Dear friends I found this very interesting :
<snipped>>>
Our current understanding of the differentiation and
connectivity of human central nervous system neurons depends
heavily on three decades of electron microscopy and histology of
neural tissues of other mammals, particularly of the tissues of
the rat and of various species of monkeys, and even of the
tissues of several species of worms and of a giant snail.
These are only some examples, and there are many others.
This, therefore, is another principle: Nerve cell function,
wherever it occurs, involves mechanisms that more often than not
have been conserved by evolution, so that for the neurobiologist
attempting to understand the human nervous system, every species
provides experiments already performed by nature. All neuro-
biologists are aware of this, but on occasion there are people in
other disciplines, or in government offices or legislatures, who
are unaware of it, and who think that research on single
cockroach nerve fibers, for example, is unrelated to problems of
human neurobiology. That idea is totally false: some species of
cockroaches have relatively large diameter nerve fibers (for
reasons indicated below), which makes it simple to do certain
electrophysiological experiments, and since the basic mechanisms
that are operating in cockroach nerve fibers are essentially
identical to those operating in human nerve fibers, the use of
the cockroach nervous system in experiments is completely
relevant for human neurobiology -- as relevant as the continuing
use of the nervous system of a mollusc called squid.
And the same considerations hold true for investigations of
other parts of the nerve cell. There are features that are unique
to neurons, common to nearly all neurons no matter what the
species, but not found in other cells. Neurons, for example, have
special structures such as neurotubules that are not found in
other cells, but which are found in neurons of many species. And
the structures of synapses, the places where nerve cells are
connected to each other, have a remarkable universality in
nature, a boon for the neurobiologist. These and the other trans-
species neurobiological identities provided by the laboratory of
evolution, some of which will be discussed below, are important
and precious advantages to the research worker, and they need to
be fully utilized rather than constrained by misunderstandings of
relevance for medical science.
In summary, in the same way that molecular biology has
depended so heavily on investigations of a few species of yeast
and bacteria, investigations of mechanisms common to all living
cells, so neurobiology has depended heavily on investigations of
the nervous systems of lower forms, nervous systems which operate
by mechanisms common to all forms that have nerve cells.
Let us now consider some of the elements of these
mechanisms, both global and local, elements of the relation
between the behavior of nerve cells and the behavior of the
complete organism -- but with emphasis on the human nervous
system. We can use these elements as a framework to identify
certain important principles, and also terms and concepts that
will provide us with a language for future reports.
In the first place, we can say with confidence that
particular behaviors and behavior sequences in humans are clearly
the result of the development of particular sets of connections
among the neurons in the brain. This is certainly true in
general, even if we cannot yet point to small-scale connections
as the basis for small-scale behaviors. But for large-scale
behaviors such as sensation and perception in the various sensory
modalities, language, emotions, hunger, thirst, and so on, we
know, in general, what parts of the brain and central nervous
system are involved, and with more and more human clinical
material, and experimental results with animals, our understand-
ing continues to increase. <snipped> ......
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Cheers,
+----| Joao Paulo de Carvalho |------ +
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+--------| Salvador-Bahia-Brazil |------+
