Auditory System Flashcards
what is sound?
refers to change in air pressure generated by vibrating air molecules
is sound physical or chemical energy?
physical
what is sound measured in?
decibels on a log scale
parameters of sound
amplitude: loudness
frequency:pitch
what is timbre?
complexity of the sound wave or multiple frequencies combined
what would a low amplitude sound look like?
what would a high amplitude sound look like?
what would a low frequency sound look like?
what would a high frequency sound look like?
one challenge of the auditory system is…
breaking down a sound into their frequency components
the ear successfully breaks down ____ into _____ that make up a sound
waveforms, smaller sine waves
what are the 3 main challenges of teh auditory system?
- detect and code the amplitude and relevant frequencies
- dynamically modulating this process in a context specific manner
- using information for hearing and sound localization
what three parts is the ear composed of?
outer ear, middle ear, inner ear
label this diagram:
A: ear canal
B: inner ear
C: pinna
D: ear drum
E: middle ear
F: eustachian
what does the outer ear consist of?
pinna and ear canal
function of the pinna
funnels sound into the middle and inner ear (amplification) and plays a role in sound localization
the pinna ____ filters sound waves depending on the ____ of their source
differentially, elevation
frequency range for whales
20-100,000 hz
frequency range for bats
1500-100,000 hz
frequency range for humans
20-20,000 hz
frequency range for frogs
600-3,000hz
frequency range for fish
20-3,000 hz
frequency range for crickets
500-5,000 hz
frequency range for birds
Variable across species, but top
end usually well below 10,000 Hz
what does the middle ear consist of?
the ear drum (tympanic membrane) and 3 small ossicles (malleus, incus, stapes)
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
sounds amplified by the _____ causes vibrations of the _____
outer ear, eardrum
information is amplified through the ____ and causes the ____ to go to the ____
middle ear, vibration, inner ear
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.
without the middle ear, ____ of sound energy would reflect
> 99.9%
main effects of middle ear arise from:
- size of the ear drum relative to stapes (~35X)
- lever action of the ossicles
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!
label this diagram:
A: malleus
B: incus
C: stapes
D: tympanic membrane
E: base of stapes in oval window
what two things is neural control of the middle ear performed by?
- trigeminal nerve
- facial nerves
trigeminal nerve
innervates the tensor tympani muscle that works to move the malleus.
facial nerves
innervate the stapedius muscle that works to move the stapes.
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.
softer sounds cause the muscles to ____ to allow more ____
relax, sound transfer
hyperacusis
increase acuity and hypersensitivity to sound, caused by lesions affecting trigeminal and facial motor output.
what does the inner ear consist of?
the cochlea
what is the cochlea responsible for?
converting sound waves into eletrical signals the brain can interpret
vibrations become ____ and are passed from the ____ into the _____
fluid pressure waves, oval window, cochlea
once fluid pressure waves are at the cochlea, what are they converted to?
nerve impulses
describe the cochlea structure
spiral structure, bisected by the cochlear parition
whats the cochlear partition?
a flexible structure that supports the basilar membrane and the tectorial membrane.
the inner ear is a ____ consisting of three parts. what are these?
bony labyrinth, the vestibule, semicircular canals (balance), and cochlea.
what is the bony labyrinth filled with?
Filled with perilymph (~CSF, low K+ compared to hair cell)
membranous labyrinth
lodged within the bony labyrinth in the inner ear and has the same general form, but is smaller.
what is the membranous labyrinth filled with?
Filled with endolymph (high K+ compared to hair cell)
what are the fluid filled compartments of the cochlea?
scala vestibuli, scala media, and scala tympani
cochlear is partitioned by:
reisners membrane and basilar membrane
reisners membrane
divides the scala vestibuli and scala media.
basilar membrane
divides the scala media and scala tympani.
label this diagram:
A: vestibular nerve
B: auditory nerve
C: oval window
D: stapes
E: round window
F: cochlea
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
stria vascularis
a capillary loop containing numerous blood vessels, produces endolymph
transduction from mechanical to electrical energy occurs in the ____ and is performed by ____
organ of corti, hair cells
hair cells release ____ to ____ to elicit APs
glutamate, spinal ganglion cells
displacement of the basilar membrane due to sound waves causes…
displacement of hair cells in the tectorial membrane
what drives transduction?
