Figure 3. V_th is hyperpolarized during the active and inactive portions of the fictive scratch cycle.

A shows extensor (GS) ENG activity during ipsilateral fictive scratch (top trace) and the intracellular membrane potential recording and current injection (middle traces) for a GS motoneurone in a preparation with an intact spinal cord. The shaded area denotes the portion illustrated in C on an expanded timescale. The V_th for action potentials before fictive scratch was −39.4 mV and was elicited by a 19 nA rectangular current pulse. The current was increased to 28 nA to ensure spiking during the hyperpolarized phase of the SDP. C shows the thresholds of the current-evoked action potential and the action potential evoked by the SDP were similar and hyperpolarized by −2.1 mV compared to control (B). Note the spikes are truncated in panels B and C.