ABSTRACT
The main oesophageal motor neurone (OD1) of the rock lobster is an unpaired bifurcating nerve cell. The cell body is located in the oesophageal ganglion and the left and right axonal branches pass through the left and right commissural ganglia to innervate all the oesophageal dilator muscles.
Three types of potentials are recorded in the cell body in vitro; each type is associated with an extracellular spike recorded from the nerves connecting the ganglia.
Comparison between the three types of potentials (and the extracellular spikes) and collision experiments shows that all three are spikes.
Spontaneous collisions can sometimes occur and it is concluded that one spike is generated in the oesophageal ganglion (somatofugal a-spike) while the other two are generated in the left commissural ganglion (somatopetal b-spike) or the right commissural ganglion (somatopetal c-spike).
Each spike initiating zone is synaptically driven.
The commissural zones fire short phasic bursts; each burst is composed of only one type of spike (b-or c-). The oesophageal (a-) zone gives a tonic discharge interrupted when the other zones are firing. Finally, combined firing of the spike initiating zones can generate three different patterns of discharge.
OD1 participates in the oesophageal motor rhythm produced by two oscillators (one in each commissural ganglion) which fire alternated series of bursts.
It is concluded that the three axonal spike initiating zones enable the motor neurone (1) to follow the oesophageal motor rhythm at any time regardless of which oscillator is in operation and (2) to co-ordinate phasic and tonic activation of the oesophageal dilator muscles.
