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F20-9527-Cochlear Implants > Wk2a - CI's and Ear Anatomy > Flashcards

Wk2a - CI's and Ear Anatomy Flashcards

1
Q

What is the most common type of hearing loss?

A

Sensorineural

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2
Q

Where does SNHL originate?

A

Cochlear hair cells, which do not regenerate

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3
Q

Which part of the anatomy needs to be functional in order for a CI to be effective?

A

The Auditory Nerve

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4
Q

CI’s electrically stimulate the AN across the ______ array

A

Tonotopic

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5
Q

How do CI’s work?

A

By artificially stimulating the auditory system with electrical current, bypassing the outer, middle, and inner ear functions.
- in this way, it achieves the sensation of hearing

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6
Q

Do CI’s restore normal hearing?

A

No - they provide the “sensation” of hearing. They try to replicate the function of the hair cells, but this is not “all the way there” yet.

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7
Q

Describe the “internal” and “external” components of CIs

A

Internal - implanted portion/ electrodes

External - speech processor and induction coil

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8
Q

How does the output of CI’s differ from hearing aids?

A
  • Both detect sound
  • The CI output is electrical, not acoustic.
  • HA’s amplify sound
  • HA’s send sound through normal channels of system; CI’s bypass the outer, middle, and inner ear
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9
Q

What are the 4 components of CIs?

A

Microphone (located in speech processor)
Transmitter coil (held against head by magnet)
Receiver coil (directs info from external component to electrode)
Electrode

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10
Q

Describe the classical CI candidate

A

Bilat severe to profound SNHL

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11
Q

How long do CI surgeries usually take?

A

2-3 hours; consist of placing electrode array into cochlea and internal component behind ear; released the same day (children) - adults c/ complications may be kept overnight

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12
Q

Will patients start hearing immediately after surgery?

A

No - usually wait a month to receive external transmitter to allow for swelling to decrease and wound to heal
- 1 month post-surgery, sound processor is fitted and pt is instructed

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13
Q

Where do CIs primarily generate action potentials?

A

Spiral ganglion - signals are sent by AN to brain where it recognizes signals as sounds.

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14
Q

Where do we find the modiolus?

A

Middle of cochlea (which takes 2.5 turns around it)

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15
Q

Does the electrode reach the apex of the cochlea?

Which compartment does it lie in?

A

No - approx 1.x turns (out of 2.5)

Electrode lays in the scala tympani.

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16
Q

What are the 2 types of electrode arrays (based on location)?

A
  1. Lateral-wall electrode array (straight electrode; less traumatic, deeper insertion; lies closer to lateral wall of cochlea)
  2. Perimodiolar electrode array (also in scala tympani; close to modiolus; “natural” curvature; advantageous b/c lies closer to spiral ganglion, but requires more pressure/trauma to be inserted)
    - further from spiral ganglion means more current is needed to stimulate it
    - perimodiolar reaches less of the spiral ganglions b/c not as deep, therefore lat wall reaches more lower frequencies
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17
Q

Which electrode array can reach deeper? Does it require more or less current than the other option?

A

Lateral-wall electrode array

- needs more current b/c further from spiral ganglion

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18
Q

Which electrode array has more convexity?

A

Perimodiolar electrode array

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19
Q

What type of acoustical changes is the outer ear used for?

A

Spectral filtering (e.g. elevation) and amplification in the canal

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20
Q

What functions does the middle ear perform?

A
  • enhances most relevant frequencies by 20 dB

- stapedius reflex

21
Q

What characteristics does the inner ear have regarding frequency, amplitude, and timing?

A
  • broad frequency range (20 Hz-20 kHz) and high resolution (~1Hz)
  • dynamic range (>100 dB)
  • high temporal resolution (~4ms)
  • “top down” optimized properties (OHC) - behave as cochlear amplifier
22
Q

What functions should a CI offer, that are usually offered by the outer, middle, or inner ear?

A
  • broad freq range
  • high dynamic range
  • freq and temporal resolution typically achieved by hair cells
23
Q

Which compartment of the cochlea does the oval window stimulate?

A

The scala vestibuli, which circles around to the scala tympani, and ends at the round window

24
Q

What is the name of the compartment which houses the organ of corti?

A

Scala media

25
Q

Which end of the BM is narrow and stiff?

A

The base - this causes it to vibrate mostly for high frequency sounds

26
Q

Describe tonotopic organization

A

The characteristic of different regions of the basilar membrane responding to different frequencies

27
Q

Which compartment houses the electrode array?

A

Scala tympani, which is separated from scala media by the basilar membrane

28
Q

How many rows of OHCs vs IHCs?

A

3 rows of OHCs and 1 row of IHCs (closer to modiolus)

29
Q

The OHCs are attached to the _____ membrane and serve the function of pulling the ______ membrane down to amplify the sound

A

Tectorial; tectorial

30
Q

What is the purpose of the IHCs?

A

To trigger the electrical impulse that stimulates the brain

31
Q

Where does the AN originate?

A

From the OHCs and IHCs

32
Q

The fibers responsible for ___ frequency sounds coming from the basal portion of the cochlea are found on the _____ portion of the AN

A

High; Outer

33
Q

Which portion of the inner ear is responsible for the acoustic signal being transmitted into an electric impulse (known as _____).

A

Organ of Corti; transduction

34
Q

The organ of corti is represented by _______(#) hair cells (inner and outer)

A

16,000

35
Q

Cell depolarization/hyperpolarization will encode _____, _____, and ______.

A
  • Frequency, through BM location
  • Timing, through local vibration
  • Amplitude
36
Q

What are the 2 functions of the OHCs?

A
  • amplify soft sounds

- fine tune freq resolution of BM

37
Q

What is the tallest stereocilia called?

A

Kinocilium

38
Q

How are the stereocilia connected?

A

Tip-links, which open and close the cation channels

39
Q

Force towards the kinocilium ____ (opens/closes) cation channels

A

Opens

40
Q

What are the cations that flow through the tip links?

A

K+ and Ca2+

41
Q

Depolarization of the IHC activates the ____ (ascending/descending) _______ (afferent/efferent) neurons

A

ascending afferent

42
Q

Do OHCs actively or passively modify vibrations?

A

Actively through their timely change in length at a particular place of the BM (characteristic frequency)

43
Q

Does the BM vibrate in other areas besides at the characteristic frequency?

A

Yes, there is a broad, passive response in the areas close to the characteristic frequency (lower amplitude)

44
Q

How is the cochlear amplifier responsible for compression?

A

The action of the OHCs results in more gain at low input levels, bringing a response from under threshold to above threshold (linear up to a point). As the input level increases, the motion of the BM increases, and higher levels will receive less gain than lower levels.

45
Q

Approximately how many afferents per IHC?

A

10 to 20

46
Q

What type of fiber (afferent or efferent) do OHCs typically have? What do they control?Where do they originate?

A

Efferents from the superior olivary complex

- control stiffness and amplify membrane vibration via the cochlear amplifier

47
Q

Afferents of the IHCs are carried by the ____ division of the ___ cranial nerve.

A

cochlear; 8th

48
Q

The neurons of the spiral ganglion are _____, meaning they have a cell body in the spiral ganglion, an axon (distal process) towards the cochlear nucleus, and dendrites (proximal processes on IHC)

A

Bipolar; distal processes of the neurons for the nerve

F20-9527-Cochlear Implants (28 decks)

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