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Year 1: 07. Neuro Exam 3 > Lecture 2: Physiology of Auditory and Vestibular Systems > Flashcards

Lecture 2: Physiology of Auditory and Vestibular Systems Flashcards

1
Q

What is the auditory system?

A

Detects sound and uses acoustic cues to identify and locate sound sources in the environment

  • Sound: oscillations of air pressure that can vary
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2
Q

What is amplitude and frequency?

A
  • Amplitude: Sound pressure (intensity) measured by decibels
  • Frequency: numer of oscillations of pair pressure per second measured by Hz
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3
Q

Where do higher frequency sounds displace the basilar membrane?

A

Near oval window where basilar membrane is narrow and stiff

Ex: 20,000 Hz

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4
Q

Where do low frequency sounds displace the basilar membrane?

A

Near helicotrema (tip of cochlea) where the membrane is wide and flexible

Ex: 10,000 Hz

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5
Q

What is the ion distribution for endolymph found in scala media?

A

High [K+}

Low [Na+]

Bathes apical end of hair cells

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6
Q

What is the ion distribution for perilymph found in scala vestibuli and tympani?

A

Low [K+]

High [Na+]

Bathes basal end of hair cells

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7
Q

What CN transmits central axons from the primary auditory neurons of the spiral ganglion to the brainstem?

A

CN VIII (vestibulocochlear)

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8
Q

What type of receptors are hair cells?

A

Mechanoreceptors

  • Have afferent and efferent input
    • Not neuronal
  • Converts mechanical signals to electrical signals
    • Neural synapses on basal side
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9
Q

What motion of the hair cell stereocilia causes depolarization?

A

Deflection towards the Kinocilium

  • Rapid influx of K+ causes depolarization
  • Calcium channels open, releasing NT to basilar membrane
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10
Q

What motion of the hair cell stereocilia causes hyperpolarization?

A

Deflection away from the kinocilium

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11
Q

What neurotransmitter is released by the hair cells?

A

Glutamate

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12
Q

What channel on the stereocilia allows entry of K+?

A

TRPA1

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13
Q

What part of the cochlea is the stria vascularis located in?

What is its function?

A

Scala media

Maintains electrochemical properties of endolymph by pumping K+ in

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14
Q

What is the function of inner hair cells?

A

Primary source of auditory information

  • Arranged in a single layer.
  • Synapse with the peripheral terminal of a primary afferent sensory neuron
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15
Q

What is the function of the three rows of outer hair cells?

A
  • Act as amplifier
  • Boost mechanical vibrations of basilar membrane
  • Otoacoustic emissions: low-level sound emitted by the cochlea either spontaneously or evoked by an auditory stimulus
    • Originate in the superior olivary complex
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16
Q

What is the importance of otoacoustic emissions?

A

Check function of inner and middle ears in newborn hearing screen

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17
Q

What type of hair cells both send afferent neurons and receive efferent neurons?

A

Outer hair cells

18
Q

What is the function of the superior olivary nucleus?

A

Determines the direction from which a sound originates

19
Q

What neurons innervate outer hair cells?

A

Medial olivary complex neurons

20
Q

What neurons innervate inner hair cells?

A

Lateral olivary complex neurons

21
Q

What is the function of olivocochlear efferents?

A
  • Shifting response to higher sound levels
  • Decrease adaptation
  • Reduces the response to noise
  • Protect hair cells from damage to intense sounds
22
Q

What parts of the middle ear send efferents to the auditory system? From what cranial nerves?

A
  • Tensor Tympani to malleus (CN V)
  • Stapedius to stapes (CN VII)
23
Q

What is the main function of middle ear efferents?

A

Prevent damage: decrease transmission of sound (act at low frequencies)

24
Q

How does sound reach and leave the hair cells?

A
  1. Sound hits stapes, causing it to move.
  2. Scala vestibuli pressure falls below scala tympani pressure.
  3. Basilar membrane bows upward.
  4. Organ of corti shears toward hinge of tectorial membrane.
  5. Hair bundles of outer hair cells tilt toward their longer stereovilli.
  6. Transduction channels open in outer hair cells.
  7. Depolarization contracts the motor protein prestin.
  8. Contraction of outer hair cells accentuates upward movement of the basilar membrane (makes waves in endolymph).
  9. Endolymph waves beneath the tectorial membrane.
  10. Inner hair cells bend toward the longer stereovilli.
  11. Transduction channels open in the inner hair cells.
  12. Depolarization opens voltage gated Ca2+ channels.
  13. Synaptic vesicles fuse, releasing glutamate.
25
Q

What is the function of the dorsal cochlear nuclei?

A

Integrate acoustic information with somatosensory information to localize sound

26
Q

What is the function of the ventral cochlear nuclei?

A

Process temporal and spectral features of sound

27
Q

What is the function of the lateral superior olivary nucleus?

A

Generates a map of interaural intensity differences to localize source of sound

28
Q

What is the function of the medial superior olivary nucleus?

A

Generates a map of interaural time differences to localize sound

29
Q

What is the function of the inferior colliculus?

A
  • Suppresses information related to echoes, which would interfere with localization and arrives at a final estimation of localization of sound along the horizon.
  • Information about time and intensity differences converge into the IC to help create a precise origin of sound location along the horizon.
30
Q

What is the role of the medial geniculate nucleus of the thalamus in the auditory pathway?

A

Processing speech inflection

  • Lots of convergence from distinct spectral and temporal pathways
31
Q

What is the role of the primary auditory cortex in the auditory pathway?

A

Conscious perception of sound

  • Higher order processing of sound: volume, rate of frequency modulation, loudness
32
Q

What region of the primary auditory cortex responds to high frequency and low frequencies?

A

Rostral end responds to low frequency (apex of cochlea)

Caudal end responds to high frequency (base of cochlea)

33
Q

What areas are contained within the auditory (secondary) association cortex (A2)?

A

Broca’s and Wernicke’s Areas

  • Responds to more complex sounds (music) and identifying sounds and speech
34
Q

Damage to what structures causes sensorineural hearing loss?

A

Outer hair cells, especially at the base end (high frequency) of the cochlea

35
Q

Damage to what structures will cut off sensorineural auditory input to the CNS?

A

Inner hair cells

36
Q

What is a cochlear prosthesis?

A

Electrode array threaded through the cochlea to stimulate surviving nerve fibers and provide sound

37
Q

What types of rotation are detected by the horizontal, posterior, and anterior semicircular canals?

A
  • Horizontal: rotation in horizontal plane
    • think ice skating
  • Posterior: rotation backwards in the vertical plane (falling backwards)
    • trust exercise
  • Anterior: rotation forward in the vertical plane (falling forward)
38
Q

When falling backward, what is the reflex of the eye muscles?

A
  1. Posterior semicircular canal detects falling backward
  2. Superior Oblique Muscle is activated and inferior oblique muscle is inhibited
  3. Eyes move down to maintain gaze on horizon
39
Q

When falling forward, what is the reflex of the eye muscles?

A
  1. Anterior semicircular canal detects falling forward
  2. Superior Rectus Muscle is activated and inferior rectus muscle is inhibited
  3. Eyes move up to maintain gaze on horizon
40
Q

What is the function of the utricle?

A

Detects horizontal linear acceleration: forward and backward

41
Q

What is the function of the saccule?

A

Detects vertical linear acceleration: up and down

Year 1: 07. Neuro Exam 3 (16 decks)

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