Faculty of Biological and Environmental Sciences, University of Helsinki, 00014 Helsinki, Finland.
Racah Institute of Physics The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
Hear Res. 2019 Dec;384:107810. doi: 10.1016/j.heares.2019.107810. Epub 2019 Oct 10.
In modern Cetacea, the ear bone complex comprises the tympanic and periotic bones forming the tympano-periotic complex (TPC), differing from temporal bone complexes of other mammals in form, construction, position, and possibly function. To elucidate its functioning in sound transmission, we studied the vibration response of 32 pairs of formaldehyde-glutaraldehyde-fixed TPCs of Globicephala macrorhynchus, the short-finned pilot whale (legally obtained in Taiji, Japan). A piezoelectric-crystal-based vibrator was surgically attached to a location on the cochlea near the exit of the acoustic nerve. The crystal delivered vibrational pulses through continuous sweeps from 5 to 50 kHz. The vibration response was measured as a function of frequency by Laser Doppler Vibrometry at five points on the TPC. The aim of the experiment was to clarify how the vibration amplitudes produced by different frequencies are distributed on the TPC. At the lowest frequencies (<12 kHz), no clear differential pattern emerged. At higher frequencies the anterolateral lip of the TP responded most sensitively with the highest displacement amplitudes, and response amplitudes decreased in orderly fashion towards the posterior part of the TPC. We propose that this works as a lever: high-frequency sounds are most sensitively received and cause the largest vibration amplitudes at the anterior part of the TP, driving movements with lower amplitude but greater force near the posteriorly located contact to the ossicular chain, which transmits the movements into the inner ear. Although force (pressure) amplification is not needed for impedance matching in water, it may be useful for driving the stiffly connected ossicles at the high frequencies used in echolocation.
在现代鲸目中，耳骨复合体由鼓膜和耳骨组成，形成鼓膜 - 耳骨复合体（TPC），其形态、结构、位置与其他哺乳动物的颞骨复合体不同，功能也可能不同。为了阐明其在声音传递中的作用，我们研究了 32 对格氏喙鲸（Globicephala macrorhynchus）的福尔马林 - 戊二醛固定 TPC 的振动响应，格氏喙鲸是短鳍领航鲸（在日本太地合法获得）。将基于压电晶体的振动器通过手术附着在靠近听神经出口的耳蜗的一个位置上。晶体通过从 5 到 50 kHz 的连续扫描发出振动脉冲。通过激光多普勒测振仪在 TPC 的五个点上测量振动响应作为频率的函数。该实验的目的是阐明不同频率产生的振动幅度如何分布在 TPC 上。在最低频率（<12 kHz）下，没有出现明显的差异模式。在较高的频率下，TP 的前外侧唇对最高位移幅度的响应最敏感，响应幅度朝着 TPC 的后部有序地减小。我们提出，这就像一个杠杆：高频声音最敏感地接收，并在 TP 的前部引起最大的振动幅度，驱动幅度较小但力较大的运动靠近位于后部的与听小骨链的接触，听小骨链将运动传递到内耳。尽管在水中阻抗匹配不需要力（压力）放大，但它可能有助于在回声定位中使用的高频下驱动刚性连接的听小骨。
