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Harald Tichy and Ewald Gingl
Therefore, one would expect that at rapid temperature changes the exposed dendrites of the spider's warm cell and the cold cell of the saturniid moth would reach
a new temperature faster than the dendrites which are covered by cuticle and positioned beneath the base of the sensillum. This would imply that in the spider and
the moth the thermoreceptor sensitivity to rapid temperature changes is increased
by a reduced damping of the heat transfer. The more superficial dendrites should
take on the temperature of the ambient air faster than the deeper ones, if only because of the additional amount of material in which the latter are embedded. During slowly changing temperature, on the other hand, the temperature of the thermoreceptor should not lag behind that of the ambient air. Thus, during slow temperature change the size of the dendritic membrane area rather than the position of
the dendritic tip should characterize sensitivity of the thermoreceptors.
To elucidate the relationship between thermoreceptor structure and sensitivity,
the rank order for sensitivity to rapid step-like temperature change, slowly oscillating temperature change, and steady temperature was compared with the size of
the dendritic membrane area and the position of the dendritic tip (Fig. 4 A,C, Ehn
and Tichy 1996). The improvement in the signal-to-noise ratio caused by the increase in the size of the dendritic membrane area indeed increases with the square
root of the outline of the dendrites (Fig. 4A 4). The resulting square root ratios are
closely reflected in the ratios of both the values of sensitivity to slowly changing
and steady temperature (Fig. 4A 2,3).
The position of the dendritic tip seems to characterize the thermoreceptors in
terms of sensitivity to rapid temperature changes (Fig. 4A,B). The cold cell of the
satumiid moth, which has a considerably smaller dendritic membrane area than
the cold cell of cave beetle, displays the highest dynamic sensitivity; but in contrast to the cold cell of the cave beetle, the dendrite of the satumiid moth's cold
cell projects into a slender elongate socket which rises 60 11m above the antenna!
surface. Therefore, at rapid temperature changes the dendrite of the satumiid moth
is supposed to reach a new temperature level faster than that of the cave beetle
which terminates beneath the sensillum base. Further support for such a view is
provided by the warm cell of the spider which shows the second highest sensitivity
to rapid temperature changes and has a dendrite that terminates at a pore opening
on the tip of a small (height 5 11m) sensillum. Also, the low values of sensitivity
described for the cold cells of the cockroach and the migratory locust are in good
agreement with the position of their dendrites beneath the surface of the body
wall.
Harald Tichy and Ewald Gingl
Therefore, one would expect that at rapid temperature changes the exposed dendrites of the spider's warm cell and the cold cell of the saturniid moth would reach
a new temperature faster than the dendrites which are covered by cuticle and positioned beneath the base of the sensillum. This would imply that in the spider and
the moth the thermoreceptor sensitivity to rapid temperature changes is increased
by a reduced damping of the heat transfer. The more superficial dendrites should
take on the temperature of the ambient air faster than the deeper ones, if only because of the additional amount of material in which the latter are embedded. During slowly changing temperature, on the other hand, the temperature of the thermoreceptor should not lag behind that of the ambient air. Thus, during slow temperature change the size of the dendritic membrane area rather than the position of
the dendritic tip should characterize sensitivity of the thermoreceptors.
To elucidate the relationship between thermoreceptor structure and sensitivity,
the rank order for sensitivity to rapid step-like temperature change, slowly oscillating temperature change, and steady temperature was compared with the size of
the dendritic membrane area and the position of the dendritic tip (Fig. 4 A,C, Ehn
and Tichy 1996). The improvement in the signal-to-noise ratio caused by the increase in the size of the dendritic membrane area indeed increases with the square
root of the outline of the dendrites (Fig. 4A 4). The resulting square root ratios are
closely reflected in the ratios of both the values of sensitivity to slowly changing
and steady temperature (Fig. 4A 2,3).
The position of the dendritic tip seems to characterize the thermoreceptors in
terms of sensitivity to rapid temperature changes (Fig. 4A,B). The cold cell of the
satumiid moth, which has a considerably smaller dendritic membrane area than
the cold cell of cave beetle, displays the highest dynamic sensitivity; but in contrast to the cold cell of the cave beetle, the dendrite of the satumiid moth's cold
cell projects into a slender elongate socket which rises 60 11m above the antenna!
surface. Therefore, at rapid temperature changes the dendrite of the satumiid moth
is supposed to reach a new temperature level faster than that of the cave beetle
which terminates beneath the sensillum base. Further support for such a view is
provided by the warm cell of the spider which shows the second highest sensitivity
to rapid temperature changes and has a dendrite that terminates at a pore opening
on the tip of a small (height 5 11m) sensillum. Also, the low values of sensitivity
described for the cold cells of the cockroach and the migratory locust are in good
agreement with the position of their dendrites beneath the surface of the body
wall.