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you hear the gentle lack of waves the
distant calling of a seagull but then an
annoying whine interrupts the peace
getting closer and closer and closer
until whack you dispatch the offending
mosquito and calm is restored how did
you detect that noise from afar and
target its maker with such precision the
ability to recognize sounds and identify
their location is possible thanks to the
auditory system that's comprised of two
main parts the ear and the brain the
ears task is to convert sound energy
into neural signals the brains is to
receive and process the information
those signals contain to understand how
that works we can follow a sound on its
journey into the ear the source of a
sound creates vibrations that travel as
waves of pressure through particles in
air liquids or solids but our inner ear
called the cochlea is actually filled
with salt water like fluids so the first
problem to solve is how to convert those
sound waves wherever they're coming from
into waves in the fluid the solution is
the eardrum or tympanic membrane and the
tiny bones of the middle ear those
convert the large movements of the
eardrum into pressure waves in the fluid
of the cochlea when sound enters the ear
canal it hits the eardrum and makes it
vibrate like the head of a drum the
vibrating eardrum jerks a bone called
the hammer which hits the anvil and
moves the third bone called the stay
piece its motion pushes the fluid within
the long chambers of the cochlea once
there the sound vibrations have finally
been converted into vibrations of a
fluid and they travel like a wave from
one end of the cochlea to the other a
surface called the basilar membrane runs
the length of the cochlea it's lined
with hair cells that have specialized
components called stereocilia which move
with the vibrations of the cochlear
fluid and the bass
membrane this movement triggers a signal
that travels through the hair cell into
the auditory nerve then onward to the
brain which interprets it as a specific
sound when a sound makes the basilar
membrane vibrate not every hair cell
moves only selected ones depending on
the frequency of the sound this comes
down to some fine engineering at one end
the basilar membrane is stiff vibrating
only in response to short wavelength
high frequency sounds the other is more
flexible vibrating only in the presence
of longer wavelength low-frequency
sounds so the noise is made by the
seagull and mosquito vibrate different
locations on the basilar membrane like
playing different keys on a piano but
that's not all that's going on the brain
still has another important task to
fulfill identifying where a sound is
coming from for that it compares the
sounds coming in to the two ears to
locate the source in space a sound from
directly in front of you will reach both
your ears at the same time you'll also
hear it at the same intensity in each
year however a low-frequency sound
coming from one side will reach the near
ear micro seconds before the far one and
high frequency sounds will sound more
intense to the near ear because they're
blocked from the far ear by your head
these strands of information reach
special parts of the brainstem that
analyze time and intensity differences
between your ears they send the results
of their analysis up to the auditory
cortex now the brain has all the
information it needs the patterns of
activity that tell us what the sound is
and information about where it is in
space
not everyone has a normal hearing
hearing loss is the third most common
chronic disease in the world exposure to
loud noises and some drugs can kill hair
cells preventing signals from traveling
from the ear to the brain diseases like
osteoporosis freeze the tiny bones in
the ear so they no longer vibrate
and with tinnitus the brain does strange
things to make us think there's a sound
when there isn't one but when it does
work our hearing is an incredible
elegant system our ears enclose a
fine-tuned piece of pie illogical
machinery that converts the cacophony of
vibrations in the air around us into
precisely tuned electrical impulses that
distinguish claps taps sighs and flies
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dive deeper into the complex world of
your senses with this playlist
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