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Auditory System

Auditory System. Lesson 15. 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 ~. Anatomy of the Ear. Tympanic membrane Middle ear - ossicles

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Auditory System

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  1. Auditory System Lesson 15

  2. 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 ~

  3. Anatomy of the Ear • Tympanic membrane • Middle ear - ossicles • Malleus (hammer) • Anvil (incus) • Stapes (stirrup) • Inner ear - • Oval window • Cochlea - fluid filled • Round window ~

  4. Cochlea

  5. Structure: Cochlea • 2 continuous chambers • Scala Vestibuli • Scala Tympani • filled with perilymph • Scala Media • between others • filled with endolymph • high K+ concentration ~ Scala Vestibuli Scala Media Scala Tympani

  6. Uncoiled Cochlea Oval Window Scala Vestibuli Scala Media Scala Tympani Round Window

  7. Organ of Corti • Auditory receptor organ • in scala media • Tectorial membrane • roof of scala media • Basilar membrane • floor of scala media • Hair cells ~

  8. Hair Cells - Auditory Receptors • Mechanoreceptors • Anchored to basilar membrane • Cilia • tiny appendages (“eyelashes”) • top of hair cells ~

  9. Organ of Corti Tectorial Membrane Basilar Membrane

  10. Hair Cells - Transduction • Receptor Potential • Depolarization • K+ influx •  NT release from receptor • Cilia • tip-links • K+ channels • cilia bend  open/close channels ~

  11. Tip Link K+ Cilia Hair Cell Hair Cells - Transduction

  12. Force Force Resting rate Excitation Inhibition Hair Cells - Transduction APs in Cochlear Nerve Axon

  13. The Auditory Pathway • Complex pathway • focus on most direct • hierarchical processing • parallel processing • Bilateral output • contralateral stronger • ipsilateral weaker • Cochlear Nerve  Cochlear Nucleus ~

  14. The Auditory Pathway Left Right

  15. A1 A1 Auditory Pathway Thalamus: MGN Inferior Colliculus Hair Cell More NT Superior Olive Pons Cochlear Nuclei Medulla Auditory Nerve - VIII

  16. 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 ~

  17. High Medium Low Base Apex Pitch Perception • Place Theory • Place neurons • Part of basilar membrane stimulated • high frequency near oval window • low frequency near end ~

  18. Loudness Perception • Intensity • amplitude of wave • place neurons • rate of firing • rate neurons • number of neurons firing ~

  19. < 3000 Hz > 3000 Hz Sound Localization • Superior Olives • Low frequency • Phase differences • High frequency • Intensity differences ~

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