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MEDS 371
Peripheral Auditory System
Dr. Duck O. Kim
dB: decibel
SPL: sound pressure level
dB SPL = 20 log10 (pressure/ref)
ref = 20 mPa
frequency (Hz)
audible freq. range for humans: approx. 20 ~ 20,000 Hz
Davis & Silverman, 1970
dB SPL re 20 µPa
threshold of hearing
Purves
Fig 13.3
the middle ear
Impedance
transformation
middle-ear muscles:
tensor tympani - malleus
stapedius - stapes
Pickles,
Pickles,1988
1988
Bekesy, 1960
external ear
middle ear
inner ear
bas. mem. disp. amplitude
data from
human
cadavers
origin of
tonotopic
organization
Bekesy, 1960
distance from stapes (mm)
cochlea
SV
ST
temporal bone
Pickles, 1988
inner ear
Purves
fluid in ST & SV: perilymph (like CSF)
fluid in SM: endolymph (high K+)
organ of Corti
SV
RM
SM
TM
ST
BM
Smith,
1975
inner hair cell
outer hair cell
afferent
nerve
ending
afferent
afferent
nerve
ending
*
*
efferent
nerve
ending
efferent
nerve
fibers
Smith, 1975
afferent
nerve
fibers
tip-link model of hair-cell excitation
Pickles, 1984
Purves, Fig 12-8;
adapted from
Lewis & Hudspeth,
1983
Purves
Fig 13-6
threshold (dB SPL)
frequency tuning curves
cochlear
neuron
basilar
membrane
Sellick et al, 1982
Neely & Kim, 1983
frequency (kHz)
frequency tuning curves of
cochlear ganglion neurons
threshold (dB SPL)
OHC damage
normal
Robertson &
Johnstone,
1979
frequency (kHz)
HB motility
somatic
motility
OHC motilities
underlie
the cochlear
amplifier.
Neely and Kim, 1983
Brownelle et al., 1985
Kim, 1986
Hudspeth, 1997
innervation of IHCs and OHCs
by cochlear ganglion neurons
adapted from Spoendlin, 1972
Auditory nerve fibers exhibit phase locking
for low stimulus frequencies (< a few kilohertz).
stimulus: 300 Hz pure tone
Evans, 1975
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.
two codes
of frequency
in auditory
nerve fibers
val
discharge rate (spikes/s)
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
Kim et al., 1991
distance along cochlea
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
Purves Box 13-C