Page 10 - Spring 2018

The Mammalian Ear: Physics and the Principles of Evolution
Physical laws govern the operation of the ear but natural selection dominates its design.
Introduction
In the sensory worlds of animals and humans, there are major differences in the ex- tent to which the laws of physics exert an influence on the function and evolution of the senses. The chemical senses of taste and olfaction depend mainly on the three- dimensional amino acid chain structure of hundreds of genetically coded receptor molecules that, in a kind of “lock-and-key” mechanism, fit with a small molecule and lead to a response in the sensory cells. In these cases, physics mainly has roles in the distribution and binding of molecules.
Email:
a.lukashkin@brighton.ac.uk
Patrício Simões1
Email:
p.simoes@brighton.ac.uk
George W. S. Burwood1,2
Email:
burwood@ohsu.edu
Ian J. Russell1
Email:
i.russell@brighton.ac.uk
Postal:
1Sensory Neuroscience Research Group School of Pharmacy and Biomolecular Sciences University of Brighton, Brighton BN2 4GJ United Kingdom
2Present Address: Oregon Hearing Research Center Oregon Health and Science University 3181 SW Sam Jackson Park Road Portland, Oregon 97239 USA
Geoffrey A. Manley
Postal:
Cochlear and Auditory Brainstem Physiology Department of Neuroscience Hearing4all Research Centre Carl von Ossietzky University Oldenburg 26129 Oldenburg Germany
Email:
geoffrey.manley@uol.de
Andrei N. Lukashkin1
Figure 1. Structure of the human ear. Sound energy is conveyed by the pinna and auditory canal to the tympanic membrane. Vibrations of the tympanic membrane are transmitted by the middle ear bones, the malleus, incus, and stapes, to the inner ear fluid. The cochlea is a fluid-filled duct of the inner ear responsible for hearing sensation. Inset: cross section of the hearing organ, the organ of Corti. The basilar membrane divides the cochlear duct along its length and separates sounds into their constitutive frequency components. It also supports the organ of Corti that contains sensory inner hair cells that transmit auditory information to the brain and outer hair cells that amplify and sharpen vibrations of the basilar membrane. During up-and-down vibrations of the basilar membrane, the tectorial membrane displaces sensory hairs of hair cells and excites them. Modified with permission from Bruce (2017). Inset modified from Brownell (1997).
8 | Acoustics Today | Spring 2018
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