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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
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
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).
Worldwide, 1.23 billion people are
challenged by hearing loss and an esti-
Susumu Nishinaga/Science Source hearing loss (GBD, 2015; Wilson et al.,
mated half a billion have a disabling

2017). Damage to the cochlea’s hair
cell receptors or the auditory nerve
can cause sensorineural hearing

Be kind to your inner ear’s hair loss (or nerve deafness). With auditory
nerve damage, people may hear sound
cells When vibrating in response to but have trouble discerning what someone is saying (Liberman, 2015). Sensorineural hear-
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 Copyright © Bedford, Freeman & Worth Publishers.
signal. system — the eardrum and middle ear bones — that conducts sound waves to the cochlea.
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
hearing loss passed down from my grandmother and mother, thanks to a single genetic
mutation.
Toxic noise, such as prolonged exposure to ear-splitting music, is another culprit. The
cochlea’s hair cells have been likened to carpet fibers. Walk around on them and they will
spring back. But leave a heavy piece of furniture on them and they may never rebound. As a
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
sensorineural hearing loss prolonged and repeated (Roesser, 1998) (Figure 1.6-19). And if our ears ring after such expo-
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
to the cochlea’s receptor cells or bleeding.
to the auditory nerve; also called
nerve deafness. Since the early 1990s, the prevalence of teen hearing loss has increased by one-third, to
the point that this condition now affects 1 in 6 teens (Shargorodsky et al., 2010; Weichbold
conduction hearing loss
a less common form of hearing et al., 2012). After 3 hours at a rock concert averaging 99 decibels, 54 percent of teens
loss, caused by damage to the reported temporarily not hearing as well, and 1 in 4 had ringing in their ears (Derebery
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
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 in a loud nightclub, behind a power mower, or above a jackhammer should wear earplugs,
electrical signals and stimulating or they risk needing a hearing aid later.
the auditory nerve through
electrodes threaded into the Nerve deafness cannot, as yet, be reversed. One way to restore hearing is with a sort of
cochlea. bionic ear — a cochlear implant. Such implants, which had been placed in 737,000 peo-
ple as of the end of 2019, translate sounds into electrical signals that, when wired into

138 Unit 1 Biological Bases of Behavior

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