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DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
DEPT. OF PHYSIOLOGY
PHYSIOLOGY
OF
HEARING
OBJECTIVES
 Stimuli or sound waves.
 Conduction of sound
waves.
 Transduction of sound
waves.
 Neural transmission of
...
AUDITION
 For social communication.
 Melophobia – fear of music.
 The scientific study of sound waves is known
as Acous...
SOUND
 perception of pressure waves
generated by vibrating air molecules
SOUND WAVES:
 Sound travels in
Waves through media
 Alternating Compression
(dense molecules) &
Rarefaction (loose
molec...
PROPERTIES OF SOUND THE EAR
DETECTS
1- Pressure level (dB)
2- Frequency (cycle/sec = Hz)
3- Complexity
WAVE PATTERNS
 A is the record of a pure tone
 B has a greater amplitude
and is louder than A.
 C has the same
amplitud...
 The Human ear is sensitive to sounds over
a wide range of:
- Frequencies: 20 – 20,000 Hz
- Amplitudes: 0.0002 – 200 dyne...
SOUND • Amplitude determines the loudness of sound
• Amplitude is measured in decibels
Human auditory field:
 Pitch discrimination is best in the 1000- to
3000-Hz range
 Poor at high and low pitches.
 Average individuals disting...
CONDUCTION OF SOUND WAVES.
 Role of External Ear
Monday, March 28, 2016
Sound waves are collected by the Pinna and focuse...
EXTERNAL EAR FUNCTIONS:
 Collecting sound waves
 Amplification of frequencies
2000
- 4000 Hz (Resonant
Frequency of EAC)...
CONDUCTION OF SOUND
WAVES.
 Conduction from
tympanic membrane to
ear ossicles.
 Tympanic membrane
 Pressure Receiver –
...
CONDUCTION OF SOUND WAVES
MECHANICALLY FROM MIDDLE EAR
TO INNER EAR
 Impedance matching.
 Phase differential
between ova...
IMPEDANCE MATCHING.
 A person in water can not hear sound
produced out of it.
 As 99.9% sound get reflected from surface...
IMPEDANCE MATCHING BY EAR
OSSICLES BY 3 MECHANISMS
 HYDROLIC ACTION OF
TYMPANIC MEMBRANE –
 Effective vibratory area of
...
IMPEDANCE MATCHING BY EAR
OSSICLES BY 3 MECHANISMS
 LEVER ACTION OF
VESICLES.
 Handle of Malleus 1.3
times longer than L...
IMPEDANCE MATCHING BY EAR
OSSICLES BY 3 MECHANISMS
 CURVED MEMBRANE
EFFECT.
 Movement of
Tympanic membrane
more at Perip...
IMPEDANCE MATCHING BY EAR
OSSICLES BY 3 MECHANISMS
 So all these together
Increase sound
pressure 22 folds
 Impedance
Mi...
MINIMUM AUDIBILITY CURVE
 Amplification of sound –
greatest between 1000-
3000 Hz.
 below 16 & above 20000 Hz
not amplif...
PHASE DIFFERENTIAL BETWEEN
OVAL AND ROUND WINDOW.
 Sound don’t reach both
windows simultaneously.
 When oval window rece...
NATURAL RESONANCE OF
EXTERNAL EAR AND MIDDLE EAR.
 Natural Resonance –
allow some frequency to
pass more easily to inner
...
ATTENUATION REFLEX.
 Tympanic
reflex/Acoustic reflex
 Protective reflex.
 Reduces sound pressure
amplitude by Changing
...
ATTENUATION REFLEX.
 Stimulus - loud sound.
 Latent period – 40-
80ms.(sudden loud
sound; bomb explosion –
Deafness)
 R...
ATTENUATION REFLEX.
 Tensor Tympani – pull
Malleus inwards
 Stapedius – pulls
stapes outwards.
 Both makes Ossicular
sy...
ADVANTAGES OF
ATTENUATION REFLEX.
 Prevents Damage to cochlea
from loud sound.
 Attenuates & Mask all low
frequency envi...
TRANSDUCTION OF SOUND
WAVES
 Transduction of sound from
Mechanical to Electrical
occur in ORGAN OF CORTI
in inner ear.
