Medical Physics: The Ear

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  • Created by: LZ95
  • Created on: 14-04-14 13:44
What do the ossicles consist of?
Malleus (hammer), Incus (anvil) and stapes (stirrup)
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What is acoustic impedance?
Product of density and the speed of sound in materials
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What is the effect of low and high acoustic impedance on the conduction of sound?
Low: conducts sound well, High: conducts sound badly.
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What is the intensity of a sound?
Power per unit area (W/m^2) perpendicular to the direction of travel of the wave
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What is intensity proportional to?
Inverse square of the distance from the source (I ∝ 1/d^2)
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What does the ear allow us to receive spatial information about?
Direction + layout of a sound
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What is the pinna?
Collecting device that funnels sound waves into the ear canal
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What does the ear canal do?
Increases intensity of the sound by reducing the area
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What causes the ossicles to vibrate?
The vibration of the tympanic membrane due to the sound
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What does the cochlea do?
The ossicles strike the oval window of the cochlea and after the nerve cells into the cochlea detect the sound, it is converted into an electrical impulse.
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How do sound impulses travel through the cochlea?
They are sent through the fluid in the cochlea to vibrate the hair cells.
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What is an infrasound?
A sound that is below about 20Hz so it is felt rather than heard
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What is the peak sensitivity of the human ear?
3000Hz
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What 2 things does the loudness of a sound depend on?
1. Intensity 2. Energy transfer
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What is loudness measured in?
Phons
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What is the reference point used by the decibel scale?
The minimum threshold of hearing, 1x10^-12 Wm^-2
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Name 3 reasons why hearing loss may occur
1. Mechanical damage 2. Disease 3. Exposure to excessive noise
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What sort of disease can be corrected by surgery or a hearing aid?
Disease where the ossicles stop moving
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When would total hearing loss occur?
If the disease destroyed the nerve fibres in the cochlea
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What can excessive noise do?
Break off the hairs of the hair cells
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How does aging affect hearing?
Higher frequencies are not heard as well
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Name 2 features of the ear which increases the amplitude of the sounds
1. Ossicles act as a lever, magnifying the force by a factor of 1.3 2. Area of oval window is only one twentieth of the area of the eardrum, so pressure is increased
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How do sound waves travel through the fluid in the cochlea?
As pressure waves
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What is energy transferred by the wave proportional to?
The square of the amplitude
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Why is the shape of the pinna ideal for making sense of the position of a sound?
It is shaped so that sounds at the front of the head are detected more easily than at the back of the head.
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How are the vibrations of the oval window transferred in the fluid in the cochlea?
As pressure waves
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How are high frequency sounds detected?
The cause only the first part of the basilar membrane to vibrate
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How is pitch interpreted?
Different frequencies cause different sections of hair cells to vibrate
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What is meant by the sensitivity of the ear?
Its ability to detect small changes in intensity
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What does the loudness of a certain frequency depend upon?
Rate at which energy is transferred through a given area.
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What is the equation for the perceived change in loudness?
Change in intensity/initial intensity
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What does the dB scale NOT measure?
Loudness
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Other cards in this set

Card 2

Front

What is acoustic impedance?

Back

Product of density and the speed of sound in materials

Card 3

Front

What is the effect of low and high acoustic impedance on the conduction of sound?

Back

Preview of the front of card 3

Card 4

Front

What is the intensity of a sound?

Back

Preview of the front of card 4

Card 5

Front

What is intensity proportional to?

Back

Preview of the front of card 5
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