Anatomy Physiology and
Disorders of the Hearing
Perry C. Hanavan, Au.D.
Audiologist
Major Divisions of the Ear
Peripheral Mechanism
VIII
Outer Middle Inner
Cranial
Ear
Ear
Ear
Nerve
Central Mechanism
Brain
Question
What is the purpose of the pinna?
A. Cosmetics
B. Sound collector
C. Same side localization
D. A and B
E. A, B and C
Outer Ear
Virtual Tour of the Ear
Pinna
Pinna
Preauricular Tags
Preauricular Pits
EAM
External
Auditory
Meatus
Cerumen
Q-tips
Function
Microtia
EAM resonance
Anotia
Atresia
Pinna
Question
Another name for pinna?
A. External auditory meatus
B. External auditory canal
C. Ear lobe
D. Auricle
E. None of the above
Function of Outer Ear
•
•
•
•
•
Collect sound
Localization
Resonator
Protection
Sensitive
(earlobe)
• Other?
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
External Auditory Meatus
• Extends from the pinna to the tympanic membrane
– About 26 millimeters (mm) in length and 7 mm in diameter in
adult ear.
– Size and shape vary among individuals.
• Protects the eardrum
• Resonator
– Provides about 10 decibels (dB) of gain to the eardrum at around
3,300 Hertz (Hz).
• The net effect of the head, pinna, and ear canal is that
sounds in the 2,000 to 4,000 Hz region are amplified by 10
to 15 dB.
– Sensitivity to sounds greatest in this frequency region
– Noises in this range are the most hazardous to hearing
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
Question
Cerumen should be routinely removed from
the ear canal?
A. True
B. False
Cerumen
• The purpose of wax:
– Repel water
– Trap dust, sand particles, microorganisms, and other debris
– Moisturize epithelium in ear
canal
– Odor discourages insects
– Antibiotic, antiviral, antifungal
properties
– Cleanse ear canal
Embryological Development
• External Ear Development
Disorders of the Outer Ear
Accessory auricle
Additional pinna or auricular tissue
Anotia
Congenital absence of pinna
Cleft pinna
Congenital fissure of the pinna
Coloboma lobuli
Congenital fissure of the earlobe
Macrotia
Congenital excessive enlargement of the auricle
Microtia
Congenital small pinna
Melotia
Congenital displacement of the pinna
Low-set-ears
Congenitally displaced pinna
Polyotia
Additional pinna on one or both sides
Preauricular tags
Small appendage anterior to pinna
Scroll ear
Rim (helix) of pinna is rolled forward and inward
Outer Ear Hearing Disorders
• Outer ear
• CHARGE
• Down Syndrome
– Ears small and low set
• Fetal Alcohol
Syndrome
– Deformed ears
• DiGeorge syndrome
– Low set ears
Grow Ear?
External Ear Care
Hazardous to health:
• Ear candling
• Swabs
• Foreign objects
Time of Onset
Congenital
Present at birth
Acquired
Occurring after birth
Adventitious
Occurring after birth
Acute
Sudden onset or short duration
Chronic
Long duration
Sudden
Rapid onset
Gradual
Occurring slowly
Temporary
Limited duration
Permanent
Irreversible
Progressive
Increasing in degree over time
Fluctuating
Increasing and decreasing in degree of loss
Middle Ear
The function of the middle ear is to?
A. Cause middle ear infections in young
children
B. Amplify sounds
C. Interpret sounds
D. Analyze sounds
E. None of the above
Middle Ear
The Eustachian tube is a part of the middle
ear?
A. No, it is a part of the inner ear
B. No, it isn’t part of the hearing mechanism
C. Yes
D. I don’t know
Middle Ear
Which is not true?
A. There are two middle ear muscles
B. There are three ossicles
C. There are three layers of
tympanic membrane tissue
D. The acoustic reflex occurs from
soft sounds
E. The stapes is the smallest bone in
the human body
Middle Ear
Virtual Tour of the Ear
Middle Ear Cavity
Tympanic Cavity
Tympanic Membrane
Ossicles
Middle Ear Muscles
Eustachian Tube
Mastoid
Ossicles
Middle Ear Muscles
Mastoid
Eustachian Tube
Function
Amplifier
Cholesteatoma
Temporal bone fractures
Otitis Media
PE tubes
Otosclerosis
Function of Middle Ear
• Conduction
– Conduct sound from the outer ear to the inner ear
• Protection
– Creates a barrier that protects the middle and inner areas from
foreign objects
– Middle ear muscles may provide protection from loud sounds
• Transducer
– Converts acoustic energy to mechanical energy
– Converts mechanical energy to hydraulic energy
• Amplifier
– Transformer action of the middle ear
– only about 1/1000 of the acoustic energy in air would be
transmitted to the inner-ear fluids (about 30 dB hearing loss)
The middle ear:
A. Converts acoustic energy to hydraulic
B. Converts hydraulic energy to mechanical
C. Converts acoustic energy to mechanical
D. Converts acoustic energy to electrical
E. Converts mechanical to electrical
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
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
The pars tensa portion of the TM:
A. Consists of 2 layers of tissue
B. Consists of 4 layers of tissue
C. Consists of 1 layer of tissue
D. Consists of 3 layers of tissue
E. Consists of 5 layers of tissue
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.
