the auditory system Flashcards
(20 cards)
what is sound
-physical movement of air particles
-individual particles move backwards and forward even though when they vibrate it looks like they’re moving forwards quickly
-air particles hit one another hence why it doesnt look like they’re moving far
whats compressed and rarefied air
-compressed= lots of air particles
-rarefied= not many air particles
what are the 2 properties of sound
-frequency
-intensity
what is frequency
-Number of compressed or rarefied patches of air that pass by our ears each second, expressed as Hertz (Hz)
whats intensity
-Air pressure difference between peaks and troughs, expressed as decibels (dB)
whats human hearing range
-20 Hz to 20,000 Hz
-4000 Hz is the best hearing for humans
what the threshold of conversational speech
-high sound pressure= louder background noise so louder speech level
-low sound pressure= quieter background noise so quieter speech
what does the human auditory system consist of: outer ear
-pinna:
=outer ear
=not too useful for locality of sound
=simple in humans
=if you have a flat ear, you can’t hear sounds in a vertical plane
-external auditory Canal:
=outer ear
=helps us locate sound
=2.5 cm into skull
what does the human auditory system consist of: middle ear
-stapes (touches oval window)
-malleus
-incus
-all of middle ear= air filled compartments
-sound from eardrum-> start of inner ear (oval window)
-tympatic membrane:
=eardrum
=big membrane stretched across entirety of eardrum
=can get perfurated
=as sound hits it, it hits bones around it
what does the human auditory system consist of: inner ear
-cochlea implant- fluid membrane stimulates cells
what are the The ossicles of the middle ear
-Ossicles = latin for ‘little bones’
-malleus= hammer, attached at the opposite end to tympanic membrane
-incus= anvil
-stapes= stirrup
-stapes pushed by movement from tympanic membrane
-middle ear takes tympanic membrane and concentrates it to the oval window (larger force on a smaller window)
-this happens because cochlea is filled with fluid which is harder than air
How does the middle ear transfer sound?
-Ossicles amplify sounds:
=exerts ~20 times more pressure on the oval window than on the tympanic membrane
=overcomes the greater impedance of cochlear fluid
-The oval would barely move if it was moved directly by sound due to the air-fluid interface, as fluid has a greater inertia (impedance).
-Impedance matching – air and water have different impedances i.e. the tendency of each medium to oppose movement brought about by a pressure wave
-3rd membrane= round window-> lets the fluid push out so there isn’t too much of a build up of pressure
what different frequencies can you hear in the cochlea
-low at apex
-higher as you move along
whats the The basilar membrane
-found in the middle of the cochlea
-horizontal in the middle of cochlea
-built differently as you go along it
-base= narrow, thick and stiff to move
-apex= wide, thin and floppy to move
-high frequency move the base
-low frequencies move the wide bit at the apex
whats the The travelling wave of the basilar membrane
-Different frequency sounds cause maximal displacement of the basilar membrane in different regions
-Tonotopic map- different tones and frequencies of the tones, kept right throughout auditory system
whats the Anatomy of the cochlea
-Scala vestibuli and scala tympani filled with perilymph (very much like ECF)
-Scala media filled with endolymph- you go deaf when the fluid starts having the wrong composition
-Hair cells found in the organ of Corti
-full of different fluids
-scala vestibular- ends gets pushed until it goes into the apex
-scala tympani gets fluid from the scala vestibular
whats the Anatomy of the organ of Corti
-Hair cells have hair bundles at their apex (hair bundles move around )
-Inner hair cells (IHCs) (would be deaf if lost as they send signals to the brain to say that sound has come in) = primary sensory receptors
-Outer hair cells (OHCs) (they send some signals to the brain but wouldn’t go deaf if you lost it, they amplify movement of basilar membrane) = cochlear amplifier
what are hair bundles
-Located at the top (apical) part of hair cells
-Made of stereocilia
-Stereocilia connected by tip links
-smaller and taller steriocilia connect by tip links which causes hair bundles to move back and forth
-this stretched the tip links and when they stretch Mechanoelectrical transducer channel open
what happens when Basilar membrane displacement causes movement of hair bundles
-stapes moves outwards:
=BM moves upwards
=Hair bundles pushed towards taller stereocilia
=Tip links stretch
-Stapes moves inward
=BM moves downwards
=Hair bundles pulled towards shorter stereocilia
=Tip links relax
what are IHCs and how do they work
-the primary sensory receptors
-membrane that separates base from hair bundle- sound wave travels down this
-lots of K+ moves Into hair cell and causes depolarisation
-therefore graded potential generated in hair cells- spreads to base of cell which opens the voltages gated ion channels where glutamate (e.g.) moves across synapse and binds to receptors
-graded potential only found in EPSP generated synapses
