Download Sound Transduction 1

Sound Transduction 1
Or, if the a tree falls in a forest and no one is
around does it still reflect light?
What is Resonance?
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Resonance
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Characteristic frequency response
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Density & Tuning Sharpness
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Hi dense = Lo Sharpness
Size/Cavity
Breaking Glass Demo
The Outer Ear:
All about resonance
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Pinna
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Flange
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~1 – 7000 Hz resonance
Why such high frequencies?
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~3 - 4000 Hz resonance
Concha
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Immobile cartilage side of head
Thoughts?
Directionality
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Finger in folds demo
Spectral Filter (e.g., Rayker et al., 2004)
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Resonance Frequencies
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~1000 – 7000 Hz
Notch Filter
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~ 700, 3500, 7000, 14000 Hz
Outer Ear: con’t
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Meatus
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Cartilaginous – bone
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Wax + Hair
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Density & Resonance
3000 Hz resonator
Dirt Filter
Tympanic Membrane
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Elastic Skin stretched across a bony ring
Stiff cone (2 mm height)
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High Fidelity Transfer
Middle Ear:
The Saga Continues
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The Impedance Problem
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Tympanic Membrane to Oval
Window (stapedial footplate)
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Getting sound to the sensors
Orders of magnitude size
difference
Ossicular chain
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Malleus – Incus – Stapes –
Stapedial Footplate
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High density benefits!
More middle ear goodness
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Air filled pressure equal to outside
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Eustacian Tube regulation
High intensity sound response
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Multiple muscles
Sound attenuators
Quick Interruption!
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TLA 1: Hearing Under Water (HUW)
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Why is this important?
Ingredients:
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Stick your ear, or a friend’s ear under water
Make sound in air and under water and listen with:
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Sound source (Clicker?)
Still water (bath, sink, pool)
Out of water ear
Under water ear
Questions: Which produces the loudest sound? Is it
difficult to determine directionality?
Into the Inner Ear
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Major subdivisions of the Bony Labyrinth
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Vestibular & Auditory
Auditory-side = Cochlea
Cochlea
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Cavity within bone, Fluid-filled caverns
Curls like a snail
Life in the Cochlea
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Three major subdivisions
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Scala Vestibuli: Largest cavity, filled
with perilymph (e.g., Ricci & Fettiplace, 1998)
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Scala Media: Smallest cavity, filled
with endolymph (e.g., Ricci & Fettiplace, 1998)
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Positively charged Sodium Ions (Na+)
More positively charged Potassium &
Calcium Ions (K+, Ca++)
Where the action is!!!
Scala Tympani: Mid size cavity,
filled with perilymph
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Connected to Scala Vestibuli
Scala Media, come get some!
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‘Organ of Corti’
Organ o’ Corti contains
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Basilar Membrane (base)
Tectorial Membrane
Inner Hair Cells
Outer Hair Cells
Hair cells embedded in Bas.
Membrane
Outer Hair Cells contact Tect.
Membrane
Basilar Membrane
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Properties of the
Basilar Membrane
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Apex thin and stiff,
Base broad and flexible
Standing Waves
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Upward spread of
masking
Why do higher
Frequencies get masked
by lower frequencies?
Why does it matter that the Basilar
Membrane moves?
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Hair cell magic
Outer Hair Cells
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~ 12,000 in three rows
Afferent and Efferent
connections
Attached to muscle fiber
Inner Hair Cells
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~ 3,000 in single row
Afferent connection
Passive Motion
Actual Transduction!
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Wave along Basilar
Membrane
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Causes inner hair cell
shearing
Shearing opens channel
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Endolymph in Scala
Media attracts perilymph
in Scala Tympani
Charges up Hair cell to
cause neural firing
What are the outer hair cells doing?
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Outer Hair cells motile & embedded in
Tectorial Membrane
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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
The big picture
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Outer/Middle ear filter and intensify sound
Inner ear detects sound
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Inner Hair Cell movement along the basilar
membrane
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Converts Mechanical energy to Electrical energy
(nerve impulse)
Outer hair cells help modulate movement along
the basilar membrane
Questions?