply to the nerves. With thickening of the vascular wall, a slight expansion of the lumen of the artery is observed, but the rate of increase in the thickness of its wall exceeds the increase in its lumen, which leads to disruption of the hemodynamics of the nerve. With age, the tortuosity of the fibers decreases: the ability of the nerves to compensate for physiological stretching and minor pathological damage that occurs in the process of life decreases.

GENERAL PRINCIPLES OF THE COURSE AND BRANCHING OF NERVES

1. All large nerves (nerve trunks) go together with blood vessels, forming neurovascular bundles surrounded by common connective tissue sheaths. Each such bundle usually consists of a nerve, an artery, two veins and several lymphatic vessels.

2. All nerves go to organs along the shortest path, i.e. mainline. If organs move during intrauterine development, the nerve lengthens accordingly and follows them.

3. According to the principle of bilateral symmetry, all nerves are paired (right and left) and run symmetrically from the brain and spinal cord, which lies along the center line of the body.

4. According to the principle of segmentation, nerves extend from those segments of the brain that correspond to the rudiments of muscles - myotomes, from which these muscles originate. Muscles formed from several myotomes have several sources of innervation and from them one can trace the “former segmentation”.

5. Nerves enter bones together with blood vessels through nutrient openings at the places where muscle tendons and ligaments are attached; into skeletal muscles - mainly from the inner surface, in the region of the geometric center of the muscle; Nerves often enter internal organs from a concave surface, forming, together with the vessels, the gates of the organ.

6. The division of nerves into branches occurs in three types:

A) trunk type- the nerve gives off lateral branches to all organs located along its route;

b) dichotomous type- the nerve is divided into two equal nerves;

V) loose type- the nerve splits into several small branches.

7. Along their course, nerves can exchange their nerve fibers with nearby nerves and then intertwine with each other to form plexuses ( plexus). Nerve plexuses are formed in connection with the differentiation of tissues and organs. They are complex compounds where exchange occurs between nerve fibers, bundles, nerves. Plexus provides polysegmental innervation and can distribute, replace and even restore nerve impulses. According to the principle of topography, they can be external or internal. TO internal include plexuses in the central nervous system, nerve trunks (axillary nerve, facial nerve), nerves and in the walls of internal organs (terminal). External plexuses are formed by branches of the spinal nerves (cervical, brachial, lumbar, sacral, caudal).

SPINAL GANGLIA AND NERVES

The central nervous system communicates with the peripheral nervous system through nerve roots. The roots of the spinal nerves have a significant difference in their structure from the nerves. They have almost no epineurium and perineurium, so the bundles of nerve fibers are surrounded only by the endoneurium, which originates from the pia mater. Therefore, the amount of connective tissue in the roots of the s/m nerves is significantly less than in the nerves and ranges from 0.06% to 3.6% of the total cross-sectional area.

Formation of spinal nerves (nervi spinales ) . All spinal nerves are formed by two roots (rootlets): dorsal and ventral. The dorsal (radix dorsalis) is usually classified as sensitive, due to the location of the spinal ganglion (ganglion spinalis), which is formed by sensory neurons, and the ventral (radix ventralis) is classified as motor. In this case, the nerve fibers of both roots initially run straight, then unite into a common nerve trunk, where they intertwine and even form plexuses inside the bundles.

Only in lancelet and lamprey dorsal and ventral roots go to the periphery by independent nerves. Beginning with sharks (cartilaginous fish), due to symmetrical myomeria and the formation of vertebrae, both roots of the spinal nerves connect with each other into a common nerve trunk.

Two branches depart from the common mixed nerve trunk before exiting the spinal canal:

1) branch to the membranes of the spinal cord (r.meningeus);

2) the white connecting branch (r.communicans albus) (preganglionic fiber), which goes to the sympathetic ganglion (ganglia trunci symphathici) and receives from it the gray connecting branch (r.communicans griseus) (postganglionic fiber), which then merges with the common nerve trunk.

Then the trunk is divided into dorsal (n.dorsales) and ventral nerves (n.ventrales), according to the division of the trunk muscles into dorsal and ventral muscle cords.

The dorsal spinal nerves innervate the supravertebral muscle group and skin, and the ventral nerves innervate the muscles of the infravertebral muscle group, as well as the muscles of the walls of the cavities and limbs. Each dorsal and ventral s/m nerve is divided into lateral and medial branches to innervate the superficial and deep layers of muscles and organs.

