Cochlear Potentials and OEA ll Flashcards
What is the DPOAE in brief?
(Distortion Product OAE)
Named based on the fact that there are “distortion products” or an output that was not present in the input. Therefore, in addition to the two frequencies presented appearing in the output, there is also another frequency
In DPOAE, the external signal contains_______________________________________
two primary tones: F1 and F2
In DPOAE, the cochlea produces
______________________________________________________________________
its own sound that was not introduced in the signal
How does the DPOAE show that the cochlea is non-linear?
There is not a one-to-one in input and output if you are getting a new product in the output.
What is the formula in DPOAE for the product produced?
2F1-F2 where F1 is less than F2.
How are DPOAE generated?
The sounds are generated from inside the cochlea but not clear yet on how.
What do we call the new components that are generated by a nonlinear system?
Distortion products
The production of DPOAE depends on:
an active mechanism near the area of primary tones
What are the main clinical uses of OAE? (3)
- A screening tool to see outer hair cell function
- Evaluating brainstem function by using OAE suppression (in development, not currently used)
-Evaluation of cochlear function
Where are the OHC cochlear efferent system innervated from?
Cochlear efferent system from the superior olivary complex
What do suppression tests help to evaluate?
Presenting sound to the contralateral ear means that the OAE can be suppressed and theoretically should be able to evaluate the integrity of the brainstem (ie.is there an issue in that level)
What is the limitation of suppression tests?
The limitation is the poor signal to noise ratio and the variation in response
What is the difference in myelination of type I and type II SGN?
Type 1 is myelinated and Type 2 is not
What happens at the Ranvier node for the type 1?
At the node of Ranvier, the action potentials are ‘jumping’ i.e. passing on to each one so it saves energy and increases speed.
Which Afferent SGN has a larger diameter and what does this lead to?
Type I therefore this means that there are larger AP and higher AP conduction speed.
Which Afferent SGN can be recorded easier?
Type 1
What is the total (approximate) number of SGN in humans?
30,000
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What are ribbon synapses?
Specific to the auditory system; They facilitate the release of neurotransmitters by holding the vesicles close to the active zone. (Pre-synaptic regions have these ‘ribbons’)
How do ribbon synapses “look” like (appearance):
Like ribbons more like the blobby appearance
What are the two main roles of ribbon synapse relating to transmission?
Fastening the response (temporal resolution) and ensuring long lasting response.
What is the neurotransmitter of the ribbon synapse in the inner ear?
Glutamate
What is 6 evidence for glutamate being the NT of the ribbon synapse in the inner ear?
Exists in the synapse region
Synthesis system (where it is made) exists
Releases in response to a stimuli
Causes action potentials in ANF
There is a glutamate receptor (GluR)
When blocking the GluR the AP is cancelled
What direction is efferent vs afferent fibers?
The efferent is from the brain to the hair cells; Afferent is from the hair cells up to the brain
Where do efferent fibers originate from?
The neurons come from the superior olivary complex in the brainstem.
Where do peripheral fibers pass through?
Olivary cochlear bundle
What are the efferent innervation patterns of IHC and OHC? (2)
LOC efferent fibers synapse on afferent terminal
MOC efferent fibers synapse on OHC body
What can we see in this image relating to OHC? (2)
- There is a much larger efferent terminal than afferent
- OHC Bottom is mainly covered by efferent synapses
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