Peripheral & Central Auditory Processing 1 Flashcards
(103 cards)
1
Q
How does hearing loss initially manifest?
A
- Difficult to hear in noisy environment
- May require to lip read
- Gets worse as you get older
2
Q
What is sound?
A
- Vibrations of objects –> which set up pressure waves in the surrounding air
- Elastic property of air –> allows these pressure waves to propagate (spread)
3
Q
What is the shape of sound?
What are the 2 parts of a sound wave?
A
- Sine Wave
- Compression & Rarefaction
4
Q
During pure tones, what is frequency related to?
A
- Frequency of the tone is directly related to the pitch of the sound
- Amplitude is related to perceived loudness
5
Q
If a sound has a particular frequency. It is a ….
A
Pure Tone Sound
6
Q
What is the relationship between frequency & pitch + amplitude & loudness?
A
- Logarithmic Relationships
- Double in Frequency –> Increases Pitch by 1 Octave
- Double in Amplitude –> Increase Loudness by 6dB
7
Q
What is a property of sounds with a clear pitch?
A
- Frequencies are related
- They are all multiples of a fundamental frequency
8
Q
What are sounds that have all integer multiples of a ‘fundamental frequency’ called?
What does the sound sound like?
A
- Harmonically Related
- Sounds like a sound with a clear pitch
(e.g. lowest common denominator)
9
Q
What makes up complex sounds?
A
- Frequency components (i.e. different sine waves)
10
Q
What dies a Fourier analysis help us do?
A
- Plot the amplitude (& phase) for each frequency component of a sound
- This gives us a sound spectrum
- Giving us a compact representation for signals that contain oscillations
11
Q
How do you do a fourier analysis?
What is the graph you get called?
A
- Convert PRESSURE as a function of TIME
- to AMPLITUDE as a function of DIFFERENT FREQUENCIES
- Sound Spectrum
12
Q
What is the advantage of using a Fourier Analysis?
A
Gives you a compact respresentation of signals that contains oscillations
(graphs contain lots of complicated mini-waves –> thus it helps you to not have to track sound every second –> you can present sound as different frequencies with the amount of each frequency)
13
Q
What is meant by narrowband?
A
- Sound contains energy at a narrow range of frequencies
(Pure tone is an extreme example of a narrowband)
These sounds are periodic and may evoke an identifiable pitch
14
Q
What is meant by broadband sounds?
Give examples
A
- Contain energy at a lot of different frequencies
- e.g. noises & clicks (natural broadband sounds)
15
Q
What does a spectrogram do?
A
- Divides sounds up into short-time segments –> then calculates a spectra for each time segment in turn
- This helps you track changes of sounds over time (as a sound spectrum only gives you it in one split moment)
Ear effectively converts sound into a spectrogram
16
Q
What are the 3 dimensions of a spectrogram and how are they represented?
A
- Time (x-axis)
- Frequency (y-axis)
- Energy (colour)
*
17
Q
What does the outer ear consist of?
A
- Pinna (odd bumps and folds)
- Concha
- Ear Canal
18
Q
Which part of the ear is considered to be unique to each person (like a finger print)?
A
- Pinna (bumps and folds on it)
19
Q
Which part of the external ear changes the nature of sound in a subtle way?
A
- Pinna
20
Q
What is the function of a pinna?
A
- Collect all the sound that hits it
- Directs the sound into the ear canal (thus acts to amplify sound)
21
Q
How is the pinna involved in sound localisation?
A
- Sound hits the ear –> bounces around in a complex way
- Depending on where it came from –> sound bounces in a different way
(Causing subtle changes to nature of the sound)
22
Q
How is the outer ear involved in localisation?
A
- Incoming sounds –> are filtered by outer ear –> in a way that depends upon location of the sound source in the vertical plane (elevation)
- It is also important in horizontal plane (but only if you have hearing loss in one ear)
23
Q
What happens to the frequency if a sound is presented to you at a higher inclinication level?
A
- Higher Frequency
24
Q
What happens to the frequency if a sound is presented to you at a lower inclinication level?
A
- Lower Frequency
25
What would happen if you had no pinna?
* Would not be able to localise sound above, below, infront or behind you
26
Name the **2 main functions** of the **outer** **ear**.
1. **Sound Amplification** (transforms acoustic energy at the tympanic membrane - pinna transfer function)
2. **Sound Localisation** (pinna transfers function depending upon sound source position in vertical plane)
Collects & funnels sounds to eardrum but does so differently depending on sound source location
27
Name the **3 bones** in the **middle** **ear**.
