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[Neuroscience] Re: Evolution of Central Nervous System

r norman via neur-sci%40net.bio.net (by r_s_norman At _comcast.net)
Sun Nov 12 12:08:46 EST 2006


On 12 Nov 2006 08:06:40 -0800, "sharon" <sharon192837465 At yahoo.com>
wrote:

>> > > .If something touch you, neuroscience states that it is carried through
>> > > electrical signals to neurons in our brain.
>> > >
>> > > But this sensitive plant does not have brain or neurons. Then how does
>> > > the plant 'feel' the touch and 'react' to it?
>> >
>> > Because it isn't the brain or neurons that is the source of consciousness.
>
>My question on the Alligator? Nobody answered this. How far along is
>the Alligator in its evolution compared to man? Is it localized
>response, or central nervous system (a reflect created in the brain).
>
>Evolution of Central Nervous System Formation and Function in Embryos
>of Marine Invertebrates. Program Leader: Prof. Hideki Katow ...
>http://www.cir.tohoku.ac.jp/e/programs/1999/KatowHideki.htm
>
>Google evolution "central nervous system"
>
>It is the ethical dilemma that for decades has troubled the rich and
>aspiring the world over: when you place a live lobster in a pot of
>boiling water, does it feel pain? Norwegian scientists were asked to
>investigate pain, discomfort and stress in invertebrates and claim now
>to have discovered that the answer is no. Their conclusion applies also
>to crabs and to live worms on a fish hook. None of these feel a thing.
>Which is good news for Norwegian fishermen at least.
>http://www.guardian.co.uk/international/story/0,,1408022,00.html
>
>Google evolution "invertebrate feel no pain"
>
>And frogs, amphibian, can be placed in a pot of warm water, and the
>temperature raised, and the frog will set there until its boiling (or
>is this another common legend?)
>
>How developed are some species' central nervous system?
>
>>
>> Here is an example of an animal that acts on reflex.
>> http://www.metacafe.com/watch/20107/alligator_trick_gone_wrong/
>>
>> this is one incident. Young asian sticks his hand into gators mouth,
>> and it snaps.
>>
>> On television, another man would perform putting his head into the
>> gator's mouth. He survived to tell it only took a drop of his sweat
>> falling on the tongue, and the gator reflexively snaps its mouth shut.
>> I don't know if this is communicated through to the brain, or if it is
>> caused by a local reflex in the mouth.

Sharon, you are raising several very different issues with very
different types of answers.  On the one hand you are asking about
reflexes, On the other you are asking about brain and central nervous
system.  On the third you are asking about alligators.  On the fourth
you are asking about invertebrates and the evolution of nervous
systems.  On the fifth you are asking about pain and consciousness.
And the way you ask indicates you know very little about animals and
nervous systems.

All animals except sponges have some form of nervous system that
controls movement and behavior.  All these animals except Cnidaria
(jellyfish, corals and anemones, hydra) have a central nervous system
with an enlargement at the head end usually called a brain.
Vertebrates have a central nervous system composed of the brain and
the spinal cord.  Alligators are simply another kind of vertebrate, a
member of a group formerly called reptiles (why "reptiles" are no
longer considered a proper category is another long story). They have
a larger and more complex brain than, say, a frog, but less elaborate
than a mammal. 

To be completely thorough here, and in response to the original
posting about plant movements, there are many cells in many organisms
other than animals that have neuron-like properties and produce
electrical responses to stimuli that are capable of controlling other
cells to produce some form of movement.  Such a response might be
analogous to what we call a reflex in animals.    Responsiveness to
the environment is simply a characteristic of all living things,
plants, fungi, and bacteria included.

Reflexes function through nervous system activity as an "automatic" or
"pre-wired" response to a stimulus.  In rare cases, the reflex can
occur without the involvement of the central nervous system.  This
happens in the Cnidaria (which do not have a central nervous system),
in animals like the octopus, which has an extensive network of
peripheral neurons, and in our own gut which has also has an extensive
network of neurons of its own, the so-called enteric nervous system.
However most of the reflexes you ask about do involve the central
nervous system.  This may involve the spinal cord (or longitudinal
nerve cord or peripheral ganglia) the make up part of the central
nervous system, or they may involve the brain.   So whether the brain
is involved or not makes no difference whether something is a reflex.
When your pupils constrict in response to light, the brain is
involved..

The question of "pain" and "consciousness" is a very complex one and
different people answer questions about non-human pain and
consciousness in very different ways for very different reasons.  What
we call "conscious" behavior in humans is a very controversial
question even in defining just what we mean.  Whatever it means, it
certainly involves not just having a brain, but having a particular
organization of brain which might also involve having a brain of
sufficient size to manage that particular organization.  It is
generally believed that only mammals have a brain of sufficient size
and complexity to even consider the notion.  And even in mammals, it
is generally believed that only primates, and only great apes, and
perhaps only humans have that capability.   Still, a tremendous
variety of animals shows extremely complex, well organized, goal
oriented behavior that is clearly responsive both to the immediate
environment and stimulation and to the animals internal state and even
to the animals long term needs.  This type of behavior is found in
molluscs (especially octopus) and in arthropods (especially in certain
insects).  In most cases, the brain is part of the machinery involved.
In some cases, animals are capable of performing extremely complex
behavior controlled entirely by "lower" parts of the central nervous
system, what would correspond to our own spinal cord.

Pain is a more difficult subject because many animals produce a
specific behavioral responses to extremely strong stimuli or to injury
or damage to tissues.  It is also true that many animals carry on
behavior quite well even though they suffer severe physical injury.
What we call "pain" involves more than just feeling a very intense
form of stimulation.  There are specific circuits in specific parts of
the brain that are involved in the extreme unpleasantness that these
stimuli provoke.  It is not at all clear whether animals that do not
have those brain circuits feel what we call pain or whether they feel
what we call extremely intense stimuli but without all the
associations (the so-called "affective" nature of pain).  It is also a
very human characteristic that people who feel awful putting lobsters
in a pot of boiling water often have absolutely no compunction against
swatting mosquitos or wasps or other nuisances even though these
animals have just as complex a brain as does the lobster.  









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