4. Function of Outer Ear
• Collect sound
• Localization
• Resonator
• Protection
• Sensitive
5. Pinna
• The visible portion that is
commonly referred to as "the
ear"
• Helps localize sound sources
• Directs sound into the ear
• Each individual's pinna
creates a distinctive imprint
on the acoustic wave
traveling into the auditory
canal
6. External Auditory Canal
• lateral portion-cartilage
• medial portion-osseous
• lined with epidermal (skin)
tissue
• hairs in lateral part
• cerumen (ear wax) secreted
in lateral part.
7. Outer Ear Functions 1
• Amplification / Filtering
-- increases sounds between 1500 and 7000 Hz by 10 to 15
dB
-- because of the resonance of
Concha -- 5000 Hz
E.A.Canal -- 2500 Hz
9. Outer Ear Resonance
• Influence of pinna (p)
• Influence of ear canal
(m)
• Combine influence (t)
• At 3000 Hz, the final
amplification (t) is 20
dB
10. Cerumen
• The purpose of wax:
– Repel water
– Trap dust, sand particles, micro-
organisms, and other debris
– Moisturize epithelium in ear
canal
– Odor discourages insects
– Antibiotic, antiviral, antifungal
properties
– Cleanse ear canal
11. Outer Ear Hearing Disorders
• Down Syndrome
– Ears small and low set
• Fetal Alcohol
Syndrome
– Deformed ears
• DiGeorge syndrome
– Low set ears
14. Middle Ear
Tympanum:
Timpani, or kettledrums, are musical
instruments in the percussion
family.
A type of drum, they consist of a
skin called a head stretched over a
large bowl commonly made of
copper.
They are played by striking the head
with a special drum stick called a
timpani stick.
Timpani evolved from military
drums to become a staple of the
classical orchestra in the 17th
century.
Today, they are used in many types
of musical ensembles including
classical orchestra
15. Tympanic Membrane
• The eardrum separates the outer
ear from the middle ear
• Creates a barrier that protects the
middle and inner areas from
foreign objects
• Cone-shaped in appearance
– about 17.5 mm in diameter
• The eardrum vibrates in response
to sound pressure waves.
• The membrane movement is
incredibly small
– as little as one-billionth of a
centimeter
16. Middle Ear – 3 compartments
• The tympanic cavity is a small chamber, about 1 cm3 in
size, lying in the depth of the temporal bone, between the
tympanic membrane and the internal ear.
• In front, through the Eustachian tube, the tympanic cavity
communicates with the nasopharynx;
• behind, through the entrance into the mastoid antrum (aditus
ad antrum mastoideum), communicates with the latter and
the cells of the mastoid Process.
17. TYMPANIC CAVITY
• It is customary to divide the into three parts:
• the middle and biggest part, mesotympanum, corresponding to the
pars tensa of the drum
• the upper part, epitympanum, lying above the former and also known
as the epitympanic recess or attic;
• the lower part, hypotympanum, lying below the drum level.
18. Epitympanum
• Lies above the level of the
short process of the malleus
• Contents:
– Head of the malleus
– Body of the incus
– Associated ligaments and
mucosal folds
19. Mesotympanum
• Contents:
– Stapes
– Long process of the incus
– Handle of the malleus
– Oval and round windows
• Eustachian tube exits from the anterior aspect
• Two recesses extend posteriorly that are often not
visible directly
– Facial recess
• Lateral to facial nerve
• Bounded by the fossa incudis superiorly
• Bounded by the chorda tympani nerve laterally
– Sinus tympani
• Lies between the facial nerve and the medial wall of the
mesotympanum
20. Hypotympanum
• Lies inferior and medial to
the floor of the bony ear
canal
• Irregular bony groove that is
seldom involved by
cholesteatoma
21. Eustachian Tube
• The eustachian tube connects the front wall of the
middle ear with the nasopharynx
• The eustachian tube also operates like a valve,
which opens during swallowing and yawning
– This equalizes the pressure on either side of the
eardrum, which is necessary for optimal hearing.
– Without this function, a difference between the static
pressure in the middle ear and the outside pressure may
develop, causing the eardrum to displace inward or
outward
• This reduces the efficiency of the middle ear and less acoustic
energy will be transmitted to the inner ear.
23. Transformer/Amplifier
• Transform the vibrating motion of the eardrum into motion of
the stapes.
