N

nasal polyp A noncancerous, fleshy growth
within the interior NOSE. Polyps are outgrowths of
the mucous membrane and extend from the
membrane on a stemlike projection called a pedi-
cle. Polyps have a rich BLOODsupply and bleed eas-
ily. Because of this and because there is a chance
for them to become cancerous over time, doctors
prefer to surgically remove them. Nasal polyps
that form in the air passages and SINUSES can
obstruct the flow of air, interfering with BREATHING.
Chronic irritation (such as from ALLERGIC RHINITIS)
and INFECTION(such as SINUSITIS) seem to encourage
the growth of polyps; treating the underlying con-
ditions helps prevent polyps from recurring. Mul-
tiple nasal polyps are common in people who
have CYSTIC FIBROSIS.
See also INTESTINAL POLYP; VOCAL CORD POLYP.

nasal vestibulitis A bacterial INFECTION of the
HAIRfollicles around the base of the nostrils that
results in INFLAMMATIONand irritation of the tis-
sues. Symptoms include redness, swelling, and
PAIN. Sometimes the tissue becomes raw and
bleeds. Nasal vestibulitis typically develops with
extended sneezing and nose blowing such as
occurs with COLDSand ALLERGIC RHINITIS. Treatment
with topical and occasionally oral ANTIBIOTIC MED-
ICATIONSgenerally resolves the infection within 10
to 14 days, though symptoms should improve
within 2 or 3 days. Most people experience com-
plete recovery with no residual complications,
though occasionally an ABSCESS develops that
requires further medical care.
See also BLOWING THE NOSE; SNEEZE.

noise exposure and hearing Excessive exposure
to noise can temporarily or permanently damage
hearing. Excessive noise exposure is the most pre-

ventable cause of HEARING LOSSand accounts for as

much as 60 percent of impaired hearing ability.

Several natural mechanisms attempt to protect

the EARfrom damage due to loud noises. The tym-

panic REFLEXserves to stiffen the structures of the

middle ear, reducing their ability to amplify

sound. In response to a loud noise, two muscles in

the middle ear reflexively contract. The tensor

tympani MUSCLE pulls on the malleus, and the

stapedius muscle pulls on the stapes—the first and

third bones, respectively, of the auditory ossicles.

The effect of this reflex straightens the ossicular

chain (the sequence of the ossicles), restricting the

movement of the bones and dampening their abil-

ity to amplify and transfer sound waves. The ear

also may experience a temporary threshold shift

in response to sudden loud noises, such as gun-

shots and fireworks. The burst of noise appears to

stun the HAIRcells, rendering them nonresponsive

to sound waves in the relevant frequency range. A

temporary threshold shift causes sounds to seem

muffled. As long as there is no further exposure to

loud noise, the hair cells gradually return to func-

tion and hearing returns to normal. However,

continued or repeated exposure results in the

damage becoming permanent.

Measuring Sound Volume

The unit of measure for sound volume is the deci-

bel (dB). The decibel system is logarithmic; each

increase of 10 dB represents a 10-fold increase in

sound volume. A noise that measures 60 dB, such

as the sound of normal conversation, is 10 times

louder than a noise that measures 50 dB, such as

the sound of falling rain. A clap of thunder, 120

dB, is 10 times louder than shouting directly into

someone’s ear, 110 dB. A rock concert (130 dB) is

10 times louder than thunder.

36