9. THE MAUTHNER CELL
307
7Right
v
M cellresponses =
Left EMG
n
Fig. 28. Ventral root records during ipsilateral and contralateral Mauthner axon
stimulation. The upper set of traces show the Mauthner ceIl responses: the top is the
excitatory one ( corresponding to the ipsilateral Mauthner axon), stimulus applied
at a fixed time; the traces below this (proceeding downward) show the inhibitory
one (contralateral Mauthner axon), timed to occur at various time intervals before
and after the excitatory one. The lower set of traces show the output in the ventral
root; the upperniost of these is the response to the excitatory Mauthner cell alone
and proceeding downward the responses for the various Mauthner cell intervals
shown in the upper set of traces. Note that the bottom ventral root record is the
crossed excitatory response to contralateral Mauthner axon stimulation ( cf. Fig. 8).
Calibrations: vertical, 200 p V ; horizontal, 2 msec.
the excitatory pathway to the latter inotoneurons, and to those on the
opposite side of the cord which are responsible for the crossed excitatory pathway (Section IV, A ) ?
We cannot exclude the possibility that hitherto unrecognized Mauthner axon collaterals run to “nonprimary” motoneurons or to interneurons