Lecture 10 - Auditory System (Part 1) - Peripheral Transduction

Question 1

What type of waves are sounds waves and what regions do these sound waves include?

Answer 1

-longitudinal waves with areas or rarefraction (particles are far apart) or compression (particles are close together)

Question 2

What does the amplitude of a sound wave correspond to and in what unit is it measured?

Answer 2

volume in dB

Question 3

What does the frequency of a sound wave relate to and what unit is it measured in?

Answer 3

the pitch of the sound; high pitch-high frequency; low pitch=low frequency; in Hz

Question 4

Why does the medium in which the sound is in matter?

Answer 4

it affects the speed with which the sound travels; in liquid or solid media compared to air sound travels faster

Question 5

What is the outer ear?

Answer 5

helps funnel sound waves into the ear, the pinna is important in focusing sound waves into the ear

Question 6

What is the middle ear?

Answer 6

where the middle ear ossicles are (malleus, incus, and stapes) and where the tympanic membrane; transduces the mechanical signal of sound by the stapes tapping on the oval window

Question 7

What is the inner ear?

Answer 7

It is the site of auditory transduction and it converts mechanical sound into an electrical signal which can be conveyed to different regions of the brain via the cochlear nerve; starts at the oval window which is the membrane bound barrier on the outer surface of the cochlea and the cochlea is filled with endolymph fluid which is potassium rich

Question 8

What does the tympanic membrane of the middle ear do?

Answer 8

block the entrance to the middle ear and receives sound waves funneled through the outer ear and moves rhythmically in the pattern of the sound wave

Question 9

What do the middle ear ossicles or the malleus incus and stapes do?

Answer 9

the malleus receives the mechanical transduction from the tympanic membrane and transfers it to the incus which transfer it to the stapes which taps on the entrance to the inner ear which is the oval window

Question 10

What does CN VII or the facial nerve control?

Answer 10

the stapedius muscle which can dampen the extent to which the stapes moves

Question 11

What does CN V or the trigeminal nerve control?

Answer 11

tensor tympani which controls how taught the tympanic membrane is affecting how much it will transduce mechanical signals to the malleus

Question 12

Where is the organ of corti and what structures does it contain?

Answer 12

-it is found within the cochlea of the inner ear
-has inner and outer hair cells
-has two membranes the tectorial membrane and the basilar membrane

Question 13

What does the basilar membrane do?

Answer 13

forms the base of the organ of corti and it is stationary during auditory transduction
-the basilar membrane as a tonotopic frequency map with the highest frequencies at the basal end close to the oval window and the lowest frequencies at the apical end close to the round window

Question 14

What is the tectorial membrane?

Answer 14

sits atop the inner and outer hair cells and shifts in a rhythmic pattern with the movement of the endolymph fluid surrounding the organ of corti

Question 15

In the tonotopic map of the basilar membrane where are the highest frequencies found?

Answer 15

the basal end of near the oval window

Question 16

In the tonotopic map of the basilar membrane where are the lowest frequencies found?

Answer 16

apical end near the round window

Question 17

What is an inner hair cell or IHC?

Answer 17

-directly responsible for auditory transduction; their afferent projections cochlear nerve which is one of the two branches of CN VIII the vestibulocochlear nerve
-they are in a single row and they extend their tips below the tectorial membrane which means when the tectorial membrane moves the IHCs move

Question 18

What are outer hair cells?

Answer 18

-responsible for modulating auditory transduction by adjusting the tension of the tectorial membrane by adjusting the tension of the tectorial membrane; receive incoming projections from the brainstem nuclei; have their tips embedded in the tectorial membrane so they can modulate tension; arranges in rows of three in a v formation; responsible for otoacoustic sounds

Question 19

What takes place in the organ of corti in the cochlea when auditory transduction is occurring?

Answer 19

1. mechanical transduction of the sound wave (tapping by stapes on oval window causes the endolymph fluid to move)
2. causes a tectorial shift in membrane causing bending of stereocilia of the inner hair cells
3. according to the tip-link hypothesis this generates tension which causes the tension-gated potassium channels of the hair cells to open causing potassium to rich the hair cells causing depolarization
4. electrical signal conveyed to cochlear nerve