• The middle ear enhances the transfer of acoustical energy in
two ways:
– The area of the eardrum is about 17 times larger than the oval window
• The effective pressure (force per unit area) is increased by this amount.
– The ossicles produce a lever action that further amplifies the pressure
• Without the transformer action of middle ear, about 1/1000 of
acoustic energy in air transmitted to inner-ear fluids (about 30
dB loss).
• Malleus and incus vibrate together, transmitting the sound
waves from the eardrum to the footplate of the stapes (this
pushes the oval window in and out)(mechanical energy)
24. Middle Ear Muscles
• Tensor tympani
– Attached to malleus
– Innervated by V, trigeminal nerve
• Stapedius
– Attached to stapes
– Innervated by VII, facial nerve
• Middle Ear Muscle Function:
– Help maintain ossicles in proper position
– Protect inner ear from excessive sound
levels
• When ear exposed to sound levels above
70 dB, the muscles contract, decreasing
amount of energy transferred to inner ear
– This protective reflex termed "acoustic
reflex"
25. Ligaments of Middle Ear
• Function
– restrict and confine
the effect of ossicles
to act as a lever
– restrict movements to
reduce the chance of
damage to the inner
ear
– prevents distortion to
sound
26. Middle Ear Functions
• Impedance Matching -- amplification of
sounds to overcome difference in
impedance between the air of EAC and the
fluid of the inner ear.
• Filtering -- resonant frequency is
approximately 1000 Hz, functions as
bandpass filter.
• Acoustic Reflex -- Contraction of Stapedius
muscle in response to loud sounds
27. Middle Ear Function
• Impedance Matching is accomplished through pressure
increase produced by the middle ear.
• From 2 main effects:
Reduction in AREA
Increase in FORCE
28. Reduction in AREA
• sound striking the (relatively large) tympanic membrane
• is delivered to the (much smaller) stapes footplate
• Areal Ratio = 18.6 to 1
29. Increase in FORCE
• The malleus and incus act like a lever
• Whenever there is a pivot:
• Force x Length in = Force x Length out
• Force is greater on short side (Think of wheeled luggage)
• Malleus manubrium = 1.3 times as long as Incus long
process
30. Leverage
• Small force (baby’s weight) supports man
• because of the difference in length on either side of
the pivot point
31. Increase in Pressure
• Remember that Press. = Force/Area
• force is increased 1.3 times
• area is decreased 18.6 times
• Pressure is increased 24.2 times (27.7 dB)
32. Other Key Middle Ear Function
• Oval Window Isolation-- Sound striking the tympanic
membrane is delivered through the ossicular chain to the
oval window
• Without the middle ear, both the oval and round windows
would receive sound energy and energy would cancel out.
33. Tympanometry
• Acoustic measures of middle ear health
• Made using an immittance (or impedance) bridge:
– PRESSURE PUMP/MANOMETER
– MINIATURE SPEAKER
– MICROPHONE
– ALL CONNECTED THROUGH A SMALL PROBE
INSERTED IN EAR CANAL
34. Compliance: opposite of stiffness.
• middle ear system is not massive, largely a
stiffness-controlled system.
• Changes in stiffness/compliance have large
effects on functioning of system.
• at point where air pressure in canal and
middle ear are equal the most sound will be
conducted through.
35. Tympanogram:
• A plot of middle ear compliance as a function of
ear canal pressure
• Pressure is swept from +200 to -200 or -400 dPa
• Should see peak at point where pressures are
equal
36. Tympanogram types:
• A: peak between +200 and -200 dPa: normal
• C: peak beyond -200 dPa: neg pressure
• B: no peak flat tymp: effusion
• As: peak but shallow: stiff: otosclerosis
• Ad: peak off scale: floppy: dysarticulation
39. Otosclerosis
• Develops most frequently between ages of
10 and 30.
• About 10–15% of patients have unilateral
loss.
• Affects women more frequently than men
by a ratio of 2:1.
• Pregnancy once thought to be a risk factor
for the development and / or worsening of
otosclerosis…recent studies have disputed
this.
• May progress to nerve deafness called
cochlear otosclerosis.
