Peripheral & Central Auditory Processing 1 Flashcards Preview

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Flashcards in Peripheral & Central Auditory Processing 1 Deck (103):

How does hearing loss initially manifest?

  • Difficult to hear in noisy environment
  • May require to lip read
  • Gets worse as you get older


What is sound?

  • Vibrations of objects --> which set up pressure waves in the surrounding air
  • Elastic property of air --> allows these pressure waves to propagate (spread)


What is the shape of sound?

What are the 2 parts of a sound wave?

  • Sine Wave
  • Compression & Rarefaction

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During pure tones, what is frequency related to?

  • Frequency of the tone is directly related to the pitch of the sound
  • Amplitude is related to perceived loudness


If a sound has a particular frequency. It is a ....

Pure Tone Sound


What is the relationship between frequency & pitch + amplitude & loudness?

  • Logarithmic Relationships
  • Double in Frequency --> Increases Pitch by 1 Octave
  • Double in Amplitude --> Increase Loudness by 6dB


What is a property of sounds with a clear pitch?

  • Frequencies are related
  • They are all multiples of a fundamental frequency


What are sounds that have all integer multiples of a 'fundamental frequency' called?

What does the sound sound like?

  • Harmonically Related
  • Sounds like a sound with a clear pitch

(e.g. lowest common denominator)


What makes up complex sounds?

  • Frequency components (i.e. different sine waves)


What dies a Fourier analysis help us do?

  • Plot the amplitude (& phase) for each frequency component of a sound
  • This gives us a sound spectrum
  • Giving us a compact representation for signals that contain oscillations

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How do you do a fourier analysis?

What is the graph you get called?

  • Convert PRESSURE as a function of TIME
  • Sound Spectrum

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What is the advantage of using a Fourier Analysis?

Gives you a compact respresentation of signals that contains oscillations

(graphs contain lots of complicated mini-waves --> thus it helps you to not have to track sound every second --> you can present sound as different frequencies with the amount of each frequency)


What is meant by narrowband?

  • Sound contains energy at a narrow range of frequencies

(Pure tone is an extreme example of a narrowband)

These sounds are periodic and may evoke an identifiable pitch


What is meant by broadband sounds?

Give examples

  • Contain energy at a lot of different frequencies
  • e.g. noises & clicks (natural broadband sounds)


What does a spectrogram do?

  • Divides sounds up into short-time segments --> then calculates a spectra for each time segment in turn
  • This helps you track changes of sounds over time (as a sound spectrum only gives you it in one split moment)

Ear effectively converts sound into a spectrogram


What are the 3 dimensions of a spectrogram and how are they represented?

  • Time (x-axis)
  • Frequency (y-axis)
  • Energy (colour)

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What does the outer ear consist of?

  • Pinna (odd bumps and folds)
  • Concha
  • Ear Canal


Which part of the ear is considered to be unique to each person (like a finger print)?

  • Pinna (bumps and folds on it)


Which part of the external ear changes the nature of sound in a subtle way?

  • Pinna

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What is the function of a pinna?

  • Collect all the sound that hits it
  • Directs the sound into the ear canal (thus acts to amplify sound)


How is the pinna involved in sound localisation?

  • Sound hits the ear --> bounces around in a complex way
  • Depending on where it came from --> sound bounces in a different way

(Causing subtle changes to nature of the sound)

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How is the outer ear involved in localisation?

  • Incoming sounds --> are filtered by outer ear --> in a way that depends upon location of the sound source in the vertical plane (elevation)
  • It is also important in horizontal plane (but only if you have hearing loss in one ear)


What happens to the frequency if a sound is presented to you at a higher inclinication level?

  • Higher Frequency


What happens to the frequency if a sound is presented to you at a lower inclinication level?

  • Lower Frequency


What would happen if you had no pinna?

  • Would not be able to localise sound above, below, infront or behind you


Name the 2 main functions of the outer ear.

