Sound Transduction 1

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Sound Transduction 1

• Or, if the a tree falls in a forest and no one is
  around does it still reflect light?

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What is Resonance?

• Resonance
• Characteristic frequency response
• Density Tuning Sharpness
• Hi dense Lo Sharpness
• Size/Cavity
• Breaking Glass Demo

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The Outer Ear All about resonance

• Pinna
• Immobile cartilage side of head
• Flange
• 3 - 4000 Hz resonance
• Concha
• 1 7000 Hz resonance
• Why such high frequencies?
• Thoughts?
• Directionality
• Finger in folds demo
• Spectral Filter (e.g., Rayker et al., 2004)
• Resonance Frequencies
• 1000 7000 Hz
• Notch Filter
• 700, 3500, 7000, 14000 Hz

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Outer Ear cont

• Meatus
• Cartilaginous bone
• Density Resonance
• 3000 Hz resonator
• Wax Hair
• Dirt Filter
• Tympanic Membrane
• Elastic Skin stretched across a bony ring
• Stiff cone (2 mm height)
• High Fidelity Transfer

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Middle Ear The Saga Continues

• The Impedance Problem
• Getting sound to the sensors
• Tympanic Membrane to Oval Window (stapedial
  footplate)
• Orders of magnitude size difference
• Ossicular chain
• Malleus Incus Stapes Stapedial Footplate
• High density benefits!

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More middle ear goodness

• Air filled pressure equal to outside
• Eustacian Tube regulation
• High intensity sound response
• Multiple muscles
• Sound attenuators

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Quick Interruption!

• TLA 1 Hearing Under Water (HUW)
• Why is this important?
• Ingredients
• Sound source (Clicker?)
• Still water (bath, sink, pool)
• Stick your ear, or a friends ear under water
• Make sound in air and under water and listen
  with
• Out of water ear
• Under water ear
• Questions Which produces the loudest sound? Is
  it difficult to determine directionality?

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Into the Inner Ear

• Major subdivisions of the Bony Labyrinth
• Vestibular Auditory
• Auditory-side Cochlea
• Cochlea
• Cavity within bone, Fluid-filled caverns
• Curls like a snail

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Life in the Cochlea

• Three major subdivisions
• Scala Vestibuli Largest cavity, filled with
  perilymph (e.g., Ricci Fettiplace, 1998)
• Positively charged Sodium Ions (Na)
• Scala Media Smallest cavity, filled with
  endolymph (e.g., Ricci Fettiplace, 1998)
• More positively charged Potassium Calcium Ions
  (K, Ca)
• Where the action is!!!
• Scala Tympani Mid size cavity, filled with
  perilymph
• Connected to Scala Vestibuli

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Scala Media, come get some!

• Organ of Corti
• Organ o Corti contains
• Basilar Membrane (base)
• Tectorial Membrane
• Inner Hair Cells
• Outer Hair Cells
• Hair cells embedded in Bas. Membrane
• Outer Hair Cells contact Tect. Membrane

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Basilar Membrane

• Properties of the Basilar Membrane
• Apex thin and stiff, Base broad and flexible
• Standing Waves
• Upward spread of masking
• Why do higher Frequencies get masked by lower
  frequencies?

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Why does it matter that the Basilar Membrane
moves?

• Hair cell magic
• Outer Hair Cells
• 12,000 in three rows
• Afferent and Efferent connections
• Attached to muscle fiber
• Inner Hair Cells
• 3,000 in single row
• Afferent connection
• Passive Motion

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Actual Transduction!

• Wave along Basilar Membrane
• Causes inner hair cell shearing
• Shearing opens channel
• Endolymph in Scala Media attracts perilymph in
  Scala Tympani
• Charges up Hair cell to cause neural firing

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What are the outer hair cells doing?

• Outer Hair cells motile embedded in Tectorial
  Membrane
• Theory 1. Stiffen to attenuate sound along the
  basilar membrane, shear to add energy to the
  basilar membrane
• Theory 2. Stiffen to raise the Tectorial membrane
  away from the inner hair cells, shear to lower
  the Tectorial membrane and obstruct the inner
  hair cells

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The big picture

• Outer/Middle ear filter and intensify sound
• Inner ear detects sound
• Inner Hair Cell movement along the basilar
  membrane
• Converts Mechanical energy to Electrical energy
  (nerve impulse)
• Outer hair cells help modulate movement along the
  basilar membrane

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Questions?