Transcript Physics 1251 The Science and Technology of Musical Sound

Physics 1251
The Science and Technology
of Musical Sound
Unit 2
Session 12 MWF
The Human Ear
Physics 1251
Unit 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.”
Physics 1251
Unit 2 Session 12
The Human Ear
Ludwig van Beethoven
(1770-1827)
9 th Symphony (Choral)
Composed when he
was profoundly deaf.
Physics 1251
1′ Lecture:
Unit 2 Session 12
The Human Ear
The human ear is a highly sensitive sound
receptor in which
• pressure fluctuations in the outer ear are
transformed
• into vibrations of small bones (the ossicles) in
the middle ear
• that are ultimately communicated to the
cochlea located in the inner ear,
• where the vibrations are further transformed
by stereocilia (hair cells)
• into neural impulses distributed by frequency.
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of Ear
Middle Ear
Outer Ear
Inner Ear
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of the Ear
• 80/20Outer
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.
Physics 1251
Unit 2 Session 12
The Human Ear
Outer Ear
• Pinna ——→
• Meatus ———→
←— Tympanium
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of Ear
Middle Ear
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of the Ear
• 80/20Middle
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.
Physics 1251
Unit 2 Session 12
The Human Ear
Tympanic Membrane (Ear Drum)
micrograph
(view from inside)
←————— Tympamium
←——— Malleus and ligaments
Physics 1251
Unit 2 Session 12
The Human Ear
The Ossicles
Malleus ——→
←—— Incus
←—— Stapes
Physics 1251
Unit 2 Session 12
The Human Ear
Ossicles
(Micrographs)
Malleus
Incus
Malleus Incus
Tympanium
Stapes
Stapes
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of Ear
Inner Ear
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of the Ear
• 80/20Inner
Ear:
Cochlea – (the Snail) converts
displacement into neural impulses.
Auditory Nerve – neural impulses to
brain
Semicircular canals – detect motion
and orientation
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of Inner Ear
←—— Semicircular Canals
Oval Window
Round Window
←—— Cochlea
Physics 1251
Unit 2 Session 12
The Human Ear
Cochlea
(micrograph)
“The Snail”
•
•
o~ oval window
r~ round window
2 mm
Physics 1251
Unit 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 “
Physics 1251
Unit 2 Session 12
The Human Ear
Anatomy of Cochlea
Micrograph
Section
Basilar
——————→
Membrane
© Kansas State School of Medicine
Physics 1251
Unit 2 Session 12
The Human Ear
Microstructure
of Cochlea
Basilar
——————→
↑
Membrane
Organ of
↑
Auditory Nerve → →
Corti
Physics 1251
Unit 2 Session 12
The Human Ear
Stereocilia (Hair Cells)
Physics 1251
Unit 2 Session 12
The Human Ear
Outer Hair Cell in Cross Section
Physics 1251
Unit 2 Session 12
The Human Ear
Inner Hair Cells
Synapse
⇘
Afferent
Efferent
Physics 1251
Unit 2 Session 12
The Human Ear
Organ of Corti and Basilar Membrane
Vibration
←———
Outer
Hair Cells
←————— Inner Hair Cells
Physics 1251
Unit 2 Session 12
The Human Ear
Detail of Hair Cell
Stereocilia
Physics 1251
Unit 2 Session 12
The Human Ear
Action of Hair Cell
Vibration ))))
Neurotransmitter
released
Nerve
Hair Cell
Depolarizes
Hair Cell
Physics 1251
Unit 2 Session 12
The Human Ear
Function of Stereocilia
Stimulation
in HC
Causes neurotransmitter to
stimulate neuron
in Auditory Nerve
Physics 1251
Unit 2 Session 12
The Human Ear
Frequency Response of Hair Cells
Physics 1251
Unit 2 Session 12
The Human Ear
Frequency Discrimination in Cochlea
•
20 Hz to 20 kHz (typical in Humans)
•
Resonances in Basilar membrane and in HC
cause spatial separation by frequency.
•
Differential movement of membranes
stimulate HC.
•
Minimum stimulation required for response.
Inhibition of neighbors causes non-linear
response.
Physics 1251
Unit 2 Session 12
The Human Ear
Neuronal Decoding of Sound (Schematic)
Low Frequency
High Frequency
Frequency response
localized in Cochlea
Physics 1251
Unit 2 Session 12
The Human Ear
Neuronal Response to Sound
•
•
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.
Physics 1251
Unit 2 Session 12
The Human Ear
80/20Repeated
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.
Stereocilia do regenerate daily.
Physics 1251
Unit 2 Session 12
The Human Ear
Hearing Loss due to Over Stimulation
causes Excitotoxicity
Too much Ca2+ poisons the
neuron.
Physics 1251
Unit 2 Session 12
The Human Ear
Extreme Acoustic Trauma
Guinea Pig Stereocilia damage (120 dB sound)
Control, not exposed
After Exposure
Physics 1251
Unit 2 Session 12
The Human Ear
How do you protect yourself?
Ear Plugs
Wear Them!
Physics 1251
Unit 2 Session 12
The Human Ear
How does Anatomy affect perception?
•
•
•
•
Frequency response
Loudness perception
Phase insensitivity
Deafness
• Disruption of “acoustic chain.”
• Nerve death.
•
Remedies
• Restore chain or increase amplitude
Physics 1251
Unit 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.
Physics 1251
Unit 2 Session 12
The Human Ear
•
Physiology determines function.
•
No phase detection mechanism.
•
Large “non-linear” range of 12 orders of
magnitude in intensity
•
Three (3) orders of magnitude in frequency (20
Hz to 20 kHz).
•
Trauma (due to loud sounds) is a cause of
deafness.