Contribution of the incudo-malleolar joint to middle-ear sound transmission

Abstract

The malleus and incus in the human middle ear are linked by the incudo-malleolar joint (IMJ). The mobility of the human IMJ under physiologically relevant acoustic stimulation and its functional role in middle-ear sound transmission are still debated. In this study, spatial stapes motions were measured during acoustic stimulation (0.25-8 kHz) in six fresh human temporal bones for two conditions of the IMJ: (1) normal IMJ and (2) IMJ with experimentally-reduced mobility. Stapes velocity was measured at multiple points on the footplate using a scanning laser Doppler vibrometry (SLDV) system, and the 3D motion components were calculated under both conditions of the IMJ. The artificial reduction of the IMJ mobility was confirmed by measuring the relative motion between the malleus and the incus. The magnitudes of the piston-like motion of the stapes increased with the reduced IMJ mobility above 2 kHz. The increase was frequency dependent and was prominent from 2 to 4 kHz and at 5.5 kHz. The magnitude ratios of the rocking-like motions to the piston-like motion were similar for both IMJ conditions. The frequency-dependent change of the piston-like motion after the reduction of the IMJ mobility suggests that the IMJ is mobile under physiologically relevant levels of acoustic stimulation, especially at frequencies above 2 kHz. The malleus and incus in the human middle ear are linked by the incudo-malleolar joint 10 (IMJ). The mobility of the human IMJ under physiologically relevant acoustic stimulation and 11 its functional role in middle-ear sound transmission are still debated. In this study, spatial 12 stapes motions were measured during acoustic stimulation (0.25-8 kHz) in six fresh human 13 temporal bones for two conditions of the IMJ: (1) normal IMJ and (2) IMJ with 14 experimentally-reduced mobility. Stapes velocity was measured at multiple points on the 15 footplate using a scanning laser Doppler vibrometry (SLDV) system, and the 3D motion 16 components were calculated under both conditions of the IMJ. The artificial reduction of the 17 IMJ mobility was confirmed by measuring the relative motion between the malleus and the 18 incus. The magnitudes of the piston-like motion of the stapes increased with the reduced IMJ 19 mobility above 2 kHz. The increase was frequency dependent and was prominent from 2-4 20 kHz and at 5.5 kHz. The magnitude ratios of the rocking-like motions to the piston-like 21 motion were similar for both IMJ conditions. The frequency-dependent change of the piston-22 like motion after the reduction of the IMJ mobility suggests that the IMJ is mobile under 23 physiologically relevant levels of acoustic stimulation, especially at frequencies above 2 kHz. 24 2

Stapes displacement and intracochlear pressure in response to very high level, low frequency sounds

“…It is also possible that compliance in the incudomalleolar joint contributes significantly to a reduction in stapedial motion, and that this compliance may itself be nonlinear, taking up some displacement that might otherwise be transmitted to the cochlear fluid at high sound pressure levels (Hüttenbrink 1988, Lauxmann et al 2012). One recent report (Gerig et al 2015) finds that IM joint mobility is not a major contributor to ossicular chain compliance at frequencies below 2 kHz. We do not discount the possible contribution of the IM joint (or other components of the ossicular chain) to the nonlinearity observed in this study, but believe it to be of secondary importance at very low frequencies.…”

A MEMS Condenser Microphone-Based Intracochlear Acoustic Receiver

“…2014-0544). Preparation of the human temporal bone for ICSP measurements followed a standard surgical approach [41], [42]. Prior to drilling access to the inner ear, a standard conformity test of the ME was performed by quantifying the TBME-01353-2016 6 ME transfer function and comparing it to the ASTM practice ME standards [3], [43].…”

“…1) was drilled approximately 2.5 mm beside the round window with a diamond burr of 0.7 mm diameter under water to prevent entry of air into the cochlea. A loudspeaker (ER-2, Etymotic Research, US) and a reference microphone (ER-7C, Etymotic Research, US) were placed into the artificial EC and acoustically sealed using a foam insert as done in earlier experiments [41], [42]. Acoustic excitation signals were generated by an audio analyzer (APx585 Audio Analyser, Audio Precision Inc., US) and amplified by an audio amplifier (RMX 850, QSC Audio Products, US).…”

“…There was a maximal deviation of 3.5 dB between 1.5 to 3 kHz across the three ICARs, indicating good repeatability. These differences may have been partially related to time dependent changes of the temporal bone preparation [41] and to the discrepancies of a maximum of +/-3 dB between the pre-and post-experimental calibrations. Reference [19] presented inner ear pressure measurements in the ST of six human temporal bones using miniature fiberoptic based sound pressure sensors [14], [15] (cf.…”

Human ossicular-joint flexibility transforms the peak amplitude and width of impulsive acoustic stimuli

“…As research has progressed, others have found that the IMJ displays a frequency-dependent mobility, becoming more mobile at higher frequencies (Guinan and Peake, 1967; Willi et al , 2002). Contemporary work has supported the idea that the IMJ is mobile at frequencies above 2 kHz (Gerig et al , 2015), as well as under quasi-static loading conditions (Ihrle et al , 2016). The ISJ has received relatively less scrutiny than the IMJ, though a number of studies have demonstrated that it is functionally mobile at hearing frequencies (Nakajima et al , 2005; Zhang and Gan, 2011) and that fixing it causes changes in sound transmission (Hato et al , 2003; Alian et al , 2013).…”