Sound-power collection by the auditory periphery of the Mongolian gerbil M e r i o n e s u n g u i c u l a

Abstract

This is the first paper of a series dealing with sound-power collection by the auditory periphery of the gerbil. The purpose of the series is to quantify the physiological action of the gerbil's relatively large tympanic membrane and middle-ear air cavities. To this end the middle-ear input impedance ZT was measured at frequencies between 10 Hz and 18 kHz before and after manipulations of the middle-ear cavity. The frequency dependence of ZT is consistent with that of the middle-ear transfer function computed from extant data. Comparison of the impedance and transfer function suggests a middle-ear transformer ratio of 50 at frequencies below 1 kHz, substantially smaller than the anatomical value of 90 [Lay, J. Morph. 138, 41-120 (1972)]. Below 1 kHz the data suggest a low-frequency acoustic stiffness KT for the middle ear of 970 Pa/mm3 and a stiffness of the middle-ear cavity of 720 Pa/mm3 (middle-ear volume V MEC of 195 mm3); thus the middle-ear air spaces contribute about 70% of the acoustic stiffness of the auditory periphery. Manipulations of a middle-ear model suggest that decreases in V MEC lead to proportionate increases in KT but that further increases in middle-ear cavity volume produce only limited decreases in middle-ear stiffness. The data and the model point out that the real part of the middle-ear impedance at frequencies below 100 Hz is determined primarily by losses within the middle-ear cavity. The measured impedance is comparable in magnitude and frequency dependence to the impedance in several larger mammalian species commonly used in auditory research. A comparison of low-frequency stiffness and anatomical dimensions among several species suggests that the large middle-ear cavities in gerbil act to reduce the middle-ear stiffness at low frequencies. A description of sound-power collection by the gerbil ear requires a description of the function of the external ear.

Structures that contribute to middle-ear admittance in chinchilla

“…While the variance in the computed magnitude and angle of Y TOC at low frequencies and the variance near 2000 Hz adds some uncertainty, Y TOC and are generally similar, and the differences between the two are attributable to an air-space bullar-hole anti-resonance in the bullar-hole open case (Guinan and Peake 1967;Lynch 1981;Ravicz et al 1992). This antiresonance is described in the next section.…”

“…Heim de Balsac 1936;Legouix and Wisner 1955). The families and species most investigated in this regard are the Heteromyidae (kangaroo rats and their relatives (Webster 1961(Webster , 1962 Webster 1975, 1984; Webster and Plassman 1992)), Gerbillinae (Lay 1972(Lay , 1974Ravicz, Rosowski and Voigt 1992) and the sand cat, Felis margarita (Huang et al 2002). These studies found a consistent association between anatomical specializations, i.e.…”

“…(The range of accurate admittance estimation was determined from measurements in test loads of varied admittance, e.g. Ravicz et al 1992).…”

“…(The range of accurate admittance estimation was determined from measurements in test loads of varied admittance, e.g. Ravicz et al 1992).Complications introduced by the use of the broad-band chirps were limited stimulus energy at low frequencies and the potential for low-frequency distortion produced by the large 1000 -5000 Hz stimulus and response components. These complications were averted by the use of the low-pass stimulus.…”

Effect of Opening Middle-Ear Cavity on Vibrations of Gerbil Tympanic Membrane

“…The effects of the middle-ear cavity on the response of the ear have been investigated using admittance, impedance and other measurements in human (Zwislocki, 1962), guinea pig (Zwislocki, 1963), rabbit (Møller, 1965), cat (Møller, 1965;Guinan & Peake, 1967;Lynch et al, 1994), lion (Huang et al, 1997), gerbil (Ravicz et al, 1992;Teoh et al, 1997) and chinchilla (Rosowski et al, 2006). In these studies, it was found that opening the middle-ear cavity has the following effects on the response of the middle ear:…”