Download 9.6 Hearing and Equilibrium

9.6 Hearing and Equilibrium
The Ear:
• Used for hearing and equilibrium
• The inner ear contains sensory
cells called hair cells for both
functions
• Each hair cells has between 30
and 150 cilia… responding to
stimuli
• The ear can be divided into 3 main sections:
• 1) outer ear
•
→The pinna
•
→The auditory canal
• 2) middle ear
•
→Eardrum (tympanic membrane)
•
→Ossicles (malleus, incus, stapes)
•
→Oval window
•
→Eustachian tube
• 3) inner ear
•
→Vestibule
•
→Semicircular canals
→Cochlea
The Outer Ear
– The pinna: outer ear
flap that collects and
directs the sound
– The auditory canal
(ear canal): carries
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
• Sound is a form of energy
that converts into electrical
impulses for interpretation.
• Sound must travel through a
medium such as air (but also
water and solids) to be
heard.
The Middle Ear
• Air filled chamber that holds 3
small bones called ossicles.
– malleus (hammer), incus
(anvil) and stapes (stirrup)
• Sound vibrations strike the
eardrum and are transmitted to
the malleus, then the incus and
lastly the stapes.
• The stapes strikes the membrane
covering the oval window in the
inner wall of the middle ear and
amplifies the sound.
• Muscles joining the bones of the
middle ear protect the inner ear
from excessive noise.
After receiving vibrations from the ossicles, the
oval window pushes inwards towards the fluidfilled cochlea.
Fluid waves within the cochlea convert them into
electrical impulses (sound) using the Organ of
Corti in the inner ear.
Equalizing pressure in the middle ear
• The eustachian tube
goes from the middle
ear to the mouth and
the chambers of the
nose and helps to
equalize pressure. This
is the site that builds up
with fluids in an ear
infection.
The Inner Ear: Organ of Corti
• The Organ of Corti is the actual
hearing apparatus in the
cochlea. The organ of Corti is
located in the cochlea. 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.
• The hair cells are covered in a
gelatinous coating and sit on
the basilar membrane.
The Inner Ear: Organ of Corti
• As fluid waves pass through the cochlear canals,
the basilar membrane moves up and down causing
the hair cells to hit the membrane above called the
tectorial membrane.
• As hairs bend, messages are sent through sensory
nerves at their base to the cochlear nerve and
eventually the auditory nerve that leads to the brain.
Organ of Corti
• BBC Science & Nature Human Body and Mind Nervous System Layer
Effect of Sound Waves on
Cochlear Structures
Loudness
• Receptor hair cells on the
basilar membrane trigger
an action potential that is
carried to the brain
• The louder the sound, the
more hair cells are
stimulated.
• Hair cells can be
damaged if the sound is
too loud.
Pitch
• Low frequency waves (bass) 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.
This can cause ‘ringing’ in
your ears.
Equilibrium and the Inner Ear
• An area called the
vestibule is connected
to the middle ear by the
oval window and has two
small sacs: the utricle
and the saccule that 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.
Anatomy of the Ear Learning Activity
Static Equilibrium
• Movement along one plane
(head position)
• Controlled by the saccule and
utricle. Cilia from hair cells
are suspended in a gelatinous
material containing CaCO3
granules called otoliths.
• When the head is in a normal
position, otoliths do not move
but when the head moves,
gravity acts on otoliths,
causing gelatinous material to
shift and hair receptors to
bend. Movement of hair
receptors stimulates nerves
that relay info about head
position to brain.
Dynamic Equilibrium:
• Provides information during
movement
• While moving, balance is
maintained by 3 semi-circular
canals, each of which has a
small pocket called an ampulla
• Rotational stimuli cause the
fluid and hence the otoliths in
these canals to move.