Re: Communication between cells...

[Howard Pattee <***>]

At 01:31 PM 1/20/05 -0500, Judith asks:
> Why do they assume that there
> are only chemical signals? Medical science has demonstrated, for
> instance, that there are also electrical signals (which is how heart
> cells are able to beat in unison with each other). So if there are two
> modes of communication between cells, there's a good possibility that
> there are more.

Yes, as you say there there are electrical signals like action potentials
that travel along axons in the muscles and brain. However, electrical
signals are not nearly as specific as chemical shapes, so they are almost
always mediated by complex molecular structures. In other words, the
information capacity of electrical signals is small. It is entirely
temporal (i.e., one dimensional) while binding sites in molecules can
carry large amounts of information in one shape and they are not so
crucially dependent on timing. 

Roughly speaking, electrical signals are important for rate-dependent
coordination movements of muscles (sensorimotor controls) and for
decoding temporal inputs in the brain (e.g. speech and music). Chemical
signals work better for metabolic and reproductive coordination that are
not so dependent on rates. Of course, at the molecular level, the
electrical forces always coexist right along with all the other forces.

It is not considered likely that more forces will be found except
possibly at the fundamental particle level, and they would not apply at
the energies required by life as we know it. But one should never say
never.
 
Howard