Physics of the Ear Flashcards
What is the function of the ear?
To amplify the small pressure changes and convert them into electrical signals which can be interpreted by the brain.
What is the function of the outer ear?
To collect and direct sound into the auditory canal.
What is the function of the middle ear?
To transfer the sounds vibrations from the tymphonic membrane to the oval window.
What is the function of the inner ear?
To increase pressure produced by the middle ear to produce vibrations that are converted to electrical signals and send them to the brain.
What is the function of the ear canal?
To modify the sound through resonance properties.
What is the function of the ear drum?
To vibrate when hit by sound waves. (by 10^-11 m)
What are the english names for the bones in the middle ear?
Hammer, anvil and stirrup.
What are the latin names for the bones in the middle ear?
Malleus, incus and stapes.
What is the collective name for the bones in the middle ear?
Ossicles.
What is the function of the ossicles?
To amplify sound by a factor of 1.3 and to transfer oscillations to the oval window.
What is the oval window?
The entrance to the cochlea.
What is the vestibule?
The cavity lying between the oval window and the cochlea.
What is the cochlea?
A three-chambered tube filled with fluid.
What are the chambers in the cochlea called and what are they filled with?
One is the vestibular chamber which is joined to the tympanic chamber; they are filled with perilymph fluid.
The last is the cochlea duct and that is filled with endolymph fluid.
What are the two fluids in the cochlea called?
Perilymph and endolymph.
What separates the cochlea duct and the tymphanic chamber?
The basilar membrane.
What is the basilar membrane?
The membrane that separates the cochlea duct and the tympanic membrane. It supports a layer of sensory hair cells on its inner surface.
What is the purpose of the sensory hair cells?
They move to the vibrations produced by the waves that travel along the perilymph, and produce electrical signals which are sent to the brain.
Define the threshold of hearing.
The lowest intensity of sound that can be heard by the ear at 1kHz
At which frequency is the normal human ear most sensitive?
3000Hz
What are the main features of hearing loss?
As frequency increases, loss increases.
What are the main features of noise related hearing?
The loss of hearing is at a maximum at 4kHz.
State the main difference between the dB scale and the adapted dBA scale used to measure sound intensity levels.
dBA scale is dependent on frequency, dB is not.
Sound intensity levels are usually measured in decibels. Why is a logarithmic scale used?
- The ear has a logarithmic response to sound
- To accommodate a very wide range of sound intensities to which an ear can respond
- perceived change in loudness is proportional to fractional change in intensity
- logarithmic scale means that numerical values on the scale represent ratios of two sounds, expressed as the log of that ratio
What is the frequency of the threshold of hearing?
1 x10^-12
What is the unit of the threshold of hearing?
Wm^-2
Why was it necessary to introduce the dBA scale?
It takes account of the frequency dependence of the sensitivity of the ear.
Describe the dB graph.
flat - same response at all frequencies
Describe a dBA graph.
most sensitive at 3kHz
crosses dB line at 1kHz
How is a dBA graph obtained?
- A sound is listened to at a frequency of 1kHz and intensity level 10dB
- Same sound is listened to at a different frequency and loudness, loudness is altered.
- Switch between 1kHz, 10dB and new frequency, new loudness until new loudness is perceived
- Repeat for frequencies between 20Hz and 14-20kHz
Define attenuation and state what causes it.
reduction in intensity as a wave travels through a medium due to absorption
Define intensity.
power per unit cross sectional area
