The nervous system is a system in network formed of the bodies of the direction, Nerf S, Cerveau, Spinal-cord, etc It coordinates the muscular movements, controls the operation of the bodies, conveys sensory information and motor coaches towards the Effecteur S, and, in the animals equipped with a brain Limbique, babbit metal the emotions, and those equipped with a cognitive brain , babbit metal intellect.

At the vertebrate ones one distinguishes the central Nervous system traditionally (Encéphale and Moelle spinale (Spinal-cord in the old anatomical nomenclature)) peripheral Nervous system (sensorimotor cranial nerves, rachidian nerves and enteric system).

The central nervous system is composed of highly specialized nervous cells called neurons. The nervous cells establish between them connections, the synapses. Billion these synapses contributes to the treatment of only one Stimulus. Those are conveyed by related fibers of the Spinal-cord until the Cerveau, the axons which constitute them are generally surrounded by a called white substance sheath of Myéline. This sheath is generated by the cells of Schwann in the peripheral nervous system and by the Oligodendrocyte S in the central nervous system. The nervous system is responsible for the good performance of the vegetative and driving activities. To the level of the spinal-cord, a series of sensitive cells in T bring back the nervous message of vegetative or driving nature transmitted by the sensory Capteurs sensitive to the pressure, the temperature, the touch, the pain or the stretching (spindle neuromusculaire), the cellular body of this nervous cell being exceptionally in the ganglion spinal of the posterior root of marrow, to marrow to constitute the principal afférence of sensory stimuli. These stimuli can inform the brain in a way conscious of what does without in the body or our Environnement for a conceptual image, from a memorizing, a judgment or a voluntary answer or on standby of an adequate regulation reflex by traversing ascending ways of of which ways intéroceptives, proprioceptive conscious and unconscious and exteroceptive.

Those undergo then the Rétrocontrôle nervous system via interneurones and of the pyramidal ways or extrapyramidales downward for then leaving the former horns of the Spinal-cord in the form of efferent fibers in order to innerver the vital bodies or the muscles. Finally the nervous system often jointly acts with the hormonal system and is cartographiable with a very large plasticity not according to the Phrénologie but according to the types of associative related fibers in sensory and driving surfaces.

Terminology and vocabulary

• central Nervous system ( SNC ): portion of the nervous system made up of the Brain, the cerebral Trunk, the Cerebellum and the Spinal-cord. It has a role of reception, treatment, integration and emission of the nervous messages. The whole of the central nervous system is protected by an osseous envelope: the cranial box for the Brain and the Spinal column for the spinal-cord, like by other protective fabric envelopes: the Meninges.
• Brain: the central Body supervising the Nervous system. It is in particular the center of the conscious thought.
• cerebral Trunk: Portion of the brain which makes the junction between the Cerveau, the Cervelet and the Spinal-cord. The cerebral trunk makes up from top to bottom of the Mésencéphale, the Pont of Varole (or annular protuberance), and of the Medulla (or medulla oblongata).
• Cerebellum: Antiquated portion of the brain, connected simultaneously with the dorsal face of the cerebral trunk, exerting the functions of maintenance of the posture, balances, coordination between the movements, gestural memory.
• Spinal-cord: She plays a part of transmission of the nervous messages between the brain and the remainder of the body but she provides also a clean function of integration and emission of nervous signals, in particular in the Réflexe peripheral S.
• Nervous system: it is consisted of the sensitive Nerf S and engines resulting from marrow and the cerebral trunk.
• autonomous Nervous system ( SNA ): it is consisted of the nerves and nerve-knots which manage the automatic functions of regulation (in opposition to the “conscious” functions). One divides it into Nervous system sympathetic nerve and parasympathetic Nervous system.
  Les glands adrenal medullas is regarded as a nervous structure belonging to the system sympathetic nerve, and is directly controlled by SNA, although their role is hormonal secretion of Catécholamine S.
• céphalo-rachidian Liquide ( LCR ): liquid in which the brain and the spinal-cord bathe, of a volume of approximately 150 ml at the adult man. He renews himself very quickly and has functions of mechanical protection, anti-infectious, nutritive.
• Nerve: anatomical structure made up of nervous fibers, being born (generally) from the spinal-cord and finishing on its target (skin, muscle, body, gland…) or of the bodies of the directions to join the SNC.