42. • Cochlea
• Made up of 2 ½ turns
• EAC Malleus, incus, stapes
Oval window cochlea
• Three Smaller canals
– Scala vestibula
– Scala media
– Scala tympani
• The ends of scala vestibula and
scala tympani meets at the
helicotrema
44. Cochlea is Divided into 3 “Scala”
• Scala Vestibuli
– Reissner’s Membrane
• Scala Media
– Basilar Membrane
• Scala Tympani
• Helicotrema - the
opening between 2
outer Scala
45. Fluids filling the Inner Ear
• Perilymph- in S. Vestibuli and S. Tympani
– High Sodium / Low Potassium concentrations
– Low Voltage (0 to +5 mV)
• Endolymph- in S. Media
– High Potassium / Low Sodium concentrations
– High Positive Voltage (85 mV)
46. Cochlear Functions
• Transduction- Converting acoustical-mechanical energy
into electro-chemical energy.
• Frequency Analysis-Breaking sound up into its component
frequencies
47. Transduction-
• Inner Hair Cells are the true sensory
transducers, converting motion of
stereocilia into neurotransmitter release.
Mechanical Electro-chemical
• Outer Hair Cells have both forward and
reverse transduction--
Mechanical Electro-chemical
Mechanical Electro-chemical
48. VESTIBULAR ANATOMY
• Located in the labyrinth
• 3 orthogonally oriented
semicircular canals
• 2 otolith organs (utrile and
saccule)
49. OTOLITHS
• Utriculus and Sacculus
• Lie at right angles (utricle – horizontal,
saccule – vertical)
• Responsible for detecting linear
acceleration (tilt and translation; up,
down, tilt)
• Gravity and straight line motion
Macula
Sensory organ of the otiliths
Covered by otolithic membrane
(mucopolysaccaharide gel covered by
superficial otoconia (CaCO3), higher
specific gravity to endolymph
Otoconia are sensitive to gravity due to their
higher specific gravity
53. Vestibulo-Cochlear Nerve
• Type: Special sensory (SSA)
• Components:
Vestibular part: conveys
impulses associated with
balance of body (position
& movement of the head)
Cochlear part: conveys
impulses associated with
hearing
• Vestibular & cochlear parts leave the ventral surface of brain
stem through the pontomedullary sulcus (lateral to facial nerve),
run laterally in posterior cranial fossa and enter the internal
acoustic meatus along with 7th nerve.
54. Vestibular Nerve
• The vestibular nerve fibers make
dendritic contact with hair cells of the
membranous labyrinth.
• Their cell bodies (1st order neurons)
are located in the vestibular
ganglion within the internal auditory
meatus.
• Their central processes:
1. Mostly end up in the lateral,
medial, inferior and superior
vestibular nuclei (2nd order
neurons) of the rostral medulla,
located beneath the lateral part
of the floor of 4th ventricle
2. Some fibers go to the
cerebellum through the inferior
cerebellar peduncle
1
2
55. Cochlear (Auditory) Nerve
• The cochlear nerve fibers
make dendritic contact with
hair cells of the organ of
Corti within the cochlear
duct of the inner ear.
• Their cell bodies (1st order
neurons) are located within
the cochlea in the spiral
ganglion.
• Their central processes
terminate in the dorsal and
ventral cochlear nuclei (2nd
order neurons), which lie
close to the inferior
cerebellar peduncle (ICP)
ICP
ICP
56. • Lesion of vestibulocochlear nerve produces deafness
(disturbnce of cochlear nerve functions), tinnitis, vertigo,
dizziness, nausea, nystagmus, loss of balance and ataxia
(disturbnce of vestibular nerve functions)
Acoustic neuroma: a benign tumour of 8th nerve leads to
compression of the nerve leading to attacks of dizziness,
and profound deafness and ataxia
• The representation of cochlea is essentially bilateral at all
levels rostral to the cochlear nuclei
• Lesions anywhere along the pathway usually have no
obvious effect on hearing.
• Deafness is essentially only caused by damage to the
middle ear, cochlea, or auditory nerve.
58. Neurofibromatosis (NF2)
• Bilateral acoustic neuromas (tumors of the
vestibulocochlear nerve or cranial nerve VIII also known as
schwannoma) develop, often leading to hearing loss
• Multiple inherited schwannomas and meningiomas
59. Stem Cells Restore Hearing
Human stem cells regenerate auditory nerve cells in gerbils
60. Traveling wave of Bekesy
• Discovered by Gyorgy Von Bekesy (1947) (audiometer)
• As sound wave is transmitted to the oval window (where stapes is
attached), this sets the perilymph into motion within the cochlea
causing a rhythmic vibration of the basilar membrane, which stimulates
the hair cells.
