Inner Ear

Question 1

anatomy of inner ear

Answer 1

vestibule and cochlea

Question 2

vestibule

Answer 2

receptors for balance

Question 3

modiolus

Answer 3

hollow core of cochlea
contains the auditory nerve and cell bodies of auditory neurons which forms spiral ganglion surrounded by osseous spiral lamina

Question 4

osseous spiral lamina

Answer 4

a bony shelf

winds around the modiolus

Question 5

3 scalae chambers

Answer 5

scala vestibuli
scala media
scala tympani

Question 6

2 membranes to separate scalae

Answer 6

Reissner’s membrane

Basilar membrane

Question 7

Reissner’s membrane

Answer 7

separates scala media from scala vestibuli

Question 8

helicotrema

Answer 8

scala vestibuli and tympani connect

joint opening at the apex of the cochlea

Question 9

endolymph

Answer 9

fluid in scala media

high K+, low Na+

Question 10

perilymph

Answer 10

fluid in scala vestibuli and tympani

high Na+, low K+

Question 11

organ of corti

Answer 11

sits on basilar membrane

composed of auditory receptors (hair cells), their supporting cells, and their nerve supply ends

Question 12

inner hair cells (IHCs)

Answer 12

innervated by Type I fibers
90-95% of Type I fibers connect to IHCs
have one row in organ of corti
afferent innervation: many-to-one
flask shape

Question 13

outer hair cells (OHCs)

Answer 13

3-5 rows in organ of corti
innervated by Type II fibers
5-10% of Type II fibers connect to OHCs
cylindrical shape
afferent innervation: one-to-many
basal nucleus

Question 14

tectorial membrane

Answer 14

an acellular, gelatinous membrane
fixed only on its inner edge–attached to spiral limbus
contact with the tips of the longest stereocilia of the OHCs, no contact with IHCs
moves in wind-shield-wiper motion

Question 15

traveling wave of the basilar membrane

Answer 15

displacement of BM is caused by perilymph
wave travels from base to apex
wave grows gradually in amplitude, meets a maximum point then dies out quickly
frequency selective
base = high frequency
apex = low frequency

Question 16

frequency selectivity

Answer 16

BM responds selectively to frequencies

Question 17

tuning curve

Answer 17

sharply tuned

agggh IDK

Question 18

characteristic frequency (CF)

Answer 18

best frequency
the frequency of a sound at which the BM response is highest (amp is highest)
non-linear

Question 19

intensity resolution

Answer 19

nonlinearity at CF

linearity at non-CF

Question 20

2 types of cochlear mechanincs

Answer 20

passive and active

Question 21

passive cochlear mechanics

Answer 21

represented as broadly-tuned component of the traveling curve
determined by physical properties of BM

Question 22

active cochlear mechanics

Answer 22

produce sharp tuning at CF
amplify the traveling wave as it passes through the cochlea
result from an active source of mechanical energy in the cochlea
OHCs are responsible for active mechanics –> OHC loss results in the loss of sharply-tuned components of the traveling wave and nonlinearity

Question 23

response process of hair cells in cochlea

Answer 23

deflection of stereocilia –> opening of K+ ion channels –> depolarization of hair cells –> release of neurotransmitters

Question 24

how does deflection of the stereocilia occur?

Answer 24

OHCs: shearing (breaking) force between stereocilia and tectoral membrane
IHCs: movements of fluids in the subtectorial space causes bending of the stereocilia

Question 25

how are the K+ ion channels opened?

Answer 25

K+ ion channels open at the tip of the stereocilia only when the stereocilia deflects away from the modiolus

Question 26

how are the hair cells depolarized?

Answer 26

K+ ions flow into hair cells –> hair cells depolarize

Question 27

what happens when the neurotransmitter is released?

Answer 27

Glutamate is sent to the synaptic cleft –> activates the auditory nerve fibers

Question 28

properties of responses of hair cells

Answer 28

frequency selectivity

intensity resolution