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
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Tuesday, December 02, 2008 |
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| Graphical Simulations |
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Cochlear traveling wave
Sound, which consists of pressure changes in the air, is captured by the external ear, enters the ear canal, and vibrates the eardrum (tympanum) and the tiny associated bones (ossicles) of the middle ear: the hammer (malleus), anvil (incus), and stirrup (stapes). The last acts as a piston that produces pressure changes in the liquid-filled, snail-shaped inner ear (cochlea). This input sets the elastic basilar membrane (unrolled in the simulation for ease of visualization) into oscillation. Because the top end (apex) of the basilar membrane is broad and soft, it responds best to low-frequency stimuli; the bottom end (base) is narrow, taut, and thus most sensitive to high pitches. When a complex sound such as J. S. Bach's Toccata and Fugue in D Minor is heard, each constituent musical tone excites the basilar membrane in a specific place. The actual movements are much faster, at the frequencies of the tones, and far smaller, of atomic dimensions. Movements of the basilar membrane are detected by some 16,000 hair cells situated along its length; their electrical responses trigger firing in nerve fibers that communicate information to the brain. © 1997 Howard Hughes Medical Institute. This animation may be used, copied, and distributed, without modification and with the foregoing copyright notice included, for non-commercial scientific or educational purposes only; any other use requires the written permission of Howard Hughes Medical Institute (contact bricken@hhmi.org).
Download QuickTime Movie
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Mechanoelectrical transduction
Contiguous stereocilia are connected by an elastic gating spring, presumably the filamentous tip link (orange), that is attached to the gate (yellow) of a transduction channel (red). When a positive stimulus is applied to the hair bundle (green arrow), shear between the stereocilia increases the tension in the tip link and makes channel opening more probable. In reality, each channel flickers between its open and closed configurations thousands of times a second. © 2004 A. J. Hudspeth. This and the subsequent Flash demonstrations were implemented by Mr. J. Herman.
Download Flash Animation
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Adaptation to positive stimulation
When a protracted positive stimulus (green arrow) is applied to the hair bundle, the transduction channel initially opens under the influence of the extended gating spring. Over a few tens of milliseconds, however, the channel is thought to slide down the stereocilium, relaxing the gating spring and reducing the probability that the channel is open. © 2004 A. J. Hudspeth.
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Adaptation to negative stimulation
A prolonged negative stimulus (green arrow) at first slackens the gating spring and closes the transduction channel. A myosin Ic based molecular motor is then believed to ascend the actin-filled core of the stereocilium, restoring tension to the gating spring and increasing the probability of channel opening. Positive and negative adaptation together assure that the hair bundle remains optimally sensitive at whatever position it is held. © 2004 A. J. Hudspeth.
Download Flash Animation
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Ca2+-dependent channel reclosure
Shortly after a hair bundle is deflected in the positive direction (green arrow), a Ca2+ ion (chartreuse) traverses the transduction channel and binds to a cytoplasmic site nearby. This interaction promotes reclosure of the channel; tightening of the associated gating spring then pulls the bundle in the direction opposite that of stimulation. The Ca2+ ion is subsequently extruded by a Ca2+ pump (purple). When the timing of channel reclosure is correct, this system serves as an amplifier of mechanical stimuli that sensitizes and tunes the ear. © 2004 A. J. Hudspeth.
Download Flash Animation
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