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S2 Neuroscience > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

vestibular system consists of…

A

1) membranous labyrinth and sensory receptor (endorgan)
- housed in in the bony labyrinth (series of cavities in the temporal bone)
2) cranial nerve VIII
3) vestibular nuclei
4) ascending and descending tracts

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2
Q

where are the vestibular nuclei located

A

lie on the floor of the 4th ventricle at the junction of the medulla and pons

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3
Q

vestibular system functions

A

sensory system
influences muscle tone in appendicular and axial muscles for control of postural support and balance (vestibulo-spinal and vestibulocollic reflexes)
provides conscious awareness of spatial orientation

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4
Q

vestiublar system: sensory system function

  • vestibular signals come from…
  • signals generated by…
  • regulate…
A

vestibular signals from labyrinths
generated by head movement
regulate eye position in the orbit during head movements in order to assure a stable image on the retina (vestibulo-ocular reflex)

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5
Q

membranous labyrinth

-what is it

A

series of tubes made of fine membranes that contain the peripheral sensory receptors (hair cells) of the vestibular system

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6
Q

membranous labyrinth contains a fluid called…

A

endolymph

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7
Q

membranous labyrinth

-separated from _____ by _____

A

separated from the bone cavity within the petrous part of the temporal bone (bony labyrinth) by a fluid called perilymph

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8
Q

vestibular appartus receptors

-location

A

very specific sites within the membranous labyrinth
five sites on each side
-one in each of the three semicircular canals
-two in the vestibule

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9
Q

the vestibule is composed of…

A

otolith organs

  • saccule
  • utricle
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10
Q

semiciruclar canals

  • how many
  • arrangement
  • names
A

3
arranged at right angles to each other
horizontal, anterior, posterior

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11
Q

horizontal canals

  • orientation
  • activated with…
A

in horizontal plane when the head is flexed forward 30 degrees
activated with rotation around the body axis

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12
Q

anterior and posterior canals

-activated with…

A

activated with rotation in an oblique orientation between the frontal and sagittal planes
work together on opposite sides of body

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13
Q

semicircular canals

-overall function

A

perform the dynamic function of detecting angular velocity of the head in all planes
especially important for stabilizing the eyes during head movement

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14
Q

semicurcular canals

-filled with

A

endolymph

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15
Q

semicurcular canals: ampullae

  • location
  • contain
A

located at base of canals

contain hair cells called crista

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16
Q

semicurcular canals: crista (hair cells)

  • innervated by…
  • protrude…
A

peripheral ends of the vestibular nerve fibers

protrude upwards into a gelatinous material called the cupula

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17
Q

semicurcular canals

  • angular movement (rotation) causes the endolymph to…
  • -as a result…
A

endolymph lags behind (inertia) in the opposite direction

causes displacement of the cupula, thereby moving the hair cells

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18
Q

semicurcular canals

-mechanical deflection of the hair cells produces a…

A

receptor potential that may either depolarize or hyperpolarize the vestibular nerve that is tonically active

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19
Q

semicurcular canals

-vestibular nerve resting discharge rate

A

100 to 300 spikes per second

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20
Q

semicurcular canals

-effect on the resting discharge rate depends on…

A

direction the hair cells bend

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21
Q

semicurcular canals

  • each hair cell is made up of…
  • depolarization occurs when…
  • hyperpolarization occurs when…
A

two types of projections
-kinocilium (one)
-stereocilium (40-70)
depolarization occurs when the stereocilium bend towards the kinocilium
hyperpolarization occurs when the stereocilium bend away from the kinocilium

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22
Q

semicurcular canals

-example of how direction of rotation is determined by the vestibular nerve (L rotation)

A

with rotation around the body axis to the left, the hair cells in the L horizontal canal become more depolarized, resulting in an increase in frequency of action potentials along the L vestibular nerve
hair cells in the R horizontal canal become more hyperpolarized, resulting in a decrease in the frequency of action potentials along the R vestibular nerve

