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
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
3
Q
High frequencies will have a greater deflection WHERE on the basilar membrane?
A
Where it is narrow and still
4
Q
Low frequencies will have greater deflection WHERE on the Basilar Membrane?
A
Where it is loose and flexible
5
Q
How is the freuqency of sound (pitch) coded for?
A
Where there is the greatest amt. of deflection in the Basilar Membrane
6
Q
What does the Auditory system do and how?
A
Detects sound
Uses acoustic clues to identify and locate sound sources in environment
7
Q
What is sound?
A
Oscillations of air pressure that vary rapidly w/ time
8
Q
What is amplitude?
A
Sound pressure (intensity) specificity by a scale of sound pressure level (SPL)in decibel
9
Q
What are the units for amplitude?
A
Decibels
10
Q
What are the units for frequency?
A
Hz
11
Q
What is frequency?
A
Number of oscillations of air pressure per second
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
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
14
Q
What is tonotopy?
A
Distinct location interpret discrete frequencies
I.e. base of BM = high freq.
(Apex of BM = low freq.)
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)
16
Q
Does the tectorial membrane move?
A
No, it is stationary
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
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
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
20
Q
What are inner hair cells responsible for?
Why?
A
For hearing
~90% of cochlear nerve fibers come from inner hair cells
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
22
Q
How are stereocilia connected to one another?
A
Tip links that transmits force to an elastic gated spring
23
Q
When the stereocilia transmit the force caused by the shearing of the organ of corti what happens?
A
TRPA1 channels open
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
25
What is the result of TRPA1 channels not requiring receptor potentials?
Increased sensitivity of response
26
What bathes the stereocilia?
Endolymph of cochlear duct (K+ rich)
27
Where are the tips and bodies of the stereocilia of outer hair cells?
Tips - in TM
Bodies - resting on BM
28
What causes the basilar membrane to be upwardly displaced?
Pressure in Scala tympani >> than pressure of Scala Vestibuli
29
What will the upward displacement of the BM create and cause?
Creates shearing force a
Results in LATERAL displacement of stereocilia toward longest stereovilli and thus DEPOLARIZATION
30
When the TRPA1 channels open do to the lateral displacement of outer hair cells, what will happen?
K+ floods the cells and depolarization occurs
Will activate intracellular contractile proteins, accentuating upward bowing of BM and making waves in the endolymph
31
The endolymph waves caused by the depolarization of the outer hair cells, causes what?
Will move beneath the tectorial membrane and cause INNER hair cells to bend toward the longer stereovilli
32
What happens when the inner hair cells bend toward their longest stereovilli?
TRPA1 channels open and cause influx of K+ and depolarization
33
What will result from the depolarization of the inner hair cells?
Voltage gated Ca++ channels open at base of cells
Causing influx of Ca++ and fusing of NTR vesicles with BM
34
What will the synaptic vesicles activated by the CA++ influx from inner hair cells do?
Release glutamate (ACh) into synaptic cleft
Glutamate will stimulate afferent cochlear nerve fibers at spiral ganglion neurite
Signal transmitted to CNS
35
What happens if the Basilar membrane if displaced downward?
◦ Creates shearing force that results in hyperpolarization of hair cell
36
What are the characteristics of ENDOlymph?
Where is it found?
What produces it?
K+ rich fluid, Na poor
Fills cochlear duct and membranous labyrinth, bathes apical ends of hair cells, in Scala Media
Produced by Scala Vascularis
37
What are the characteristics of PERIlymph?
Where is it found?
What produces it?
K+ poor fluid, Na rich
Bathes basal end of cochlear hair cells
Found in Scala vestibule and Scala tympani
38
Where is the stria vascularis located?
In Scala media
| lateral wall of cochlear duct
39
What is the function of the stria vasicularis?
Produce endolymph (K+ rich)
^will provide optimal conditions for hair cell depolarization
40
What is the structure of the stria vascularis?
Stratified epithelial cells that extend cytoplasmic processes and folds around capillaries of intraepithelial plexus
41
What does the intraepithelial plexus in the Stria vascularis do?
Release K+ which is transported across tightly joined cells at strial surface into the endolymph
42
What does the endolymph create?
What will this do?
What does it form?
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)
43
What is one of the main sites of drug entry to access inner hair cell?
Blood labyrinth barrier formed by endolymph
44
What do ototoxic drugs do?
Causing?
Disrupt function of stria vascularis
Diminished endocochlear potential and impacting hearing
45
What could disrupt the function of the Stria Vascularis?
Ototoxic drugs
| Carbon monoxide
46
What is the function of inner hair cells?
Primary source of auditory info?
47
How are the inner hair cells arranged?
In a single layer
48
What do the inner hair cells synapse with?
Peripheral terminal of primary afferent sensory neurons
49
What are the primary hair cells?
Outer hair cells
50
What is the function of the outer hair cells?
Amplify sound waves that result in movement of the Basilar Membrane
51
What kind of cells are the outer hair cells?
Contractile cells
| Specialized type of epithelial cells w/ contractile properties that boosts mechanical vibrations of Basilar membrane
52
How are outer hair cells arranged?
3 rows
53
What do outer hair cells form synapses with?
Sensory afferent peripheral terminals from spiral ganglion
Terminals from efferent neurons
54
What are otoacoustic emissions?
Sounds made by the ear itself that are measured in the EAM
55
How does the ear make a sound?