Classification of spinal nerves

All s/m nerves are topographically divided into cervical, thoracic, lumbar, sacral and caudal. The number of pairs of s/m nerves, except for the cervical and caudal ones, corresponds to the number of vertebrae.

1) Cervical s/m ( n. cervicales ) 8 pairs emerge through the intervertebral foramen and are divided into dorsal and ventral branches. Both the dorsal and ventral cervical s/m nerves form plexuses with each other.

a ) Dorsal branches(r.dorsalis) innervate the semispinous muscle of the head, spinous muscle of the neck, longissimus muscle of the neck, plaster muscle, trapezoid muscle..., skin. Individual branches are characterized by a certain course and zone of innervation, and therefore receive a special name.

These include greater occipital nerve (n. occipitalis major), going to the occipito-atlas, atlanto-axial joints, their muscles and the skin of this area.

In addition, the dorsal branches of the 3, 4, 5, 6 cervical s/m nerves form the deep cervical plexus

b) Ventral branches(r.ventralis) innervate the long muscle of the head, long muscle of the neck, and sternomandibular muscle. Special branches include:

The great auricular nerve (n. auricularis magnus) innervates the muscles of the auricle and the skin of the base of the head;

The phrenic nerve (n. phrenicus) goes into the chest cavity and branches in the diaphragm;

The supraclavicular nerve (n.supraclavicularis) branches in the skin of the shoulder joint, shoulder and dewlap.

In addition, the ventral branches of the 5, 6, 7, 8 cervical s/m nerves and the ventral branches of 1, 2 thoracic s/m nerves are involved in the formation of the brachial plexus (plexus brachialis). The brachial plexus is located on the medial surface of the scapula, ventral to the scalene muscle, and 8 main nerves emerge from it to innervate the thoracic limb.

2) Thoracic s/m nerves ( n. thoracici ) , the number of their pairs corresponds to the number of vertebrae of a certain animal species. The thoracic s/m nerves are also divided into dorsal and ventral branches.

a) Dorsal branches innervate the extensors of the spinal column, dorsal dentate cranial m., rhomboid m., trapezoid m., skin….

b) Ventral branches 1 and 2 are involved in the formation of the brachial plexus, and the rest are called intercostal nerves (n.intercostals) and go along with the vessels of the same name in the intercostal spaces.

3) Lumbar s/m nerves ( n . lumbales ) . Their number corresponds to the number of lumbar vertebrae.

A) Dorsal branches The lumbar s/m nerves innervate the lumbar extensors, gluteal muscles, and the skin, and from them the cranial gluteal cutaneous nerves (n.cutanei glutei craniales) arise.

b) Ventral the branches form the lumbar plexus (plexus lumbalis). 6 main nerves emerge from it to innervate the abdominal walls, external reproductive organs and the pelvic limb.

4) Sacral s/m nerves ( n . sacrales ) . Their number corresponds to the number of sacral vertebrae.

A) Dorsal branches innervate the extensors of the hip joint, the skin of the croup and the middle gluteal cutaneous nerves (n.cutanei glutei media) originate from them.

b) The ventral branches form the sacral plexus (plexus sacralis). 5 main nerves emerge from it to innervate the pelvic limb and organs of the pelvic cavity.

5) Caudal s/m nerves ( n. caudales ) , in the amount of 5-6 pairs, form the caudal plexus. The dorsal (ventral) branches of the caudal s/m nerves unite to form the dorsal (ventral) nerve of the tail, which goes to the tip of the tail.

CRANIAL GANGLIA AND NERVES

There are 12 pairs of cranial nerves (n.cranii) in domestic animals. They are formed primitively, i.e. their dorsal and ventral roots retain their independence. Some of the cranial nerves - 5, 7, 8, 9 and 10 pairs contain ganglia, therefore, they are homologous to the dorsal spinal nerves, and the nerves without ganglia - the 3, 4, 6 and 12 pairs are homologous to the ventral s/m nerves. As for the 1st and 2nd pairs, in their origin they stand apart from all other nerves and represent “a part of the brain extended to the periphery.”

Classification of cranial nerves. Depending on the origin, structure and objects of innervation, cranial nerves are divided into three groups: sensory, motor and mixed.

Sensory cranial nerves their development is associated with the development of the receptor apparatus and the appearance of sensory organs. These include 1, 2 and 8 pairs.

1) 1 pair - olfactory nerves ( n. n. olfactorii , 15-20 threads) are formed by processes of receptor cells of the olfactory epithelium of the mucous membrane of the nasal cavity. They penetrate through the perforated plate of the ethmoid bone into the olfactory bulbs and go to the nuclei of the olfactory brain.