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23
Q

semicurcular canals

  • signal from hair cells is _____ due to _____
  • therefore, semicircular canals are _____ receptors, with a response lasting howlong?
A

signal from the hair cells is temporary because of a spring-like action of the cupula, which restores it to its resting position
the semicircular canals are rapidly adapting receptors, with a response lasting 20 seconds or less

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24
Q

semicurcular canals

  • threshold level
  • -as a result…
A 
low threshold (highly sensitive receptors)
respond to very small angular changes
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25
Q

semicurcular canals

  • response from the rector is _____
  • i.e.
A

response from receptor is graded

i.e. as velocity increases, more hair cells are activated, each to a greater degree

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26
Q

otolithic organs

  • functions
  • important role as a result of their functions
A

detect linear acceleration and deceleration of the head
encode the static position of the head with respect to gravity
important role
-maintain the head upright in space and modulate postural muscle tone relative to the position of the head

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27
Q

structurally, what are the utricle and saccule

A

two large chambers located between the semicircular canals and cochlear duct

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28
Q

both ends of the semicircular canals are continuous with the…

A

utricle

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29
Q

utricle and saccule are filled with…

A

endolymph

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30
Q

utricle and saccule

-overproduction of endolymph results in…

A

Meniere’s disease

  • auditory disturbances
  • severe vertigo
  • nausea
  • nystagmus
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31
Q

name of the sensory organ on the wall of the utricle and saccule

A

macula

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32
Q

macula

  • covered with…
  • hair cells project into…
A

covered with a gelatinous layer with embedded small crystals of calcium carbonate called otoconia
hair cells project into the gelatinous layer

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33
Q

macula hair cells

-synapse with…

A

synapse at their base with the sensory axons of the vestibular nerve (same as with the hair cells of the ampulla)

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34
Q

when the head is upright, what is the positioning of the…

  • macula of the utricle
  • macula of the saccule
A

utricle
-macula in horizontal plane
saccule
-macula vertical

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35
Q

why is the complex arrangement of macula in the utricle and saccule necessary
-these receptors are _____

A

allows for the utricle and saccule to be sensitive to static head tilt in multiple planes
receptors are non-adapting and continue to respond at all times

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36
Q

the anatomical relationship between the utricle, macula, and semicircular canals is clinically significant in which condition

A

benign paroxysmal positional vertigo (BPPV)

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37
Q

BPPV

  • pathophysiology
  • symptoms
A

otoconia from the macular organs break loose and float into the semicircular canals, most commonly the posterior canal
with specific head motions, this “debris” stimulates (increases the inertia of the cupula) the hair cells in the ampula and produces symptoms of vertigo, characteristic nystagmus, and sometimes nausea

38
Q

vestibular portion of 8th cranial nerve

  • type of nerve
  • cell bodies form _____ near _____
A

bipolar nerve

cell bodies form Scarpa’s ganglion near the internal auditory meatus

39
Q

vestibular portion of 8th cranial nerve

-after leaving Scarpa’s ganglion, the central processes….

A

join the cochlear fibers
travel in the internal auditory canal, along with the facial nerve, pass through temporal bone into the posterior fossa, and enter the brainstem at the pontomedullary junction

40
Q

vestibular nuclei

-primary vestibular afferents synapse on…

A

2nd order neurons in the vestibular nuclei of the brainstem and in the cerebellum

41
Q

vestibular nuclei

-form a _____

A

diamond-shaped complex located in each side of the brainstem in the floor the 4th ventricle

42
Q

vestibular nuclei

-surrounded by….

