ReMed Magazine
Sciences de la Santé
The Nervous System : Overview
Y A H I A B E L L O U C H E
Abstract
Adepolarization state called action potential in the centrifugal
compartment (axons); while local potentials are mainly passive
and of an electrotonic nature and later ones are only possible
because of a group of speci�ic ionic channels (Voltage
dependent sodium and potassium channels mainly). Induced
by a stimulus ( which can be electrical, mechanic, chemical or
physical), this excitation is the platform of information coding
and neural interactions, reinforced by some focal intercellular
connections called synapses where the signal “jumps” from a
cell to another through liberation of chemical substances in the
synaptic cleft for most of them (some electrical synapses use
direct cytosol connection), these linking points are the source
of neural circuits diversity, in the other hand, the nervous
system contains many other variable cellular types such as
astrocytes, oligodendrocytes and microglia whose main role is
to maintain the parameters of the microenvironment within the
limits compatible with the neural functioning requirements
and participate in neural interaction optimization by increasing
conduction velocity and synaptogenesis dynamics within the
CNS.
No system in the human body, can match the nervous system in
terms of organization, hierarchy and ef�iciency, characters
imposed by the nature of its functions, every biological process
is somehow, connected and is regulated by a nervous
mechanism, the set of the nervous system parameters supposes
a role of a processor, that treats the input arrived by means of
peripheral receivers in order to determine the adjustments and
the modi�ications necessary, coming out as an adaptive
response, the anatomy, and the general mechanisms
responsible for these functions are the subject of our
discussion.
Keywords: Central Nervous System, Peripheral Nervous
System, Autonomic Nervous system, neuron, dendrite, axon.
Cellular level of the Nervous System organization
Basing on the cell concept, the neuron (nervous cell) is
recognized as the nervous system’s most fundamental unit, the
origin of the majority of our brain functions. The neurons are
polymorphic highly differentiated cells characterized -besides
the standard subcellular components- by an extensive
branching out of the cellular soma, while these branches
(dendrites, axons) assure a transport function for signals from
and out of the soma, this last, is the site of activity regulation,
message integration and mediators synthesis, these functions
originate from an arsenal of genetically coded proteins and one
of the most developed cytoskeletal systems in existence, which
highlights the remarkable level of neurons specialization and
explains the loss of regeneration capacity for most of neural
cellular types known for some as the “Noble tissue”.
In addition, the neurons are excitable cells, which implicates
the existence of an ephemeral ionic conduction change leading
to a set of ionic movements through a lipid bilayer membrane
and a membrane potential values change de�ining a local
depolarization in the centripetal compartment (dendrites and
soma), and a self-maintained .
Histological /Anatomic levels
In a macroscopic view of the nervous system, we can
distinguish two morphological entities within its different
parts, a �irst, grey (called grey matter), hosts mostly the somas,
which quali�ies it to play a role of processing centers, while the
other is white (White matter) where we can �ind the axons of
the somas covered by a myelin sheath (enhancing the
membrane’s capacitance) who plays mostly the role of linking
cables.
Central Nervous System
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Anatomically speaking, the nervous system is divided into two
parts: The Central Nervous System (CNS) resulting from the
organization of nervous tissue around a �luid core, ventricles
(Brain), and continues with the medullary central cavity (Spinal
cord). At the top, around the lateral ventricles, the cerebral
hemispheres, with a grey multilobar cortex covering a white
matter mass that include some grey nuclei called basal ganglia.
Occupying the summit of neural functioning diagram, the
cortex is the treating center for almost every neural impulse
and the source of the output to peripheral effectors later on
with the linking done by the white mass under it, with relative
specialization of some areas, as of the basal ganglia, it has been
established that they are (with the cerebellum) the �ilters of
neural output towards motor effector especially.
The diencephalon (regroups the thalamus, hypothalamus and
the epithalamus) around the third ventricle, are mainly
projection and cortical excitability regulators, except the
hypothalamus, hormonal and metabolic regulation center
through its inferior branch, the pituitary gland which interacts
and commands almost every gland in thebody, under it, the
brain stem, one of the most conserved structures in the animal