Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Upcoming SlideShare
Physiology of hearing
Physiology of hearing
Loading in …3
×
1 of 36

Physiology Of Hearing

153

Share

Physiology Of Hearing

Related Books

Free with a 30 day trial from Scribd

See all

Physiology Of Hearing

  1. 1. PHYSIOLOGY OF HEARING Crisbert I. Cualteros, M.D.
  2. 3. acoustics <ul><li>Sound – a change in pressure (particle displacement)within an elastic medium </li></ul><ul><li>- wave form </li></ul><ul><li>- emanates from a vibrating system </li></ul><ul><li>- travels faster in denser medium </li></ul><ul><li>Intensity – refers to the strength of the sound; the - psychoacoustic equivalent of intensity is loudness </li></ul>
  3. 4. acoustics <ul><li>Decibel - the unit used to measure the intensity of a sound </li></ul><ul><li>- named after Alexander Graham Bell </li></ul><ul><li>- One – tenth of a Bel </li></ul><ul><li>- range of human hearing 0 – 120 dB </li></ul><ul><li>dB = 10 logIm / I ref </li></ul><ul><li>where: </li></ul><ul><li>Im = measure intensity </li></ul><ul><li>I ref = reference intensity </li></ul>
  4. 5. acoustics <ul><li>The decibel scale has the following characteristics: </li></ul><ul><li>1. It is logarithmic and incorporates a ratio </li></ul><ul><li>2. It is not linear (i.e., an increase from 1 to 3 dB is not equal to an increase from 5 to 7 dB) </li></ul><ul><li>3. It is a relative measure (i.e., 0 dB does not indicate the absence of sound) </li></ul><ul><li>4. It is expressed with different reference levels </li></ul>
  5. 6. acoustics <ul><li>Frequency – refers to the number of cycles (complete oscillations) of a vibrating body per unit of time; the psychoacoustic equivalent of frequency is pitch. </li></ul>
  6. 7. acoustics <ul><li>Hertz (Hz) – unit used to measure frequency </li></ul><ul><li>- formerly called cycles per second or cps </li></ul><ul><li>- the human ear is capable of hearing from 20 – 20,000 Hz </li></ul>
  7. 8. acoustics <ul><li>Pure tone – a single frequency sound; rarely occur in nature </li></ul><ul><li>Complex sound – has more than one frequency </li></ul><ul><li>Noise – an aperiodic complex sound </li></ul>
  8. 9. acoustics <ul><li>Resonant frequency – the frequency at which a mass vibrates with the least amount of external force </li></ul><ul><ul><ul><li>External auditory canal - 3000 Hz </li></ul></ul></ul><ul><ul><ul><li>Middle ear - 800 Hz </li></ul></ul></ul><ul><ul><ul><li>Tympanic membrane - 800 – 1600 Hz </li></ul></ul></ul><ul><ul><ul><li>Ossicular chain - 500 – 2000 Hz </li></ul></ul></ul>
  9. 10. PROPERTIES OF SOUND <ul><li>Sound </li></ul><ul><li>External auditory canal </li></ul>
  10. 11. EXTERNAL EAR <ul><li>- funnel-shaped “collector” </li></ul><ul><li>of sounds </li></ul><ul><li>- localization </li></ul><ul><li>pinna </li></ul>
  11. 12. EXTERNAL EAR <ul><li>- directs sound waves </li></ul><ul><li>- 2 to 4 kHz </li></ul><ul><li>- 10 to 15 dB </li></ul><ul><li>- total occlusion hearing loss </li></ul><ul><li>not more than 40 dB </li></ul><ul><li>- earplugs / earmuffs attenuate </li></ul><ul><li>sound <30 dB </li></ul><ul><li>External auditory canal </li></ul>
  12. 13. EXTERNAL EAR <ul><li>- monaural hearing </li></ul><ul><li>- binaural hearing </li></ul><ul><li>cannot localize sounds </li></ul><ul><li>localize sounds </li></ul>
  13. 14. <ul><li>sound </li></ul><ul><li>EAC </li></ul><ul><li>middle ear </li></ul>
  14. 15. MIDDLE EAR <ul><li>air-filled </li></ul><ul><li>- 1 to 2 cc </li></ul>
