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Smell
Taste
Hearing, equilibrium (balance)
Vision (separate lecture)
The special senses are those that have their
own organ devoted to them.
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Olfactory receptors are CHEMORECEPTORS; a
special type of neuron which senses particular
chemicals and those are what triggers an action
potential.
Chemoreceptors are at the roof of the nasal cavity.
There are hundreds of thousands of types, and
they can smell a wide variety of substances.
They are extremely sensitive, and can detect parts
per billion, as in the scent of natural gas…just a
few molecules will start an action potential!
The olfactory nerve goes through the cribiform
plate to form the OLFACTORY BULB (one of the
shortest nerves in the body) and into the limbic
system.
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 Scientists
who are trying to find a
way to make neurons divide to
heal nerve injuries often study the
body’s only mitotic neurons
(undergo mitosis).
 These neurons are the olfactory
receptors.
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The Bulgarian man, who
was paralyzed after a
knife attack in 2010,
can walk after doctors
in Poland transplanted
nerve cells from his
nose into his severed
spinal cord.
The successful operation was the first of its
kind for regenerative medicine, and Fidyka is
believed to be the first man to walk again after
having a completely severed spinal cord.
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People who
experience
imaginary odors
have what are
called “unicate
fits”.
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Figure 16.3a, b
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Sensed on taste buds, which are located mostly on the
tongue surface, but are also on the palate, pharynx, and
a few on the lips.
Taste buds have specialized cells, which increase
surface area and use chemoreceptors.
They are surrounded by support cells (like glia). They
synapse on sensory neurons, which go to the facial
nerve (which is a motor nerve!).
Someone with a damaged facial nerve (Bell’s palsy)
cannot easily taste sweet, sour, or salty substances.
Taste buds are the only parts of the nervous system
that can regenerate completely.
The taste information is sent to the primary gustatory
(taste) cortex, located in the parietal lobe of the brain.
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Figure 16.1a, b
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How many different tastes are
there? Dozens. Salt, sweet, bitter,
and sour are only a few.
Where are they located on the
tongue? All tastes are located all
over the tongue.
The picture in the book was drawn
120 years ago by an anatomist
that knew his drawing was not
right; he just wanted to use it as a
starting point for further
experimentation.
You can prove it is wrong by
putting salt on the tip of your
tongue or sugar on the side. Can
you taste it? If so, this picture is
wrong!
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Taste appreciation is also involved in
texture (a mealy apple is not as good),
temperature (cold pizza tastes
different than warm), and smell
(perfume or cigarette smoke clog the
senses and decrease taste).
 There are dozens of taste receptors,
hundreds of thousands of smell
receptors, so the subtly of taste is
from smell.
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Foods people like are in opposite proportion to the
numbers of taste receptors for that.
People that love sweets have FEWER taste receptors
for sweets, so they crave more taste of sweet
things.
If you dislike something, it’s because you have lots
of receptors for it.
Also, as you get older, you become less tolerant of
sweets and more tolerant of bitter tastes (like beer
and coffee).
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The catfish has over 27,000 taste buds. (What
could be so tasty on the bottom of a pond?)
Flies taste with their feet.
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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 through AIR.
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The Outer (External) Ear
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Figure 16.17a
Ear Crease and Heart Disease
•
•
•
A diagonal earlobe crease is a potential indicator of coronary artery disease.
This crease is called “Frank’s sign”
Whereas a “normal” earlobe is smooth, an earlobe with a crease has a fold,
straight line, or wrinkle that appears to cut the earlobe in half.
Having an ear crease predicts an 80% chance of coronary artery disease in
individuals younger than 40 years. The poor vascularity of this area allows it
to show signs of clogged arteries.
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2. MIDDLE EAR is an AIR filled space with
structures.
The TYMPANIC MEMBRANE (ear drum), also
called the tympanum, vibrates in response to
sound.
Attached to it are 3 bones (auditory ossicles):
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.
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Structures of the Middle Ear
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Figure 16.17b
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The middle ear is open to the nasopharynx (back of
the throat) 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 from mucous or has a watery
secretion in it from infection, 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.
