Biomedical Engineering Reference
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Figure 19.1. Single spikes are elicited by the leading edge of electrical pulses. (a) Voltage
clamp response to a 3ms 50A cathodic pulse (solid trace). Large current transients are
seen (horizontal arrows) at pulse onset and offset (timing given by square wave above.
The response was sensitive to TTX (dotted trace) but only in the time period immediately
following the pulse onset (gray box). (b) Subtracting the TTX record from control extracts
the spike which is similar to light-elicited spikes (dotted trace). (c) Voltage clamp response
to a 200sec 50A electrical pulse (solid line). Large transient currents are again seen
at pulse onset and offset (horizontal arrows). The response here was also TTX sensitive
(dotted trace). (d) Subtracting the TTX record from control extracts the spike.
pulse under control conditions and in TTX (Figure 19.1c, solid and dotted lines
respectively) were different, again suggesting the presence of neuronal activity.
Subtraction again revealed the presence of a spike (Figure 19.1d). The response
to a short pulse in control conditions was always triphasic, consisting of an
upward, downward and then second upward deflection. In TTX, the response
was always biphasic (no second upward deflection). In later experiments with
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