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External Ear Structures
 Auricle
 Pinna
 Collects

sound waves
Basically like a funnel!
 Elastic
cartilage and skin
composition
 Auditory
canal
 External
acoustic meatus or the
external ear canal
 Guides sound wave to
tympanic membrane
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Middle Ear
Structures
Also referred to as the tympanic cavity

Tympanic Membrane

Ear ossicles
 Eardrum
 Vibrates in response to sound waves,
transmitting vibrations to middle ear
 Connective tissue composition

Malleus, Incus, Stapes


Oval window


Ossicles vibrate in response to vibration of
tympanic membrane
Separates middle ear from inner ear;
stapes connected
Round Window
 Vibrates opposite to vibrations entering the
inner ear through the oval window
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Eustachian Tube


~36 mm in length, ~3 mm in
diameter
Connects middle ear to throat



Closes and opens to equalize
pressure on tympanic membrane
and within middle ear
As you age, tube becomes more
upright (45° angle vs. 10°)
Child’s tube is shorter in length
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Inner Ear Structures

Labyrinth of communicating chambers
Two Divisions
Membranous Labyrinth



Semicircular canals (3): detect balance
of the body
Vestibule: central part of labyrinth;
equilibrium
Bony Labyrinth

Cochlea: coiled canal of dense bone
tissue of the skull; shaped like a snail
 Divided into three fluid-filled parts.
 Two are canals for the
transmission of pressure
 Third is the sensitive organ of
Corti
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Cochlea Chambers

Pressure Canals:

Vestibular canal and tympanic canal

Filled with perilymph



Almost identical to CSF
These canals transmit the movement
of air/vibrations from outer/middle
ear to cause movement of liquid and
the basilar membrane
Organ of Corti

Contains the fluid endolymph
Differs from perilymph in terms of
their electrolytes
 If the membranes are ruptured, mixing
of the fluids causes hearing
impairment
© 2009 The McGraw-Hill Companies, Inc. All rights reserved

Organ of Corti

“A masterpiece of cellular microarchitecture”
Unique strip of epithelial
cells allows for transduction of
auditory signals into nerve
impulses
 Transduction
occurs through
vibrations of structures in the
inner ear causing displacement of
cochlear fluid and movement of
“hair” cells at the organ of Corti
 “Hair”
cells = mechanosensory cells
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Organ of Corti

Projecting from the tops of
the hair cells are tiny finger
like projections
called stereocilia
 Arranged
in a gradated fashion
with the shortest stereocilia
on the outer rows and the
longest in the center.
 This gradation is thought to
be the most important
anatomical feature, allowing
the sensory cells superior
tuning capability
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
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4.
5.
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The Hearing
Process
35-8
Sound waves collected through
external ear canal and funneled to
the tympanic membrane
Waves cause tympanic membrane
to vibrate
Ossicles amplify vibrations
The mechanical energy from movement of the middle ear bones
pushes the oval window in the cochlea.
This force moves the cochlea's fluids that, in turn, stimulate tiny
hair cells of the organ of Corti
Movement of hairs converted into nerve impulses
• Length of
stereocilia stimulated relays information regarding pitch
and amplitude
Impulses are transmitted by auditory nerve to the brain for
interpretation
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
35-9
Equilibrium
Position of Body/Movement
 Above
the cochlea are two interconnecting chambers filled
with endolymph, the sacculus and utriculus – part of the
vestibule
 On their inner surface are patches of hair cells to which are
attached thousands of tiny spheres of calcium carbonate
(CaCO3) – ear stones or otoliths
 Gravity pulls these otoliths downward. As the head is
oriented in different directions, the otoliths shift their
position.
 Impulses
initiated in the hair cells are sent back to the brain.
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Equilibrium (Ctd.)

Motion of the body in regards to balance is detected in the
semicircular canals
Three canals that are found in each body plane (sagittal,
transverse, frontal)
 Contain microscopic hairs, cilia; contain endolymph fluid
 Whenever the head is moved, the fluid within the canals lags;
this stimulates the hair cells to send impulses back to the brain.
 When the hair cells send messages that are incongruent with
what the eyes are seeing and our body is feeling, as may occur
in a boat or aircraft during rough weather, motion sickness can
result  Sensory conflict


Some people also suffer severe dizziness because otoliths
have become dislodged from their utriculus (following a
blow to the head) and settled in a semicircular canal.
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Ear Wax




Cerumen; naturally produced by your body
Produced in sebaceous and modified apocrine
glands of the ear
Coats the ear canal to moisturize it, fight off
infection, keep dust, dirt, and other debris from
getting inside ear
20 to 50 percent fat
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
The Aging Ear






External ear larger / earlobe
longer
Cerumen dryer and prone to
impaction
Ear canal narrower
Eardrum shrinks and appears dull
and gray
Ossicles do not move as freely
Semicircular canals less sensitive
to changes in position – affects
balance
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Hearing Loss
Symptom of a disease, not a normal part of aging
Conductive hearing loss


Interruption in
transmission to inner ear
Causes
 Obstruction
of ear canal
 Infection of middle ear
 Reduced movement of
stirrup
Sensorineural hearing loss


Sound waves not
perceived by brain as
sound
Causes
 Hereditary
 Repeated
exposure to loud
noises / viral infections
 Side effect of medication
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
“Cauliflower Ear”




Cauliflower ear is medically known as
an auricular hematoma.
The external ear is made of cartilage and it
is the shape of the cartilage that gives the
ear its distinctive shell-like shape. The
cartilage is lined by perichondrium, a tight
layer of connective tissue.
Auricular hematoma occurs when the ear
cartilage is injured
Trauma results in fluid or blood collecting
between the perichondrium and the
cartilage. This blood or fluid can become
permanent and scarred, resulting in the
appearance of cauliflower ear.
© 2009 The McGraw-Hill Companies, Inc. All rights reserved