9. THE MAUTHNER CELL
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tions of membrane potential) in the Mauthner cell body and dendrites
means that incoming nerve volleys, even of constant size, fire off Mauthner impulses with latencies that may vary by perhaps 0.1-0.2 msec or
more, which is too imprecise for the sort of experiments described below.
This particular problem is not met with when the axon itself is excited.
B. Choice of Recording Technique
The only certain indication that a Mauthner neuron has been excited
is the direct recording of its electrical response. The tail flip, caused
by a stimulus applied either to the VIIIth nerve or to the spinal cord
or by a vibrational stimulus or any other kind of stimulus, is not proof
of Mauthner neuron activation; indeed, it can sometimes be caused
when it is certain that the spinal motoneurons are not being excited
from the Mauthner neurons. One useful response described later (Section IV, A ) , involving the activity of muscles of the eyeballs, jaw, and
operculi, does not tell whether only one or both Mauthner cells are
being activated. This is a point of fundamental importance; as we shall
see, any trunk or tail movements associated with the synchronous firing
of both Mauthner cells must be attributed to the coincidental activation
of other (non-Mauthner) systems.
C. Selective Recording from an Individual Mauthner Cell
Tasaki et al. (1954) first showed that stimulation of the whole spinal
cord (in Japanese catfish) caused the firing in the medulla of a cell
which, from its location, the ease with which it could be successfully
penetrated with a microelectrode, and the short latency of the response,
they took to be the Mauthner cell. However, the proof of this, and
the discovery of how selectively to locate the cell, followed from the
elegant experiments of Furshpan and Furukawa (1962) who made some
important and fundamental observations. One of the most fruitful was
that concerning the giant, predominantly negative potential which they
recorded near the excited Mauthner cell in the goldfish (Fig. 5a). This
extracellular potential seemed to have its origin at an extremely localized
spot, somewhat less than 25 , U in diameter, where it was maximal in size.
Figure 6 shows the relation between size of this potential-the “negative
spike”-and distance from the spot where it was largest (the negative
spike focus). This shows that in such an experiment when the electrode
tip records a negative spike of more than 15-20 mV, it is very close
(probably less than 25 p ) to the focus, and it is then outside an active
273
tions of membrane potential) in the Mauthner cell body and dendrites
means that incoming nerve volleys, even of constant size, fire off Mauthner impulses with latencies that may vary by perhaps 0.1-0.2 msec or
more, which is too imprecise for the sort of experiments described below.
This particular problem is not met with when the axon itself is excited.
B. Choice of Recording Technique
The only certain indication that a Mauthner neuron has been excited
is the direct recording of its electrical response. The tail flip, caused
by a stimulus applied either to the VIIIth nerve or to the spinal cord
or by a vibrational stimulus or any other kind of stimulus, is not proof
of Mauthner neuron activation; indeed, it can sometimes be caused
when it is certain that the spinal motoneurons are not being excited
from the Mauthner neurons. One useful response described later (Section IV, A ) , involving the activity of muscles of the eyeballs, jaw, and
operculi, does not tell whether only one or both Mauthner cells are
being activated. This is a point of fundamental importance; as we shall
see, any trunk or tail movements associated with the synchronous firing
of both Mauthner cells must be attributed to the coincidental activation
of other (non-Mauthner) systems.
C. Selective Recording from an Individual Mauthner Cell
Tasaki et al. (1954) first showed that stimulation of the whole spinal
cord (in Japanese catfish) caused the firing in the medulla of a cell
which, from its location, the ease with which it could be successfully
penetrated with a microelectrode, and the short latency of the response,
they took to be the Mauthner cell. However, the proof of this, and
the discovery of how selectively to locate the cell, followed from the
elegant experiments of Furshpan and Furukawa (1962) who made some
important and fundamental observations. One of the most fruitful was
that concerning the giant, predominantly negative potential which they
recorded near the excited Mauthner cell in the goldfish (Fig. 5a). This
extracellular potential seemed to have its origin at an extremely localized
spot, somewhat less than 25 , U in diameter, where it was maximal in size.
Figure 6 shows the relation between size of this potential-the “negative
spike”-and distance from the spot where it was largest (the negative
spike focus). This shows that in such an experiment when the electrode
tip records a negative spike of more than 15-20 mV, it is very close
(probably less than 25 p ) to the focus, and it is then outside an active