Slide 3

Spikes Initiate in the Axon Initial Segment in Purkinje Neurons

Figure 3.   Example comparison of a recorded action potential versus voltage sensitive dye imaging.  The dye responds quickly to changes in membrane potential (within 5 microseconds), so follows the kinetics of action potentials faithfully (although there may be noise in the signal).  Example here is from squid giant axon  (Ross et al. J. Membrane Biol. 33: 141-183; 1977).