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Flashcards in Hearing Deck (38):

What is being detected when we perceive sound?

Wavelength: pitch

Amplitude: loudness

Waveform: tone/timbre



Briefly describe how different elements of the anatomy of the auditory system are involved in sound perception?

Tympanic membrane moves ossicles

Ossicles move oval window

Cochlea tranforms physical motion of oval window into a neural response 


What is the function of the ossicles?

Matches the impedance of air to that of fluid in inner ear


Describe the pressure that the ossicles must overcome?

Pressure 200 fold greater at tympanic membrane compared to inner ear 

Size: tympanic memrane > oval window (20:1) 

Lever action of ossicles: 1.3:1


Describe the three chambers of the cochlea?

Scala vestibuli

Scala media

Scala tympani

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Where are the basilar membrane and tentorial membrane located? 

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Describe the basilar membrane?

Wider at apex than base

Stiffer at base

Base responds to high frequencies, apex responds to low frequencies

(Like a flipper)

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What is the function of the basilar membrane?

Vibrates in response to sound waves 

(certain areas vibrate depending on frequency)


Describe the functional arrangement of the basilar membrane?

Tonotopic encoding of sound

Low frequencies at apex, high frequencies at base 


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Where is the Organ of Corti situated?

In middle of cochlea 

Sandwiched between basilar membrane and reticular lamina

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What does the Organ of Corti consist of?

Auditory receptors: inner and outer hair cells

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Where do the inner and outer hair cells sit in relation to other inner ear structures?

Sit on top of basilar membrane

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What is the function of the Organ of Corti?

Transduces soundwaves into neural signals


Describe the hair cells of the inner ear?

Inner and outer

Each hair cell has about 100 stereocilia

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Describe the attachments of the sterocilia?

Hair cell to tectorial membrane 

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Describe the role of the stereocilia?

bending of stereocilia causes neuronal signalling


Describe how soundwaves initiate auditory transduction?

Movement causes basilar membrane to osciallte

Causes stereocilia to move

Shear force of stereocilia against tectorial membrane causes ion conductances 

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What is the tallest stereocilium in a hair bundle called?


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Describe how opening and closing of K channels within a hair cell is achieved?

K channels partially open

Deflection of hair bundle towards kinocilium causes more opening of channels > depolarisation 

Hyperpolarisation > channel closure 

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What is the effect of depolarisation in the hair bundles?

Depolarisation > opening of voltage-dependent Ca channels > glutamate release 

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How does membrane potential differ according to different movements of hair bundles?

Asymmetric changes

Larger depolarisations than hyperpolarisations 


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Describe the difference in K within the chambers of the cochlea?

Scala media: high K

Scala tympani: low K

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Describe the difference in function between the inner and outer hair cells?

Inner: for hearing

Outer: amplify movements of basilar membrane (depolarisation > contraction, hyperpolarisation > elongation)


Describe the effect of loss of OHCs?

Basilar membrane movement is 100 fold less > loss of hearing 


What can cause loss of OHCs?

Antibiotics and other medications 


Describe the auditory pathway?

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How is sound from both ears integrated?

Extensive crossing across midline at brainstem level 

Information from cochlear nuclei on either side communicate at superior olivary complex

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Describe the superior olivary complex?

Conists of lateral and medial superior olives and trapezoid body

These structures are crucial for working out where sound is coming from


What are the functions of the medial and lateral superior olives?

MSO: localisation of sound by measuring time delay

LSO: localisation of sound by sensing intensity differences 


Describe the duplex theory of sound localisation?

Provides an explanation for the ability of humans to localise sounds by time differences between the sounds reaching each ear and differences in sound level entering the ears.

1) Time that sound arrives at each ear

2) Interaural intensity differences 


Which sound frequencies are involved in each part of the duplex theory?

1) Time that sound arrives at each ear > low frequencies

2) Interaural intensity difference > high frequencies


Describe how sound localisation is achieved using time differences?

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Describe how interaural intensity difference is used to localise sound?

Info carried down to cochlear nuclei and down to LSO

Excitation to higher centres

At same time, processes to contralteral trapezoid body > communicates with inhibitory neuron in TB > TB sends inhibitory singal to ipsilateral LSO 

At same time, same process is happening in opposite ear

So, brain gets relative amount of excitation and inhibition from each ear to determine where sound is coming from 

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Describe the orgnaisation of the auditory cortex?

Columnar organisation: cells in same column are tuned to the same frequency

Also, alternating regions of input from both ears (excitatory from one ear, inhibitory from other)

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Describe the representation of sounds in the auditory cortex?

Asymmetric representation

Speech sounds: left

Environmental sounds: both hemispheres

Music: right 


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Describe the time frame within which sudden sensorineural hearing loss occurs?

Sudden loss of hearing of at least 30db within 3 hours to 3 days 


What are the causes of sudden hearing loss?

10-15% have known cause:

Peripheral causes (meningitis, metastasis...)

Central causes (MS)

Cochlear causes (infection, autoimmune disease, trauma, vascular...)


Which structures in the superior olive are importnat in which components of the duplex theory?

MSO - time differences

LSO & TB - intensity differences