Fig. 4. Histograms show the distribution of membrane capacitance in the three groups of sensory neurons. CAP (+) = capsaicin responsive; CAP (−) = capsaicin unresponsive; Fent (+) = fentanyl sensitive; Fent (−) = fentanyl insensitive. Most of the CAP-sensitive cells were smaller than the CAP-insensitive cells. There was, however, considerable overlap among the groups, with some of the CAP-sensitive, fentanyl-sensitive neurons being much larger than any of the CAP-insensitive neurons.