the compression and resulting shearing forces cause the cilia to move
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
more than __ of the ___ contracts are on ____
95%, afferent (SGCs heading to cochlear nucleus), inner hair cells
more than ___ contact each _____
20 afferent fibers, inner hair cell (and no others)
more than ___ of ___ contacts are on the ____
90%, efferent (neurons from superior olivary complex), outer hair cells
T/F: the arrangement of outer hair cells in the cochlea is the same from that of inner hair cells
false, it differs.
hair cells are embedded in the
tectorial membrane
outer hair cells have how many rows?
3 or 4
inner hair cells have how many rows?
1
stereocillia
hair-like protrusions on hair cells.
kinocilium
tallest stereocillium, makes connection with the tectorial membrane
sterocillia synapse onto ____ via a _____
ganglion cells, ribbon synapse
outer hair cells have ____, where changes in ____ lead to changes in the _____
contractile ability, membrane potential, size of outer hair cells
prestin
a transmembrane molecule that has chloride-binding sites; called the molecular motor.
when the membrane is hyperpolarized what happens with prestin?
chloride ions influx into the cell, bind to prestin,l and this leads to elongation.
when the membrane is depolarized what happens with prestin?
chloride ions efflux, leaving the prestin molecule, and this leads to contraction.
when the basilar membrane moves, the cilia on outer hair cells bend towards…
the tallest stereocillia
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.
why does K+ enter the cell?
Because endolymph has a higher concentration of K+ compared to a hair cell.
when depolarized, the ____ loses the ____ and the cell ____
prestin molecule, chlorine, shrinks/contracts
shrinkage/contraction pulls the basilar membrane ___, closer to the ____, which causes OHC ____ and prestin ____
upward, tectorial membrane, hyperpolarization, elongation
adaptation helps…
shift the baseline of neurons to allow for response changes to occur within the dynamic range.
why is tip link tension lost with sustained depol in hair cells?
because the “tether” is moved by the stereocilia.
adaptation is mediated by
myosin motors
slow adaptation ensures when the motor slides down the ____, allow ____
stereocilia, channels to close
the basilar membrane has specific properties that allow it to be tuned for _____ to create _____
mechanical frequencies, standing waves
what happens if we have big hair cells?
= big membrane = big capacitance = big time constant = cannot respond quickly to inputs
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).
basal end of the basilar membrane has a max amplitude for ____ frequencies
high
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.
What is the helicotrema, and where is it located in the cochlea?
is the point of the cochlea where the basilar membrane terminates.
How does the apical end of the basilar membrane differ in terms of thickness and flexibility?
The apical end is thinner and more flexible.
apical end of the basilar mem has a max amplitude for ____ frequencies
low
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.
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.
the selectivity of basilar membrane is also reflected in _____
spiral ganglion cells
SGCs undergo ______; they tend to prefer a certain frequency. this allows for ______.
frequency tuning, selective patterns of firing
best frequency
he frequency with a minimum amplitude needed to evoke an AP
place code
each neuron has a best frequency that depends on its place in the cochlea
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
how do cochlear implants work?
can retrieve hearing by putting electrode and transducer into cochlea and send current pulses to different parts of membrane
the electrodes of cochlear implants
stimulate different places on the basilar membrane
a transducer in cochlear implants
can analyze incoming sounds and stimulate the electrode accordingly
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.
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
inner hair cells make ____ with _____ that project to the _____.
ribbon synapses, spiral ganglion cells, cochlear nucleus
ribbon synapse
an electron-dense ribbon holds vesicles close to the active site.
in ribbon synapse, there is _____ that promotes rapid NT release
tight vesicle-calcium channel coupling
____ receptors that sense ____ and elicit APs in spinal ganglion cells
AMPA, glutamate
SGCs connecting to the same inner hair cell have …
heterogenous properties
hair cells utilize ____ channels
L-type Ca2+
hair cells reply on ____
ribbon synapses
what are mutations of the otoferlin gene associated with?
deafness map
In an immature mouse, where is otoferlin expressed?
in both inner and outer hair cells
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.