 ...
VIBRATION OF BASILAR
MEMBRANE.
 Sound waves from middle
ear pass to inner ear
through Oval window by
in & out movement of...
STIMULATION OF HAIR CELLS
 Movement of basilar
membrane causes organ of
corti to move up & down.
 Hair of the outer hair...
STIMULATION OF HAIR CELLS
 As organ of Corti Moves
up, tectorial membrane
slide foreward moving
stereocilia Away from
lim...
STIMULATION OF
HAIR CELLS
 Bending of stereocilia
stimulate hair cells
 Depolarization – as
stereocilia bend away
from l...
MEMBRANE POTENTIAL
CHANGE IN HAIR CELLS
 Change in membrane
potential is directly
proportional to degree
of displaement.
...
RESTING MEMBRANE
POTENTIAL FROM HAIR CELLS
 At rest 2 potentials are
recorded
 Endocochlear potential.
 Resting potenti...
ENDOCOCHLEAR POTENTIAL.
 Endolymph in scala media secreted
by stria vascularis has
 High conc of Na-K-ATPase & unique
el...
RESTING POTENTIAL OF HAIR
CELLS.
 Each hair cell has negative
RMP with -70 mv.
 At the upper end of hair cell
potential ...
ACTION POTENTIAL IN HAIR
CELLS
 Cochlear Microphonic
potential
 Gating of K channels is
controlled by movement of
stereo...
COCHLEAR MICROPHONIC
POTENTIAL
 Similar to generator potential as
 No latency or refractory period.
 Do not obey all or...
ACTION POTENTIAL IN
AUDITORY NERVE.
 As hair cells Depolarize –
Ca channels open – Ca
enters – release synaptic
transmitt...
Monday, March 28, 2016
Monday, March 28, 2016
NEURAL TRANSMISSION OF
SIGNALS.
 Spiral ganglion
 Cochlear nuclei
 Superior olivary nucleus
complex, trapezoid Nucleus
...
Monday, March 28, 2016
Monday, March 28, 2016
SALIENT FEATURES OF
AUDITORY PATHWAY.
 Bilateral representation.
 Descending pathway.
 Role in brain stem & spiral
acou...
SALIENT FEATURES OF
AUDITORY PATHWAY.
 Bilateral
Representation – form
Medulla onwards ear is
Bilaterally represented
in ...
SALIENT FEATURES OF
AUDITORY PATHWAY.
 Role in Brain Stem & Spiral
Acoustic Reflex – Integration
of Visual & Auditory
inf...
SALIENT FEATURES OF
AUDITORY PATHWAY.
 Spatial Organization – different parts of organ of
corti respond to different freq...
FEATURES OF AUDITORY
CORTEX.
 Tonotopic organization.
 Column Organization –
 Isofrequency Columns – Neurons
have same ...
FEATURES OF OTHER CORTICAL
AREAS WITH AUDITION.
 Hemispheric Specialization.
 During language learning area
22 concerned...
FEATURES OF OTHER CORTICAL
AREAS WITH AUDITION.
 Plasticity of auditory
pathways.
 If person becomes deaf
before languag...
NEURAL PROCESSING OF
AUDITORY INFORMATION
 Encoding of
Frequency.
 Encoding of Intensity
(loudness)
 Feature Detection....
ENCODING OF FREQUENCY.
 Human ear can
discriminate sound
between 60-20,000 Hz
range.
 Encoding occurs in
cochlear nerve....
Monday, March 28, 2016
PLACE THEORY OR BEKESY
TRAVELLING WAVE THEORY
 Discriminate sound between 2000-
20000 Hz.
 Basilar Membrane is Mechanica...
PLACE THEORY OR BEKESY
TRAVELLING WAVE THEORY
 This different response to different frequency is due
to systematic variat...
Monday, March 28, 2016
FREQUENCY THEORY
 Discriminate low frequency
sound below 2000 Hz.
 For very low frequency
sound there is
synchronization...
Monday, March 28, 2016
PITCH OF SOUND
 PITCH – subjective
sensation of frequency
of sound.
