GANGLION

From Big Medical Encyclopedia

GANGLION (ganglia nerve knots) — the accumulations of nervous cells surrounded with connecting fabric and cells of a glia, located on the course of peripheral nerves.

Distinguish G. of a vegetative and somatic nervous system. Share of the autonomic nervous system on sympathetic and parasympathetic and contain bodies of postganglionic neurons. To of a somatic nervous system are presented by spinal nodes and G. of the sensitive and mixed cranial nerves containing bodies of sensitive neurons and originative to sensitive portions of spinal and cranial nerves.

The embryology

the Rudiment of spinal and vegetative nodes is a ganglious plate. It is formed at an embryo in those departments of a neurotubule which border on an ectoderm. At a germ of the person on 14 — the 16th day of development the ganglious plate is located on a dorsal surface of the become isolated neurotubule. Then it is split on all length, both of its half move ventrally and in the form of neural folds lie between a neurotubule and a superficial ectoderm. Further according to segments of the dorsal party of a germ in neural folds there are centers of proliferation of cellular elements; these sites are thickened, stand apart and turn into spinal nodes. From a ganglious plate develop also sensitive a ganglion At, the VII—X pairs of cranial nerves, similar to spinal ganglions. The formative nervous cells, neuroblasts creating spinal ganglions represent bipolar cells, i.e. have two shoots departing from opposite poles of a cell. The bipolar form of sensitive neurons at adult mammals and the person remains only in sensory cells preddverno-ulit a kovy nerve, predoor and spiral gangliyev. In the others, both spinal, and cranial sensitive nodes, shoots of bipolar nervous cells in the course of their growth and development approach and merge in most cases in one general shoot (processus communis). On this sign sensitive neurocytes (neurons) are called pseudo-unipolar (neurocytus pseudounipolaris), is more rare protoneurons, emphasizing antiquity of their origin. Spinal nodes and nodes of century of N of page differ in a developmental character and structures of neurons. Development and morphology vegetative gangliyev — see. Autonomic nervous system .

Anatomy

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Histology

Fig. 1. Atypical sensitive neuron of a spinal node. Sharply expressed «okonchatost» in a nervous cell at tabes: 1 — fenestrated structures; 2 — an axon (across Doynikov).

Spinal ganglions are covered outside with a connective tissue cover which passes into a cover of back roots. The stroma of nodes is formed by connecting fabric with circulatory and limf, vessels. Each nervous cell (neurocytus ganglii spinalis) is separated from surrounding connecting fabric by a cover capsule; much less often in one capsule there is a colony of nervous cells densely adjacent to each other. The periblast of the capsule is formed by the fibrous connecting fabric containing reticulin and prekollagenovy fibers. The inner surface of the capsule is covered by flat endothelial cells. Between the capsule and a body of a nervous cell there are small cellular elements of a star-shaped or spindle-shaped form, the called gliotsitam (gliocytus ganglii spinalis) or satellites, trabant, mantle cells. They represent elements of a neuroglia, similar to lemmocytes (schwannian cells) of peripheral nerves or oligodendroglyocites of c. N of page. The general shoot beginning an aksonny hillock (colliculus axonis) departs from a body of a mature cell; then it forms several curls (glomerulus processus subcapsularis) which are located about a body of a cell under the capsule and called by an initial ball. At various neurons (large, average and small) the ball has the different complexity of a structure which is expressed in the unequal number of curls. After escaping of the capsule the axon becomes covered by a pulpy cover and on nek-rum distance from a body of a cell was divided into two branches, forming on site divisions of T - or a Y-shaped figure. One of these branches leaves r a peripheral nerve and represents the sensitive fiber forming a receptor in appropriate authority, and another comes through a back root to a spinal cord. The body of sensitive neuron — a pirenofor (the part of cytoplasm containing a kernel) — has the spherical, oval or pear-shaped shape. Distinguish large neurons from 52 to 110 nanometers in size, average — from 32 to 50 nanometers, small — from 12 to 30 nanometers. Neurons of the average size make 40 — 45% of all cells, small — 35 — 40%, and large — 15 — 20%. Neurons in gangliya of different spinal nerves are various in size. So, in cervical and lumbar nodes neurons are larger, than in others. There is an opinion that the size of a cellular body depends on length of a peripheral shoot and the area of the site innervated by it; there is also a nek-swarm a compliance between the size of a body surface of animals and the size of sensitive neurons. E.g., among fishes the largest neurons were found at the moon fish (Mola mola) having a big body surface. In spinal nodes of the person and mammals atypical neurons meet, besides. Carry the «fenestrated» cells of Kakhal which are characterized by existence of loop-shaped structures on the periphery of a cellular body and axon (fig. 1) in which loops there is always a significant amount of satellites to them; the «shaggy» cells [S. Ramone-and-Kakhal, de F. de Castro, etc.] supplied with the additional short shoots departing from a body of a cell and terminating under the capsule; cells with the long shoots supplied with kolbovidny thickenings. The listed forms of neurons and their numerous versions are not characteristic of healthy young people.