The Eustachian tube:
A. Opens when one yawns
B. Opens when one smiles
C. Opens when one blinks
D. It is always open
E. Never opens
Ossicles
• Malleus
(hammer)
• Incus (anvil)
• Stapes
(stirrup)
smallest
bone of the
body
The middle ear amplifies sound:
A. About 15 dB
B. About 25 dB
C. About 35 dB
D. About 20 dB
E. About 40 dB
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)
Transformer/Amplifier
• Area ratio
– Thumbtack
• Lever
– crowbar
Which provides the most
amplification in the middle ear?
A. The lever hypothesis
B. The area/ratio hypothesis
C. The Hanavan principle
D. I don’t know
E. None of the above
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"
The VII cranial nerve innervates:
A. Tensor tympani muscle
B. Incus
C. Stapedial muscle
D. Malleus
E. Stapes
The tensor tympani:
A. Innervated by the facial nerve
B. Innervated by the trigeminal nerve
C. Innervated by the VII cranial nerve
D. Innervated by the VIII cranial nerve
E. Innervated by the VI cranial nerve
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
Mastoid
Mastitis
A. Inflammation of the mastoid
B. Inflammation of the breast
C. Cancer of the mast cells
D. A and B
E. B and C
Question
The correct order of the ossicles from the TM
to inner ear is?
A. Anvil, hammer, stapes
B. Hammer, incus, anvil
C. Hammer, anvil, stapes
D. Stapes, anvil, hammer
E. Malleus, stapes, incus
Development of Middle Ear
• Middle Ear Development
Middle Ear Disorders
• Middle Ear disorders
–
–
–
–
–
–
–
–
–
Acute otitis media
Otosclerosis
Disarticulation
Mastoiditis
Tympanosclerosis
OME
TM Perforation
TM Retraction
Cholesteatoma
• Down Syndrome
• Treacher Collins Syndrome
• BOR Syndrome
OM/OME
Cholesteatoma
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.
Question
The Amy Tan syndrome is:
A. Down syndrome
B. BOR syndrome
C. Treacher Collins syndrome
D. Measles syndrome
E. Waardenburg syndrome
Question
The function of the inner ear:
A. Balance
B. Hearing
C. Touch
D. All the above
E. A and B
Inner Ear
Virtual Tour of the Ear
Vestibular
semicircular canals
Auditory
utricle and saccule
Cochlear
traveling wave
Vestibular
traveling wave
traveling wave
pathologies
Function of Inner Ear
• Convert mechanical sound
waves to neural impulses
that can be recognized by
the brain for:
– Hearing
– Balance
Balance
• Linear motion
• Rotary motion
Question
Which is true about the inner ear
and balance?
A. The semicircular canals detect
linear motion
B. The utricle and saccule detect
linear motion
C. The cochlea detects linear motion
D. The utricle and saccule detect
rotary motion
Cochlea
• The cochlea resembles a
snail shell and spirals for
about 2 3/4 turns around
a bony column
• Within the cochlea are
three canals:
– Scala Vestibuli
– Scala Tympani
– Scala Media
Question
The channel that houses the organ of Corti:
A. Scala tympani
B. Scala media
C. Scala vestibuli
D. Semicircular canals
E. B and D
Anatomy of the adult mammalian cochlea
Barald, K. F. et al. Development 2004;131:4119-4130
Organ of Corti
Organ of Corti
Organ of Corti
OHC vs. IHC Function
OHC Motility Models
Afferent Neural Innervations
Hair Cells
• Outer Hair
Cells
• Inner Hair
Cells
• OHC
movie
OCH Cilia Theory: Tip-links
<<<IHC
OHC >>>
OHC Cilia: Tip-links
Tip Link Protiens
Stereocilia
Stereocilia move sideways and lengthen (Oct 2, 2012)
Flexoelectric Effect
• Quiet sounds are magnified by bundles of tiny, hair-like
tubes atop "hair cells" in the ear (stereocilia: when the
tubes dance back and forth, they act as "flexoelectric
motors" that amplify sound mechanically.
• "It's like a car's power steering system. "
– " You turn the wheel and mechanical power is added.