 Higher frequency
greater is pitch.
 Discrimination...
ENCODING OF INTENSITY (LOUDNESS)
Occurs at level of cochlear nerve.
Monday, March 28, 2016
FEATURE DETECTION.
 Higher auditory
centers respond to
particular feature.
 CORTICAL Neurons
respond to shift of
Note fr...
LOCALIZATION OF SOUND IN
SPACE
 Can separate location by 1
degree.
 Center – Brain Stem relay
nuclei superior olivary
nu...
Thank
You
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Physiology of hearing

PHYSIOLOGY OF HEARING

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Physiology of hearing

  1. 1. DR NILESH KATE MBBS,MD ASSOCIATE PROF DEPT. OF PHYSIOLOGY PHYSIOLOGY OF HEARING
  2. 2. OBJECTIVES  Stimuli or sound waves.  Conduction of sound waves.  Transduction of sound waves.  Neural transmission of signals.  Encoding of signals.  Applied. Monday, March 28, 2016
  3. 3. AUDITION  For social communication.  Melophobia – fear of music.  The scientific study of sound waves is known as Acoustics. Monday, March 28, 2016
  4. 4. SOUND  perception of pressure waves generated by vibrating air molecules
  5. 5. SOUND WAVES:  Sound travels in Waves through media  Alternating Compression (dense molecules) & Rarefaction (loose molecules) waves  The simple sound is the sinusoidal wave or Pure Tone
  6. 6. PROPERTIES OF SOUND THE EAR DETECTS 1- Pressure level (dB) 2- Frequency (cycle/sec = Hz) 3- Complexity
  7. 7. WAVE PATTERNS  A is the record of a pure tone  B has a greater amplitude and is louder than A.  C has the same amplitude as A but a greater frequency, and its pitch is higher.  D is a complex wave form that is regularly repeated.  E, which have no regular pattern, are perceived as NOISE
  8. 8.  The Human ear is sensitive to sounds over a wide range of: - Frequencies: 20 – 20,000 Hz - Amplitudes: 0.0002 – 200 dyne/cm2  The human ear can detect the difference between two sounds occurring 10 μsec apart in time HOW SENSITIVE THE EAR TO SOUNDS?
  9. 9. SOUND • Amplitude determines the loudness of sound • Amplitude is measured in decibels
  10. 10. Human auditory field:
  11. 11.  Pitch discrimination is best in the 1000- to 3000-Hz range  Poor at high and low pitches.  Average individuals distinguish 2000 pitchs  Musicians- Cortical Plasticity  The pitch of the average male voice in conversation is about 120 Hz and  Average female voice about 250 Hz. PITCH OF SOUND
  12. 12. CONDUCTION OF SOUND WAVES.  Role of External Ear Monday, March 28, 2016 Sound waves are collected by the Pinna and focused into the External Auditory Canal The vibration pass down the EAC and strike the TM
  13. 13. EXTERNAL EAR FUNCTIONS:  Collecting sound waves  Amplification of frequencies 2000 - 4000 Hz (Resonant Frequency of EAC)  Providing cues about the vertical localization of a sound source (by the Degree of sound waves reflection over the Pinna)
  14. 14. CONDUCTION OF SOUND WAVES.  Conduction from tympanic membrane to ear ossicles.  Tympanic membrane  Pressure Receiver – Sensitive to Pressure Change  Resonator – Vibrate with Pressure Change.  Critically Dampens as sound ends. Monday, March 28, 2016
  15. 15. CONDUCTION OF SOUND WAVES MECHANICALLY FROM MIDDLE EAR TO INNER EAR  Impedance matching.  Phase differential between oval and round window.  Natural resonance of External Ear and Middle Ear.  Attenuation Reflex. Monday, March 28, 2016
  16. 16. IMPEDANCE MATCHING.  A person in water can not hear sound produced out of it.  As 99.9% sound get reflected from surface of water due to Impedance.  So as Air filled Middle ear conduct sound to fluid filled Inner ear most of sound get Reflected – Impedance Mismatching.  Compensated by Inner Ear by IMPEDANCE MATCHING. Monday, March 28, 2016
