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

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

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

4. Purves
Fig 13.3

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

6. Bekesy, 1960
external ear
middle ear
inner ear

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

8. cochlea
temporal bone 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 ST SM BM TM RM
Smith,
1975

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

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

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

17. Purves
Fig 13-6

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

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

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

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

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

23. 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.

24. two codes
of frequency
in auditory
nerve fibers
val

25. 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

26. 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

27. Purves Box 13-C