Wk3a - Electrical Aspects&Spread Flashcards
What is the excitable tissue?
Not the IHCs (as with normal hearing)
- It is actually the primary efferents, the dendrites, and the neurons in the spiral ganglion
What does the signal need to pass through in order to reach the excitable tissue?
- perilymph
- solid bone
- neuronal soft tissue
- each has different electrical properties. Also, distance varies with electrode type.
In a current CI, how many electrodes are there to stimulate the spiral ganglions?
Up to 22
What is channel interaction?
Where 2 electrodes stimulate the same cell body – must be accounted for, otherwise there will be mixed information
Describe electric charge
A fundamental conserved property of some subatomic particles, which determines their electromagnetic (EM) interaction
- electrically charged matter is influenced by, and produces, EM fields
Define current
A movement or flow of electrically charged particles (measured in amperes)
What is the term for an influence produced by an electric charge on other charges in its vicinity?
Electric field
What is the capacity of an electric field to do WORK on an ELECTRIC CHARGE, and what is it measured in?
Electric potential; measured in volts
Is the positive charge on the capacitor stored on the longer plates or the shorter plates?
Longer
What lies between the plates of a capacitor?
An insulator
Can charged capacitors serve as a current source?
Yes
What is resistance measured in? Give an example of a resistor
Ohms; a lightbulb, for instance - it uses current
What is the first law, which defines the relationship between current, voltage, and resistance?
I = V/R
Where is the current source in a CI?
A charged capacitor (battery pack) in the external speech processor
What are the “resistors” in a CI circuit?
The mediums that the current has to pass in order to reach the spiral ganglion (perilymph in scala tympani, and bone layer between scala tympani and spiral ganglion)
The current flow of a CI deposits charge on the surface of __ ___ and ___ cell bodies. Sufficient charge buildup can initiate an ____ _____.
AN axons; SG cell bodies; action potential
What happens to the remainder of the current after it has been deposited on the surface of AN axons?
It is picked up by the reference electrode and returned to the source
What is the reference electrode’s job?
To capture the remaining current and close the circuit
Electrode stimulation within a channel can be _____ or _______
Monopolar or Bipolar
Monopolar stimulation involves ___ active electrode and one ___ electrode
one; return
Which electrodes stimulate a large neuronal population and which stimulate a small population: monopolar or bipolar
Monopolar = large Bipolar = small
Which type of electrode can achieve higher loudness levels with lower current and why?
Monopolar - the spread of current is over a larger number of neurons, which leads to higher loudness since # of neurons stimulated affects loudness
- less power/more battery savings
Which type of electrodes do not use reference electrodes?
Bipolar - the current flows b/w 2 or more intracochlear contacts
Which types of electrodes are used less frequently?
bipolar and tripolar
Monopolar stimulation has a ____ (broad/narrow) electrical field, and can only stimulate the SG if it is between the source and the sink
Broad - can be made broader by increasing the current
Bipolar (dipole) field is ____ (more/less) restricted
More; needs a lot of current for the field to reach the spiral ganglion
What information do we need to know if the SG will be stimulated?
The electric field at the location of excitable tissue
Electric current takes the path of least resistance and has an electric field spread around it. What are the consequences of this spread?
- reduced specificity?
What are the ways CI current can be measured indirectly?
- AN tuning curves
- Inferior colliculus spread of activation (spatial tuning curves)
What are the ways CI current can be measured indirectly?
- AN tuning curves
- Inferior colliculus spread of activation (spatial tuning curves)
When measuring electric fields in a saline tank, where are the peaks (highest potential) found?
Closest to the stimulating electrode
T/F: A decrease in the electric field is seen as we move further away, both vertically and horizontally
True
Which type of stimulation results in 2 peaks in saline tank measurements?
Bipolar - correspond to source and sink
Tripolar electrode arrays show __ (#) peaks and have 3 active electrodes - what are they?
1 peak; 1 stimulating electrode and 2 sinks
Which type of electrode array has the least sharp distribution when measured in a saline tank?
Monopolar array
When measuring potential distribution in cadaver cochleas for bipolar configuration, where was the higher peak located relative to the lower peak?
Always more apically.
When measuring potential distribution in cadaver cochleas for bipolar configuration, potentials were higher when they were more ____ (basally/apically) located.
Apically - same for potential gradients (difference b/w 2 neighbouring potentials) = better spatial resolution towards apex
When measured indirectly, which type of array has a flatter tuning curve?
Which is sharper but requires more current?
Monopolar; Bipolar
T/F: the inferior colliculus has a tonotopic frequency map
True
Characteristic frequency (increases/decreases) with depth in the inferior colliculus.
Increases
Rank the following in order of frequency selectivity: Monopolar, bipolar, tripolar
Tripolar>bipolar>monopolar for impulse noise (not sustained)
T/F: Sustained monopolar stimulation does not produce a more narrow response profile
False
Initial onset responses are more (broader/narrow) than sustained responses
Broader
Can we reach the same frequency selectivity of NH using electrode arrays?
No
Which is better for frequency selectivity: monopolar, bipolar, or tripolar? Which has the lowest threshold?
Tri-polar; Monopolar
