FIG. 9.

Simplified phase diagram comparing the standard ensemble model with the living system. The bilateral absolute phase relations of the standard model (dashed lines) compared with that of the living system (solid line) with the peristaltic HN(4) interneuron as the phase reference. Two synchronous (blue) and one peristaltic (pink) phase curves are shown for both the model and the living system. The phase of the peristaltic HN(4) interneuron is indicated with a slanted green straight line and the phase of its contralateral homologue, the synchronous HN(4) interneuron, is indicated with a slanted light green straight line. The slopes of these lines reflect the conduction delays from segment to segment. Although the intersegmental phase differences among the middle and rear synchronously coordinated motor neurons are similar for the model and the living system, use of a common phase reference illustrates that model motor neuron activity is not properly phased to the synaptic input. The intersegmental phase differences among the peristaltically coordinated motor neurons in the model match the general trend of the living system, but the standard model does not capture the large intersegmental phase differences of the living system. Again, the use of a common phase reference illustrates that model motor neuron activity is not properly phased to the synaptic input. The mismatch in absolute phase between the model and the living system is smallest in the middle motor neurons and gradually increases both frontward and rearward.