Here, the incoming sound is like your hand turning the
wheel, but to drive, you need to add power to it. These
hair bundles add power to the sound. If you did not have
this mechanism, you would need a powerful hearing aid.“
– http://www.medicalnewstoday.com/articles/147081.php
OHC Somatic Motility
Question
Which cells are motile?
A. Brain cells
B. Inner hair cells
C. Outer hair cells
D. B and C
E. None of the above
OHC—With and Without Prestin
• No other cells
except OHC
• Prestin is the
motor protein
of mammalian
OHCs.
• It is highly
expressed in
OHC, and is
not expressed
in nonmotile
IHC.
OHC—With and Without Prestin
About 55 dB
difference
OHC in Prestin
Knockout
Mouse
Traveling Waves
•
•
•
•
Traveling wave
Basilar membrane
Traveling Wave info
Cochlear Traveling Wave
Question
High frequencies stimulate this part of inner
ear:
A. Apical portion of inner ear
B. Basilar portion of inner ear
C. Utricle
D. Saccule
E. Semicircular canals
Inner Ear Etiologies
• Genetic
– Connexin 26
• Excessive Noise
• Head Trauma
• Metabolic
– Diabetes, kidney disfunction, thyroid dysfunction
• Ototoxic
– Gentamiacin, cisplatin, etc.
• Disease
Connexin 26
Noise Trauma
Question
Persons with diabetes are at greater risk for
hearing loss…this would be?
A. Metabolic
B. Noise related
C. Ototoxic
D. Genetic
E. Acoustic trauma related
Question
Persons with Connexin 26 are at greater risk
for hearing loss…this would be:
A. Metabolic
B. Noise related
C. Ototoxic
D. Genetic
E. Acoustic trauma related
Developmental
• Inner Ear Embryological Development
Question
The hearing nerve is located in:
A. Eustachian tube
B. External auditory meatus
C. Internal auditory meatus
D. Organ of Corti
E. Tympani
Question
The auditory nerve is which cranial nerve:
A. VI
B. VII
C. VIII
D. V
E. X
VIII Cranial Nerve
Virtual Tour of the Ear
Auditory Branch
Auditory Branch
Vestibular Branch
Vestibular Branch
Spiral ganglion
Acoustic Tumors
Standard ABR
Cross-section of Internal Auditory
Canal
Sup. Vest Nerve
Facial Nerve
HIGHFREQUENCY
FIBERS
Acoustic Nerve
Large Tumor
Abnormal Standard ABR
TUMOR
The wave V latency used in the
standard ABR IT5 and I-V delay
measures is dominated by neural
activity from the high-frequency
regions of the cochlea. Thus, unless
the tumor affects these high-frequency
fibers sufficiently, standard ABR
latencies will be normal.
Inf. Vest Nerve
Small Tumor
Abnormal Standard
ABR
Small Tumor
Normal Standard ABR
IAM
VIII Cranial Nerve
Spiral Ganglion
Question
The Auditory Nerve is:
A. V Cranial Nerve
B. VI Cranial Nerve
C. VII Cranial Nerve
D. VIII Cranial Nerve
E. IX Cranial Nerve
Acoustic Neuroma
• Tumor
Acoustic Neuroma
Question
Another term for acoustic tumor:
A. VII cranial nerve tumor
B. Vestibular schwannoma
C. Facial nerve tumor
D. Ear schwannoma
Stem Cells Restore Hearing
Human stem cells regenerate auditory nerve cells in gerbils
Central Auditory Mechanism
Virtual Tour of the Ear
Auditory Path
Auditory Path
Central Auditory Path
Auditory Pathway - CNS
Tonotopic
Etiologies
• Central auditory processing disorders
– Brainstem
– Cerebrum
– Corpus callosum
• Learning disorders
• Vascular
– Stoke
• Head trauma
• Tumors
Nonorganic Hearing Loss
• Sometimes referred to as functional,
feigning, etc.
• No physical evidence of hearing loss
• Conscious and unconscious
• Adults: medical/legal reasons
• Children: attention, psychological, reward,
etc.
Development of the otocyst
Barald, K. F. et al. Development 2004;131:4119-4130
Inductive interactions that regulate otocyst induction and ventral patterning
Barald, K. F. et al. Development 2004;131:4119-4130
Development of the cochlear duct and organ of Corti
Barald, K. F. et al. Development 2004;131:4119-4130
Effects of modulating gene expression on development of the organ of Corti (OC)
Barald, K. F. et al. Development 2004;131:4119-4130
Generation of stereociliary bundle orientation
Barald, K. F. et al. Development 2004;131:4119-4130
Six1 expression during inner ear development
Zheng, W. et al. Development 2003;130:3989-4000