Download Ear, Hearing and Equilibrium

Ear, Hearing and Equilibrium
Exercise 27
BI 232
Introduction
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Functions: Hearing and
Equilibrium
Mechanoreception:
because the ear receives
mechanical vibrations and
translates them into nerve
impulses
Static equilibrium: able
to determine nonmoving
position
Dynamic equilibrium:
motion is detected
Hearing
Vestibular Portion
Cochlear Portion
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Middle Ear Ossicles (Bones)
Malleus
Incus
Stapes
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Vestibular Complex
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Inner Ear
Composed of three areas:
Cochlea
Vestibule
Semicircular Ducts
(canals)
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Labyrinth
Cochlea- snail shaped
Contains sensory receptors
for hearing, known as the
organ of Corti (spiral organ)
Sensory hair cells are found
in all receptor organs of the
inner ear which contain long
microvilli, called stereocilia
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These can be stimulated by gravitational
forces in the vestibule, turning movements in
the semicircular canals or sound waves in
the cochlea
• The stapes strikes
the oval window of
the cochlea
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Cochlea Uncoiled
oval
window
round
window
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vestibular duct
helicotrema
tympanic duct
Cochlear duct
containing the Organ of
Corti
Stapes pushes on fluid of vestibular duct at oval window
At helicotrema, vibration moves into tympanic duct
Fluid vibration dissipated at round window which bulges
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The
central structure is vibrated (cochlear duct)
Cochlea
Vestibulocochlear
nerve sends
impulses to the
auditory cortex of
the temporal lobe
of brain and
interpreted as
sound
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Organ of
Corti
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Vestibule
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Consists of the utricle and
saccule
Involved in the
interpretation of static
equilibrium and linear
acceleration
Regions known as maculae,
which consist of hair cells
with stereocilia and a
kinocilium grouped together
in a gelatinous mass called
otolithic membrane and
weighted with calcium
caronate stones called
otoliths
Vestibule
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As the head is accelerated
or tipped by gravity, the
otoliths cause the cilia to
bend, indicating that the
position of the head has
changed.
Visual cues play a part in
this also
When visual and
vestibular cues are not
synchronized, a sense of
imbalance or nausea can
occur
Inner Ear
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Semicircular canals
contain sensory receptors
called crista and detect
change in acceleration or
deceleration.
Dynamic equilibrium
3 semicircular ducts, each
at 90 degrees to one
another
Filled with endolymph and
has an expanded base
called an ampulla
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Ampulla of the semicircular canals
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Inside are clusters of hair
cells and supports cells
(crista ampullaris)
These cells have
stereocilia and a
kinocilium enclosed in a
gelatinous material called
the cupula.
As the head is rotated, the
endolymph pushes pushes
against the stereocilia.
Types of Hearing Loss
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Conductive hearing loss occurs when sound is not
conducted efficiently through the outer ear canal to the
eardrum and the bones of the middle ear.
Sensorineural hearing loss occurs when there is damage to
the inner ear (cochlea) or to the nerve pathways from the
inner ear to the brain.
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Weber Test
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Ring tuning fork and place on
center of head. Ask the subject
where they hear the sound.
Interpreting the test:
Normally, the sound is heard in the
center of the head or equally in
both ears.
Sound localizes toward the poor
ear with a conductive loss
Sound localizes toward the good
ear with a sensorineural hearing
loss
Rinne Test
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Place the vibrating tuning fork on
the base of the mastoid bone.
Ask patient to tell you when the
sound is no longer heard.
Immediately move the tuning fork
to the front of the ear
Ask the patient to tell you when
the sound is no longer heard.
Repeat the process putting the
tuning fork in front of the ear first
Rinne Test
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Normally, someone will hear the vibration in the air
(in front of the ear) after they stop hearing it on the
bone
Conductive hearing loss: If the person hears the
vibration on the bone after they no longer hear it in
the air.
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Bing Test
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Similar to the Rinne Test
Strike the tuning fork and
place it on the mastoid
process.
With your other hand close
off the auditory canal with
pad of finger.
A person with normal
hearing or one with
sensorineurial hearing loss
will hear the sound better
when ear canal is closed.
A person with conductive
hearing loss will not notice a
change in sound
Sound Location
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Have lab partner sit with
eyes closed.
Strike the tuning fork with
a rubber reflex hammer
above head.
Have partner describe to
you where the sound is
located.
Try the following
locations: behind head,
right side, left side, in front
of head, below chin
Postural Reflex Test
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Unexpected changes that move the body away from a
state of equilibrium cause postural reflexes to
compensate for that change.
Important for maintaining the upright position of the
body.
Negative feedback mechanisms
Find an area w/o obstacles
Stand on tiptoes and read lab manual
Lab partner should give a little nudge to left or right (not
too hard)
Barany’s Test
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Tests visual responses to
changes in dynamic
equilibrium.
Place subject in a swivel
chair with four or five
students close by.
Subject sits in chair and tilts
head forward about 30
degrees
Spin the chair about 10
times
Notice twitching of the eyes
(nystagmus) after stopping.
Romberg Test
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Tests static equilibrium
Subject stands with back
to the wall.
Don’t lean on wall
Stand for 1 minute and
have partner watch for
swaying
Do the same exercise
again but have subject
close eyes
The End
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Identify structures on models
View and identify structures on cochlea slides
Make sure that you understand the tests
What cranial nerve is being innervated with the tests
performed in lab?