8. THE LATERAL LINE ORGAN MECHANORECEPTORS
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objects such as prey. They do not respond to pressure changes per se;
canal organs could if pressure gradients were to develop between distant
organs. However, this is not likely to occur in acoustic stimulation since
the wavelength of sound in water at the frequency fishes hear is far too
long even for a sizable fish (Harris, 1967). On the other hand, a pressure
field pulsating at auditory frequency would cause the swim bladder to
change its volume synchronously and so cause near field displacement
perhaps capable of exciting lateral line organs (van Bergeijk, 1967).
Acoustic stimulation cannot thus be discarded as a possible source of
input to the central nervous system via lateral line organs.
Little is known about the central connections of the lateral line system, and even less is known about the neurophysiology of central nuclei
and pathways. The sensory nerve fibers are extensions from bipolar
neurons, the cell bodies forming a diffuse ganglion inside the brain case.
They terminate in the medulla in a nucleus closely associated with the
statoacoustic nucleus.
Much is to be learned about information processing in central nuclei:
For instance, what is the reason for the bidirectionality of the sensory
input? Do sensory fibers of opposite polarity impinge upon a common
central neuron to provide some kind of push-pull or differential action?
The efferent innervation of the peripheral organs has an inhibitory
influence on the afferent nerve discharge as shown by Russell (1968).
He tentatively suggests that the cell bodies of the efferent nerve cells
in Xenopus are either present in the medulla or in the ganglion. They
may provide a means of setting the gain of the peripheral sense organ
or they may be engaged in discrimination of adequate stimuli. It is not
known whether the efferent system is under control of the central nervous
system or whether it functions as an autonomous reflex arch.
VII. CONCLUSION
The lateral line mechanoreceptor organs provide a sophisticated system for detection of water motion. Each individual organ exhibits the
cellular components and the basic circuitry that make the organs of hearing and equilibrium in the inner ear such delicate sensors. There is reason
to believe that the process of sensory transduction in the hair cell is the
same as in the inner ear; this is true also for synaptic transmission between the hair cell and the sensory nerve fiber. Inhibition of afferent input
by efferent activity takes place in much the same way.
Consequently, lateral line organs are not only indispensable to fish,
261
objects such as prey. They do not respond to pressure changes per se;
canal organs could if pressure gradients were to develop between distant
organs. However, this is not likely to occur in acoustic stimulation since
the wavelength of sound in water at the frequency fishes hear is far too
long even for a sizable fish (Harris, 1967). On the other hand, a pressure
field pulsating at auditory frequency would cause the swim bladder to
change its volume synchronously and so cause near field displacement
perhaps capable of exciting lateral line organs (van Bergeijk, 1967).
Acoustic stimulation cannot thus be discarded as a possible source of
input to the central nervous system via lateral line organs.
Little is known about the central connections of the lateral line system, and even less is known about the neurophysiology of central nuclei
and pathways. The sensory nerve fibers are extensions from bipolar
neurons, the cell bodies forming a diffuse ganglion inside the brain case.
They terminate in the medulla in a nucleus closely associated with the
statoacoustic nucleus.
Much is to be learned about information processing in central nuclei:
For instance, what is the reason for the bidirectionality of the sensory
input? Do sensory fibers of opposite polarity impinge upon a common
central neuron to provide some kind of push-pull or differential action?
The efferent innervation of the peripheral organs has an inhibitory
influence on the afferent nerve discharge as shown by Russell (1968).
He tentatively suggests that the cell bodies of the efferent nerve cells
in Xenopus are either present in the medulla or in the ganglion. They
may provide a means of setting the gain of the peripheral sense organ
or they may be engaged in discrimination of adequate stimuli. It is not
known whether the efferent system is under control of the central nervous
system or whether it functions as an autonomous reflex arch.
VII. CONCLUSION
The lateral line mechanoreceptor organs provide a sophisticated system for detection of water motion. Each individual organ exhibits the
cellular components and the basic circuitry that make the organs of hearing and equilibrium in the inner ear such delicate sensors. There is reason
to believe that the process of sensory transduction in the hair cell is the
same as in the inner ear; this is true also for synaptic transmission between the hair cell and the sensory nerve fiber. Inhibition of afferent input
by efferent activity takes place in much the same way.
Consequently, lateral line organs are not only indispensable to fish,