Auditory System Flashcards
1
Q
what is sound?
A
refers to change in air pressure generated by vibrating air molecules
2
Q
is sound physical or chemical energy?
A
physical
3
Q
what is sound measured in?
A
decibels on a log scale
4
Q
parameters of sound
A
amplitude: loudness
frequency:pitch
5
Q
what is timbre?
A
complexity of the sound wave or multiple frequencies combined
6
Q
what would a low amplitude sound look like?
A
7
Q
what would a high amplitude sound look like?
A
8
Q
what would a low frequency sound look like?
A
9
Q
what would a high frequency sound look like?
A
10
Q
one challenge of the auditory system is…
A
breaking down a sound into their frequency components
11
Q
the ear successfully breaks down ____ into _____ that make up a sound
A
waveforms, smaller sine waves
12
Q
what are the 3 main challenges of teh auditory system?
A
- detect and code the amplitude and relevant frequencies
- dynamically modulating this process in a context specific manner
- using information for hearing and sound localization
13
Q
what three parts is the ear composed of?
A
outer ear, middle ear, inner ear
14
Q
label this diagram:
A
A: ear canal
B: inner ear
C: pinna
D: ear drum
E: middle ear
F: eustachian
15
Q
what does the outer ear consist of?
A
pinna and ear canal
16
Q
function of the pinna
A
funnels sound into the middle and inner ear (amplification) and plays a role in sound localization
17
Q
the pinna ____ filters sound waves depending on the ____ of their source
A
differentially, elevation
18
Q
frequency range for whales
A
20-100,000 hz
19
Q
frequency range for bats
A
1500-100,000 hz
20
Q
frequency range for humans
A
20-20,000 hz
21
Q
frequency range for frogs
A
600-3,000hz
22
Q
frequency range for fish
A
20-3,000 hz
23
Q
frequency range for crickets
A
500-5,000 hz
24
Q
frequency range for birds
A
Variable across species, but top
end usually well below 10,000 Hz
25
what does the middle ear consist of?
the ear drum (tympanic membrane) and 3 small ossicles (malleus, incus, stapes)
26
what does the middle ear do?
prevents reflection of sound due to resistance in air/water differences (size of ear drum and lever action)
-tranduces sound
-a little bit of amplification of sound
27
sounds amplified by the _____ causes vibrations of the _____
outer ear, eardrum
28
information is amplified through the ____ and causes the ____ to go to the ____
middle ear, vibration, inner ear
29
why arent sound waves sent directly to the cochlea from the outer ear?
- Sound propagates through air, but sensory receptors/cells are in an aqueous environment in the cochlea.
- The middle ear allows for the change in medium, so sound waves don’t just reflect off the cochlea.
30
without the middle ear, ____ of sound energy would reflect
>99.9%
31
main effects of middle ear arise from:
1. size of the ear drum relative to stapes (~35X)
2. lever action of the ossicles
32
what does the level action of the ossicles allow for?
the pressure of the ossicles to be focused onto one spot, resulting in more effective vibrations to the cochlea
-> important point of control!
33
label this diagram:
A: malleus
B: incus
C: stapes
D: tympanic membrane
E: base of stapes in oval window
34
what two things is neural control of the middle ear performed by?
1. trigeminal nerve
2. facial nerves
35
trigeminal nerve
innervates the tensor tympani muscle that works to move the malleus.
36
facial nerves
innervate the stapedius muscle that works to move the stapes.
37
what do the stapedius and tensor tympani tend to do?
stiffen the eardrum and dampen the transfer of loud sound energy from the outside world.
38
softer sounds cause the muscles to ____ to allow more ____
relax, sound transfer
39
hyperacusis
increase acuity and hypersensitivity to sound, caused by lesions affecting trigeminal and facial motor output.
40
what does the inner ear consist of?
the cochlea
41
what is the cochlea responsible for?
converting sound waves into eletrical signals the brain can interpret
42
vibrations become ____ and are passed from the ____ into the _____
fluid pressure waves, oval window, cochlea
43
once fluid pressure waves are at the cochlea, what are they converted to?
nerve impulses
44
describe the cochlea structure
spiral structure, bisected by the cochlear parition
45
whats the cochlear partition?
a flexible structure that supports the basilar membrane and the tectorial membrane.
46
the inner ear is a ____ consisting of three parts. what are these?
bony labyrinth, the vestibule, semicircular canals (balance), and cochlea.
