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

Physics 1251Physics 1251The Science and The Science and

Technology of Musical Technology of Musical SoundSound

Physics 1251Physics 1251The Science and The Science and

Technology of Musical Technology of Musical SoundSound

Unit 2Unit 2

Session 12 MWFSession 12 MWF

The Human EarThe Human Ear

Unit 2Unit 2

Session 12 MWFSession 12 MWF

The Human EarThe Human Ear

Physics 1251Physics 1251 Unit 2 Session 12Unit 2 Session 12The Human EarThe Human Ear

Foolscap Quiz:Foolscap Quiz:A student guitarist plays a chord on his electric A student guitarist plays a chord on his electric

guitar. When he mutes the strings he notices guitar. When he mutes the strings he notices that his acoustic guitar on the rack beside the that his acoustic guitar on the rack beside the amplifier is also ringing. What is the name of amplifier is also ringing. What is the name of the relevant effect and what is happening?the relevant effect and what is happening?

Resonance. The strings of the acoustic Resonance. The strings of the acoustic guitar were tuned to some frequency that guitar were tuned to some frequency that he played. The strings picked up the he played. The strings picked up the energy from the vibrations of the air that energy from the vibrations of the air that were “in resonance.”were “in resonance.”


Ludwig van BeethovenLudwig van Beethoven(1770-1827)(1770-1827)

9 th Symphony (Choral)9 th Symphony (Choral)Composed when heComposed when hewas profoundly deaf.was profoundly deaf.


11′ Lecture:′ Lecture:The The human earhuman ear is a highly sensitive is a highly sensitive

sound receptor in which sound receptor in which • pressure fluctuations in the outer ear pressure fluctuations in the outer ear

are transformed are transformed • into vibrations of small bones (the into vibrations of small bones (the

ossicles) in the middle ear ossicles) in the middle ear • that are ultimately communicated to that are ultimately communicated to

the cochlea located in the inner ear, the cochlea located in the inner ear, • where the vibrations are further where the vibrations are further

transformed by stereocilia (hair cells) transformed by stereocilia (hair cells) • into neural impulses distributed by into neural impulses distributed by

frequency.frequency.


Anatomy of EarAnatomy of Ear

Outer Outer EarEar

Middle Middle EarEar

Inner Inner EarEar


Anatomy of the EarAnatomy of the Ear• 80/2080/20Outer Ear:Outer Ear:

1.1. Pinna – (the feather) matches Pinna – (the feather) matches ear canal to outside world.ear canal to outside world.

2.2. Meatus – ( the passageway) Meatus – ( the passageway) conducts conducts sound into head.sound into head.

3. Tympanium – (the drum) 3. Tympanium – (the drum) transforms transforms pressure fluctuations pressure fluctuations into displacement.into displacement.


Outer EarOuter Ear

• Pinna Pinna ——→——→

• Meatus Meatus ———→———→←— ←— TympaniumTympanium



Middle EarMiddle Ear


Anatomy of the EarAnatomy of the Ear• 80/2080/20Middle Ear: The OssiclesMiddle Ear: The Ossicles

(little bones)(little bones)1.1. Malleus Malleus ―― (the hammer) moved (the hammer) moved

by Tympanium.by Tympanium.

2.2. Incus Incus ―― (the anvil) supported (the anvil) supported by ligaments by ligaments that protect against that protect against loud percussion.loud percussion.3. Stapes 3. Stapes ―― (the stirrup) force (the stirrup) force multiplied by multiplied by 1.3 because of 1.3 because of lever action.lever action.


Tympanic Membrane (Ear Drum) Tympanic Membrane (Ear Drum)

micrographmicrograph

((view from view from inside)inside)

←————— ←————— TympamiumTympamium←——— ←——— Malleus and Malleus and

ligamentsligaments


The OssiclesThe Ossicles

Malleus Malleus ————→→

←—— ←—— IncusIncus

←—— ←—— StapesStapes


OssiclesOssicles(Micrographs)(Micrographs)

MalleusMalleusIncusIncus

StapeStapess

MalleusMalleus IncusIncus

StapesStapesTympaniTympaniumum



Inner EarInner Ear


Anatomy of the EarAnatomy of the Ear• 80/2080/20Inner Ear: Inner Ear:

Cochlea – (the Snail) converts Cochlea – (the Snail) converts displacement into neural displacement into neural impulsesimpulses..Auditory Nerve – neural Auditory Nerve – neural

impulses to impulses to brainbrain

Semicircular canals – detect Semicircular canals – detect motion motion and orientationand orientation


Anatomy of Inner EarAnatomy of Inner Ear

←—— ←—— Semicircular Semicircular CanalsCanals

←—— ←—— CochleaCochlea

Oval Oval WindowWindow

Round Round WindowWindow


CCochleaochlea(micrograph)(micrograph)““The SnThe Snail”ail”

