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Structures of the Ear

Outer, middle, & inner ear. Structures of the Ear. Eustachian tube. “Popping” ears. Fluid behind tympanum. “Tubes in the Ears”. Cranial Nerve VIII. Ossicles: incus,malleus, stapes. For transmission & amplification. Conduction deafness: ossification of ossicle articulations.

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Structures of the Ear

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  1. Outer, middle, & inner ear Structures of the Ear Eustachian tube “Popping” ears

  2. Fluid behind tympanum “Tubes in the Ears”

  3. Cranial Nerve VIII Ossicles: incus,malleus, stapes. For transmission & amplification Conduction deafness: ossification of ossicle articulations Attenuation reflex protects cochlea from large vibrations

  4. Scala vestibuli Scala tympani

  5. Endolymph Organ of Corti

  6. Stereocilia with mechanically-gated K+ channels • Open K+ channels • Depolarize • Open Voltage-gated Ca++ channels • Release of NT from synaptic vesicles

  7. Mechanosensitive K+ channels in Stereocilia

  8. Activity of Hair Cells • Depolarization leads to more NT release • Hyperpolarization leads to less NT release

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

  10. Tonotopy in Cochlea Base Apex

  11. 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 stimulated…which 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

  12. Pure sine waves Fourier Analysis of Complex Waves Complex wave

  13. 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

  14. Audiogram Decibel = unit for expressing relative loudness on a log scale “Nerve deafness” cause by damage to hair cells.

  15. 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

  16. 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

  17. Fire!

  18. Tonotopy in Auditory Cortex

  19. Organs of Equilibrium Structures of the Ear Utricle & saccule inside

  20. Semicircular Canal • Angular acceleration • 3 planes

  21. 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+)

  22. Additional Topics • Information on cochlear implants • Hearing Aids • Understanding Speaker Frequency Response by Polk Audio’s Marketing Manager • Noise cancelling technology

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