Nerve nodes - what is it and what do they consist of?

Ganglia (otherwise - nerve nodes) - a collection of special cells. It consists of bodies, dendrites and axons. They, in turn, refer to nerve cells. Also, nerve nodes include accessory glial cells. Their task is to create a support for neurons. As a rule, the nerve ganglia are covered with connective tissues. These clusters are found not only in vertebrates, but also in some invertebrate animals. Connecting together, the nerve nodes create complex structural systems. An example is the structure of a chain or plexus. Further in the article in more detail it will be described what are the nerve gangs, how is the interaction between them. In addition, a classification and description of the main species will be provided.

Vertebrate animals

Ganglia, existing in these individuals, have some peculiarities. So, they do not enter the central nervous system. Some call them basal ganglia. However, the most correct term is the term "core". Nerve nodes and the system that they form, are the connecting elements between the components of the nervous system. They pass the impulses and control the operation of certain internal organs.

Classification

All ganglia are divided into several types. Consider the basic. The concept of "spinal ganglion" combines sensory (afferent) elements. The second type is autonomous elements. They are located in the corresponding (autonomous) nervous system. The main view is basal. Their components are neural nodes that are in white matter. It is contained in the brain. The work of neurons is to regulate some functions of the body, as well as to assist in the performance of nervous processes. There is also a vegetative type. It represents one knot of nerves. This element refers to the autonomic nervous system. These nodes pass along the spine. Vegetative ganglia are very small. Their size can be less than a millimeter, and the largest ones are commensurable with peas. The task of vegetative ganglia is the regulation of the functioning of internal organs and the distribution of impulses.

Comparison with the term "plexus"

In books, the term "plexus" is often found. It can be taken for a synonym for the word "ganglia". However, specific wafers are called plexuses. They are present in a certain amount in a closed area. A ganglion is the area of connection of synaptic contacts.

Nervous system

From the point of view of anatomy, two types are distinguished. The first is called the central nervous system. Here you can include the brain and the dorsal. The second type is a set of nodes, nerve endings and nerves themselves. This complex is called the peripheral nervous system.

The nervous system is formed by a neural tube and a ganglionic plate. To the cranial part of the first are the brain with the sense organs, to the trunk part - the spinal cord. Ganglionic plate forms spinal, vegetative nodes and chromaffin tissue. Nervous tissue exists as a component of the system that regulates the corresponding processes of the body.

General information

Nerve nodes are a union of nerve cells that go beyond the boundaries of the central nervous system. There are vegetative and sensitive species. The latter are located next to the roots of the spinal cord and cranial nerves. In shape, the spinal node resembles a spindle. Surrounded by a shell of connective tissue. It also penetrates into the unit itself, while retaining the blood vessels. Nerve cells located in the spinal cord are light, large in size, their nuclei are easily distinguishable. Neurons form groups. The components of the center of the spinal node are the processes of nerve cells and the layer of endoneurium. Scions-dendrites begin in the sensitive zone of the spinal nerves, and end in the peripheral part where their receptors are located. A rare case is the conversion of bipolar neurons into pseudo-unipolar neurons. This happens during their maturation. Out of the pseudo-unipolar neuron, there is an outgrowth that wraps the cell. It is delineated into afferent, another name "dendritic", and efferent, otherwise - axonal, parts.

Dendrites and axons

These structures cover the myelin sheaths, of which the neurolematocytes are components. Nerve cells of the spinal node are surrounded by oligodendrogli cells, which have such names as mantle gliocytes, sodium glialocytes, and also satellite cells. These elements have very small round nuclei. In addition, the envelope of these cells is surrounded by a capsule of connective tissue. Its components differ from others by oval-shaped nuclei. Biologically active substances contained in nerve cells of the spinal node are acetylcholine, glutamic acid, substance P.

Vegetative, or autonomous, structures

Autonomous nerve nodes are located in several places. First, near the spine (there are paravertebral structures). Secondly, in front of the spine (prevertebral). In addition, autonomous nodes are sometimes found in the walls of organs. For example, in the heart, bronchus and bladder. Such ganglia are called intramural. Another species is near the surface of the organs. Preganglionic nerve fibers are connected with autonomous structures . They have processes of neurons from the central nervous system. Vegetative clusters are divided into two types: sympathetic and parasympathetic. Almost all organs receive postganglionic fibers from cells that can be in both types of vegetative structures. But the impact that neurons have is different, depending on the type of clusters. So, the sympathetic action can strengthen the work of the heart, whereas the parasympathetic effect slows it down.

Structure

Regardless of the type of autonomous node, their structure almost completely coincides. Each structure is covered by a sheath of connective tissue. In the autonomic nodes there are special neurons called "multipolar". They are distinguished by an unusual shape, as well as the location of the nucleus. There are neurons with several nuclei and cells with an increased number of chromosomes. The neuronal elements and their processes are enclosed in a capsule, of which glial cells are satellites. They are called mantle gliocytes. On the upper layer of this shell is a membrane surrounded by a connective tissue.

Intramural structures

These neurons, together with the conducting pathways, can constitute a metasympathetic part of the autonomic nervous system. According to the histologist Dogel, among the intramural types of structures, cells of three varieties are distinguished. The first include long-type efferent elements of type I. These cells have large neurons, in which the dendrites are long, and the axon is short. Equal afferent nerve components are characterized by long and dendrites, and axons. And associative neurons connect the cells of the first two types.

Peripheral system

The task of nerves is to connect the nerve centers of the spinal cord, the brain and the nerve structures. Elements of the system interact through connective tissue. Nerve centers are the areas responsible for processing information. Almost all the structures under consideration consist of both afferent fibers and efferent fibers. A set of fibers, which is, in fact, a nerve, can contain not only structures protected by an electrically insulating myelin sheath. They are present and those that do not have such a "cover". In addition, nerve fibers are separated by a layer of connective tissue. It is characterized by looseness and fibrousness. This layer is called endoneurium. It contains a small number of cells, the bulk of which are collagenic reticular fibers. In this tissue are small blood vessels. Some bundles with nerve fibers surround a layer of other connective tissue - perineurium. Its components are sequentially located cells and fibers of collagen. The capsule, enveloping the entire nerve trunk (it is called epineurium), is formed from connective tissue. It, in turn, is enriched with fibroblast cells, macrophages and fat components. It contains blood vessels with nerve endings.