them, line the fluid-filled inner chamber of the
cochlea. The membrane that contains the hair cells
is the organ of Corti. Sound waves activate the hair
cells, which convert the stimulation into nerve sig-
nals. The nerve signals converge at the cochlear
nerve, which carries them to the vestibulocochlear
nerve (eighth cranial nerve) for transport to the
BRAIN. The hair cells are very sensitive and vulnera-
ble to damage from excessive noise. The longest of
the hair cells are those that respond to sounds in
the decibel range of normal speech; because of their
length, they are the most vulnerable to such dam-
age. Hair cells also break off with aging. Damaged
cochlear hair cells do not regenerate.
For further discussion of the cochlea within the
context of otolaryngologic structure and function,
please see the overview section “The Ear, Nose,
Mouth, and Throat.”
See also AGING, OTOLARYNGOLOGIC CHANGES THAT
OCCUR WITH; COCHLEAR IMPLANT; CRANIAL NERVES;
HEARING LOSS; PRESBYCUSIS.
cochlear implant An inner EAR prosthesis to
provide a degree of hearing ability for those who
have profound HEARING LOSS—greater than a 90
decibel (dB) loss of hearing—in both ears and
receive no benefit from hearing aids. This tiny
electronic device receives incoming sound waves
and translates them into frequency impulses that
stimulate undamaged auditory nerve fibers that
remain within the COCHLEA. The NERVEfibers con-
vey the impulses to the BRAINvia the cochlear
nerve. Though there are several designs of
cochlear implant, all feature external components
and internally implanted electrodes.
Because the nerve fibers within the cochlea are
limited the impulses those fibers convey to the
brain are also limited, leaving “gaps” in speech.
Over time, the person learns where these gaps are
and learns to interpret many of them into intelligi-
ble units of language. It can take adults several
years to develop proficient hearing skills. The level
of restored hearing generally correlates to the
length of time between the onset of profound
hearing loss and placement of the cochlear
implant. Children who receive cochlear implants
typically learn or regain language understanding
and speech skills more quickly than adults,
though children who have been profoundly deaf
since birth (prelingual loss of hearing) typically do
not acquire hearing and speaking skills compara-
ble to those of children who have normal hearing.
See also AUDIOLOGIC ASSESSMENT; SIGN LANGUAGE.cold sore An eruption of the HERPES SIMPLEX
virus 1 (HSV1) in the form of a sore with a crusty
scab, most commonly on the lips. Less commonly
HSV2, the variation of the herpes simplex VIRUS
that causes GENITAL HERPES, causes sores around the
MOUTH. Which variation of the herpes virus that is
responsible does not matter. People sometimes
refer to cold sores as FEVERblisters because they
tend to appear with fever or during viral infections
such as COLDS; doctors believe viral infections are
among the triggers that activate HSV1. Hormonal
shifts during MENSTRUATIONand exposure to the
sun also appear to activate HSV1.
HSV1 lies dormant in the nerve endings in the
SKINnear the sites where cold sores have previ-
ously occurred and, when activated, causes new
sores to erupt. Many people experience itching or
tingling at the site in the 24 to 36 hours before a
cold sore erupts. Doctors call this the prodrome
stage. When sores are present the herpes virus is
highly contagious and easily spread to other body
locations as well as to other people through con-
tact or shared items such as drinking glasses,
straws, and eating utensils. Rubbing the EYEafter
finger contact with a cold sore can spread the
virus to the eye, where it can infect the CORNEA
and cause scarring that can lead to blindness. Fre-
quent HAND WASHINGis an effective method for
restricting the spread of the virus.
Treatment options are limited. Doctors may
prescribe ANTIVIRAL MEDICATIONS for recurrent or
severe episodes of cold sores. These medications
appear to shorten the course of the INFECTIONfrom
the usual 7 to 10 days to 3 to 5 days when taken
or applied at the first indication (ideally in the
prodrome stage) of activation. Numerous topical
products to provide relief and moisturization are
available over the counter, though these prepara-
tions do not shorten the course of the infection.
Some people have fewer cold sores when they
take lysine supplements. Cold sores typically heal
without scarring or other complications.cold sore 17