1. Physics 1251 The Science and Technology of Musical Sound Unit 2 Session 12 MWF The Human Ear Unit 2 Session 12 MWF The Human Ear

2. Physics 1251Unit 2 Session 12 The Human Ear Foolscap Quiz: A student guitarist plays a chord on his electric guitar. When he mutes the strings he notices that his acoustic guitar on the rack beside the amplifier is also ringing. What is the name of the relevant effect and what is happening? Resonance. The strings of the acoustic guitar were tuned to some frequency that he played. The strings picked up the energy from the vibrations of the air that were “in resonance.”

3. Physics 1251Unit 2 Session 12 The Human Ear Ludwig van Beethoven (1770-1827) 9 th Symphony (Choral) Composed when he was profoundly deaf.

4. Physics 1251Unit 2 Session 12 The Human Ear 1′ Lecture: The human ear is a highly sensitive sound receptor in which pressure fluctuations in the outer ear are transformed pressure fluctuations in the outer ear are transformed into vibrations of small bones (the ossicles) in the middle ear into vibrations of small bones (the ossicles) in the middle ear that are ultimately communicated to the cochlea located in the inner ear, that are ultimately communicated to the cochlea located in the inner ear, where the vibrations are further transformed by stereocilia (hair cells) where the vibrations are further transformed by stereocilia (hair cells) into neural impulses distributed by frequency. into neural impulses distributed by frequency.

5. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of Ear Outer Ear Middle Ear Inner Ear

6. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of the Ear 80/20 Outer Ear: 80/20 Outer Ear: 1.Pinna – (the feather) matches ear canal to outside world. 2.Meatus – ( the passageway) conducts sound into head. 3. Tympanium – (the drum) transforms pressure fluctuations into displacement.

7. Physics 1251Unit 2 Session 12 The Human Ear Outer Ear Pinna ——→ Pinna ——→ Meatus ———→ Meatus ———→ ←— Tympanium

8. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of Ear Middle Ear

9. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of the Ear 80/20 Middle Ear: The Ossicles 80/20 Middle Ear: The Ossicles (little bones) 1.Malleus ― (the hammer) moved by Tympanium. 2.Incus ― (the anvil) supported by ligaments that protect against loud percussion. 3. Stapes ― (the stirrup) force multiplied by 1.3 because of lever action.

10. Physics 1251Unit 2 Session 12 The Human Ear Tympanic Membrane (Ear Drum) micrograph micrograph ( view from inside) ( view from inside) ←————— Tympamium ←——— Malleus and ligaments

11. Physics 1251Unit 2 Session 12 The Human Ear The Ossicles Malleus ——→ ←—— Incus ←—— Stapes

12. Physics 1251Unit 2 Session 12 The Human Ear Ossicles(Micrographs) Malleus Incus Stapes MalleusIncus Stapes Tympanium

13. Anatomy of Ear Inner Ear

14. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of the Ear 80/20 Inner Ear: 80/20 Inner Ear: Cochlea – (the Snail) converts displacement into neural impulses. Auditory Nerve – neural impulses to brain Semicircular canals – detect motion and orientation

15. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of Inner Ear ←—— Semicircular Canals ←—— Cochlea Oval Window Round Window

16. Physics 1251Unit 2 Session 12 The Human Ear C ochlea (micrograph) “The Sn ail” o~ oval window o~ oval window r~ round window r~ round window 2 mm

17. Physics 1251Unit 2 Session 12 The Human Ear Structure of Cochlea 1. Spiral cone 2. Divided by Basilar Membrane 3. In on top half 4. Out on bottom 5. “Sloshing “

18. Physics 1251Unit 2 Session 12 The Human Ear Anatomy of Cochlea MicrographSection Basilar ——————→ Membrane © Kansas State School of Medicine

19. Physics 1251Unit 2 Session 12 The Human Ear Microstructure of Cochlea Basilar ——————→ Membrane ↑ Organ of Corti Auditory Nerve → → ↑

