496
M. V. L. BENNETT
munication ( Bullock, 1970; Black-Cleworth, 1970; Mohres, 1957; Moller,
1970; Westby and Box, 1970). Strongly electric organs could in principle
operate in an e1ectrolocat;on system, but their use largely follows detection of prey (Bauer, 1968; Belbenoit, 1970; Pickens and McFarland,
An important reason for the earlier studies of electrosensory systems
was their extraordinary sensitivity. Thresholds of 0.01 and 0.1 pV/ cm
have been reported in behavioral experiments (Dijkgraaf and Kalmijn,
1966; Machin and Lissmann, 1960). These sensitivities exceed those of
ordinary fish by a factor of lo4 or more (Lissmann and Machin, 1958).
As it turns out, the membrane processes at electroreceptors are probably
similar to those at many other receptors. The sensitivity appears to be
mainly a result of arrangement of external structures rather than of specialization of the receptor membranes themselves. However, the electroreceptors provide a useful model for certain stages of receptor action of
much wider occurrence. This is because their specialization for detection
of extracellular signals makes accessible to the experimenter a stage of
action that is generally quite inaccessible.
1964).
11. DISTRIBUTION OF ELECTRORECEPTORS
Most electroreceptors fall into two classes: the tonic and the phasic
receptors, each with its characteristic morphological and physiological
properties. The tonic receptors are tonically and fairly rhythmically active.
They give tonic or long-lasting responses to low frequency or dc stimuli
although accommodation may be more or less marked. They are “ampullary” organs and have an obvious canal leading from receptor cavity to
exterior. Phasic receptors are sensitive to relatively high frequencies and
are insensitive to maintained or dc stimuli. They give only brief or phasic
responses to step changes in stimulating voltage. Spontaneous activity if
present is irregular under normal conditions. These receptors are “tuberous,’’ that is, there is no obvious channel from receptor cavity to exterior
and the connection is presumably by way of intercellular clefts.
There is some confusion in the literature as to nomenclature and
function of electroreceptors, and a summary of types based on the most
recent morphological and physiological data is given in Table I. All
putative and known electroreceptors have been termed “ampullary” by
Dijkgraaf (1963), but at this time it seems preferable to divide them into
ampullary or tonic receptors and tuberous or phasic receptors, the choice
of term depending on whether morphological or functional classification
is intended.
M. V. L. BENNETT
munication ( Bullock, 1970; Black-Cleworth, 1970; Mohres, 1957; Moller,
1970; Westby and Box, 1970). Strongly electric organs could in principle
operate in an e1ectrolocat;on system, but their use largely follows detection of prey (Bauer, 1968; Belbenoit, 1970; Pickens and McFarland,
An important reason for the earlier studies of electrosensory systems
was their extraordinary sensitivity. Thresholds of 0.01 and 0.1 pV/ cm
have been reported in behavioral experiments (Dijkgraaf and Kalmijn,
1966; Machin and Lissmann, 1960). These sensitivities exceed those of
ordinary fish by a factor of lo4 or more (Lissmann and Machin, 1958).
As it turns out, the membrane processes at electroreceptors are probably
similar to those at many other receptors. The sensitivity appears to be
mainly a result of arrangement of external structures rather than of specialization of the receptor membranes themselves. However, the electroreceptors provide a useful model for certain stages of receptor action of
much wider occurrence. This is because their specialization for detection
of extracellular signals makes accessible to the experimenter a stage of
action that is generally quite inaccessible.
1964).
11. DISTRIBUTION OF ELECTRORECEPTORS
Most electroreceptors fall into two classes: the tonic and the phasic
receptors, each with its characteristic morphological and physiological
properties. The tonic receptors are tonically and fairly rhythmically active.
They give tonic or long-lasting responses to low frequency or dc stimuli
although accommodation may be more or less marked. They are “ampullary” organs and have an obvious canal leading from receptor cavity to
exterior. Phasic receptors are sensitive to relatively high frequencies and
are insensitive to maintained or dc stimuli. They give only brief or phasic
responses to step changes in stimulating voltage. Spontaneous activity if
present is irregular under normal conditions. These receptors are “tuberous,’’ that is, there is no obvious channel from receptor cavity to exterior
and the connection is presumably by way of intercellular clefts.
There is some confusion in the literature as to nomenclature and
function of electroreceptors, and a summary of types based on the most
recent morphological and physiological data is given in Table I. All
putative and known electroreceptors have been termed “ampullary” by
Dijkgraaf (1963), but at this time it seems preferable to divide them into
ampullary or tonic receptors and tuberous or phasic receptors, the choice
of term depending on whether morphological or functional classification
is intended.