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What is the role of Pinna? (2)

1) Passive process - Filters and channels sound to external canal

2) Amplifies frequency around 3000 Hz


What ear structures in the outer ear are involved in frequency amplification?

Which frequencies are affected?

What is important about these frequencies?

Structures: Pinna and Channel
Frequencies: 3000 Hz
Importance: this frequency range is important for speech


What structures make up the middle ear? (4 - in order from outer to inner)

1) tympanic membrane
2) Malleus
3) Incus
4) Stapes


What is the structure of the tympanic membrane? (3)

3 layer translucent membrane
1 cm^2 vibratory surface
cone shaped


What causes the impedance mismatch?

Transmitting sound pressure wave from air (outer ear) to fluid (inner ear) is difficult and requires higher force


What are the mechanisms for Impedance matching? (3)

1) area ratio
2) lever action
3) buckling of tympanic membrane


What is the total gain of middle ear impedance matching?

31 dB


How does area ratio help impedance mismatch? What is the gain from this process?

The tympanic membrane is 14 times bigger than the oval window. Force is transduced through the Malleus --> Incus --> Stapes --> Oval window

Force is concentrated onto small area causing higher pressure

Gain: 23 dB


How does lever action help impedance mismatch? What is the gain from this process?

The length of the malleus is longer than the process of the incus creating a lever action. Ratio is 1.3 to 1

Gain: 2 dB


How does buckling of tympanic membrane help impedance mismatch? What is the gain from this process?

Buckling of the TM when it vibrates applies almost twice the force to the malleus

Gain: 6 dB


What are the three chambers of the cochlea?

Scala vestibuli
Scala media
Scala tympani


Where is Reissner's membrane located?

Bottom part of scala vestibuli


Where is the Basilar membrane?

In between the Scala media and Scala tympani.


Where is the Organ of corti?

Sits on the basilar membrane


Where are the cells for hearing (inner and outer hair cells, etc)?

Makes up the Organ of corti


Where is the stria vascularis?

What is its role? (2)

The lateral edge of the Scala Media

Role: blood supply to cochlea and responsible for ionic concentration and cochlea potential

Known as the "Cochlear battery"


Where is the spiral ligament?

Lateral most of scala media


What are Deiters cells?

These cells support each outer hair cell


What is the reticular lamina?

Keeps the outer hair cells and inner hair cells seperate from the fluid in the scala media


What are the Pillars of corti?

separate the 1 layer of inner hair cells with the 3 layers of outer hair cells


What is the tunnel of corti?

Space between 1 layer of inner hair cells and 3 layers of outer hair cells


Where is the Tectorial membrane?

On top of the stereocilia of the hair cells


What is the sprial lamina and what does it contain?

Bony shelf coming out from the modiolus and attaches to basilar membrane. Auditory nerve fibers go through and innervate nerve cells.


What is the structure of the Basilar membrane?

when uncurled: the base is narrow and stiff, the apex is wider and less stiff


How does the Basilar membrane work?

A sound wave will travel up the basilar membrane from the oval window - base to apex. The point of maximal deflection will be the pitch you want to encode


What is tonotopic organization?

Different frequencies maximally displace the basilar membrane at different points

High frequencies at base to low frequencies at apex


Which direction does an upward phase of a sound wave deflect the hair cells and stereocilia?

Hair cells: pushes up
Stereocilia: Lateral force of tectorial membrane pushing stereocilia away from modiolus


Which direction does a downward phase of a sound wave deflect the hair cells and stereocilia?

Hair cells: downward

Stereocilia: Lateral shear force of the tectorial membrane pushing stereocilia towards modiolus


What is the active mechanism of the cochlea?

Outer hair cells have motile properties - dynamic microtubules and microfilaments along membrane that allow contractile behaviors


How is the mechanical energy of the hair cells translate into electrochemical energy?