Cochlear Mechanics Flashcards
In what direction does a rarefaction deflect the basilar membrane?
Up
Stapes moves outward and round window moves inward. As a result, BM moves upward.
In what direction does a rarefaction open the ion channels at the end of the stereocilia?
A rarefraction causes deflection of cilia away from the limbus and depolarization (excitation) of the hair cell. This causes contraction of the hair cell and the ion channels open.
Tip links do what for stereocilia?
Tip links are fine elastic strands that open and close pores/ion channels on the cilia. The tip links function like a string connected to a hinged hatch. When the cilia are bent toward the tallest one, the channels open, like a trap door. Opening these channels allows an influx of potassium.
Rarefaction wave → cilia pushed towards taller cells → tension on the tip-links → trapdoor opens and allows ions to flow into the cells
Why does the traveling wave go from base to apex?
The wave travels up the cochlea from base to apex dependent only on the compliance. The base is narrow and stiff, and the apical end is wide and flexible. In response to an applied force, the stiffness limited system (base) will start before the mass limited (apex).
The tuning on the basilar membrane is improved by what?
Cochlear amplifier
How does the basilar membrane tuning of a zombie compare to an alive person?
A zombie will have an exceptionally broad tuning curve and low sensitivity compared to a living person.
How long does the traveling wave take to go from base to apex in a human?
100 m/sec at the base and about 4 m/sec at the apex
How does the tuning at the basilar membrane change with level?
Low stimulus intensities are sharply tuned. Responses become more broadly tuned and peak at lower frequencies as the stimulus intensity is raised.
Amplitude compression, lack of sharpness, and greater displacement occurs at higher intensities.
What are on the axes of a tuning curve?
X-axis= frequency (Hz or kHz). Y-axis= threshold (dB SPL)
What frequencies show linear basilar membrane input-output functions?
Off frequencies are linear
On frequencies are nonlinear
Why were von Bekesy’s original Nobel prize winning measurements questioned?
Very high intensities had to be used, he used cadavers (which becomes a problem if tuning is metabolic dependent), the cochleae were damaged, and tuning was too broad to explain frequency selectivity as measured by perception. Measurement at lower intensities and undamaged cochlea using Mossbauer technique showed better tuning.
How does the tuning curve of a hearing impaired person compared to a typical hearing person?
A typical hearing person will have a much sharper tuning curve than that of a hearing impaired person. When the cochlea is in good physiological condition it is sharply tuned and highly sensitive. Someone that is hearing impaired has damaged outer hair cells, which leads to a broader tuning curve and less sensitivity. A greater intensity is needed to reach thresholds for a person with hearing loss, which results in a much larger and broader basilar membrane displacement.
Does the amplitude of the traveling wave grow or diminish as it travels down the cochlear duct? Why?
The traveling wave amplitude grows as it travels down the cochlear duct. The partition is less stiff at the apex, so the same force will cause a greater amplitude.
It continues to grow as it travels until it reaches the very apical end because it has the most mass, which is large enough to limit movement.
After reaching the resonance point, how fast does the traveling wave dissipate? Why?
Resonance happens when stiffness and mass limitations are equal in magnitude but opposite in phase. The traveling wave moves more slowly as it gets to its resonance point. The traveling wave dies off quickly beyond the resonance point because once past the stiffness limited part, the mass limited part makes wave motion impossible. Damping starts to occur and makes amplitude decline. The pressure across the cochlear partition drops as the resonant point is reached.
