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Anat & Phys W3.2
Middle Ear Transfer Function
| Question | Answer |
|---|---|
| What is one function of the mucous membranes in the ME? What happens when one swallows? | Diffuse air from ME space into blood. Diffuse O2, then C02, then N2. The diffusion leads to a DECREASE IN PRESSURE. When swallow --- ET opens -> air rushes in ME space -> pressure equalizes |
| What are goblet cells? | Cells responsible for making mucous. When there is an imbalance in O2 and CO2 then mucous thickens. |
| What happens to the TM when there is an imbalance in pressure? | TM responds to imbalance of pressure. STIFFENS SYSTEM (effects low freq HL). |
| What happens when fluid builds up in ME space? | ADDS MASS - yields low freq HL. |
| What are the two types of ET malfunctions? | 1) Patulous ET - always open. 2) Swollen adenoids, allergies, etc. - inflamation surrounds ET in nasopharynx. |
| What is a transfer function? | The ratio of the output to the input as a function of frequency. |
| Decribe the basic ME transfer function. | 1) Incident wave reaches TM. 2) TM set into motion 3) Most sounds absorbed. 4) Some sounds reflected. 5) For the sound that gets through it sets the ossicles into motion (frictional loss occurs) 6) Some sound oscilates in ME cavity. |
| What is significant about the shape of the TM? | The core-shape of TM results in greater pressure value at the TM's apex. That allows it to transfer energy more effeciently. |
| What is the vibrational pattern of the TM? | Displacement of the TM is not uniform across the surface and not uniform across the frequencies. TM moves proportionally up to about 2k Hz and above 2k Hz moves segmentally/ |
| What are the lateral and medial points of the ossicular chain? | Lateral connection is TM. Medial connection is oval window. |
| How does the stapes move in response to sound intensities? | Low to moderate intensities - stapes rotates around a vertical axis acting like a piston. High intensities - stapes rotates around a horizontal axis and less piston-like (and less efficient). |
| What is the impedance transfer? | ME transfers vibration from large, low impedance TM to smaller, higher impedance oval window. |
| How much sound would be reflected going from air to water? | 99.9% reflected and only 0.1% would enter the cochlea. |
| What are the three mechanisms of the METF? | 1) Areal ratio (area differential) of the TM to the oval window 2) Lever action of the ossicular chain 3) Buckling action of the TM |
| What is the areal ratio of the TM to the stapes? | 17.7:1 |
| How much energy is lost without the METF? | ~30dB |
| What is the pressure increase in dB for the areal ratio account for in the METF? | ~25dB |
| What is the lever ratio of the ossicular chain? | 1.3:1 |
| What does the size difference between the malleus and the incus provide in the METF? | The malleus is larger than the incus. When some input is put into the malleus then there will be more movement on the incus. The output of the incus will be greater. |
| What is the pressure increase in dB for the lever action of the ossicles for the METF? | ~2.3 |
| What is the pressure increase in dB for the buckling of the TM? | Due to the curvature of TM, vibrations directed to TM result in greater mvmt of TM than the displacement of manubrium. BUT TM does not move evenly. Above 2kHz there is not much of an impact. There is some impact for lower freqs. No real impact overall. |
| Is the METF completely efficient? | No because there is loss of energy due to inertia, heat (friction), ligaments, etc. |
| What is the pressure ratio between the TM and the stapes? | For every 1 unit of input at TM there is 22.36 units output at the stapes. |
| How much gain does the METF provide? | None. The METF is does not provide gain, it provides pressure increase. This allows for an approximation of loudness from the source to go into the ME. |
| What is the mechanical advantage of the ME system in dB SPL? | ~27dB |
| What is the impedance mismatch at the oval window that remains after the METF? | 0.034 |
| How does the METF relate to what happens in the inner ear? | The displacement of the BM is proportional to the pressure differential across the scalae. The pressure differential is proportional to the stapes velocity. |
| What are some other mechanisms at work during the METF? | Energy lost and friction (friction impacts all freqs). Oval and round windows are assymetric to one another so that sound does not enter cochlea in-phase with one another. |
| Why do lower freqs have a harder time going through the METF? | Because the system is stiffness dominated. |
| Where does the areal ratio and lever action of the ossicles have the "biggest" bump? | 1k-4k Hz |
Created by:
duda713
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