  The action potential propagating in a nerve fibre generates accompanying
mechanical and thermal effects. The whole signal is therefore an ensemble which
includes primary and secondary components. The primary components of a signal
are the action potential itself and longitudinal mechanical waves in axoplasm
and surrounding biomembrane. These components are characterized by
corresponding velocities. The secondary components of a signal are derived from
primary components and include transverse displacement of a biomembrane and the
temperature -- these have no independent velocities but have been measured in
several experiments. A robust mathematical model is presented based on
differential equations describing the signal primary components which are
coupled into a system by coupling forces. The model includes also mathematical
formulation for establishing the secondary components following the ideas from
experimental studies.
