How the Brain Works The Facts Visually Explained by DK (z-lib.org)

BRAIN FUNCTIONS AND THE SENSES

How We Hear 74 75

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On a busy street, there are lots of
conflicting sounds, yet you can still
hear someone talking next to you.
This is because the primary auditory
cortex can filter out unnecessary
sounds and boost the signals it wants
to hear. It does this by dampening
the response to sustained sounds,
such as traffic, while enhancing more
dynamic sounds, such as speech,
and actively listening to them.
FILTERING OUT NOISE
The cochlea
The cochlea contains three fluid-
filled ducts. Vibrations travel along the
vestibular canal as wavelike movements
that are transferred to the basilar
membrane of the organ of Corti.
Residual vibrations return along the
tympanic canal to the round window.
5 6
The cochlear nerve
The electrical signals are
transported from each hair cell
through cochlear nerve endings
that join together to form the
cochlear nerve. This is responsible
for transmitting signals to specialized
groups of neurons in the brain stem.
7
The thalamus
Signals are first received in
the brain stem. From here, they travel
up to specialized neurons in the
thalamus for processing. These signals
are then sent to the primary auditory
cortex, which also feeds information
back to the thalamus.
The primary
auditory cortex
After intermediate processing in
the thalamus, the characteristics of
each sound are interpreted by the
primary auditory cortex, which
works with other cortical areas
to identify the type of sound.
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THE STAPES IS THE
SMALLEST BONE
IN THE BODY
Organ of Corti (central spiral
part of the cochlea) rests on a
basilar membrane and contains
sensitive hair cells
Electrical signals
pass along
cochlear nerve
Vestibular canal
carries sound
vibrations
Specialized cells at
top of brain stem
help determine
direction of sounds
Background
noise filtered
out
The organ of Corti
The movement of
the basilar membrane bends
sensitive hair cells in the organ
of Corti (see p.76), which is the
main organ of hearing. The hair
cells convert this movement into
electrical signals.
Primary auditory cortex
processes sound
Vibrations return
to round window
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US_074-075_How_We_Hear.indd 75 20/09/2019 12:33