2) 2nd pair - optic nerve ( n. opticus ) formed by processes of retinal ganglion cells, which form a single thick trunk. After entering the cranial cavity through the optic foramen, some of the fibers of the right and left optic nerves partially intersect and continue into the visual tracts, heading to the nuclei of the diencephalon.

3) 8 pair - vestibulocochlear the nerve (n.vestibulocochlearis) is formed by two roots (vestibular and cochlear), on each of them there are ganglia (vestibular - g.Vestibulare and cochlear - g.cochleare). Ganglia are formed by the bodies of sensory neurons, the dendrites of which perceive vestibular and auditory signals from the environment. The fibers of the vestibular root pass through the internal auditory canal and end at the bottom of the fourth cerebral ventricle, and the fibers of the cochlear root go with the facial nerve and form the trapezoid body of the medulla oblongata.

Motor cranial nerves formed by motor nerve fibers, which are processes of cells of the motor nuclei of the brain stem. These include 3, 4, 6, 11 and 12 pairs. Pairs 3, 4 and 6 innervate the muscles originating from the three pre-auricular segments (premaxillary, submandibular, sublingual).

1) 3 pair - oculomotor nerve ( n. oculomotorius ) comes out from the nuclei of the midbrain and appears in the orbit through the orbital fissure. It innervates most of the muscles of the eye and is divided into two branches: dorsal and ventral. On the ventral branch there is a parasympathetic ciliary ganglion, through which there is a path to the sphincter of the pupil.

2) 4th pair - trochlear nerve(n.trochlearis) emerges from the nuclei of the midbrain and appears in the orbit through the orbital fissure. It innervates the dorsal oblique muscle of the eye and provides rotation of the eyes.

3) 6th pair - abducens nerve ( n. abducens ) comes out from the nuclei of the medulla oblongata and appears in the orbit through the orbital fissure. It innervates the lateral rectus muscle of the eye and the retractor of the eyeball, thanks to which the closure of the eyelids becomes possible.

4) 11th pair - accessory nerve ( n. accessorius ) formed by cranial and spinal roots. The s/m roots originate from the first six cervical segments, and the cranial roots originate from the medulla oblongata. Connecting, the roots emerge as a common trunk through a torn hole. However, the cranial fibers from the medulla oblongata are woven into the 10th pair (vagus nerve) and form the recurrent nerve in it. Spinal fibers go to the brachiocephalic m., trapezius m. and sternomandibular m. (The 11th pair, as an independent nerve, separated from the vagus only in mammals.)

5) 12th pair - hypoglossal nerve ( n. hypoglossus ) exits from the nuclei of the medulla oblongata through the sublingual foramen. It connects with the first cervical s/m nerve and forms a loop of the hypoglossal nerve. Innervates the muscles of the tongue and hyoid bone, which are formed from the subbranchial myotome. It became a cranial nerve only in reptiles.

Mixed cranial nerves . Their development is closely related to the formation of the gill apparatus and the primary segmentation of the head. These include 5, 7, 9 and 10 pairs.

1) 5 pair - trigeminal nerve ( n. trigeminus ) . Based on comparative anatomical and embryological data, the 5th pair is like the dorsal roots for the 3rd and 4th pairs of cranial nerves. It is formed by two roots (dorsal and ventral), which extend from the nuclei of the midbrain and hindbrain. The trigeminal ganglion is located on the dorsal sensory root - g.trigeminale (Gasserov). Distal from the ganglion, both roots unite into a common trunk in the cranial cavity, then the trunk is divided into three nerves: orbital (n.ophthalmicus), maxillary (n.maxillaris) and mandibular (n.mandibularis). This nerve is the main sensory nerve for the teeth, skin and mucous membranes of the head area, as well as the motor nerve for the masticatory muscles.

2) 7th pair - facial nerve ( n..facialis) Based on comparative anatomical and embryological data, the 7th pair is like the dorsal root of the 6th pair of cranial nerves. It emerges from the nuclei of the medulla oblongata and leaves the cranial cavity through the facial canal of the petrous bone. In the facial canal on the nerve lies the geniculate ganglion - g.geniculi. This nerve is the main sensory nerve for the tongue (taste buds), as well as the motor nerve for all facial muscles. It contains parasympathetic fibers for the salivary glands.

