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Slide 6

Action potentials exhibit saltatory propagation in the axon of Purkinje Cells

Figure 6. Action potentials propagate in a saltatory manner. A. Spontaneously initiated action potential. Bottom frame: voltage-sensitive dye fluorescence image of the soma-axon region with the AIS, 1st and 2nd nodes as indicated. Colored frames: a time sequence of color-coded spatial map of relative membrane potential during initiation of AP shown in panel (C). Signals from detectors centered over the main axon and collaterals are shown. Color scale is in relative units with resting membrane potential shown in blue/green, half-maximum amplitude in red and peak of the AP in yellow. Individual frames are separated by 50 ms (obtained from cubic spline interpolation of original data points recorded at 100 ms intervals; see Figure 2B). At approximately 50 ms, the spike initiated in the AIS and propagated down the axon. At approximately 100 ms, the 1st node was discharged to half-maximum amplitude before the immediately adjacent axonal regions. At approximately 200 ms the region of the second axon collateral (2nd node) is approaching half maximal. B. A time sequence of changing spatial profiles of membrane potential during initiation and propagation of an action potential. The spatial plots constructed by dividing the axon into 20 regions of equal length. The average relative voltage for each region plotted as a function of distance from the soma. The time of each spatial plot in the sequence corresponds to time points indicated for color-coded frames in panel A. Note how the action potential propagates from the AIS to the 1st node, then to the 2nd node, followed by propagation into the internodal regions. C. A temporal average of 26 spontaneous action potentials for the AIS, 1st node and 2nd node with time lines corresponding to the data in parts A and B.