~Chapter 11 - Lecture Section 11.3 Flashcards
The Cochlea acts as a ___, meaning that vibrations and fluid pressure along the Cochlea act to ___ frequencies.
hydrodynamical frequency analyzer // analyze
How is the Cochlea able to act as a hydrodynamical frequency analyzer?
Through Passive mechanical properties and Active Mechanics of the outer hair cells. Phase locked firing of neurons also contributes .
Our consideration of the Passive mechanical properties of the Cochlea starts with nobel Prize winner ___.
Von Beksey
Von Beksey took human and animal cadavers, and dissected the ___ ear away and drilled a hole in the ___. He used a microscope to peer into this hole, and would place sounds to the ear and would use a ___ and ___ attached to the Cochlea to try to see how the Basilar Membrane was vibrating.
outer middle // Cochlea / strobe light // camera
Through his dissections, Von Beksey found the Basilar Membrane was ___ and ___ at the base, and quite ___ and ___ at the Apex.
narrow // stiff // narrow // wide // floppy
Von Beksey observed that when he played high frequency sounds it caused vibrations to occur near the ___.
base
Von Beksey observed that when he played low frequency sounds it caused vibrations to occur near the ___.
Apex
Von Beksey found that acoustic energy propagation (this is just vibrations) progressively ___ until the wave essentially stops with all the energy piling up/bunching up to maximally vibrate at a particular characteristic location of the ___. This characteristic location would differ for ___.
slow // Basilar Membrane // different frequencies
Each location along the Basilar Membrane oscillates best to a ___, this is largely determined by the ___.
characteristic frequency // membrane stiffness
___Hz gives the most movement in the Apex of the Basilar Membrane.
2,000
If there are big vibrations, that means that the hair cells that are embedded in the Organ of Corti that are sitting on this part of the Basilar Membrane, are going to shake back and forth ___, and those are going to be causing this Depolarization and Hyperpolarization oscillation, so they’re gonna ___ very easily. The ones that are only wiggling a little bit ___ going to be activated much.
a lot // transduce // are not
The characteristic frequency ___ as stiffness ___. So at the Base, high stiffness = ___ frequencies. At the Apex, low stiffness = ___ frequencies
decreases // decreases // high // low
The propagation of the acoustic energy along the Basilar Membrane can be summarized by the ___.
Envelope of the traveling wave/maximum excursion
Where the peak of the envelope lies is where the hair cells will be ___ activated. The peak of the envelope occurs at a ___ place along the Basilar Membrane for each frequency.
maximally // different
Hair cells are most perturbed at the ___ of the envelope.
peak
The frequency of sound that is being played to the Cochlea can be coded neuronally as the location of ___ along the basilar membrane.
peak deflection
The Cochlea can tell by knowing which hair cells are activated what the ___ of the sound is. If all the hair cells near the Apex are being activated, that means it’s a ___ pitch sound. If hair cells near the Base are being maximally activated, that is going to be a very ___ frequency.
frequency // low // high
The peaks in the Cochlea occur for ___, but the Cochlea can also have multiple peaks in response to ___.
simple Pure Tones // Complex Tones
The Cochlea acts like a filter for both ___ and ___.
Simple // Complex Tones
If we play a Complex Tone, which consists of 440, 880, and 1320Hz, when we get to the Basilar Membrane, there will be ___ distinct peaks for ___ of those components within the Complex Tones, these are the ___. This is what is meant by ___, it separates out the different frequencies in Complex Tones in order to activate different lines going to the brain.
three // each one // Harmonics // Hydrodynamical Frequency Analyzer //
The separation of Components the way a Prism can separate white light into its different wavelengths, sometimes makes the Cochlea be called an ___. The Basilar Membrane is a ___, sometimes called an “auditory prism”.
Auditory Prism // frequency analyzer
There is abundant evidence for ___.
Von Bekesy’s Place Theory
What is a Tonotopic Map?
An ordered map of characteristic frequencies along the length of the Cochlea
If recordings are made of the electrical activity of ___ or ___ you get a Tonotopic Map.