47
what is the bony labyrinth filled with?
Filled with perilymph (~CSF, low K+ compared to hair cell)
48
membranous labyrinth
lodged within the bony labyrinth in the inner ear and has the same general form, but is smaller.
49
what is the membranous labyrinth filled with?
Filled with endolymph (high K+ compared to hair cell)
50
what are the fluid filled compartments of the cochlea?
scala vestibuli, scala media, and scala tympani
51
cochlear is partitioned by:
reisners membrane and basilar membrane
52
reisners membrane
divides the scala vestibuli and scala media.
53
basilar membrane
divides the scala media and scala tympani.
54
label this diagram:
A: vestibular nerve
B: auditory nerve
C: oval window
D: stapes
E: round window
F: cochlea
55
label this diagram:
A: tunnel of corti
B: spiral ganglion
C: scala tympani
D: inner hair cells
E: basilar membrane
F: outer hair cells
G: reisners membrane
H: scala media
I: scala vestibuli
56
stria vascularis
a capillary loop containing numerous blood vessels, produces endolymph
57
transduction from mechanical to electrical energy occurs in the ____ and is performed by ____
organ of corti, hair cells
58
hair cells release ____ to ____ to elicit APs
glutamate, spinal ganglion cells
59
displacement of the basilar membrane due to sound waves causes...
displacement of hair cells in the tectorial membrane
60
what drives transduction?
the compression and resulting shearing forces cause the cilia to move
61
label this diagram:
A: tectorial membrane
B: stereocilia
C: afferent axons
D: basilar membrane
E: inner hair cells
F: tunnel of corti
G: efferent axons
H: outer hair cells
62
more than __ of the ___ contracts are on ____
95%, afferent (SGCs heading to cochlear nucleus), inner hair cells
63
more than ___ contact each _____
20 afferent fibers, inner hair cell (and no others)
64
more than ___ of ___ contacts are on the ____
90%, efferent (neurons from superior olivary complex), outer hair cells
65
T/F: the arrangement of outer hair cells in the cochlea is the same from that of inner hair cells
false, it differs.
66
hair cells are embedded in the
tectorial membrane
67
outer hair cells have how many rows?
3 or 4
68
inner hair cells have how many rows?
1
69
stereocillia
hair-like protrusions on hair cells.
70
kinocilium
tallest stereocillium, makes connection with the tectorial membrane
71
sterocillia synapse onto ____ via a _____
ganglion cells, ribbon synapse
72
outer hair cells have ____, where changes in ____ lead to changes in the _____
contractile ability, membrane potential, size of outer hair cells
73
prestin
a transmembrane molecule that has chloride-binding sites; called the molecular motor.
74
when the membrane is hyperpolarized what happens with prestin?
chloride ions influx into the cell, bind to prestin,l and this leads to elongation.
75
when the membrane is depolarized what happens with prestin?
chloride ions efflux, leaving the prestin molecule, and this leads to contraction.
76
when the basilar membrane moves, the cilia on outer hair cells bend towards...
the tallest stereocillia
77
bending towards tallest stereocilliar causes...
tip links (connection between stereocilia, open K+ channels) of the OHC hair bundle to open allowing inflow of K+ which depolarize the OHC.
78
why does K+ enter the cell?
Because endolymph has a higher concentration of K+ compared to a hair cell.
79
when depolarized, the ____ loses the ____ and the cell ____
prestin molecule, chlorine, shrinks/contracts
80
shrinkage/contraction pulls the basilar membrane ___, closer to the ____, which causes OHC ____ and prestin ____
upward, tectorial membrane, hyperpolarization, elongation
81
adaptation helps...
shift the baseline of neurons to allow for response changes to occur within the dynamic range.
82
why is tip link tension lost with sustained depol in hair cells?
because the “tether” is moved by the stereocilia.
83
adaptation is mediated by
myosin motors
84
slow adaptation ensures when the motor slides down the ____, allow ____
stereocilia, channels to close
85
the basilar membrane has specific properties that allow it to be tuned for _____ to create _____
mechanical frequencies, standing waves
86
what happens if we have big hair cells?
= big membrane = big capacitance = big time constant = cannot respond quickly to inputs
87
describe the structure of the basilar membrane
basilar membrane is thick and pointed on one end (basal end) and tapered on the other (apical end).
