The Rockefeller University - Laboratory of Sensory Neuroscience

Hair Cells of the Inner Ear

Transfer characteristics
of the hair cell's afferent synapse

Coherent motion of stereocilia assures the
concerted gating of hair-cell transduction channels

The structural and functional differentiation of
hair cells in a lizard's basilar papilla suggests
an operational principle of amniote cochleas

Analysis and functional evaluation of the hair-cell
transcriptome

Three-dimensional architecture of hair-bundle
linkages revealed by electron-microscopic
tomography

A two-step mechanism underlies the planar
polarization of regenerating sensory hair cells

Specificity of afferent synapses onto
plane-polarized hair cells in the
posterior lateral line of the zebrafish

Thursday, February 09, 2012

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Dynamical instability and the ear's active process

The ears of vertebrates are endowed with an active process with four characteristics. First, the sensitivity of hearing is enhanced about one-hundredfold by mechanical amplification of the ear's inputs. Second, the active process sharpens frequency discrimination, improving our ability to resolve different tones. Next, as sounds become louder, the ear grows progressively less sensitive; this compressive nonlinearity allows us to respond to sounds over a trillionfold range of intensity and justifies the use of the logarithmic decibel scale to measure the perceived loudness of sound. Finally, in a very quiet environment an ear may display spontaneous otoacoustic emission, the production of sound by the ear itself. All four of these properties emerge if the mechanoreceptive hair cells possesses an active process poised near a dynamical instability, the Hopf bifurcation. Both experiments and modeling studies demonstrate that, at least in non-mammalian tetrapods, the active process emerges from the interplay of negative hair-bundle stiffness with two motor processes, myosin Ic-based adaptation and Ca2+ dependent reclosure of transduction channels.