Structures of the Ear

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Structures of the Ear
Outer, middle, inner ear
Eustachian tube
Popping ears
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Tubes in the Ears
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Cranial Nerve VIII
Ossicles incus,malleus, stapes. For
transmission amplification
Conduction deafness ossification of ossicle
articulations
Attenuation reflex protects cochlea from large
vibrations
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Scala vestibuli
Scala media
Scala tympani
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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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Mechanosensitive K channels in Stereocilia
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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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Pitch (frequency) 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

Tonotopy
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Fourier Analysis of Complex Waves
Complex wave
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Auditory Ranges

• Humans 20- 20,000 Hz optimal 1000-4000 Hz
• Whales 20 - 100,000 Hz
• Bats 1500 - 100,000 Hz
• Frogs 600 - 3000 Hz
• Fish 20 - 3000 Hz
• Crickets 500 - 5000 Hz

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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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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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Fire!
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Tonotopy in Auditory Cortex
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Structures of the Ear
Organs of Equilibrium
Utricle saccule inside
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Semicircular Canal

• Angular acceleration
• 3 planes

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Vestibular Apparatus

• Hair cells
• NT release dependent upon degree of bending of
  kinocilium and microvilli
• For utricle and saccule otolith membrane
• For ampula of semi-circular canals cupula
• 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