3) 9 pair - glossopharyngeal nerve ( n. glossopharyngeus ) . It emerges from the nuclei of the medulla oblongata with 4-5 roots through the ragged foramen. Upon exiting the cranial cavity, it has a petrosal ganglion - g.proximale, formed by the bodies of sensory neurons. The nerve of general sensitivity for the root of the tongue, velum and pharynx, as well as the motor nerve for the pharyngeal dilators. It contains parasympathetic nerve fibers for the salivary glands. It does not have a corresponding motor root due to the reduction of the postauricular myotomes.

4) 10 para-vagus nerve ( n. vagus ). It leaves the nuclei (sensitive, motor, parasympathetic) of the medulla oblongata with 10-15 roots through the foramen lacerum. Upon exiting the cranial cavity, it has a jugular ganglion - g. proximale, and when connected to the sympathetic trunk - nodular ganglion - g. distale. The vagus nerve is complex in composition, provides parasympathetic innervation to the organs of the neck, chest and abdominal cavities, and also contains sensory and motor fibers (muscles of the pharynx and larynx). It belongs to the autonomic nervous system.

Thus, along the course of the cranial nerves (5, 7, 8, 9, 10) there are cranial ganglia, which are formed by the bodies of sensory neurons. These same nerves contain motor (formerly visceral) fibers that served the gill muscles in the distant past. In mammals, they innervate derivatives of the gill muscles: chewing muscles (5th pair); facial m. (7 pair); pharyngeal dilator (9 pairs); pharyngeal constrictors, laryngeal muscles, smooth muscles of internal organs (10 pair); trapezoidal and brachiocephalic m. (11 pair).



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, pseudounipolar 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 membrane that contains blood and lymphatic capillaries. This shell performs protective and trophic functions.

The dendrite is part of the peripheral nerve. At the periphery it forms a sensitive nerve fiber where the receptor begins. Another neuritic axon extends towards the spinal cord, forming the dorsal root, which enters the spinal cord and ends 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. The loose fibrous connective tissue of the membrane contains a large number of blood vessels that supply the brain, numerous nerve fibers, terminal apparatus 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 follows the relief of brain tissue, and the arachnoid, which runs along elevated areas without going into the recesses, there is a subarachnoid (subarachnoid) space, permeated with thin collagen and elastic fibers that connect the membranes to 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, an intermediate zone, and lateral horns.

In the hind horns allocate spongy layer. It contains a large number of small interneurons. Gelatinous layer(substance) contains glial cells and a small number of interneurons. In the middle part of the posterior horns is located dorsal horn nucleus, 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 fascicle 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 run as 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 diffusely located. 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 spinal cord apparatus. 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 communication between the spinal cord and parts of the brain. The bundles are separated by glial septa. At the same time, they distinguish ascending paths, which 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 capable of regenerating, but this process is very long. If the nerve cell body is preserved. Then the fibers regenerate.

DEVELOPMENT.

1. Neural tube – CNS – Gray and white substance Vegetative

2. Neural crest - Peripheral. – Ganglion system

nervous nerves and and

nervous system somatic

endings of nervous s-ma

Table of derivatives and classification of the nervous system

During development, neural crest cells are distributed along the sides of the neural tube and therefore further develop in the lateral sections.

At the same time, neuroglial cells and sensitive pseudounipolar neurons are released from the neural crest cells on the sides of the NT, the axons of which grow into the gray matter of the spinal cord.

Some neural crest cells quickly move deep into the body and penetrate the wall of developing organs, or between them. These are the ganglia of the autonomic nervous system.

STRUCTURE OF GRAY AND WHITE MATTER

SPINAL CORD

The spinal cord consists of symmetrical halves. The gray matter is connected by gray commissures, and the white matter is divided in front by a fissure and in the back by a connective tissue septum.

The gray matter in the middle of the SC resembles the letter “H” and it is distinguished: -

Dorsal - posterior

Lateral – lateral

Ventral - anterior horns.

In the center runs the spinal canal, filled with cerebrospinal fluid. Its walls are lined with ependymocytes.

Gray matter consists of neurocyte bodies surrounded by astrocytes and a dense network of their processes. The axons of neurocytes are barely covered with myelin, and the dendrites are without myelin.

Among the cells are:

Radicular - axons are part of the anterior root

Internal - processes located within the spinal cord

Tufted - shaped bundles of white matter and go up or down.

The bodies of these cells lie in groups and are called nuclei.

In the hind horns(from the periphery to the center) distinguish between the spongy layer, the gelatinous substance, the own nucleus and the thoracic nucleus

All neurocytes of the dorsal horns are associative in function.

The spongy layer contains small neurons and large gliocytes.

