Contribution from individual PSCs to Gin. (A) During rhythmic activity in the ventral root (L2, lower trace), the membrane current (upper trace) consists of fast events, presumably PSCs, in positive and negative direction on a modestly fluctuating baseline. (B) The current in response to a 10-mV step in the command potential was converted to the corresponding conductance by dividing it by the driving voltage (10 mV). The upper curve gives the conductance with synaptic activity (dotted line gives SEM), and the lower gives the conductance after TTX application. The hatched area gives avGsyn. Inset shows 10 excitatory PSCs (EPSCs) and 10 inhibitory PSCs (IPSCs), also converted into conductances (EPSGs and IPSGs). The largest PSGs were of the same magnitude as the basal Gin without synaptic activity. (C) Distribution of amplitudes of the peak conductance of EPSGs and IPSGs, as measured in the soma of one cell, is shown as a histogram of filled and open bars, respectively. These amplitudes were detected at a holding potential of −47 mV. Gin without synaptic activity (continuous line) and the synaptic addition to this conductance (dotted line) are shown below the histogram.