BRAIN FUNCTIONS AND THE SENSESHow We Hear
How We Hear
The world is full of noise. It travels as sound waves
through the air until it reaches our ears. There, they
are turned into electrical impulses and sent to the
brain for decoding into meaningful sounds.
Picking up sound
Hearing involves the conversion of a sound wave into an
electrical impulse that the brain can interpret. Sound waves
are carried from the outer to the middle ear, where they cause a
series of bones and membranes to vibrate. These vibrations then
reach the cochlea, where they become electrical impulses. These
are passed to the brain stem and thalamus, where direction,
frequency, and intensity are perceived. The data is then sent for
processing by the left and right sides of the auditory cortex. The
left side identifies the sound and gives it meaning, while the
right side assesses the quality of the sound.AUDITORY CANAL
OUTER EAR
OSSICLES
(MIDDLE EAR BONES)MALLEUS
(HAMMER) BONE
INCUS
(ANVIL) BONE
S TAPE S
(STIRRUP) BONE
M
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D
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E A R D R U M
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LEA
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The outer ear
Sound waves are caught
by the outer ear, which funnels
them inside the head via the
auditory canal.
1
The auditory canal
The sound waves travel along the
auditory canal to the eardrum. The auditory
canal is lined with tiny hairs that filter out
foreign objects.
2
The eardrum
The eardrum, or tympanic
membrane, is a thin layer of
fibrous tissue that forms a
barrier between the outer ear
and the middle ear. It vibrates
when the sound waves traveling
up the auditory canal hit it.
3
Ossicles
Vibrations are passed through
the eardrum to a set of connected
bones called ossicles—the malleus,
incus, and stapes bones. The stapes
bone pushes and pulls on another
membrane, called the oval window.
This transmits sound to the inner ear.
4
Vibrations make bones
rattle against each other
Oval window
Round window
Eustachian tube connects
middle ear to nose and mouth
Sound waves travel
through air
Sound waves
vibrate eardrum
US_074-075_How_We_Hear.indd 74 07/10/2019 11:04