Abstract
An experimental study on the acoustic reflex of tympanic muscles was carried out from various points of view.
First, the observation on the effect of an acoustic tympanic muscle reflex indicated by cochlear electrical response resulted in the following facts.
a) The change of amplitude of microphonic response of the animal, in which the tensor tympani was cut, to the definite noise is larger than that without cutting, and especially at the lower frequency the decrease of amplitude of microphonic potential is observed.
b) When the stapedius is cut, the change of amplitude of microphonics is larger than that of tensor-tympani-cut group at the lower frequency.
c) With exposure to the same noise, the decrease of micorophonic potential is more remarkable in the group where both tendons of the tensor tympani and of the stapedius are cut than in the group of a single cut.
d) In the general application of anticonvulsant, the microphonic potential increases temporarily and markedly, however, it gradually decreases with time.
e) Immediately after the injection of curare preparation into the unilateral carotis, the microphonic potential in the injected side, as well as general application, temporarily and remarkably increases.
In this time, by increasing the intensity of the stimulating tone source the microphonic potential grows larger and larger.
f) When the exposure of both ears to noise and the curare injection to the unilateral carotis were carried out simulataneoulsy, the decrease of microphonic potential in the injected side, especially atthe lower frequency, was larger than that in the non-injected side.
Next, the observation of an objective audiogram based upon the new point of view by use of conditioned response shows the following results.
g) In the cut group of the tendon of tensor tympani, the loss of hearing power in the cut side, which increases gradually by lengthening the time of exposure to noise, is remarkably large in comparison with that in non-cut side.
In the frequency distinction, the loss in the shorter duration of exposure is larger in the high and middle frequency zones than in the lower one, and that in the longer duration reveals the pattern of C5-dip since the loss at the higher frequency zone in the cut side gradually increases.
h) The normal audiogram of a conditioned dog and the audiogram of the same dog in general anesthesia show that general anesthesia results in the elevation of threshold to the exposure and also in the loss of hearing power especially in the lower and middle frequency zones rather than that in the higher frequency zone.
