Ears 2

Question 1

inner ear parts

Answer 1

Oval Window –
Cochlea –
Auditory-Vestibular Nerve –
Vestibular Labyrinth –

Question 2

oval window

Answer 2

vibrates, sends sound waves through cochlea

Question 3

cochlea

Answer 3

“snail”! Pea-sized organ in which sound is transduced

organ for transduction of sound wave signals into neural signals

Question 4

auditory-vestibular nerve

Answer 4

brings sound info to brain

Question 5

vestibular labyrinth

Answer 5

vestibular organ of interconnected chambers

Question 6

auditory pathway stages

Answer 6

Sound waves enter auditory canal
Tympanic membrane vibrates
Ossicles vibrate - malleus, incus, stapes
Oval window vibrates
Cochlear fluid - sends wave down basilar membrane
Sensory neuron response to the brain

Question 7

basilar membrane

Answer 7

Membrane running down the middle of the cochlea
Thinner and stiffer at base (near oval window)
Wider and floppier at apex (like a swim flipper)
Covered with hair cells

Question 8

how does basilar membrane work

Answer 8

Stapes contacts oval window, moves in and out like piston as sound transmitted
Fluid pumped in waves through spiral of cochlea
Fluid movement bends basilar membrane near base
Wave moves towards apex (far end)
Hairs on cells lining membrane move back and forth with flow

Question 9

basilar membrane more

Answer 9

Pressure at oval window, pushes fluid in cochlea, round window membrane bulges out
Basilar membrane vibrates as a wave, with one position moving at its maximum

Question 10

high v low frequencies basilar membrane

Answer 10

High frequencies die out early close to base

Low frequencies travel farther along basilar membrane

Question 11

tonotopic organization

Answer 11

spatial arrangement where different frequencies vibrate specific parts of the basilar membrane

Question 12

Presbycusis -

Answer 12

loss of flexibility of basilar membrane in older people, generates a loss of hearing at higher frequencies

Question 13

organ of corti

Answer 13

A long basilar membrane, The Organ of Corti hold hair cells
As basilar membrane moves up and down, the Tectorial membrane moves up and down which pushes on hair cells.
Bending Hair cells triggers a neural signal in spiral ganglion cells (bipolar cells).

Question 14

damage where can cause nerve deafness

Answer 14

organ of corti

Question 15

inner hair cells

Answer 15

main transmitters of sound

spiral ganglions receive 95% of innervations from these cells even though they are outnumbered 3:1 by outer hair cells

Question 16

outer hair cells

Answer 16

may amplify low intensity sound vibrations by rapidly changing their cell length

Question 17

why is sound transduction cause mostly by inner hair cells

Answer 17

3X more Outer hair cells than Inner hair cells, but most transduction of sound by Inner hair cells.
One spiral ganglion cell synapses with many outer hair cells.
Many (10) spiral ganglion cells will synapse with one inner hair cell, therefore most sound detection caused by inner hair cells.

Question 18

Flapping OF WHAT helps move hairs

Answer 18

tectorial membrane

Question 19

sound transduction

Answer 19

As the basilar membrane moves up, the tectorial membrane pushes the stereocilia of hair cells one direction.
As the basilar membrane moves down, the tectorial membrane pushes the stereocilia of hair cells the other direction.

Question 20

sound transduction cont

Answer 20

Tip links (elastic filament) attach stereocilia, provide a mechanical spring to open and close TRPA1 channels.
When stereocilia straight, TRPA1 channels partially open, some K+ flows in.
As basilar membrane moves up and down, the tectorial membrane pushes stereocilia to bend left and right.
In one direction, channels are pulled open (depolarization), in other direction, channels pulled shut (hyperpolarization)

Question 21

place theory

Answer 21

Place on the basilar membrane that vibrates the most sends signal to a certain position in the auditory cortex (tonotopic map) – each area correlated with specific pitch

Question 22

frequency theory

Answer 22

For lower frequencies, neurons fire at the frequency of the wave (for example, a 20Hz sound might make neuron fire 20 times per second)

Question 23

low v intermediate v high frequencies

Answer 23

Low Frequencies: (Below 200 Hz)
Only Phase Locking (No characteristic frequencies below 200 Hz)
Intermediate Frequencies: (200 Hz-4,000 Hz)
Both Tonotopic Mapping and Phase Locking
High Frequencies: (Above 4,000 Hz)
Only Tonotopic Mapping (Too fast to fire in phase)

Question 24

Sound Intensity or Loudness is encoded by:

Answer 24

Number of neurons firing – Louder more neurons fire.

Firing rate of neurons – Louder faster firing rate.

Question 25

Louder sounds cause the basilar membrane to be

Answer 25

displaced over a greater area causing the activation of more hair cells and to be displaced with a greater amplitude which causes greater depolarizations and hyperpolarizations leading to a greater firing rate of spiral ganglion cells.

Question 26

one auditory pathway

Answer 26

Spiral ganglion (one side)-synapse from hair cells forms Auditory-Vestibular Nerve

Ventral cochlear nucleus of medulla (one side)

Superior olive of medulla (both sides)

Inferior colliculus of midbrain (both sides)

MGN of thalamus (both sides)

Auditory cortex (both sides)