Nervous fabric

The nervous fabric is a fabric of the epithelial type which ensures the integrated operation of the animal organizations. The cell responsible for this activity is the Neuron, specialized in the communication of proximity with other cells in the same way standard. It is thus a fabric which pushed the intercellular communication in its center with its extrème. Schematically, the nervous fabric receives the sensory information since receiving , integrates them and causes an adapted reaction of the organization by transmitting information to the Effecteur S (the principal ones being the Muscle S and the Glande S). The complexity of nervous fabric at certain organizations leads to reactions extrèmement complex and varied.

The nervous fabric is different from the hormonal system by the fact that the communication between cells are with short and very short distance whereas the hormones act on the whole organization.

Organization and function

Distributed in all the organization, the nervous fabric is organized in a system, the Nervous system. Thanks to a network of specialized cells, the neurons, the nervous system perceives information coming from the mediums interior and outside via sensory receiving and decodes them to bring an appropriate response of the organization.

At the vertebrate ones, the Nervous system is épineurien. It is subdivided in two parts: the central nervous system and the peripheral nervous system. Constituted macroscopically of gray substance and white substance, the central nervous system includes/understands the Encéphale (Cerveau, cerebral Tronc, Cervelet) placed in the cranial box and the Spinal-cord, placed in the rachidian Canal of the Spinal column. The peripheral nervous system includes/understands the different nerves connecting the Organes to the central nervous system as well as nervous relays, called nerve-knots. The nervous system of chordés more primitive is similar to this close than the brain is absent, the structure of fabric on the level of the head not being different from that from the remainder from the tube neural.

In the invertebrates Hyponeurien S, the nervous system consists of a double chain of ganglia located in ventral position from which the motor nerves and sensitive leave. Frequently, the former ganglia are amalgamated in a brain providing the most advanced functions of the nervous system. At certain groups, like molluscs, this structure, because of evolution, is not very visible.

The third type of observed nervous, observed in the most primitive animals is the formation of a diffuse fabric without identifiable structures within other fabrics. One meets it in the animals diploblastic (jellyfishes, corals, etc) and in the primitive worms. In certain animals, the neurons can gather within ganglia, but without those Ci seeming to have an additional organization as in the more advanced animals.

Components

Neuron

The nervous fabric contains Neuron S (or nervous cells) provided with cytoplasmic prolongations which, engainés or not, form nervous fibers. The neurons can be various types according to their localization (brain, cerebellum, nerve-knot). Thanks to their prolongations, the Neuron S establish relations is with other neurons, via synapses interneuronales.

Névroglie (known as Gliales cells)

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Elements of support are associated with the neurons. They are the cells of the névroglie which are ten times more than the Neuron S. There are two types of névroglie which contain each different cellular type. The interstitial névroglie in the central nervous system, the epithelial névroglie which borders the cavities contained in the central nervous system (ventricles, channel of the épendyme…) and the peripheral névroglie in the peripheral nervous system.

Interstitial Névroglie

It is known as also epithelial. It will constitute the cells épendimères which paper the cavities physiological of nervous fabric like the ventricular cavities.

Astrocyte

The astrocytes are spangled cells provided with many cellular prolongations. These prolongations go to the meeting of the Neuron S to support them and to the meeting of the blood capillaries thus forming the hematocephalic Barrière.

Functions

Support of the neurons. They maintain the coherence of nervous fabric.
Guidance of the Neuroblaste S during their movements during the processes of maturation of nervous fabric.
hematocephalic Barrier. The astrocytes prevent the passage of the ion Potassium, the amino-acids, the Neurotransmetteur S, the Hormone S and many drugs in the intercellular medium in order to not géner the activity of the neurons on the level of the synapses and the transmission of the potential of action. They control the Glycémie intercellular medium which is thus not subjected to the variation of the blood glycemia.
They eliminate waste and the Neurotransmetteur S by rejecting them into blood.

There exist two types of astrocytes according to their localization: protoplasmic astrocytes in the gray substance and the fibrous astrocytes in the white substance.

Oligodendrocytes

The oligodendrocytes are cells provided with small cytoplasmic prolongations very few. These prolongations surround the Axone S and myélinisent them thus accelerating the transmission of the nerve impulse. They constitute 75% of the volume of the central nervous system. Specific of the myelinisation of the central nervous system, they can myéliniser several fibers nervous whereas the Cellules of Schwann (SNP) are specific of a fiber when they myélinisent it (indeed, the Fibers Amyélinisées Schwanniennes consist of several cylindraxes for only one cell of Schwann).

Microgliocytes

In fact small spangled cells derive from Monocyte S brought by blood. They are the Macrophage S of the central nervous system. They can by activation adopt the shape in spindle and thus move in nervous fabric. They secrete growth factors essential to the operation of the Neuron S and oxidizing free radicals which attack the micro-organisms.

Peripheral Névroglie

Névroglie perpipheric contains the Cellules of Schwann which constitute the sheath of Myéline peripheral nervous system.

Colorings

Two types of particular colorings are used to study nervous fabric on the level of the central system: " Bichrome s" and of the silver impregnations. " Bichrome s", like Dominici, associate a basic dye (Bleu of toluidine) highlighting the basophilic structures (blocks of Nissl, the core) and an acid cytoplasmic dye. The absence of conjunctive fabric on the level of the central nervous system makes useless the use of a third dye. The techniques of silver impregnation make it possible to mitigate the lack of colorability of the cytoplasmic prolongations of the nervous cells by revealing the cytosquelette (neurofibrilles) particularly abundant in these prolongations.

Internal bonds

Nervous system

External bonds

digital Atlas of microscopic morphology - Medical college of Namur (FUNDP - LabCeTi)

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