cochlear and auditory system Flashcards
sound
mechanical energy causing vibrations detected by the ears
compressed air
dense particles (peak)
rarefied air
less dense particles (trough)
frquency
how many peaks (compressed) and troughs (rarefied) within a second 1 peak in 1 second= 1 hertz
decibel scale is a
logarithmic scale
intensity /amplitude
Air pressure difference between peaks and troughs, expressed as decibels (dB)
physioloical ranges of freq and intenisy for humans
Don’t have the same threshold of frequency for every sound
100-10,000 hertz for speech
Average of speech 60 DBs
Anything above 100dbs is damaging to ears
human hearing range
20Hz to 20,000 Hz
pinna
outer ear (latin for wing) more sensitive to sounds from in front than behind
localisation of sound from above or below (vertical)
//AKA oricle
after pinna sound goes
down the extnerla auditory cancel through bone of skull until it hits tympanic membrane (drum)
middle ear
vibration movesback and forth on drum causing oscillations on oval window (much smaller)- bottom of cochlea
oval window movement makes fluid move in cochlea
the ossicles of the middle ear
latin for ‘little bones’
hammer, anvil and stirrup
malleus to incus
has a rigid connection (have to move together)
incus to stapes
has a flexible connection (important for how sound moves are transferred through middle ear)
how the middle ear transfers sound
Sound wave is spread out across quite wide area of tymp drum
Oval window is 20x smaller than tymp drum (so the pressure would be much more concentrated)
Middle ear concentrates the sound onto the oval window – it is amplified
Important because moves from air filled env in middle air to fluid filled env in cochlea
There is more resitsant at back of oval window than the tymp mem
Pressure is relived from the cochlea on the round window (because cochlea is sealed)
high pitch
high freq
low pitch
low freq
volume
amplitude
extnerl and middle ear
only used for hearing
inner ear
for hearing and maintaining equilibrium
tympanic membrane
ear drum
boundary between external and middle ear
Impedance matching
air and water have different impedances i.e. the tendency of each medium to oppose movement brought about by a pressure wave.
when sound comes through ear
the ear drum vibrates
goes through to bones (ossicles)
these amplify the sound waves
tympanic cavity focuses pressure of sound waves so they’re strong enough to move fluid in inner ear
using osicle bones- malleus (hammer), incus (anvil) and stapes (stirrup)
these project vibrations to another membrane - the superior oval window- setting the fluid in inner ear into motion
waves transduced into electrical signals
cochlea 3 layers (scale vestibulili, scala media, scala tympani)
the basilar membrane vibrates at different pitches along it’s length
base - high freq and
apex- low freq
organ of court gets tickled with hair cells
when triggered opens mechanically gated sodium channels
this influx causes graded potentials, if enough an action potential to CNS (vai cochlear nerve, auditory pathway, and cortex)
how does the brain know the sound
detects pitch of sound based on location of hair cells being triggered
loud sound=more movement=more frequent AP
how does basil membrane displacement affect hair cells
stapes moves outward
basilar membrane moves upwards
hair cells depolarise
(out and up- depolarise)
stapes moves inward
basilar membrane moves donwards
hair cells hyperpolarise
(in and down - hyper polarise)
hair bundles are connected by
tip links
hair bundles are surrounded by endolymph within the scala media
mechanoelectrical transducer channel
inner hair cells - the primary sensory receptors
Apical at the top – surround by endolymoh (high na) and positive potential (80mv more positive than perilymph)
Forces positive ions to move from endo to perilymp via hair cells
And can only do that when channels in hair cell bundles are open
High potassium moving into the hair cell makes it more positive and leave via other channels in side
Depolarization of K moving in open voltage gated calcium channels
At the base of the cell calcium comes in and causes release of synaptic vesicles with glutamate (excitatory)
Glutamate crosses synapse and activates AMPA or the other one it binds to
Causing ESPs — AP to auditory brain stem
endolymph
higher K+
+80mv
perilymph
low K+
0Mv
outer hair cells are electromotile
act as the cochlear amplifier
OHCs change in size when bundles are stimulated
BM moves upwards hair bundles move towards taller stereo cilia OHC depolarises OHC contracts OHC becomes shorter amplifies upwards movement of BM