Gelatinous substance – neuroglia also predominate.

The nucleus proper lies in the center of the dorsal horn. This is a collection of cell bodies of large neurons, the axons of which pass to the other side and rise up into the brain.

The cells of the thoracic nucleus are also large. Their axons go to the cerebellum in the white matter on the same side of the spinal cord.

In the area lateral horns There are medial and lateral nuclei involved in the sympathetic division of the autonomic system. These are association neurons of the autonomic nervous system.

Cells of the medial nucleus transmit information to the cerebellum, and the lateral nucleus transmits information to the periphery as part of the anterior roots for innervation of internal organs.

Front horns the widest and contain large cells from 100 to 140 microns, which lie in the form of five nuclei. These are motor neurons. Their processes form the anterior roots of the spinal cord, which control skeletal muscles. Therefore, the nuclei are called motor.

There are medial and lateral groups of nuclei.

Medial – innervated muscles of the back and torso

Lateral - innervated muscles of the limbs and therefore developed in the cervical and lumbar regions.

White matter– contains fibers and does not contain tet neurocytes at all. Fibers are processes of cells partially covered with a membrane. The processes are grouped into bundles by function and therefore distinguish bundles or pathways that carry information from sensory, motor or interneurons. Sensory pathways are afferent pathways, motor pathways are efferent pathways. Examples: sensitive pathways – tender and wedge-bundle of Flexig-Gowers; pyramidal path - motor - pyramidal path.

On the outside, the white matter of the spinal cord is covered with a layer of collagen and elastic fibers and glychocytes. This is the pia mater. Many vessels from it penetrate into the spinal cord.

SPINAL GANGLION (sensory ganglia)

This is a thickening along the dorsal roots of the spinal cord.

The body is formed by a dense connecting capsule, from which partitions with vessels extend inward.

The ganglion is a cluster of bodies of pseudounisexual senses. neurocytes, which lie more on the periphery, closer to the vessels of the capsule.

The body of each neuron is surrounded by oligodendrocytes, which are called mantle cells. As always their functions:

Nutritious;

Protective

Support

Demarcating.

Neurocytes- these are modified biopolar cells, the axons of which enter the SC, forming its dorsal roots. Their dendrites bring here information from receptors from the periphery.

Note that in supporting and protecting the peripheral nervous system, connective tissue plays an active role compared to the central nervous system. This also applies to the connective tissue sheaths of all peripheral nerves, which include:

Epineurium – outer membrane;

Perineurium – separates bundles of fibers (pathways);

Endoneurium – isolates individual processes.

The spinal cord and spinal ganglion, forming a chain of neurons, are responsible for the innate unconditioned reflexes of the body.

Somatic reflex arc

Three-neuron reflex arc-

This is a chain of three neurons:

Sens.pseudo-unit.N.SG

Associate.n.pos.horns SM

Engine n. front horns SM

Receptor – dendrite – body

Two-neuron somatic reflex arc- this is a chain of two neurocytes: sensory.

engine

From the previous description, exclude the interneuron

Now remember the classic example, when touching a hot object we withdraw our hand - this is an example of a somatic reflex arc, but look at this finger - it turned red, and this is the work of the autonomic nervous system, it turns out that the sensitive neuron transmitted information to both the somatic and autonomic nervous system system.

It can only be like this:

VEGETATIVE REFLECTOR ARC (sympathetic department)

Receptor – dendrite…..etc.

In the autonomic reflex arc, pre- and postganglionic fibers are distinguished. Pre are myelinated (white), and postganglionic are non-myelinated (gray).

AUTONOMIC GANGLION

1) arrangement of cells

2) multipolar cells

3) all 4 types (MYTH) (sympathetic)

This is an accumulation of neurocyte bodies, which, unlike the spinal ganglion, are multipolar and can be different in function - motor, associative, sensory and secretory.

The autonomic ganglion consists of:

According to Dogel: 1). double long axon

2). equiprotrusion.sense.

3). equal length ass.

Based on the presence of cells of different functions, the reflex arc can be closed within the ganglia themselves, without going beyond the boundaries of the autonomic nervous system, for which it received the name autonomous, independent.

PRINCIPAL STRUCTURE OF THE VEGETATIVE

NERVOUS SYSTEM.

Sympathetic department:

Associated nuclei of the lateral horns of the SM

Chains of pre- and paravertebral ganglia along the spine

Parasympathetic department:

Center – 3,7,9,10 craniocerebral.

Periphery. – intramural plexuses inside organs – intramural ganglia.