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Doctors issue new guidelines
for treating kids' ear
infections, http://fxn.ws/YRnUv
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Structures of the Middle Ear
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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.
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The Inner (Internal) Ear
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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 called the vestibular
system. It is responsible for balance and
consists of three parts:
– Semicircular Canals
– Utricle
– Saccule
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Semicircular canals:
Utricle
Superior
Saccule
Posterior
Vestibulocochlear
nerve (CN VIII)
Lateral
Cochlea
Stapes
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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; that will trigger an action potential in
the hair cells here.
Therefore the HAIR CELLS in this region are
receptors for HEARING.
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COCHLEA
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Hair Cells
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Organ of Corti
• The sensory organ in the cochlea, which sits along the
entire length of the basilar membrane and contains the
sensory hair cells.
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• Within the organ of Corti, there is a
difference in electrical charge (electrical
potential) between inside and outside the
hair cells.
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Organ of Corti
• When the basilar membrane moves in response to
sound waves entering the cochlea, the organ of Corti
moves with it, and this movement causes inner hair cells
in a small area to open tiny transport gates (similar to
trapdoors), which allows electrically charged ions to flow
through. This causes an action potential to be sent along
the auditory nerve to the brain.
• The area from which the action potential arises provides
information to the brain as to the pitch of the sound
(rather as if the organ of Corti was a piano), and the rate
of nerve firing provides information about the loudness of
the sound. ORGAN OF CORTI VIDEO
• HOW HEARING WORKS VIDEO
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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 exits
through the internal acoustic meatus and
takes the signals to the temporal lobe of 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 your head’s
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 when
walking 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 float above
the hair cells, but if you tip your head to the side, they will
land on and stimulate the hairs on that side.
That tells you what position your head is in and gives you a
sense of equilibrium.
Therefore, the HAIR CELLS in this region are receptors for
equilibrium and the OTOLITHS are an essential component of
this process.
The axons travel as the vestibulocochlear nerve, but they will
separate later because they need to get to the cerebellum.
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Anatomy and Function of the Otoliths
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Figure 16.21b
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Inflammation of the semi-circular canals give
you a sense of motion when you’re not
moving. The symptom is called VERTIGO
(dizziness). The diagnosis is LABYRINTHITIS.
This can be debilitating.
Sometimes only one canal is affected, so you
only get dizzy if you turn your head one way.
It can be caused by sinus infections, excess
salt consumption, viral infections, stress. It is
more common in smokers than non-smokers.
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Benign paroxysmal positional vertigo (BPPV)
The Epley maneuver helps relieve the
dizziness and spinning symptoms by moving
the calcium particles out of the sensitive
semicircular canals and into another inner
chamber of the ear, where they don’t cause
symptoms.
The exercise simply involves lying down and
rolling your head in such way so that the
particles fall out.
Epley Maneuver 1
Epley Maneuver 2
http://www.youtube.com/watch?v=ZqokxZRbJfw
http://www.youtube.com/watch?v=pa6t-Bpg494
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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.
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House Ear Clinic
◦ Dr. Luxford
◦ Chapman Ave, Orange
◦ARTIFICIAL EARS VIDEO
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“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 hair cells of 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:
◦ Conductive hearing loss: sound is transmitted
through the bone, and 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.
◦ 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.
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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
VIDEO
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Do NOT hold your nose and blow. That can
rupture the tympanic membrane!
Try chewing gum or swallowing while tilting
head backwards.
You could hold your nose and swallow…that
is gentler than blowing.
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Hearing Loss
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Hearing aids can help with partial hearing loss such as that caused by
chronic noise exposure, but they do so by amplifying sound waves rather
than restoring lost hearing. Most amplify all sound waves equally, which
is why it may be difficult for someone wearing a hearing aid to carry on a
conversation in a noisy restaurant.
Some of the newer and more expensive hearing aids are programmable,
so the level of amplification can be adjusted depending on the noise level
of one's surroundings. Through the use of cochlear implants, there is
hope today for people who have little or no hearing due to cochlear
damage.
