Hearing Flashcards
(126 cards)
1
Q
What are the three anatomical regions of the ear?
A
Inner, middle and external ear.
2
Q
What is the role of the pinna?
A
It directs sound waves into the ear canal, which causes vibration of the tympanic membrane.
3
Q
Name the three ossicles.
A
Malleus.
Incus.
Stapes.
4
Q
What is the role of the ossicles?
A
To transmit soundwaves to the fluid filled inner ear.
5
Q
What happens when the stapes footplate moves into the oval window?
A
The membrane of the round window bulges outward in response.
6
Q
What does the outward movement of the round window lead to?
A
It allows fluid to move within the cochlea, causing activation of auditory receptors on the organ of Corti.
7
Q
Name the sensory organ of the inner ear.
A
The organ of Corti.
8
Q
Where is the organ of Corti located?
A
On top of the basilar membrane.
9
Q
The cochlea is stimulated by soundwaves. Where do the vibrations of the soundwaves move to next?
A
They travel along the basilar membrane and activate the outer hair cells.
10
Q
Describe how the vibration of the basilar membrane is amplified.
A
Soundwaves activate the OHCs, causing movement of their hair bundles.
Since the hair bundles are embedded in the tectorial membrane, the movement of the OHCs is projected to the tectorial membrane.
Therefore, the motile response evoked in the hair bundles of the OHCs amplifies the vibration of the basilar membrane.
11
Q
Describe the anatomy of the hair bundles of the OHCs.
A
Protrude from the top of the OHC.
Made up of the tips of stereocilia.
Embedded in the tectorial membrane.
12
Q
Describe the two ways in which IHCs detect the amplified vibration of the basilar membrane.
A
Through the increased movement in the fluid-filled environment of the cochlea.
Via the tectorial membrane, since the tips of the IHCs are also embedded in this.
13
Q
What happens when the IHCs detect the amplified vibrations of the basilar membrane?
A
They transduce the mechanical vibration into a neural signal.
14
Q
What is the main function of the cochlea?
A
To analyse and convert the vibrations caused by sound into a pattern of electrical signals that can be conveyed along the auditory nerve fibres to the brain.
15
Q
What are the three steps of the cochlea’s main function?
A
Sensory transduction.
Processing of the signal.
Neurotransmission.
16
Q
Name the two membranes that separate the cochlea into three separate chambers.
A
Basilar membrane.
Reissner’s membrane.
17
Q
Name the three chambers of the cochlea.
A
Scala media.
Scala vestibuli.
Scala tympani.
18
Q
Which chamber(s) of the cochlea contain endolymph?
A
Scala media.
19
Q
Which chamber(s) of the cochlea contain perilymph?
A
Scala vestibuli.
Scala tympani.
20
Q
In which chamber is the organ of Corti found?
A
Scala media.
21
Q
Which ion is found in a high concentration within endolymph?
A
Potassium.
22
Q
Which ion is found in a high concentration in perilymph?
A
Sodium.
23
Q
The cochlea is a hydromechanical frequency analyser. What does this mean?
A
The amplitude of the vibrations varies along the length of the basilar membrane. Frequency of tone is mapped tonotopically along its length.
24
Q
Which section of the basilar membrane responds to high frequencies?
A
The basal turn.
25
Which section of the basilar membrane responds to low frequencies?
The apical turn.
26
What is the frequency range at which humans can perceive sound?
20Hz - 20kHz.
27
What are infrasounds?
All sounds below human hearing range.
28
What are ultrasounds?
All sounds above human hearing range.
29
What are transient evoked otoacoustic emissions?
Sounds emitted by the cochlea in response to an acoustic stimulus of a very short duration, e.g. a tone burst or click.
30
How are transient evoked otoacoustic emissions used diagnostically?
It is a diagnostic objective test for hearing function, usually to determine whether a hearing problem is due to mechanical or electrophysiological pathology.
31
Name the two acellular membranes in the cochlea.
Basilar membrane (BM).
Tectorial membrane (TM).
