Flashcards in Neuro - auditory system 1 + 2 Deck (62)
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
What is the structure of the tympanic membrane? (3)
3 layer translucent membrane
1 cm^2 vibratory surface
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?
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?
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