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

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. General Outline P4 General Outline P4

- Cochlear Mechanotransduction

- Neuroanatomical Organization

P4: Auditory Perception

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture.

Sensory Coding and Transduction

Cochlear Mechanotransduction

Mammalian Auditory Pathway


6 critical steps


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


Summary


http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/

Transverse waves

Longitudinal waves

Type of waves


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


Summary

Compression

Decompression

Compression


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)


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


Fourier synthesis

“Saw tooth wave”


Fourier synthesis

“Square wave”


Fourier synthesis

“Pulse train

wave”


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.

A Sensor Called Ear


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




Ele

vati

on (

deg

)

-40

-20

0

+20

+40

+60

The Pinna creates Sound source position dependent spectral clues.

Frequency

“EAR PRINT”

Ele

vati

on

(d

eg)

-40

-20

0

+20

+40

+60

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



Barn Owls have Asymmetric Ears and Silent Flight.

One ear points upwards, the other downwards.



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)



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)



The cochlea’s core component is the Organ of Corti, the sensory organ of hearing



Cochleardeficits cause Sensorineural hearing loss

Its receptors (the hair cells) provide the sense of

hearing

The Organ of Corti mediates mechanotransduction:



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.


Cochlear anatomy

Sensory Coding of Sound


Cochlear anatomy (straightened)



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



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


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



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


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


Sensory Coding of SoundSensory input is tonotopic


Sensory Coding of SoundProcessing of Sounds: Anatomy


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


Effects of an “active”cochlea

20

80

70

60

50

40

30

20

10

3

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).


20

80

70

60

50

40

30

20

10

3

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

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]


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)

Q ui ckTi me™ and a TI FF (LZW) decompressor are needed to see thi s pi cture. The Problem of HearingThe Problem of Hearing

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)


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.


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?


21/04/23 Joseph Dodds 2006 52


Organ of Corti

Basilar Membrane

Auditory nerve

Inner Hair cell

OuterHair cells

Sensory Coding of SoundSummarySummary


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


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.


Nerve



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.


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.


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


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.

Rob van der Willigen

Documents

Transcript of Rob van der Willigen