Understanding functioning and evolution of bird middle ear mechanics: a functional morphological analysis
20 December 2018
Campus Drie Eiken, O.06 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Biology
Peter Aerts & Joris Dirckx
PhD defence Raf Claes - Facultyof Science, Department of Biology
It is of interest to understand how nature succeeded in evolving a single-ossicle ear that is flexible enough to cope with ambient pressure changes and still have the ability to transfer sound energy from the eardrum to the inner ear. However, little is known on the functional morphology of this system. Insights in functioning of the avian single-ossicle ear could be helpful in the development of more improved Total Ossicular Replacement Prosthesis for humans, as these lack the ability to cope with pressure fluctuations.
In Chapter 1, a morphological description of the middle ear components of 12 different birds species is provided, based on micro-CT scanning. These characteristics are linked to their hearing capabilities as published in literature. Overall, this study suggests that there is little effect of middle ear morphology on sound transmission.
Chapter 2 investigates in domestic chickens, by means of micro-CT, to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters than in hens because of their louder vocalization. Craniokinesis caused a flattening and slackening of the eardrum in roosters.
In Chapter 3, data are presented of audio recordings at the level of the entrance of the outer ear canal of crowing roosters. These data show that a protective mechanism is needed as sound pressure levels can reach amplitudes of 142.3 dB. Micro-CT scans of a rooster and hen head show that in roosters the auditory canal closes when the beak is opened. In hens the diameter of the auditory canal only narrows.
In Chapter 4, it was experimentally tested whether reflexive opening of the pharyngotympanic tube to restore ambient middle ear pressure is present in chicken and mallard. Our experiments do not support the presence of a short loop reflexive control of pressure equilibration via the pharyngotympanic tube.
Chapter 5 provides a quantitative description of columellar footplate and tympanic membrane (extrastapedius) motion in domestic chickens under quasi-static pressure conditions. Both extrastapedius and columellar footplate displacements show a non-linear S-shaped curve as a function of pressure indicating non-linear response characteristics of the middle ear components. The lateral piston-like displacement of both the columellar footplate and extrastapedius are smaller than the medial piston-like displacements. Columellar footplate piston displacements are always smaller than the extrastapedius piston displacements.