Auditory nerve fibres // individual hair-cells
Auditory nerve fibres that are coming from the Base respond best to ___ frequencies, and Auditory Nerve Fibres that are coming from the Apex respond best to ___ frequencies.
high // low
Characterizing the frequency responses of individual hair cells or Auditory nerve fibres is kind of like when we were studying the visual system and we would present ___ to a visual cortex neuron and you would measure the spike rates.
different orientations
For the auditory system, recall that you will still get some hair cell activation even if it’s further away from the ___ of the envelope of the travelling wave. So you will still get some responses to frequencies that the cells ___, so instead, the way auditory hair cells and auditory nerve fibres are characterized is by measuring the ___, and the ___ the threshold the more sensitive the cell is to that frequency.
peak // don’t prefer // threshold // lower
What is Characteristic Frequency (CF)?
Characteristic Frequency (CF) is the point on the frequency tuning curve that has the lowest threshold
A key for the Von Bekesy Place Theory is that the Characteristic Frequency changes in an ___, moving from the ___ to the ___. So when you record from neurons near the Base, they will have a CF that is very ___, and neurons near the Apex, auditory nerve fibres or auditory hair cells, will have a ___ CF.
orderly manner // Base // Apex // high // low-frequency
Curves become ___ at higher frequencies, this only works when you use a linear x-axis. This is important for ___.
wider // pitch perception
The ___ of hair cells along the Cochlea has enabled a Bionic Ear to be put into use. Bionic Ears are possible because of the ___ in the Cochlea.
Tonotopic arrangement // Tonotopic Map
An Electronic Cochlear implant that allows those who either have ___ or ___ to hear again.
congenital deafness // acquired deafness
In a Bionic Ear, there is an ___ that is fed through the boney tubes of the ___, it coils around such that near the end of the electrode that is stimulating cells near the ___ for low-frequency sounds, and at the back of the electrode where it’s just entering, that is near the ___ for high-frequency sounds.
Electrical stimulation through each one of the electrode sites bypasses damaged hair cells to activate the ___ directly and can produce a fairly sophisticated ___ of pitch.
electrode // Cochlea // Apex // Base // auditory nerve fibres // representation
Bionic Ears stimulate the ___ and ___, which then directly activate the ___ to produce a sophisticated representation of ___.
Apex // Base // auditory nerve fibres // pitch
Where was the first Bionic Ear made, and how long have they been around?
Australia, and they have been around for at least 20 years
In the first few models of Bionic Ears, what was hearing like?
There was only a few frequencies in early models, so the sound was blips and blops and difficult to make out, so it was coupled with lip-reading.
What do more modern versions of Bionic Ears feel like?
As more channels were added in later versions it would actually start to sound like digitized speech sounds
Some parts of ___ don’t work with new evidence.
Place Theory
Von Bekesy’s mechanical model of the Cochlea predicts that there will be ___ discrimination between tones that have very similar envelopes of the travelling wave. Yet, psychophysical evidence shows that we are ___ at distinguishing tones of ___.
poor // good // similar frequencies
Can humans distinguish tones of similar frequencies?
Yes
When animal experimentation was able to film living Basilar Membranes, these living Basilar Membranes showed ___ in their vibrational envelopes than previously measured from cadavers by Von Beksey.
sharper peaks
The Cochlea can emit a sound called ___. This can be heard in ___ ears, and sounds like a ___ noise
Otoacoustic Emissions // dogs // buzzing
Healthy Basilar membranes show that the Outer hair cells respond to sound by changing their ___. It’s a tiny change, maybe ___ of its length
length // 5%
This contraction of Outer hair cells in response to sound is called the ___.
Motile Response
The Inner hair cells are always ___, and they are for sending sound info to the ___, but the Outer hair cells that change length are responsible for the ____.
the same length // Central Nervous System // Motile Response
The Inner hair cells carry ___. These send ___ neural output to all the ___, that’s important for gathering a bunch of info about the stimulus.
sound information // diverging // Auditory nerve fibres
The Outer hair cells are providing the ___. They don’t have to be that precise, they are sending ___ into a few auditory nerve fibres.
