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Physiology Of The Auditory And Vestibular System Flashcards

1
Q

How is the structure of the Basilar Membrane near the oval and round windows?

What frequencies are heard here?

A

Narrow and stiff

High

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2
Q

What How is the structure of the Basilar Membrane near the helicotrema?

What frequencies are heard here?

A

Wider and more flexible

Low frequencies

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3
Q

High frequencies will have a greater deflection WHERE on the basilar membrane?

A

Where it is narrow and still

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4
Q

Low frequencies will have greater deflection WHERE on the Basilar Membrane?

A

Where it is loose and flexible

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5
Q

How is the freuqency of sound (pitch) coded for?

A

Where there is the greatest amt. of deflection in the Basilar Membrane

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6
Q

What does the Auditory system do and how?

A

Detects sound

Uses acoustic clues to identify and locate sound sources in environment

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7
Q

What is sound?

A

Oscillations of air pressure that vary rapidly w/ time

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8
Q

What is amplitude?

A

Sound pressure (intensity) specificity by a scale of sound pressure level (SPL)in decibel

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9
Q

What are the units for amplitude?

A

Decibels

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10
Q

What are the units for frequency?

A

Hz

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11
Q

What is frequency?

A

Number of oscillations of air pressure per second

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12
Q

What is the sound pathway?

A 
Sound waves —> stapes
—>Scala vestibule press. << Scala tympani press. 
—> waves in BM (vibration)(bows up)
—> pressure differential 
—> force against Tectorial Membrane
—> outer hair cells of stereocilia displaced 
—> depolarization activates protein 
—> endolymph waves in cochlear duct 
—> inner hair cellls 
—> depolarization 
—> Ca channels open
—>vesicles fuse and release glutamate (ACh)
—> cochlear nerve fibers
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13
Q

Why does the inner ear have tonotopy?

A

Due to the structure of the Basilar membrane that detects certain pitches at certain locations

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14
Q

What is tonotopy?

A

Distinct location interpret discrete frequencies

I.e. base of BM = high freq.
(Apex of BM = low freq.)

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15
Q

How does the vibration of the basilar membrane create a pressure differential?

A

‣ Due to the closed strucutre of the cochlea (w/ 1 pt. Of entrance and 1 pt.of exit for the dissipation of energy)

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16
Q

Does the tectorial membrane move?

A

No, it is stationary

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17
Q

What does the pressure differential created by the vibration of the BM cause?

A

Shearing force against stationary tectorial membrane that displace the stereocilia of the outer hair cells

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18
Q

What doe the outer hair cells do to the sound signal?

A

Amplify the signals that are then process by inner hair cells

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19
Q

Are both outer and inner hair cells activated by the Tectorial membrane?

A

No - only the outer

Inner hair cells are not in direct contact and are activated by endolymph movement in cochlear duct

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20
Q

What are inner hair cells responsible for?

Why?

A

For hearing

~90% of cochlear nerve fibers come from inner hair cells

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21
Q

How does depolarization of both inner and outer hair cells occur?

A

When cation channels open at apex of stereocilia and cause rapid influx of K+ into cell

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22
Q

How are stereocilia connected to one another?

A

Tip links that transmits force to an elastic gated spring

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23
Q

When the stereocilia transmit the force caused by the shearing of the organ of corti what happens?

A

TRPA1 channels open

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24
Q

What are TRPA1 channels?

Slow or rapid acting?

What kind of potentials do they require?

A

Mechanotransduction channels that open in response to force from stereocilia

Rapid (response w/in 50 us)

Do not require receptors potentials, with vibrations as small as 0.3 vm can cause channel opening

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25
Q

What is the result of TRPA1 channels not requiring receptor potentials?

A

Increased sensitivity of response

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26
Q

What bathes the stereocilia?

A

Endolymph of cochlear duct (K+ rich)

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27
Q

Where are the tips and bodies of the stereocilia of outer hair cells?

A

Tips - in TM

Bodies - resting on BM

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28
Q

What causes the basilar membrane to be upwardly displaced?

A

Pressure in Scala tympani&raquo_space; than pressure of Scala Vestibuli

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29
Q

What will the upward displacement of the BM create and cause?

A

Creates shearing force a

Results in LATERAL displacement of stereocilia toward longest stereovilli and thus DEPOLARIZATION

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30
Q

When the TRPA1 channels open do to the lateral displacement of outer hair cells, what will happen?

A

K+ floods the cells and depolarization occurs

Will activate intracellular contractile proteins, accentuating upward bowing of BM and making waves in the endolymph

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31
Q

The endolymph waves caused by the depolarization of the outer hair cells, causes what?

A

Will move beneath the tectorial membrane and cause INNER hair cells to bend toward the longer stereovilli

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32
Q

What happens when the inner hair cells bend toward their longest stereovilli?

A

TRPA1 channels open and cause influx of K+ and depolarization

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33
Q

What will result from the depolarization of the inner hair cells?

A

Voltage gated Ca++ channels open at base of cells

Causing influx of Ca++ and fusing of NTR vesicles with BM

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34
Q

What will the synaptic vesicles activated by the CA++ influx from inner hair cells do?

