Auditory System Flashcards
1
Q
What are the three section of the ear?
A
outer middle and inner ear
2
Q
Where is the organ embedded?
A
petrous portion of the temporal bone, the hardest bone in the body
3
Q
What is the function of the outer ear?
A
- To capture sound an to focus it the tympanic membrane
- To amplify some frequencies by resonance in the canal.
- To protect the ear from external threats (wax (chemical and mechanical protection) and hair)
- Pinna
4
Q
What is the main function of the middle ear?
A
- Amplification
- Tympanic box
5
Q
How does the middle ear amplify?
A
- Focusing vibrations from large surface area (tympanic membrane) to smaller surface area (oval window) - entrance to inner ear
- The change in surface area means the pressure is increased
- Using leverage from the incus-stapes joint to increase the force on the oval window
6
Q
What is the inner ear?
A
cochlea
7
Q
How does the inner ear function?
A
- Its function is to transduce vibration into nervous impulses
- While doing so, it also produces a frequency (or pitch) and intensity (or loudness) analysis of the sound
8
Q
What are the 3 parts of the cochlea?
A
- Scala vestibuli
- scala tympani
- Scala media
9
Q
What is the scala vestibuli and scala tympani?
A
Bone structures, contain perilymph (high in sodium) - joined
10
Q
What is the scala media?
A
Membranous structure, contains endolymph (high in potassium)
11
Q
What is located in scala media?
A
Organ of Corti (hearing organ)
12
Q
What is the basillar membrane?
A
where the organ of Corti lies in
13
Q
How is the basillar membrane arranged?
A
tonotopically, base ( narrow and tight and thicker), apex (wide and loose and thinner)
14
Q
What does tonotopically mean?
A
same principals as xylophone - sensitive to different frequencies at difference point along its length - high frequency comes vibrations of membrane have higher amplitude on base, lower frequency vibration high amplitude nearer apex
15
Q
What does the organ of corti contain?
A
thousands of hair cells: inner hair cells (IHC) and outer hair cells (OHC)
16
Q
How are IHC organised?
A
one column
17
Q
How are OHC organised?
A
3 columns
18
Q
What does the tectorial membrane above the hair cells allow?
A
-Hari defelction which depolairses. the cell
19
Q
Which hair cells are in constant contact with tectroial membrane?
A
OHC , and these assist contact with the IHC
20
Q
What do IHC do?
A
- Carry 95% of afferent information of auditory nerve
- Transduce sound into nerve impulses
21
Q
What do OHC do?
A
- Carry 95% of efferent of auditory nerve
- Modulate the sensitivity of the response
- can contract to move the IHC closer or further from tectorial membrane
- So if closer to IHC that hair. cell will transduce the cell and if kept away IHC cant transduce sound
22
Q
What are the hairs of the hair cells called?
A
stereocilia
23
Q
What does the deflection of the sterocilila towards the longest cilium cause?
A
open K+ channels
24
Q
What does the ionic interchange do?
A
Depolarises cell and neurotransmitter is liberated
25
What do higher amplitudes of sound cause?
more vibrations - greater deflection of steroclili and more K+ channel opening and all vice versa
26
What does depolarisation do?
Opens K+ channels
27
What does hyperpolarisation do?
Closes K+ channels
28
What is the process of transmitter?
1. All hairs are linked, deflection open K+ channels
2. Depolarisation so release excitatory neurotransmitter (glutamate)
3. Neurotrmasitter goes into afferent nerve
29
Why is endolymph helpful?
High K+ so enough to depolarise cell
30
What direction does sound travel?
Vibration of tympanic membrane, to ossicles, which amplify. and focus. in oval. window to perilymph to cochlea which move basillar membrane and then depends of on frequency (base or apex), IHC/OHC deflect on with tectorial membrane then. K+ channel
31
When is the mechanical movement enough for IHC to touch tectorial membrane?
When basilar membrane, cells move in one direction and might touch tectorial membrane, so make sure tectorial membrane touch IHC - happens when sound is loud enough
32
What happens if the sound is too soft and the displacement of the basillar membrane. is not enough?
Not transduced by IHC - mechancial movement not enough, OHC will contract and shorten length to make tectorial membrane touch cilia of IHC
33
What happens if the sound is too loud?
Too much loudness too much discomfort, and OHC can elongate and push away tectorial membrane so not all sound transduce so less loudness (active amplifier)
34
What happens if OHC don't work?
Only hear very narrow range of loudness
35
Where do spiral ganglions from each cochlea project?
via auditory vestibular nerve (VIII) to the ipsilateral cochlear nuclei (monoaural neurons)
36
How does auditory information crosses? Where does it go after
1. crosses at the superior olive level
- after this point all connections are bilateral
2. then inferior colliculus
3. Medial geniculate body (thalamus)
4. Auditory cortex (cerebral hemisphere)
- Processing of sound in brainstem not just detecting
37
How is hearing organised?
tonotopically (continued through central auditory pathway)
- High freq in base of cochlea and low freq in. apex of cochlea
- All frequencies needed to discriminate speech
38
What is frequency/pitch (Hz)?
