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Brain and Behavior Exam 2 > Lec 20 Vestibular System > Flashcards

Lec 20 Vestibular System Flashcards

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1
Q

What two things does the vestibular system sense?

A

head motion and head position in space by supplying info about

  • angular acceleration via semicircular canals
  • linear acceleration via otolith organs
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2
Q

To what effector pathways does vestibular system distribute its sensory info?

A

to regions that

  • control eye movements/maintain stable faze during head movement [vestibulo-ocular reflex + otolith-ocular reflex]
  • postural equilibrium [vestibulo-spinal tracts]
  • maintain head stability during body movement [vestibulo-colic reflex]
  • autonomic function [vestibulo-autonomic reflex]
  • conscious perception of balance [vestibulo-thalamo-cortical projections ]
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3
Q

What is result of damage to vestibular system?

A
  • poor balance, dizziness, vertigo, motion sickness, fainting
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4
Q

What is structure of semicircular canals?

A
  • bony canals oriented in orthoganol planes [horizontal, anterior, posterior]
  • filld with perilymph + contain membranous chambers filled with endolymph
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5
Q

What is the ampulla of semicircular canal?

A
  • swelling at one end of each canal
  • the structure from which sensory epithelium [crista ampullaris] with hair cells and support cells hangs [like a swing/hammock from 1 wall of ampulla to the other]
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6
Q

What is the cupula?

A

dense gelatinous solution from which hair cell bundles protrude

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7
Q

What happens in semicircular canal when there is angular head acceleration?

A
  • endolymph fluid in the membranous chambers moves –> differentially displaces cupula to exert force on hair cell stereocilia
  • in turn depolarizes or hyperpolarizes hair cell receptor potential [which activates or inhibits sensorineural transduction]
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8
Q

What are the two otolith organs? purpose of each?

A 
saccule = vertical acceleration
utricle = horizontal acceleration
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9
Q

What is structure of otolith organs?

A
  • filled with endolymph, surrounded by perilymph

- sensory epithelial with hair/support cells oriented horizontally in utricle or vertically in saccule

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10
Q

Where is cochlea located with respect to semicircular canals?

A

cochlea is more anterior/medial than semicircular

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11
Q

Which of the semicircular canals is most superior? most inferior?

A 
superior = anterior
inferior = posterior
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12
Q

What is the macula?

A

the sensory epithelial of the otolith organs

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13
Q

what are otoconia?

A

calcium-carbonate crystals that cover the otolithic membrane

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14
Q

What happens to otoconia in linear head accelerations?

A

they are displaced –> causes shear force on stereociliarly bundles that activates or inhibits sensorineural transduction via changes in potential

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15
Q

What is equivalent to the crista ampullaris in the cochlea?

A

basilar membrane

both are sensory sheets which contain hair cells

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16
Q

What can damage hair cells?

A
  • trauma
  • vascular disease
  • aminoglycoside toxicity
  • normal aging they diminish in number
17
Q

What is contained in a hair bundle? how does it work?

A
  • contains many sterocilia [St] and a single kinocilium [Ki] that is bigger
  • displacement of stereocilia toward kinocilium –> depolarization
  • displacement of stereocilia away from kinocilium –> hyperpolarization
18
Q

What are the 3 planes of the semicircular canals?

A 
horizontal = both L and R in same plane, horizontal but skewed 30 degrees above earth horizontal
RALP = right anterior, left posterior
LARP = left anterior, right posterior
19
Q

What does the saccule detect?

A

linear acceleration in vertical plane

20
Q

what does the utricle detect?

A

linear acceleration in horizontal plane

21
Q

What are the maculae? its equivalent in the other part of the vestibular system?

A

sensory sheets of the otolith organs

equivalent in the semicircular canals = crista ampullaris

22
Q

Where are the cell bodies located for both canal and otolith primary afferents?

A

scarpa’s ganglion in temporal petrous bone

23
Q

Where do the vestibular nerve fibers from canal/otolith terminate?

A

the vestibular nuclei in the medulla/caudal pons

4 –> superior, inferior, medial, lateral

24
Q

What is the path from inner ear to vestibular cortex [for conscious perception of balance]?

A
  • canal/otolith bipolar afferent receive input from hair cells and form cochlear portion of CN VIII
  • terminate in vestibular nuclei in medulla and caudal pons [plus a few in cerebellum]
  • superior/lateral vestibular nuclei neurons cross midline –> VP of thalamus
  • VP –> vestibular cortex in parietal lobe just posterior to S1 somatosensory cortex
25
Q

What is blood supply to vestibular nuclei?

A

PICA

26
Q

What structures make up the vestibular cortex?

A

2 places

  • posterior parietal cortex
  • cortex posterior to primary somatosensory cortical face area [just posterior to postcentral gyrus]
27
Q

What is the vestibulo-ocular reflex [VOR]?

A
  • compensatory eye movement that stabilizes gaze during head rotation
  • afferent = detection of head movement by vestibular CN 8
  • efferent= oculomotor/abducens in direction opposite to that of head movement [coordinated lateral rectus + medial rectus firing]
28
Q

What is the path of afferent vestibulo-ocular reflex [VOR]?

A
  • CN8 carrying fibers from horizontal semicircular canals synapse on medial vestibular nucleus
  • medial vestibular nucleus axons
29
Q

what is the brainstem arc of the VOR?

A
  • axons from medial vestibular nucleus project to contralateral CN VI nucleus –> excites both contralateral lateral rectus motor neuron + interneuron that synapse in ipsilateral CN III nucleus via MLF
  • axons from medial vestibular also project to ipsilateral CN VI nucleus where inhibit ipsilateral lateral rectus efferents so no excitation of contralateral medial rectus
30
Q

What are the two descending motor tracts from the vestibular nuclei? function?

A
  1. lateral vestibulospinal tract [LVST]
    - balance + postural control, influence motor neurons in spinal cord
  2. medial vestibulospinal tract [MVST] [= vestibulo-colic path]
    - maintains stability of head on neck as body moves
31
Q

Where does the lateral vestibular nucleus project to? terminate? function?

A
  • all levels of ispilateral spinal cord via lateral vestibulospinal tract
  • terminates on medial motor neurons
  • activates antigravity muscles
  • cerebellum influences posture in part by modulating activity of vestibular nuclei
32
Q

Where does the MVST project to? function?

A
  • sends bilateral projects to cervical and upper thoracic spinal cord via medial longitudinal fasciculus [MLF]
  • in medulla MLF is just dorsal to tectospinal tract
  • regulates head pos by activating neck muscles in response to canal stimulation [vestibulo-colic reflex] –> ex. lunge forward activates neck extension
33
Q

What is the vestibulo-sympathetic reflex?

A

VSR = vestibular otolith organs provide direct input to allow for adjustments in BP during locomotion and changes in body position

  • vestibular nuclei receive primarily vestibular input and send projections to brainstem presympathetic control centers

from there –> path converges with baroreflex

34
Q

What can commonly happen in VSR dysfunction?

A
  • orthostatic hypotension [common in elderly]
35
Q

Which of the functional paths of vestibular system are under cerebellar control?

A

all 5

36
Q

What is the crista ampullaris?

A

sensory sheet in ampulla containing hair cells

- the swing/hammock in the ampulla

Brain and Behavior Exam 2 (21 decks)

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