hearing

Question 1

place principle

Answer 1

cochlea is a filter and is tonotopically organised so that frequency is detected by spatial representation from base to apex

(frequency coding)

Question 2

volley principle

Answer 2

low frequencies are detected by temporal firing of nerve fibres in time to the frequency of the stimulus
- at high Hz it cannot match the timing (due to refractory periods)

(frequency coding)

Question 3

describe outer hair cells

Answer 3

• are electromotile
• contract in sync with traveling wave to amplify the energy inside the cochlear
• contain the motor protein prestin in the cell membrane
• 3-5 rows
• mostly surrounded by fluid
• efferent activity dominates, modulating cells that alter input into CNS

Question 4

role of the stria vascularis

Answer 4

pumps K+ into the endolymph - generating an electrical potential

Question 5

depolarisation and repolarisation of the hair cells is mediated by what?

Answer 5

K+ from the endolymph

- driven by endocochlear potential

Question 6

what maintains sensitivity of the stereocilia channels

Answer 6

myosin molecules at the end of the connection changes the tension on the actin linkage, allowing it to always be on the verge of opening

Question 7

role of hair cell stereocilia and how this is achieved

Answer 7

transduction
- converts mechanical stimuli into an electrical response within the cell

vertical motion at the organ of corti is converted into radial motion at the stereocilia

Question 8

describe the spatial organisation of frequency

Answer 8

for every frequency there is a place along the organ of corti where there is maximal response

-theres a point along the membrane that has a specific stiffness and mass that allows it to resonate for a specific Hz

Question 9

role of the round window

Answer 9

to ensure the energy makes it across into the dense fluid via the oval window

is flexible and when the oval window moves in the round window moves out allowing a transfer of energy

Question 10

what is essential for sensory cells to operate

Answer 10

the maintenance of a voltage and ion concentrations

Question 11

inner hair cells

Answer 11

• surrounded by supporting cells
• innervated by 90% of afferent nerves
• main input to CNS
• single cell layer

Question 12

ways in which the middle ear amplifies sound to the inner ear

Answer 12

1. area difference between eardrum and stapes
   - tympanic membrane is a large structure that transmits pressure to the small stepes
2. lever ratio malleus:incus
   - malleus longer than incus causing more force on tympanic membrane
3. lever ratio tympanic membrane
   - conical shape acts as a lever causing changes is size of displacement and an increase in force

Question 13

intensity coding

Answer 13

• either by the number of fibres activated or by the rate at which they are activated (rate of firing)
• as intensity increases, the number of fibres and rate activated increases

Question 14

role of the cochlear nucleus

Answer 14

• relay station for all nerves going to the cochlea

- recieves info of the the Hz and intensity of stimulus and time at which sound appears

Question 15

dorsal cochlear nucleus

Answer 15

• dominate part of CN
• projects directly to midbrain
• more complex processing possible important for speech detection