Cochlear Potentials and OEA Flashcards
What are the 3 types of potentials?
Endocochlear potential,
Receptor potential,
Neuro-action potential
What is another name for the endocochlear potential?
Endolymphatic Potential
How are endocochlear potentials recorded?
Recorded locally through stria vascularis. (Measuring as close as possible)
What type of signal is endocochlear potential?
DC signal
What is DC signal?
The electric charge (current) only flows in one direction.
What is AC current?
AC current is an electric charge that changes direction periodically
Fill the chart comparing macro and microelectrode:
What kind of graph is this?
EcochG
What kind of stimuli is played in the EcochG?
Tone Bursts
Where are the measurements of CM taken from?
Round window
What are the three sections on this graph?
Cochlear Microphonics,
Summating Potential,
Compound Action Potential
How is the CM related to the acoustic signal?
It mimics the acoustic signal
What does the cochlear microphonic work as?
A microphone
How is CM related to the receptor potential?
The stereocilia deflection leads to the receptor potential of the hair cell and the CM reflects this.
Where is the cochlear microphonic generated?
In the Organ of Corti
What is an example of an AC signal in real life ?
AC signal can be the signals carried in radios or electrical wire
What is the example of a DC signal in real life?
DC can be the battery in a flashlight or our laptop
What are the two signals in the cochlea that are alternating current?
CM (generated by membrane potential of HC)
and CAP
AC membrane potential and
stereocilia deflecting:
* Laterally: _________________
* Medially: _________________
* Back and forth, AC mimicking sound wave
AC membrane potential and
stereocilia deflecting:
* Laterally: depolarization
* Medially: hyperpolarization
* Back and forth, AC mimicking
sound wave
What are the two signals in the cochlea that are direct current?
Endocochlear Potential
Summating Potential
What happens to the potential when there is a deflection change in the stereocilia (ie. The steps of polarizing) ?
A deflection leads to the the potential changing from resting🡪 depolarizing🡪 repolarizing🡪 Hyperpolarizing🡪Repolarizing
What are the two ways to record the CM?
Intracellular and extracellular
What does it mean that the CM has a non-linear input output relationship relative to the stimulus?
Non-linear means that while the intensity level (the stimulus dB) is increased, the CM amplitude also increases BUT it does reach a point where it will not increase and eventually at higher intensity levels will “roll-over” which means the amplitude of the CM will decrease at those levels
What are the four characteristics of the CM?
- Copies the input signal waveform (This feature is used in canceling CM by alternating average)
- No latency
- Sensitive to the Status of the cochlear (i.e damage)
- Non-linear
What are the three evidences supporting that the source of the CM are the hair cells?
- Short latency indicating it is not a higher brain process;
- Intracellular recording of OHC receptor potential represents CM waveform, largest amplitude
- Elimination OHC almost eliminates CM (smaller CM)
Specifically which hair cell is related to CM?
OHC
Where do CAP come from?
It comes from the auditory nerve and is made of many of the individual fiber discharges
Why do we only see a CAP at the onset and offset of sound?
We know that there is synchronized firing of the neurons all together, however, the refractory period of neurons allows us to see the CAP since this is the time they are not synchronized (after the onset and at onset)
Where are the action potentials generated?
Ranvier’s nodes.
What are CAP?
CAP are the sum of APs from different ANFs and different nodes taken from a nerve trunk
What is the difference between N1 and N2?
The N1 latency is about 1ms and the N2 is 1.5-2ms (ie. The N2 is later)
To be recorded, CAP require:
synchronized firing of ANFs in order to be recorded
What are three factors that lead to better synchrony?
- High frequency region ANF’s (due to higher speed of traveling wave and narrower region involved)
- Transient signals (the signal with a fast change in time, such as slicks)
- myelination
What does it mean if the CAP is not synchronized?
Could possibly mean a disorder, auditory neuropathy
How does the summating potential (SP) look on the CM graph?
It is an elevation of the baseline
Why does SP have this appearance? (2)
- Potassium accumulation in the hair cell during sound stimulation
- Stronger at high-frequency due to lack of time for removing K
Where are SP generated from?
Equally from the outer and inner hair cell.
What is SP’s latency like?
No latency from the signal like CM
What kind of potential is the SP?
A receptor potential
What does it mean that the cochlea is a sound generator?
The cochlea makes a sound that is heard in the ear canal (so cool!)
What are the two main categories of OAE’s?
Spontaneous and evoked;
What are the four types of evoked OAE’s?
Transient evoked,
Stimulus evoked,
Electrically evoked
Distortion products
SOAE and Evoked OAE all involve a_____________________________________________
new sound generated by cochlea
(specifically by OHCs)
Where are the sounds of OAE produced from?
By the outer hair cell of the cochlea.
How is the Transient Evoked OAE recorded? (2)
A earpiece is used where there is a plug to block out the external noise and then there is also a tubing to deliver sound;
There is a microphone and speaker component since you are delivering sound via the speaker and the microphone is recording the response from the ear.
For the speaker to be accurate during TEOAE, it must have:
Speaker must have very good
temporal response: no ringing
Who has the TEOAE?
Everyone with normal ears
What are two factors affecting latency in TEOAE?
- Signal frequency (higher frequency, shorter latency)
- Signal intensity ( higher
intensity, shorter latency)
Describe the relationship of each of the two factors to have shorter latency in TEOAE:
Shorter latency is with a higher frequency and higher intensity.
What is the shape of the intensity function in TEOAE? What does this mean?
Non linear
While the response of the TEOAE will increase with the intensity, eventually, at higher intensity levels, the response will actually not increase.
(OHC for this measurement and we know that the active mechanism is larger and gain is larger at a lower sound level)
How does the evoked spectrum compare to the stimuli?
The spectrum is narrower than its stimuli.