* Malleus
* Incus
* Stapes
28
Why is 99.9% of sound reflected from cochlea?
What is the conseuqence of this?
* Due to **impedence** of **fluid** in the **cochlea**
* **30dB sound loss** due to **impedence** **mismatch** between **_air_** & **_fluid_**
29
By how much do the **middle** **ear** **bones** overcome the **loss** of **sound**?
* +34dB
30
What are the **3 methods** used to **undergo** **impedence** **matching?**
1. Reduce Area
2. Increase Force
3. Buclking of Ear Drum
31
How does the middle ear **reduce** **area**?
By how much does this **increase** **sound** **pressure**?
* Area ratio of the ear drum : stapes footplate (20:1)
* +26dB
(tympanic membrane is much bigger than the footplate of the stapes --\> so focused onto a smaller area)
32
How does the middle ear **increase force**?
By how much does this **increase** **sound** **pressure**?
* Lever action of the ossicles (1.3:1)
* +2dB
33
What is the third method that causes the increase in sound pressure?
By how much does this **increase** **sound** **pressure**?
* Buckling of the Ear drum
* 2x increase in pressure
* +6dB
When the ear drum vibrates it also buckles (complex) --\> this is equivalent to a secondary lever effect --\> causing an increase in pressure
34
How does the middle ear amplify different frequencies?
* It does **_not_** **amplify** **all** **frequencies** to the **same** **level**
35
At what frequency does it amplify well?
* **1 kilohertz** (around level of human speech)
* However **higher** & **lower** **frequencies** --\> it is **_not_** as good
36
Which **muscle** in which **reflex** is activated to **protect** **hearing**?
* **Stapedius Muscle**
* Contracts in the **Middle** **Ear** **Reflex**
* **Contract** --\> oscilles unable to move (amplification not allowed)
* **Relax** --\> oscilles able to move (amplification allowed)
The reflex controls the amount of amplification
37
How does the **middle** **ear** **enhance** **sound**?
* Enhances sound **transmitted** to **inner** **ear**
* Done in a **controlled** & **frequency-dependent** way
38
What are the dimensions of the cochlea?
* 1cm wide
* 5mm from base to apex
* Snail-shaped (coiled)
39
How does the **cochlea** connect to the **middle** **ear**?
* Via the **footplate** of the **stapes** --\> which rests against the **oval** **window**
40
After the fluid in the cochlea moves --\> what moves?
* Round window
41
Name the 3 layers in the cochlea. Where are they in relation to each other?
* Scala **Vestibuli** (top)
* Scala **Media** (middle)
* Scala **Tympani** (bottom)
42
Where do hair cells sit?
Down what do they send signals?
What do they respond to?
* Sit on the **basilar** **membrane**
* Respond to **movements** of **fluid** (created by sound vibration)
* Send signals down the **auditory** **nerve** (cranial nerve VIII)
43
What is found in the 3 layers of the cochlea?
* **Scala Vestibuli** & **Scala** **Tympani** --\> contains **_PERILYMPH_**
* **Scala** **Media** --\> contains **_ENDOLYMPH_**
44
What is the composition of endolymph?
* High K+
45
What is the composition of perilymph?
* Low K+
46
What maintains the **composition** of the **endolymph**?
* Very High K+ Concentration
* Unusual in the body
* Due to **stria** **vascularis**
* **Sits** in the **lateral wall**
* Actively **increases** **K+ concentration** of **endolymph**
47
What would happen if K+ dropped in endolymph?
* **Complete Deafness**
* Needs to be maintained at a **high** **level** by **stria** **vascularis** (lateral wall of scala media)
48
What is the **membranous** **labrinyth** made up of?
What does it **comprise** of?
* **Semi-Circular Canals + Otolithic Organs**
* Contains **endolymph**
49
Why do syndromes/diseases affecting balance and vestibular apparatus affect hearing?
* Fluid environment of the **vestibular** **apparatus** is **continuous** with that of the **cochlea**
* Problems usually come together (e.g. mania syndrome)
50
What do **vibrations** do to the **basilar** **membrane**?
* Causes complex deflections
* Complicated waveform
51
What determines where the peak/centre of the fixed point on the basilar membrane will be?
* **Depends** on the **frequency** (stapes will vibrate at a certain frequency causing fluid to vibrate at that frequency causing the peak at a certain point)
52
What is the wave from the ovale window (stapes) called?
* Travelling Waveform
53
What deteremines where the wave peaks are on the basilar membrane?