Motile Response // converging inputs
The Motile Response is triggered by either ___ of the ___, or it can be controlled with ___, so from the ___ to the ear.
deflection // Cilia // Central Feedback // brain
Deflection of the Cilia: There is a protein that lines the cell walls of these cell walls called ___, and it binds ___ in its ___.
Prestin // Chloride ions (Cl-) // resting state/Hyperpolarized state
When there is a deflection towards the ___ side of the Cilia, and you have ___ of the hair cell, the Prestin protein ___ the Cl ions and it ___ and ___, which leads to this pulling up or shrinking of the ___.
long // Depolarization // unbinds // contracts // shrinks // hair cell
You get oscillation between when the hair cells are long, and when they deflect, they pull up on the Basilar Membrane, this is like an ___ of whatever sound is already vibrating the membrane. That is why the Cilia of the outer hair cells have to be attached to the ___, they have to be able to pull on it and be connected. It’s like they are doing little chin-ups, pulling themselves and the entire basilar membrane up to amplify the oscillations that are already present to cause the deflection of the Cilia in the first place.
amplification // Tectorial Membrane
The Motile Response ___ and ___ ___ of the basilar membrane to create ___ peaks.
reinforces // shapes // vibrations // sharper
The Motile Response is sometimes called the ___.
Cochlear Amplifier
When the Basilar Membrane has a normal response with the Cochlear Amplifier present, in response to a low pitch sound, it has a travelling wave envelope that has a ___ peak.
very sharp
When the Basilar Membrane is treated with Furosemide, it removes the ___. Now, in response to a low pitch sound, we see now that the peak is not only ___, but it’s also ___, so there’s a ___ activation of all the hair cells, but that activation is ___.
Motile Response/Cochlear Amplifier // much lower // broader // broader // weaker
Furosemide is a ___, which poisons the ___ and causes it to no longer work, this can lead to ___.
loop diuretic // Motile Response // permanent hearing loss
How do we code for frequency (pitch)?
Place Code and Timing Code
What is Place Code?
Neurons in the Basilar membrane code different frequencies via their location along the length of the Basilar Membrane
Place Code: Hair cells that are close to the ___ will encode high frequencies, and Hair cells that are close to the ___ will encode low frequencies.
Base // Apex
As the Basilar Membrane is going up and down, the ___ of the hair cells are wagging back and forth at the frequency of the ___, and what is created is a ___.
Cilia // sound stimulus // Timing Code
What is Timing Code?
The Frequency of the sound is reflected in the firing of the neuron(s), the pattern of firing.
Timing Code: Every time the hair cells are deflected to the ___ there is a lack of firing.
short side/are Hyperpolarized
Timing Code: every time the hair cells are deflected to the ___ there is a burst of firing.
long side/ are Depolarizing
What is Phase Locking?
The firing of neurons in synchrony with the phase of the stimulus.
For low frequency sounds, a single neuron could keep track of the Oscillations very well, this is referred to as ___.
Phase Locking
The firing of the single action potential always ___ the ___ of the stimulus. This is fine for ___ frequencies.
matches // peak // low
Cells are known to fire ___spikes/s
20-200
When you start to increase the frequency in the ___Hz range, a single neuron cannot fire this quickly due to its ___, and might start to miss ___.
700-1,000 // Absolute Refractory Period // cycles
How can the auditory system compensate for the Absolute Refractory Period?
The Volley Principle
Single fibres might catch every few peaks, but then it has the other fibres that will fire at that peak that they missed, this is referred to as the ___.
Volley Principle
The Volley Principle is possible due to ___ hair cells sending ___ projections to many auditory nerve fibres.
Inner // Diverging
When you record from many fibres over time, the population oscillation follows ___ frequencies. This can overcome the ___ of these auditory nerve fibres and work up to about ___Hz, which is way faster than the Absolute Refractory Period would allow for ___ neuron.
higher // Absolute Refractory Period // 1,000-5,000 // a single
The Volley Principle allowing the timing code to extend up to ___Hz allows human speech to be encoded not only by the ___ but also by the ___.
5,000 // Place Code // Timing Code
