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Central nervous system
The central nervous system represents the largest
part of the nervous system. Together with the peripheral nrvous
system, it has a fundamental role in the control of behaviour.Since
the strong theoretical influence of cybernetics in the fifties,
the is conceived as a system devoted to information processing,
where an appropriate motor output is computed as a response toa
sensory input. Yet, many threads of research suggest that motor
activity exists well before the maturation of the sensory systems
and then, that the senses only influence behaviour without dictating
it. This has brought the conception of the CNS as an autonomous
system.
The whole CNS originates from the neural plate, a
specialised region of the ectoderm, the most external of the three
embryonic layers. During embryonic development, the neural plate
folds and forms the neural tube. The internal cavity of the neural
tube will give rise to the ventricular system. The regions of the
neural tube will differentiate progressively into transversal systems.
Firs, the whole neural tube will differentiate into its two major
subdivisions: spinal cord and brain . Consecutively, the brain will
differentiate into brainstem and prosencephalon. Later, the brainstem
will subdivide into rhombencephalon and mesencephalon, and the prosencephalon
into diencephalon and telencephalon.
In the adult, the is covered by the meninges, the
brain is protected by the skull and the spinal cord by the vertebrae.
The rhombencephalon gives rise to the pons, the cerebellum and the
medulla oblongata, its cavity becomes the fourth ventricle. The
mesencephalon gives rise to the tectum, pretectum, cerebral peduncle
and its cavity develops into the mesencephalic duct or cerebral
aqueduct. The diencephalon gives rise to the subthalamus, hypothalamus,
thalamus and epithalamus, its cavity to the third ventricle. Finally,
the telencephalon gives rise to the striatum (caudate nucleus and
putamen), the hippocampus and the neocortex, its cavity becomes
the lateral (first and second) ventricles.
The basic pattern of the is highly conserved throughout
the different species of vertebrates and during evolution. The major
trend that can be observed is towards a progressive telencephalisation:
while in the reptilian brain that region is only an appendix to
the large olfactory bulb, it represent most of the volume of the
mammalian CNS. In the human brain, the telencephalon covers most
of the diencephalon and the mesencephalon. Indeed, the allometric
study of brain size among different species shows a striking continuity
from rats to whales, and allows us to complete the knowledge about
the evolution of the CNS obtained through cranial endocasts.
Ammonium nitrate decomposes into gases including
oxygen when heated ; however, ammonium nitrate can be induced to
decompose explosively by dtonation. Large stockpiles of the material
can be a major fire risk due to their supporting oxidation, and
may also detonate, as happened in the Texas City disaster of which
led to major changes in the regulations for storage and handling.
There are two major classes of incidents resulting
in explosions:In the first case, the explosion happens
by the mechanism of shock to detonation transition.
The initiation happens by an explosive charge going
off in the mass, by the detonation of a shell thrown
into the mass, or by detonation of an explosive mixture
in contact with the mass. The examples are Kriewald,
Morgan, Oppau, Tessenderloo, and raskwood.
In the second case, the explosion results from a fire
that spreads into the ammonium nitrate itself , or to
a mixture of an ammonium nitrate with a combustible
material during the fire . The fire must be confined
at least to a degree for successful transition fro a
fire to an explosion a phenomeon known as "transition
fro a decomposition or deflagration", o Pure, compact
AN is stable and very difficult to initiate. However,
there are numerous cases when even imure AN didn't explode
in a fire.
Ammonium nitrat decomposes in temperatures aboves stable and will
stop decomposing once the heat source is removed, but in presence
of catalysts (combustible materials, acids, metal ions, chlorides
the reaction can become self-sustaining (known as self-sustaining
decomposition, This is well-known phenomenon with some types of
NPK fertilizers, and is responsible for loss of several cargo ships.
Historically significant accidental explosions
In 1918, a fire broke out in the amatol loading plant
in Morgan, New Jersey. Over pounds of explosives were
present on site, of tha up to and fire, bu did not detonate.
On September 21, 1921 a heavy explosion of a mixture
of ammonium nitrate and ammonium sulfate detonated during
attempts to break up the caked pile with blasting charges
(an operation apparently performed several times before,
with casualties (according to other sources, 50 or over
1000), occurred in the city of Oppau on the grounds
of BASF near Ludwigshafen in Germany). Over 700 homes
were destroyed, the plant isappeared entirely and was
replaced with a crater 50 ft deep and 250 ft in diameter,
and the shock was felt 150 miles away. This was the
largest man-made disaster in German history.
In in Nixon, New Jersey, ammonium nitrate was being
recovered from amatol in order to be used as a fertilizer,
when a fire broke out.
In April 4 and The barrels were stored in a warehouse
with varying humidity for 6 years, so it is believed
that they were ignited by friction of their nitrate-impregnatet
a bomb-makng plant in Milan, Tennessee, killing four.
The Texas City Disaster on Aprilof ammonium nitrate
caught fire and then exploded on board of the SS Grandcamp,
heavily damaging the port and killing 581 people, injuring
over more, and igniting the SS High Flyer, which exploded
later, adding to the death toll. This is the best-known
ammonium-nitrate related disaster.
In September 21, 2001, at 10:15 am in the ) fertilizer
factory in Toulouse, France. The explosion occurred
in a warehouse where the off-specification granular
AN was stored flat, separated bypartitions. About 2tons
is said to be involved in the explosion, resulting in
31 people dead and 2,442 injured, 34 of them seriously.
The blast wave shattered windows in 1.5-3 kilometer
distance and the resulting crater was 10 meters deep
and 50 meters wide. The exact cause remains unknown.
The material damage was estimated at 2.3 billion Euros.
The Ryongchon disaster in April 22, 2004, in North Korea
is suspected to have a shipment of ammonium nitrate
involved, together with other explosives.
Other uses
The most common use of ammonium nitrate is in fertilizers.Ammonium
nitrate is also used in instant cold packs. In this
use, ammonium nitrate is mixed with water in an endothermic
reaction, which absorbs 26.2 kilojoules of heat per
mole of reactant.Due to its low temperature, non-toxic
decomposition products, it finds use in gas generator
applications such as airbags.Ammonium nitrate is also
used in the treatment of titanium ores.Ammonium nitrate
fertilizer is also used in the synthesis of methamphetamine.Ammonium
nitrate is used in survival kits mixed with zinc dust
and ammonuim
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