Nevous System

The_Mutant_Boy strangeone at neverland.net
Sun Nov 3 13:59:14 EST 1996


Melissa M wrote:
> 
> Does anyone one have any info on the nervous system. I know it is a big
> topic but any info would be appreciated!!

The human brain is a fuzzy-logic neural network that can contain on the
order of significantly over a terabyte of inter-relative connections. 
Humans can contain on the order of a hundred trillion cells, of which a
percentage of those would be within the brain.  Many of the cells in the
human brain are called 'glial' cells, which act as scaffolding and
structural support for the neurons which code for information.  Many
neurons are 'mylenated', which means that the neurons have a layer of
'insulation' around the neural 'wires'.  Mylenated nerve tissue is white
- in the brain known as 'white matter', and non-mylenated tissue is
grey, known as 'grey matter'.  In general, mylenated tissue will
transfer information over long distances like 'cables' will, whereas
grey matter will inter-relate the phenomenon and do the correlations we
know of as 'thinking' on many levels.

The human nervous system, like the nervous system of all vertebrates,
and the nervous systems of many invertebrates including insects, is
organized on the basis of sensory information going into the brain from
the dorsal side and motor information coming out of the ventral side. 
Dorsal is in general 'toward the spine' and ventral is 'toward the gut',
dorsal-back ventral-front in humans, and in four legged animals
dorsal-up ventral-down.  That is why the occipital lobe, which takes in
and correlates visual information in the cerebrum is in the 'back' of
the head, even though the eyes are in the front (a longer distance),
because sensory information in general goes up the dorsal side.

A neuron will transmit and process information by taking 'inputs' from
'dendrites' which will project from the neuron.  They will in general
output information in projections called 'axons'.  Axons and dendrites
will join between different neurons at junctions called 'synapses'. 
Information will travel along neurons by opening and closing 'channels'
across the cell membrane that let ions of potassium, sodium, calcium,
and a few other ions less used like chlorine pass into or out of the
cell.  The ions are charged, and buildup and crossing of ions across the
membrane will set up 'electric potentials' which will travel down the
length of the neuron.  When the potential reaches the end of the neuron
in the axon, chemicals known as 'neurotransmitters' are emitted into the
synapse, and will bond with 'receptors' in the dendrite of another cell
to open channels there.  If enough channels are opened, the charge on
the next cell membranes will reach a potential which will cause it to
'fire', and send a cascade of actions in place which will send a signal
to virtually all of that neuron's axons, and on down the line.  Most
psychoactive drugs operate by interacting with different
neurotransmitter mechanisms, although some operate by interacting with
ion transport, and a few are known as 'neuropeptides' which change the
operation of some neurons.  When a neuron fires, it will change its
receptors in a fashion that will modify their susceptability to firing
in the future.  This in general enables most 'short term memory'
functions.  Eventually, new axons and dendrites will be grown in those
inter-relative paths used most frequently.  This results in general in
long term memory.

The nervous system is divided into the 'sympathetic' and
'parasympathetic' systems.  The parasympathetic system uses
acetyl-choline as its major neurotransmitter, and is used when one is
'passive' or 'at rest'.  When one is excited or anxious one uses the
sympathetic system.  Dopamine, nor-adrenaline, and adrenaline, known of
as 'catacholamines' (due to its chemical structure), and serotonin are
in general the major sympathetic neurotransmitters.  Also GABA,
glutamine, nitrous oxide, and other chemical compounds as well act as
neurotransmitters involved in such functions as sleep and other
functions.

Some functions in the human body will continue to work if all neural
connections to the brain are severed.  The human heart will still beat
if nerves connected to it are severed, although it may speed up and slow
down less easily.  Next to and within the spinal cord are various grey
matter nerve centers known as 'ganglions'.  These will produce the 'knee
jerk' responses when a hammer will hit your knee.  They also in general
do certain automatic things like help to flex certain muscles but
simultaneously relax opposing muscles when you are say 'extending your
arm'.  Your breathing and certain other automatic functions are
controlled in your 'hind brain' and medulla oblongata.  In your 'mid
brain' and lymbic system are controlled certain functions like
concentrating attention on a certain phenomenon, and rapid 'emotional'
responses as well.  In keeping with the general pattern of
dorsal-sensation ventral-action, the thalamus, which is dorsal in the
mid-brain, deals with pain-pleasure and the like.  More ventral, the
hypothalamus and amygdala will deal with emotional expression.  Ventral
and connected to the hypothalamus is the pituitary gland, which, along
with the hypothalamus, will release various hormones which may at times
be modulated by the long term 'mood' of the person.  Also, within the
midbrain on the dorsal side there is the pineal gland which acts as a
'timekeeping' gland, which regulates night-day sleep cycles.  Somewhat
seperate from the general mid brain is the cerebellum, which regulates
such functions as balance and coordination.  It interacts with the
cerebrum to produce the general motor control used by athletes.

In the cerebrum at the very top of the brain, many of the higher
cognitive processes occur.  Sensory information from the eyes, and
graphical information, are processed in the occipital lobe in the back
or dorsal side of the cerebrum.  A magnifying glass will 'invert' an
image when it is shown on a piece of paper.  Likewise the human retina
will recieve an inverted image at the back of the eye.  That inverted
image is then sent to the back of the cerebrum and not reinverted. 
Since our occipital lobes have 'seen' upside-down images since birth, we
have never known otherwise, and so the occipital lobe goes on processing
visual information in that manner.  On the two 'sides' of the cerebrum
are the temporal lobes.  They recieve 'hearing' or auditory input from
the ears.  On a midline between the front-ventral and back-dorsal
sections of the cerebrum are lines which recieve sensation from the
body, and slightly more ventral is an adjacent line sends motor output
to specific sections of the body.  Going from the bottom and side, to
the top; the larnyx, the mouth, the face, the hands, the torso, and
finally the legs at the top recieve sensation and send motor output. 
The 'mouth and larnyx' is on the side, and the side frontal lobes deal
in speech and language just as speach and language are dealt with on the
'hearing' side as well in the temporal lobes. More specifically, it has
in general been found that 'nouns' are more stored in the temporal lobes
where as 'verbs' (action), are stored in the lateral (side) frontal
lobe. In the medial (toward center) and top frontal lobe, as well as the
medial and top 'parietal lobe'-(on the dorsal side) you would naturally
deal with such functions as actions in space, mathematics, and the
like.  The more abstract, theoretical, and complex functions are dealt
with in such areas that are more removed from the direct sensory input
and motor output areas.  Reading and writing are areas that would
naturally be situated closer to areas dealing with the hands (which you
use to write), although many thought processes are distributed
throughout the brain.  In the central sections of the cerebrum removed
from sensory input and motor output areas, there is a projection of
white matter neurons that go from the dorsal to the ventral removed
areas. When this white matter projection is damaged you have what is
known as 'autism'.  There is a fissure that is between the temporal
lobes and the frontal lobes on each side of the brain.  Differences
between 'slant' of these fissures in the right and left side lead to the
'specialization' of the hemispheres.  Much of the cerebrum has been
mapped out, however there are still some investigations going on with
respect to exact regions in the midbrain and their functions.  'Smell
and taste' in general may connect with the olfactory bulb and/or proceed
into the mid-brain, where the information may then be relayed elsewhere
in the brain.

Such information has been collected from investigations in the 1950's
and before on to the present, using brain surgery on animals, X-rays,
CAT scans, PET scans, and electroencephalography, as well as studies of
persons with brain tumors and stroke victims.  For more information
consult various textbooks, also other persons in these newsgroups... .




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