Download CCC 11 Ear

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Outer Ear
Middle Ear
Inner Ear
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1. OUTER EAR consists of the PINNA and the
EXTERNAL AUDITORY CANAL.
The pinna is the cartilage of the ear; it acts as a
funnel to capture the sound.
If you cup your hands to your ears (do it now),
you’ll notice the sound of my voice is louder.
If you rolled up a piece of paper like a funnel
and put it to your ear, it functions like the
pinna.
The transmission of sound vibrations through
the outer ear occurs chiefly through AIR.
The Outer (External) Ear
Figure 16.17a
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2. MIDDLE EAR is an AIR filled space with
structures.
The TYMPANIC MEMBRANE (ear drum)
vibrates in response to sound.
Attached to it are 3 bones: The MALLEUS
(hammer), INCUS (anvil), and the STAPES
(stirrup) are the smallest bones in the body.
Together, they are only one inch long.
Their function is to amplify sound
vibrations. The malleus vibrates the incus,
which vibrates the stapes.
Structures of the Middle Ear
Figure 16.17b
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The middle ear is open to the nasopharynx by
way of the AUDITORY TUBE (also called
eustachian tube or nasopharyngeal tube),
which is only the thickness of a pencil lead.
If this tube is closed, the ears feel plugged up.
The function of the auditory tube is to equalize
the pressure of the middle ear and the outside
air so the ear bones can vibrate.
Tubes are put in the tympanic membrane to
drain fluids in kids with frequent ear infections.
Structures of the Middle Ear
Figure 16.17b
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3. INNER EAR exists within the temporal
bone (petrous portion).
It is a complex structure. It is located in a
bony cavity called the BONY LABYRINTH
(“maze”).
The bony labyrinth is filled with a fluid called
PERILYMPH, which is similar to CSF. The bony
labyrinth is the only place where perilymph is
found.
The Inner (Internal) Ear
Figure 16.17b
Inner Ear
• Within the bony labyrinth is a snail-shaped
structure, called the MEMBRANOUS
LABYRINTH, which is filled with ENDOLYMPH.
• The snail-shaped structure is divided into two
main components. One is the COCHLEA (“snail
shell”). This is responsible for hearing.
• The other structure is responsible for balance
and consists of three parts:
– Semicircular Canals
– Utricle
– Saccule
Semicircular canals:
Utricle
Saccule
Vestibulocochlear
nerve
Cochlea
Stapes
Instead of drawing the cochlea curled up,
I’ve drawn it laying out straight.
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Inside the cochlea are special neurons called
HAIR CELLS; their axons form CN VIII.
The stapes is attached to the OVAL WINDOW,
and vibrations cause the endolymph to
vibrate; the hair cells here transmit this
vibration.
Therefore the HAIR CELLS in this region are
receptors for HEARING.
COCHLEA
Hair Cells
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Low frequencies (like the longer strings of a
piano) cause a response in the tip of the
cochlea.
High frequencies cause a response at the
larger end of the cochlea.
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The axons of the hair cells form CN VIII, the
VESTIBULOCOCHLEAR NERVE, which takes the
signals to the brain.
Therefore, the cochlea is where the hearing
receptors are located, so the cochlea is
responsible for all of the hearing of sounds.
However, the ear does more than just hear; it
is also responsible for balance and
equilibrium.
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This system regulates balance.
It is also within the inner ear.
SEMI-CIRCULAR CANALS (Three of them, all in
different planes) determine movement in
three planes.
Within each semi-circular canal is endolymph
and hair cells, whose axons go to the
cerebellum.
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When you move in one direction, like sliding
across the room, the fluid sloshes like a cup
of coffee, and it triggers the hair cells.
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Attached to the semi-circular canals are two joined
structures called the UTRICLE and the SACCULE.
These also contain HAIR CELLS and ENDOLYMPH.
Within the endolymph here are OTOLITHS (“ear
rocks”) which are calcium deposits.
When you stand perfectly upright, these otoliths
fall directly down and bend the HAIR CELLS (a
special type of neuron) on the lower cells. When
you tip your head to the side, they will stimulate
the hairs on that side.
The otoliths stimulate the hair cells to tell you what
position your head is in and give you a sense of
equilibrium.
Therefore, the HAIR CELLS in this region are
receptors for equillibrium and the OTOLITHS are an
essential component of this process.
Anatomy and Function of the Otoliths
Figure 16.21b
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Inflammation of the semi-circular canals give
you a sense of motion when you’re not
moving = VERTIGO (dizziness) or
LABYRINTHITIS.
