Hearing Research Center, Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, 02215, MA, United States.
Hearing Research Center, Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, 02215, MA, United States.
Hear Res. 2021 Dec;412:108372. doi: 10.1016/j.heares.2021.108372. Epub 2021 Oct 22.
The inner hair cells in the mammalian cochlea transduce mechanical signals to electrical signals that provide input to the auditory nerve. The spatial-temporal displacement of the inner hair cell stereocilia (IHCsc) relative to basilar membrane (BM) displacement is central to characterizing the transduction process. This study specifically focuses on measuring displacement of the stereocilia hair bundles in the radial dimensions where they are most sensitive. To simplify the mechanical response of the cochlear partition, a mechanical probe was used to drive the BM. Optical imaging was used to measure radial displacement of the inner hair cell stereocilia local to the probe in ex vivo gerbil cochleae. The mechanical probe displaced the BM in the transverse direction using sinusoidal stimuli with frequencies ranging from 10 Hz to 42.5 kHz. IHCsc displacement measurements were made in the radial dimension as a function of their longitudinal location along the length of the BM. The results were used to quantify the frequency response, longitudinal space coupling, traveling wave velocity, and wavelength of the radial displacement of the stereocilia. The measurements were centered at two best frequency locations along the BM: Proximal to the round window (first turn), and in the second turn. At both locations, frequency tuning was seen that was consistent with published place maps. At both locations, traveling waves were observed simultaneously propagating basal and apical from the probe. The velocity of the traveling waves at the center frequency (CF) of the location was higher in the first turn than in the second. As the stimulus frequency increased and approached CF for a location, the traveling wavelength decreased. Differential motion of the BM and IHCsc was observed in the second turn as the stimulus frequency increased toward CF. The longitudinal coupling measured in this study was longer than observed in previous studies. In summary the results suggest that the shape of the wave patterns present on the BM are not sufficient to characterize the displacement of the IHCsc.
哺乳动物耳蜗内毛细胞将机械信号转化为电信号，为听觉神经提供输入。内毛细胞（IHC）静纤毛相对于基底膜（BM）位移的时空位移是表征转导过程的关键。本研究特别关注测量静纤毛毛束在其最敏感的径向尺寸上的位移。为了简化耳蜗隔板的力学响应，使用机械探针驱动 BM。光学成像用于测量离体沙鼠耳蜗中探针附近内毛细胞静纤毛的径向位移。机械探针使用频率范围从 10 Hz 到 42.5 kHz 的正弦刺激在横向方向上驱动 BM。对静纤毛位移的测量是作为其在 BM 长度上的纵向位置的函数在径向尺寸上进行的。结果用于量化径向位移的频率响应、纵向空间耦合、行波速度和波长。测量以 BM 上的两个最佳频率位置为中心：靠近圆窗（第一圈）和第二圈。在这两个位置，都观察到了与已发表的位置图一致的频率调谐。在这两个位置，都观察到行波同时从探针向基底和顶端传播。在位置的中心频率（CF）处，行波的速度在第一圈比在第二圈高。随着刺激频率的增加并接近位置的 CF，行波的波长减小。当刺激频率向 CF 增加时，在第二圈中观察到 BM 和 IHCsc 的差动运动。本研究中测量的纵向耦合比以前的研究观察到的更长。总之，结果表明，BM 上存在的波型的形状不足以表征 IHCsc 的位移。