88
basal end of the basilar membrane has a max amplitude for ____ frequencies
high
89
How does the thickness and stiffness of the basal end of the basilar membrane relate to the frequency of sound?
basal end, being thicker and stiffer, exhibits maximum amplitude for high frequencies.
90
What is the helicotrema, and where is it located in the cochlea?
is the point of the cochlea where the basilar membrane terminates.
91
How does the apical end of the basilar membrane differ in terms of thickness and flexibility?
The apical end is thinner and more flexible.
92
apical end of the basilar mem has a max amplitude for ____ frequencies
low
93
Where does the body break down sound into different frequencies in the auditory system?
basilar membrane is the first point where the body breaks down sound into different frequencies.
94
what is this graph showing?
spiral ganglion cell vs basilar membrane tuning curves
-> The basilar membrane is tuned to certain frequencies, but the tuning is broader than the tuning of SGCs.
The cochlea is most likely an active system with a positive feedback loop that accounts for higher cochlear sensitivity.
95
the selectivity of basilar membrane is also reflected in _____
spiral ganglion cells
96
SGCs undergo ______; they tend to prefer a certain frequency. this allows for ______.
frequency tuning, selective patterns of firing
97
best frequency
he frequency with a minimum amplitude needed to evoke an AP
98
place code
each neuron has a best frequency that depends on its place in the cochlea
99
T/F: nerves collecting at different places along the basilar membrane would all have the same best frequencies
false, different places will have different best frequencies
100
how do cochlear implants work?
can retrieve hearing by putting electrode and transducer into cochlea and send current pulses to different parts of membrane
101
the electrodes of cochlear implants
stimulate different places on the basilar membrane
102
a transducer in cochlear implants
can analyze incoming sounds and stimulate the electrode accordingly
103
auditory scene analysis
the auditory system is able to separate the different acoustic inputs coming into the ear to generate the “sounds” we hear.
- Require learning early in life.
104
both the ____ and the ____ must be extracted and connected with their location. this occurs in the _____.
signal structure (frequencies), envelope (amplitude modulation of the individual frequencies), cortex
105
inner hair cells make ____ with _____ that project to the _____.
ribbon synapses, spiral ganglion cells, cochlear nucleus
106
ribbon synapse
an electron-dense ribbon holds vesicles close to the active site.
107
in ribbon synapse, there is _____ that promotes rapid NT release
tight vesicle-calcium channel coupling
108
____ receptors that sense ____ and elicit APs in spinal ganglion cells
AMPA, glutamate
109
SGCs connecting to the same inner hair cell have ...
heterogenous properties
110
hair cells utilize ____ channels
L-type Ca2+
111
hair cells reply on ____
ribbon synapses
112
what are mutations of the otoferlin gene associated with?
deafness map
113
In an immature mouse, where is otoferlin expressed?
in both inner and outer hair cells
114
As the mouse matures, where does otoferlin become more localized, and what does this localization indicate?
Otoferlin becomes more localized to the bottom of inner hair cells at the ribbon synapse, indicating its involvement in vesicular release.
115
What is the impact of otoferlin knockout (KO) in mice on auditory brainstem response (ABR)?
Lack of ABR indicates that otoferlin is essential for information propagation through the auditory system.
116
What do the current-voltage relationships of calcium channels in inner hair cells show in otoferlin KO mice?
There is less vesicle fusion in otoferlin KO mice
117
How are ribbon synapses similar to capacitors, and what happens during fusion?
Ribbon synapses, like capacitors, expand during fusion, increasing capacitance.
118
What happens to Ca2+ current and capacitance in otoferlin KO mice despite the same current?
Ca2+ current is the same, there is no change in capacitance in otoferlin KO mice
119
_____ exocytosis is almost ____ in the absence of oterferlin
Ca2+ triggered, completely abolished
120
What is caged calcium, and what happens during a UV flash?
Caged calcium is when compounds prevent calcium ions from interacting with cell components. A UV flash usually elicits a large amount of exocytosis, but in otoferlin KO, there is much less
121
Why do people speculate that otoferlin acts as a calcium sensor?
Reduced exocytosis in otoferlin KO led to speculation that otoferlin acts as a calcium sensor.
122
With what stages of release machinery does otoferlin interact?
Otoferlin interacts with SNAREs and endocytic proteins, including adaptor protein 2 (AP2), playing a role in vesicle recycling.
123
What role may SNAREs play in the absence of synaptotagmin in hair cells, and why?