Outer hair cells could cause BM to move backward toward oval window, thru middle ear via ossicles, and displace Tectorial membrane causing sound
56
What do otoacoustic emissions help us assess?
Inner and middle ear functions in infants
57
Where do Otoacoustic emissions originate?
In superior olivary complex as olivocochlear efferents
58
What neurons make up olivocochlear efferents?
| What will they do?
Medial olivary complex neurons innervate OUTER hair cells
Lateral olivary complex neurons innervate INNER hair cells
59
What will OAE testing measure?
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
Otoacoustic emissions can screen for what?
What can it not detect?
Sensorineural hearing loss
Will not detect auditory neuropathy
61
How do olivocochlear efferents protect the cochlear during intense sounds?
Reduce electromotility of outer hair cells
Decrease basilar membrane motility
Reduce response of IHCs of auditory nerve fibers
62
What are the medial ear efferents?
Tensory tympani
| Stapedius
63
How do medial ear efferents protect the cochlea during intense sounds?
Tensor tympani —> malleus & Tympanic Membr. To attenuate sound
Stapedius n —> Stapes to attenuate sound
64
When will medial ear efferents act?
In bilateral response to high sound levels
At low frequencies
65
How do medial ear efferents improve speech discrimination?
Prevent low frequency masking
66
What is damage to medial ear efferents implicated in?
Tinnitus
67
What are the autonomic efferents from?
What kind of fibers are they?
Function?
From CN 8
Sympathetic adrenergic fibers
Regulates vascular tone in blood supply to cochlea
68
What does the Dorsal cochlear nucleus do?
integrates acoustic info with somatosensory info
69
What does the ventral cochlear nucleus do?
begins processing of temporal and spectral features of sound
70
What is the role of the Superior Olivary Nucleus?
major role in determining the direction from which a sound originates
71
What is the function of the Medial superior olivary complex?
Innervate outer hair cells to generate map of interaural TIME DIFFs to help location sound
72
What is the function of the Lateral Superior Olivary Complex?
Innervate INNER hair cells to generate map of interaural INTENSITY differences to help localize SOURCE of sound
73
What do the MSO and LSO receive input from?
Glutamate
74
What are the roles of the inferior colliculus?
Suppress info from ECHOS
Helps final estimation of SOUND LOCALIZATION along horizon
75
What converges onto the Inferior colliculus?
What will this do?
MSO and LSO
Info about time and intensity differences helps create precise origin of sound location along horizon
76
Where is the Medial Geniculate nucleus
In thalamus
77
What converges onto the Medial Geniculate Nucleus?
Inferior colliculus - spectral and temporal pathways
78
What info is integrated at the MEdial Geniculate Nucleus?
What does this allow for?
Intensity, frequency, binaural properties of sound
Allows for features of speech inflections to be processed
79
What is A1?
Primary auditory cortex
80
What is A2?
Secondary auditory association cortex
81
What is the role of the Primary Auditory Cortex?
Conscious perception of sound
Higher order processing of sound (loudness, modulation in volume, rate of frequency modulation)
82
What is the Secondary Auditory Association Complex composed of?
Multiple areas including Broca’s, Wernicke’s, etc.
83
What is the role of A2?
Responds to more complex sounds (music)
ID’s a sound (names it)
Speech
84
What doesn’t maintain the tonotopic map well?
Secondary auditory association cortex
| Less specifically organized
85
What causes sensorineural hearing loss?
Problem in inner ear w/ hair cells or with cochlear nerve
86
How do hair cells regenerate?
They do not
87
How does a cochlear implant work?
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
Where is the electrode array of a cochlear implant inserted?
Into cochlea thru oval window
Will sit in cochlear duct along afferent from CN 8
89
What will activate the anterior semicircular canal?
Example?
Rotation in vertical plane forward
Ex.: tripping forward
90
What will activate the horizontal semicircular canal?
Rotation in horizontal plane
(Pirouette)
Rotation in vertical plane BACKWARDS
(Tripping backwards)
91
What will activate the Utricle?
Linear accel. Forward and backwards
Ex.: running forwards
92
What will activate the Saccule?
Linear acceleration up and down
Ex.: jumping up
93
What is an importnat function of Outer Hair cells that can be measured?
Otoacoustic emissions
94
Where are hair cells positioned?
Along the length of the cochlear spiral
95
What do hair cells receive
Afferent innervation from?
Efferent innervation from?
Afferent from Spiral Ganglia
Efferent from Superior Olivary Complex
96
What is the role of the Superior colliculus with audition?
SC takes location data from IC and adds final dimension (vertical height) to create a spatial map of sound’s location
97
In the Auditory Association COrtex (A2), what activates rostral areas vs. caudal areas?
More rostral areas = low frequencies
More caudal areas = higher frequencies
98
How does salt evoke the secretion of serotonin?
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
How does Sour evoke secretion of Serotonin?
Evoked by H+ ions
Depolarizaiton, increased intracellular Ca
Serotonin release
100
How does Sweet, bitter, and Umami evoke secretion of ATP?
Bind taste GPCR
Signaling cascade
Increased intracellular CA
TRPM5 activation, influx of Na
Depolarization
Release of ATP
101
What is the signal transduction pathway for smell?
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
How does signal transduction occur for taste?
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
What is the only sensory modality that is not relayed thru the thalamus?
Olfaction
104
What does normal taste sensation require?
Olfaction
105
What does the periamygdaloid cortex do?
Integrates odor induced emotional responses
106
Where are discriminative aspects of taste processed?
VPM of thalamus
