320
J. DIAMOND
Other junctions on the lateral dendrite have the conventional electron-microscopic appearances of chemically transmitting synapses ( Fig.
34C), and we may take it that some of these correspond to the ipsilateral
VIIIth nerve enclings which do not seem to be electrically coupled (Fig.
33, B l ) . They must be responsible for some of the longer latency e.p.s.ps,
the earliest of which has a synaptic delay of about 0.4-0.5 msec. These
chemically transmitting endings have not been identified unequivocally,
but they could include the “bulb endings” of Held-Auerbach, which
cover the proximal half of the lateral dendrite (Figs. 4 and 34D) and
are believed to derive directly from the VIIIth nerve, although it is
not clear whether this is the ipsilateral or the contralateral one (see
Bodian, 1942; Ketzlaff, 1957); they could also be the small endings
which are scattered all over the lateral dendrite, and indeed over
the whole cell (Figs. 4 and 34D and E ) . Many of the endings on the
soma (and possibly the lateral dendrite too), and probably all those
on the ventral dendrite, derive from neurons situated in a variety
of regions of the brain (see legend to Fig. 4), and many of these will
be activated, when vestibular excitation occurs, in addition to the
direct VIIIth nerve fibers to the Mauthner cells.
C. The Vestibular System and the Swim Bladder
Furukawa and his colleagues have shown that the stimulus which
causes activity in certain groups of the VIIIth nerve fibers is sound,
which acts primarily on hair cells in the lagena and the sacculus
(Furukawa and Ishii, 1967a). It seems certain that a sudden vibrational
stimulus in the vicinity of the fish will cause the more-or-less synchronous
activation of both large and small myelinated fibers running to the
lateral dendrite and other regions of the ipsilateral Mauthner cell, and
quite probably, as we shall see, to the contralateral cell also. What
then are the chances of one cell being fired in advance of the other?
If the vibration originated closer to one vestibular system than the other,
it would seem likely to affect the nearer Mauthner cell earlier and
possibly to a greater extent than the opposite one, but there is one
condition which could greatly influence this result. The diagram in
Fig. 35 (taken from von Frisch, 1936) shows the relation of the swim
bladder in the Ostariophysi (which includes both tench and goldfish)
to the vestibular apparatus. It can be seen that vibrations could be
transmitted via the body wall to the swim bladder, and then via the
Weberian ossicles, the perilymphatic space and the endolymphatic transverse canal, directly and probably equally to the lagena and sacculus
J. DIAMOND
Other junctions on the lateral dendrite have the conventional electron-microscopic appearances of chemically transmitting synapses ( Fig.
34C), and we may take it that some of these correspond to the ipsilateral
VIIIth nerve enclings which do not seem to be electrically coupled (Fig.
33, B l ) . They must be responsible for some of the longer latency e.p.s.ps,
the earliest of which has a synaptic delay of about 0.4-0.5 msec. These
chemically transmitting endings have not been identified unequivocally,
but they could include the “bulb endings” of Held-Auerbach, which
cover the proximal half of the lateral dendrite (Figs. 4 and 34D) and
are believed to derive directly from the VIIIth nerve, although it is
not clear whether this is the ipsilateral or the contralateral one (see
Bodian, 1942; Ketzlaff, 1957); they could also be the small endings
which are scattered all over the lateral dendrite, and indeed over
the whole cell (Figs. 4 and 34D and E ) . Many of the endings on the
soma (and possibly the lateral dendrite too), and probably all those
on the ventral dendrite, derive from neurons situated in a variety
of regions of the brain (see legend to Fig. 4), and many of these will
be activated, when vestibular excitation occurs, in addition to the
direct VIIIth nerve fibers to the Mauthner cells.
C. The Vestibular System and the Swim Bladder
Furukawa and his colleagues have shown that the stimulus which
causes activity in certain groups of the VIIIth nerve fibers is sound,
which acts primarily on hair cells in the lagena and the sacculus
(Furukawa and Ishii, 1967a). It seems certain that a sudden vibrational
stimulus in the vicinity of the fish will cause the more-or-less synchronous
activation of both large and small myelinated fibers running to the
lateral dendrite and other regions of the ipsilateral Mauthner cell, and
quite probably, as we shall see, to the contralateral cell also. What
then are the chances of one cell being fired in advance of the other?
If the vibration originated closer to one vestibular system than the other,
it would seem likely to affect the nearer Mauthner cell earlier and
possibly to a greater extent than the opposite one, but there is one
condition which could greatly influence this result. The diagram in
Fig. 35 (taken from von Frisch, 1936) shows the relation of the swim
bladder in the Ostariophysi (which includes both tench and goldfish)
to the vestibular apparatus. It can be seen that vibrations could be
transmitted via the body wall to the swim bladder, and then via the
Weberian ossicles, the perilymphatic space and the endolymphatic transverse canal, directly and probably equally to the lagena and sacculus