Physiology of Auditory and Vestibular System

Question 1

What are characteristics of the basilar membrane near the oval and round windows?

Answer 1

narrow and stiff

HIGH frequency sounds (20,000 Hz)

Question 2

What are characteristics of the basilar membrane near the helicotrema?

Answer 2

wider and flexible

LOW frequency sounds (20 Hz)

Question 3

Auditory system

Answer 3

detects sound and uses acoustic cues to identify and locate sound sources in the environement

Question 4

Sound

Answer 4

oscillations of air pressure that vary rapidly with time

Question 5

Amplitude

Answer 5

sound pressure (intensity) specified by a scale of sound pressure level (SPL) in decibels

Question 6

Frequency

Answer 6

number of oscillations of air pressure per second (Hz)

Question 7

Tonotopy of inner ear

Answer 7

high frequency sounds produce maximal displacement at base (closest to stapes)

low frequency sounds produce maximal displacement at apex (furthest from stapes)

Question 8

What does the vibration of the basilar membrane create?

Answer 8

pressure differential

Question 9

What does the pressure differential in the inner ear cause?

Answer 9

shearing force against stationary tectorial membrane, causing the stereocilia of the outer hair cells to be displaced in that plane

Question 10

How are the inner hair cells activated?

Answer 10

fluid movement in cochlear duct (not in direct contact with tectorial membrane)

Question 11

How does depolarization of the hair cell occur?

Answer 11

opening of cation channels at the apex of sterocilia

Question 12

How are TRPA1 channels open and what do these channels do?

Answer 12

stereocilia are connected to each other via tip links that transmit force to an elastic gating spring that open the TRPA1 channel

mechanotransduction channel: rapid response, do not require receptor potentials, increase sensitivity of the response

Question 13

Endolymph

Answer 13

K+ rich filling the cochlear duct and membranous labyrinth 
Bathes apical end of hair cells
Similar to ICF (high K+; low Na+)
Found in scala media
Produced by stria vascularis

Question 14

Perilymph

Answer 14

K+ poor fluid
Bathes basal end of cochlear hair cells
Similar to ECF (high Na+; low K+)
Found in scala vestibuli and scala tympani

Question 15

Steps in depolarization of a hair cell

Answer 15

1) TRPA1 ion channels open when tip links join
2) entry of K+ depolarizes hair cell
3) opens voltage-gated calcium channels at base
4) NT filled vesicles fuse with basilar membrane
5) NT released (glutamate) into the synaptic cleft
6) afferent cochlear nerve fibers stimulated and transmit signal to brain

Question 16

Where are the tips of the stereocilia on the hair cells embedded?

Answer 16

tectorial membrane

Question 17

Where are the bodies of the hair cells located?

Answer 17

basilar membrane

Question 18

What does an upward displacement of the basilar membrane cause?

Answer 18

shearing force that results in lateral displacement of stereocilia

Question 19

What does mechanical displacement of the stereocilia in a lateral direction cause?

Answer 19

depolarization of the hair cell

Question 20

What does the downward displacement of the basilar membrane create?

Answer 20

shearing force that results in HYPERPOLARIZATION

Question 21

Which cells are responsible for hearing?

Answer 21

inner hair cells

about 90% of cochlear fibers come from inner hair cells

Question 22

Which cells are responsible for amplification of signals?

Answer 22

outer hair cells

Question 23

Scala Vestibuli

Answer 23

filled with perilymph

connects at large end to oval window

Question 24

Scala Media

Answer 24

filled with endolymph

in between scala vestibuli and scala tympani

Question 25

Scala Tympani

Answer 25

filled with perilymph | connects at large end to round window

Question 26

Stria Vascularis

Answer 26

located in lateral wall of cochlear duct (scala media) produces endolymph with high levels of K+ that fills entire membranous labyrinth functions to maintain electrochemical properties of endolymph

Question 27

Function of endocochlear potential

Answer 27

high potential serves to drive + ions into the hair cell down their concentration gradient maintained by stria vascularis forms blood labyrinth barrier (BLB) = one of the main sites of drug entry to access the inner hair cell

Question 28

What are the effects of ototoxic drugs and carbon monoxide on the ear?

