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Auditory System
Lesson 15
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The Stimulus
What kind of energy is sound? mechanical movement of air molecules
Waves intensity = amplitude pitch = frequency (wavelength)
Audible range in humans 20 Hz – 20 kHz ~
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Anatomy of the Ear Tympanic membrane Middle ear - ossicles
Malleus (hammer) Anvil (incus) Stapes (stirrup)
Inner ear - Oval window Cochlea - fluid filled Round window ~
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Cochlea
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Structure: Cochlea
2 continuous chambers Scala Vestibuli Scala Tympani filled with perilymph
Scala Media between others filled with endolymph high K+ concentration ~
Scala Media
Scala Tympani
Scala Vestibuli
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Uncoiled Cochlea
Scala Media
Scala Vestibuli
Scala Tympani
Round Window
Oval Window
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Organ of Corti
Auditory receptor organ in scala media
Tectorial membrane roof of scala media
Basilar membrane floor of scala media
Hair cells ~
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Hair Cells - Auditory Receptors Mechanoreceptors
Anchored to basilar membrane Cilia
tiny appendages (“eyelashes”) top of hair cells ~
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Basilar Membrane
Tectorial Membrane
Organ of Corti
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Receptor Potential Depolarization K+ influx NT release from receptor
Cilia tip-links K+ channels cilia bend open/close channels ~
Hair Cells - Transduction
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Hair Cell
Cilia
K+
Tip Link
Hair Cells - Transduction
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Force Force
Inhibition Resting rate Excitation
APs in Cochlear Nerve Axon
Hair Cells - Transduction
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The Auditory Pathway
Complex pathway focus on most direct hierarchical processing parallel processing
Bilateral output contralateral stronger ipsilateral weaker
Cochlear Nerve Cochlear Nucleus ~
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The Auditory Pathway
Left Right
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Hair Cell
More NT
Auditory Nerve - VIII
Cochlear NucleiMedulla
Inferior Colliculus
Thalamus: MGN
Superior OlivePons
Auditory Pathway
A1 A1
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Pitch Perception
Frequency Theory Rate neurons
vibration of basilar membrane frequency vibration frequency APs text max. frequency = 1000 Hz (1 kHz)
Low frequency sounds only < 100 - 200 Hz ~
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Pitch Perception
Place Theory Place neurons
Part of basilar membrane stimulated high frequency near oval window low frequency near end ~
Base Apex
High Medium Low
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Loudness Perception
Intensity amplitude of wave
place neurons rate of firing
rate neurons number of neurons firing ~
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Sound Localization
Superior Olives Low frequency
Phase differences High frequency
Intensity differences ~
< 3000 Hz
> 3000 Hz