A

inferior cerebellar peduncle laterally
pontine reticular formation medially
middle cerebellar peduncle rostrally
nucleus and spinal tract of the trigeminal nerve ventrally

43
Q

vestibular nuclei

-main nuclei

A

superior
lateral
medial
descending (inferior and spinal)

44
Q

vestibular nuclei

-nucleus Y importance

A

integrative

45
Q

vestibular nuclei

-different methods of organization

A

in some areas, there is convergence of sensory input from multiple vestibular receptors (e.g. canals and otolith) onto 2nd order neurons
in other locations, there is clear topographic organization of input from specific endorgans to specific nuclear areas

46
Q

vestibular nuclei

-_____ areas support the vestibular nuclei in the task of _____

A

surrounding brainstem areas support the vestibular nuclei in the task of controlling eye movements in the horizontal and vertical planes

47
Q

vestibular nuclei

  • in general, each nucleus receives input from…
  • what is the exception
A

both the semicircular canals and otoliths
exception
-lateral nucleus receives majority of its vestibular input from the utricle

48
Q

fibers from the cerebellar flocculonodular lobe and fastigial nucleus terminate in _____

A

all four vestibular nuclei

49
Q

afferents to the vestibular nuclei from _____ are relayed through _____
-what is their function

A 
from the eyes as well as from the neck and limbs
relayed through the cerebellum
help modulate
-vestibulo-ocular
-vestibulocollic
-vestibulospinal reflexes
50
Q

how does the cerebellum exert influence on limb extensor tone

A

indirectly through tonic inhibition of the lateral vestibular nucleus

51
Q

vestibular nuclei: ascending projections

  • to the…
  • travel via…
A

to the motor nuclei of the extraocular eye muscles in the pons and midbrain
tarvel via the MLF that runs in the floor of the fourth ventricle

52
Q

vestibular nuclei: descending projections

  • travel via…
  • travel to…
A

via

  • MLF
  • lateral vestibulospinal tract ipsilaterally
  • medial vestibulospinal tract to both sides of the spinal cord
53
Q

the _____ and _____ of the cerebellum receive extensive input from the vestibular nuclei

A

fastigial nuclei

flocculonodular lobe

54
Q

vermis

  • what is it
  • receives input from…
  • function
A

principal region of the spinocerebellum
receives input from the vestibular nuclei
info is integrated with somatosensory mapping from the limbs and trunk

55
Q

what serves the third function of the vestibular system involving perception of self in space

A

ascending vestribulo-thalamo-cortical projections

56
Q

ascending vestibulo-thalamo-cortical projections

  • travel in _____ adjacent to _____
  • what fibers carry this information
  • terminate in…
A

travel in reticular formation adjacent to the MLF and lateral lemniscus (auditory pathway)
carried by secondary fibers from the lateral and superior vestibular nuclei
terminate in thalamus

57
Q

ascending vestibulo-thalamo-cortical projections: thalamocortical projections

  • project to
  • function
A

project to regions of the parietal lobe (association areas)

produce a subjective sensation of rotation and body displacement

58
Q

ascending vestibulo-thalamo-cortical projections: thalamocortical projections

  • does not project to…
  • why is this impoortatn?
A

does not project to primary somatosensory cortex

therefore there is no perception of specific location in space (proprioception)

59
Q

peripheral vestibular endorgan blood supply

A

labyrinthine artery

  • most often a branch of the AICA
  • occasionally branches directly off of the basilar artery
60
Q

labyrinthine artery ischemia

  • how possible is it?
  • results in…
A

highly susceptible to ischemia

results in hearing loss and sudden onset of vertigo

61
Q

area of brainstem containing the vestibular nuclei blood supply

A

PICA (caudal aspects) AICA (rostral aspects)

62
Q

area of brainstem containing the vestibular nuclei

-specific clinical syndromes with symptoms of vestibular system involvement occur with occlusitons of the…

A

basilar artery
labyrinthine artery
AICA
PICA

63
Q

vestibulo-ocular reflex (VOR)

-function

A

maintain stable vision during head motion

64
Q

VOR

-describe the reflex

A

when head is turned to the left, the L vestibular nerve increases firing and right decreases firing
these changes in firing rates influence discharge from the medial vestibular nuclei, which in turn sends signals via the MLF to activate R abducens nucleus (R lateral rectus) and L oculomotor nucleus (L medial rectus)
inhibitory impulses are sent to nuclei that control the antagonistic muscles that result in a lateral compensatory eye movement towards the right called nystagmus

65
Q

nystagmus

  • characterized by…
  • nystagmus named by direction of…
A

slow phase away from midline (caused by vestibular input) and a fast phase as eyes rebound towards midline
named by direction of fast phase because it is more readily identified

66
Q

in the VOR example, what would we call that nystagmus?