• Each point in the basilar membrane moves at the same frequency as the
stimulus
• Each frequency creates a different pattern of frequency
– Higher frequency = more vibrations; interpreted at the proximal portion of
cochlea
– Lower frequency = less vibrations; distal portion of cochlea
– Base (high frequency); apex (low frequency)
62. • Central Pathways
• Cochlear neucleus
• Superior olivary complex
• Lateral lemniscus
• Inferior colliculus
• Medial geniculate bodies
• Auditory cortex (Brodmann’s areas
41 and 42)
63. Etiologies
• Central auditory processing disorders
– Brainstem
– Cerebrum
– Corpus callosum
• Learning disorders
• Vascular
– Stoke
• Head trauma
• Tumors
64. Nonorganic Hearing Loss
• Sometimes referred to as functional,
• No physical evidence of hearing loss
• Conscious and unconscious
• Adults: medical/legal reasons
• Children: attention, psychological, reward, etc.
65. 66
How Sound Travels Through The Ear...
1. Acoustic energy, in the form of sound waves, is channeled into the ear canal by the
pinna
2. Sound waves hit the tympanic membrane and cause it to vibrate, like a drum,
changing it into mechanical energy
3. The malleus, which is attached to the tympanic membrane, starts the ossicles into
motion
4. The stapes moves in and out of the oval window of the cochlea creating a fluid motion
5. The fluid movement causes membranes in the Organ of Corti to shear against the
hair cells
6. This creates an electrical signal which is sent up the Auditory Nerve to the brain
The brain interprets it as sound!
68. Acoustics
Sound
• It is the energy waves of particle displacement, both compression (more
dense) and rare
action (less dense) within an elastic medium; triggers sensation of hearing.
Amplitude of sound
• extent of vibratory movement from rest to farthest point from rest in
compression and rare faction phases of energy waves.
Intensity of sound
• It is the amount of sound energy through an area per time; refers to sound
strength or magnitude; psychoacoustic correlate is loudness.
69. Sound pressure
• sound force (related to acceleration) over a surface per unit
time.
Decibel (dB)
• unit to express intensity of sound; more specially the
logarithm of the ratio of two sound intensities. One-tenth of
a Bel (named for Alexander Graham Bell).
70. Frequency
• The number of cycles (complete oscillations) of a vibrating
medium per unit of time; psychoacoustic correlate is pitch.
Time of one cycle is period.
Hertz (Hz)
• in acoustics, unit to express frequency (formerly cycles per
second or cps).
71. • Human ear capable of hearing from approximately 20 to 20,000 Hz.
• Pure tone: single-frequency sound; rarely occurs in nature.
• Complex sound: sound comprising more than one frequency.
• Noise: aperiodic complex sound. Types of noise frequently used in
clinical audiology
72. Tuning Fork Tests
• The most useful fork is the 512-Hz fork. A 256-Hz fork
may be felt rather than heard.
• In addition, ambient noises are also stronger in the low
frequencies, around 250 Hz. It is essential to striking the
fork gently to avoid creating overtones.
73. Weber Test
• It is a test of lateralization.
• The tuning fork is set into motion and its stem is placed on
the midline of the patient’s skull.
• patient must state where the tone is louder
74. A. Normal hearing or equal amounts of hearing loss in both
ears (conductive, sensorineural, or mixed loss) will
experience a midline sensation.
B. Unilateral sensorineural loss will hear the tone in the better
ear.
C. Unilateral conductive loss will hear the tone in the poorer
ear.
75. Rinne test
• A test compares a patient’s air and bone conduction hearing.
• The tuning fork is struck and its stem placed rst on the mastoid
process (as closely as possible to the posterosuperior edge of the
canal without touching it), then approximately 2 inch (5 cm) lateral to
the opening of the external ear canal.
• patient reports whether the tone sounds louder with the fork on the
mastoid or just outside the ear canal.
76. • Normal hearing or sensorineural hearing loss will perceive the tone as
louder outside the ear canal (positive Rinne).
• Conductive hearing loss will perceive the sound as louder when placed on
the mastoid (negative Rinne).
A negative Rinne with the 512-Hz fork indicates a 25-dB or greater
conductive hearing loss.
A negative Rinne with a 256-Hz fork implies an air–bone gap of at least 15
dB.
A negative Rinne with a 1024-Hz fork suggests an air–bone gap of 35 dB
or more.
