Rob van der Willigen
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Transcript of Rob van der Willigen
Rob van der WilligenRob van der Willigen
http://www.mbfys.ru.nl/~robvdw/DGCN22/Anatomy_Physiology/http://www.mbfys.ru.nl/~robvdw/DGCN22/Anatomy_Physiology/DGCN22_2011_Anatomy_Physiology_Part1.pptDGCN22_2011_Anatomy_Physiology_Part1.ppt
Auditory PerceptionAuditory Perception
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- Cochlear Mechanotransduction
- Neuroanatomical Organization
P4: Auditory Perception
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Sensory Coding and Transduction
Cochlear Mechanotransduction
Mammalian Auditory Pathway
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6 critical steps
Sensory Coding and Transduction
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Physical Dimensions of Sound
Amplitude
- height of a cycle
- relates to loudness
Wavelength (λ)- distance between peaks
Phase (Φ)- relative position of the peaks
Frequency (f )- cycles per second- relates to pitch
Summary
Recapitulation previous lectures
( ) sin(2 )x t A f t
Sound is a longitudinal pressure wave: a disturbance travelling through a medium (air/water)
The Adequate Stimulus to Hearing
http://www.kettering.edu/~drussell/demos.html
Recapitulation previous lectures
Summary
The Adequate Stimulus to Hearing
http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/
Transverse waves
Longitudinal waves
Type of waves
The Adequate Stimulus to Hearing
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html
Particles do NOT travel, only the disturbance
Particles oscillate back and forth about their equilibrium positions
Distance from source
Du
rati
on
Recapitulation previous lectures
Summary
Compression
Decompression
Compression
Physical Dimensions of Sound
http://www.physpharm.med.uwo.ca/courses/sensesweb/
Time or Distance from the source
Pre
ssu
re
High
Low
LOUD soundLarge change in amplitude
SOFT soundSmall change in amplitude
In air the disturbances travels with the 343 m/s, the speed of soundAmplitude is a measure of pressure
Am
plit
ud
eAmplitude (A)
Physical Dimensions of Sound
Time or Distance from source
Pre
ssu
re
High
Low
LOW pitched soundLow frequency Long wavelengthPressure changes are slow
T is the Period (duration of one cycle)λ is wavelength (length of one cycle)f is frequency (speed [m/s] / λ [m]) or (1/T[s])
HIGH pitched soundHigh frequencyShort wavelengthPressure changes are fast
Frequency (f) ; Period (T) ; Wavelength (λ)
One cycle
The Mathematics of Waves
)sin()( tAtx
Phase is a relative shift in time or space
)sin()( tAtx
The Mathematics of WavesFourier’s
Theorem
Time domain Frequency domain
Jean Baptiste Fourier (1768-1830)
“Fourier synthesis”
“Fourier analysis”
Any complex periodic wave can be “synthesized” by adding its harmonics (“pure tones”) together with the proper amplitudes and phases.
The Mathematics of WavesFourier’s
TheoremLinear Superimposition of Sinusoids to build complex waveforms
If periodic repeating
01
( ) cos( )n n nn
x t A A t
1 nn
The Mathematics of Waves
Fourier synthesis
“Saw tooth wave”
The Mathematics of Waves
Fourier synthesis
“Square wave”
The Mathematics of Waves
Fourier synthesis
“Pulse train
wave”
The Mathematics of Waves
Transfer from time to frequency domain
Time domain
Superposition
Frequency domain
Fourier Analysis
The Mathematics of WavesSuperpositi
onWaves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles.
Two waves (with the same amplitude, frequency, and wavelength) are traveling in opposite directions.
The summed wave is no longer a traveling wave because the position and time dependence have been separated.
The Mathematics of WavesSuperpositi
onWaves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles.
Waves in-phase (Φ=0) interfere constructively giving twice the amplitude of the individual waves.
When the two waves have opposite-phase (Φ=0.5 cycle), they interfere destructively and cancel each other out.
The Mathematics of WavesSuperposition
Most sounds are the sum of many waves (pure tones) of different Frequencies, Phases and Amplitudes.
Through Fourier analysis we can know the sound’s amplitude spectrum (frequency content).
At the point of overlap the net amplitude is the sum of all the separate wave amplitudes. Summing of wave amplitudes leads to interference.
Sensory Coding and Transduction
A Sensor Called Ear
Sensory Coding and Transduction
Peripheral Auditory Peripheral Auditory SystemSystem
Outer Ear:
- Extents up to Eardrum
- Visible part is called Pinna or Auricle
- Movable in non-human primates
- Sound Collection
- Sound Transformation
Gives clues for sound localization
Sensory Coding and Transduction
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Ele
vati
on (
deg
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-40
-20
0
+20
+40
+60
The Pinna creates Sound source position dependent spectral clues.
