The physics of hearing: fluid mechanics and the active process of the inner ear

Abstract

Most sounds of interest consist of complex, time-dependent admixtures of tones of diverse frequencies and variable amplitudes. To detect and process these signals, the ear employs a highly nonlinear, adaptive, real-time spectral analyzer: the cochlea. Sound excites vibration of the eardrum and the three miniscule bones of the middle ear, the last of which acts as a piston to initiate oscillatory pressure changes within the liquid-filled chambers of the cochlea. The basilar membrane, an elastic band spiraling along the cochlea between two of these chambers, responds to these pressures by conducting a largely independent traveling wave for each frequency component of the input. Because the basilar membrane is graded in mass and stiffness along its length, however, each traveling wave grows in magnitude and decreases in wavelength until it peaks at a specific, frequency-dependent position: low frequencies propagate to the cochlear apex, whereas high frequencies culminate at the base. The oscillations of the basilar membrane deflect hair bundles, the mechanically sensitive organelles of the ear's sensory receptors, the hair cells. As mechanically sensitive ion channels open and close, each hair cell responds with an electrical signal that is chemically transmitted to an afferent nerve fiber and thence into the brain. In addition to transducing mechanical inputs, hair cells amplify them [...]

86 pages, 24 figures

References in corpus (6)

• A ratchet mechanism for amplification in low-frequency mammalian hearing
• Fluctuation-response theorem for the active noisy oscillator of the hair-cell bundle
• Waves on Reissner's membrane: a mechanism for the propagation of otoacoustic emissions from the cochlea
• Dual contribution to amplification in the mammalian inner ear
• Cochlear-bone wave can yield a hearing sensation as well as otoacoustic emission
• Unidirectional mechanical amplification as a design principle for an active microphone

Cited by in corpus (13)

• Mechanical Surface Waves Accompany Action Potential Propagation
• Optimized structures for vibration attenuation and sound control in Nature: a review
• Modelling Active Non-Markovian Oscillations
• A bifurcation integrates information from many noisy ion channels
• Noise-Induced Chaos and Signal Detection by the Nonisochronous Hopf Oscillator
• Chimera states and frequency clustering in systems of coupled inner-ear hair cells
• Chaos stabilizes synchronization in systems of coupled inner-ear hair cells
• An immersed boundary model of the cochlea with parametric forcing
• Seashell-inspired polarization-sensitive tonotopic metasensor
• Hair cells in the cochlea must tune resonant modes to the edge of instability without destabilizing collective modes
• A flexible anatomical set of mechanical models for the organ of Corti
• Mechanochemical feedback drives complex inertial dynamics in active solids
• Active energy harvesting and work transduction by hair-cell bundles in bullfrog's inner ear