Anatomy of the Ear
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Anatomy of the Ear
Perry C. Hanavan
Audiologist
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Major Divisions of the Ear
Peripheral Mechanism Central Mechanism
Outer Ear
Middle Ear
Inner Ear
VIII Cranial Nerve
Brain
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Question
• Why do we have an outer ear, pinna?
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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
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Pinna
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Function of Outer Ear
• Collect sound• Localization• Resonator• Protection• Sensitive
(earlobe)• Other?
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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
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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
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Outer Ear Resonance
• Influence of pinna (p)• Influence of ear canal
(c) • Combine influence (t)• At 3000 Hz, the final
amplification (t) is 20 dB
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Cerumen
• The purpose of this natural wax:– Repel water– Trap dust, sand particles, micro-organisms, and
other debri– Moisturize epithelium in ear canal– Odor discourages insects– Antibiotic, antifungal properties– Cleanse ear canal
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Embryological Development
• External Ear Development
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Outer Ear Hearing Disorders
• Outer ear• CHARGE• Down Syndrome
– Ears small and low set
• Fetal Alcohol Syndrome– Deformed ears
• DiGeorge syndrome– Low set ears
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External Ear Care
Hazardous to health:
• Ear candling
• Swabs
• Foreign objects
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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
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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)
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Middle Ear
TympanumTimpani, 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. Unlike most drums, they produce a definite pitch when struck. 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
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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
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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.
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Ossicles
• Malleus (hammer)
• Incus (anvil)• Stapes
(stirrup) smallest bone of the body
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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)
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Transformer/Amplifier
• Area ratio– Thumbtack
• Lever– crowbar
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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"
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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
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Development of Middle Ear
• Middle Ear Development
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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
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Inner Ear
Auditory
Vestibular
Virtual Tour of the Ear
Vestibular
semicircular canals
utricle and saccule
Cochlear
traveling wave
traveling wave
traveling wave
pathologies
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Function of Inner Ear
• Convert mechanical sound waves to neural impulses that can be recognized by the brain for: – Hearing– Balance
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Balance
• Linear motion
• Rotary motion
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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
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Barald, K. F. et al. Development 2004;131:4119-4130
Anatomy of the adult mammalian cochlea
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Organ of Corti
• End organ of hearing
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Organ of Corti
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Organ of Corti
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OHC vs. IHC Function
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OHC Motility Models
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Afferent Neural Innervations
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Hair Cells
• Outer Hair Cells
• Inner Hair Cells
• OHC movie
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OCH Cilia Theory: Tip-links
<<<IHC
OHC >>>
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OHC Somatic Motility
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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.
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OHC—With and Without Prestin
About 55 dB difference
OHC in Prestin Knockout Mouse
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Traveling Waves
• Traveling wave
• Basilar membrane
• Traveling Wave info
• Cochlear Traveling Wave
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Inner Ear Etiologies
• Genetic
• Excessive Noise
• Head Trauma
• Metabolic
• Ototoxic
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Connexin 26
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Noise Trauma
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Developmental
• Inner Ear Embryological Development
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VIII Cranial Nerve
Auditory BranchVestibular Branch
Virtual Tour of the Ear
Auditory Branch
Vestibular Branch
Spiral ganglion
Acoustic Tumors
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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
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Spiral Ganglion
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Acoustic Neuroma
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Central Auditory Mechanism
Auditory Path
Virtual Tour of the Ear
Auditory Path
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Central Auditory Path
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Etiologies
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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.
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Barald, K. F. et al. Development 2004;131:4119-4130
Development of the otocyst
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Barald, K. F. et al. Development 2004;131:4119-4130
Inductive interactions that regulate otocyst induction and ventral patterning
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Barald, K. F. et al. Development 2004;131:4119-4130
Development of the cochlear duct and organ of Corti
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Barald, K. F. et al. Development 2004;131:4119-4130
Effects of modulating gene expression on development of the organ of Corti (OC)
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Barald, K. F. et al. Development 2004;131:4119-4130
Generation of stereociliary bundle orientation
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Zheng, W. et al. Development 2003;130:3989-4000
Six1 expression during inner ear development