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Mechanism of hearing



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The mechanism of hearing
The mechanism of hearing
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Mechanism of hearing

  1. 1. Mechanism Of Hearing Anirudha K
  2. 2. Sound • Waves of Compression and Rarefaction
  3. 3. • Mechanical conduction – Conductive apparatus • Transduction of mechanical energy to electrical energy – Sensory system of Cochlea • Conduction of Electrical Impulses to the brain – Neural pathway
  4. 4. Conduction… ♦External Ear (Pinna) – Collects the sound – Funnel shape – Localisation of Sound ♦External Auditory Canal – Directs the sound waves ♦Reaches the Tympanic Membrane
  5. 5. Middle Ear • Impedence Matching 1. Lever action of Ossicles 2. Hydraulic action of Tympanic membrane 3. Curve of Tympanic membrane 4. Phase difference Maintainance 5. Natural resonance of External and Middle ear
  6. 6. 1.Lever Action of Ossicles Length of Long process of malleus Length of Long process of Incus 1.3=
  7. 7. 2.Hydraulic action of TM Area of Tympanic Membrane Area of Footplate of Stapes 55 3.2 17.1 Total Transformer Ratio = 17.1 × 1.3 = 22.1
  8. 8. 3. Curve of the Tympanic membrane • Movements of the tympanic membrane are more at the periphery than at the centre where the handle of malleus is attached.
  9. 9. Phase difference between Round and Oval Windows • If no tympanic membrane was present, the sound would have struck both the Round and oval Window simultaneously, thus cancelling the vibrations produced since they are two ends of a continuous channel. • Ossicular chain – Preferential Path to Oval Window… • So when Oval window is in compression, Round window is in Rarefaction ,and Vice Versa…
  10. 10. Natural Resonance of External and Midlde Ear • Natural Resonance of – External Ear canal : 3000Hz – Tympanic Membrane :800-1600Hz – Middle ear : 800Hz – Ossicular Chain : 500-2000Hz Greatest Sensitivity of Sound transmission is between : 500Hz – 3000Hz Which is fortunately the frequencies most important to humans in day-to-day life…
  11. 11. Transduction of Mechanical energy to Electrical Energy Movement of Stapes Footplate Oval Window Movement of Cochlear Fluid : Perilymph Movement of Basillar membrane Movement of Organ of Corti Shearing force between Tectorial Membrane and Hair Cells Distorsion of Hair cells Cochlear Microphonics Nerve Impulse
  12. 12. Neural Pathway
  13. 13. ThanQ…