This can be debilitating.
Sometimes only one canal is affected, so you
only get dizzy if you turn your head one way.
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When your eyes get one set of information
that conflicts with the vestibular structures,
such as when you are high up in the air or
strobe lights flashing, or reading in a car.
Whether the vertigo is from visual or
vestibular disturbances, your body interprets
the signals as a poison invasion, so it initiates
a vomit reflex.
“Cauliflower Ear”
Hematoma auris or Traumatic auricular hematoma
Common in boxers and wrestlers
A blood clot or other fluid collects
under the perichondrium. This
separates the cartilage from the
overlying perichondrium that is its
source of nutrients, causing the
cartilage to die.
This leads to a formation of fibrous
tissue in the overlying skin.
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Conductive hearing loss happens when there
is a problem conducting sound waves
through the outer ear, tympanic membrane
(eardrum) or middle ear (ossicles). It may be
caused from excess wax, damaged eardrum,
or arthritis of the ossicles.
Hearing loss from nerve damage
(sensorineural) is a problem in the
vestibulocochlear nerve (Cranial nerve VIII),
the inner ear, or central processing centers of
the brain.
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Weber Test: only tests unilateral problems. A
tuning fork is touched to the middle of the
forehead:
◦ Nerve damage: sound is heard louder in the normal
ear because the damage is to the nerve, so bone
conduction of the sound is ineffective.
◦ Conductive hearing loss: sound is heard louder in
the problem ear (earwax, etc) because reflected
soundwaves cannot escape the ear canal, so they
penetrate deeper into the inner ear.
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Performed by placing a vibrating tuning fork
on the mastoid process until sound is no
longer heard, the fork is then immediately
placed just outside the ear. Normally, the
sound is audible at the ear, indicating a
positive Rinne test.
If they cannot hear the sound at the ear, it is
a negative Rinne test, and indicates
Sensorineural hearing loss
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A cochlear implant is a small, complex electronic device that can
help to provide a sense of sound to a person who is profoundly deaf
or severely hard-of-hearing. The implant consists of an external
portion that sits behind the ear and a second portion that is
surgically placed under the skin. An implant has the following parts:
A microphone, which picks up sound from the environment.
A speech processor, which selects and arranges sounds picked up
by the microphone.
A transmitter and receiver/stimulator, which receive signals from the
speech processor and convert them into electric impulses.
An electrode array, which is a group of electrodes that collects the
impulses from the stimulator and sends them to different regions of
the auditory nerve.
An implant does not restore normal hearing. Instead, it can give a
deaf person a useful representation of sounds in the environment
and help him or her to understand speech.
http://video.yahoo.com/watch/421542/2418338
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Excess noise
Frequent sinus infections (or allergies)
Medicines
◦ Excess Tylenol or aspirin, antibiotics, sedatives, antidepressants)
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Lack of blood flow (anemia, hypertension, diabetes, age)
Drugs (marijuana, caffeine)
Foods (soy, wheat, chocolate, red wine)
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Symptoms of nerve damage:
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◦ Tinnitus: ringing in the ears
◦ If damage is not severe, axons can regenerate and tinnitus will
go away
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The rest of this lecture is not test material
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The stapes becomes fixed, cannot move, and
dampens sound conduction.
Stapedotomy: A portion of the stapes is
removed and replaced with a titanium-nickel
prosthesis.
Stapedotomy
Stapedotomy
Prosthesis
Stapedotomy
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Hearing damage from headphones is more
common than from loudspeakers, because
people listen at higher volumes.
Even at comparable volumes, hearing damage
from headphones is higher than with
loudspeakers, due to the close coupling of
the transducers to the ears.
How long can you listen at certain
volumes without damage?
90 dbA
92 dbA
95 dbA
97 dbA
100 dbA
102 dbA
105 dbA
110 dbA
115 dbA
8 hrs
6 hrs
4 hrs
3 hrs
2 hrs
1.5 hrs
1 hr
0.5 hr
0.25 hr or less
60 dB
70 dB
80 dB
90 dB
100 dB
110 dB
120 dB
130 dB
140 dB
150 dB
Everyday conversation, ringing telephone.
Restaurant.
Heavy city traffic, alarm clock at 2 feet, factory
noise, vacuum cleaner, garbage disposal.
Subway trains, motorcycle, workshop tools, lawn
mower.
Chain saw, pneumatic drill.
Dance club.
Rock concert speaker sound, sandblasting,
thunderclap.
Jet take off.
gunfire Nerve damage occurs immediately
rock music peak