Auditory and Vestibular System

Question 1

Compare endolymph to perilymph in terms of potassium concentration, which end of hair cells it contacts, and where it is found

Answer 1

Endolymph — potassium-RICH fluid filling cochlear duct and membranous labyrinth; bathes APICAL end of hair cells. Found in SCALA MEDIA.

Perilymph — potassium-POOR fluid filling bony labyrinth; bathes BASAL end of cochlear hair cells. Found in SCALA VESTIBULI and SCALA TYMPANI.

Question 2

In terms of regions of the basilar membrane and position of oval window vs. helicotrema, where are high frequency vs. low frequency sounds registered?

Answer 2

High frequency sounds = near oval window, where basilar membrane is narrow and stiff

Low frequency sounds = near helicotrema where basilar membrane is wide and flexible

Question 3

Hair cells are mechanoreceptors that are stiff, graded in size, and rich in actin. Stereocilia exist on their ___ surface, while neural synapses are on the ______ surface

Answer 3

Apical; basal

Question 4

Following deflection of stereocilia, ____ ions enter the cell from endolymph and depolarize it.

Answer 4

K+

Question 5

Following deflection of stereocilia, K+ ions enter the cell from endolymph and depolarize it.

The electrochemical gradient driving this results from what 2 factors?

Answer 5

Large endolymphatic potential (K+ concentration gradient)

Large electrical gradient (scala media has high positive charge)

Question 6

Deflection of stereocilia causes depolarization, release of NT _______ and generation of APs in CN 8. Stereocilia are linked together and deflect as a bundle. Deflection toward the tallest stereocilia causes _____ while deflection in the opposite direction causes _____

Answer 6

Glutamate; depolarization; hyperpolarization

Question 7

What are the ion channels in the hair cells that allow K+ in to initiate depolarization?

Answer 7

TRPA1

Question 8

Activation of TRPA1 and influx of K+ allows voltage gated ____ channels to open which is what triggers release of _____ at the postsynaptic cell, a spiral ganglion neurite

Answer 8

Ca; glutamate

Question 9

What structure maintains the electrochemical properties of the endolymph?

Answer 9

Stria vascularis

Question 10

Difference in function between inner hair cells vs. outer hair cells of basilar membrane

Answer 10

Inner hair cells = type I afferents; primary source of auditory info (transmission)

Outer hair cells = type II afferents; amplification

Question 11

In terms of hair cell innervation, hair cells receive afferent innervation from the ____ _____ and efferent innervation from the _____ ____ ____

Answer 11

Spiral ganglia; superior olivary complex

Question 12

Function of dorsal cochlear nuclei

Answer 12

Determine location of sound

Question 13

Function of ventral cochlear nuclei

Answer 13

Determine nature of sound (high vs. low frequency)

Question 14

Function of medial superior olivary nucleus (primary nucleus of superior olivary complex)

Answer 14

Difference in TIME of arrival to ears

Question 15

Function of lateral superior olivary nucleus

Answer 15

Differences in INTENSITY

Question 16

Function of superior colliculus vs. inferior colliculus

Answer 16

SC: takes location data from IC and adds final dimension (vertical height) to create spatial map of sounds location

IC: Suppresses info related to echoes, which would interfere with localization and arrives at a final estimation of localization of sound along horizon

Question 17

Function of primary auditory cortex (A1) vs. association (A2)cortex

Answer 17

A1 = Beginning to interpret sound

A2 = processing complex sounds, name sounds, speech undulations

Question 18

First site in brainstem where information from both ears converges

Answer 18

Superior olivary complex

Question 19

Relay station in auditory pathway located in the thalamus, allows processing of speech inflections

Answer 19

Medial geniculate nucleus

Question 20

In the tonotopic map of the primary auditory cortex, more rostral areas are activated by ____ frequencies while more caudal areas respond to _____ frequencies

Answer 20

Low; higher

Question 21

3 types of efferent input to the auditory system

Answer 21

Olivocochlear efferents
Middle ear muscle motor neurons
Autonomic innervation of inner ear

Question 22

Olivocochlear efferents originate in the superior olivary complex

Medial OC neurons innervate ____ hair cells while lateral OC neurons innervate ____hair cells

The main function of these efferents is ______

Answer 22

Outer; inner

Protective

[shifts responses to higher sound levels]

Question 23

Function of middle ear efferents

Answer 23

Tensor tympani to the malleus (from CN V)

Stapedius to the stapes (from CN VII)

May prevent damage and prevent low frequency masking which improves speech discrimination

Question 24

What are otoacoustic emissions? What are their clinical importance?

Answer 24

The ear can emit sound — either spontaneous or evoked. Spontaneous occur in 1/3 of people and evoked are used to test for hearing loss

Clinically important for newborn hearing screen, tinnitus, and ototoxicity

Question 25

Type of hearing loss caused by damage to hair cells or nerve fibers or both

Answer 25

Sensorineural hearing loss

[caused by noise damage, ototoxic drugs, age]

Question 26

Which type of hair cells are more susceptible to injury in terms of sensorineural hearing loss? Which area of the cochlea is more susceptible?

Answer 26

Outer hair cells

Base (high frequency) of cochlea is more susceptible

Question 27

What structures detect rotational acceleration vs. forward/backward linear acceleration vs. vertical linear acceleration?

Answer 27

Rotational acceleration (horizontal, anterior, posterior) = semicircular canals

Horizontal linear acceleration = utricle

Vertical linear acceleration = saccule

Question 28

Rotation in the horizontal plane is best detected by what ear structure?

Answer 28

Horizontal semicircular canal

Question 29

Rotation in the vertical plane backwards maximally activates what ear structure?

Answer 29

Posterior semicircular canal

Question 30

Rotation in the vertical plane forwards maximally activates what ear structure?

Answer 30

Anterior semicircular canal

Question 31

Regardless of which direction we fall, our reflexes are designed to keep out eyes on the _______

Answer 31

Horizon

[while rotating, our eyes rotate horizontally, if you fall forward your eyes move up, if you fall backward your eyes move down]

Question 32

When the horizontal semicircular canal is active, the ipsilateral _____ m. is activated while the ipsilateral ______ m. is inhibited

Answer 32

Medial rectus; lateral rectus

Question 33

When the posterior semicircular canal is activated, the _____m. is activated while the ____ m. is inhibited so that the eyes move down to continue to focus on a point as you fall backwards

Answer 33

Superior oblique; inferior oblique

Question 34

When the anterior semicircular canal is activated, the ____ m. is activated and the _____ m. is inhibited so that the eyes move up to continue to focus as you fall forward

Answer 34

Superior rectus; inferior rectus

Question 35

________ resides inside the vestibular apparatus (in the membranous labyrinth)

_______ surrounds the vestibular apparatus (in the bony labyrinth)

Answer 35

Endolymph (high [K+])

Perilymph (high [Na+])

Question 36

The vast majority of the cortical and cerebellar involvement of the vestibulooptic reflexes is to _____ the reflex to allow for voluntary motion

Answer 36

Suppress