20. Physics 1251Unit 2 Session 12 The Human Ear Stereocilia (Hair Cells)

21. Physics 1251Unit 2 Session 12 The Human Ear Outer Hair Cell in Cross Section

22. Physics 1251Unit 2 Session 12 The Human Ear Inner Hair Cells Afferent Efferent Efferent Synapse ⇘

23. Physics 1251Unit 2 Session 12 The Human Ear Organ of Corti and Basilar Membrane Outer Outer ←——— Hair Cells ←——— Hair Cells ←————— Inner Hair Cells Vibration

24. Physics 1251Unit 2 Session 12 The Human Ear Detail of Hair Cell Stereocilia

25. Vibration )))) Physics 1251Unit 2 Session 12 The Human Ear Action of Hair Cell Hair Cell Depolarizes Neurotransmitter released Hair Cell Nerve

26. Physics 1251Unit 2 Session 12 The Human Ear Function of Stereocilia Stimulation in HC Causes neuro- transmitter to stimulate neuron in Auditory Nerve

27. Physics 1251Unit 2 Session 12 The Human Ear Frequency Response of Hair Cells

28. Physics 1251Unit 2 Session 12 The Human Ear Frequency Discrimination in Cochlea 20 Hz to 20 kHz (typical in Humans) 20 Hz to 20 kHz (typical in Humans) Resonances in Basilar membrane and in HC cause spatial separation by frequency. Resonances in Basilar membrane and in HC cause spatial separation by frequency. Differential movement of membranes stimulate HC. Differential movement of membranes stimulate HC. Minimum stimulation required for response. Inhibition of neighbors causes non-linear response. Minimum stimulation required for response. Inhibition of neighbors causes non-linear response.

29. Physics 1251Unit 2 Session 12 The Human Ear Neuronal Decoding of Sound (Schematic) Frequency response localized in Cochlea High Frequency Low Frequency

30. Physics 1251Unit 2 Session 12 The Human Ear Neuronal Response to Sound Frequency → Where? The location where in the Cochlea the stereocilia are stimulated. Frequency → Where? The location where in the Cochlea the stereocilia are stimulated. Intensity → How many? The number of HC that are stimulated by the sound determines the perceived loudness. Intensity → How many? The number of HC that are stimulated by the sound determines the perceived loudness.

31. Physics 1251Unit 2 Session 12 The Human Ear 80/20 Repeated acoustic trauma can cause permanent and profound hearing loss or deafness. If you have experienced temporary hearing loss due to loud sounds you have had a warning. you have had a warning. Stereocilia do regenerate daily.

32. Physics 1251Unit 2 Session 12 The Human Ear Hearing Loss due to Over Stimulation causes Excitotoxicity Too much Ca 2+ poisons the neuron.

33. Physics 1251Unit 2 Session 12 The Human Ear Extreme Acoustic Trauma Control, not exposed After Exposure Guinea Pig Stereocilia damage (120 dB sound)

34. Physics 1251Unit 2 Session 12 The Human Ear How do you protect yourself? Ear Plugs Wear Them!

35. Physics 1251Unit 2 Session 12 The Human Ear How does Anatomy affect perception? Frequency response Frequency response Loudness perception Loudness perception Phase insensitivity Phase insensitivity Deafness Deafness Disruption of “acoustic chain.”Disruption of “acoustic chain.” Nerve death.Nerve death. Remedies Remedies Restore chain or increase amplitudeRestore chain or increase amplitude

36. Physics 1251Unit 2 Session 12 The Human Ear Summary: Anatomy : Outer, Middle and Inner Ear. Function: Outer – converts pressure fluctuations to displacement. Middle – amplifies displacement, protects against loud noise. Inner – converts displacement to neural impulses, sorted by frequency.

37. Physics 1251Unit 2 Session 12 The Human Ear Physiology determines function. Physiology determines function. No phase detection mechanism. No phase detection mechanism. Large “non-linear” range of 12 orders of magnitude in intensity Large “non-linear” range of 12 orders of magnitude in intensity Three (3) orders of magnitude in frequency (20 Hz to 20 kHz). Three (3) orders of magnitude in frequency (20 Hz to 20 kHz). Trauma (due to loud sounds) is a cause of deafness. Trauma (due to loud sounds) is a cause of deafness.