A

Release glutamate (ACh) into synaptic cleft

Glutamate will stimulate afferent cochlear nerve fibers at spiral ganglion neurite

Signal transmitted to CNS

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35
Q

What happens if the Basilar membrane if displaced downward?

A

◦ Creates shearing force that results in hyperpolarization of hair cell

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36
Q

What are the characteristics of ENDOlymph?

Where is it found?

What produces it?

A

K+ rich fluid, Na poor

Fills cochlear duct and membranous labyrinth, bathes apical ends of hair cells, in Scala Media

Produced by Scala Vascularis

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37
Q

What are the characteristics of PERIlymph?

Where is it found?

What produces it?

A

K+ poor fluid, Na rich

Bathes basal end of cochlear hair cells

Found in Scala vestibule and Scala tympani

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38
Q

Where is the stria vascularis located?

A

In Scala media

lateral wall of cochlear duct

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39
Q

What is the function of the stria vasicularis?

A

Produce endolymph (K+ rich)

^will provide optimal conditions for hair cell depolarization

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40
Q

What is the structure of the stria vascularis?

A

Stratified epithelial cells that extend cytoplasmic processes and folds around capillaries of intraepithelial plexus

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41
Q

What does the intraepithelial plexus in the Stria vascularis do?

A

Release K+ which is transported across tightly joined cells at strial surface into the endolymph

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42
Q

What does the endolymph create?
What will this do?

What does it form?

A

Creates high endocochlear potential (+80 mV) that is maintained by stria vascularis

Drives +ions into hair cells down conc. Gradient (depolarization)

Forms blood labyrinth barrier (BLB)

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43
Q

What is one of the main sites of drug entry to access inner hair cell?

A

Blood labyrinth barrier formed by endolymph

44
Q

What do ototoxic drugs do?

Causing?

A

Disrupt function of stria vascularis

Diminished endocochlear potential and impacting hearing

45
Q

What could disrupt the function of the Stria Vascularis?

A

Ototoxic drugs

Carbon monoxide

46
Q

What is the function of inner hair cells?

A

Primary source of auditory info?

47
Q

How are the inner hair cells arranged?

A

In a single layer

48
Q

What do the inner hair cells synapse with?

A

Peripheral terminal of primary afferent sensory neurons

49
Q

What are the primary hair cells?

A

Outer hair cells

50
Q

What is the function of the outer hair cells?

A

Amplify sound waves that result in movement of the Basilar Membrane

51
Q

What kind of cells are the outer hair cells?

A

Contractile cells

Specialized type of epithelial cells w/ contractile properties that boosts mechanical vibrations of Basilar membrane

52
Q

How are outer hair cells arranged?

A

3 rows

53
Q

What do outer hair cells form synapses with?

A

Sensory afferent peripheral terminals from spiral ganglion

Terminals from efferent neurons

54
Q

What are otoacoustic emissions?

A

Sounds made by the ear itself that are measured in the EAM

55
Q

How does the ear make a sound?

A

Outer hair cells could cause BM to move backward toward oval window, thru middle ear via ossicles, and displace Tectorial membrane causing sound

56
Q

What do otoacoustic emissions help us assess?

A

Inner and middle ear functions in infants

57
Q

Where do Otoacoustic emissions originate?

A

In superior olivary complex as olivocochlear efferents

58
Q

What neurons make up olivocochlear efferents?

What will they do?

A

Medial olivary complex neurons innervate OUTER hair cells

Lateral olivary complex neurons innervate INNER hair cells

59
Q

What will OAE testing measure?

A

Presence or absence of sound waves generated by cochlear outer hair cells in response to sound

Evaluates hearing from middle to outer hair cells

60
Q

Otoacoustic emissions can screen for what?

What can it not detect?

A

Sensorineural hearing loss

Will not detect auditory neuropathy

61
Q

How do olivocochlear efferents protect the cochlear during intense sounds?

A

Reduce electromotility of outer hair cells

Decrease basilar membrane motility

Reduce response of IHCs of auditory nerve fibers

62
Q

What are the medial ear efferents?

A

Tensory tympani

Stapedius

63
Q

How do medial ear efferents protect the cochlea during intense sounds?

A

Tensor tympani —> malleus & Tympanic Membr. To attenuate sound

Stapedius n —> Stapes to attenuate sound

64
Q

When will medial ear efferents act?

A

In bilateral response to high sound levels

At low frequencies

65
Q

How do medial ear efferents improve speech discrimination?

A

Prevent low frequency masking

66
Q

What is damage to medial ear efferents implicated in?

A

Tinnitus

67
Q

What are the autonomic efferents from?

What kind of fibers are they?

Function?

A

From CN 8
Sympathetic adrenergic fibers

Regulates vascular tone in blood supply to cochlea

68
Q

What does the Dorsal cochlear nucleus do?

A

integrates acoustic info with somatosensory info

69
Q

What does the ventral cochlear nucleus do?

A

begins processing of temporal and spectral features of sound

70
Q

What is the role of the Superior Olivary Nucleus?

