7. THE LABYRINTH
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activity is augmented in the canals undergoing ampulla-leading and inhibited in those undergoing ampulla-trailing displacement.
It is reasonable to assume that the resting discharge recorded in the
afferent nerve fibers derives from constant excitatory activity at the
synapse between hair cell and afferent nerve endings. This may result
from constant percolation of transmitter substance across the synapse.
Excitation may then result from an increase in transit of transmitter substance, inhibition from the cessation of its flow. The modulations in the
amount of transmitter substance discharge must then in their turn be
governed by the state and direction of deformation of the hair processes.
However, the intermediate links in the chain of events between mechanical deformation and electric activity in the afferent nerves are not yet
clearly understood. It is now certain that the polarization of the hair cells
as described above is an important factor in the mode of functioning of
the semicircular canal. Their orientation on the cristae is uniform. On the
crista of the horizontal canal the kinocilia in the individual hair bundles
point away from the canal end of the ampulla toward the ampulloutricular opening. Thus ampulla-trailing acceleration will lead to a deflection of the hair bundle in order to make the kinocilium bend toward
the side of its basal foot. Such a deformation is excitatory. On the cristae
of the vertical canal the kinocilia of the individual hair bundles uniformly
point toward the canal end of the ampulla and away from the ampulloutricular opening. The hair bundles undergo excitatory deflection in this
case during ampulla-leading acceleration.
Postrotatory aftereffects in the form of poststimulatory depression and
postinhibitory augmentation of the discharge activity are clearly correlated with well-known effector responses such as the postrotatory eye
nystagmus.
A functional correlation between the discharge activity in the six semicircular canals and the reflex responses of the six eye muscles was established, and it satisfactorily fulfilled all aspects of Sherringtonian muscle
antagonism with respect to the labyrinthine eye reflexes (Lowenstein and
Sand, 1940a).
The existence of a resting discharge in the end organs of the semicircular canals is functionally highly significant. Above all it serves here
as the background for bidirectionality, i.e., for the sensitivity of a given
semicircular canal to rotations in opposite direction which lead to an
increase or decrease in the impulse discharge rates. Apart from this, the
steady influx of spontaneous activity from the sense organ into the central
nervous system must contribute to the maintenance of muscle tonus. This
was directly demonstrated in the pike, Esox lucius, where operative interruption of the nerve supply to one horizontal ampulla led to a pro-
217
activity is augmented in the canals undergoing ampulla-leading and inhibited in those undergoing ampulla-trailing displacement.
It is reasonable to assume that the resting discharge recorded in the
afferent nerve fibers derives from constant excitatory activity at the
synapse between hair cell and afferent nerve endings. This may result
from constant percolation of transmitter substance across the synapse.
Excitation may then result from an increase in transit of transmitter substance, inhibition from the cessation of its flow. The modulations in the
amount of transmitter substance discharge must then in their turn be
governed by the state and direction of deformation of the hair processes.
However, the intermediate links in the chain of events between mechanical deformation and electric activity in the afferent nerves are not yet
clearly understood. It is now certain that the polarization of the hair cells
as described above is an important factor in the mode of functioning of
the semicircular canal. Their orientation on the cristae is uniform. On the
crista of the horizontal canal the kinocilia in the individual hair bundles
point away from the canal end of the ampulla toward the ampulloutricular opening. Thus ampulla-trailing acceleration will lead to a deflection of the hair bundle in order to make the kinocilium bend toward
the side of its basal foot. Such a deformation is excitatory. On the cristae
of the vertical canal the kinocilia of the individual hair bundles uniformly
point toward the canal end of the ampulla and away from the ampulloutricular opening. The hair bundles undergo excitatory deflection in this
case during ampulla-leading acceleration.
Postrotatory aftereffects in the form of poststimulatory depression and
postinhibitory augmentation of the discharge activity are clearly correlated with well-known effector responses such as the postrotatory eye
nystagmus.
A functional correlation between the discharge activity in the six semicircular canals and the reflex responses of the six eye muscles was established, and it satisfactorily fulfilled all aspects of Sherringtonian muscle
antagonism with respect to the labyrinthine eye reflexes (Lowenstein and
Sand, 1940a).
The existence of a resting discharge in the end organs of the semicircular canals is functionally highly significant. Above all it serves here
as the background for bidirectionality, i.e., for the sensitivity of a given
semicircular canal to rotations in opposite direction which lead to an
increase or decrease in the impulse discharge rates. Apart from this, the
steady influx of spontaneous activity from the sense organ into the central
nervous system must contribute to the maintenance of muscle tonus. This
was directly demonstrated in the pike, Esox lucius, where operative interruption of the nerve supply to one horizontal ampulla led to a pro-