9. THE MAUTHNER CELL
315
in some of the motoneurons on both sides, then the crossing inhibition
would arrive too late at certain of them to prevent their firing, and the
result would be obviously undesirable bilateral ( i.e., opposed) muscle
activity. On the other hand, if the noise were inhibitory, then the two
Mauthner impulses would need to be separated by at least 0.3 msec
before any reflex movements would occur. We believe that this interval
may be too great to be of use to the fish, that it is unlikely to be often
achieved, and that the repeated experimental finding of 0.15 msec as
the minimum separation required for effects is of significance; these
points are considered in the next section.
VIII. THE EXCITATION OF THE MAUTHNER CELLS
A. The Need for Asynchronous Firing of the Two Cells
From the characteristics of the spinal system, we know that the
largest response to a single stimulus likely to activate the Mauthner
neurons is the unilateral powerful movement resulting from the firing
of only one of the two cells. But if an appropriate stimulus in the
environment could cause both cells to respond, it is clearly of great
importance, again taking account of the spinal system, that they do not
fire synchronously or even within about two-tenths of a millisecond of
one another (Fig. 12). This need for asynchronous firing must be regarded as of fundamental importance in Mauthner cell function. We
must now consider the sorts of physiological stimuli which could cause
the Mauthner cells to fire, the properties of these stimuli and the sensory
pathways, and the brain circuitry of which the Mauthner cells are a
part, which could help to bring about the time separation between the
Mauthner impulses required for successful reflex effects.
B. The VIII Cranial Nerves: “Electrical” and “Chemical”
Excitation of the Mauthner Cells
From anatomical studies, it is certain that there is an important direct
input to the Mauthner cells from the ipsilateral VIIIth nerve andalthough less easy to recognize histologically-a probable one from
the contralateral VIIIth nerve also (Fig. 1). Of the greatest interest
here are the prominent VIIIth nerve myelinated fibers which contribute
the large “club endings” on the lateral dendrite (Figs. 1, 4, and 34A).
Furshpan and Furukawa (1962) showed that these are excitatory to the
315
in some of the motoneurons on both sides, then the crossing inhibition
would arrive too late at certain of them to prevent their firing, and the
result would be obviously undesirable bilateral ( i.e., opposed) muscle
activity. On the other hand, if the noise were inhibitory, then the two
Mauthner impulses would need to be separated by at least 0.3 msec
before any reflex movements would occur. We believe that this interval
may be too great to be of use to the fish, that it is unlikely to be often
achieved, and that the repeated experimental finding of 0.15 msec as
the minimum separation required for effects is of significance; these
points are considered in the next section.
VIII. THE EXCITATION OF THE MAUTHNER CELLS
A. The Need for Asynchronous Firing of the Two Cells
From the characteristics of the spinal system, we know that the
largest response to a single stimulus likely to activate the Mauthner
neurons is the unilateral powerful movement resulting from the firing
of only one of the two cells. But if an appropriate stimulus in the
environment could cause both cells to respond, it is clearly of great
importance, again taking account of the spinal system, that they do not
fire synchronously or even within about two-tenths of a millisecond of
one another (Fig. 12). This need for asynchronous firing must be regarded as of fundamental importance in Mauthner cell function. We
must now consider the sorts of physiological stimuli which could cause
the Mauthner cells to fire, the properties of these stimuli and the sensory
pathways, and the brain circuitry of which the Mauthner cells are a
part, which could help to bring about the time separation between the
Mauthner impulses required for successful reflex effects.
B. The VIII Cranial Nerves: “Electrical” and “Chemical”
Excitation of the Mauthner Cells
From anatomical studies, it is certain that there is an important direct
input to the Mauthner cells from the ipsilateral VIIIth nerve andalthough less easy to recognize histologically-a probable one from
the contralateral VIIIth nerve also (Fig. 1). Of the greatest interest
here are the prominent VIIIth nerve myelinated fibers which contribute
the large “club endings” on the lateral dendrite (Figs. 1, 4, and 34A).
Furshpan and Furukawa (1962) showed that these are excitatory to the