32
Where does the organ of Corti sit in relation to the BM and TM?
Above the BM.
Below the TM.
33
Name the three cells that make up the organ of Corti.
Inner hair cells (IHCs).
Outer hair cells (OHCs).
Supporting cells.
34
Stereocilia project from the apex of IHCs and OHCs. Name the four places that they are embedded.
TM.
Supporting cells.
Stria vascularis on the lateral wall.
Auditory efferent nerve fibres.
35
Describe the role and location of the IHCs and OHCs.
They are the mechanosensory receptors of the inner ear found in the cochlear and the vestibular membranes.
36
In three sentences, summarise how sound is transduced.
Auditory stimuli is received in the form of mechanical energy called sound waves.
OHCs amplify this energy, which stimulates the IHCs.
The mechanical energy is transduced into an electrical neural signal.
37
Why are supporting cells rich in cytoskeletal proteins?
To provide mechanical support to the organ of Corti.
38
Name a specific supporting cell in the cochlea.
Deiter's cells.
39
How do Deiter's cells support the inner ear?
They employ cross-bracing.
40
How do Deiter's cells protect the IHCs and OHCs?
They contain a protein that pumps potassium ions to ensure hair cells fire properly. Without this, potassium can build up and kill hair cells, causing deafness.
41
Describe two similarities between IHCs and OHCs.
They have similar rows of stereocilia in their bundle structure.
They can both perform mechanoelectrical transduction.
42
Describe two differences between IHCs and OHCs.
They have different shapes of stereocilia in their bundle structure.
They have different innervation.
43
Describe the structure of IHCs.
Flask shaped.
Mitochondria dispersed.
Central nucleus.
44
Describe the structure of OHCs.
Cylindrical.
Mitochondria mostly lateral.
Basal nucleus.
45
Describe how OHC stereocilia are arranged.
V-shaped formation.
Arranged in 3 rows of small, intermediate and tall.
Protrude from apical surface.
46
Describe the bundle structure of stereocilia.
Form precise rows and are linked by various extracellular filaments.
47
What are tip links?
Links that protrude from the top of short and intermediate stereocilia.
48
What are lateral links?
Links between the rows and contact regions of stereocilia.
49
What is the role of actin in stereocilia?
Forms the core of stereocilium.
50
Stereocilia hair bundles are the site of what?
Mechanoelectrical transduction.
51
Where are hair bundles found?
On the apical surface of hair cells.
52
Hair cells are sensitive to what?
Deflections of the hair bundle along the axis of sensitivity.
53
How does the direction of deflection of hair bundles affect transduction?
Deflections in a positive direction lead to excitation.
Deflections in a negative direction lead to inhibition.
54
What is the evidence for gating spring action in excitatory transduction?
The direction of deflection directly governs the operation of MET channels through tensioning of the tip links.
55
What are MET channels?
Mechanoelectrical transduction channels.
56
How does deflection of the hair bundle in a positive direction lead to excitatory transduction?
This deflection increases tension on the tip link, opening the MET channel and allowing calcium and potassium ion influx. This depolarises the hair cell.
57
What is believed to be calcium's role in excitatory transduction?
It evokes the rapid relaxation process that closes the MET channel and ensures fast adaptation.
58
What drives the transduction of sound waves into an electrical neural signal?
Homeostatic mechanisms with the cochlea, specifically the scala media, generate a battery called the endocochlear potential.
59
Fully explain hair cell transduction and neurotransmission.
The BM moves up in response to fluid movement in the scala tympani.
This displaces the taller stereocilia against the TM.
Ion channels at the tips of the stereocilia open, allowing potassium flow along the electrical gradient to depolarise the cell.
Upon depolarisation, voltage-gated calcium channels at the base of the cell open.
Calcium influx causes synaptic vesicles to fuse to the cell membrane.
NT is released into the synaptic cleft between the hair cell and cochlear nerve fibres.
The NT causes depolarisation of the afferent fibre.
An action potential is transmitted along the cochlear nerve fibre.