  15. 16. MIDDLE EAR <ul><li>- handle </li></ul><ul><li> embedded in the TM </li></ul><ul><li>- neck </li></ul><ul><li> tensor tympani inserts </li></ul><ul><li>- head </li></ul><ul><li> articulates with ant. surface of </li></ul><ul><li>incus body in the epitympanum </li></ul><ul><li>malleus </li></ul>
  16. 17. MIDDLE EAR <ul><li>- short process projects backward </li></ul><ul><li>- long incus passes downward </li></ul><ul><li>articulated with head of </li></ul><ul><li>stapes </li></ul><ul><li>incus </li></ul>
  17. 18. MIDDLE EAR <ul><li>- oval window </li></ul><ul><li> </li></ul><ul><li>inner ear </li></ul><ul><li>stapes </li></ul>
  18. 19. - axis of rotation:  line from short process of incus to neck of malleus MIDDLE EAR
  19. 20. MIDDLE EAR CONDUCTION A. Problem – transmission of sound between 2   99.9% reflected 0.1 % transmitted   IMPEDANCE MATCHING 20-35 dB loss    different media (air  liquid)
  20. 21. MIDDLE EAR CONDUCTION B: TRANSDUCER MECHANISM 1. ratio of drum/ footplate area   vibrating TM 55 sq. mm. foot plate 3.5 sq. mm. = 17 (25 to 30 dB) ______________ ______________ =
  21. 22. MIDDLE EAR CONDUCTION B. TRANSDUCER MECHANISM 2. Lever mechanism Length long process malleus Length long process incus ______________________________ =1.3 (2.5 dB)
  22. 23. MIDDLE EAR CONDUCTION <ul><li>B. TRANSDUCER MECHANISM </li></ul><ul><ul><li>3. Phase difference/ Protection of the round window </li></ul></ul><ul><ul><ul><li>release valve </li></ul></ul></ul><ul><ul><ul><li>sound waves striking both windows simultaneously  waves cancel each other </li></ul></ul></ul><ul><ul><ul><li>different location / position ( phase difference ) </li></ul></ul></ul><ul><ul><ul><li> ~ 4 dB change </li></ul></ul></ul>
  23. 24. MIDDLE EAR CONDUCTION <ul><li>B. TRANSDUCER MECHANISM </li></ul><ul><ul><li>4. Natural resonance and efficiency of the outer and middle ear (500 to 3000 Hz) </li></ul></ul>
  24. 25. MIDDLE EAR CONDUCTION <ul><li>B. TRANSDUCER MECHANISM </li></ul><ul><ul><li>5. shape of the tympanic membrane </li></ul></ul><ul><ul><ul><li>Curved cone </li></ul></ul></ul>
  25. 26. Middle ear conduction
  26. 27. INTRINSIC MUSCLES OF THE MIDDLE EAR Tensor Tympani Stapedius
  27. 28. Sound  EAC  Middle Ear  Inner Ear (Footplate)  
  28. 29. INNER EAR CONDUCTION <ul><li>The Stapes moves back and forth at the oval </li></ul><ul><li>window  fluid displacement within the cochlea </li></ul><ul><li>These waves cause up and down displacement of </li></ul><ul><li>the basilar membrane which then pivots around the osseous lamina </li></ul>
  29. 30. INNER EAR CONDUCTION C. This results in side to side motion of the hair cells in relation to the tectorial membrane in which they are embedded . D. This shearing action initiates a local electrical potential, COCHLEAR MICROPHONIC, which trigger a nerve impulse.
  30. 31. INNER EAR CONDUCTION E. Portion of cochlear stimulated High Frequency  Lower hair cells Low Frequency  Apical cells F. Loudness - number of elements firing
  31. 32. BONE CONDUCTION <ul><li>Conductive mechanism of ME may be by-passed; natural structures stimulated directly through bone conduction </li></ul><ul><li>Principle behind tuning fork tests </li></ul>
  32. 33. Conscious auditory pathway
  33. 34. Auditory pathway <ul><li>Sound EAC Middle ear </li></ul><ul><li>Inner ear eighth nerve lateral lemniscus </li></ul><ul><li> (medulla) </li></ul><ul><li>Dorsal & ventral nuclei Inferior colliculus </li></ul><ul><li>Medial geniculate body (thalamus) Auditory cortex </li></ul>
  34. 35. auditory pathway
  35. 36. <ul><li>salamat! </li></ul><ul><li>Pls visit: http://crisbertcualteros.page.tl </li></ul>

×