Audition and Equilibrium

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Otitis media middle ear infection
tube to relieve pressure and allow drainage.
Popping ears and equalization of pressure
across tympanic membrane.
Conduction deafness ossification of ossicle
articulations
Attenuation reflex protects cochlea from large
vibrations loud sounds
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Scala vestibuli
Scala media
Scala tympani
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(No Transcript)
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Mechanosensitive K channels in Stereocilia
Composition of endolymph
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Stereocilia with mechanically-gated K channels

• Open K channels
• Depolarize
• Open Voltage-gated Ca channels
• Release of NT from synaptic vesicles

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Activity of Hair Cells

• Depolarization leads to more NT release
• Hyperpolarization leads to less NT release

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• All hair cells nearly identical
• Basilar membrane thickens toward the apex

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Tonotopy in Cochlea
Base
Apex
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Coding for Pitch frequency tone Intensity

• Base .... high pitch (treble)
• Apex .... low pitch (bass)
• Pitch coded by location of vibrations of Organ
  of Corti Which hair cells are stimulatedwhich
  set of sensory axons have action potentials
• Intensity coded by degree of displacement of
  stereocilia of hair cells and ultimately the
  frequency of action potentials in those axons
  that are active

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Auditory Range

• Humans 20- 20,000 Hz optimal 1000-4000 Hz

Demo of auditory range and presbycusia
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Audiogram
Decibel unit for expressing relative loudness
on a log scale
Nerve deafness cause by damage to hair cells.
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Fourier Analysis of Complex Waves
Complex wave
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Pathway to Temporal Lobe
In Brainstem
Organ of Corti Hair Cells
Cochlear Ganglion Spiral Ganglion
Superior Olive
Cochlear Nuclei

• VIII cranial nerve
• Medial geniculate nucleus of thalamus

MG of Thalamus
Auditory Cortex
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Sound Localization

• Low frequency by delay in arrival of soundwave
  between ears
• High frequency by attenuation of intensity
• Processed in Superior Olive
• Practical Applications?

L or R speaker w/ hi and lo frequency tone
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Tonotopy in Auditory Cortex
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Organs of Equilibrium
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Semicircular Canal

• Angular acceleration
• Three semicircular canals per ear in 3 planes

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Utricle and Saccule For static
equilibrium (orentation to gravity)
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Vestibular Apparatus

• Hair cells
• NT release dependent upon degree of bending of
  kinocilium and microvilli
• For ampula of semi-circular canals cupula
• For utricle and saccule otolith membrane
• Stereocilia in Endolymph (Hi K, low Na)

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Additional Topics

• Information on cochlear implants
• Hearing Aids
• Understanding Speaker Frequency Response by Polk
  Audios Marketing Manager
• Noise cancelling technology