* Sound Frequency
54
Where is the **wave** **peak** during **_low_** **frequency** **sounds**?
* **Close** to **Apex** (i.e. centre)
55
Where is the **wave** **peak** during **_high_** **frequency** **sounds**?
* **Close** to **Base** (i.e. near ovale window)
56
What happens if there is a complex sound? (in terms of basilar membrane)
* **More than 1 frequency**
* Therefore **different** **energies**
* Movements of the **basilar** **membrane** will be at **multiple** **different** **points**
57
What is the equation that links **stiffness** (k), **mass** (m) & **frequency** (w)?
w2 = k/m
58
Where is the basilar membrane **most** **stiff**?
* **Base** (near ovale window)
59
What happens in terms of stiffness from base to apex?
* **Stiffness decreases** as you go from the **base** to the **apex**
60
How does mass change as you go from the base to the apex?
* **Base** --\> Little Mass
* **Apex** --\> Lots of Mass
* The **mass** **increases** as you go towards the **apex**
61
Where does **low frequency** **sound** produce **movement** on the **basilar** **membrane**?
* **Apex** of the **Basilar** **Membrane**
62
Where does **_high_ frequency** **sound** produce **movement** on the **basilar** **membrane**?
* **Base** of the **Basilar** **Membrane**
63
What two properties of an object determine the frequency they are likely to vibrate at?
1. Stiffness (rigidity)
2. Mass
64
What is the **mass** & **rigidity** like at the **apex**?
* Apex
* Wide & Floppy
* **Large Mass** & **Low Rigidity**
65
What is the **mass** & **rigidity** like at the **base**?
* Base
* Narrow & Rigid
* **Small Mass** & **High Rigidity**
66
What frequency does the base 'like'?
High Frequency
67
What determines the frequency of the Basilar Membrane vibration?
1. Mass
2. Stiffness
68
What is the **stiffness** & **mass** like at the base?
* Stiff
* Less Mass
69
70
What is the **stiffness** & **mass** like at the **apex**?
* Less Stiff
* More Mass
71
What is the basilar membrane like?
* Acoustic Prism
* Takes in light --\> splits it up into lots of different frequencies
72
What is the component of the **basilar** **membrane** that **responds** **to** **sound** called?
* Organ of Corti
73
What does the Organ of Corti do?
* Converts **movement of the basilar membrane** into **electrical activity**
74
What does the **up-down movement** of the **basilar** **membrane** cause?
* **Tectorial** **Membrane** --\> to **slide** **sideways** over the **membrane**
* Causes **sideways** **displacement** of the **hair** **cell** **bundles** in the **cochlear** **hair** **cells**
(sliding of tectorial membrane to one side relative to basilar membrane pushes hairs in a particular direction (towards depolarisation or hyperpolarisation)
75
How are the **adjacent** **stereocilia** joined up?
* Tip-Links
76
How does **transduction** by the **hair** **cells** take place?
* **Stereocilia** of the **hair** **cell** **bundles** connected via **tip** **links**
* **Movement** of the **bundle** **changes** the **tension** on the **tip** **links** --\> causing **opening**/**closing stretch** **sensitive K+ channels**
* **K+ Channel Opening** --\> causes **influx** of **K+** from **endolymph** --\> causing **depolarisation** of the **hair cell membrane**
* This causes **opening** of **voltage-gated Ca2+ channels** --\> **increasing** **probability** of **transmitter** **release**
77
How does the hair work?
* Hairs **vary** in **length**
* Connected to a **stretch-sensitive K+ channel**
* If they move in **one** **way** --\> **distance** **between** **hair** either **increases**/**decreases** --\> causing an **increase**/**decrease** in **tension** in the **tip-links** --\> thus **opening/closing K+ channels**
78
What happens if the distance between hair cells decrease, therefore tension in tip-link decreases?
* Hyperpolarisation
79
What happens if the distance between hair cells increases, therefore tension in tip-link increases?
* Increase in tension
* Open K+ channels
* Depolarisation
80
What happens when K+ channels open?
* **K+ flood in** from **endolymph**
* This causes **voltage-gated Ca2+ channe**l to **open** --\> causing an i**ncrease in intracellular Ca2+**
* This causes **depolarisation**
* Causing **NT release (glutamate)**
81
What are the 2 types of hair cells?
What are they both connected to?
1. Inner Hair Cells (IHCs)
2. Outer Hair Cells (OHCs)
Both connected to Auditory Nerve Fibres
82
What is the function of the **Inner Hair Cells (IHCs)**?
