The Spike of Coombs et al. Exhibits a "Kink" and a "biphase" in the Phase Plot
Figure 5. We digitized one of the spikes illustrated by Eccles and plot the phase plot of the spike. On the left is the action potential and its first derivative. On the right is the phase plot of dV/dt versus Vm for this spike. Note the "kink" and the biphasic nature of the phase plot of the action potential. The kink arises from the back-propagation into the soma of the spike in the initial segment of the axon.