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G. SHELTON
dominant one. It may be that two opposing groups are unnecessary for
oscillation; certainly there is no a priori reason why a single neuron
group should not show alternating periods of activity and quiescence.
At some level of integration bursts of activity, which do alternate in a
general way, must be produced since the discharges from motor neurons
are known to be of this nature. None of the suggestions made so far accounts satisfactorily for the extensive variation in behavior occurring in
different neurons in both the normal and the immobilized animal. This
variety is particularly difficult to explain in a scheme which assumes
two fairly uniform and opposing populations. Some of the components
in the oscillator must be different to the extent that they can become
silent or continuously active under some conditions without causing
complete disintegration of the rhythmic system (Fig. 15).
IV. THE ROLE OF MECHANORECEPTORS IN
RESPIRATORY REGULATION
Although the evidence reviewed above suggests that the respiratory
center can function in a rhythmic manner in the absence of feedback
from mechanoreceptors, there is no doubt that they have a significant
part to play in the normal fish. In elasmobranchs it has been known for
some time that the breathing rate is in some way related to the volume
of water which is allowed to flow over the gills from cannulae in the
mouth or spiracles (Lutz, 1930; Ogden, 1945). Satchell (1961) confirmed these results and showed that the response was produced as a
result of mechanoreceptor stimulation by the movements of ventilation.
It was totally independent of the oxygen content of the inspired water.
Sharks decrease their breathing rate by prolonging the period of
oro- and parabranchial expansion and extending the pause after this
inspiratory period; the opposite occurs when the breathing rate goes
up. Satchell (1959) showed that stimulation of the branchial branches
of the IXth and Xth cranial nerves, or the prespiracular branch of the
VIIth, stopped or slowed breathing by increasing the duration of the
pause. Inflation of a balloon inside the pharynx produced a similar result. It was suggested that these experiments demonstrated the existence of inhibitory pathways to the respiratory center in the branchial
nerves. It also seemed clear that the pathways originated in pharyngeal
mechanoreceptors, and support for this came from recordings of sensory
discharges in the branchial nerves during contraction of oro- and parabranchial cavities. Satchell and Way (1962) examined activity from the
pharyngeal mechanoreceptors in more detail. They were found on the
G. SHELTON
dominant one. It may be that two opposing groups are unnecessary for
oscillation; certainly there is no a priori reason why a single neuron
group should not show alternating periods of activity and quiescence.
At some level of integration bursts of activity, which do alternate in a
general way, must be produced since the discharges from motor neurons
are known to be of this nature. None of the suggestions made so far accounts satisfactorily for the extensive variation in behavior occurring in
different neurons in both the normal and the immobilized animal. This
variety is particularly difficult to explain in a scheme which assumes
two fairly uniform and opposing populations. Some of the components
in the oscillator must be different to the extent that they can become
silent or continuously active under some conditions without causing
complete disintegration of the rhythmic system (Fig. 15).
IV. THE ROLE OF MECHANORECEPTORS IN
RESPIRATORY REGULATION
Although the evidence reviewed above suggests that the respiratory
center can function in a rhythmic manner in the absence of feedback
from mechanoreceptors, there is no doubt that they have a significant
part to play in the normal fish. In elasmobranchs it has been known for
some time that the breathing rate is in some way related to the volume
of water which is allowed to flow over the gills from cannulae in the
mouth or spiracles (Lutz, 1930; Ogden, 1945). Satchell (1961) confirmed these results and showed that the response was produced as a
result of mechanoreceptor stimulation by the movements of ventilation.
It was totally independent of the oxygen content of the inspired water.
Sharks decrease their breathing rate by prolonging the period of
oro- and parabranchial expansion and extending the pause after this
inspiratory period; the opposite occurs when the breathing rate goes
up. Satchell (1959) showed that stimulation of the branchial branches
of the IXth and Xth cranial nerves, or the prespiracular branch of the
VIIth, stopped or slowed breathing by increasing the duration of the
pause. Inflation of a balloon inside the pharynx produced a similar result. It was suggested that these experiments demonstrated the existence of inhibitory pathways to the respiratory center in the branchial
nerves. It also seemed clear that the pathways originated in pharyngeal
mechanoreceptors, and support for this came from recordings of sensory
discharges in the branchial nerves during contraction of oro- and parabranchial cavities. Satchell and Way (1962) examined activity from the
pharyngeal mechanoreceptors in more detail. They were found on the