Figure 1.

Experimental setup of the in vivo bone–nerve preparation and spike discrimination. A, Schematic of the electrophysiological setup. B, Whole-nerve recording and rasters of single-unit activity in response to a ramp-and-hold pressure stimulus applied to the marrow cavity. Action potentials from single mechanically activated units were discriminated by their amplitude and duration using Spike Histogram software. An example of a single spike for each unit is at the left of each raster. C, Relationship between conduction velocity and amplitude of action potentials. Action potential amplitude (in μV; peak-to-peak) was plotted against conduction velocity (in m/s) for 51 single units activated by high-intensity intraosseous pressure stimuli (≥300 mmHg) during recordings made from seven animals. Units that also responded to stimulation of surrounding tissues (white circles) had very large action potential amplitudes (>120 μV) and conducted in the Aβ range (≥14.3 m/s). Units with conduction velocities in the C-fiber range (<2.5 m/s) had the smallest action potential amplitudes (<40 μV peak-to-peak; gray circles). All other units, with action potential amplitudes of >40 μV peak-to-peak that did not respond to the stimulation of surrounding tissues, had Aδ conduction velocities (black circles). A/D, Analog to digital.