  1. Sound Amplification (transforms acoustic energy at the tympanic membrane - pinna transfer function)
  2. Sound Localisation (pinna transfers function depending upon sound source position in vertical plane)

Collects & funnels sounds to eardrum but does so differently depending on sound source location


Name the 3 bones in the middle ear.

  • Malleus
  • Incus
  • Stapes

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Why is 99.9% of sound reflected from cochlea?

What is the conseuqence of this?

  • Due to impedence of fluid in the cochlea
  • 30dB sound loss due to impedence mismatch between air & fluid


By how much do the middle ear bones overcome the loss of sound?

  • +34dB


What are the 3 methods used to undergo impedence matching?

  1. Reduce Area
  2. Increase Force
  3. Buclking of Ear Drum

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How does the middle ear reduce area?

By how much does this increase sound pressure?

  • Area ratio of the ear drum : stapes footplate (20:1)
  • +26dB

(tympanic membrane is much bigger than the footplate of the stapes --> so focused onto a smaller area)


How does the middle ear increase force?

By how much does this increase sound pressure?

  • Lever action of the ossicles (1.3:1)
  • +2dB


What is the third method that causes the increase in sound pressure?

By how much does this increase sound pressure?

  • Buckling of the Ear drum
  • 2x increase in pressure
  • +6dB

When the ear drum vibrates it also buckles (complex) --> this is equivalent to a secondary lever effect --> causing an increase in pressure


How does the middle ear amplify different frequencies?

  • It does not amplify all frequencies to the same level


At what frequency does it amplify well?

  • 1 kilohertz (around level of human speech)
  • However higher & lower frequencies --> it is not as good

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Which muscle in which reflex is activated to protect hearing?

  • Stapedius Muscle
  • Contracts in the Middle Ear Reflex
  • Contract --> oscilles unable to move (amplification not allowed)
  • Relax --> oscilles able to move (amplification allowed)

The reflex controls the amount of amplification

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How does the middle ear enhance sound?

  • Enhances sound transmitted to inner ear
  • Done in a controlled & frequency-dependent way


What are the dimensions of the cochlea?

  • 1cm wide
  • 5mm from base to apex
  • Snail-shaped (coiled)


How does the cochlea connect to the middle ear?

  • Via the footplate of the stapes --> which rests against the oval window

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After the fluid in the cochlea moves --> what moves?

  • Round window


Name the 3 layers in the cochlea. Where are they in relation to each other?

  • Scala Vestibuli (top)
  • Scala Media (middle)
  • Scala Tympani (bottom)

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Where do hair cells sit?

Down what do they send signals?

What do they respond to?

  • Sit on the basilar membrane
  • Respond to movements of fluid (created by sound vibration)
  • Send signals down the auditory nerve (cranial nerve VIII)


What is found in the 3 layers of the cochlea?

  • Scala Vestibuli & Scala Tympani --> contains PERILYMPH
  • Scala Media --> contains ENDOLYMPH

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What is the composition of endolymph?

  • High K+


What is the composition of perilymph?

  • Low K+


What maintains the composition of the endolymph?

  • Very High K+ Concentration
  • Unusual in the body
  • Due to stria vascularis
  • Sits in the lateral wall
  • Actively increases K+ concentration of endolymph


What would happen if K+ dropped in endolymph?


  • Complete Deafness
  • Needs to be maintained at a high level by stria vascularis (lateral wall of scala media)


What is the membranous labrinyth made up of?

What does it comprise of?

  • Semi-Circular Canals + Otolithic Organs
  • Contains endolymph


Why do syndromes/diseases affecting balance and vestibular apparatus affect hearing?

  • Fluid environment of the vestibular apparatus is continuous with that of the cochlea
  • Problems usually come together (e.g. mania syndrome)


What do vibrations do to the basilar membrane?

  • Causes complex deflections
  • Complicated waveform

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What determines where the peak/centre of the fixed point on the basilar membrane will be?

