Physiology of hearing 21st july 11

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Physiology of hearing 21st july 11

  1. 1. PHYSIOLOGICAL BASIS OF HEARING
  2. 5. FUNCTION OF EXTERNAL EAR
  3. 7. FUNCTION OF MIDDLE EAR
  4. 8. FUNCTIONS OF MIDDLE EAR: 1. IMPEDANCE MATCHING
  5. 9. <ul><li>1.Diameter of TM is 17 times </li></ul><ul><li>2.ossicolar lever action increases the pressure 1.3 times </li></ul><ul><li>Total increase will be 22 times </li></ul>
  6. 10. 2.ATTENUATION REFLEX
  7. 11. STRUCTURE OF INNER EAR
  8. 13. FUNCTION OF INNER EAR <ul><li>The inner ear has 2 main functions: </li></ul><ul><li>Mechanical frequency analysis: </li></ul><ul><li>2. Sensory transduction: </li></ul><ul><li>Generated pressure waves which </li></ul><ul><li>are transformed into neural impulse. </li></ul>
  9. 14. BASEMENT MEMBRANE 1. FREQUENCY ANALYSIS
  10. 15. PLACE PRINCIPLE
  11. 16. 2.SENSORY TRANSDUCTION IN INNER EAR Reticular lamina Rod of corti Pillar cell
  12. 17. SENSORY TRANSDUCTION IN INNER EAR <ul><li>Kinocilia / Stereocilia are Linked </li></ul><ul><li>Displacement Opens K + Channels </li></ul><ul><li>Depolarization -> release of glutamate </li></ul><ul><li>K + flows through cell </li></ul><ul><li>Glutamate -> increase spike rate in auditory nerve </li></ul>
  13. 18. ENDOCOCHLEAR POTENTIAL
  14. 20. <ul><li>Lesions of inner ear or </li></ul><ul><li>cochlear nuclei ,pons will </li></ul><ul><li>produce total N deafness </li></ul><ul><li>Lesions central ,cochlear </li></ul><ul><li>Nuclei primarily affect the </li></ul><ul><li>ability to localize sound </li></ul><ul><li>direction </li></ul>Primary Auditory area 41,42 Tranverse temporal gyri of Heschl
  15. 21. Pathophysiology of hearing <ul><li>Conduction deafness </li></ul><ul><li>Sensorineural deafness </li></ul>
  16. 22. <ul><li>Common tests differentiating b/w nerve & bone conduction </li></ul><ul><li>1.Rinnes </li></ul><ul><li>2.Webers </li></ul><ul><li>3.Audiometer </li></ul>
  17. 23. Rinnes compares AC-BC <ul><li>Normal : AC >BC Rinnes + ve </li></ul><ul><li>Conductive deafness: BC > AC Rinnes – ve </li></ul><ul><li>Sensorinueral deafness: Reduced rinnes +ve </li></ul><ul><li>AC >BC </li></ul>
  18. 24. Webers compares bone conduction of 2 ears, <ul><li>Normal : centralized </li></ul><ul><li>Conductive deafness: lateralized to diseased </li></ul><ul><li>Sensorinueral deafness:lateralized to normal </li></ul>
  19. 25. THANK YOU
  20. 27. TONOTOPICAL MAPPING
  21. 28. br of inf col 41,42
  22. 30. Loss of high frequency tones in old age
  23. 31. stapedius TT

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