A

major role in determining the direction from which a sound originates

71
Q

What is the function of the Medial superior olivary complex?

A

Innervate outer hair cells to generate map of interaural TIME DIFFs to help location sound

72
Q

What is the function of the Lateral Superior Olivary Complex?

A

Innervate INNER hair cells to generate map of interaural INTENSITY differences to help localize SOURCE of sound

73
Q

What do the MSO and LSO receive input from?

A

Glutamate

74
Q

What are the roles of the inferior colliculus?

A

Suppress info from ECHOS

Helps final estimation of SOUND LOCALIZATION along horizon

75
Q

What converges onto the Inferior colliculus?

What will this do?

A

MSO and LSO

Info about time and intensity differences helps create precise origin of sound location along horizon

76
Q

Where is the Medial Geniculate nucleus

A

In thalamus

77
Q

What converges onto the Medial Geniculate Nucleus?

A

Inferior colliculus - spectral and temporal pathways

78
Q

What info is integrated at the MEdial Geniculate Nucleus?

What does this allow for?

A

Intensity, frequency, binaural properties of sound

Allows for features of speech inflections to be processed

79
Q

What is A1?

A

Primary auditory cortex

80
Q

What is A2?

A

Secondary auditory association cortex

81
Q

What is the role of the Primary Auditory Cortex?

A

Conscious perception of sound

Higher order processing of sound (loudness, modulation in volume, rate of frequency modulation)

82
Q

What is the Secondary Auditory Association Complex composed of?

A

Multiple areas including Broca’s, Wernicke’s, etc.

83
Q

What is the role of A2?

A

Responds to more complex sounds (music)

ID’s a sound (names it)

Speech

84
Q

What doesn’t maintain the tonotopic map well?

A

Secondary auditory association cortex

Less specifically organized

85
Q

What causes sensorineural hearing loss?

A

Problem in inner ear w/ hair cells or with cochlear nerve

86
Q

How do hair cells regenerate?

A

They do not

87
Q

How does a cochlear implant work?

A

Internal component w/

Receiver to decode signal and deliver it to electrode array

Electrode array to stimulate a particular cochlear nerve afferent along the BM and thus mimic tonotopy of BM by stimulating nerves at discrete frequencies

88
Q

Where is the electrode array of a cochlear implant inserted?

A

Into cochlea thru oval window

Will sit in cochlear duct along afferent from CN 8

89
Q

What will activate the anterior semicircular canal?

Example?

A

Rotation in vertical plane forward

Ex.: tripping forward

90
Q

What will activate the horizontal semicircular canal?

A

Rotation in horizontal plane
(Pirouette)

Rotation in vertical plane BACKWARDS
(Tripping backwards)

91
Q

What will activate the Utricle?

A

Linear accel. Forward and backwards

Ex.: running forwards

92
Q

What will activate the Saccule?

A

Linear acceleration up and down

Ex.: jumping up

93
Q

What is an importnat function of Outer Hair cells that can be measured?

A

Otoacoustic emissions

94
Q

Where are hair cells positioned?

A

Along the length of the cochlear spiral

95
Q

What do hair cells receive

Afferent innervation from?

Efferent innervation from?

A

Afferent from Spiral Ganglia

Efferent from Superior Olivary Complex

96
Q

What is the role of the Superior colliculus with audition?

A

SC takes location data from IC and adds final dimension (vertical height) to create a spatial map of sound’s location

97
Q

In the Auditory Association COrtex (A2), what activates rostral areas vs. caudal areas?

A

More rostral areas = low frequencies

More caudal areas = higher frequencies

98
Q

How does salt evoke the secretion of serotonin?

A

slat thru epithelial Na+ channel (ENaC)

Increased Na in saliva and tongue

Na+ diffuses down gradient into cell

Depolarizes membrane, increasing Ca+

Releases Serotonin

99
Q

How does Sour evoke secretion of Serotonin?

A

Evoked by H+ ions

Depolarizaiton, increased intracellular Ca

Serotonin release

100
Q

How does Sweet, bitter, and Umami evoke secretion of ATP?

A

Bind taste GPCR

Signaling cascade

Increased intracellular CA

TRPM5 activation, influx of Na

Depolarization

Release of ATP

101
Q

What is the signal transduction pathway for smell?

A
  1. Voltage sensitive
  2. Odorant binds receptors
  3. Golf second messenger system stimulated
  4. Depolarization
  5. AP if threshold reached
  6. NTR release from central terminal of bipolar cell
102
Q

How does signal transduction occur for taste?

A
  1. Relatively voltage INsensitive
  2. Receptor activation of GPCR + other 2nd messenger systems
  3. Increase of intracellular Ca
  4. Depolarization
  5. Release of Serotonin or ATP onto peripheral terminal of primary afferent neurons
103
Q

What is the only sensory modality that is not relayed thru the thalamus?

A

Olfaction

104
Q

What does normal taste sensation require?

A

Olfaction

105
Q

What does the periamygdaloid cortex do?

A

Integrates odor induced emotional responses

106
Q

Where are discriminative aspects of taste processed?

A

VPM of thalamus

..3 (16 decks)

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