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MEDS 371 Peripheral Auditory System Dr. Duck O. Kim

MEDS 371 Peripheral Auditory System Dr. Duck O. Kim. dB: decibel SPL: sound pressure level dB SPL = 20 log 10 (pressure/ref) ref = 20 m Pa. dB SPL re 20 µPa. Davis & Silverman, 1970. threshold of hearing. frequency (Hz). audible freq. range for humans: approx. 20 ~ 20,000 Hz. Purves

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MEDS 371 Peripheral Auditory System Dr. Duck O. Kim

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  1. MEDS 371 Peripheral Auditory System Dr. Duck O. Kim

  2. dB: decibel SPL: sound pressure level dB SPL = 20 log10 (pressure/ref) ref = 20 mPa

  3. dB SPL re 20 µPa Davis & Silverman, 1970 threshold of hearing frequency (Hz) audible freq. range for humans: approx. 20 ~ 20,000 Hz

  4. Purves Fig 13.3

  5. middle-ear muscles: tensor tympani - malleus stapedius - stapes Pickles, 1988 the middle ear Impedance transformation Pickles, 1988

  6. Bekesy, 1960 external ear middle ear inner ear

  7. data from human cadavers bas. mem. disp. amplitude origin of tonotopic organization Bekesy, 1960 distance from stapes (mm)

  8. temporal bone cochlea SV ST Pickles, 1988

  9. inner ear

  10. Purves

  11. fluid in ST & SV: perilymph (like CSF) fluid in SM: endolymph (high K+)

  12. organ of Corti SV RM SM TM Smith, 1975 BM ST

  13. afferent inner hair cell outer hair cell afferent nerve ending afferent nerve ending * afferent nerve fibers efferent nerve ending * efferent nerve fibers Smith, 1975

  14. tip-link model of hair-cell excitation Pickles, 1984

  15. Purves, Fig 12-8; adapted from Lewis & Hudspeth, 1983

  16. Purves Fig 13-6

  17. frequency tuning curves cochlear neuron threshold (dB SPL) basilar membrane Sellick et al, 1982 Neely & Kim, 1983 frequency (kHz)

  18. frequency tuning curves of cochlear ganglion neurons OHC damage normal threshold (dB SPL) Robertson & Johnstone, 1979 frequency (kHz)

  19. OHC motilities underlie the cochlear amplifier. HB motility somatic motility Neely and Kim, 1983 Brownelle et al., 1985 Kim, 1986 Hudspeth, 1997

  20. innervation of IHCs and OHCs by cochlear ganglion neurons adapted from Spoendlin, 1972

  21. Auditory nerve fibers exhibit phase locking for low stimulus frequencies (< a few kilohertz). stimulus: 300 Hz pure tone Evans, 1975

  22. Phase locking of auditory nerve fibers lead to neural coding of inter-aural time difference (ITD), a cue for sound location. Phase locking may also contribute to coding of sound frequency.

  23. two codes of frequency in auditory nerve fibers val

  24. code of sound intensity increase of sound intensity -> (1) increase of discharge rates of auditory nerve fibers (with low spontaneous rates); (2) increase of number of excited auditory nerve fibers discharge rate (spikes/s) Kim et al., 1991 distance along cochlea

  25. hearing loss examples_____ conductive hearing loss otosclerosis otitis media impaction of ear canal sensorineural hearing loss acoustic trauma ototoxic drugs Meniere’s disease mixed hearing loss presbycusis

  26. Purves Box 13-C

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