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In order to understand the
complexed phenomena that take place at the
central nervous system's level,
let's look over its structural schema.
All the central nervous system
parts interact.
For
a better understanding and with a didactic
purpose, I decide to present the nervous system
in two, main categories which are also devided in
two subcategories.
| Central
nervous system contains the
brain and the spinal cord. Peripheral
nervous system consists the
nerves that connect different areas of
the brains to the spinal cord and
different body parts.
The somatic
nervous system colects
information from the tegument and muscle
receptors about the external stimuli and
send them to the central nervous system
(this explains why we feel pain,
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physical pressure and temperature
variation). The somatic nervous system motor
nerves send the impulses from the central nervous
system to the muscles causing the voluntary
movement, and allows the body to maintain its
equilibrium and adjust its posture.
Vegetative
nervous system sends the nervous
impulses from or to the internal organs,
controlling the breathing and digestive process,
and cardiac activity.
The human brain consist in 3 concentric layers:
The internal layer contains: rachidian
bulb that controls the breathing process and
postural reflexes; cerebellum that controls the
motor activity; thalamus - the relay station of
the sensorial information that comes from the
sensorial level; hypothalamus,that plays an
important role in controling the emotions and
homeostasis: and reticular system, which crosses
some of the structures mentioned above, and
controls the wakefulness state and body
excitability.
The limbic system together with
the hypothalamus controls some of the instinctual
activities such as feeding, aggression, running
from danger, and choosing the sexual partner;
This nervous structure plays also an important
role in the memory and attention process.
The external layer called the
cerebral cortex is formed from two cerebral
hemispheres. It plays a significant role in
several processes like sensorial, decision
taking, learning and thinking process. The cortex
contains the central centers of the analyzators
and association areas, and controls the specific
movements.
The base unit of the nervous system is a
specialized cell called the neuron.
The neuron body is formed from short extensions
called dendrites and a long,
unique extension called axon.
When the dendrites or neuronal body is
stimulated, a nervous impulse forms which is send
out through the axon. The sensitive neurons send
the received signals from the sensory organs to
the cerebral segments of the nervous system,
while the motor neurons send out the signals from
the nervous system to the muscles and endocrine
glands.
A nerve is formed from the
axonal fibers of hundreds or even thousands of
neurons, and contains sensitive and motor fibers.
At the neuron level, the information is send out
in one direction as a biochemical impulse (called
nervous impulse or action
potential) from the dendrites to the end
of the axon. The action potential is caused by a
self-programmed mechanism called depolarization.
According to this mechanism, the cellular
membrane permeability changes for different types
of ions (atoms or electrical molecule) that enter
and leave the cell.
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