Transcript ANATOMY AND PHYSIOLOGY OF THE EAR

ANATOMY AND
PHYSIOLOGY OF THE EAR
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Main Components of the
Hearing Mechanism
Outer Ear
 Middle Ear
 Inner Ear
 Central Auditory Nervous System
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Structures of the Outer Ear
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Auricle (Pinna)
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Collects sound
Helps in sound
localization
Most efficient in
directing high
frequency sounds
to the eardrum
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External Auditory Canal
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Approximately 1¼ inch in
length
“S” shaped
Lined with cerumen glands
Outer 1/3rd cartilage; inner
2/3rds mastoid bone
Increases sound pressure at the
tympanic membrane by as
much as 5-6 dB (due to
acoustic resonance)
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Mastoid Process
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Bony ridge behind the
auricle
Provides support to
the external ear and
posterior wall of the
middle ear cavity
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Tympanic Membrane
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Thin membrane
Forms boundary
between outer and
middle ear
Vibrates in response
to sound
Changes acoustical
energy into
mechanical energy
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The Ossicular Chain
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A: Malleus
B: Incus
C: Stapes
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Ossicles are smallest
bones in the body
Act as a lever system
Footplate of stapes
enters oval window of
the cochlea
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Eustachian Tube
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Lined with mucous
membrane; connects middle
ear to back of the throat
(nasopharynx)
Equalizes air pressure
Normally closed except
during yawning or
swallowing
Not a part of the hearing
process
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Stapedius Muscle
Connects the stapes to the middle ear wall
 Contracts in response to loud sounds; known
as the Acoustic Reflex
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Structures of the Inner Ear
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Cochlea - Snail-shaped
organ with a series of fluidfilled tunnels; converts
mechanical energy into
electrical energy
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Structures of the Inner Ear (Cont.)
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Oval Window – located at the footplate
of the stapes; when the footplate vibrates,
the cochlear fluid is set into motion
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Round Window – functions as the pressure
relief port for the fluid set into motion
initially by the movement of the stapes in
the oval window
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Organ of Corti
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The end organ of
hearing; contains
stereocilia and hair
cells.
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Hair Cells
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Frequency-specific
High pitch sounds = base of cochlea
Low pitch sounds = apex of cochlea
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When the basilar membrane
moves, a shearing action
between the tectorial membrane
and the organ of Corti causes
hair cells to bend
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Vestibular System
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Consists of three semicircular canals
Shares fluid with the
cochlea
Controls balance
No part in hearing process
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Central Auditory System
8th Cranial Nerve or “Auditory Nerve”
carries signals from cochlea to brain
 Fibers of the auditory nerve are present in
the hair cells of the inner ear
 Auditory Cortex: Temporal lobe
of the brain where sound is
perceived and analyzed
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How Sound Travels Through
The Ear...
Acoustic energy, in the form of sound waves, is channeled into
the ear canal by the pinna. Sound waves strike the tympanic
membrane, causing it to vibrate like a drum, and changing it
into mechanical energy. The malleus, which is attached to the
tympanic membrane, starts the ossicles into motion. (The
middle ear components mechanically amplify sound). The
stapes moves in and out of the oval window of the cochlea
creating a fluid motion. The fluid movement within the
cochlea causes membranes in the Organ of Corti to shear
against the hair cells. This creates an electrical signal which
is sent via the Auditory Nerve to the brain, where sound is
interpreted!
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QUESTIONS?
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