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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?. Resonance Characteristic frequency response Density & Tuning Sharpness Hi dense = Lo Sharpness Size/Cavity Breaking Glass Demo.

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Sound Transduction 1

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  1. Sound Transduction 1 Or, if the a tree falls in a forest and no one is around does it still reflect light?

  2. What is Resonance? • Resonance • Characteristic frequency response • Density & Tuning Sharpness • Hi dense = Lo Sharpness • Size/Cavity • Breaking Glass Demo

  3. 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

  4. Outer Ear: con’t • 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

  5. 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!

  6. More middle ear goodness • Air filled pressure equal to outside • Eustacian Tube regulation • High intensity sound response • Multiple muscles • Sound attenuators

  7. 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 friend’s 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?

  8. 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

  9. 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

  10. 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

  11. 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?

  12. 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

  13. 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

  14. 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

  15. 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

  16. Questions?

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