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THE EAR
is a sensory organ
responsible for both hearing
and maintenance of balance
composed of three sections:
the outer, middle and inner
ear.
The Outer Ear:
The Pinna: the outer flap that
funnels sound towards the
auditory canal
Auditory Canal: a tube that
carries sound towards the
eardrum, it contains wax
secreting cells; the wax traps
dust etc.
The Middle Ear:
Tympanic Membrane (Ear
drum):a membrane that
closes off entry into the
middle ear; vibrates when
sound waves reach it.
Ossicles: three small bones
(Hammer, anvil and stirrup)
that amplify the sound
vibrations from the ear drum
and carry them to the oval
window.
Oval Window: a small
membrane that seperates
the middle from the inner
ear. Transmits vibrations
from the ossicles to the
inner ear.
Eustachian Tube: a tube that
connects the middle ear with
the throat; used to equalize
pressure between the
atmosphere and the middle
ear.
The Inner Ear:
Vestibule: contains two
small sacs called the Utricle
and Saccule, aid in
establishing head position.
(Static Equilibrium)
Semicircular Canals: 3 tubes
arranged at different angles,
filled with a fluid that helps in
establishing body position
(Dynamic Equilibrium)
Cochlea: a snail shaped organ
containing a fluid and
specialized hair cells that move
when vibrations from the oval
window occur. The hair cells
respond differently to sound
waves of different frequencies
and intensities.
Auditory Nerve: transmits
information to the brain from
the inner ear on balance and
sound.
STEPS INVOLVED IN
HEARING
sound is a form of energy that
travels in waves
it is the movement of these
waves that initiates the
hearing process:
1.When sound waves reach
your ear; they push against the
tympanic membrane causing it
to vibrate.
2. The vibrations are
transferred to the ossicles;
which concentrate and amplify
the sound.
3. The vibrations from the last
bone, the stirrup, cause the
movement of the Oval Window
inwards
4. The movement of the
window initiates movement of a
fluid found within the Cochlea.
5. This fluid movement
stimulates the Basilar
Membrane of the Organ of
Corti; the technical name given
to the hearing apparatus in the
Cochlea.
6. Attached to the basilar
membrane are Hair Cells that will
bend in response to the
stimulation.
7. The bending hair cells
stimulate sensory neurons that
transmit the information
through the Auditory Nerve to
the Temporal Lobe of the
Cerebrum.
Different Hair cells have
different threshold levels that
will depolarize depending on
the frequency or intensity of
the sound.
Maintenance of Balance
two components to balance:
1. Static Equilibrium:
balance involving the position
or movement of the head.
head position is determined by
the two fluid filled sacs (Utricle
and Saccule) found in the
vestibule.
in the fluid are suspended
particles called OTOLITHS.
when the head moves, the
otoliths moves; this causes
movement of the hair cells that
line the interior of the sacs
the hair cells stimulate sensory
neurons that carry information to the
brain, through the auditory nerve,
regarding head position
2. Dynamic Equilibrium
balance involving the movement of
the body
involves the movement of the fluid
found in the SEMICIRCULAR
CANALS
when we move, the fluid moves
causing the movement of hair
cells that line the canals.
when the hair cells move,
they stimulate sensory
neurons which will carry
information regarding body
position to the brain through
the auditory nerve.