Rhythm generation. (A) Summary of firing patterns and endogenous properties interactions of the six different types of CPG interneurons in a SO-driven rhythm. The SO was depolarized for the duration of the traces (horizontal bar) to drive the feeding rhythm. Four cycles of feeding activity are shown with vertical solid lines dividing feeding cycles and vertical dashed lines separating out the protraction (P), rasp (R) and swallow (S) phases within each feeding cycle. The CPG interneurons fire during one of the three phases of the feeding cycle as indicated by the background colors. Asterisks indicate that the neuron has endogenous properties that contribute to network function (B) Synaptic connections and transmitters of the CPG interneurons and motoneurons. (C) Computer simulations of the two-cell (top) and three-cell (bottom) CPG networks. Dots, inhibitory synaptic connections; bars excitatory synaptic connections; resistor symbols, electrotonic synaptic connections. Abbreviations: Ach = acetylcholine; glu = L-glutamate; PIR = post-inhibitory rebound. See Abbreviations for all definitions of neuron types.