* **Passive**
* Respond to **vibration** of the **basilar membrane**
* Perform a process of **mechano-electrical transduction** (convert mechanical energy to electrical)
* They **release NT** onto **Auditory** **Nerve** **Fibres** (electro-chemical transduction) --\> **transmitting** **information** along **auditory** **nerve**
83
What happens at **low** frequencies in terms of membrane potential?
* **Membrane** **potential** of the **hair** **cell** --\> **follows every cycle** of the **stimulus** (AC response)
* **Fluctuate** **rapidly** (but can keep up)
84
What happens at **high** frequencies in terms of membrane potential?
* Membrane potential is **unable** to **follow** **individual** **cycles**
* Therefore **remains** **depolarised** **throughout** **duration** of the **stimulus** (DC response)
Cannot keep up anymore with the rapid fluctuations (around 4000 hertz) --\> thus cell will depolarise and not change (frequency too high)
85
What happens at intermediate frequencies?
* Membrane potential exhibits a mixed AC + DC response
86
What is the function of Outer Hair Cells (OHCs)?
* **Active**
* **Electric-mechanical transduction**
* They **contract** --\> **feed** **energy** **back** into the **basilar** **membrane**
Electric signals feedback into it to cause mechanical mvoement so that it moves the basilar membrane --\> causing positive feedback (IHCs and OHCs propogate each other)
* Takes **small signals/vibrations** and **amplifies** them to make **movement** of **BM** even **bigger**
87
What are the important implication of OHC function?
* Process is responsible for **sensitivity** **of** **hearing**
* Vulnerable to damage by **_NOISE_** or **_OTOTOXIC DRUGS_**
88
What do OHCs contain which allows them to change their shape/length when they are depolarised?
* Prestin
89
What are the OHCs connected to and why is it important?
* **Connected** to **Basilar** **Membrane**
* Therefore causes **movement** of the **BM**
* This **amplifies** **vibrations** of the **basilar** **membrane**
90
Generally, what are the active cochlea's 2 main functions?
1. Increase Sensitivity
2. Increase Tuning
91
How do OHCs increase sensitivity & tuning?
* **Increase** **gain** in the **cochlea** by **boosting** **vibrations** --\> this also results in **narrow** **tuning**
92
What happens if **OHCs** are **not** **working** (i.e. just passive sound)?
* **Most** of the **Adjacent Basilar Membrane** will **move (displace)** too at a **similar** **level**
* Therefore will **not be tightly tuned**
* **Not much difference** between **different** **points**
* Reduced **sensitivity**
* Reduced **tuning**
93
What happens if OHCs are not working? (generally)
* **Remove the Tuning**
* **Less Sensitive**
* Need **louder** **sounds** for **auditory** **nerve** **fibres** to **respond** (cause there is no 'help')
94
OHC FUNCTION
95
Why does a healthy cochlea 'generate sound'?
* Due to **active** **mechanical** **feedback** (electro-mechanical transduction) of the **OHCs**
96
How is the theory about OHCs incorporated in baby hearing tests?
* **OHC amplification system** --\> technically **produces** **sounds** that were **_not_** **put** in **at all** (produces own sounds)
* Therefore if you feed **2 frequencie**s --\> you should get a **third** if the **OHC is working fine**
* If it is **not** there --\> **problem** with **hearing** --\> need **further checks**
97
What are the effects of antibiotics on hearing?
* **Antibiotics** can affect **Organ of Corti**
* Cause **wiping out of the hairs** on the **hair** **cells**
* Need to do **hearing** **test** **after** to **ensure** they are **okay**
98
What can cause damage to **Outer Hair Cells**?
* Drugs
* Noise
99
Specifically what antibiotic can cause hair damage (on OHCs)?
Why is this AB usually given?
* **_Kanamycin_**
* Often given to children for **juandice** & **other conditions** --\> but too much causes **hair cell destruction**
100
What are the outer & middle ear important for?
* **Transmitting** **sound** to the **inner** **ear**
* In a **form** **compatible** with the **fluid** **environment** of the **inner** ear
101
What is special about the basilar membrane?
* Tuned to **sound frequency**
* **Splits** **complex** **sounds** into **constituent** **components** (e.g. acoustic prism)
102
What are inner hair cells?
* Mechano-electrical transducers
* Convert mechanical deflections into electrical potentials
103
What are OHCs?
* **Electro-mechanical transducers**
* Enhance the **_sensitivity_** and **_tuning_** of sound
