9/2 Auditory System - Crockett Flashcards Preview

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Flashcards in 9/2 Auditory System - Crockett Deck (18)

conductive apparatus 




fx: transform sound waves into mechanical vibrations

  • have to compensate for loss of energy that occurs when sound goes from gaseous medium to fluid medium


  • external auditory meatus (ear canal)
  • tympanic membrane
  • ossicles → amplify force at oval window, help compensate for diff in impedance between middle ear (air) and inner ear (fluid)
    • malleus
    • incus
    • stapes


ossicle conditions that can cause hearing loss

1. otosclerosis: footplate of stapes gets locked in place due to bone growth around annular ligament

test with Rinne's test : if bone doncutance is more sensitive than air conducted stumuli → disease process with ossicles!

  • 512 tuning fork
  • use in conjunction with Weber's test
  • results...
    • conduction deafness: low freq loss
    • sensory deafness: high freq loss


how is sound conducted?

  • tympanic membrane shakes → ossicles conduct sound → fluid moves (from scala vestibuli to/through scala tympani)
  • cochlea transforms fluid waves into neural activity


Organ of Corti has 1 inner and 3 outer rows of hair cells (sensory receptors)

  • kinocilium is lost during devpt, but basilar plate gives cell same kind of polarity
  • as basilar membrane vibrates, stereocilia are bent
    • outer hair cells are embedded in tectorial membrane, bend due to shearing action
    • inner hair cells are NOT embedded, bend due to fluid movement


auditory hair cells

have clusters of stereocilia at apical ends ordered by size

kinocilium is lost during devpt; have a basal body instead

  • bending of sterocilia towards basal body → depolarization
  • bending away from basal body → hyperpolarization


mechanically sensitive ion channels

  • hair cells act like 'electrical valves'
  • tips of stereocilia are linked by protein filaments
  • when stereocilia bend, they open mechanosensitive ion channels in stereocilia → let in depolarizing K current
    • upward deflection = depol
    • downward deflection = hyperpol


functions of inner and outer hair cells

inner hair cells : detection of sound

outer hair cells : amplification and dampening of sound via motor function

  • contract and elongate in synchrony with sound-sensitive receptor potentials due to action of motor proteins (prestins)


ototoxic agents

can affect both auditory and vestibular fx

common ototoxins:

  • aminoglycoside antibiotics (streptomycin, gentamicin)
  • salicylates

trophic factors may help protect hair cells


hair cell efferents

hair cells are innervated by efferents from superior olivary nuclear complex

  • outer hair cells: mostly contralateral innervation
    • medial olivocochlear bundle
    • direct efferent connection, small afferent connection
  • inner hair cells (type I): mostly ipsilateral innervation
    • lateral olivocochlear bundle
    • axoaxonic contacts with bipolar cells


perception of pitch


2 concepts

temporal coding

2 concepts explain how you can use multiple neurons to hear high freq sound

  • phase locking: detection of waves in regular pattern, in a certain interval
  • volley principle: fire, skip a few waves, fire again
    • works to approx 5000Hz


place coding

different regions of the cochlea are selectively responsive to different freqs of sound

  • basilar membrane is stiff near oval window and flexible near apex
  • individual hair cells may be tuned electrically and mechanically at diff points along basilar membrane

hair cells have stereocilia that vary in length

  • stereocilia at base are short/stiff, at apex are long/flexible
  • in lower vertebrates, hair cell membranes show spontaneous oscillations which systematically vary in frequency over teh length of the basilar membrane, matching its mechanical resonance


innervation of hair cells

90% of bipolar cells located in the spiral ganglion innervate inner hair cells

  • inner hair cells are innervated by 10 afferents each

10% of spiral ganglion cells innervate outer hair cells

  • a single primary sensory afferent can innervate multiple outer hair cells
  • outer hair cells also directly innervated by efferent fibers


cell types in cochlear nucleus

ventral cochlear nucleus

  • stellate cells (multipolar) : fire in regular trains
  • chopper : have specific tuning cures, resp for frequency coding
  • bushy cells : receive input from one or a few massive axonal terminals (end bulbs) and fire a single axon potential at onset of sound. role in sound localization, sharpening tuning

dorsal cochlear nucleus

  • fusiform cells : role in locating sounds at diff elevations, respond to a broad range of freqs 


ascending auditory pathway

characterized by bilateral representation at every level above cochlea

implication: cant get deafness in ONE ear except in cases of damage to CN VIII or cochlear nuclear complex

  • CAN see problems with localization of sound in other injury!


localization of sound in space

time differences : medial superior olivary nucleus

  • low freq is the most useful (large wavelengths)
  • time diff in signals received from right and left ears (and lengths of axons of neurons transmitting them) allows for localization of sound

intensity differences : lateral superior olivary nucleus (and medial nucleus of trapezoid)

  • high freq is most useful


auditory cortex

  • organized in columns
  • also has topographical organization (sections that correspond to apex and base of cochlea)


cortical pathologies

cortical deafness (bilateral lesions)

auditory verbal agnosia: don't recog speech sounds

auditory non-verbal agnosia: don't recog environmental sounds

unilateral lesions (probs with localization of sound)


cortical lateralization of fx

left auditory cortex is usually bigger than right bc that's where the speech center is

  • speech sounds tend to be perceived on left
  • environmental sounds and music perceived more on right



  • tonal (subjective) 
  • non-tonal (objective) - YOU can hear it too, along with pt

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