physiology of hearing Flashcards
what are some facts about the ear canal?
- to protect ear drum as it is very sensitive
- has six cubic cm cavity which resonates at 3 kHz
- sounds would be more intense at ear drum if we didn’t have ear canal
what are some facts about the pinna?
- common feature in mammals
- pick up sound better and concentrate sound on ear drum
- helps sensitivity of our hearing
- most birds don’t have pinnae
what are some facts about the middle ear ossicles?
- 3 bones in there
- birds only have 1 bone in this system - this makes their hearing to only go up to 10-12 kHz
- ossicular mass and middle ear volume determine the frequency limits of hearing
- reason why animals hearing ranges are similar but shifted along are because of middle ear
- bigger volume of middle ear = more easily sound can go through ear
- top end of hearing determined by mass of ossicles
- evolutionary push to have small bones in middle ear
what are some facts about the cochlea?
- contains fluid
- top and bottom pieces are joint together
- sound wave comes into the top and then spirals itself down the cochlea
- fluid is not compressible so pressure wave goes somewhere
- make the membrane vibrate up and down which sparks process of hearing
- bottom end of the cochlear resonates with high frequencies vs top which resonates with low frequencies
what is the basilar membrane like?
the basilar membrane is narrow, light and stiff at the bottom and wide, heavy and floppy at the top
how is the membrane of the cochlea a bit like a harp?
- membrane in the cochlea is a bit like a harp
- a harp has short, light strings at one end and long, heavy ones at the other
where would you find perilymph and endolymph and what are they?
- in cochlea
- perilymph is the same stuff you have in your body in the lymphatic system
- endolymph is different because the structure on the outside of it is active and pumping potassium ions into it, charging it up
what are some facts about the organ of corti?
- very structured
- 2 different types of hair cells
- more outer hair cells (active things)
- detect movements/vibrations
- nerve activations going into the two types of hair cells
what do afferent nerves in organ of corti do?
afferent sends info from periphery to brain - incoming info
what do efferent nerves in organ of corti do?
efferent send info from brain to periphery - brain sending signals all the way down to cochlea and instructing it
what happens with the tuning of the auditory nerve?
tuning of the auditory nerve: pure tone thresholds curves for individual auditory nerve fibres
what happens during phase locking of auditory nerve?
- the firing or neurons preferentially at a certain phase of an amplitude-modulated stimulus
- it can help to synchronize an output oscillator signal with a reference signal
“the tendency of a neuron to fire action potentials at particular phases of an ongoing periodic sound waveform”
what is the effect of the basiliar membrane motion on the “bundles” of streocilia?
- BM vibrates as sound passes through
- stapes puts pressure waves into scala vestibuli
- round window allows wave to exit cochlear
- hair cells being activated/pushed around makes them respond
how do hair cells help us hear?
- tip links connect each stereocilium in the bundle to the next
- they pull open ion channels during deflection of the bundle
- hair cells can change voltage in response to the movement
how does amplification of OHCs work?
- sound > BM movement > IHC voltage change > auditory nerve response
- at BM movement: OHC voltage change > OHC length change and repeat (positive feedback amplification)
- this makes a huge difference: amplification from OHCs can be 60 dB for low-level sounds, but reduces with increasing sound level, explaining slow loudness growth
