Transcript 9.6 Hearing and Equilibrium

9.6 Hearing and Equilibrium
The Ear:
• Used for hearing and
equilibrium
• The inner ear contains
sensory cells for both
functions
• Each hair cells has between
30 and 150 cilia…
responding to stiumuli
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The ear can be divided into three main sections:
1) The outer ear
→The pinna
→The auditory canal
2) The middle ear
→Eardrum (or tympanic membrane)
→Ossicles
→Oval window
→Eustachian tube
3) The inner ear
→Vestibule
→Semicircular canals
– →Cochlea
The Outer Ear
– The pinna: outer ear
flap that collects the
sound
– The auditory canal:
carries the sound to
the eardrum and is
lined with specialized
sweat glands that
produce earwax (used
to trap foreign
particles, preventing
them from entering the
ear.)
The Middle Ear (Tympanic
Membrane)
• Air filled chamber that holds the
three small bones: the ossicles.
– The three ossicles are the
malleus (hammer), the incus
(anvil) and the stapes (stirrup)
• Sound vibrations that strike the
eardrum are first concentrated
withing the malleus, transmitted
to the incus and then the stapes.
• The stapes strikes the membrane
covering the oval window in the
inner wall of the middle ear.
• The oval window amplifies the
sound
• The Eustachian tube goes from
the middle ear to the mouth and
the chambers of the nose and
helps to equalize pressure. This
is also the site that builds up with
fluids in an ear infection.
The Inner Ear
• The vestibule is connected to
the middle ear by the oval
window and has two small
sacs: the utricle and the
saccule. They help establish
head position.
• There are three semicircular
canals that are arranged at
different angles that helps
identify body movement with
the fluid inside them.
• The cochlea is shaped like a
snail’s shell and contains two
rows of specialized hair cells
that respond to sound waves
of different frequencies and
intensities and changes them
into nerve impulses.
Anatomy of the Ear Learning Activity
Hearing and Sound
• Sound is a form of energy
that must be converted
into an electrical impulse
before you can interpret
it.
• Sound must travel
through a medium to be
heard
• Air most commonly, but
also water and solids
Hearing and Sound
• Sound travels fastest in solids, then
liquids, then gases.
• Muscles joining the bones of the middle
ear protect the inner ear from excessive
noise
• Loud noises cause these muscles to
contract, constricting the malleus, while a
second muscle contracts, pulling the
stapes away from the oval window.
1. The oval window receives vibrations from
the ossicles and is pushed inwards
2. The cochlea receives fluid waves and
converts them into electrial impulses
(sound)
BBC Science & Nature - Human Body
and Mind - Nervous System Layer
Organ of Corti
• The hearing apparatus in
the cochlea
• A single inner row, and
three outer rows of
specialized hair cells
• The hair cells are covered
in a gelatinous coating
• Hair bending sends a
message through sensory
nerves
Effect of Sound Waves on
Cochlear Structures
Pitch and Loudness
• Identified by the
cochlea structure
narrowing and hairs
getting shorter as it
coils
• Receptor hair cells on
the basilar membrane
trigger an action
potential that is
carried to the brain
Bass
• Low frequency waves move to the wider
more elastic area of the cochlea to vibrate
Animation: Effect of Sound Waves on Cochlear Structures (Quiz 1)
Mechanical Stimulation
• The basilar
membrane will
respond to jarring
blows … particularly
to the head
• The vibrations
resonate through the
skull, and pass onto
the cochlea
Equilibrium
Static Equilibrium:
• Movement along one
plane
– Ex. Head position
• Controlled by the saccule
and utricle. Cilia from
hair cells are suspended
in a gelatinous material
containing CaCO3
granules called ooliths.
• When the head is in a
normal position, ooliths
do not move.
Dynamic Equilibrium:
• Provides information
during movement
• While moving,
balance is maintained
by three semi-circular
canals…each of
which has a small
pocket called an
ampulla
• Rotational stimuli
cause the fluid in
these canals to move