Lecture 19; Sound 3 Flashcards
Describe the transfer of sound to the inner ear:
The external ear resonates the sound (makes it louder) this displaces the tympanic membrane, displacing the ossicular tree, which articulates and the stapes oscillates the round window
This causes displacement of the fluid which causes the sensory cells to connect with the tectorali membrane and transduction to occur
The round window is a membranous layer that can move to allow fluid displacement.
Describe what happens when the stapes articulates;
Movement in the stapes in the oval window sets up a traveling wave on the organ of corti and basilar membrane
As the travelling wave moves along the organ of corti what happens?
The wave increases in amplitude, decreasing wavelength but maintaining frequency until the point of resonance.
What does the point of resonance signify on the organ of corti?
The point of resonance occurs at a single frequency.
The point of resonance will be defined by the mass and stiffness of the structures (organ of corti)
Additional mechanisms enables this to form a peak of activity and around this area threshold/ sensory cells will be stimulated.
Different frequencies will change the point of resonance.
Describe HZ organisation of the organ of corti;
Base = High frequencies (near oval window)
Apex = low frequencies
Position of peak of travelling wave varies spatially with frequency
How is complex sound processed by the organ of corti?
- Multiple resonate frequencies occur
How does the organ of corti act as a mechanical filter?
Gradient in mechanical properties along length generates mechanical filter
Describe the mechanical properties along the basilar membrane;
Gradual gradient;
Basal end: Thick, narrow and stiff
Apical end: Thin wide and compliant
how is the cochlea mapped?
Tonotopically mapped
- Hz distribution (ability to seperate freqeuncies) thus at those resonating points, those sensory cells are activated and sound is transduced.
Does tonotopicity extend beyond the basilar membrane?
Yes it extends into the cortices where some neurons only respond to specific frequencies..
What sort of motion is the vertical motion of the organ of corti translated to in the sensory cells?
Vertical motion of the organ of corti is converted into radial motion at the stereocilia. (as they rub against the tectorali membrane, which leads to sensory transduction)
Describe radial movement and sensory cell depolarisation;
Movement in one radial direction generates depolarisation, while movement in the other causes hyperpolarisation (but only in the one plane)
What part of the IHC and OHC are the sensory transducers?
The stereocilia are the transduction elements
Describe the stereocilia:
There are an array of different length stereocilia. B/w the longer and shorter one there are little bridges and this is where the transduction channels are.
What are the bridges between stereocilia called?
tip links (transduction channels)
What are tip links?
- Dont know what constitutes the channels
- Mechanical, electrical transduction channels (linking mechanical motion to electrical transduction)
- Made up a single cadhedrin molecule with a proteocadhedrin molecule at either end.
Are transduction channels found in tip links?
No, they movement of the stereocilia causes the tip links to pull, opening the transduction channel son the stereocilia, enabling ions to flow into the cell and activate it.
