12-13 January 2016
External Ear
Structures:
 Pinna
 auditory
canal
 ear drum
Function:
 Funnel
and
conduct
sound to
middle ear
Middle Ear
Structures:
Ossicles
 Malleus
 Incus
 Stapes
 Eustacian /
auditory
tube
Function:
 Amplify
and
conduct
sound to
inner ear
Inner Ear
Structures:
Osseous
labyrinth
 Semicircular
canals
 Vestibule
 cochlea
Function:
 Receive
sound and
equilibrium
stimuli
NOTE:
Diagrams are
misleading.
The entire
inner is bony,
except for the
labyrinth
which is a
series of
cavities
(spaces)
within the
bone.
Function:
Function: to funnel and conduct sound to the middle ear
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Pinna collect sound waves and direct to the tympanic
membranes … but in humans, not very effectively.
Cerumen (ear wax) lines the external auditory canal.
◦
◦
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Antibacterial
Also discourages bugs, mold, etc.
Lubricates ears
Helps trap / remove foreign particles
The tympanic membrane (ear drum)
vibrates when sound waves hit it,
transmitting the sound to the
middle ear
A reflex tightens the ear drum in
response to loud, low-pitched sounds –
this reduces the sound transmitted to the
ear and protectes our hearing
Ear Wax Blockage
 Ear wax can become impacted, usually from hearing aid
use or inappropriate methods of cleaning the ears
 Can cause temporary loss of hearing
Otitis Externa (Swimmer’s Ear)
 Infection of external auditory ear canal, usually due to
excess moisture in the ear canal (such as from
swimming), though cuts and scrapes to the ear canal
can also become infected.
Picture through an
otoscope. Notice that
the canal is red but the
ear drum is clear and
not bulging.
Function:
Function: to AMPLIFY the sound and conduct it to the oval
window of the inner ear.
How? The tympanic membrane transmits sound to the three
ossicles. The ossicles act like levers, amplifying the sound and
transmitting it to the
oval window, a
membrane-covered
opening to the
inner ear.
Structure
 Tube that connects the middle ear to the nose and throat
 Mostly closed, but opens when we move our jaw
Why do we have it?
 Equalize pressure in the middle ear
 Drain fluids to the throat
Remember: the tympanic
membrane seals the middle ear
from the outer ear – so the only
way for air / fluids to leave the
middle ear is through the
eustachian tubes
This is why its helpful to
yawn or chew gum on a
plane ride
Otitis media (middle ear inflammation / infection) –
 Inflammation (often with the buildup of infected fluids) within
the middle ear
 Visible with an otoscope as a bulging eardrum
 Usually caused from a respiratory infection
 Babies who are allowed to drink bottles while lying down are
also very likely to get ear infections
 Much more common in young children, because their
Eustachian tubes are narrower and more horizontal
myringotomy–
 Ear tubes are often recommended for children who
experience chronic middle ear infections or fluid build-up
 The tube is placed in the ear drum, but performs the
functions of a eustachian tube – ventilating and draining the
middle ear.
Hearing takes place within the cochlea of the inner ear.

Cochlea is a long, curled cavity with three layers
◦ 2 layers of perilymph – a plasma-like fluid
◦ In-between: a system of membranes that contain the
organ of Corti and the mechanoreceptors (hair cells) that
create the nerve impulse
The top diagram is a
cross-section of the
cochlear cavity.
Take a moment to
figure out …
• What fills the scala
vestibuli?
• The scala tympani?
• The cochlear duct?
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When the stapes beats against the oval window, it
causes pressure waves within the perilymph
The movement of the perilymph disturbs the cilia
(receptors) of the Organ of Corti, generating a
nerve impulse
Different frequencies
(pitch) vibrate the
membrane in
different locations.
High pitches are
heard that the front,
low at the back.
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When the stapes beats against the oval window, it
causes pressure waves within the perilymph
The movement of the perilymph disturbs the cilia
(receptors) of the Organ of Corti, generating a
nerve impulse
The round window is
a membrane-covered
opening just below
the oval window. It
bulges to keep the
pressure waves from
bouncing back.
Watch me!
Just for fun!
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What were our objectives, and what did you
learn about them?
What was our learner profile trait and how did
we exemplify it?
How does what we did today address our unit
question?