w2 Flashcards
(37 cards)
How is the electrode array of a cochlear implant threaded into the cochlear?
Through the round window
Describe the loudness decibel ranges for the following:
a) Normal hearing
b) Mild hearing loss
c) Moderate hearing loss
d) Severe hearing loss
e) Profound hearing loss
a) 0-20 dB
b) 20-40 dB
c) 40-60 dB
d) 60-90 dB
e) >90 db
What are the target neurons for a cochlear implant?
Spiral ganglion cells
Which of the 3 stimulation modes has the lowest power consumption and is the most common? Monopolar, Bipolar, Common ground
Monopolar.
however, bipolar is most effective physiologically (slightly better efficacy/resolution of sound).
How does the monopolar stimulation mode work
current passed between one intracochlear electrode and one (or more) extracochlear electrodes (either on telemetry device or as a ball electrode).
How does the bipolar stimulation mode work
current passed between a pair of electrodes, both within the cochlea (intracochlear). Nomenclature is BP+X where X defines the number of electrodes between the two electrodes.
How does the common ground stimulation mode work
current passed between an intracochelar electrode and all the other intracochlear electrodes connected together.
When sound comes in, the outer ear enhaces the sound levels and moves the tympanic membrane (eardrum) back and forth => the malleus (hammer), stapes (stirrup), and incus (anvil) amplify the movement => fluid pushes through the OVAL WINDOW to bend the hair cells => an action potential is fired in the auditory nerve to the brain. From this, what are the 2 primary forms of deafness?
Conductive: damage to the outer or middle ear, blockage, fluid, poor movement of the ossicles, Atresia (closed orifices) or Stenosis (narrowing spaces).
Sensorineual: damage to hair cells from genetics, infection, medications, trauma, autoimmune, aging (presbycusis).
what is the difference between inner and outer hair cells
Inner hair cells initiate afferent action potentials when the basilar membrane moves. Outer hair cells receive
efferent action potentials and “tune” the Tectorial Membrane.
What is tinnitus
ringing in the ear. The most common cause is damage or loss of the hair cells in the cochlea of the inner ear. This may happen as people age or from prolonged exposure to loud noise. However, there may be other causes, such as earwax blockage.
describe how a cochlear implant delivers sound
Microphones on the sound processor pick up sounds and the processor converts them into digital signals. This signal is transferred through the coil to the implant just under the skin. The implant sends the signals
down the electrode into the cochlea. The auditory nerve fibres pick up the signals.
How are auditory nerves recruited (fired) by electrodes?
the elctrodes emit biphasic, constant current pulses between selected electrodes.
It is Biphasic to minimize DC. Typical stimulation rates about 1 kHz.
what is a modiolus (cochlea)
Spongy bone inside cochlea. The cochlear nerve and spiral ganglion is situated inside it.
Why can’t the stimulation parameters be constant?
Nerves are fired by current in the modiolus since this generates voltages in the tissue in proportion to this. Changing impedances affects the voltage. Want to maintain constant current in the modiolus irrespective of the electrode impedance.
Constant current is maintained via voltage stimulators that maintain constant voltage between the electrodes so that the current in the modiolus adjusts accordingly when the electrode impedance changes.
why might the impedance of the cochlear implant’s electrode change?
The impedance near the electrode can change due to scar tissue changes.
what is Tonotopy
the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain.
why is pitch imporant for humans to distinguish
Important for vowel recognition (formants). Pitch discrimination ability correlates with speech perception.
how is loudness processed in the brain (normally and electrically)
normally - Loudness is determined primarily by how many auditory nerves fire.
electrically - It is approxamately equal to the charge per phase
how do cochlear implants transmit loudness
they send in more current (longer phases) through the electrodes and more fibres fire.
what are the two types of electrode array, and what are their characteristics
Perimodiolar: pre curved to match the cochlea. Closer to the target neurons. Lower current required, reduced spread of excitation (thin current density/position peak). This placement also improves hearing performance i.e. more medial better hearing.
Lateral wall: Straight, flexible. Simple and atraumatic to insert. Wider spread of excitation (wide current density/position peak).
How can cochlear implants be customized to suit people who have complete or partial dysfunction of the VIIIth nerve bilaterally due to: Acoustic tumours, VIIIth nerve avulsion (head trauma), or Total cochlea ossification?
Auditory Brainstem Implants. It stimulates the surface of the cochlear nucleus.
What is the purpose of the extracochlear electrode (EC1)
the intracochlear stimulation may cause twitching, this channel is to help prevent that.
what does “programming” a cochlear implant mean?
Setting stimulation settings.
Electrodes have settings for threshold and comfort levels. Each electrode’s parameters are typically programmed for each individual patient based on their auditory perceptions in response to electrical stimuli.
Additional details like rate, input dynamic range etc. are also adjustable.
What is NRT
Neural response telemetry. stimulates the nerve with one electrode pair and then measures the response of the nerve firing with another electrode pair. This information is used to automatically program the cochlear implant. Useful for patients like babies who can’t give feedback.