• o~ oval windowo~ oval window• r~ round windowr~ round window

2 mm2 mm


Structure of CochleaStructure of Cochlea

1. Spiral cone1. Spiral cone2. Divided by2. Divided by Basilar Basilar Membrane Membrane

3. In on top 3. In on top halfhalf

4. Out on 4. Out on bottombottom

5. “Sloshing “5. “Sloshing “


Anatomy of CochleaAnatomy of Cochlea

MicrographMicrographSectionSection

Basilar Basilar ————————————→ → MembraneMembrane

© Kansas State School of Medicine© Kansas State School of Medicine


Microstructure Microstructure

of Cochleaof Cochlea

Basilar Basilar ——————→ ——————→ MembraneMembrane

↑↑

Organ of Organ of CortiCortiAuditory Nerve Auditory Nerve → →

→→

↑↑


Stereocilia (Hair Cells)Stereocilia (Hair Cells)


Outer Hair Cell in Cross SectionOuter Hair Cell in Cross Section


Inner Hair CellsInner Hair Cells

Afferent Afferent

EfferentEfferent

Synapse ⇘


Organ of Corti and Basilar MembraneOrgan of Corti and Basilar Membrane

OuterOuter ←——— ←——— Hair Hair CellsCells

←————— ←————— Inner Hair Inner Hair CellsCells

Vibration Vibration


Detail of Hair CellDetail of Hair Cell

StereociliaStereocilia

Vibration Vibration ))))))))


Action of Hair CellAction of Hair Cell

Hair CellHair CellDepolarizesDepolarizesNeurotransmittNeurotransmitt

er releaseder released

Hair CellHair CellNerveNerve


Function of StereociliaFunction of Stereocilia

Stimulation Stimulation

in HCin HC

Causes neuro-Causes neuro-

transmitter totransmitter to

stimulate neuronstimulate neuron

in Auditory Nervein Auditory Nerve


Frequency Response of Hair CellsFrequency Response of Hair Cells


Frequency Discrimination in CochleaFrequency 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 Resonances in Basilar membrane and in HC cause spatial separation by HC cause spatial separation by frequency.frequency.

• Differential movement of membranes Differential movement of membranes stimulate HC.stimulate HC.

• Minimum stimulation required for Minimum stimulation required for response. Inhibition of neighbors response. Inhibition of neighbors causes non-linear response.causes non-linear response.


Neuronal Decoding of Sound Neuronal Decoding of Sound (Schematic)(Schematic)

Frequency Frequency response response

localized in localized in CochleaCochlea

High Frequency

Low Frequency


Neuronal Response to SoundNeuronal Response to Sound

• FrequencyFrequency → → WhereWhere? The location ? The location where in the Cochlea the where in the Cochlea the

stereocilia stereocilia are stimulated.are stimulated.• IntensityIntensity → → How manyHow many? The ? The

number of number of HC that are stimulated HC that are stimulated by the sound by the sound determines the determines the perceived loudness.perceived loudness.


80/2080/20Repeated acoustic trauma can Repeated acoustic trauma can cause permanent and profound cause permanent and profound hearing loss or deafness.hearing loss or deafness.

If you have experienced temporaryIf you have experienced temporary

hearing loss due to loud soundshearing loss due to loud sounds

you have had a warning.you have had a warning.

Stereocilia do regenerate daily.Stereocilia do regenerate daily.


Hearing Loss due to Over Stimulation Hearing Loss due to Over Stimulation

causes Excitotoxicitycauses Excitotoxicity

Too much CaToo much Ca2+2+ poisons the neuron.poisons the neuron.


Extreme Acoustic TraumaExtreme Acoustic Trauma

Control, not Control, not exposedexposed

After After ExposureExposure

Guinea Pig Stereocilia damage (120 dB Guinea Pig Stereocilia damage (120 dB sound)sound)


How do you protect yourself?How do you protect yourself?

Ear PlugsEar PlugsWear Wear Them!Them!

Wear Them!Wear Them!Wear Them!Wear Them!


How does Anatomy affect perception?How does Anatomy affect perception?

• Frequency responseFrequency response• Loudness perceptionLoudness perception• Phase insensitivityPhase insensitivity• DeafnessDeafness

• Disruption of “acoustic chain.”Disruption of “acoustic chain.”• Nerve death.Nerve death.

• RemediesRemedies• Restore chain or increase amplitudeRestore chain or increase amplitude


Summary:Summary:

Anatomy : Outer, Middle and Inner Anatomy : Outer, Middle and Inner Ear.Ear.

Function: Function: Outer Outer – converts pressure fluctuations – converts pressure fluctuations

to displacement.to displacement.

Middle Middle – amplifies displacement, – amplifies displacement, protects against loud noise.protects against loud noise.

Inner Inner – converts displacement to neural – converts displacement to neural impulses, sorted by frequency. impulses, sorted by frequency.


• Physiology determines function.Physiology determines function.

• No phase detection mechanism.No phase detection mechanism.

• Large “non-linear” range of 12 orders of Large “non-linear” range of 12 orders of magnitude in intensitymagnitude in intensity

• Three (3) orders of magnitude in Three (3) orders of magnitude in frequency (20 Hz to 20 kHz).frequency (20 Hz to 20 kHz).

• Trauma (due to loud sounds) is a cause Trauma (due to loud sounds) is a cause of deafness.of deafness.

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

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