Re: Which organism has the smallest brain?
- From: "g" <gillawton@xxxxxxxxxxxxx>
- Date: Thu, 7 Jul 2005 16:55:58 -0400 (EDT)
"r norman" <rsn_@xxxxxxxxxxxx> wrote in message
news:daj877$2n9$1@xxxxxxxxxxxxxxxxxxxxxx
> On Tue, 5 Jul 2005 08:51:33 -0400 (EDT), me@xxxxxxxxxxxxxxxxxxxxxxx
> wrote:
>
>>I am trying to find out which organism has the smallest brain. By brain
>>I mean neuron, cluster of neurons, or anything resembling a neuron. As
>>far as I can tell it is C. Elegans with 302 neurons. Is there no living
>>ancestor to the C. Elegans that has a smaller number?
>>
>
> "Smaller" has many meanings. Nematodes in general have fixed and
> small cell numbers. C elegans happens to be the one picked for
> extensive study, but there are probably thousands more in a similar
> situation. Parasites in general have reduced many internal organs
> and systems. Ascaris is a very large parasitic nematode with 162
> neurons in its central nervous system. No doubt there are others with
> fewer. Possibly Trichina may be such an example, or some hookworm or
> pinworm. I don't know who may have counted neurons in these.
>
> Rotifers, though, are much smaller in physical size. A single
> individual may be smaller than a large protozoan like an amoeba or a
> Paramecium. They also have very few cells. So these are probably the
> organisms with, literally, the smallest brains.
>
> Of course, as the common refrain goes, size isn't everything! You have
> to consider what you do with what you have. Among animals, sponges
> have no nervous system of any kind and Cnidaria (jellyfish, Hydra,
> anemones, ...) have a "diffuse" neural network although there are some
> concentrations of cells. However they do not have a central nervous
> system at all, so no brain as officially defined. However, you are
> more generous in your definition and would include them. They
> generally do have more neurons than a nematode.
>
> If you want just small pieces of a nervous system, probably the record
> is the cardiac ganglion of the lobster (or crab, crayfish ... any
> crustacean). This collection of just nine neurons sits inside the
> heart and is responsible for producing the heartbeat. It functions
> perfectly well totally isolated from the rest of the nervous system
> and does something -- produce rhythmic activity -- that might be
> deemed somewhat complex. For true complexity, look at the crustacean
> stomatogastric ganglion. It has fewer than 30 cells but produces a
> whole series of rather complexly patterned activity to control the
> movements of the gastric mill. Furthermore, it can change from one
> pattern to a completely different one under different conditions. It
> gets my vote for "most with the least".
>
This response is so excellent I could not bring myself to snip any of it.
Let me add, however, that there seems to be an abundance of evidence,
generally, to manifest as a valid "issue" that nature abounds with
small brained creatures doing the most "prevailing" with the least
neurological hardware.
I have contended elsewhere that it is BOTH a fact that the human brain
has guided such things as animal husbandry and architectural wonders
AND a fact that guided such things as the development of a sufficient
number of nuclear weapons and biotoxins to render Earth uninhabitable
by himself. If Earth is ill, mankind may be the etiological agent.
And if Earth might be viewed (as some view it) as holistically a living
thing, then it may be gearing up for is own apoptosis, lest it metastasize
and spoil a universe.
(:>)
g
.
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