Audition and Central Auditory Pathways

Question 1

What structures are injured to cause deafness?

Answer 1

hair cells

Question 2

What structures are still intact for deaf people that allow the use of cochlear prostheses?

Answer 2

afferent fibers from hair cells

Question 3

How do cochlear prosthetics work?

Answer 3

bypass hair cells by implanting multiple electrodes into scala tympani to directly activate different afferent nerve fibers based on the different auditory stimuli

Question 4

What is an auditory stimulus?

Answer 4

rapid fluctuations in air pressure, rarefaction and compression of air molecules

Question 5

What is the amplitude of an auditory stimulus?

Answer 5

the magnitude of pressure change

Question 6

What scale measures the physical magnitude of sound stimuli? How much do you have to increase the sound pressure to compensate for a 40 dB loss of hearing?

Answer 6

decibel, 100x

Question 7

Where in the auditory system does frequency analysis occur?

Answer 7

basilar membrane in the cochlea

Question 8

Why is there a 30 dB transmission loss of incident energy at the oval window?

Answer 8

cochlea is fluid filled and it is harder to impart fluid motion than air motion, only 1/1000 of the energy transmits

Question 9

What does the change in area from 60 mm^2 in the tympanic membrane to 3 mm^2 in the oval window do?

Answer 9

amplifies the pressure transmitted by 20 fold at the oval window (to help compensate for loss of incident energy due to fluid)

Question 10

Why is the lever action of the ossicular chain important?

Answer 10

increases the pressure felt at the tympanic membrane by 1.3 to help compensate for transmission loss

Question 11

What is tympanometry? What is measured? What pathology is tested for?

Answer 11

technique to measure impedance of middle ear to sound, measure the amount of sound waves reflected using a mic, tests for conductive hearing loss which presents with more sound waves reflected back

Question 12

What changes in the basilar membrane as you go from base to apex?

Answer 12

gets wider and gets less stiff

Question 13

Does deflection increase or decrease as you move towards apex of basilar membrane? What about phase lag?

Answer 13

both increase

Question 14

What happens when stapes moves into the oval window? when it moves out? what does this create?

Answer 14

when it moves in compresses fluid to create downward bulge in round window, when it moves out creates an upward bulge, together it creates a full traveling wave

Question 15

What is the envelope?

Answer 15

maximum deflection in the basilar membrane a specific frequency will reach before dissipating quickly

Question 16

Where do high frequency waves deflect near? low frequency waves?

Answer 16

high frequency closest to base, low frequency closest to apex

Question 17

Why is the activation of certain receptors correlated to hearing certain frequencies?

Answer 17

because receptors are arranged in an orderly manner along the basilar membrane and the frequency affects the deflection pattern of the basilar membrane to narrowly activate a certain area on the membrane (because of position of max stimulation)

Question 18

How can you activate a hair cell that is not at the exact area of maximum deflection?

Answer 18

increasing sound intensity since it increases the amplitude of the envelope and can incidentally stimulate hair cells near the point of maximal deflection

Question 19

How does pushing on the basilar membrane stimulate hair cells?

Answer 19

deflecting basilar membrane shears cilia of hair cells in one direction, affects the permeability of the auditory cell membrane to allow change in current

Question 20

If cilia shears towards kinocilia, does this depolarize or hyperpolarize the hair cell?

Answer 20

depolarizes

Question 21

Where are the short and stiff hair cells? Longer and less stiff?

Answer 21

base of basilar membrane, apex of basilar membrane

Question 22

Are hair cells spontaneously active?

Answer 22

yes

Question 23

What does mechanical activation does to the spontaneous voltage oscillations of hair cells?

Answer 23

amplifies them because the characteristic frequency of oscillation matches the frequency that is most responsive to mechanical stimuli

Question 24

What does the central auditory system detect, pure tone or patterns?

Answer 24

patterns

Question 25

How many divisions of cochlear nuclei are there? do they all receive innervation from CN VIII?

Answer 25

3 (dorsal, posteroventral, anteroventral), yes the full range of frequencies represented in each of the 3 nuclei

Question 26

Is there tonotopic distribution of frequencies in the nuclei?

Answer 26

yes, high frequency dorsally, low frequency ventrally

Question 27

Is tonotropy maintained in A1?

Answer 27

yes, high frequency is rostral, low frequency is caudal

Question 28

As you go perpendicular to the cortex, what kind fields of cells do you see?

Answer 28

more complex fields (may need change in frequency or pattern to be activated, etc)

Question 29

Is auditory cortex needed for pitch discrimination? What does it do?

Answer 29

No, it analyzes pitch patterns