Anatomy Physiology and Disorders of the Hearing

Perry C. Hanavan, Au.D.

Audiologist

Major Divisions of the Ear

Peripheral Mechanism Central Mechanism

Outer Ear

Middle Ear

Inner Ear

VIII Cranial Nerve

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

Pinna

External Auditory Meatus

Virtual Tour of the Ear

Pinna

Preauricular Tags

Preauricular Pits

EAM

CerumenQ-tips

Microtia

Anotia

Atresia

Function

EAM resonance

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, micro-

organisms, 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

Tympanic CavityTympanic Membrane

OssiclesMiddle Ear Muscles

Eustachian TubeMastoid

Virtual Tour of the Ear

Middle Ear Cavity

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

Auditory

Vestibular

Virtual Tour of the Ear

Vestibular

semicircular canals

utricle and saccule

Cochlear

traveling wave

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

Barald, K. F. et al. Development 2004;131:4119-4130

Anatomy of the adult mammalian cochlea

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

Auditory BranchVestibular Branch

Virtual Tour of the Ear

Auditory Branch

Vestibular Branch

Spiral ganglion

Acoustic Tumors

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.

TUMOR

Large TumorAbnormal Standard ABR

Small TumorAbnormal Standard

ABR

Small TumorNormal Standard ABR

Standard ABR

HIGH-FREQUENCY

FIBERS

Facial Nerve Sup. Vest Nerve

Inf. Vest NerveAcoustic Nerve

Cross-section of Internal Auditory Canal

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

Auditory Path

Virtual Tour of the Ear

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.

Barald, K. F. et al. Development 2004;131:4119-4130

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

Zheng, W. et al. Development 2003;130:3989-4000

Six1 expression during inner ear development