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UID:5bdc20091cc51fc1949573283d872318
CATEGORIES:Mathematical Physics Seminar
CREATED:20220324T121427
SUMMARY:Making an effort to listen: mechanical amplification by ion channels and myosin molecules in hair cells of the inner ear
LOCATION:Zoom
DESCRIPTION:<p>Abstract: As the gateway to human communication, the sense of hearing is
  of enormousAs the gateway to human communication, the sense of hearing is 
 of enormousimportance in our lives. Hearing commences with the capture of s
 ound energy by haircells, the ear's sensory receptors, which convert that e
 nergy into electrical signals thatthe brain can then interpret. Each hair c
 ell is a cylindrical epithelial cell surmounted by ahair bundle, an erect c
 luster of 20-300 rigid, actin-filled rods termed stereocilia.Mechanical for
 ce deflects the hair bundle and thereby excites the hair cell and itsassoci
 ated nerve fibers.Uniquely among our sensory receptors, the hair cell is no
 t a passive recipient ofstimuli, but instead uses an active process to enha
 nce its inputs. This active processamplifies mechanical stimuli by as much 
 as a thousandfold, greatly increasing oursensitivity to weak sounds. Amplif
 ication is accompanied by frequency tuning, whichyields a frequency resolut
 ion of less than 0.2 %, one thirtieth of the interval between pianokeys. Th
 e active process produces a compressive nonlinearity that renders the earse
 nsitive to sounds over a millionfold range of amplitude or a trillionfold r
 ange of power.Finally, the active process can be so exuberant as to become 
 unstable; as a result, in avery quiet environment most normal ears spontane
 ously emit sound!As a result of the cooperative gating of mechanically sens
 itive ion channels, a hairbundle is dynamically unstable: the relation betw
 een the bundle's displacement and theforce required to accomplish it posses
 ses two stable fixed points separated by a regionof negative stiffness. Thi
 s situation fosters amplification or oscillation when the hairbundle is pus
 hed into its region of instability by molecular motors, specifically the my
 osinmolecules associated with adaptation of the transduction apparatus to s
 ustained stimuli.Experiments on individual hair bundles indicate that the b
 undle's operation near thisinstability—a Hopf bifurcation—accounts for the 
 four characteristics of the active process.</p>
CONTACT:Jim Hudspeth - Rockefeller University
DTSTAMP:20260907T061418
DTSTART;TZID=America/New_York:20220413T104500
DTEND;TZID=America/New_York:20220413T114500
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