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Neuro Endo 3 > Physiology of Auditory and Vestibular System > Flashcards

Physiology of Auditory and Vestibular System Flashcards

1
Q

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

A

narrow and stiff

HIGH frequency sounds (20,000 Hz)

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2
Q

What are characteristics of the basilar membrane near the helicotrema?

A

wider and flexible

LOW frequency sounds (20 Hz)

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3
Q

Auditory system

A

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

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4
Q

Sound

A

oscillations of air pressure that vary rapidly with time

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5
Q

Amplitude

A

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

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6
Q

Frequency

A

number of oscillations of air pressure per second (Hz)

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7
Q

Tonotopy of inner ear

A

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

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

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8
Q

What does the vibration of the basilar membrane create?

A

pressure differential

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9
Q

What does the pressure differential in the inner ear cause?

A

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

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10
Q

How are the inner hair cells activated?

A

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

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11
Q

How does depolarization of the hair cell occur?

A

opening of cation channels at the apex of sterocilia

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12
Q

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

A

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

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13
Q

Endolymph

A 
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
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14
Q

Perilymph

A

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

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15
Q

Steps in depolarization of a hair cell

A

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

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16
Q

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

A

tectorial membrane

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17
Q

Where are the bodies of the hair cells located?

A

basilar membrane

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18
Q

What does an upward displacement of the basilar membrane cause?

A

shearing force that results in lateral displacement of stereocilia

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19
Q

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

A

depolarization of the hair cell

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20
Q

What does the downward displacement of the basilar membrane create?

A

shearing force that results in HYPERPOLARIZATION

21
Q

Which cells are responsible for hearing?

A

inner hair cells

about 90% of cochlear fibers come from inner hair cells

22
Q

Which cells are responsible for amplification of signals?

A

outer hair cells

23
Q

Scala Vestibuli

A

filled with perilymph

connects at large end to oval window

24
Q

Scala Media

A

filled with endolymph

in between scala vestibuli and scala tympani

25
Q

Scala Tympani

A

filled with perilymph

connects at large end to round window

26
Q

Stria Vascularis

A

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

27
Q

Function of endocochlear potential

A

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

28
Q

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

A

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

29
Q

Properties of inner hair cells

A
  • primary source of auditory info
  • single layer
  • synapse with peripheral terminal of primary afferent sensory neuron
  • efferent neuron modulates
30
Q

Properties of outer hair cells

A
  • 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
31
Q

Otoacoustic emissions

A
  • 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
32
Q

When is OAE testing done?

A
  • 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
33
Q

Actions of olivocochlear efferents

A
  • reduce electromotility of outer hair cells
  • decrease basilar membrane motion
  • reduce responses of inner hair cells and auditory nerve fibers
34
Q

Actions of medial ear efferents

A
  • 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
35
Q

Actions of autonomic efferents

A
  • arises from CN VIII
  • sympathetic adrenergic fibers
  • regulates vascular tone in blood supply to cochlea
36
Q

Dorsal (posterior) cochlear nuclei

A

integrate the acoustic information with somatosensory information

37
Q

Vetral (anterior) cochlear nuclei

A

begins processing the temporal and spectral features of the sound

38
Q

Medial superior olivary complex

A

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

39
Q

Lateral superior olivary complex

A

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

40
Q

Inferior Colliculus

A
  • 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
41
Q

Medial geniculate nucleus

A
  • 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
42
Q

Primary auditory cortex (A1)

A
  • essential in conscious perception of sound

- higher order processing of sound

43
Q

Secondary auditory cortex (A2)

A
  • 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
44
Q

Cochlear Implant purpose

A
  • 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
45
Q

Activating force of anterior semicircular canal

A

rotation in vertical plane forwards

46
Q

Activating force of horizontal semicircular canal

A

rotation in horizontal plane

47
Q

Activating force of posterior semicircular canal

A

rotation in vertical plan backwards

48
Q

Activating force of utricle

A

linear acceleration forward and backward

49
Q

Activating force of saccule

A

linear acceleration up and down

Neuro Endo 3 (13 decks)

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