Answer 28

disrupt function of stria vascularis and diminish the endocochlear potential and impact hearing

Question 29

Properties of inner hair cells

Answer 29

- primary source of auditory info - single layer - synapse with peripheral terminal of primary afferent sensory neuron - efferent neuron modulates

Question 30

Properties of outer hair cells

Answer 30

- primary cells that amplify sounds waves that result in the movement of the basilar membrane - contractile cells - 3 rows - synapse with afferent peripheral terminals from the spiral ganglion as well as with terminal from efferent neurons

Question 31

Otoacoustic emissions

Answer 31

- low-level sound emitted by the cochlea either spontaneously or evoked by an auditory stimulus - originate in the superior olivary complex - known as olivocochlear efferents - medial cochlear complex neurons innervate outer hair cells - lateral olivary complex neurons innervate inner hair cells

Question 32

When is OAE testing done?

Answer 32

- in infants to assess the function of the inner and middle ears - measures presence or absence of sound waves generated by the cochlear outer hair cells in response to sound stimuli - used to screen sensorineural hearing loss - cannot detect auditory neuropathy

Question 33

Actions of olivocochlear efferents

Answer 33

- reduce electromotility of outer hair cells - decrease basilar membrane motion - reduce responses of inner hair cells and auditory nerve fibers

Question 34

Actions of medial ear efferents

Answer 34

- tensor tympani to the malleus and tympanic membrane (attenuates sound) - stapedius muscle to stapes (from CN VIII) - bilateral response to the high sound levels - contractions decrease transmission of sound - act at low frequencies - may prevent damage - may prevent low frequency masking (improving speech discrimination) - may protect hair cells from damage to intense sounds - implicated in tinnitus

Question 35

Actions of autonomic efferents

Answer 35

- arises from CN VIII - sympathetic adrenergic fibers - regulates vascular tone in blood supply to cochlea

Question 36

Dorsal (posterior) cochlear nuclei

Answer 36

integrate the acoustic information with somatosensory information

Question 37

Vetral (anterior) cochlear nuclei

Answer 37

begins processing the temporal and spectral features of the sound

Question 38

Medial superior olivary complex

Answer 38

receives glutamatergic input and generates map of interaural TIME differences to help localize sound

Question 39

Lateral superior olivary complex

Answer 39

receives glutamatergic input and generates map of interaural INTENSITY differences to help localize the source of the sound

Question 40

Inferior Colliculus

Answer 40

- suppresses info related to echoes - info about time and intensity differences converge here to help create a precise origin of sound location along the horizon

Question 41

Medial geniculate nucleus

Answer 41

- part of thalamus - lots of convergence from distinct spectral and temporal pathways - allows for processing features of speech inflections - precise info regarding intensity, frequency, and binaural properties of sound are integrated and relayed onward

Question 42

Primary auditory cortex (A1)

Answer 42

- essential in conscious perception of sound | - higher order processing of sound

Question 43

Secondary auditory cortex (A2)

Answer 43

- composed of multiple areas (Broca's, Wernickes, etc.) - less specifically organized in tonotopic arrangement than primary auditory cortex - responds to more complex sound (music), identifying (naming) a sound, and speech

Question 44

Cochlear Implant purpose

Answer 44

- internal component includes receiver and electrode array - receiver decodes signal and delivers to electrode - electrode array inserted into cochlea through oval window along afferents from CN VIII - electrical signals along electrode will stimulate particular cochlear nerve afferent along basilar membrane - electrode array mimics tonotopy of basilar membrane and stimulate nerves at discrete frequencies

Question 45

Activating force of anterior semicircular canal

Answer 45

rotation in vertical plane forwards

Question 46

Activating force of horizontal semicircular canal

Answer 46

rotation in horizontal plane

Question 47

Activating force of posterior semicircular canal

Answer 47

rotation in vertical plan backwards

Question 48

Activating force of utricle

Answer 48

linear acceleration forward and backward

Question 49

Activating force of saccule

Answer 49

linear acceleration up and down