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.
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
How are ribbon synapses similar to capacitors, and what happens during fusion?
Ribbon synapses, like capacitors, expand during fusion, increasing capacitance.
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
_____ exocytosis is almost ____ in the absence of oterferlin
Ca2+ triggered, completely abolished
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
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.
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.
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.
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.
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
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).
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).
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.
what are the 3 cochlear nucleus divisions?
Anteroventral (AVCN)
Posteroventral (PVCN)
Dorsal (DCN)
T/F: each auditory nerve fiber innervates all 3 CN divisions
true
neurons best frequencies change as you move more ____ into the ____
medially, cochlear nucleus
more medial:
prefer higher freq
more lateral:
prefer lower freq
end bulbs of SGCs make strong contact with ____ in the CN
bushy cells
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
what do end bulbs engulf and why?
the soma of bushy cells to make a foolproof connection
how many end bulbs typically engulf a bushy cell?
2-3
VCN bushy cells show _____ of phase locking relative to their _____ inputs
improved precision, auditory nerve fiber
temporal features are ____ by the ____ of multiple SGC end bulbs onto a single bushy cell
enhanced, convergence
what is an ITD?
interaural time difference, time it takes for sound to hit the other ear after reaching one ear
if the speed of sound is 343m/s and the distance between human ears is 20cm, what is the ITD?
approx 600 microseconds
what is the localization accuracy for sources in front of the listener
1 degree
what is the localization accuracy for sources to the side?
15 degrees
how finely can humans discern ITDs?
as small as 10 microseconds
MSO neurons only respond when…
they receive coincident excitatory inputs from both ears
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
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
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
how is the MSO organized?
tonotopically to emphasize low freuqnecies
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
the ____ occurs within the _____ range
characteristics/best delay, physiologically relevant range
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
is peak spacing of ITD functions related to the period of the stimulus
yes
what does IPD refer to
interaural phase differences, difference in the phase of a waves that reaches each ear
what influences IPD
is dependent on the frequency of the sound wave and the ITD
how can inphase stimuli be achieved
a high enough shift in IPD will result in two ears receiving in phase stimuli
does the speed in achieving in phase stimuli differ?
happens quicker for higher freqs and slower for lower
the head generates an acoustic shadow to create…
interaural intensity differences (IIDs)
what are IIDs used to do?
localize high-frequency sounds
below about 1000hz…
there is no IID bcuz the head is small compared to the wavelength
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
IIDs are computed in the…
lateral superior olive (LSO)
LSO tonotopic representation devotes more space to…
high frequency stimuli
what are neurons in the LSO excited by?
IIDs that favour the ipsilateral ear
what are neurons in the LSO inhibited by?
IIDs that favour the contralateral ear
what is the excitation/inhibition of LSO neurons called?
binaural suppression
where does excitation occur from?
directly from the CN
where does inhibition occur from?
the contralateral CN to the ipsilateral medial nucleus of trapezoid body (MNTB)
where does the MNTB send an inhibitory neuron to?
the ipsilateral LSO and MSO
label this diagram:
a: LSO
b: inhibitory neuron
c: MNTB
d: calyx
the MNTB is excited by individual ______ input from the ______
globular bushy cell, contralateral VCN
calyx of held
a synapse of globular bushy cells from the VCN onto the cell body of the principal neuron in the MNTB.
T/F: the calyx of held is the smallest synapse in the brain
false, it is the largest!
MNTB cells inhibit the ___ and ___ via ____
LSO, MSO, glycine
sound location is determined by the balance between…
excitation and inhibition
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.
cues for sound localization in the vertical/sagittal plane
pinna filtering
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
the discharge patterns of neurons in theCN are more ___ than those of auditory nerve fibers
complex
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.
many discharge patterns are shaped by ____ interactions of excitation and inhibition
time dependent
Outer hair cells in the basilar membrane of the cochlea experience ______ through _______
lateral inhibition, two-tone suppression.
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.
how many classes of spectral response are found in the CN?
5
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
