The current most highly regarded specific conception of the synapse
is largely due to and has been best described by Eccles (5): “ ...
the synaptic connections between nerve cells are the only functional
connections of any significance. These synapses are of two types,
excitatory and inhibitory, the former type tending to make nerve cells
discharge impulses, the other to suppress the discharge. There is now
convincing evidence that in vertebrate synapses each type operates
through specific chemical transmitter substances ...”. In response to
a presentation by Hebb (10), Eccles was quoted as saying, “One final
point, and that is if there is electrical interaction, and we have seen
from Dr. Estable’s work the complexity of connections, and we now know
from the electronmicroscopists that there is no free space, only 200
Å clefts, everywhere in the central nervous system, then everything
should be electrically interacted with everything else. I think this is
only electrical background noise and, that when we lift with specific
chemical connections above that noise we get a significant operational
system. I would say that there is electrical interaction but it is just
a noise, a nuisance.” Eccles’ conclusions are primarily based on data
obtained in the peripheral nervous system and the spinal cord. But
there is overwhelming reason to expect that cellular interactions in
the brain are an entirely different affair. For example, “The highest
centres in the octopus, as in vertebrates and arthropods, contain many
small neurons. This finding is such a commonplace, that we have perhaps
failed in the past to make the fullest inquiry into its implications.
Many of these small cells possess numerous processes, but no axon. It
is difficult to see, therefore, that their function can be conductive
in the ordinary sense. Most of our ideas about nervous functioning are
based on the assumption that each neuron acts essentially as a link in
some chain of conduction, but there is really no warrant for this in
the case of cells with many short branches. Until we know more of the
relations of these processes to each other in the neuropile it would
be unwise to say more. It is possible that the effective part of the
discharge of such cells is not as it is in conduction in long pathways,
the internal circuit that returns through the same fiber, but the
external circuit that enters other processes, ...” (3).