Figure 3.

All action potentials of a train initiate in the axon initial segment. A, Voltage-sensitive dye fluorescence image of the soma–axon region in recording position shown on top. Traces below are AP signals evoked by repetitive soma stimulation at 200 Hz (bottom trace). Signals were recorded by an electrode in the soma (black) and optically from AIS and first node of Ranvier (blue and green) as indicated on the image. The scale bar illustrates percentage ΔF/F for the optical signals. B, Comparison of AP waveforms from the AIS (green) and first node (blue) for the first and ninth spike in the train. C, Latency difference between the first node and AIS for the nine spikes in the train; AIS discharges first for all spikes. The equation is the best linear fit of the data, and the slope of this line is not significantly different from zero (p = 0.89; n = 3 cells). Error bars indicate SEM.