Seeking references on animals with fully understood nervous systems (??horseshoe crab)

Richard Norman rsnorman at mediaone.net
Mon Jul 30 10:11:45 EST 2001

On 27 Jul 2001 00:02:19 -0700, tropbob at aol.com (Bob Els) wrote:

>Thanks everybody for the information and references. I am writing a
>book a part of which will convey the "mechanicalness" of a simple
>nervous system. I wanted the part to be solid and compelling. That's
>why the need for authoritative references. Additionally it would be
>great for some readable references for readers who wanted more
>The Aplysia californica is indeed the animal to use. Still, after
>going through several books ("From Neuron to Brain", 3rd ed, Nicholls
>et al,"Neuron Networks and Motor Behavior" by Kupfermann et al,
>"Spikes" - just for some of the introduction - by Rieke et al) I am
>surprised at how complex the subject is even for this most simple and
>well-known animal. Yet it is better to know the truth - I will need to
>change slightly the direction of the section in the book. (I have to
>admit that my awe of the living part of the universe increases the
>more I dig into this material - it is one thing to know something in
>general terms but quite another to see it in concrete details - and to
>realize that this sort of thing is all around us - indeed in us.).
>There was a lot of information in your responses and again I want to
>thank you. Wilms' point that any neuroscience text will have plenty of
>info was helpful since Kandel's book seems completely unobtainable.
>Wilms' phrase "many behavioural aspects" indicated that even with this
>most well-know animal not all behaviors have been mapped to certain
>groups of neurons, let alone how it is connected with individual
>neurons; Deperaux's information about the C. Elegans and the horseshoe
>crab, and more info on Aplysia and Kandel, and info about what nerves
>are easy to study (not many); Murray's project on artificial brains;
>Teo's interesting information on the Medicinal Leech and the
>interesting phase diagram on the website; and Maxwell's reference to
>Kandel's book, and diplomatic corrections to the terms I was using to
>search on horseshoe crab, and information on horse shoe crab material
>and Hartline's work.
>I will definitely drop the horseshoe crab and go with Aplysia. So that
>the reader can get an idea of the complexity of this sea hare -
>another question. What would be a good reference for finding out how
>many neurons ants have?
>Neither Amazon.com nor Barnes and Noble website nor Border's website
>have Kandel's book, Behavioural biology of Aplysia. Nor did our
>University Library (University of Nevada Las Vegas) have the book. So
>I put in a request to our library system for an inter-library loan to
>see if it will show up.

Sorry to be late getting in on this thread.  Certainly the best known
system is Caenorhabditis, where every cell is known.  But as you found
out, knowing the cells does not "explain" the behavior.  A good
metaphor is the genome -- knowing the sequence really doesn't explain
how the organism works.  Aplysia and leech systems are well studied,
as are many crustacean and insect systems.  One well studied
crustacean system is the stomatogastric ganglion.  (A nice source is
http://www.pbrc.hawaii.edu/STG/ )

The "nine neuron" reference is almost certainly to the crustacean
cardiac ganglion, the first "small neural system" to be described.
Some lobsters do, indeed, have exactly nine neurons in this ganglion.
The behavior is relatively simple -- periodic bursts of action
potentials to make the heart contract.  The details are more complex,
though: active bursting properties of cells (non-Hodgkin-Huxley
behavior) etc. and electrotonic interaction between cells. These are
common to many "simple" systems but are usually ignored in computer
simulations of "brain".

And consider the behavior of a Cnidarian like an anemone.  With only a
nerve net (no central nervous system at all) it can capture and
immobilize prey, contracting its tentacles to stuff food into its
mouth. When faced with hostile conditions, it can even unloose itself
from its support and, belying its "sessile" nature", tumble away to
find a new habitat.  Even a Paramecium can exhibit seemingly "complex"
behavior.  Even single cells are capable of very involved,
coordinated, seeming goal-seeking behavior and cell networks multiply
that complexity by orders of magnitude.  So you might want to pull
back on the "fully understood" aspect of your subject.  Not even an
electron is fully understood!

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