Sensory Transduction: Auditory and Vestibular System

Question 1

what ion causes depolarisation to occur in the hair cells of the ear?

Answer 1

K+ influx from endolymph

Question 2

explain how the hair cells cause sensory afferent signals to be produced?

Answer 2

cilia move towards kinocilum 
K+ channels open due to tip link 
hair cell depolarises 
Ca2+ channels open 
vesicles of glutamate released to synapse with sensory afferent neurone

Question 3

more APs are generated when cilia move towards kinocilum - true or false?

Answer 3

true

Question 4

what are the ganglia of scarpa and where are they located?

Answer 4

located in vestibular nerve just after CNVIII splits

contain cell bodies of sensory neurones

Question 5

explain how sound is produced and how we hear it?

Answer 5

object (eg vocal cord) vibrate
air pressure changes
air vibrates in 3 dimensions towards ear
causes eardrum, incus, malleus and stapes to vibrate
stapes footplate vibration causes fluid in cochlea to move over hair cells (transduction)

Question 6

what properties of the middle ear make it useful at amplifying sound?

Answer 6

area ratio of tympanic membrane to stapes footplate is 20:1 (decreasing area over which the noise is exerted increases the pressure of noise)

lever action of the ossicles (malleus higher than incus) - increases pressure of noise

buckling of ear drum - middle is attached to malleus therefore moves less and preserves force

Question 7

what membrane separated the scala vestibuli and media?

Answer 7

reissner’s membrane

Question 8

what membrane separated scala media and tympani?

Answer 8

basilar membrane

Question 9

which of the scala vestibuli, media and tympani regress at the apex of the cochlea?

Answer 9

media no longer exists - fluid in scala vestibuli and tympani mix

Question 10

what is meant by the tonotopy of the basilar membrane?

Answer 10

particular spatial arrangement of frequencies detected

Question 11

the basilar membrane vibrates within the fluid of the cochlea - true or false?

Answer 11

true - it is flexile and therefore can move with fluid

it is the widest and floppiest at the apex

Question 12

do we have more inner or outer hair cells?

Answer 12

outer (15000-20000 compared to 3500 inner)

Question 13

what is the role of the tectorial membrane?

Answer 13

vibrates and brushes against hair cells, making them move and release neurotransmitter

Question 14

what ganglion is located near the organ of corti, containing sensory neuron cells?

Answer 14

spiral ganglion

Question 15

why must potassium be redistributed into the endolymph?

Answer 15

causes problems such as deafness otherwise

mutations in any genes coding for K channels or transporters have the potential to cause deafness

Question 16

how do the outer hair cells amplify found?

Answer 16

have motor proteins on their sides which get compressed and change the length of overall hair cell
this moves the basilar membrane more, and the inner cell moves with this membrane
inner hair cell then fires more sensory afferent transduction signals

Question 17

describe the pathway from the cochlea to the primary auditory cortex?

Answer 17

cochlea -> cochlear nuclei -> superior olivary nuclei -> nucleus of lateral leminiscus -> inferior colliculus -> medial geniculate nucleus -> primary auditory cortex

Question 18

which nuclei in the brainstem is important for the localisation of sound in space and how does it do this?

Answer 18

superior olivary nucleus - senses time at which sound reaches ear (intra-aural time difference)

Question 19

what is the calyx of held?

Answer 19

large nerve terminal ending with lots of vesicle active zones ready to discharge upon signal
they usually react to high frequency sounds

Question 20

what 2 questions does the vestibular system function to answer?

Answer 20

where am i going?

which way is up?

Question 21

what do the semicircular canals sense?

Answer 21

head angular acceleration (rotation)

Question 22

what do the utricle and saccule detect?

Answer 22

head linear acceleration
saccule = vertical movement
utricle = horizontal movement

Question 23

which of the semicircular canals share a plane?

Answer 23

left anterior and right posterior (and vice versa)

both horizontal are also in same plane

Question 24

what is the otocania?

Answer 24

CaCO3 bio-crystals which help mechanical forces to reach the sensory hair cells in the utricle and saccule

Question 25

what are the 3 vestibular reflexes and what do they do?

Answer 25

vestibulo-ocular = moves eyes in opposite direction of head moving so vision remains still

vestibulo-colic = keeps head on level playing field when you walk

vestibulo-spinal = adjusts posture when rapidly changing position