Aural Rehab: Cochlear Implants pt.1

Hearing mechanism overview (processes)

• pinna collects sound → funneled through ear canal → tympanic membrane vibrates → middle ear impedance matches → cochlear → organ of corti (tonotopic organization) → hair cells → spiral gangilan cells → VIII CN → primary auditor codex (brain)

Cochlea Info

• 2 ½ turns

• tonotopic organization

  • base = high frequency

  • apex = low frequency

Organ of Corti Info

1. outer hair cells (12,000)

   1. cochlear amplifier

2. sheering force

1. inner hair cells (3,500)

   1. ions move in and out to signal spiral ganglian cells (8-20) to fires action potential

First point of electricity in the ear is where?

spiral ganglian cells (part of VIII CN)

Cochlear Implant Parts

1. external

   1. sound processor

      1. microphones

      2. speech processor

   2. cable

   3. transmitting coil/headpiece

2. internal

   1. magnet receiver

   2. electrode array (whole line)

      1. electrodes (boxes)

Cochlear Implant Sound Process

1. microphone picks up sound

2. speech processor digitalizes sound into electrical coded signals

3. signals sent though cable to transmitting coil

4. coil sents signals as FM radio signals to internal

5. delivers electrical energy to electrode array

6. electores stimulate auditory nerve fibers in cochlea

7. sends to brain

Success with a CI is highly dependent on what?

VIII CN

CI Manufacturers

Advanced Bionics

Cochlear

Med El

How to change manufactures?

explantation and replantation

Who completes CI surgery?

neurotologist ? (ENT specializes in neural stuff)

Initial appointment is how long after surgery?

6 weeks

Audiologist can do what during surgery?

do testing in OR to see if CI is working

Bacterial meningitis can do what to the cochlea?

Ossify (turn to bone)

failure rate is dependent on…

patient, pathology, surgical technique, implant chosen (by surgeon)

CI encode what well

time and temporal cues

CI do NOT encode what well?

frequency

Electrode inside cochlea how far?

• 1 ½ turns at most

  • problem for frequency resolution