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Sense Organs
High!!
Yoooo-eeeee ???
drrrr – rrrr - rrrr
Alan Stevens
Ear
Structure and functions of the different parts of the human ear
Functioning of the human ear in:
•
•
Hearing (include the role of the organ of Corti without mention of its structure)
Balance
Adaptations of the various parts of the ear for their functions
Cause and treatment of the following hearing defects:
•
•
Middle ear infections (treatment using grommets)
Deafness (treatment using hearing aids and cochlear implants)
The link between hearing defects and speech disorders
The use of sign language by deaf people
INVESTIGATIONS
Model of the ear
ADDITIONAL
Attitudes towards blind and deaf people
The rights of blind and deaf people
Alan Stevens
Some Tips
• MODELS & APPARATUS even from the
physical sciences, ARE CRUCIAL !
• The arrows in the previous slide show how
various aspects from the Exam Guideline can
be linked to save time
• Note the areas in red (previous slide). They
are possible LO3 options
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Structure
MODELS ARE CRUCIAL ! ! !
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Alan Stevens
Hearing
Pinna
•“catches" the sound
waves
•helps you determine the
direction of a sound
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The Eardrum (tympanic membrane)
• The eardrum is rigid, and very sensitive.
Even the slightest air-pressure fluctuations
(or sound) will move it back and forth.
• Separates outer ear from middle ear
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Ossicles
Amplifies Sound
•The malleus, (hammer ): Picks up
vibrations from eardrum ; is longer
than the incus, moves a greater
distance, transferring a greater
force to the incus (energy = force x
distance).
•The incus (anvil):
•The stapes (stirrup): The main
amplification due to size
difference between eardrum and
stirrup. The eardrum surface area
= 55 square millimeters, surface
area of stapes faceplate =3.2 mm2.
Sound energy from larger to
smaller surface area, increases
the pressure
Alan Stevens
Fluid Wave in the Cochlea
Know: Stapes, Oval Window, Round
Window, Organ of Corti, Hair cells
• Stapes “pistons” sound waves
through oval window to fluid of
cochlea
• Hair cells in cochlea (part of organ
of Corti) convert mechanical
vibrations into chemical impulse
• Impulse transported by cochlear
nerves to brain
• High sounds (high frequency) let
hair cells at beginning of cochlea
vibrate,
• Lowest sounds (low frequency) at
end of cochlea
• Round window vibrates
ALTERNATELY with oval window to
dissipate excess vibrations
Alan Stevens
Decibel scale (dB)
The smallest audible sound (near total silence) is 0 dB. A
sound 10 times more powerful is 10 dB. A sound 100
times more powerful than near total silence is 20 dB. A
sound 1,000 times more powerful than near total silence
is 30 dB. Here are some common sounds :
•
•
•
•
•
•
•
Near total silence - 0 dB
A whisper - 15 dB
Normal conversation - 60 dB
A lawnmower - 90 dB
A car horn - 110 dB
A rock concert or a jet engine - 120 dB
A gunshot or firecracker - 140 dB
Alan Stevens
Any sound above 85 dB
can cause hearing loss
Balance
Utricle & Sacculus:
Hair cells detect
position of head
Utricle + Saccule
=
Semicircular canals:
Hair cells detect
movement of head &
body
Alan Stevens
Glue Ear and Grommets
• The lining of the middle ear 'sweats' fluid all the
time and this fluid usually empties out automatically
when our ears "pop", for example when we swallow
or yawn.
• When a middle ear infection or a head cold occurs
this fluid may not be able to empty out as it normally
would (especially in children).
• The fluid is thin at first, but if the middle ear stays
inflamed the fluid can't get out and air also can't get
in, this fluid may become thick, like glue.
Alan Stevens
Grommets are very small ventilation tubes made
of plastic that are about 2mm in width. The
grommet sits in the eardrum with one flange
sitting on the inside and one on the outside of
the eardrum.
They have a small hole in the centre which
allows fresh air to enter the middle ear to
keep it free of fluid.
Alan Stevens
Hearing Disorders and Deafness
Causes:
• Heredity
• Diseases such as ear infections and meningitis
• Trauma
• Certain medicines
• Long-term exposure to loud noise
• Ageing
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Two main types of hearing loss:
• Damaged to your inner ear or auditory nerve.
This type is permanent.
• The other kind happens when sound waves
cannot reach your inner ear. Earwax build-up,
fluid or a punctured eardrum can cause it.
Possible treatments include hearing aids,
cochlear implants, special training, certain
medicines and surgery.
Alan Stevens
Hearing Aids
• A hearing aid is a small electronic device that you
wear in or behind your ear. It magnifies sound
vibrations entering the ear. That makes some sounds
louder. A hearing aid can help people hear more in
both quiet and noisy situations.
• Hearing aids help people who have hearing loss from
damage to the small sensory cells in the inner ear.
The damage can occur as a result of disease, aging,
or injury from noise or certain medicines.
Alan Stevens
Cochlear Implants
For people who are profoundly deaf or severely
hard-of-hearing can get help from them. The
implant consists of two parts.
Alan Stevens
Parts of Cochlear Implant
External:
• one or more microphones to pick up sound from the
environment
• a speech processor sends electrical sound signals to
a transmitter,
• a transmitter, behind the external ear, transmits
power and the processed sound signals to the
internal device by electromagnetic induction,
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Internal:
• A receiver and stimulator secured in bone beneath
the skin, converts the signals into electric impulses
and sends them through an internal cable to
electrodes,
• an array of up to 24 electrodes wound through the
cochlea, sends impulses to the nerves in the cochlea
and then directly to the brain through the auditory
nerve system.
Alan Stevens
Sign language
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• The elements of a sign are Handshape (or
Handform), Orientation (or Palm Orientation),
Location (or Place of Articulation), Movement,
and Non-manual markers (or Facial
Expression), summarised in the acronym
HOLME.
• The recipient of a signed message can read
meanings carried by the hands, the facial
expression and the body posture in the same
moment.
Alan Stevens