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F20-9527-Cochlear Implants > Wk3a - Electrical Aspects&Spread > Flashcards

Wk3a - Electrical Aspects&Spread Flashcards

1
Q

What is the excitable tissue?

A

Not the IHCs (as with normal hearing)

- It is actually the primary efferents, the dendrites, and the neurons in the spiral ganglion

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2
Q

What does the signal need to pass through in order to reach the excitable tissue?

A
  • perilymph
  • solid bone
  • neuronal soft tissue
  • each has different electrical properties. Also, distance varies with electrode type.
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3
Q

In a current CI, how many electrodes are there to stimulate the spiral ganglions?

A

Up to 22

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4
Q

What is channel interaction?

A

Where 2 electrodes stimulate the same cell body – must be accounted for, otherwise there will be mixed information

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5
Q

Describe electric charge

A

A fundamental conserved property of some subatomic particles, which determines their electromagnetic (EM) interaction
- electrically charged matter is influenced by, and produces, EM fields

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6
Q

Define current

A

A movement or flow of electrically charged particles (measured in amperes)

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7
Q

What is the term for an influence produced by an electric charge on other charges in its vicinity?

A

Electric field

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8
Q

What is the capacity of an electric field to do WORK on an ELECTRIC CHARGE, and what is it measured in?

A

Electric potential; measured in volts

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9
Q

Is the positive charge on the capacitor stored on the longer plates or the shorter plates?

A

Longer

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10
Q

What lies between the plates of a capacitor?

A

An insulator

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11
Q

Can charged capacitors serve as a current source?

A

Yes

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12
Q

What is resistance measured in? Give an example of a resistor

A

Ohms; a lightbulb, for instance - it uses current

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13
Q

What is the first law, which defines the relationship between current, voltage, and resistance?

A

I = V/R

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14
Q

Where is the current source in a CI?

A

A charged capacitor (battery pack) in the external speech processor

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15
Q

What are the “resistors” in a CI circuit?

A

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)

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16
Q

The current flow of a CI deposits charge on the surface of __ ___ and ___ cell bodies. Sufficient charge buildup can initiate an ____ _____.

A

AN axons; SG cell bodies; action potential

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17
Q

What happens to the remainder of the current after it has been deposited on the surface of AN axons?

A

It is picked up by the reference electrode and returned to the source

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18
Q

What is the reference electrode’s job?

A

To capture the remaining current and close the circuit

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19
Q

Electrode stimulation within a channel can be _____ or _______

A

Monopolar or Bipolar

20
Q

Monopolar stimulation involves ___ active electrode and one ___ electrode

A

one; return

21
Q

Which electrodes stimulate a large neuronal population and which stimulate a small population: monopolar or bipolar

A 
Monopolar = large
Bipolar = small
22
Q

Which type of electrode can achieve higher loudness levels with lower current and why?

A

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

23
Q

Which type of electrodes do not use reference electrodes?

A

Bipolar - the current flows b/w 2 or more intracochlear contacts

24
Q

Which types of electrodes are used less frequently?

A

bipolar and tripolar

25
Q

Monopolar stimulation has a ____ (broad/narrow) electrical field, and can only stimulate the SG if it is between the source and the sink

A

Broad - can be made broader by increasing the current

26
Q

Bipolar (dipole) field is ____ (more/less) restricted

A

More; needs a lot of current for the field to reach the spiral ganglion

27
Q

What information do we need to know if the SG will be stimulated?

A

The electric field at the location of excitable tissue

28
Q

Electric current takes the path of least resistance and has an electric field spread around it. What are the consequences of this spread?

A
  • reduced specificity?
29
Q

What are the ways CI current can be measured indirectly?

A
  • AN tuning curves

- Inferior colliculus spread of activation (spatial tuning curves)

30
Q

What are the ways CI current can be measured indirectly?

A
  • AN tuning curves

- Inferior colliculus spread of activation (spatial tuning curves)

31
Q

When measuring electric fields in a saline tank, where are the peaks (highest potential) found?

A

Closest to the stimulating electrode

32
Q

T/F: A decrease in the electric field is seen as we move further away, both vertically and horizontally

A

True

33
Q

Which type of stimulation results in 2 peaks in saline tank measurements?

A

Bipolar - correspond to source and sink

34
Q

Tripolar electrode arrays show __ (#) peaks and have 3 active electrodes - what are they?

A

1 peak; 1 stimulating electrode and 2 sinks

35
Q

Which type of electrode array has the least sharp distribution when measured in a saline tank?

A

Monopolar array

36
Q

When measuring potential distribution in cadaver cochleas for bipolar configuration, where was the higher peak located relative to the lower peak?

A

Always more apically.

37
Q

When measuring potential distribution in cadaver cochleas for bipolar configuration, potentials were higher when they were more ____ (basally/apically) located.

A

Apically - same for potential gradients (difference b/w 2 neighbouring potentials) = better spatial resolution towards apex

38
Q

When measured indirectly, which type of array has a flatter tuning curve?
Which is sharper but requires more current?

A

Monopolar; Bipolar

39
Q

T/F: the inferior colliculus has a tonotopic frequency map

A

True

40
Q

Characteristic frequency (increases/decreases) with depth in the inferior colliculus.

A

Increases

41
Q

Rank the following in order of frequency selectivity: Monopolar, bipolar, tripolar

A

Tripolar>bipolar>monopolar for impulse noise (not sustained)

42
Q

T/F: Sustained monopolar stimulation does not produce a more narrow response profile

A

False

43
Q

Initial onset responses are more (broader/narrow) than sustained responses

A

Broader

44
Q

Can we reach the same frequency selectivity of NH using electrode arrays?

A

No

45
Q

Which is better for frequency selectivity: monopolar, bipolar, or tripolar? Which has the lowest threshold?

A

Tri-polar; Monopolar

F20-9527-Cochlear Implants (28 decks)

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