SNAREs may act as a replacement for synaptotagmin, which hair cells lack.
124
What role does otoferlin play in vesicle recycling, and which endocytic protein is involved?
it interacts with adaptor protein 2 (AP2) for the rapid clearance of exocytosed material from the vesicular release site.
125
What condition is associated with a mutation in the otoferlin gene, and what are its characteristics?
Temperature-dependent deafness, involving hearing deficits often observed during fevers
126
How do intracellular voltage changes in inner hair cells vary with different frequencies of stimulation?
At low frequencies, they show oscillations (alternating current), while at high frequencies, they lose the oscillations (direct current).
127
What is phase-locking, and where is it observed?
Phase-locking is when the probability of firing an action potential is highest at a certain phase of the cycle of a sound wave stimulus. It is observed in SGCs (auditory nerve fibers).
128
Up to what frequency does phase-locking occur, and what happens at higher frequencies?
Phase-locking occurs up to 10 kHz. At higher frequencies, the neuron cannot fire as consistently but still fires most at a certain phase.
129
what are the 3 cochlear nucleus divisions?
Anteroventral (AVCN)
Posteroventral (PVCN)
Dorsal (DCN)
130
T/F: each auditory nerve fiber innervates all 3 CN divisions
true
131
neurons best frequencies change as you move more ____ into the ____
medially, cochlear nucleus
132
more medial:
prefer higher freq
133
more lateral:
prefer lower freq
134
end bulbs of SGCs make strong contact with ____ in the CN
bushy cells
135
what does strong contact between end bulbs and bushy cells result in?
results in a loss of fine control of the neuron as branching is lost
136
what do end bulbs engulf and why?
the soma of bushy cells to make a foolproof connection
137
how many end bulbs typically engulf a bushy cell?
2-3
138
VCN bushy cells show _____ of phase locking relative to their _____ inputs
improved precision, auditory nerve fiber
139
temporal features are ____ by the ____ of multiple SGC end bulbs onto a single bushy cell
enhanced, convergence
140
what is an ITD?
interaural time difference, time it takes for sound to hit the other ear after reaching one ear
141
if the speed of sound is 343m/s and the distance between human ears is 20cm, what is the ITD?
approx 600 microseconds
142
what is the localization accuracy for sources in front of the listener
1 degree
143
what is the localization accuracy for sources to the side?
15 degrees
144
how finely can humans discern ITDs?
as small as 10 microseconds
145
MSO neurons only respond when...
they receive coincident excitatory inputs from both ears
146
what does the jeffress model explain?
how the brain detects small differences in the timing of sounds, is based on the convergence of variable length axonal delay lines onto neural coincidence detectors
147
how does the jeffress model achieve sound localization based on ITDs?
through convergence of variable length axonal delay lines onto neural coincidence detectors, w diff branching patterns of AVCN axon projecting to the MSO on ipsilateral and contralateral sides
148
what is the specificity of each coincidence detector in the Jeffress Model?
each responds maximally to a single ITD, corresponding to a single sound source direction in the horizontal plane
149
how is the MSO organized?
tonotopically to emphasize low freuqnecies
150
label the diagram:
a: end bulb
b: auditory nerve
c: ipsilateral delay
d: MSO
e: contralateral delay
f: endbulb
g: ipsilateral side
h: contralateral side
151
the ____ occurs within the _____ range
characteristics/best delay, physiologically relevant range
152
when do MSO neurons exhibit max firing in terms of ITDs?
occurs when the ITDs result in stimuli from the right and left ear being in phase
153
is peak spacing of ITD functions related to the period of the stimulus
yes
154
what does IPD refer to
interaural phase differences, difference in the phase of a waves that reaches each ear
155
what influences IPD
is dependent on the frequency of the sound wave and the ITD
156
how can inphase stimuli be achieved
a high enough shift in IPD will result in two ears receiving in phase stimuli
157
does the speed in achieving in phase stimuli differ?
happens quicker for higher freqs and slower for lower
158
the head generates an acoustic shadow to create...
interaural intensity differences (IIDs)
159
what are IIDs used to do?
localize high-frequency sounds
160
below about 1000hz...
there is no IID bcuz the head is small compared to the wavelength
161
due to the _____, a sound coming from a source located to one side of the head will have a ____, or be louder, at the ear nearest to the sound
head shadow, higher intensity
162
IIDs are computed in the...
lateral superior olive (LSO)
163
LSO tonotopic representation devotes more space to...
high frequency stimuli
164
what are neurons in the LSO excited by?