  17. 17. IMPEDANCE MATCHING BY EAR OSSICLES BY 3 MECHANISMS  HYDROLIC ACTION OF TYMPANIC MEMBRANE –  Effective vibratory area of tympanic membrane (55mm2) is more than stapes oval window surface area(3.2mm2)  So force produced by sound concentrated over small area  Amplifying Pressure on Oval Window Monday, March 28, 2016
  18. 18. IMPEDANCE MATCHING BY EAR OSSICLES BY 3 MECHANISMS  LEVER ACTION OF VESICLES.  Handle of Malleus 1.3 times longer than Long process of Incus, providing Mechanical Leverage Advantage.  So Ossicles increases force of movement by 1.3 times. Monday, March 28, 2016
  19. 19. IMPEDANCE MATCHING BY EAR OSSICLES BY 3 MECHANISMS  CURVED MEMBRANE EFFECT.  Movement of Tympanic membrane more at Periphery than at Center where Malleus is attached.  So provide some leverage. Monday, March 28, 2016
  20. 20. IMPEDANCE MATCHING BY EAR OSSICLES BY 3 MECHANISMS  So all these together Increase sound pressure 22 folds  Impedance Mismatching is mostly compensated.  If remove ossicles loud sound hear as whisper. Monday, March 28, 2016
  21. 21. MINIMUM AUDIBILITY CURVE  Amplification of sound – greatest between 1000- 3000 Hz.  below 16 & above 20000 Hz not amplified.  Human ear can perceive pitch between 16-20000 Hz  Maximum sensitivity 1000- 3000 Hz Monday, March 28, 2016
  22. 22. PHASE DIFFERENTIAL BETWEEN OVAL AND ROUND WINDOW.  Sound don’t reach both windows simultaneously.  When oval window receive compression, round window receive rarefaction.  If sound reaches simultaneously no movement of Perilymph & no hearing. Monday, March 28, 2016
  23. 23. NATURAL RESONANCE OF EXTERNAL EAR AND MIDDLE EAR.  Natural Resonance – allow some frequency to pass more easily to inner ear.  External auditory canal – 3000 Hz  Tympanic membrane – 800-1600 Hz.  Middle ear – 800 Hz.  Ossicular chain – 500-2000 Hz. Monday, March 28, 2016
  24. 24. ATTENUATION REFLEX.  Tympanic reflex/Acoustic reflex  Protective reflex.  Reduces sound pressure amplitude by Changing mobility & Transmission properties of Ear ossicles. Monday, March 28, 2016
  25. 25. ATTENUATION REFLEX.  Stimulus - loud sound.  Latent period – 40- 80ms.(sudden loud sound; bomb explosion – Deafness)  Reflex Activity – contraction of 2 muscles  Tensor tympani  Stapedius. Monday, March 28, 2016
  26. 26. ATTENUATION REFLEX.  Tensor Tympani – pull Malleus inwards  Stapedius – pulls stapes outwards.  Both makes Ossicular system rigid & no vibrations.  Sound intensity Decreased by 30-40 db. Monday, March 28, 2016
  27. 27. ADVANTAGES OF ATTENUATION REFLEX.  Prevents Damage to cochlea from loud sound.  Attenuates & Mask all low frequency environmental sounds & allow person to concentrate on sounds above 1000 Hz.  Reduces sound produced during vocalization & chewing. Monday, March 28, 2016
  28. 28. TRANSDUCTION OF SOUND WAVES  Transduction of sound from Mechanical to Electrical occur in ORGAN OF CORTI in inner ear.  Vibration of Basilar membrane.  Stimulation of hair cells  Membrane potential change in hair cells  Neural transmission of signals. Monday, March 28, 2016
  29. 29. VIBRATION OF BASILAR MEMBRANE.  Sound waves from middle ear pass to inner ear through Oval window by in & out movement of stapes.  Wave spread along Scala Vestibuli to Scala tympani as a travelling wave.  As it passes it Vibrate basilar membrane. Monday, March 28, 2016
  30. 30. STIMULATION OF HAIR CELLS  Movement of basilar membrane causes organ of corti to move up & down.  Hair of the outer hair cells are embedded in Tectorial Membrane.  As both Tectorial membrane & basilar membrane moves, they slide each other with movement. Monday, March 28, 2016