Frequency
“EAR PRINT”
Ele
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(d
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+20
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Frequency kHz
Am
pli
tud
e (d
B)In humans mid-
frequencies also exhibit a prominent notch that varies in frequency with changes in sound source elevation (6 – 11 kHz)
Elevation
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Barn Owls have Asymmetric Ears and Silent Flight.
One ear points upwards, the other downwards.
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Middle Ear: (Conductive hearing loss)- Mechanical transduction (Acoustic Coupling)- Perfect design for impedance matching Fluid in inner ear is much harder to vibrate than air
- Stapedius muscle: damps loud sounds
Three bones (Ossicles) A small pressure on a large area (ear drum) produces a large pressure on a small area (oval window)
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Inner Ear:
The Cochlea is the auditory portion of the ear
Cochlea is derived from the Greek word kokhlias "snail or screw" in reference to its spiraled shape, 2 ¾ turns, ~ 3.2 cm length (Humans)
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
The cochlea’s core component is the Organ of Corti, the sensory organ of hearing
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
Cochleardeficits cause Sensorineural hearing loss
Its receptors (the hair cells) provide the sense of
hearing
The Organ of Corti mediates mechanotransduction:
Peripheral Auditory Peripheral Auditory SystemSystem
Sensory Coding and Transduction
The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, thousands of hair cells are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells.
The Organ of Corti mediates mechanotransduction:
Hair CellsHair CellsSensory Coding and
Transduction
(A) Scanning electron micrograph of hair bundle (bullfrog sacculus;
David P. Corey's Lab.). This top view shows the stereocilia arranged in order of increasing height.
(B) Model for mechanotransduction. Deflection of a hair cell's bundle causes the stereocilia to bend and the tip links between them to tighten.
(C) Ion channels attached to intracellular elastic elements (ankyrin repeats) open in response to tension on the rather inextensible tip link.
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Cochlear anatomy
Sensory Coding of Sound
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Cochlear anatomy (straightened)
Sensory Coding of Sound
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Pressure waves distort basilar membrane on the way to the round window of tympanic duct:
- Location of maximum distortion varies with frequency of sound
- Frequency information translates into information about position along basilar membrane
Tonotopic coding
Sensory Coding of Sound
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Travelling wave theory von Bekesy: Waves move down basilar membrane stimulation increases, peaks, and quickly tapers
Periodic stimulation of the Basilar membrane matches frequency of sound
Location of peak depends on frequency of the sound, lower frequencies being further away
Sensory Coding of SoundTravelling Wave TheoryTravelling Wave Theory
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Cochlear Fourier AnalysisCochlear Fourier AnalysisHigh f
Med f
Low f
Periodic stimulation of the Basilar membrane matches frequency of sound
BASE APEX
Location of the peak depends on frequency of the sound, lower frequencies being further away
Position along the basilar membrane
Sensory Coding of Sound
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Location of the peak depends on frequency of the sound, lower frequencies being further away
Location of the peak is determined by the stiffness of the membrane
Travelling wave theory von Bekesy: Waves move down basilar membrane
Sensory Coding of Sound Place TheoryPlace Theory
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Thick & taut near baseThin & floppy at apex
TONOTOPIC PLACE MAP
Sensory Coding of SoundSensory Input is TonotopicSensory Input is Tonotopic
LOGARITHMIC: 20 Hz -> 200 Hz
2kH -> 20 kHz each occupies 1/3 of the basilar membrane
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Sensory Coding of SoundSensory input is tonotopic
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Sensory Coding of SoundSensory input is tonotopic
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Sensory Coding of SoundProcessing of Sounds: Anatomy
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The COCHLEA:
Decomposes sounds into its frequency components
Sensory Coding of SoundSensory Input is Non-linearSensory Input is Non-linear
Has direct relation to the sounds spectral content
Represents sound TONOTOPICALLY
Has NO linear relationship to sound pressureHas NO direct relationship to the sound’s location in the outside world
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Effects of an “active”cochlea
20
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0 2 3 4 5 6 7 8 9
Frequency (kHz)
10 11 121
40
BM
Ve
loci
ty(d
B r
e.
1µ/s
)
60
Iso-level curves show sharp tuning at low sound levels, broader tuning at high levels.
Response is strongly compressive around the so-called characteristic frequency (CF).
Requires functioning outer hair cells.
Cochlear nonlinearityCochlear nonlinearityActive processing of
sound
The response of the BM at location most sensitive for ~ 9 KHz tone (CF).The level of the tone varied from 3 to 80 dB SPL (iso-intensity contours).
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20
80
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50
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30
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0 2 3 4 5 6 7 8 9
Frequency (kHz)
10 11 121
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BM
Ve
loci
ty(d
B r
e.
