Auditory Nervous System

Question 1

Where does the auditory nervous system begin?

Answer 1

At the hair cells of the cochlea

Question 2

What is sound?

Answer 2

Energy imparted in waves through a medium

Question 3

What are the 9 steps of sound transduction in the conductive auditory system?

Answer 3

1.) Sound travels through external ear and strikes TM
2.) Ossicles attached to TM move back and forth
3.) Stapes footplate moves in and out of the oval window
4.) Movement of stapes compresses the fluid inside the cochlea
5.) The fluid vibration causes the basilar membrane to move
6.) BM displacement deflects stereocilia on the HCs
7.) Movement of stereocilia opens ion channels
8.) Potassium ions flow from the positively-charged endolymph into the negatively-charged hair cells
9.) Inner hair cells depolarize and release glutamate

Question 4

Where is perilymph found?

Answer 4

Scala vestibuli and scala tympani

Question 5

What is the charge of perilymph?

Answer 5

0mV

Question 6

Where is endolymph found?

Answer 6

Scala media

Question 7

What is the charge of endolymph?

Answer 7

+80mV

Question 8

What is another name for the charge of endolymph?

Answer 8

Endocochlear potential

Question 9

Where is cortilymph found?

Answer 9

Under the reticular lamina/tectorial membrane

Question 10

Which ion depolarizes hair cells?

Answer 10

Potassium (K)

Question 11

What gradient is potassium flowing down?

Answer 11

Flowing down its electrical gradient

Question 12

What is the charge inside of the hair cells?

Answer 12

-45-70mV

Question 13

Why is the electrical gradient for K so powerful?

Answer 13

The endolymph is also very highly positive

Question 14

Which structure recycles potassium?

Answer 14

Stria vascularis

Question 15

What happens is stria vascularis cells die off?

Answer 15

It decreases the charge of the endolymph

Question 16

Why are people who have decreased endolymph/endocochlear potential better hearing aid candidates?

Answer 16

They just need a higher intensity sound to tip the stereocilia

Question 17

What hearing condition is common with stria vascularis dying off?

Answer 17

Presbycusis

Question 18

What NT creates an EPSP to fire a charge?

Answer 18

Glutamate

Question 19

Without IHC…..

Answer 19

You can’t hear complex sounds

Question 20

Without outer hair cells…

Answer 20

Your thresholds are a lot higher

Question 21

What is the internal auditory meatus?

Answer 21

Hole through petrous temporal bone

Question 22

What is the cerebello-pontine angle?

Answer 22

Location between IAM and cochlear nucleus

Question 23

What is contained in the IAM and CPA?

Answer 23

7th and 8th cranial nerves

Question 24

What are the 3 fundamental pieces of information about a sound?

Answer 24

1.) Frequency
2.) Intensity
3.) Phase

Question 25

What is a characteristic frequency?

Answer 25

The ideal frequency for eliciting response from a neuron; Requires the lowest stimulus level to elicit a response

Question 26

Neurons will respond to stimuli other than CC, but...

Answer 26

The stimulus must be a higher level

Question 27

What is a tuning curve?

Answer 27

The envelope of the thresholds required for provoking response across all the frequencies

Question 28

Where are the low frequencies at on the auditory nerve?

Answer 28

Central core of the auditory nerve

Question 29

Where are the high frequencies at on the auditory nerve?

Answer 29

Extend to outer layers

Question 30

How is the auditory nerve organized?

Answer 30

Tonotopically

Question 31

What does the similarity between the tuning curves of the auditory nerve and the BM tell us?

Answer 31

The auditory nerve faithfully represents the auditory processing of the cochlea and transmits that info to the brain

Question 32

What is a rate-level function?

Answer 32

Increases in stimulus levels lead to increased neural discharge rate, but discharge rates eventually plateau

Question 33

What does the plateau in the discharge rate tell us?

Answer 33

It is the point at which an increased stimulus level does not lead to increase in discharge rate

Question 34

What is phase locking?

Answer 34

Action potential firing locks to the period of the stimulus

Question 35

What are the two pathways of the central auditory system?

Answer 35

1.) Primary pathway is an ascending (afferent) parallel system 2.) Descending (efferent) systems

Question 36

What does the auditory nerve synapse with?

Answer 36

Cochlear nucleus

Question 37

Where is the tonotopic organization of the cochlea and auditory nerve preserved?

Answer 37

The cochlear nucleus

Question 38

What does the cochlear nucleus synapse to?

Answer 38

Superior Olivary Complex

Question 39

What is the importance of the SOC?

Answer 39

First site in CANS to receive binaural input

Question 40

Where do auditory nerves connect to?

Answer 40

The cochlear nucleus on the ipsilateral side as the cochlea

Question 41

Where do both CN connect to?

Answer 41

Both the ipsilateral and contralateral SOC

Question 42

At what point in the CANS is info from both ears?

Answer 42

The SOC and above

Question 43

What 2 mechanisms combine to provide info about localizing sound in azimuth?

Answer 43

1.) Interaural time difference 2.) Interaural level difference

Question 44

Interaural time difference is effective for...

Answer 44

Low frequency sounds

Question 45

Interaural level difference is effective for...

Answer 45

High frequency sounds

Question 46

What do olivocochlear efferent tracts connect to?

Answer 46

Connect from the SOCs to the cochleae

Question 47

What are efferent tracts?

Answer 47

Descend from auditory cortex to lower CANS structures

Question 48

What are the 2 pathways of the olivocochlear efferent system?

Answer 48

Medial and Lateral

Question 49

What does the medial tract of the olivocochlear efferent system do?

Answer 49

Inhibits electromobility of the outer hair cells

Question 50

What does the lateral tract of the olivocochlear efferent system do?

Answer 50

Induces IPSPs in the afferent dendrites of the spiral ganglion neurons

Question 51

What does the SOC connect to?

Answer 51

Inferior colliculus through the lateral lemniscus

Question 52

What are the 2 potential functions of the IC?

Answer 52

1.) Refines frequency processing of the CN 2.) Refines the binaural processing of the SOC

Question 53

Use of these 2 things may aid in sound localization in 3 dimensions

Answer 53

Frequency analysis and binaural processing

Question 54

What does the IC connect to?

Answer 54

Medial geniculate body of the thalamus

Question 55

What does the MGB connect to?

Answer 55

Auditory cortex

Question 56

Where is the auditory cortex?

Answer 56

Deep in the temporal lobe

Question 57

Which of Brodmann's areas make up the auditory cortex?

Answer 57

41 and 42

Question 58

Populations of cells in the auditory cortex respond to...(3)

Answer 58

1.) Amplitude 2.) Frequency 3.) Phase

Question 59

The auditory cortex has little reaction to...

Answer 59

Simple tonal stimuli

Question 60

The cells in the auditory cortex work together to...

Answer 60

Process the complexities of high-level auditory stimuli like speech

Question 61

What is subjective tinnitus?

Answer 61

Perception of hearing but without the evoked sound signal

Question 62

What is objective tinnitus?

Answer 62

Perception of internal sounds produced by the body

Question 63

What is subjective tinnitus often a consequence of?

Answer 63

Peripheral auditory system injury

Question 64

How is the limbic system related to tinnitus?

Answer 64

1.) Amygdala is implicated in strong emotional responses to tinnitus 2.) Habituation of tinnitus may reduce activity in the parahippocampal gyrus region