Wk2a - CI's and Ear Anatomy Flashcards
What is the most common type of hearing loss?
Sensorineural
Where does SNHL originate?
Cochlear hair cells, which do not regenerate
Which part of the anatomy needs to be functional in order for a CI to be effective?
The Auditory Nerve
CI’s electrically stimulate the AN across the ______ array
Tonotopic
How do CI’s work?
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
Do CI’s restore normal hearing?
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.
Describe the “internal” and “external” components of CIs
Internal - implanted portion/ electrodes
External - speech processor and induction coil
How does the output of CI’s differ from hearing aids?
- 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
What are the 4 components of CIs?
Microphone (located in speech processor)
Transmitter coil (held against head by magnet)
Receiver coil (directs info from external component to electrode)
Electrode
Describe the classical CI candidate
Bilat severe to profound SNHL
How long do CI surgeries usually take?
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
Will patients start hearing immediately after surgery?
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
Where do CIs primarily generate action potentials?
Spiral ganglion - signals are sent by AN to brain where it recognizes signals as sounds.
Where do we find the modiolus?
Middle of cochlea (which takes 2.5 turns around it)
Does the electrode reach the apex of the cochlea?
Which compartment does it lie in?
No - approx 1.x turns (out of 2.5)
Electrode lays in the scala tympani.
What are the 2 types of electrode arrays (based on location)?
- Lateral-wall electrode array (straight electrode; less traumatic, deeper insertion; lies closer to lateral wall of cochlea)
- 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
Which electrode array can reach deeper? Does it require more or less current than the other option?
Lateral-wall electrode array
- needs more current b/c further from spiral ganglion
Which electrode array has more convexity?
Perimodiolar electrode array
What type of acoustical changes is the outer ear used for?
Spectral filtering (e.g. elevation) and amplification in the canal
What functions does the middle ear perform?
- enhances most relevant frequencies by 20 dB
- stapedius reflex
What characteristics does the inner ear have regarding frequency, amplitude, and timing?
- 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
What functions should a CI offer, that are usually offered by the outer, middle, or inner ear?
- broad freq range
- high dynamic range
- freq and temporal resolution typically achieved by hair cells
Which compartment of the cochlea does the oval window stimulate?
The scala vestibuli, which circles around to the scala tympani, and ends at the round window
What is the name of the compartment which houses the organ of corti?
Scala media
Which end of the BM is narrow and stiff?
The base - this causes it to vibrate mostly for high frequency sounds
Describe tonotopic organization
The characteristic of different regions of the basilar membrane responding to different frequencies
Which compartment houses the electrode array?
Scala tympani, which is separated from scala media by the basilar membrane
How many rows of OHCs vs IHCs?
3 rows of OHCs and 1 row of IHCs (closer to modiolus)
The OHCs are attached to the _____ membrane and serve the function of pulling the ______ membrane down to amplify the sound
Tectorial; tectorial
What is the purpose of the IHCs?
To trigger the electrical impulse that stimulates the brain
Where does the AN originate?
From the OHCs and IHCs
The fibers responsible for ___ frequency sounds coming from the basal portion of the cochlea are found on the _____ portion of the AN
High; Outer
Which portion of the inner ear is responsible for the acoustic signal being transmitted into an electric impulse (known as _____).
Organ of Corti; transduction
The organ of corti is represented by _______(#) hair cells (inner and outer)
16,000
Cell depolarization/hyperpolarization will encode _____, _____, and ______.
- Frequency, through BM location
- Timing, through local vibration
- Amplitude
What are the 2 functions of the OHCs?
- amplify soft sounds
- fine tune freq resolution of BM
What is the tallest stereocilia called?
Kinocilium
How are the stereocilia connected?
Tip-links, which open and close the cation channels
Force towards the kinocilium ____ (opens/closes) cation channels
Opens
What are the cations that flow through the tip links?
K+ and Ca2+
Depolarization of the IHC activates the ____ (ascending/descending) _______ (afferent/efferent) neurons
ascending afferent
Do OHCs actively or passively modify vibrations?
Actively through their timely change in length at a particular place of the BM (characteristic frequency)
Does the BM vibrate in other areas besides at the characteristic frequency?
Yes, there is a broad, passive response in the areas close to the characteristic frequency (lower amplitude)
How is the cochlear amplifier responsible for compression?
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.
Approximately how many afferents per IHC?
10 to 20
What type of fiber (afferent or efferent) do OHCs typically have? What do they control?Where do they originate?
Efferents from the superior olivary complex
- control stiffness and amplify membrane vibration via the cochlear amplifier
Afferents of the IHCs are carried by the ____ division of the ___ cranial nerve.
cochlear; 8th
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)
Bipolar; distal processes of the neurons for the nerve