  31. 31. STIMULATION OF HAIR CELLS  As organ of Corti Moves up, tectorial membrane slide foreward moving stereocilia Away from limbus.  As organ of Corti Moves Down, tectorial membrane slide backward moving stereocilia towards limbus. Monday, March 28, 2016
  32. 32. STIMULATION OF HAIR CELLS  Bending of stereocilia stimulate hair cells  Depolarization – as stereocilia bend away from limbus.  Hyperpolarization – as stereocilia bends towards limbus. Monday, March 28, 2016
  33. 33. MEMBRANE POTENTIAL CHANGE IN HAIR CELLS  Change in membrane potential is directly proportional to degree of displaement.  Describe under 2 conditions  At rest  During stimulation. Monday, March 28, 2016
  34. 34. RESTING MEMBRANE POTENTIAL FROM HAIR CELLS  At rest 2 potentials are recorded  Endocochlear potential.  Resting potential of hair cells. Monday, March 28, 2016
  35. 35. ENDOCOCHLEAR POTENTIAL.  Endolymph in scala media secreted by stria vascularis has  High conc of Na-K-ATPase & unique electrogenic K pump  So it has high K conc & electrically positive to perilymph.  So potential developed between Endolymph & Perilymph is Endolymphatic potential or Endocochlear potential  + 80 mv. Monday, March 28, 2016
  36. 36. RESTING POTENTIAL OF HAIR CELLS.  Each hair cell has negative RMP with -70 mv.  At the upper end of hair cell potential difference between ICF & endolymph is -150 mv  Large negative potential & lack of K conc difference make hair cells highly sensitive. Monday, March 28, 2016
  37. 37. ACTION POTENTIAL IN HAIR CELLS  Cochlear Microphonic potential  Gating of K channels is controlled by movement of stereocilia.  As stereocilia bend away from Limbus – K channels open – Depolarization.  As stereocilia bend towards Limbus – K channels close– Hyperpolarization. Monday, March 28, 2016
  38. 38. COCHLEAR MICROPHONIC POTENTIAL  Similar to generator potential as  No latency or refractory period.  Do not obey all or none law.  Resistance to ischemia & anesthesia.  Base of cochlea respond to all frequency, apex respond to low frequency of sound.  When organ of corti damaged due to prolonged exposure to loud sound, potential produced by this band of sound is abolished. Monday, March 28, 2016
  39. 39. ACTION POTENTIAL IN AUDITORY NERVE.  As hair cells Depolarize – Ca channels open – Ca enters – release synaptic transmitter – activates receptor sites on afferent neurons – Action Potential.  Loudness of sound determine Frequency of Action Potential. Monday, March 28, 2016
  40. 40. Monday, March 28, 2016
  41. 41. Monday, March 28, 2016
  42. 42. NEURAL TRANSMISSION OF SIGNALS.  Spiral ganglion  Cochlear nuclei  Superior olivary nucleus complex, trapezoid Nucleus & N of lateral lemniscus.  Inferior colliculus  Medial geniculate body.  Auditory cortex (41,42, 22,21,20) Monday, March 28, 2016
  43. 43. Monday, March 28, 2016
  44. 44. Monday, March 28, 2016
  45. 45. SALIENT FEATURES OF AUDITORY PATHWAY.  Bilateral representation.  Descending pathway.  Role in brain stem & spiral acoustic reflex.  Role in general arousal.  Spatial organization.  Features of auditory cortex.  Features of other cortical areas with audition. Monday, March 28, 2016
  46. 46. SALIENT FEATURES OF AUDITORY PATHWAY.  Bilateral Representation – form Medulla onwards ear is Bilaterally represented in Auditory pathway.  Descending Pathway – there is significant Descending pathway forming feed-forward & feedback loop. Monday, March 28, 2016
  47. 47. SALIENT FEATURES OF AUDITORY PATHWAY.  Role in Brain Stem & Spiral Acoustic Reflex – Integration of Visual & Auditory information occurs due to interconnection between Superior & Inferior Colliculi.  Role in General Arousal – Due to Auditory Pathway collateral to Reticular Formation & Cerebellum Monday, March 28, 2016