The nervous cell or neuron

The nervous cell is formed by a principal part, the body of the cell, from which are resulting from the prolongations.

The body of the nervous cell

Structure

As for any cell, the body of the neuron includes/understands a cytoplasm and a core.

The cytoplasm is limited by a cytoplasmic membrane. It contains filaments which one highlights by special colorings and which one calls of the neurofibrilles . It contains moreover many enclaves (especially lipidic) and a formed special body of corpuscles of which the number, the form and the situation vary according to the function of the cell; they are the body of Nissl .

The core does not present a characteristic of structure compared to the other cells. It is limited by a nuclear membrane and contains chromatin and nucleoles.

Form

The shape of the body of the neuron is however variable according to the area, but rather constant in a given area: pyriforme cells on the level of the cerebellum, pyramidal cells on the level of the cerebral bark.

Cut

It also varies from 6 to 140 micrometers.

Prolongations of the nervous cell

They are constant, it is indeed thanks to its prolongations which the nervous cell comes into contact with the bodies that it innerve or the other neurons. The nervous cell presents two kinds of prolongations: the dendrites and the axon .

Dendrites

They are prolongations established on the cellular body which is presented in the form of arborisations fine and short, irregularly laid out and finishing in very many ramifications.

cell type, some having several dendrites, of other by having one.

The fact essential to know is that dendrites, which are conductive nerve impulse, cannot, under the normal physiological conditions, to lead this impulse that in only one direction, of the end of the arborisations of dendrite towards the body of the cell (direction known as cellulipète ). The direction of conduction of the impulse differentiates dendrites from the axon.

The axon

Him the name of cylindraxe is also given. The axon is presented in the form of a lengthened stem, of smooth surface, invariable gauge. There exists one axon by nervous cell, whereas it can exist several dendrites. The axon is sometimes very short, but its length is sometimes considerable: for the peripheral nerves for example, the driving neuron is located at the level of the spinal-cord and the termination of cylindraxe on the level of the driving plate of the muscle that it innerve, which represents a long way sometimes several decimetres. The cylindraxe finishes like dendrites by irregular and ramified arborisations.

Here still, the fact essential to retain is that the cylindraxe, just like dendrites, lead the nerve impulses only in one direction, generally of the body of the nervous cell towards the final arborisations of the axon (direction known as cellulifugal ) but it can potentially lead them in the two directions. It is what occurs for the sensory neurons from the skin, which do not have dendrites but an axon with two junctions: one moving towards the sensory periphery and receivers and worms the central nervous system. The potential of action is thus propagated receivers along the first junction of the axon in the direction cellulipète then passes in the second branch, this time in the cellulifugal direction until the central nervous system. Since in this case of figure, we do not have an axon and a dendrite, but an axon ramified in two branches, the final part of this axon can release from the neuro-transmitters in synapses known as while passing to carry out very fast actions following sensory stimulation without awaiting an answer of the central nervous system, definitely longer to react. It is this presence of synapses which makes it possible to say that we rather deal with axon than with a dendrite.

Synoptic table

Intéroceptives ways

August 1st Also called viscéroceptives ways. They include/understand the organic feelings, the visceral pain. These ways are discriminatives letting pass only the pain.

Pyramidal ways

They are the ways of motricity " volontaire" , specific of the Vertebrate ones. They leave the driving cortex then pass by the ventral area of the hindbrain (where they form small protuberances of triangular section from where the pyramidal term), reach the spinal-cord and continue with the Motoneurone S. In the majority of the cases, only one neuron is used as connection between the cortex and the motoneurone.

Joint action of the nervous system and the hormonal system

The distinction between nervous system and hormonal system is sometimes fuzzy, in particular because of the Neurohormone S: they are molecules produced by neurons under the control of impulses nervous but poured in blood. Many neurohormones are produced in the Hypothalamus and are poured in blood in the Neurohypophyse (Example: Oxytocin, Vasopressine…).

Driving and sensory surfaces and cerebral plasticity

The part of the nervous system dedicated to the action of the muscles forms, with the Squelette and the muscular Système, the locomotor Appareil.

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