  • Depends on the frequency (stapes will vibrate at a certain frequency causing fluid to vibrate at that frequency causing the peak at a certain point)


What is the wave from the ovale window (stapes) called?

  • Travelling Waveform


What deteremines where the wave peaks are on the basilar membrane?

  • Sound Frequency

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Where is the wave peak during low frequency sounds?

  • Close to Apex (i.e. centre)


Where is the wave peak during high frequency sounds?

  • Close to Base (i.e. near ovale window)


What happens if there is a complex sound? (in terms of basilar membrane)

  • More than 1 frequency
  • Therefore different energies
  • Movements of the basilar membrane will be at multiple different points


What is the equation that links stiffness (k), mass (m) & frequency (w)?

w2 = k/m


Where is the basilar membrane most stiff?

  • Base (near ovale window)


What happens in terms of stiffness from base to apex?

  • Stiffness decreases as you go from the base to the apex


How does mass change as you go from the base to the apex?

  • Base --> Little Mass
  • Apex --> Lots of Mass
  • The mass increases as you go towards the apex

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Where does low frequency sound produce movement on the basilar membrane?

  • Apex of the Basilar Membrane


Where does high frequency sound produce movement on the basilar membrane?

  • Base of the Basilar Membrane


What two properties of an object determine the frequency they are likely to vibrate at?

  1. Stiffness (rigidity)
  2. Mass


What is the mass & rigidity like at the apex?

  • Apex
  • Wide & Floppy
  • Large Mass & Low Rigidity


What is the mass & rigidity like at the base?

  • Base
  • Narrow & Rigid
  • Small Mass & High Rigidity


What frequency does the base 'like'?

High Frequency


What determines the frequency of the Basilar Membrane vibration?

  1. Mass
  2. Stiffness


What is the stiffness & mass like at the base?

  • Stiff
  • Less Mass



What is the stiffness & mass like at the apex?

  • Less Stiff
  • More Mass


What is the basilar membrane like?

  • Acoustic Prism
  • Takes in light --> splits it up into lots of different frequencies

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What is the component of the basilar membrane that responds to sound called?

  • Organ of Corti


What does the Organ of Corti do?

  • Converts movement of the basilar membrane into electrical activity

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What does the up-down movement of the basilar membrane cause?

  • Tectorial Membrane --> to slide sideways over the membrane
  • Causes sideways displacement of the hair cell bundles in the cochlear hair cells

(sliding of tectorial membrane to one side relative to basilar membrane pushes hairs in a particular direction (towards depolarisation or hyperpolarisation)

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How are the adjacent stereocilia joined up?

  • Tip-Links

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How does transduction by the hair cells take place?

  • Stereocilia of the hair cell bundles connected via tip links
  • Movement of the bundle changes the tension on the tip links --> causing opening/closing stretch sensitive K+ channels
  • K+ Channel Opening --> causes influx of K+ from endolymph --> causing depolarisation of the hair cell membrane
  • This causes opening of voltage-gated Ca2+ channels --> increasing probability of transmitter release

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How does the hair work?

  • Hairs vary in length
  • Connected to a stretch-sensitive K+ channel
  • If they move in one way --> distance between hair either increases/decreases --> causing an increase/decrease in tension in the tip-links --> thus opening/closing K+ channels


What happens if the distance between hair cells decrease, therefore tension in tip-link decreases?

  • Hyperpolarisation


What happens if the distance between hair cells increases, therefore tension in tip-link increases?

  • Increase in tension
  • Open K+ channels
  • Depolarisation


What happens when K+ channels open?

  • K+ flood in from endolymph
  • This causes voltage-gated Ca2+ channel to open --> causing an increase in intracellular Ca2+
  • This causes depolarisation
  • Causing NT release (glutamate)


What are the 2 types of hair cells?

What are they both connected to?

