Neural regulation of respiration.

We would suggest that during the evolution of the mammalian respiratory neural networks the primitive centers in the cervical cord as well as the ventral respiratory group which evolved in fish have been preserved and are capable of functioning in the absence of the dorsal respiratory group generator which evolved with air breathing. We believe that these pattern generators are separate from the identified respiratory units that have so far been studied and that the apparent reciprocal inhibition observed in the identified cells results from synchronized excitatory and inhibitory inputs arising from the pattern generator itself. We believe that the model of such a system shown in Figure 3 is consistent with the observations cited in the previous section and inconsistent with models involving a single site for a pattern generator or interaction between various populations of known or identified respiratory units.