A person with a cochlear implant wears a microphone picks up sounds
and sends them to a processor, which relays signals to a small receiver
implanted beneath the scalp. The receiver transmits signals through a
number of electrodes to the origin of the cochlear nerve. Cochlear
implants are not yet capable of producing all of these sounds of normal
hearing, but they do allow people who have them to understand speech
and perceive sounds such as alarms and telephones.
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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.
Cochlear Implant http://www.youtube.com/watch?v=SmNpP2fr57A
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Hearing Loss
• Otitis media is an infection of the middle ear that can lead to
conduction deafness. It typically occurs when an upper
respiratory infection, such as a cold, leads to swelling of the
auditory tibe, creating a vacuum that pulls fluid into the middle
ear. The fluid provides an ideal environment for bacteria or
viruses, and the pressure it exerts causes symptoms such as
pain, ringing in the ears, and hearing loss. The loss is usually
incomplete, and rarely permanent. However, when such
hearing loss occurs in very young children, it can delay their
speech development. If the tympanic membrane ruptures
under pressure, it usually heals on its own in a matter of
weeks. If it does not rupture, fluid may linger in the middle
ear, and in some cases a tube must be surgically inserted for
drainage.
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Hearing Loss
• Noise exposure is a common and usually preventable cause of
nerve deafness. Noise volume is measured in units called decibels.
Any noise above a level of 80 dB could result in damage to the hair
cells of the ear. Eventually, the hair cells disappear completely. If
listening to city traffic for extended periods can damage hearing, it
stands to reason that frequent attendance at rock concerts,
constantly playing a stereo loudly, or using earphones at high
volume is also damaging to hearing. The first sign of danger could
be temporary hearing loss, a feeling of fullness in the ears, muffled
hearing, or ringing in the ears. If you have any of these symptoms,
modify your listening habits immediately to prevent further damage.
If exposure to noise is unavoidable, specially designed noise
reduction earmuffs are available, and it is also possible to purchase
earplugs made from a compressible, spongelike material at the
drugstore or sporting goods store. These earplugs are not the same
as those worn for swimming, and they should not be used
interchangeably.
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Hearing Loss
• Aside from loud music, noisy indoor or outdoor
equipment, such as a rug cleaning machine or a
chainsaw, is also troublesome. Even motorcycles
and recreational vehicles such as snowmobiles
can contribute to gradual loss of hearing.
• Exposure to intense sounds of short duration,
such as a burst of gunfire, can result in an
immediate hearing loss. Hunters may have a
significant hearing reduction in the ear opposite of
the shoulder where the gun is carried. The butt of
the rifle offers some protection to the ear nearest
the gun when it is shot.
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Hearing Loss
• Certain over-the-counter and prescription
drugs have the potential to cause nerve
deafness when taken in combination or
excessive amounts. Such medications
include anti-inflammatory drugs such as
aspirin, ibuprofen, Tylenol, antibiotics,
anticancer drugs, quinine, and certain
blood pressure medications. Sometimes
hearing is restored when a person stops
taking the medication, but in other cases
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the damage is permanent.
Hearing Loss
• One uncommon cause of deafness is
autoimmune inner ear disease. This
occurs when a person's immune system
turns against normal, healthy tissue.
• The person experiences symptoms such
as dizziness and ringing in the ears in
addition to hearing loss. Although it can
be treated with drugs that suppress the
immune system, the drugs themselves can
have serious side effects, and may only
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slow the disease.
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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
◦ http://health.learninginfo.org/tinnitus.htm
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When a person dies, hearing is the last sense
to go. The first sense lost is sight.
The roar that we hear when we place a
seashell next to our ear is not the ocean, but
rather the sound of blood surging through
the veins in the ear.
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Deaf Baby with Hearing Aid:
https://www.youtube.com/watch?v=UUP02yT
KWWo
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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.
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Stapedotomy
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Stapedotomy
Prosthesis
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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.
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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
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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. 8 hrs
Chain saw, pneumatic drill. 2 hrs
Dance club. 30 minutes
Rock concert speaker sound, sandblasting,
thunderclap. 15 minutes or less
Jet take off.
gunfire Nerve damage occurs immediately
rock music peak
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