60
Why is there a large potential difference between the hair bundles in endolymph and the hair cell interior?
Hair bundles are bathed in potassium-rich endolymph at +80mV.
The electrical gradient within the IHC is -70mV.
61
What does the large potential difference between the hair bundles in endolymph and the hair cell interior lead to?
It creates a force of 150mV that, once ion channels open, drives potassium into the cell. This increases the range of the cell's graded electrical response to mechanical displacement.
62
Why are IHCs the main output stage of the cochlea?
They transmit almost all acoustic information to the brain because they synapse with 90-95% of type I auditory nerve fibres.
63
What is the spiral ganglion (SG)?
The first part of the auditory pathway.
64
Where is the SG found?
It spirals around the cochlea in Rosenthal's canal.
65
Name the two types of neuron that SG contains.
Type I spiral ganglion neuron.
Type II spiral ganglion neuron.
66
Which type of SGN is myelinated and which is unmyelinated?
Myelinated = type I.
Unmyelinated = type II.
67
Where do both SGNs project to?
The cochlear nuclei.
68
What percentage of afferent nerve fibres do type I SGNs contribute to?
85-95%.
69
What percentage of afferent nerve fibres do type II SGNs contribute to?
5-15%.
70
Which type of SGN innervates IHCs with its peripheral process and which innervates OHCs with its peripheral process?
IHC = type I.
OHC = type II.
71
Which type of SGN innervates spherical-bushy cells with its central process and which innervates cells in the cochlear nuclei with its central process?
Spherical-bushy cells = type I.
Cells in the cochlear nuclei = type II.
72
What is the role of cells in the cochlear nuclei?
They contribute to efferent control of the cochlear amplifier.
73
Why is efferent control of the cochlear amplifier important?
It is necessary for speech discrimination in noise, sound localisation and protection from noise-induced hearing loss.
74
What is speech discrimination in noise?
The ability to hear a conversation over the noise in a club or party, for example.
75
Which neurons make up the auditory nerve?
Bipolar auditory neurons.
76
The peripheral processes of auditory neurons form synapses with which cells?
Hair cells.
77
The central processes of auditory neurons form synapses with which cells?
Cochlear nucleus cells in the brainstem.
78
How do hair cells support the maintenance and survival of auditory neurons?
They provide trophic support, such as BDNF (brain-derived neurotrophic factor) and NT-3 (neurotrophin-3).
79
What do auditory neurons synthesise?
High-affinity tyrosine receptor kinases: TrkB and TrkC.
80
What is the transitional zone (TZ)?
The interface between the PNS and CNS.
81
What is the evidence that there is tonotopic mapping of frequency of tone on the BM?
The auditory nerve fibres are tuned to different frequencies, representing the tonotopic axis of the BM.
82
What are the three main roles of cochlear nuclei?
Decode intensity of sound stimulus.
Analyse temporal parameters like duration of sound stimulus.
Maintain and transmit the frequency analysis previously carried out at the level of the cochlea.
83
What is the endbulb of Held?
The first synapse in the central auditory brain implicated in the pathway that processes the precise timing features of sound critical for sound feature detection and for localising sounds.
84
Where are spherical-bushy cells located?
At the endbulb of Held.
85
What does the ascending branch of the cochlear nerve innervate?
Anteroventral cochlear nucleus (AVCN). (This axosomatic synapse is the endbulb of Held.)
86
What does the descending branch of the cochlear nerve innervate?
Posteroventral cochlear nucleus (PVCN).
87
Which neuron carries the frequency, timing and intensity information about a sound stimulus to the cochlear nerve?
Type I SGN.
88
Which two specialised cells respond continuously throughout a sound stimulus?
Globular and spherical neurons.
89
What is the onset response and which cell is responsible for it?
Octopus cells fire at the beginning of the stimulus.
90
What is the pauser response and which cell is responsible for it?
Fusiform cells of the dorsal cochlear nucleus (DCN) do not fire at the beginning of the stimulus, but turn on after the beginning.
91
Where does the auditory pathway project to from the cochlear nuclei?
