Figure 4.

Upper panels: A, histogram of activity. B, popliteal blood flow. C, arterial blood pressure (ABP). Arrows indicate the time of injection. Note that the fibre shown at the left responds immediately as soon as blood flow increases. No change was observed during vehicle injection. Lower panel: response to venous occlusion of a group IV afferent fibre, which also responded to papaverine and venous contraction (not shown). The response to the occlusion of the vena cava suggests that the receptive field of this ending is located on the venular side of the muscle circulation.