Cycles per second, perceived tone
39
What is Amplitude/loudness (dB)?
Sound pressure, subjective attribute correlated with physical strength.
40
What is the human range of hearing?
Frequency: 20–20,000Hz
Loudness: 0 dB to 120 dB sound pressure level (SPL)
41
Why is the decibel scale used?
- (a log scale) is useful because the range of sensitivity is very large
- allows us to compress the scale on a graph, and reflect the fact that many physiological processes are non-linear (i.e. they can respond to both very low and very high values)
42
How does hearing change with age? What type of sounds?
- decreases with age, particularly higher frequencies
| - medium and low frequencies could be affected with the progression of a hearing loss
43
What are the aims in hearing assessment?
- Is there a hearing loss? If yes…
- Of what degree?
- Of what type?
44
What are the different procedure for hearing assessment?
1. Tunning fork
2. Audiometry
3. Central processing assessment
4. Tympanometry
5. Otoacustic Emission
6. Electrocochleography
7. Evoked potentials
45
How are tuning forks used?
1. establish the probable presence or absence of a hearing loss with a significant conductive component
2. used to provide early and general information, when audiometry is not available or possible
- Not specific just to see if symmetric
- Weber and Rinne test
46
What is pure tone audiometry?
- Science of measuring hearing acuity for variations in sound intensity and frequency
- Good
- test at different frequencies
- Both ears seperately
- Difference between airconduction and bone condition (outer and middle ear vs just inner ear)
47
What is an audiometer?
device used to produce sound of varying intensity and frequency
48
What is an audiogram?
- The audiogram is where the hearing thresholds are plotted to define if there is a hearing loss or not
- A normal hearing threshold is located between 0 – 20dB
49
What is central processing assessment?
- Assessment of hearing abilities other than detection
| - Verbal and non verbal tests
50
What are examples of central processing assessment?
1. Sound localization
2. Filtered speech
3. Speech in noise
51
What is tympanometry?
used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal
52
What are the most common results in tympanometry?
* A – normal
* C – negative middle ear pressure
* B
* Middle ear effusion
* Perforation of tympanic membrane
* Eustachian (pharyngotympanic) tube dysfunction
* Occluded ear canal
53
What is a Otoacousitc emission (OAEs)?
- normal cochlea produces low-intensity sounds called OAEs
| - These sounds are produced specifically by the outer hair cells as they expand and contract
54
When do you test OAEs?
part of the newborn hearing screening and hearing loss monitoring
55
What is electrocochleography?
1. 0.2-4.0 ms, electrical activity from the cochlea and eighth nerve
2. Evoked by clicks or tone burst
56
What is auditory brainstem response (ABR)?
1. 1.5-10.0 ms, electrical activity from the eighth nerve and brainstem nuclei and tracts
2. Evoked by clicks
57
What are Late Responses (N1-P2, P300, MMN, and more)?
1. 80-500+ ms, electrical activity from the primary auditory and association cortex
2. Evoked by tone burst and oddball paradigm.
58
When would you use ABR?
1. ABR is more commonly used in clinic
2. Does not require attention from the patient
3. Alterations in the latency of waves can point to the location of the deficit.
4. Objective measurement commonly used in babies and children
59
When would cortical potentials be affected?
- on neurological conditions or processing problems
| - About processing
60
What is conductive hearing loss?
Problem is located in outer or middle ear problem with transmission to inner ear
61
What is sensorineural hearing loss?
Problem is located in the inner ear or the auditory nerve
62
What is mixed hearing loss?
- Conduction and transduction of sound are affected
| - Problem affects more than one part of the ear
63
How is hearing loss measured?
mild, moderate, severe or profound
64
What could cause outer ear conductive hearing loss?
- Wax
- Foreign body
- Cerum impactation
65
What could cause middle ear conductive hearing loss?
- Otitis
| - Ostosclerosis
66
What is otitis?
Bubbles can be seen through the ear drum, suggesting there is liquid inside the middle ear
67
What could be the cause of inner ear sensorineural hearing loss?
- Prebycusis
| - Ototoxicity
68
What could be the cause of nerve sensorineural hearing loss?
VIII nerve tumour
69
What are treatment options for hearing loss?
1. Underlying cause
2. Hearing
3. Cochlear implants
4. Brainstem implants
70
What do hearing aids do?
amplify the sound, does not replace any structure (lots of different. types)
71
What does cochlear implant do?
replaces the function of the hair cells by receiving sound, analysing it, transform it into electrical signals and sending an electric impulse directly to the auditory nerve
72
What is needed for a cochlear implant?
functional auditory nerve to function
73
When would you have brainstem implant?
When the auditory nerves are the affected structures, the electrical signals can be send to a set of electrodes placed directly into the brainstem
74
Why would you not have a brainstem implant?
very risky, then it is advised for people with bilateral important auditory nerve damage