Fig. 2. Atypical sensitive neuron of a spinal node with multiple shoots and thickenings on their ends (it is specified by shooters) at rheumatic heart disease.

The age and the postponed diseases affect structure of spinal ganglions — in them appears considerably bigger, than at healthy, amount of various atypical neurons, in particular with the additional shoots supplied with kolbovidny thickenings as, e.g., at rheumatic heart disease (fig. 2), stenocardia, etc. Clinical observations, and also pilot studies on animals showed that sensitive neurons of spinal nodes react much quicker the intensive growth of additional shoots on various endogenous and exogenous harm, than motor somatic or vegetative neurons. This ability of sensitive neurons sometimes is expressed considerably. In cases hron, irritations again formed shoots can be twisted (in the form of winding) around a body of own or next neuron, reminding a cocoon. Sensitive neurons of spinal nodes, as well as other types of nervous cells, have a kernel, various organellas and inclusions in cytoplasm (see. Nervous cell ). Thus, distinctive property of sensitive neurons spinal and nodes of cranial nerves is their bright morfol, the reactivity which is expressed in variability of their structural components. It is provided with a high level of protein synthesis and various active agents and testifies to their functional mobility.

The physiology

In physiology the term «ganglion» is applied to designation of several types of functionally various nervous educations.

At backboneless G. play the same role, as c. N of page at vertebrata, being the highest coordination centers of somatic and vegetative functions. In an evolutionary row from worms to cephalopod mollusks and arthropod G., processing all information on a condition of surrounding and internal environment, reach high degree of the organization. This circumstance, and also simplicity of anatomic preparation, rather big sizes of bodies of nervous cells, possibility of introduction in som of neurons under direct direct vision at the same time of several microelectrodes made G. of invertebrates a popular object neyrofiziol, experiments. On neurons of roundworms, oktapod, a decapod, Castropoda and cephalopod mollusks by methods of an electrophoresis, direct measurement of ion activity and a voltage clamp conduct researches of mechanisms of generation of potentials and process of synoptic transfer of excitement and braking, often impracticable on the majority of neurons of mammals. Despite evolutionary distinctions, the main elektrofiziol, constants and neyrofiziol, mechanisms of work of neurons are in many respects identical at invertebrates and the highest vertebrate animals. Therefore researches G., have invertebrates obshchefiziol. value.

At vertebrata somatosensory cranial and spinal G. are functionally same. They contain bodies and proximal parts of shoots of the afferent neurons transferring an impulsation from peripheral receptors in c. N of page. In somatosensory G. there are no synoptic switchings, efferent neurons and fibers. So, spinal G.' neurons at a toad are characterized by the following the main elektrofiziol, parameters: specific resistance — 2,25 kOhm/cm 2 for depolarizing and 4,03 kOhm/cm 2 for the hyper polarizing current and with a specific capacity of 1,07 mkf/cm 2 . Full entrance resistance of neurons of somatosensory G. is significantly lower, than the corresponding parameter of axons therefore at a high-frequency afferent impulsation (to 100 impulses in 1 sec.) carrying out excitement can be blocked at the level of a body of a cell. In this case action potentials, though are not registered from a body of a cell, continue to be carried out from a peripheral nerve to a back root and remain even after an extirpation of bodies of nervous cells on condition of an intaktnost of T-shaped branchings of axons. Therefore, excitement som of neurons of somatosensory G. for momentum transfer from peripheral receptors to a spinal cord is not obligatory. This feature for the first time appears in an evolutionary row at tailless amphibians.

