FIGURE 10-13 Tuning Curves Graphs plotted by the sound wave frequency and amplitude energy required to increase the firing rate of two axons in the cochlear nerve. The lowest point on each tuning curve is the frequency to which that hair cell is most sensitive. The curve at left is centered on a frequency of 1000 Hz, the midrange of human hearing; the curve at right is centered on a frequency of 10,000 Hz, in the high range.