The superior olivary complex.
92
Which neurons respond to interaural time differences (ITDs)?
Medial superior olive neurons.
93
Which neurons respond to interaural level differences (ILDs)?
Lateral superior olive neurons.
94
How is ITD used to localise a sound?
If a sound comes from the right, the right ear will hear it a millisecond before the left ear. Therefore, it uses the ITD between both ears hearing the sound.
95
How is ILD used to localise a sound?
It is the difference in loudness and frequency distribution between the two ears. If a loud sound comes from the right, the right ear will hear it louder than the left.
96
Define binaural localisation of sound.
The use of ITD and ILD to determine the direction a sound is coming from and locate its source.
97
What feature of the superior olivary complex makes binaural localisation possible?
The preservation of tonotopic mapping that originated on the BM.
98
What are the lateral lemniscus nuclei composed of?
Different neuronal groups organised between the ascending fibres of the lateral lemniscus.
99
What are the two regions of the lateral lemniscus nuclei?
Ventral nucleus.
Dorsal nucleus.
100
Describe the anatomy of the ventral nucleus.
Composed of monaural neurons.
Receives information from the ipsilateral ventral cochlear nucleus.
Neurons are not arranged tonotopically.
101
Describe the anatomy of the dorsal nucleus.
Composed of binaural neurons.
Receives information from both ears.
102
What is the role of the ventral nucleus?
Processes the duration of complex sounds, which is important for understanding language.
103
Name the two parts of the inferior colliculus (IC).
External and dorsal cortices.
Central nucleus.
104
How are the external and dorsal cortices of the IC organised?
Into neuronal layers without precise tonotopic organisation.
105
What is the central nucleus of the IC composed of?
A large group of tonotopically-organised neurons.
106
From which three areas does the central nucleus of the IC receive input?
Cochlear nuclei.
Superior olivary complex.
Lateral lemniscus.
107
Describe how the central nucleus of the IC receives frequency information.
Receives low frequency information from the ipsilateral ear.
Receives high frequency information from the contralateral ear.
108
What are the two main roles of the IC neurons?
Frequency analysis.
Decoding ITD and ILD.
109
Which fibres mediate the activity of IC neurons?
Descending fibres from the cortex and the thalamus (medial geniculate body (MGB).
110
Name the three subdivisions of the medial geniculate body (MGB).
Ventral.
Medial.
Dorsal.
111
Which subdivision of the MGB is tonotopically organised?
Ventral.
112
Which subdivision of the MGB is not tonotopically organised?
Dorsal.
113
Which subdivision of the MGB projects to the auditory cortex?
Ventral.
114
What information does the ventral subdivision of the MGB respond to?
Different features of sounds.
115
What information does the medial subdivision of the MGB respond to?
Multisensory inputs modifiable by personal experience.
116
What information does the dorsal subdivision of the MGB respond to?
Complex sounds.
117
Describe the excitation : excitation category of binaural stimuli.
Summation from both ears.
118
Describe the excitation : inhibition category of binaural stimuli.
Suppression from one ear on the other.
119
Name the two streams of the auditory cortex.
Anterior auditory pathway.
Posterior auditory pathway.
120
Which two areas of the association cortex are auditory signals conducted to from the auditory cortex?
Prefrontal and posterior parietal cortex.
121
What is the anterior auditory pathway believed to be involved in?
Identifying sounds.
122
What is the posterior auditory pathway believed to be involved in?
Locating sounds.
123
What is the main role of Broca's area?
Motor aspects of speech.
124
What is the main role of Wernicke's area?
Comprehension and production of language.
125
What is the Wernicke-Geschwind model?
Written word (early visual processing) and spoken word (early auditory processing) feed down the two different pathways into the inferior frontal cortex where semantic association is made and also into the supplementary motor area for premotor coding.
126
Describe the involvement of corticofugal projections in distinguishing speech buried in background noise.
The corticofugal projection pathways contain the requisite circuitry to implement predictive coding mechanisms to facilitate perception of complex sounds.