A

left beating

67
Q

eye movements are parallel to the plane of ____

A

the canal that has been stimulated

68
Q

is nystagmus normal?

A

yes, it is a normal response to rotatory head velocity

69
Q

a pathologic nystagmus is doe to lesions either in the _____ or _____

A

peripheral vestibular organ

central vestibular nuclei or pathways

70
Q

vestibulo-spinal reflex

-influences…

A

ipsilateral extensors

-primarily of the axial musculature and the LE (anti-gravity) muscles

71
Q

output of the lateral vestibular nucleus gives rise to…

A

lateral vestibulospinal pathway

72
Q

lateral vestibulospinal pathway

-axons are seen in cross section where?

A

as they pass through the inferior vestibular nucleus

73
Q

vestibulo-collic reflex

-how does it get its name

A

from the musculature of the neck

74
Q

vestibulo-collic reflex

  • uni- or bilateral?
  • most active through….
A

bilateral

most active through the cervical and upper thoracic regions of the spine

75
Q

vestibulo-collic reflex

-primary source of these fibers is from…

A

medial vestibular nuclei of both sides

76
Q

vestibulo-collic reflex

  • while one side of the system is sending _____ signals to _____, the other side is carrying signals that _____
  • why is this concept important?
A

while one side is sending excitatory signals to the extensors of the UE and axial musculature on both sides, the other side is carrying signals that are decreasing, but are also going to both sides
important concept since the control of axial musculature is dependent on this balance of increasing and decreasing signals

77
Q

superior vestibular nucleus

-major input

A

semicircular canals
cerebellum
contralateral vestibular nuclei

78
Q

superior vestibular nucleus

-major output

A 
MLF to oculomotor nuclei
cerebellum
dosal pontine RF
adjacent RF
thalamus
79
Q

superior vestibular nucleus

-function

A

maintain eye position during head movement
arousal
conscious awareness of spatial orientation

80
Q

lateral vestibular nucleus (Deiter’s)

-major input

A

cerebellum
utricle and saccule
semicircular canals (minimal)

81
Q

lateral vestibular nucleus

-major output

A

ipsilateral lateral vestibulo-spinal tract

thalamus

82
Q

lateral vestibular nucleus

-function

A

facilitates antigravity limb tone through vestibulospinal reflexes
spatial orientation

83
Q

medial vestibular nucleus

-major input

A 
semicircular canals - primary horizontal
utricle and saccule
cerebellum
contralateral vestibular nuclei
reticular formation
84
Q

medial vestibular nucleus

-major output

A

bilateral medial vestibulo-spinal tract
MLF to oculomotor nuclei
cerebellum
adjacent RF

85
Q

medial vestibular nucleus

-function

A

coordination of eye, head and neck movements
gaze holding in the horizontal plane
head control and stability - head turning and righting

86
Q

inferior (spinal or descending) vestibular nucleus

-major input

A

utricle and saccule

cerebellum

87
Q

inferior (spinal or descending) vestibular nucleus

-major output

A

cerebellum
RF
contralateral vestibular nuclei

88
Q

inferior (spinal or descending) vestibular nucleus

-function

A

integrates vestibular signals from two sides with signals from cerebellum and RF

89
Q

nucleus Y

-major input

A

utricle and saccule

90
Q

nucleus Y

-major output

A

RF

contralateral vestibular nuclei

91
Q

nucleus Y

-function

A

integrates vestibular signals from two side with signals from cerebellum and RF

S2 Neuroscience (25 decks)

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