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Plasticity
A term that encompasses and increasing number of cellular
mechanisms but generally denotes the capacity of cells, most notably neurons, to
change. Traditionally it included almost exclusively synaptic processes (short
term, such as facilitation, depression, etc, or long term, such as LTP, LTD,
etc). However, similar short and long-term changes, often compensatory
(homeostatic) in nature, involve the excitable properties of neurons, through
activity-dependent modifications of voltage-gated ion channels outside the synapse. These
channels are also increasingly acknowledged to undergo plasticity. A great recent Nature Insight
issue on the subject has been published:
"Plasticity and Neuronal Computation", Nature (2004), 431: 759-803
Humans
This is my peeve subject. Humans are animals, just
as any other animal, in spite of the traditional distinction between animals
and humans. Furthermore, higher animals (or plants) are no higher than any other
animals (or plants). They may be more or less complex. But ALL animals
that exist at this
moment are equally "high". They all have made it through the intricacies of evolution
and survived selection since their appearance on Earth. One could perhaps argue that
vertebrates are higher than invertebrates, or that mammals are higher than fish,
because the former appeared on the scene later than the latter, but that
depends on the precision of the archeological records, which we all know is
often subject to considerable change. Moreover, not because fish appeared
on Earth before mammals, did they stop evolving. They just went a different path
and they became fancy creatures that have survived in their own particular
environment as well as their mammalian relatives. The only animals that
could be appropriately argued to be "lower" are those whose perished along the
way.
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