132
R. W. MURRAY
phasic response, called "paradoxical" by Sand to emphasize its negative
sign, can be extremely sensitive, reaching -90 impulses/sec/ "C for example in the ampullae of Scyllium. (Hensel, 1955); but in the lateral line
the sensitivity is much less (-0.3 impulse/sec/"C; Sand, 1938). NO
phasic response has been described in teleosts (Hoagland, 1935). The
tonic response is usually described as positive only, i.e., faster when hot
(e.g., Hoagland, 1935; Sand, 1938) with Qlo values ranging between 1.5
and 3. But in ampullae of dogfish from the warmer waters of the Mediterranean (Hensel, 1955) this positive relationship is seen to be merely
the lower part of a peaked curve having its maximum around 20"-25°C
and falling back to zero again by 30°C. Thus the responses of the ampullae, both phasic and tonic, are seen to parallel almost exactly those of
the cold fibers in mammalian skin.
The stretch receptors from the pelvic fin of rays, when put under
tension to establish a continued impulse discharge, showed tonic and
insensitive phasic responses virtually identical with those of the lateral
line organs ( Sand, 1938).
If the ampullae are not temperature receptors, then it may be possible
to turn the argument the other way around, namely, that the fish are
not in fact normally subjected to temperature changes fast enough to
elicit significant impulse frequency responses from the ampullae. The
normal functioning of the system in response to its proper stimuli (e.g.,
electroreception) is not therefore distributed.
However, the thermal sensitivity is clearly of interest to sensory physiologists for it provides a model of the action of mammalian cold fibers.
In this connection, for example, Murray (1966) has stressed the very
dissimilar anatomical organization of the many nervous structures which
exhibit the same kind of negative phasic response superimposed on a
less sensitive positive tonic change. Ampullae of Lorenzini have sensory
synapses on receptor cells, mammalian cold fibers have free nerve endings,
motor nerves in crustaceans have no natural terminal structures when
excised, and so on. Murray argues from this diversity that the thermal
responses represent one of the basic properties of nerve membrane, and
temperature receptors are those nervous structures in which this property
is most highly developed.
REFERENCES
Andrews, C. W. (1952). Sensitivity of fish to light and the lateral line system.
Bailey, S. E. R. (1969). The responses of sensory receptors in the skin of the green
lizard, Lacerta uiTidis, to mechanical and thermal stimulation. Comp. Biochem.
Physiol. ZOO^. 25, 240-243.
PhysioZ. 29, 161-172.
R. W. MURRAY
phasic response, called "paradoxical" by Sand to emphasize its negative
sign, can be extremely sensitive, reaching -90 impulses/sec/ "C for example in the ampullae of Scyllium. (Hensel, 1955); but in the lateral line
the sensitivity is much less (-0.3 impulse/sec/"C; Sand, 1938). NO
phasic response has been described in teleosts (Hoagland, 1935). The
tonic response is usually described as positive only, i.e., faster when hot
(e.g., Hoagland, 1935; Sand, 1938) with Qlo values ranging between 1.5
and 3. But in ampullae of dogfish from the warmer waters of the Mediterranean (Hensel, 1955) this positive relationship is seen to be merely
the lower part of a peaked curve having its maximum around 20"-25°C
and falling back to zero again by 30°C. Thus the responses of the ampullae, both phasic and tonic, are seen to parallel almost exactly those of
the cold fibers in mammalian skin.
The stretch receptors from the pelvic fin of rays, when put under
tension to establish a continued impulse discharge, showed tonic and
insensitive phasic responses virtually identical with those of the lateral
line organs ( Sand, 1938).
If the ampullae are not temperature receptors, then it may be possible
to turn the argument the other way around, namely, that the fish are
not in fact normally subjected to temperature changes fast enough to
elicit significant impulse frequency responses from the ampullae. The
normal functioning of the system in response to its proper stimuli (e.g.,
electroreception) is not therefore distributed.
However, the thermal sensitivity is clearly of interest to sensory physiologists for it provides a model of the action of mammalian cold fibers.
In this connection, for example, Murray (1966) has stressed the very
dissimilar anatomical organization of the many nervous structures which
exhibit the same kind of negative phasic response superimposed on a
less sensitive positive tonic change. Ampullae of Lorenzini have sensory
synapses on receptor cells, mammalian cold fibers have free nerve endings,
motor nerves in crustaceans have no natural terminal structures when
excised, and so on. Murray argues from this diversity that the thermal
responses represent one of the basic properties of nerve membrane, and
temperature receptors are those nervous structures in which this property
is most highly developed.
REFERENCES
Andrews, C. W. (1952). Sensitivity of fish to light and the lateral line system.
Bailey, S. E. R. (1969). The responses of sensory receptors in the skin of the green
lizard, Lacerta uiTidis, to mechanical and thermal stimulation. Comp. Biochem.
Physiol. ZOO^. 25, 240-243.
PhysioZ. 29, 161-172.