  1. Inner Hair Cells (IHCs)
  2. Outer Hair Cells (OHCs)

Both connected to Auditory Nerve Fibres

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What is the function of the Inner Hair Cells (IHCs)?

  • Passive
  • Respond to vibration of the basilar membrane
  • Perform a process of mechano-electrical transduction (convert mechanical energy to electrical)
  • They release NT onto Auditory Nerve Fibres (electro-chemical transduction) --> transmitting information along auditory nerve

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What happens at low frequencies in terms of membrane potential?

  • Membrane potential of the hair cell --> follows every cycle of the stimulus (AC response)
  • Fluctuate rapidly (but can keep up)


What happens at high frequencies in terms of membrane potential?

  • Membrane potential is unable to follow individual cycles 
  • Therefore remains depolarised throughout duration of the stimulus (DC response)

Cannot keep up anymore with the rapid fluctuations (around 4000 hertz) --> thus cell will depolarise and not change (frequency too high)


What happens at intermediate frequencies?

  • Membrane potential exhibits a mixed AC + DC response

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What is the function of Outer Hair Cells (OHCs)?

  • Active
  • Electric-mechanical transduction
  • They contract --> feed energy back into the basilar membrane

Electric signals feedback into it to cause mechanical mvoement so that it moves the basilar membrane --> causing positive feedback (IHCs and OHCs propogate each other)

  • Takes small signals/vibrations and amplifies them to make movement of BM even bigger


What are the important implication of OHC function?

  • Process is responsible for sensitivity of hearing
  • Vulnerable to damage by NOISE or OTOTOXIC DRUGS


What do OHCs contain which allows them to change their shape/length when they are depolarised?

  • Prestin


What are the OHCs connected to and why is it important?

  • Connected to Basilar Membrane
  • Therefore causes movement of the BM
  • This amplifies vibrations of the basilar membrane


Generally, what are the active cochlea's 2 main functions?

  1. Increase Sensitivity
  2. Increase Tuning


How do OHCs increase sensitivity & tuning?

  • Increase gain in the cochlea by boosting vibrations --> this also results in narrow tuning

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What happens if OHCs are not working (i.e. just passive sound)?

  • Most of the Adjacent Basilar Membrane will move (displace) too at a similar level
  • Therefore will not be tightly tuned
  • Not much difference between different points
  • Reduced sensitivity
  • Reduced tuning


What happens if OHCs are not working? (generally)

  • Remove the Tuning
  • Less Sensitive
  • Need louder sounds for auditory nerve fibres to respond (cause there is no 'help')



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Why does a healthy cochlea 'generate sound'?

  • Due to active mechanical feedback (electro-mechanical transduction) of the OHCs

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How is the theory about OHCs incorporated in baby hearing tests?

  • OHC amplification system --> technically produces sounds that were not put in at all (produces own sounds)
  • Therefore if you feed 2 frequencies --> you should get a third if the OHC is working fine
  • If it is not there --> problem with hearing --> need further checks 

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What are the effects of antibiotics on hearing?

  • Antibiotics can affect Organ of Corti
  • Cause wiping out of the hairs on the hair cells
  • Need to do hearing test after to ensure they are okay


What can cause damage to Outer Hair Cells?

  • Drugs
  • Noise


Specifically what antibiotic can cause hair damage (on OHCs)?

Why is this AB usually given?

  • Kanamycin
  • Often given to children for juandice & other conditions --> but too much causes hair cell destruction

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What are the outer & middle ear important for?

  • Transmitting sound to the inner ear
  • In a form compatible with the fluid environment of the inner ear


What is special about the basilar membrane?

  • Tuned to sound frequency
  • Splits complex sounds into constituent components (e.g. acoustic prism)


What are inner hair cells?

  • Mechano-electrical transducers
  • Convert mechanical deflections into electrical potentials


What are OHCs?

  • Electro-mechanical transducers
  • Enhance the sensitivity and tuning of sound