Fig. 5. Examples of partially adapting (A) and tonic (B) quail IPC responding to an abrupt inspired CO₂ down-step. Measured spike trains are shown in black. The heavy gray line shows chemoreceptor discharge rate from cycle triggered stimulus histogram averaged over 0.25 s intervals. We found examples of tonic and partially adapting chemoreceptors in all species studied, but IPC with large magnitude adaptation and higher peak discharge rates were more common in small birds, and IPC with lower peak discharge rates and smaller magnitude adaptation were more common in large birds (see text).