1µ/s
)
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Cochlear nonlinearityCochlear nonlinearityActive processing of
sound
The response of the BM at location most sensitive for ~ 9 KHz tone (CF).The level of the tone varied from 3 to 80 dB SPL (iso-intensity contours).
BM input-output function for a tone at CF (~9 kHz, solid line) and a tone one octave below (~4.5 kHz) taken from the iso-intensity contour plot.
INPUT level (dB SPL)O
UTP
UT
Resp
onse
in d
B
CF= 9 kHz
~4.5kHz
Frequency [kHz]
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Cochlear nonlinearityCochlear nonlinearity
1) Reduced gain: Higher thresholds in quiet; loss of audibility as measured with pure-tone audiogram2) Loss of nonlinearity: Reduced dynamic range; quiet sounds lost but loud sounds just as loud: Loudness Recruitment
GAIN equals Amplitude of motion divided by
Amplitude of stimulus pressure
No nonlinearity post mortem
Basilar-membrane intensity-velocity coding functions for a chinchilla using a tone at the 10 kHz
Rugero et al. (1997)Rugero et al. (1997)
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Tonotopie blijft in het auditief systeem tot en met de auditieve hersenschorsbehouden.
“De samenstelling van een geluid uit afzonderlijke tonen is te vergelijken met de manier waaropwit licht in afzonderlijke kleuren uiteenvalt wanneer het door een prisma gaat .”
John A.J. van Opstal (Al kijkend hoort men, 2006; John A.J. van Opstal (Al kijkend hoort men, 2006; p. 8)p. 8)
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Neurons within a brain area may be organized topographically (or in a map), meaning that neurons that are next to each other represent stimuli with similar properties.
Mapping can be an important clue to the function of an area. If neurons are arrayed according to the value of a particular parameter, then that property might be critical in the processing performed by that area.
Neurons do not need to be arranged topographically along the dimensions of the reference frame that they map, even if its neurons do not form a map of that space.
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Problem I: Sound localization can only result from the neural processing of acoustic cues in the tonotopic input!
Problem II: How does the auditory system parse the superposition of distinct sounds into the original acoustic input?
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21/04/23 Joseph Dodds 2006 52
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Organ of Corti
Basilar Membrane
Auditory nerve
Inner Hair cell
OuterHair cells
Sensory Coding of SoundSummarySummary
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Mechanotransduction: Step 5:
Vibration of basilar membrane causes vibration of hair cells against Tectorial membrane (TM):
Movement displaces stereocilia/kinocilia,
opens ion channels in hair cell membranes
Rush of ions depolarizes hair cells,
which initiates the release of neurotransmitters
NEXT WEEKNEXT WEEKCochlear Innervation & Auditory
Nerve
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Neural responses in the AN: Step 6Information about region and intensity of cochlear stimulation is relayed to CNS over cochlear branch of vestibulocochlear nerve (VIII):
Called the auditory nerve (AN):
Has sensory neurons in spiral ganglion of cochlea
Carries neural information to cochlear nuclei (CN) of midbrain for distribution to other (more higher) brain centers.
NEXT WEEKNEXT WEEKCochlear Innervation & Auditory
Nerve
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NEXT WEEKNEXT WEEKCochlear Innervation & Auditory
Nerve
type 1
type 2
Inner hair cells: Main source of afferent signal in auditory nerve. (~ 10 afferents per hair cell)
Outer hair cells: Primarily receiving efferent inputs.
Type I neurons (95% of all ganglion cells) have a single ending radially connected to IHCs.Type II small,
unmyelinated neurons spiral basally after entering the organ of Corti and branch to connect about ten OHCs, in the same row.
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The Auditory NerveThe Auditory NerveFTC versus
FRCFTC data indicate the characteristics of the cochlea from which has been eliminated the non-linear response characteristics of the cochlear nerve excitation process.
Response Rate versus Frequency Curve
(FRC)
FRC data indicate the limits which may be set upon the central representation of the cochlear filtering by the non-linear rate behavior of the cochlear fibers.
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Place Theory:
Place of maximum vibration along basilar membrane correlates with the place of the Tuning curve (or FTC=Frequency Threshold Curve) along the frequency axis.
Shown are tuning curves measured by finding the pure tone amplitude that produces a criterion response in an 8th nerve fiber (cat).
Tuning curves for four different fibers (A-D) are shown.
The Auditory NerveThe Auditory NerveFrequency Selectivity: CF & place
theory
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Cochlear nonlinearityCochlear nonlinearityOHC motor driven by the Tectorial
membrane
A virtuous loop. Sound evoked perturbation of the organ of Corti elicits a motile response from outer hair cells, which feeds back onto the organ of Corti amplifying the basilar membrane motion.