PHY-2464 Physical Basis of Music

PHY2464 -The Physical Basis of Music

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PHY-2464Physical Basis of Music

PHYPHY--24642464Physical Basis of MusicPhysical Basis of Music

Presentation 5Human Ear

Taken largely from Sam Matteson’s Unit 2 Sessions 12 & 13

Sam TrickeyJan. 26, 2005

Presentation 5Presentation 5Human EarHuman Ear

Taken largely from Sam Matteson’s Unit 2 Sessions 12 & 13

Sam TrickeyJan. 26, 2005

PHYPHY--2464 2464 Pres. 5 Human EarPres. 5 Human Ear

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

9th Symphony (Choral)9th Symphony (Choral)Composed when he wasComposed when he wasprofoundly deaf (from 1820profoundly deaf (from 1820onward).onward).


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The The earear is a highly sensitive sound receptor in which is a highly sensitive sound receptor in which •• outer ear pressure fluctuations are transformed into outer ear pressure fluctuations are transformed into •• vibrations of small bones (the vibrations of small bones (the ossiclesossicles) in the middle ) in the middle ear that ultimately are communicated toear that ultimately are communicated to•• the cochlea, in the inner ear, where the vibrations are the cochlea, in the inner ear, where the vibrations are further transformed by further transformed by stereociliastereocilia (hair cells) into (hair cells) into •• neural impulses distributed by frequency and scaled neural impulses distributed by frequency and scaled by intensity.by intensity.


Anatomy of EarAnatomy of Ear

Outer EarOuter Ear

Middle EarMiddle Ear

Inner EarInner Ear


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Outer Ear AnatomyOuter Ear AnatomyPinnaPinna –– (the feather) matches ear canal to outside (the feather) matches ear canal to outside

world. This is the ear we see. world. This is the ear we see.

MeatusMeatus –– ( the passageway) conducts sound into ( the passageway) conducts sound into head. This is the “ear canal”.head. This is the “ear canal”.

TympaniumTympanium –– (the drum) transforms (the drum) transforms pressure pressure fluctuations into displacement.fluctuations into displacement.


Outer EarOuter Ear

•• PinnaPinna ————→→

•• MeatusMeatus ——————→→ ←←—— TympaniumTympanium


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Middle EarMiddle Ear


Middle Ear Anatomy: The Middle Ear Anatomy: The OssiclesOssicles (little bones)(little bones)

MalleusMalleus (the hammer) (the hammer) -- moved by moved by TympaniumTympanium..

IncusIncus ― (the anvil) supported by ligaments that ― (the anvil) supported by ligaments that

protect against loud percussion.protect against loud percussion.

StapesStapes ― (the stirrup) force multiplied by 1.3 ― (the stirrup) force multiplied by 1.3

because of lever action.because of lever action.


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

(view from inside)(view from inside)

←←—————————— TympamiumTympamium

←←—————— MalleusMalleus and ligamentsand ligaments


The OssiclesThe Ossicles

MalleusMalleus ————→→

←←———— IncusIncus

←←———— StapesStapes


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OssiclesOssicles(Micrographs)(Micrographs)

MalleusMalleus IncusIncus

StapesStapes

MalleusMalleus IncusIncus

StapesStapesTympaniumTympanium



Inner EarInner Ear


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Inner Ear Anatomy: Inner Ear Anatomy:

CochleaCochlea –– (the Snail) converts displacement into (the Snail) converts displacement into neural impulses neural impulses

Auditory NerveAuditory Nerve –– neural impulses to brainneural impulses to brain

Semicircular canalsSemicircular canals –– detect motion & orientationdetect motion & orientation


Inner Ear Anatomy Inner Ear Anatomy

←←———— Semicircular CanalsSemicircular Canals

←←———— CochleaCochleaOval WindowOval Window

Round WindowRound Window


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Cochlea “The Snail”Cochlea “The Snail”(micrograph)(micrograph)

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

2 mm2 mm


Structure of CochleaStructure of Cochlea1. Spiral cone1. Spiral cone2. Divided by2. Divided by

BasilarBasilarMembraneMembrane

3. In on top half3. In on top half4. Out on bottom4. Out on bottom5. “Sloshing5. “Sloshing ““


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Microstructure Microstructure of Cochleaof Cochlea

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

Organ of Organ of CortiCortiAuditory NerveAuditory Nerve →→ →→ ↑↑


Organ of Organ of CortiCorti and Basilar Membraneand Basilar Membrane

OuterOuter←←—————— Hair CellsHair Cells

←←—————————— Inner Hair CellsInner Hair Cells

VibrationVibration


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StereociliaStereocilia (Hair Cells)(Hair Cells)


Outer Hair Cell in Cross SectionOuter Hair Cell in Cross Section


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Detail of Hair CellDetail of Hair Cell(note: “hair” in geometric(note: “hair” in geometricsense only.)sense only.)

StereociliaStereocilia

VibrationVibration ))))))))


Action of Hair CellAction of Hair Cell

Hair CellHair CellDepolarizesDepolarizesNeurotransmitter Neurotransmitter

releasedreleased

Hair CellHair CellNerveNerve


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Frequency Discrimination in CochleaFrequency Discrimination in Cochlea•• 20 Hz to 20 kHz (typical in human beings)20 Hz to 20 kHz (typical in human beings)

•• Resonances in Basilar membrane and in Hair Resonances in Basilar membrane and in Hair Cells (HC) cause spatial separation by frequency.Cells (HC) cause spatial separation by frequency.

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

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


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

Frequency response Frequency response localized in Cochlealocalized in Cochlea

High Frequency

Low Frequency


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Neuronal Response to SoundNeuronal Response to Sound•• Frequency Frequency →→ WhereWhere? The location in the ? The location in the

Cochlea at which the Cochlea at which the stereociliastereocilia are stimulated.are stimulated.•• Intensity Intensity →→ How manyHow many? The number of ? The number of HC that HC that

are stimulated by the sound determines the are stimulated by the sound determines the perceived intensity (loudness).perceived intensity (loudness).


VorsichtVorsicht! Caution! ! Caution! Repeated acoustic trauma can cause permanent and Repeated acoustic trauma can cause permanent and

profound hearing loss or deafness.profound hearing loss or deafness.

If you have experienced temporary hearing loss due If you have experienced temporary hearing loss due to loud sounds you have had a warning.to loud sounds you have had a warning.

StereociliaStereocilia do regenerate daily (but cannot do regenerate daily (but cannot overcome loud sound abuse).overcome loud sound abuse).


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Example Damage from Extreme Acoustic TraumaExample Damage from Extreme Acoustic Trauma

Control, not exposedControl, not exposed After ExposureAfter Exposure

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


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


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PHYPHY--2464 2464 Pres. 5 Sound Intensity LevelsPres. 5 Sound Intensity Levels

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

Outer Outer –– converts pressure fluctuations to converts pressure fluctuations to displacement.displacement.

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

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

PHYPHY--2464 2464 Pres. 5 Sound Intensity LevelsPres. 5 Sound Intensity Levels

Summary (concluded):Summary (concluded):•• Physiology determines function.Physiology determines function.•• No phase detection mechanism.No phase detection mechanism.•• Large “nonLarge “non--linear” range of 12 orders of linear” range of 12 orders of magnitude in intensitymagnitude in intensity•• Three (3) orders of magnitude in frequency (20 Hz Three (3) orders of magnitude in frequency (20 Hz to 20 kHz).to 20 kHz).•• Trauma (due to loud sounds) is a cause of Trauma (due to loud sounds) is a cause of deafness.deafness.

PHY-2464 Physical Basis of Music

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