  48. 48. SALIENT FEATURES OF AUDITORY PATHWAY.  Spatial Organization – different parts of organ of corti respond to different frequency.  There is Tonotopic organization in cochlear nuclei maintained in superior olivary nucleus, inferior colliculus, MGB & auditory cortex.  Same as Retinotopic organization & Somatotopic organization. Monday, March 28, 2016
  49. 49. FEATURES OF AUDITORY CORTEX.  Tonotopic organization.  Column Organization –  Isofrequency Columns – Neurons have same characteristic frequency.  Summation Columns – Neurons responsive to binaural than Monaural inputs.  Suppression Columns – Neurons less responsive to Binaural than Monaural stimulation. Monday, March 28, 2016
  50. 50. FEATURES OF OTHER CORTICAL AREAS WITH AUDITION.  Hemispheric Specialization.  During language learning area 22 concerned with processing of auditory signals related to speech is more active on left than right.  Area 22 on right side is more concerned with melody, pitch & sound intensity. Monday, March 28, 2016
  51. 51. FEATURES OF OTHER CORTICAL AREAS WITH AUDITION.  Plasticity of auditory pathways.  If person becomes deaf before language skills developed, Viewing sign language activates auditory association area.  Musicians have larger auditory area & larger cerebellum than non- musicians. Monday, March 28, 2016
  52. 52. NEURAL PROCESSING OF AUDITORY INFORMATION  Encoding of Frequency.  Encoding of Intensity (loudness)  Feature Detection.  Localization of Sound in space Monday, March 28, 2016
  53. 53. ENCODING OF FREQUENCY.  Human ear can discriminate sound between 60-20,000 Hz range.  Encoding occurs in cochlear nerve.  Explained by Theories of Hearing. Monday, March 28, 2016
  54. 54. Monday, March 28, 2016
  55. 55. PLACE THEORY OR BEKESY TRAVELLING WAVE THEORY  Discriminate sound between 2000- 20000 Hz.  Basilar Membrane is Mechanical Analyzer of sound frequency.  Pattern of movement of basilar membrane is that of Travelling Wave.  Basilar membrane Near oval window vibrate in response to sound of Higher frequency & Near Apex respond to Lower Frequency. Monday, March 28, 2016
  56. 56. PLACE THEORY OR BEKESY TRAVELLING WAVE THEORY  This different response to different frequency is due to systematic variations in Mechanical Properties in basilar membrane.  So Higher frequencies are represented in Basal turn & Lower Near Apex.  So same response by Hair cells & Auditory Nerve fibres.  Thus there is Spatial Organization of Auditory pathways from hair cells to Auditory Cortex. Monday, March 28, 2016
  57. 57. Monday, March 28, 2016
  58. 58. FREQUENCY THEORY  Discriminate low frequency sound below 2000 Hz.  For very low frequency sound there is synchronization between frequency of sound & rate of discharge through cochlear nerve.  So Frequency of Action potential in auditory nerve determine Loudness than pitch. Monday, March 28, 2016
  59. 59. Monday, March 28, 2016
  60. 60. PITCH OF SOUND  PITCH – subjective sensation of frequency of sound.  Higher frequency greater is pitch.  Discrimination of pitch also depend on  Loudness  Duration. Monday, March 28, 2016
  61. 61. ENCODING OF INTENSITY (LOUDNESS) Occurs at level of cochlear nerve. Monday, March 28, 2016
  62. 62. FEATURE DETECTION.  Higher auditory centers respond to particular feature.  CORTICAL Neurons respond to shift of Note from high to low frequency. Monday, March 28, 2016
  63. 63. LOCALIZATION OF SOUND IN SPACE  Can separate location by 1 degree.  Center – Brain Stem relay nuclei superior olivary nucleus.  Clues –  Time lag between entry of sound in 2 ears  Difference in intensity that reaches 2 ears. Monday, March 28, 2016
  64. 64. Thank You

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PHYSIOLOGY OF HEARING

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