introduction to auditory Flashcards
what is sound
pressure chg through a medium
wha tis the speed of sound in air
340 m/s
pure tone
sound can be dipicted as a sinusoidal wave.
- increase pressure followed by decresaes
amplitude
or “sound level” or “sound intensity”, expressed on a logarithmic scale in
decibels (dB) sound pressure level (SPL)
frequency
related to pitch; expressed in Hertz (Hz, cycles per second)
- 400 Hz = 400 cycles/s
phase
this is mostly ignored by human hearing
timbre
the harmonic content
physics of sound
- how can we chg the amplitude or frequency of sound
depending on how much vibration induced by the tuning fork we chan chg the amplitude or frequency
- more movement = more frequency of sound
what are the parts of the outer ear
pinnia
auditory canal
tympanic membrane
pinnia
localize sound
- function diminished in humans
auditory canal
filled with air
tympanic membrane
communicates with the middle ear
inner ear
- sensory organs are located here
middle ear
contains 3 ossicles that transmit sound from outer ear to inner and amplify sound
ossicular chain
- malleus rests on tympanic membrane and moves with the vibrations of the tympanic membrane
what is Impendance matching ( middle ear)
- what is the movement ratio between the stapes and the malleus
transmits air vibrations into fluid vibrations
-Movement ratio of 1 : 1.3 (more movement at the stapes than on the malleus)
Amount of pressure on oval window is greater than at the tympanic membrane
Impendance matching :
how does the tynpanic membrane compare to the oval window? what does this do
Tympanic membrane is larger than oval window by ca. a factor of 18.6, which
increases sound wave pressure by ~15 times
impendance matching
inner ear filled with fluid
how is middle ear important in dentistry
communicates with oral cavity bc infections in the oral cavity can be communicated to the ear
the cochlea ( inner ear)
spiral structure, made of bone
- inside there are 3 compartments
what are the 3 compartments of the cochlea
scala vestibuli - communicates with oval window
- scala tympani - communicates with middle ear via round window ( pressure releaser)
- cochlear partition
how can changes of a sound be produced in the cochlea
- ## stapes appliespressure to oval window which is transmitted into the cohclea
The place theory for frequency encoding in the cochlea
- different frequencies induce vibrations i. different locations in the cochlear partition
- high frequency near the base
- low frequency near the apex
The organ of corti
innervated by CN VIII
what is mechanotransdcution
- how does this occur
translating mechanincal stimulus to action potetntials
- by the inner hair cells ( contain cilia
what are the inner hair cells innervated by
CN VIII
what happens to kinocilium
disapears in adults
what keeps the stereocilia together
the ankle links
- tip links
lateral links
play a role in transduction bc thye are anchored by a stretch receptor that can be opened or closed depending on how the mebrane is stretched
- if the tip link is stretched it opens the channel and allows ions to enter thte cilia and thus hair cell which depolarizes the cell which is a part of the mechanotransduction process
mechanotransduction
image of pathway that wasnt on the power point, you took ohoto add
how do hair cells go back to regular mebrane potential
- no more K entering
- volatage gated ca channels close
cell becomes hyperpolarized
endolymph vs perilymph
- endo - had high K and low na channels
peri - has low K and high Na channels - this allows for diffusion down a gradient
Each auditory nerve fiber responds
to a narrow range of frequencies
- what happens to place theory
- in response to realease in gltamate the afferent cells depolarize
- each auditory fiber
what do the outer hair cells do in the cochlea
OHC use stretch receptors associated with the stereocilia at their tips to
sense vibrations and convert them to electrical currents.
- But only in outer hair cells are these currents used to control length changes which parallel,
and reinforce, the incoming mechanical vibration.
what do inner hair cells do in comparison to OHCs
The inner hair cells send the auditory signal to the auditory nerve, but the outer hair cells
modulate the response.
otoacoustic emmsions OAE
- is used to test for hearing in babies
- they are produced by the movembet of outer hair cells in response to sounds
ascending auditory pathway
- cochlear nuclus»_space; superior olivary nucleus» inferior collliculus»medial geniculate nucleyus» auditory cortex
cortical tonotopy
Cortical representation of sound
intensities
different nuerons respond differently to sounds with diff amplitude
Experience-dependent development of
tonotopic maps
- tonotopic map in auditory complex is platic
- during development it changes with experience
- on the left the blue is low freq and red is high ( smooth destributions )
- on the right you see more green whcih means that when young they heard sounds at this frequnecy more so there are more in adult
what is the lowest detectable sound?
- what is the amplitude of speech
- what amplitude does the ear get damaged
-0 dB SPL=10-16watts/cm2
- 60 dB SPL
- 140 dB SPL
what is the difference between the faintest and loudest humans can hear.
120dB, and the sensitivity is about 1dB SPL
Humans can detect 0dB SPL sounds at 3kHz, but require 40dBSPL
sounds at 100Hz
what happens with mild , moderate , and severe hearing loss
what is presbycusis
hearing loss as you age
which sounds do you lose first
high fequency
what is the range of frequency we can detect
Range between 20 Hz to 20kHz, on average
what sound frequency are we most sesnistive to? why
Far more sensitive to sounds between 1 - 4kHz
- we use this for speech
what sounds can humans discriminate
Humans can discriminate two sounds that differ by 0.3% at 3kHz,
but require at least 3% difference at 100Hz
what is the auditory brain stem response
- measuring resposes above the brainstem
human hearing: location and direction:
what os the angular ( direction) discrimination in humans
angular (direction) discrimination: humans can discriminate two sound
sources that are located as little as 3 degrees apart
how does binaural hearing work
- acts in 2 ways
- For sounds above 1kHz, the head strongly shadows the sound,
making it weaker for the distal ear - - For sounds below 1kHz, human hearing relies on time and level
differences between the arrival to the proximal vs distal ear
head shadow
duplex theory of sound localization
Interaural Time Differences
(ITDs) dominate sound
localization at low
frequencies
Interaural Level Differences
(ILDs) dominate sound
localization at high
frequencie
how do we know when a sound is infront
- same response in both ears
how do we know if sound is 90 degrees away
- here sound more in the right ear
interaural level differences
sound localization in rooms
In a everyday rooms, the sound energy reaching the ears consist of
* sound travelling on a direct path from the source, and
* reverberant energy (sound reflected off surfaces).
We are normally not aware of reverberation, although it does
influence subjective sound quality.
echo suppresion
- what are the time reigons
1) Summing localization (< 1 ms delay): two events fused: perceived
location is a weighted sum of the two.
2) Precedence effect (ca. 1-5 ms delay): Only one sound perceived:
direction of first sound dominant.
3) Echo threshold (> 5 ms delay): Two sounds heard. ( echo)
what are the 2 types of deafness
- conduction - something in periophery is affectd like the ear drum or tympanic membreane
- sensorineural deafeness
what is incleuded in conduction deafness
- punctured ear drum
- otitis media
- otosclerosis
what is incleded in sensorineural deafness
- rebulla
- degenreation of inner hair cells
- professional deafness ( exposure to loud sounds)
- prebycusis
rinnies test
- bone condution: put vibration on skull to rely on bone transimition to cochlea - if they dont hear then its conduction hearing loss
- air conduction: put vibration fork next to ear in the air - dont hear = sensory hearinf loss
