Auditory 1 Flashcards
Sound comes in the form of ___ created by
pressure waves
increases and decreases in air pressure (compression and rarefaraction of sound wave)
Sound has 2 distinct qualities that contribute to audition
1) intensity (loudness)
2) frequency (pitch)
Intensity coresponds to __, measured in
pressure compressing air of sound wave
measured in dB SPL
normal = 7-8 orders of magnitude
Equation for intensity of sound
Standard reference Pressure =
Normal auditory threshold =
dB SPL = 20 log(P1/P2)
Standard reference pressure (P^2) = 20X10^-6 N/m2
Normal auditory threshold = 1000 Hz
Frequency define
measured in ___
normal range for human =
freq = # of times per second sound wave reaches peak compression (max intensity) or rarefraction (min intensity)
measured in Hz
range = 20 Hz - 14 kHz
Define auditory threshold
lowest intensity of sound heard by human ear at given freq
Describe audiogram axes
how do you perform audiogram
X-axis = freq Y-axis = intensity
play series of tones for patient of progressively lower intensity at each freq
patient says when they hear tone and lowest intensity tone (and correspond freq) plotted
what is normal hearing in relation to auditory threshold
dramatic decline in auditory threshold (another way of saying it?)
normal hearing = relatively constant auditory threshold ~0 at all freq
incr in minimum intensity of sound detected
Acoustic impedance mismatch describe
differences in impedance btwn middle ear and inner ear
= resistance to flow
fluids > impedance than air
what is importance of differences in impedance
how does ear compensate
sound wave moves from air to fluid, significant portion of wave deflected at interface (approx 30 dB intensity lost)
ear compenste for loss of impedance with ossicles
three ossicles (med to lateral) connecting what to what
what is function?
stapes, incus, malleus
connecting TM of middle ear and oval window (connection btwn inner and middle ear)
bones amplify intensity by ~28 dB to compensate for intensity loss
amplification by ossicles is result of ?
1) pressure sound wave from TM concentrated on to much smaller surface of stapes
P = F/A so decr A, incr P or intensity
2) middle bones like lever to incr force transmit to inner ear
Sensorineural vs conductive hearing loss
conductive hearing loss = damage to elements of mechnaical transmission of sound waves thru ear (canal, TM, ossicles)
Sensorineural hearing loss = damage to hair cells or nerve fibers
causes of sensorineural hearing loss
XS loud noises
ototoxic drugs
age = presbycusis
causes of conductive hearing loss
otitis media= fluid disrupt conduct otosclerosis = ossicles not move well atresia = ear canal misshape perforation/rupture TM incr pressure in mid ear with altitude
How does sound elicit movement of basilar membrane to cochlea
1) sound thru middle ear
2) amplify by ossicles
3) transmit to oval window
4) window opens into cochlea
How does sound transmit from cochlea
5) pressure sound wave compresses fluid in scala vestibuli causing downward movement of BM
6) compresses fluid in scala tympani and bulges round window
or
6) transmit from vestibuli to scala tympani via helicotrema
Parts of cochlea
1) scala media (separated from scala tympani by BM)
organ of Corti (inner hair cells) sit on top of BM in media
2) scala tympani
3) scala vestibuli
What is helicotrema
hole in basement membrane connecting scala vestibuli and scala tympani
How does compression and rarefaction differ at BM?
compression = incr pressure and follow sequence
Rarefaction = pressure drops and sequence reverses
what is a tonotopic map?
basilar membrane not uniform
wave generated by compress oval window not symmetric wave with compress/rarefaction of same amplitude –> created by base, apex, intermed basilar membrane
distinguish btwn base, apex, and intermediate parts of basilar membrane structurally
base = near oval and round window = small and rigid
apex = large and “floppy”
intermediate = in btwn
distinguish btwn base, apex, and intermediate parts of basilar membrane in terms of freq
base = highest amplitude with high freq
apex = low freq
intermediate = in btwn
–> creates tonotopic map
hair cells sit on what?
inner hair cell - name of projection? - send where and contact what - base vs tip surrounded by? -
hair cells sit on BM within organ of corti of scala media (both inner and outer)
sends stereocilia into scala media to tectorial membrane and surrounded by K+ fluid = endolymph
base surrounded by K+ low fluid = perilymph
why do hair cells along BM rspond to diff freq
inner hair cell move in response to movement of BM
since portions of BM are vibrated max at certain freq, hair cells also respond based o position on BM
