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Flashcards in Sound Perception Deck (36)
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1

What frequencies can we hear sounds ranging between?

20 and 20,000 Hz
20 times per second to 20,000 times per second
We are good at detecting soft sounds, perceiving very small differences

2

How many pure tones can we differentiate up too?

1500 pure tones

3

What is the main function of the outer ear?

Captures sound signals
Amplifies mid frequencies
Vertical direction coding

4

What is the main function of the middle ear?

Protection
Impedance matching

5

What is the main function of the inner ear?

Frequency analysis
Transduction

6

What are the 2 sections of the outer ear?

Pinna
Meatus

7

What does the pinna do?

Affects high frequency sounds by interference between the echoes reflected off its different structures - different frequencies are amplified by different amounts depending on the origin of the sound in the vertical place - brain interprets these changes as direction (if sound is coming from the floor or air)

8

What does the meatus (ear canal) do?

Links the pinna to the ear drum
Resonates at around 2kHz so that frequencies in that region are transmitted better to the cochlea - corresponds to human speech frequency region

9

What does the middle ear consist of?

Three ossicles (tiny bones)
Malleus - hammer
Incus - anvil
Stapes - stirrup

10

What do the three ossicles do?

Transmit vibrations from ear drum to the smaller oval window - the ear drum is much larger than the window so ossicles serve as amplifiers

11

What is impedance matching?

It enables air vibrations (sound) to be efficiently transformed into fluid vibration - turns a large amplitude vibration in air into a small amplitude vibration into fluid

12

What would happen without a middle ear?

Most of the sound would bounce off the cochlea (inner ear)

13

What is the function of the inner ear: the cochlea?

To transform a mechanical signal into neural responses in the 8th cranial nerve
Snail shaped, three chambered tube

14

What are the chambers in the cochlea separated by?

The basilar membrane, on which sits the organ of corti

15

What does the arch in the middle of the organ of corti do?

Separates the inner hair cells from the outer hair cells - on top of these sits the tectorial membrane which is attached along its inner edge

16

What are the stereocillia?

Outer hair cells

17

Where are the stereocillia embedded?

In the tectorial membrane

18

Where are the inner hair cells embedded?

No where, they are free and moved by movement of the fluid (endolymph) that fills the space between the hair cells and tectorial membrane

19

What is endolymph?

Fluid which fills the space between the hair cells and tectorial membrane - bends the hairs

20

What happens when inner hair cells are bend towards the stereocilium?

The cells voltage is increased
more neurotransmitter is released
auditory nerves connected to the hair cell increase firing rate

21

What happens when inner hair cells are bend away from the stereocilium?

the cells voyage is decreased
less neurotransmitter is released
auditory nerves connected decrease their firing rate

22

What is the function of inner hair cells?

Turn mechanical movement of the basilar membrane into neural firing of the auditory nerve (transduction)

23

What do the inner hair cells excite?

The synapses of fibres of the afferent (ear to brain) auditory nerve - each of the 3,000 inner hair cells have 10 auditory nerves attached to it with different diameters, thresholds and rates

24

What is the role of the outer hair cells?

Sharpening
the outer hair cells have synapses from the efferent (brain to ear) fibres, so the brain controls the mechanical properties of the ear
they exhibit motility - act as tiny motors that amplify the mechanical movement of the basilar membrane
responsible for high sensitivity (low thresholds) and sharp turning (high frequency resolution) or normal hearing

25

What does motility mean?

The outer hair cells act as tiny motors that amplify the mechanical movement of the basilar membrane

26

Where does hearing loss come from?

Damage to the outer hair cells

27

What does sound produce?

A travelling wave down the basilar membrane

28

What do different frequencies of sound give?

Maximum vibration at different places along the basilar membrane

29

The cochlea - base and apex

Near the basis it is wider and narrower at the apex, but inside the basilar membrane the basis is narrow and stiff while towards its apex it is wider and more flaccid - opposite

30

Where does the vibration to high frequency tones peak?

At the base of the membrane