lecture 27: Hearing Flashcards
(31 cards)
what are sound waves
the compression of air
decibels
unit for audible noises
what do the different decibels correspond to
0 = threshold of hearing
30 = very quiet room, whispered speech
60= normal speech
70 = traffic noise, vacuum cleaner
80 = EU mobile electronic device volume limit
100 = large machine eg: tractor
110 = chain saw
120 = threshold of discomfort, loud concert
130 = jet takeoff
140 = pain, immediate permanent hearing damage
what does the pinna do
cartilaginous bit, designed to catch our airwaves
what are the three smallest bones in the ear
- incus
- malleus
- stapes (touching oval window)
what is the function of the three smallest bones
–> without these bones you can’t hear very well
- as the membrane vibrates back and forth, it causes these three bones to interact with each other
what can cause the ear to not vibrate well
if we increase internal difference but not external, we end up with a pressure difference which means it doesn’t vibrate as well
what is the oval window
another membrane in the middle ear
what does the eustachian tube do
- drains into sinuses, equilibriate the pressure, need to be able to correct the pressure in the middle ear so we aren’t affecting how it vibrates
- also to drain away gunk
what does the tympanic membrane do
- air waves causes it to flex
- so when the pressure waves hit it, it moves (oscillates back and ford)
what is the pathway through which the ear transfers sound waves from air to fluid
- tympanic membrane deflects
- middle ear bones move, and vibrate on oval window
- membrane in oval window moves
- basiliar membrane moves
what is the cochlea used for
mechanism by which we transduce vibrations in the ear into audible signals
what is important about the structure of the basilar membrane
– > its flexible
therefore when the stirrup presses on the oval membrane it causes vibrations here
what is the scala media in the cochlear filled with
–> endolymph
- high in potassium, mimics intracellular fluid
what is scala vestibuli and scala tympani filled with
–> perilymph
- extracellular fluid, pushing on entire structure
what is the organ of corti
the apparatus by which we hear things
how does the tuning of the basilar membrane work
- transmission of sound waves across the scala media causes the basilar membrane to oscillate at a point along its length that is in tune with the frequency of the pressure waves
- high pitch sounds cause the basilar membrane to oscillate at a point close to the oval window
- low pitch sounds cause the basilar membrane to vibrate closer to its apex
mechanism of the deflection of stereocilia
- vibration of basilar membrane at a specific point causes deflection of sterocilia on overlying hair cells at that point
- in this way, hair cells become depolarized at a location along the BM that corresponds to the pitch of the sound
where is the tectorial membrane
- runs the entire length of the cochlea apparatus and sits above the hair cells
what happens if the hairs move towards the kinocilium or away from it
- it is going to alter the membrane potential of the cell
- connected to potassium gated ion channels
mechanism of the kinocilium
- mechanical deformation toward the kinocilium opens K+ channels in the stereocilia
- mechanical deformation away from the kinocilium causes the K+ channels to close
how does signal transduction in hair cells work
- hair cells are caused to move by the vibration of the basilar membrane
- therefore the pitch of the sound causes the hair cells to be activated at a specific point along the BM
- this triggers firing of the afferent axon at a location that corresponds to the pitch of the sound
- the point of origin of the sensory axons is preserved in their projections to auditory cortex, so the BM is “mapped” in the brain
what are the different sound qualities
- pitch
- intensity
- duration
- direction
pitch (frequency)
discrimination is determined by activity in hair cells at specific points on basilar membrane
