auditory & vestibular physiology

Question 1

what fluid bathes the apical end of hair cells

Answer 1

endolymph

Question 2

what is the ionic makeup of endolymph

Answer 2

high K

low Na

Question 3

what is the ionic makeup of perilymph

Answer 3

low K

high Na

Question 4

what fluid bathes the basal end of hair cells

Answer 4

perilymph

Question 5

where is endolymph found within the cochlea

Answer 5

scala media

Question 6

where is perilymph found within the cochlea

Answer 6

scala vestibuli

scala tympani

Question 7

axons of the spiral ganglion project to the brainstem via what nerve

Answer 7

auditory nerve (aka cochlear branch of CN VIII)

Question 8

where do higher frequency sounds maximally displace the basilar membrane

Answer 8

at the base

Question 9

near the helicotrema, do higher or lower frequency sounds maximally displace the basilar membrane

Answer 9

low frequency

Question 10

near the oval window, do higher or lower frequency sounds maximally displace the basilar membrane

Answer 10

higher frequency

Question 11

where is the basilar membrane narrow and stiff

Answer 11

at the base, near the oval window

Question 12

where is the basilar membrane wide and flexible

Answer 12

at the apical end, near the helicotrema

Question 13

what kind of cells are hair cells

Answer 13

mechanoreceptors (specialized epithelial cells)

Question 14

what fluid are the cilia of the hair cells bathed in

Answer 14

endolymph

Question 15

what drives potassium into the hair cell

Answer 15

potassium concentration gradient (low K at the basal side of the hair cell)
electrical gradient (high positive charge within scala media)

Question 16

what does the potassium influx of the hair cell cause

Answer 16

depolarization of the cell => opening of voltage gated Ca channels

Question 17

what does the calcium influx of the hair cell cause

Answer 17

realease of glutamate to afferent n. => spiral ganglion

Question 18

what occurs following deflection of hair cell cilia TOWARDS the kinocilium

Answer 18

depolarization

Question 19

what occurs following deflection of cilia AWAY FROM the kinocilium

Answer 19

hyperpolarization

Question 20

through what channels does K enter the hair cells

Answer 20

TRPA1

Question 21

what causes TRPA1 channels to open

Answer 21

when cilia deflects toward kinocilium, chain of proteins open TRPA1

Question 22

what structure maintains electrochemical properties of endolymph

Answer 22

stria vascularis

Question 23

what do inner hair cells do and how are they arranged

Answer 23

primary source of auditory information

arranged in one row along cochlear spiral

Question 24

what do outer hair cells do and how are they arranged

Answer 24

act as an amplifier - boost or dampen mechanical vibrations of basilar membrane
arranged in three rows along cochlear spiral

Question 25

from where do hair cells receive efferent innervation

Answer 25

superior olivary complex

Question 26

from where do hair cells produce afferent innervation

Answer 26

spiral ganglion

Question 27

what are type II afferent neurons

Answer 27

single afferent from many outer hair cells => brainstem

Question 28

what are type I afferent neurons

Answer 28

neurons from one or more inner hair cells => brainstem

Question 29

what happens after sound hits the stapes?

Answer 29

pressure within scala vestibuli falls below that of scala tympani

Question 30

what happens as a result of decreased pressure in the scala vestibuli

Answer 30

basilar membrane bows upward => organ of corti shears toward hinge or tectorial membrane

Question 31

what protein facilitates contractile activity of outer hair cells

Answer 31

prestin

Question 32

what occurs as a result of shearing of the organ of corti

Answer 32

cilia of over hair cells tilt toward kinocilium => K+ channels open and cell depolarizes

Question 33

what occurs as a result of depolarization of outer hair cells

Answer 33

contraction of prestin protein => accentuated upward movement of basilar membrane, making waves in endolymph

Question 34

what occurs as a result of waves in the endolymph hitting the tectorial membrane

Answer 34

inner hair cells bend toward kinocilium, TRPA1 channels open => => glutamate released

Question 35

what is the first site within the brainstem where information from both ears converges

Answer 35

superior olivary complex

Question 36

what nucleus generates a map of interaural time differences and why

Answer 36

medial superior olivary nucleus (MSO) | helps w/ localization

Question 37

what nucleus generates a map of interaural intensity differences and why

Answer 37

lateral superior olivary nucleus (LSO) | helps w/ localization

Question 38

how does the inferior colliculus perform horizontal localization

Answer 38

by suppressing information relating to echoes

Question 39

what occurs at the superior colliculus within the auditory pathway

Answer 39

vertical height is added to the information received from inferior colliculus, creating a spatial map of sound location

Question 40

which part of the primary auditory cortex is activated by low frequency sounds

Answer 40

more rostral (anterior) areas

Question 41

which part of the primary auditory cortex is activated by signals from the base of the cochlea

Answer 41

more caudal (posterior) areas

Question 42

what are the three sources of efferent input to the auditory system

Answer 42

- olivocochlear efferents - middle ear muscle motor neurons - autonomic innervation of inner ear

Question 43

between what structures do medial olivocochlear efferent travel

Answer 43

superior olivary complex => OUTER hair cells

Question 44

between what structures do lateral olivocochlear efferent travel

Answer 44

superior olivary complex => inner hair cells

Question 45

what is the function of olivocochlear efferents

Answer 45

shifts responses to higher sound levels and reduces response to noise

Question 46

what is the function of middle ear efferents

Answer 46

prevent damage by decreasing transmission of loud sounds

Question 47

what are the two middle ear efferents and from what CNs do they arise

Answer 47

tensor tympani from CN V | stapedius from CN VII

Question 48

in what situations are otoacoustic emissions seen

Answer 48

evoked OAE are normal in people without hearing loss

Question 49

what is measurement of OAE used for

Answer 49

- newborn hearing screen - evaluation of tinnitis - evaluation of possible ototoxicity

Question 50

are outer or inner hair cells more susceptible to damage

Answer 50

outer hair cells

Question 51

what is the result of injury to inner hair cells

Answer 51

cuts off auditory input to CNS

Question 52

how do cochlear prostheses work

Answer 52

electrodes in cochlead stimulate nerve fibers

Question 53

what sensation do the semicircular canals detect

Answer 53

rotation

Question 54

what sensation does the utricle detect

Answer 54

linear acceleration forward and backward

Question 55

what sensation does the saccule detect

Answer 55

linear acceleration up and down

Question 56

which semicircular canal best detects rotation in the vertical plane BACKWARDS

Answer 56

posterior semicircular canal

Question 57

which semicircular canal best detects FORWARD rotation in the vertical plane

Answer 57

anterior semicircular canal

Question 58

what muscles are active/inhibited when you fall forward

Answer 58

active: superior rectus inhibitied: inferior rectus eyes move UP

Question 59

what muscles are active/inhibited when you fall backward

Answer 59

active: superior oblique inhibited: inferior obligue eyes move DOWN

Question 60

what muscles are active/inhibited in the eye ipsilateral to rotation when spinning

Answer 60

active: medial rectus inhibited: lateral rectus contralateral eye does the opposite

Question 61

what fluid surrounds the vestibular apparatus

Answer 61

perilymph