Physiology and Biophysics of Auditory and Vestibular function

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Physiology and Biophysics of Auditory and
Vestibular function

• Dr. Charles CapadayProfessor DirectorBrain
  and Movement LaboratoryCRULRG, F-65002601 de la
  Canardiere, Québec City (QC), G1J 2G3,
  Canadahttp//www.BrainAndMovementLab.org/

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The sensitivity of the ear is remarkable.

• Some facts
• At 2-3 kHz the threshold of hearing intensity
  is about 10-16 W/cm2.
• This corresponds to a pressure variation of
  2.9 x 10-4 dyn/cm2, the background atmospheric
  pressure is 1.013 x106 dyn/cm2 (101.3 kPa).
• Random pressure variations due to thermal
  motion of air molecules is 0.5 x 10-4 dyn/cm2 !
  The sensitivity of the ear is thus close to the
  theoretical limit, being just above the thermal
  noise level.
• At the threshold power level (10-16 W/cm2)
  the displacement of the air molecules is less
  than the size of the molecules themselves!

From which it is readily apparent ltsmilegt that
only 0.1 of the sound energy enters the water.
Water is a very good sound barrier.
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The sensitivity of the ear is partly due to its
mechanical construction which amplifies sound
pressure

• The area of the eardrum is 30 times larger
  than that of the oval window. So by Archimides
  principle
• The ossicles act as a lever system with a
  mechanical advantage of about 2.
• The ear canal has a resonant frequency circa
  3 kHz, amplifying the pressure by a factor of
  about 2.
• Thus, 2 x 30 x 2 120. However,

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What we will explain
Sensitivity curve of human ear
Sound Localization
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Why primary afferent fibre firing rate is
nonlinearly related to stimulus intensity (but
not always)
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(No Transcript)
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The mammalian central auditory pathways (for
dummies version).
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A1 is tonotopically organized
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Neural Mechanisms of sound localization

• The medial superior olive transforms a time code
  into a place code.

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The Barn Owls Story
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A measured behaviour and its underlying neural
systems
See, T. Carew. Behavioural Neurobiology. Sinauer
Associates, 2000.