IIDs that favour the ipsilateral ear
165
what are neurons in the LSO inhibited by?
IIDs that favour the contralateral ear
166
what is the excitation/inhibition of LSO neurons called?
binaural suppression
167
where does excitation occur from?
directly from the CN
168
where does inhibition occur from?
the contralateral CN to the ipsilateral medial nucleus of trapezoid body (MNTB)
169
where does the MNTB send an inhibitory neuron to?
the ipsilateral LSO and MSO
170
label this diagram:
a: LSO
b: inhibitory neuron
c: MNTB
d: calyx
171
the MNTB is excited by individual ______ input from the ______
globular bushy cell, contralateral VCN
172
calyx of held
a synapse of globular bushy cells from the VCN onto the cell body of the principal neuron in the MNTB.
173
T/F: the calyx of held is the smallest synapse in the brain
false, it is the largest!
174
MNTB cells inhibit the ___ and ___ via ____
LSO, MSO, glycine
175
sound location is determined by the balance between...
excitation and inhibition
176
cues for sound localization in the horizontal/azimuth plane?
- Monaural cues
- Static binaural cues: ITD, IID
- Dynamic binaural cues: IID changes with head rotation in the azimuth plane.
177
cues for sound localization in the vertical/sagittal plane
pinna filtering
178
the VCN contains...
Spherical bushy cells: in the rostral AVCN
Globular bushy cells: in the caudal AVCN
Stellate/Multipolar cells: in the AVCN/PVCN
Octopus cells: in the PVCN
Granule cells: similar to the cerebellum
179
the discharge patterns of neurons in theCN are more ___ than those of auditory nerve fibers
complex
180
different neurons can respond to the same input in very different ways:
- Some are sustained.
- Some are phasic (phase-locked)
- Some are only tuned to the onset of the stimulus.
181
many discharge patterns are shaped by ____ interactions of excitation and inhibition
time dependent
182
Outer hair cells in the basilar membrane of the cochlea experience ______ through _______
lateral inhibition, two-tone suppression.
183
When a tone elicits a certain response (firing rate), a second tone…
In the + area: increases the firing rate.
In the - area: decreases the firing rate.
184
how many classes of spectral response are found in the CN?
5
185
what is the initial synapse of the central aud pathway from inner hair cells?
inner hair cells synapse with spiral ganglion cells, which project to the cochlear nuclei (DCN, AVCN, PVCN) in the medulla
186
describe the direct pathway of the central auditory system
Information travels from the cochlear nucleus, both contralaterally and ipsilaterally, to the inferior colliculus. It then continues to the thalamic medial geniculate nucleus (MGN) and finally reaches the primary auditory cortex (A1) on the superior temporal gyrus.
187
Which structure provides auditory input for the reflective control of eye movement?
The inferior colliculus projects to the superior colliculus, providing auditory input for reflective control of eye movement.
188
What is the role of the superior olivary complex in the indirect auditory pathway?
Neurons from the ventral cochlear nucleus (VCN) terminate in the nuclei of the superior olivary complex. This pathway processes relative sound timing and intensity in both ears to estimate the spatial location of a sound source.
189
Is the indirect auditory pathway bilateral or unilateral in processing?
The indirect auditory pathway is bilateral; information from both ears is processed by both sides of the brain.
190
How is the tonotopic organization of the basilar membrane reflected in the auditory cortex?
The tonotopic organization observed in the basilar membrane and cochlear nucleus is also present in the auditory cortex.
191
What is the primary function of Wernike's area in the brain?
located on the dominant side of the brain, is involved in the interpretation of auditory information and language processing.
192
Where is Broca’s area located, and what is its role?
on the opposite side of the brain from Wernike's area. It is involved in speech production.
193
What types of sounds are cortical cells in the primary auditory cortex tuned to?
Cortical cells in the primary auditory cortex are tuned to precise sequences of complex sounds, particularly ethologically important sounds such as animal calls.
194
Describe the procedure of otoacoustic emissions.
Otoacoustic emissions involve presenting a brief click to the ear. As this sound travels through the basilar membrane, outer hair cells vibrate, activating the auditory pathway in reverse. The resulting vibrations can be detected by a microphone, with high-frequency components arriving first and low-frequency components arriving later.