Vegetative G. of vertebrata in the functional plan can be divided on sympathetic and parasympathetic. In all vegetative G. there is a synoptic switching from preganglionic fibers to postganglionic neurons. In most cases synoptic transfer is carried out in the chemical way by means of acetylcholine (see. Mediators ). In parasympathetic tsiliarny G. of birds electric momentum transfer by means of so-called potentials of connection, or potentials of communication is found. Electric transfer of excitement through the same synapse is possible in two directions; in the course of ontogenesis it forms after chemical. Functional value of electric transfer is not clear yet. In sympathetic G. of amphibians a small amount of synapses with chemical transfer of not cholinergic nature is revealed. In response to strong single irritation of preganglionic fibers of sympathetic G. in a postganglionic nerve first of all there is an early negative wave (O-wave) caused by exciting postsynaptic potentials (VPSP) at activation of N-holinoretseptorov of postganglionic neurons. Brake postsynaptic potential (TPSP) arising in postganglionic neurons under the influence of the catecholamines allocated by chromaffin cells in response to activation of their m-holinoretseptorov creates the positive wave following 0 wave (P-wave). The late negative wave (PO-wave) reflects VPSP of postganglionic neurons at activation of their m-holinoretseptorov. Completes process a long late negative wave (DPO-wave) arising owing to summation of VPSP of not cholinergic nature in postganglionic neurons. In normal conditions at height of the O-wave at achievement of VPSP of size 8 — 25 mV there is an extending potential of excitement with an amplitude of 55 — 96 mV, lasting 1,5 — 3,0 ms, accompanied with a wave of after hyperpolarization. The last significantly masks waves of P and PO. At height of after hyperpolarization excitability decreases (the period of a refrakternost) therefore usually the frequency of categories of postganglionic neurons does not exceed 20 — 30 impulses in 1 sec. On the main elektrofiziol. to characteristics vegetative G.' neurons are identical to the majority of neurons of c. N of the village of Neyrofiziol. feature of neurons of vegetative G. is lack of true spontaneous activity at a deafferentation. Among pre-and postganglionic neurons neurons of groups B and C on Gasser's classification — Erlangera, based on elektrofiziol, characteristics prevail nerve fibrils (see). Preganglionic fibers extensively branch therefore the irritation of one preganglionic branch leads to emergence of VPSP in many neurons of several G. (a phenomenon of animation). In turn on each postganglionic neuron the bombway of many preganglionic neurons differing on a threshold of stimulation and speed of carrying out (a phenomenon of convergence) terminates. Conditionally the measure of convergence can be considered the attitude of amount of postganglionic neurons towards amount of preganglionic nerve fibrils. In all vegetative G. it more unit (except for a tsiliarny ganglion of birds). This relation increases in an evolutionary row, reaching the person of size 100:1 in sympathetic G. The animation and convergence providing space summations) nervous impulses, in combination with temporary summation are a basis of the integrating function G. during the processing of a centrifugal and peripheral impulsation. Through all vegetative G. there pass afferent ways which bodies of neurons lie in spinal G. For the lower mesenteric G., a celiac texture and some intramural parasympathetic G. existence of true peripheral reflexes is proved. The afferent fibers which are carrying out excitement with a small speed (apprx. 0,3 m/s), enter G. as a part of postganglionic nerves and terminate on postganglionic neurons. In vegetative G. the terminations of afferent fibers are found. The last inform c. N of page about the changes happening in G. functional chemical.

Pathology

In a wedge, practice most often meets ganglionitis (see), called also by a simpato-ganglionitis — the disease connected with defeat gangliyev a sympathetic trunk. Defeat of several nodes is defined as a polyganglionitis, or truncitis (see).

Spinal a ganglion are quite often involved in patol, process at radiculitises (see).

See also Nervous system .

Short anatomic characteristic nervous gangliyev (nodes)

Bibliography Brodsky V. Ya. Trophicity of a cell, M., 1966, bibliogr.; Dogel A. S. A structure of spinal nodes and cells at mammals, Notes imp. Academician of sciences, t. 5, No. 4, page 1, 1897; Milokhin A. A. A sensitive innervation of vegetative neurons, new about idea of the structural organization of a vegetative ganglion, L., 1967; bibliogr.; P about with to and G. I., Zhirnov A. A. N. and Saddler island and M. V. Comparative histochemistry of sensory cells spinal gangliyev and motor cells of a spinal cord, Dokl. Academy of Sciences of the USSR, it is new, gray., t. 96, JSfc 4, page 821, 1953; With to about to V. I. Fiziologiya vegetative gangliyev, L., 1970, bibliogr.; B. M. Obshchaya's falcons Ganges-liologiya, Perm, 1943, bibliogr.; I r y-gin H. E. and Yarygin V. N. Pathological and adaptive changes of neuron, M., 1973; de Castro F. Sensory ganglia of the cranial and spinal nerves, normal and pathological, in book: Cytol a. cell. path, of the nervous system, ed. by W. Penfield, v. 1, p. 91, N. Y., 1932, bibliogr.; Clara M. Das Nervensystem des Menschen, Lpz., 1959.

E. A. Vorobyova, E. P. Kononova; A. V. Kibyakov, V. N. Uranov (physical.), E. K. Plechkova (embr., gist.).

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