lecture 12 - adrian rees

Question 1

position of maximal displacement depends on the frequency of the sound
low frequency = maximal displacement at the…

Answer 1

apex

Question 2

high frequency = maximal displacement at the…

Answer 2

base

Question 3

displacement of basilar membrane excites…

Answer 3

hair cells

Question 4

laser interferometry

Answer 4

shine a laser beam at the BM and some of the laser light is reflected
if the BM is moving, then we get doppler shift in the frequency of the laser beam
its possible to measure the reflective light from the basilar membrane and compare it with the incident light and allows you to make measurements of the BM displacement

Question 5

tuning of the BM is very similar to the tuning of the…

Answer 5

auditory nerve fibres

Question 6

the BM responds to much quieter sounds when the animal is…

Answer 6

alive
(some kind of amplification process in the motion of the BM hat explains the difference between the post mortem response and the response in the living animal)

Question 7

the BM vibrates up and down in response to sound. this causes the tectorial membrane to move over the top of the

Answer 7

hair cells
this causes the stereocilia on the surface of the hair cells to be moved back and forth

Question 8

hair cells depolarise when stereocilia bend towards the…

Answer 8

tallest stereocilia (hyperpolarise when bent towards the shortest)

Question 9

the excitation phase is when the basilar membrane moves upwards and the stapes is moving outwards. this is during the _________ phase of the sound

Answer 9

rarefaction

Question 10

how many rows or inner and outer hair cells are there

Answer 10

3 OHC
1 IHC

Question 11

what seals off the stereocilia from the rest of the hair cells

Answer 11

the reticular lamina
keeps the stereocilia bathed in endolymph and the rest of the hair cells in perilymph

Question 12

what connect the top of one stereocilia to another

Answer 12

tip links

Question 13

when the stereocilia bend towards the tallest then the tip links stretch and causes opening of mechano-electrical transducer (MET) channels which are at the top of the stereocilia and they allows ions to enter the stereocilia and therefore the hair cells. when the stereocilia bend in the opposite direction then the tip links slacken and the MET channels close.
what ion moves through the MET channels

Answer 13

potassium

Question 14

potassium ions go into the hair cell because of the voltage gradient

Answer 14

the voltage in the endolymph is +90mV
voltage inside the hair cells is -40mV

Question 15

IHC:
when potassium enters it causes the cell to depolarise (less negative) and that triggers the opening of….

Answer 15

calcium channels

Question 16

calcium channels allow calcium to enter the cell and it triggers the vesicles filled with NT in the IHCs to dock with the membrane and release the NT onto the neurones of the auditory nerve fibres that are contacting the IHC

Question 17

when you first push the stereocilia the current is large
but over time the current…

Answer 17

reduces

Question 18

rapid adaptation

Answer 18

direct effect on the MET channel. Ca entry into stereocilia resets sensitivity of the MET channel

Question 19

slow adaptation

Answer 19

link sliding down the stereocilia closes the channel
OR
Ca inside the stereocilium makes the MET channel more difficult to open

Question 20

if you depolarise and hyperpolarise outer hair cells they change their…

Answer 20

length

Question 21

depolarisation causes the OHC to

Answer 21

shorten

Question 22

hyperpolarisation causes the OHC to

Answer 22

lengthen

Question 23

this is due to what protein

Answer 23

prestin

Question 24

to test whether it was prestin causing the motility they expressed prestin gene into kidney tubule cells

Answer 24

tubule cells (not normally motile) now show motility

Question 25

OHC motility is dependent of intracellular…

Answer 25

Chloride ions

Question 26

prestin molecules are in the membrane of the OHC.
prestin molecules can bind to a chloride ion.
if the chloride ion sits on the cytoplasmic side of the prestin molecules then the size of the molecule…

Answer 26

shortens

Question 27

if the chloride ion sits on the extracellular side of the prestin molecule the size of the molecule…

Answer 27

increases

Question 28

if we depolarise the cell that will pull chloride ions towards the inside of the cells (as the inside of the cell is relatively posititve)
if we hyperpolarise the cell and make the inside of the cell negative the chloride ion will move away from the inside of the cell towards the extracellular side.
so this causes a changes in the length of the prestin molecules therefore causing change in length of the OHC

Question 29

the displacement of the BM is amplified by the…

Answer 29

motion of the OHC