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Perhaps the most intriguing part
of the hearing process is the hair
cells — “quivering bundles that let us
hear” thanks to their “extreme sensi-
tivity and extreme speed” (Goldberg,
2007). A cochlea has 16,000 of them,
which sounds like a lot until we com-
pare that number with the eye’s 130
million or so photoreceptors. But
consider a hair cell’s responsiveness.
Deflect the tiny bundles of cilia on its
tip by only the width of an atom (!), and
the alert hair cell, thanks to a special
protein, will trigger a neural response
(Corey et al., 2004).
PRACTICE Worldwide, 1.23 billion people are
challenged by hearing loss and an esti-
Argumentation (SP 4) mated half a billion have a disabling
hearing loss (GBD, 2015; Wilson et al.,
(Out of class) How much danger- Susumu Nishinaga/Science Source 2017). Damage to the cochlea’s hair
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
ously loud noise are teens exposed cell receptors or the auditory nerve
to on a daily basis? Have students can cause sensorineural hearing
loss (or nerve deafness). With auditory
explore the following questions: Be kind to your inner ear’s hair nerve damage, people may hear sound
cells When vibrating in response to but have trouble discerning what someone is saying (Liberman, 2015). Sensorineural hear-
• How loud (in decibels) are the sound, the hair cells (shown here lining ing loss is more common than conduction hearing loss from damage to the mechanical
the cochlea) produce an electrical
different levels of volume on signal. system — the eardrum and middle ear bones — that conducts sound waves to the cochlea.
a typical MP3 player? Do the Occasionally, disease damages hair cell receptors, but more often the culprit is biological
changes linked with heredity and aging. I [DM] understand — as one who lives with severe
manufacturers provide this hearing loss passed down from my grandmother and mother, thanks to a single genetic
information? Why or why not? mutation.
Toxic noise, such as prolonged exposure to ear-splitting music, is another culprit. The
• Survey a group of peers who cochlea’s hair cells have been likened to carpet fibers. Walk around on them and they will
listen to MP3 players. At what spring back. But leave a heavy piece of furniture on them and they may never rebound. As a
level, on average, do they listen general rule, any noise we cannot talk over (loud machinery, fans screaming at a concert or
sports event, our favorite playlist blasting at maximum volume) may be harmful, especially if
to their music? sensorineural hearing loss prolonged and repeated (Roesser, 1998) (Figure 1.6-19). And if our ears ring after such expo-
• How loud is a typical concert? the most common form of sures, we have been bad to our unhappy hair cells. Just as pain alerts us to possible bodily
hearing loss, caused by damage
harm, ringing of the ears alerts us to possible hearing damage. It is hearing’s equivalent of
What do musicians do today Copyright © Bedford, Freeman & Worth Publishers.
to the cochlea’s receptor cells or
bleeding.
to protect their hearing? to the auditory nerve; also called Since the early 1990s, the prevalence of teen hearing loss has increased by one-third, to
nerve deafness.
Should concert promoters conduction hearing loss the point that this condition now affects 1 in 6 teens (Shargorodsky et al., 2010; Weichbold
et al., 2012). After 3 hours at a rock concert averaging 99 decibels, 54 percent of teens
offer earplugs at the door of a less common form of hearing reported temporarily not hearing as well, and 1 in 4 had ringing in their ears (Derebery
loss, caused by damage to the
concerts? Why or why not? mechanical system that conducts et al., 2012). Teen boys more than teen girls or adults blast themselves with loud volumes
sound waves to the cochlea. for long periods (Widén et al., 2017; Zogby, 2006). Greater noise exposure may help explain
Ask students to come up with at cochlear implant a device why men’s hearing tends to be less acute than women’s. Anyone who spends many hours
for converting sounds into
least one recommendation for electrical signals and stimulating in a loud nightclub, behind a power mower, or above a jackhammer should wear earplugs,
or they risk needing a hearing aid later.
their classmates to protect their the auditory nerve through Nerve deafness cannot, as yet, be reversed. One way to restore hearing is with a sort of
electrodes threaded into the
hearing based on their research. cochlea. bionic ear — a cochlear implant. Such implants, which had been placed in 737,000 peo-
Be sure they provide scientifically ple as of the end of 2019, translate sounds into electrical signals that, when wired into
derived evidence that supports their
conclusion. 138 Unit 1 Biological Bases of Behavior
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138 Unit 1 Biological Bases of Behavior
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