Lecture 11 - structure and function of the auditory system

Question 1

What are sound waves?

Answer 1

vibrations in the air that cause particles in the air to compress together.

Question 2

What are frequency units (Hz)?

Answer 2

cycles (or repetitions) per second.

Question 3

What is sound intensity measured in?

Answer 3

decibels - a logarithmic scale (if a sound is 10dB there is 10x the power, if the sound is 100dB there is 100x the power.

Question 4

What does the fundamental frequency correspond to?

Answer 4

the repetition rate of the sound

Question 5

Describe what makes up the outer ear and what the function is.

Answer 5

pinna and ear canal
collects and focuses sound waves

Question 6

Describe what makes up the middle ear and what the function is.

Answer 6

tympanic membrane and ossicles
transmission of vibrations to cochlea

Question 7

Describe what makes up the inner ear and what the function is.

Answer 7

cochlea
amplification of vibrations (outer hair cells)
transduction of mechanical vibrations to electrical nerve signals (inner hair cells)

Question 8

What are the 3 ossicles?

Answer 8

malleus (hammer)
incus (anvil)
stapes (stirrup)

Question 9

How many rows of outer hair cells are there?

Answer 9

3

Question 10

What do outer hair cells do?

Answer 10

actively move
amplifies membrane vibrations and enhances the sensitivity of inner hair cells

Question 11

What do inner hair cells do?

Answer 11

get sound into the brain
displaced passively by vibrations
turn mechanical displacements of hairs into electrical signals

Question 12

Where on the basilar membrane are low frequency sounds located?

Answer 12

apex

Question 13

Where on the basilar membrane are high frequency sounds located?

Answer 13

base

Question 14

What are otoacoustic emissions?

Answer 14

activity of outer hair cells causing physical vibrations
vibrations propagate back to the tympanic membrane and into the air
can be spontaneous or sound-evoked
useful in clinical tests for cochlear health

Question 15

What 2 types of coding does the auditory pathway have?

Answer 15

1. spectral (frequency) coding
2. temporal (timing) coding

Question 16

Describe the 5 steps of the auditory pathway?

Answer 16

1. cochlear nuclei (dCN, vCN)
2. superior olivary complex (SOC)
3. Inferior colliculus (IC).
4. medial geniculate body (MGB)
5. auditory complex

Question 17

What does the superior olivary complex do?

Answer 17

helps localise where sounds are by comparing the time delay between the sound input from the left and right ear

Question 18

How is the auditory pathway organised and what does this mean?

Answer 18

tonotopically organised
organised by frequency

Question 19

What is intensity coding?

Answer 19

the dynamic range for human hearing
similar to frequency and temporal coding

Question 20

What is the loudness discomfort threshold?

Answer 20

110dB

Question 21

What is the pain threshold?

Answer 21

130dB

Question 22

What are the 2 types of auditory nerve fibres?

Answer 22

1. low spontaneous rate fibres
2. high spontaneous rate fibres

Question 23

Describe low spontaneous rate fibres.

Answer 23

• high threshold for activation
• used to being occasionally active
• needed for signal in noise processing

Question 24

Describe high spontaneous rate fibres.

Answer 24

• low threshold for activation
• used to being active for long periods of time
• necessary for hearing quiet sounds inn quiet environments
• basis of pure tone audiogram

Question 25

What is the function of the descending auditory pathway?

Answer 25

inhibition filtering of relevant stimuli selective attention auditory predictions adaptation

Question 26

Determining the localisation of sounds - what is the left to right axis?

Answer 26

- intramural time delay - processed mainly by superior olivary complex - lower contribution of intramural level difference - accurate

Question 27

Determining the localisation of sounds - what is the front/back and top/bottom?

Answer 27

- less accurate - more prone to error - head/pinna related transfer

Question 28

How does the auditory complex exist?

Answer 28

bilaterally in temporal lobes

Question 29

What are the 2 parts of the auditory complex?

Answer 29

1. primary auditory complex 2. non-primary auditory complex

Question 30

Describe the primary auditory complex.

Answer 30

- Herschl's gyrus - tucked away in the Sylvian fissure - basic and early auditory responses

Question 31

Describe the non-primary auditory complex.

Answer 31

- various fields, still debated - exists in superior temporal gyrus and plan temporale - more complex sound features

Question 32

What is the left hemisphere more optimised to process?

Answer 32

temporal processing relevant to speech

Question 33

What is the right hemisphere more optimised to process?

Answer 33

pitch processing relevant to music

Question 34

What are the 2 types of electrical brain responses to hearing?

Answer 34

1. subcortical brain responses (ABR) 2. cortex brain responses (EEG)