FIG. 8.

Action potential generation and propagation. A spike was elicited by synchronously activating 3 excitatory synapses (initial potential = −70 mV) and membrane potential was recorded at different locations. A: the whole somato-dendritic compartment charged almost simultaneously before a spike was elicited in the axon. Then the spike back-propagated into the somato-dendritic compartment. The axonal spike was larger than in the rest of the neuron. Inset: the spike upstroke on an enlarged scale. A very similar picture could be drawn for spikes elicited by step current injection (not shown). B: the model was implemented with parallel fibers demonstrating that the initiation site remains in the ascending axon. Then the spike actively propagates along the parallel fibers and toward the soma and dendrites. The distance from spike initiation site and the conduction time are indicated.