Ganglia (in other words - nerve nodes) are a collection of special cells. It consists of bodies, dendrites and axons. They, in turn, refer to nerve cells. Also, nerve nodes include auxiliary glial cells. Their task is to create a support for neurons. As a rule, the nerve ganglia are covered with connective tissues. These accumulations are found not only in vertebrates, but also in some invertebrates. Connecting with each other, the nerve nodes create complex structural systems. An example would be chain or plex structures. Further in the article, it will be described in more detail what nerve nodes are, how the interaction between them occurs. In addition, a classification and description of the main species will be given.
Vertebrates
The ganglia that exist in these individuals have some peculiarities. So, they do not enter the limits of the central nervous system. Some call them the basal ganglia. However, the term "core" is considered the most correct. The nerve nodes and the system they form are the connecting elements between the components of the nervous system. They pass impulses and control the work of certain internal organs.
Classification
All ganglia are divided into several types. Let's consider the main ones. 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 type is basal. Their components are neuronal nodes that are in the white matter. It is found in the brain. The work of neurons is to regulate certain functions of the body, as well as to assist in the implementation of nervous processes. There is also a vegetative type. It is one bundle of nerves. This element belongs to the autonomic nervous system. These knots run along the spine. The autonomic ganglia are very small. Their size can be less than a millimeter, and the largest are commensurate with peas. The task of the autonomic ganglia is to regulate the functioning of internal organs and the distribution of impulses.
Comparison with the term "plexus"
The concept of "interlacing" is often found in books. It can be taken as a synonym for the word "ganglia". However, the plexus is called specific nerve nodes. They are present in a certain amount in a closed area. And the ganglion is the junction of synaptic contacts.
Nervous system
From the point of view of anatomy, two types of it are distinguished. The first is called the central nervous system. This includes the brain and spinal cord. The second type is a collection of nodes, nerve endings and the nerves themselves. This complexis called the peripheral nervous system.
The nervous system is formed by the neural tube and the ganglionic plate. The cranial part of the first includes the brain with sensory organs, and the spinal cord belongs to the trunk region. The ganglionic plate forms the 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 an association of nerve cells that goes 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. The shape of the spinal node resembles a spindle. It is surrounded by a sheath of connective tissue. It also penetrates the node itself, while holding blood vessels in itself. The nerve cells located in the spinal ganglion are light, large in size, their nuclei are easily distinguishable. Neurons form groups. The components of the center of the spinal ganglion are processes of nerve cells and layers of endoneurium. Processes-dendrites begin in the sensitive zone of the spinal nerves, and end in the peripheral part, where their receptors are located. A frequent case is the transformation of bipolar neurons into pseudo-unipolar ones. This happens during their maturation. From the pseudo-unipolar neuron, a process emerges that wraps around the cell. It is delimited into afferent, another name is "dendritic", and efferent, otherwise - axonal, parts.
Dendrites and axons
These structures cover the myelin sheaths, which are composed of neurolemmocytes. Nerve cells of the spinal ganglion are surrounded by oligodendroglia cells, which have names such as mantle gliocytes, sodium gliocytes, and satellite cells. These elements have very small round nuclei. In addition, the shell of these cells is surrounded by a capsule of connective tissues. Its components differ from others in oval-shaped nuclei. Biologically active substances contained in the nerve cells of the spinal ganglion are acetylcholine, glutamic acid, substance P.
Vegetative or autonomous structures
Autonomic ganglions are located in several places. Firstly, 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, bronchi and bladder. Such ganglia are called intramural. Another species is located near the surface of the organs. Preganglionic nerve fibers are connected to autonomous structures. They have outgrowths of neurons from the CNS. Vegetative clusters are divided into two types: sympathetic and parasympathetic. For almost all organs, postganglionic fibers are obtained from cells that can be found in both types of vegetative structures. But the effect that neurons have differs depending on the type of clusters. Thus, sympathetic action can increase the work of the heart,while the parasympathetic slows it down.
Building
Regardless of the type of autonomous node, their structure is almost identical. Each structure is covered by a sheath of connective tissue. In 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 multiple nuclei and cells with an increased number of chromosomes. Neuronal elements and their processes are enclosed in a capsule, the components of which are glial satellite cells. They are called mantle gliocytes. On the top layer of this shell is a membrane surrounded by connective tissue.
Intramural structures
These neurons, together with pathways, may constitute the metasympathetic region of the autonomic nervous system. According to the histologist Dogel, three types of cells stand out among the intramural types of structures. The former include long-axon efferent elements of type I. These cells have large neurons with long dendrites and short axons. Equidistant afferent nerve components are characterized by long dendrites and an axon. And associative neurons connect the cells of the first two types.
Peripheral system
The task of the nerves is to provide communication to the nerve centers of the spinal cord, brain and nerve structures. Elements of the system interact through connective tissue. The nerve centers are the areas responsible forinformation processing. Almost all the structures under consideration consist of both afferent and efferent fibers. The set of fibers that is, in fact, the nerve, may contain not only structures protected by an electrically insulating myelin sheath. They also contain those that do not have such a "coverage". In addition, the nerve fibers are separated by a layer of connective tissue. It is distinguished by friability and fibrousness. This layer is called endoneurium. It contains a small number of cells, its main part is made up of collagen reticular fibers. This tissue contains small blood vessels. Some bundles with nerve fibers are surrounded by a layer of another connective tissue - the perineurium. Its components are sequentially arranged cells and fibers of collagen. The capsule enveloping the entire nerve trunk (it is called the epineurium) is formed from the connective tissue. It, in turn, is enriched with fibroblast cells, macrophages and fat components. It contains blood vessels with nerve endings.
