Measurements of Middle-Ear Function in the Mongolian Gerbil, a Specialized Mammalian Ear

Abstract

The middle ear of the Mongolian gerbil is thought to be specialized so that it can hear the 3,000-Hz and lower sounds produced by approaching predators. Evidence in the literature suggests several specializations: (1) an effect of the large middle-ear air spaces in the gerbil is to increase the sensitivity of this ear to sounds of 3,000 Hz and lower in frequency; (2) the combined action of the middle-ear cavity and the significant pars flaccida of the tympanic membrane in the gerbil ear reduces the sensitivity to sounds of frequencies below 500 Hz. This paper describes anatomical and functional measurements of stapes motion and suggests that the stiffness of the gerbil ossicular system also acts to reduce sensitivity to low-frequency sounds. The primary conclusion is that the frequency dependence of the gerbil middle ear is the result of the interaction of multiple factors, thereby complicating the relationship between single structural specializations and overall function.

Sound pressure distribution and power flow within the gerbil ear canal from 100Hzto80kHz

“…The velocity of small reflectors placed on the posterior crus of the stapes was measured with a laser-Doppler vibrometer (OPV 501/2600, Polytec PI, Waldbronn, Germany) focused through one of the bulla holes (usually posterior to the ear canal- Rosowski et al, 1999;Ravicz and Rosowski, 2004). Stapes velocity was also used to monitor the position of the probe tube: When the probe-tube tip touched the TM, stapes velocity decreased at low frequencies.…”

Encoding of temporal features of auditory stimuli in the medial nucleus of the trapezoid body and superior paraolivary nucleus of the rat

“…It seems plausible, therefore, that differences in ascending inputs and, perhaps, the presence of different cell types underlie the discrepant physiological properties of SPON neurons in the two species. Perhaps these differences resulted from evolutionary pressures engendered by the specialized requirements for lowfrequency hearing in gerbils and other desert rodents (Rosowski et al, 1999); indeed, nuclei of the superior olivary complex, and particularly the SPON and DMPO, display considerable interspecies variability in their constituent neuronal morphologies and certain aspects of their connectivity (Covey and Casseday, 1995;Grothe, 2000;reviewed in Saldaña and Berrebi, 2000).…”

Gross anatomy and arterial vascularization of the tympanic cavity and osseous labyrinth in mid‐gestational bovine fetuses

“…Study focused on tympanic membrane, ossicles, and their structural relations due to the method used in the study. Osseous chain between tympanic membrane and vestibular external wall was found to have same organization in many species investigated (Hamberger et al, 1963;Rosowski et al, 1999;Russo et al, 2002;Wysocki, 2005;Mason, 2006). Malleus forming the outermost ring of this chain did not have fully ovoid head like the ones in humans and pigs; however, it had a hemispherical head in moles as Mason (2006) reported.…”

“…However, stapes was not observed to be supplied by stylomastoid artery but by stapedial artery. A number of studies carried out on the vascularization of middle ear did not report the presence of stapedial artery; however, its presence was determined in this study and some other studies on certain mammal species like a mongolian gerbil (Rosowski et al, 1999), rats (Ortug, 2001;Yamamoto et al, 2003), fossorial rodents (Lange et al, 2004), and Talpid moles (Mason, 2006). Lange et al (2004) and Ortug (2001) observed that stapedial artery passing through intercrural foramen was surrounded by an osseous canal.…”

“…Many morphological (Axelsson and Ryan, 1988;Moriguchi et al, 1991;Wysocki, 2001) and functional studies (Webster, 1966;Ketten, 1997;Rosowski et al, 1999) have been conducted on both inner and middle ear so far. Majority of these studies aimed to make contributions to human medicine and were generally performed on experimental animals like rodents (Hornstrand et al, 1980;Rosowski et al, 1999;Lyon and Payman, 2000) and lagomorphs (Axelsson and Lind, 1973;King et al, 2007).…”