3. SOUND WAVES:
• Alternating Compression (dense molecules) & Rarefaction (loose
molecules) waves
• The simple sound is the sinusoidal wave or Pure Tone
4. 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
5. HOW SENSITIVE THE EAR TO SOUNDS?
• 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
6. PITCH OF SOUND
• 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.
7. CONDUCTION OF SOUND WAVES.
• Role of External Ear:
• Sound waves are collected by the Pinna and focused into the External
Auditory Canal
• The vibration pass down the EAC and strike the TM
8. 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)
9. 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.
10. 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.
11. 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.
12. 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
13. IMPEDANCE MATCHING BY EAR OSSICLES BY 3
MECHANISMS
• LEVER ACTION OF OSSICLES.
• 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.
14. 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.
15. 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.
16. 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.
17. 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.
19. 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.
20. 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.
21. • As organ of Corti Moves up, tectorial membrane slide foreward
moving stereocilia Awayfrom limbus.
• As organ of Corti Moves Down, tectorial membrane slide
backward moving stereocilia towardslimbus.
22. STIMULATION OF HAIR CELLS
• Bending of stereocilia stimulate
hair cells
• Depolarization – as stereocilia
bend away from limbus.
• Hyperpolarization – as
stereocilia bends towards
limbus.
23. MEMBRANE POTENTIAL CHANGE IN HAIR CELLS
• Change in membrane potential
is directly proportional to degree
of displacement.
• Describe under 2 conditions
• At rest
• During stimulation.
24. 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.
25. 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.
26. • Organ of corti - UP - Tectorial Membrane AWAY from Limbus -
Depolarization
• Organ of corti - DOWN - Tectorial Membrane TOWARDS from Limbus
- Hyperpolarization
UP
AWAY
D - Depolarisation
H - Hyperpolarisation
OWD
T
N
ards
30. E COLI MA
E - Eighth Nerve
C - Cochlear Nucleus
O - Olivary Nucleus
L - Lateral Lemniscus
I - Inferior Colliculus
M - Medial Geniculate Nucleus
A - Auditory Cortex
32. Initial Otoscopic examination
Speech test
Loud
Whisper
Tympanometry
Tuning fork test
Weber
Rinne
Schwabach
BERA
EChocG
Audiometry
Speech audiometry
Pure Tone Audiometry
OAE (Otoacoustic Emission)
33. Speech test
• Simplest of all
• Involves testing ability to hear
words without using any visual
information.
• Patient should repeat 5 words
spoken loudly at a distance of
approx. 5 metre
Click test
34. Tuning fork test
• Weber’s Test
• Vibrating tuning fork is placed on the patient's forehead (or in the middle
line).
• The vibrations are transmitted by bone conduction to cochlea
35. Rinne’s Test
• Compares the level of air and bone conduction of the same ear.
• base of a tuning fork is placed to the mastoid area (bone con.), and
then after the sound is no longer appreciated, the vibrating top is
placed near the external ear canal (air con.)
36. Schwabach’s Test
• compares the patient's bone conduction to that of the examiner's
• If the patient stops hearing before the examiner, this suggests a
sensorineural loss
• If the patient hears it longer than the examiner, this suggests a
conductive loss
37. Pure Tone Audiometry
• An audiometer is the electronic device which produces pure
tones.
• The amount of intensity that has to be raised above the normal
level is the measure of the degree of hearing impairment.
• It is plotted in the form of graph called
AUDIOGRAM
38. Air vs. Bone Conduction
• A/C (Air conduction)
• Checks the validity of entire ear system
• Tests that ipsilateral ear
B/C (Bone conduction)
• Bone vibrator is Placed on Mastoid Process
• Tests the validity of only the inner ear
• Tests better cochlea
45. Tympanometry or impedence audiometry
• Tympanometry is an examination used to test the condition of the
middle ear and mobility of the eardrum (tympanic membrane) and
the conduction bones by creating variations of air pressure in the ear
canal.
• In evaluating hearing loss, tympanometry permits a distinction
between sensorineural and conductive hearing loss
46. • Introduces a pure tone into ear canal through 3-function probe tip
• Manometer (pump) varies air pressure against TM (controls
mobility)
• Speaker introduces 220Hz probe tone
• Microphone measures loudness in ear canal
48. BERA or ABR
Auditory brainstem response (ABR) audiometry is a neurologic test of
auditory brainstem function in response to auditory (click) stimuli.
Brain stem evoked response audiometry,
Auditory brain stem response, ABR audiometry,
BAER (Brainstem auditory evoked response audiometry).
First described by Jewett and Williston in 1971
49.
50.
51.
52. Uses of BERA
1. It is an effective screening tool for evaluating cases of deafness due
to retrocochlear pathology i.e. (Acoustic schwannoma).
2. Used in screening newborns for deafness
3. Monitoting patients in intensive care units
4. Diagnosing suspected demyelination disorders
