Figure 1.

Phasic and tonic firing patterns in sympathetic neurons. A, Superimposed voltage traces recorded in current clamp from a sympathetic neuron firing in a phasic pattern (top). The neuron responded to 440 ms current pulses ranging from −100% of threshold current amplitude up to 500% of threshold current (shown below). This cell responded to all stimuli by firing one or two action potentials near the beginning of the pulse and then falling silent. B, The voltage response of the cell shown in A in response to a 500% of threshold current stimulus. C, Superimposed voltage traces recorded from a tonic cell (top) show that this cell fired repetitively throughout the duration of all stimuli above the threshold current. D, The voltage response of the cell shown in B in response to a 500% of threshold current stimulus.