Auditory system

Question 1

What is sound?

Answer 1

Vibration of air molecules causing alternating compression and rarefaction.

Question 2

What does amplitude (dB) encode?

Answer 2

Loudness of sound.

Question 3

What does frequency (Hz) encode?

Answer 3

Pitch of sound.

Question 4

Which parts of the ear are conductive vs sensory?

Answer 4

Outer & middle ear = conductive; inner ear = sensory.

Question 5

Why is impedance matching necessary?

Answer 5

More energy is needed to move fluid than air; without it only ~0.1% of sound enters cochlea.

Question 6

How do the ossicles achieve impedance matching?

Answer 6

Lever action + large area difference between eardrum and oval window (~20×) → ~26× pressure gain.

Question 7

What is the function of the ossicular (attenuation) reflex?

Answer 7

Reduces ossicle movement in loud sounds (>80 dB) via stapedius contraction.

Question 8

Why is the attenuation reflex ineffective for sudden sounds?

Answer 8

Reflex delay is 50–100 ms.

Question 9

Which three fluid-filled chambers form the cochlear duct?

Answer 9

Scala vestibuli, scala media, scala tympani.

Question 10

What fluid fills the scala media?

Answer 10

Endolymph.

Question 11

Where are inner and outer hair cells located?

Answer 11

In the Organ of Corti on the basilar membrane.

Question 12

What percentage of auditory nerve afferents synapse on inner hair cells?

Answer 12

95% (Type I fibres).

Question 13

What is the main function of IHCs?

Answer 13

Sensory transduction → generating receptor potentials and releasing transmitter.

Question 14

What is the main function of OHCs?

Answer 14

Active amplification of sound via electromotility.

Question 15

Which motor protein enables OHC electromotility?

Answer 15

Prestin.

Question 16

What are tip links composed of?

Answer 16

Cadherins CDH23 and PCDH15.

Question 17

What is the mechanotransducer channel likely formed by?

Answer 17

TMC1/2 proteins.

Question 18

Which fluid resembles CSF: perilymph or endolymph?

Answer 18

Perilymph.

Question 19

What is special about the ionic composition of endolymph?

Answer 19

Very high K⁺ (~145 mM), +80 mV potential, low Na⁺ (~1 mM).

Question 20

Which part of the basilar membrane responds to high frequencies?

Answer 20

The base (narrow and stiff).

Question 21

What minimum stereocilia displacement is detectable as sound?

Answer 21

~0.3 nm (extremely tiny).

Question 22

Why does K⁺ rush into hair cells during stimulation?

Answer 22

Large electrochemical gradient: endolymph at +80 mV vs hair cell at –60 mV (~140 mV driving force).