  Comprehending the nature of action potentials is fundamental to our
understanding of the functioning of nervous systems in general. Here we
consider their evolution and describe their functions of communication,
modulation and computation within nervous systems. The ionic mechanisms
underlying action potentials in the squid giant axon were first described by
Hodgkin and Huxley in 1952 and their findings have formed our orthodox view of
how the physiological action potential functions. However, substantial evidence
has now accumulated to show that the action potential is accompanied by a
synchronized coupled soliton pressure pulse in the cell membrane, the action
potential pulse (APPulse). Here we explore the interactions between the soliton
and the ionic mechanisms known to be associated with the action potential.
Computational models of the action potential usually describe it as a binary
event, but we suggest that it is quantum ternary event known as the
computational action potential (CAP), whose temporal fixed point is threshold,
rather than the rather plastic action potential peak used in other models. The
CAP accompanies the APPulse and the Physiological action potential. Therefore,
we conclude that nerve impulses appear to be an ensemble of three inseparable,
interdependent, concurrent states: the physiological action potential, the
APPulse and the CAP.
