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Vestibular System - CN VIII Flashcards

1
Q

The vestibular system consists of what 4 sections?

A

1) the membranous labyrinth and sensory receptor (endorgan)
2) cranial nerve VIII and its cell bodies (Scarpa’s ganglia)
3) vestibular nuclei which lie on the floor of the fourth ventricle at the junction of the medulla and pons, and
4) ascending and descending tracts.

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2
Q

What is the endorgan housed in?

A

the bony labyrinth (a series of cavities in the temporal bone)

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3
Q

What is the first role of the vestibular system? (3-fold)

A

1.As a sensory system, vestibular signals from the 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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4
Q

What is the second role of the vesitbular system? (3-fold)

A

Secondly, the vestibular system influences muscle tone in appendicular and axial muscles for control of postural support and balance (vestibulo-spinal and vestibulocollic reflexes).

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5
Q

What is the third role of the vestibular system? (3-fold)

A

The third role of the vestibular system is to provide conscious awareness of spatial orientation.

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6
Q

The peripheral endorgan in each bony labyrinth consists of a _______________________.

A

Membranous labyrinth

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7
Q

What is a membranous labyrinth?

A

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

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8
Q

The membranous labyrinth contains a fluid called:

A

endolymph

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9
Q

The membranous labyrinth is separated from the bone cavity within the ____________________________________________________by a fluid called __________________.

A

petrous part of the temporal bone (Bony labyrinth)

perilymph

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10
Q

The receptors of the vestibular apparatus are located in very specific sites within the ____________________.

A

membranous labyrinth

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11
Q

There are ______ receptor sites on each side, one in each of the three semicircular canals and two in the ____________ (otolith organs)

A

five

semicircular canals

vestibule

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12
Q

What are 2 otolith organs?

A

saccule and utricle

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13
Q

Semicircular canals =

A

three canals arranged at right angles to each other.

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14
Q

The horizontal canal is in a horizontal position when the head is:

A

flexed forward to 30 degrees.

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15
Q

The horizontal canal is activated with ________________ around the body axis.

A

rotation

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16
Q

The anterior and posterior canals are activated with rotation in an ______________________________ between the frontal and sagittal planes and work together on _____________ sides of body.

A

oblique orientation

opposite

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17
Q

Together, the semicircular canals perform the dynamic function of:

A

detecting angular velocity of the head in all planes

**especially important for stabilizing the eyes during head movement.

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18
Q

Function of semicircular canals: Canals are filled with?

A

enolylmph

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19
Q

Function of semicircular canals: Ampullae are located at the base of canals contain hair cells called?

A

crista

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20
Q

Function of semicircular canals: The hair cells are innervated by the peripheral ends of the:

A

vestibular nerve fibers

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21
Q

Function of semicircular canals: Hair cells protrude ______________ into gelatinous material called ______________.

A

upwards

cupula

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22
Q

Function of semicircular canals: Angular movement (rotation) causes the endolymph to lag behind (inertia) in the ______________ direction, causing displacement of the cupula, thereby ________________.

A

opposite

thereby moving the hair cells

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23
Q

Function of semicircular canals: Mechanical deflection of the hair cells produces a receptor potential that may either ________________________ or ______________________ the vestibular nerve that is ______________ active, with a resting discharge rate of ______________________________.

A

depolarize or hyperpolarize

tonically

100 to 300 spikes per second

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24
Q

Function of semicircular canals: The effect on the resting discharge rate depends on the _____________________________.

A

direction the hair cells bend

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25
Q

Function of semicircular canals: Each hair cell is made up of two types of projections ____________ (one) and __________(40-70).

A

kinocilium

stereocilium

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26
Q

Function of semicircular canals: Depolarization occurs when the stereocilium bend towards the ____________.

A

kinocilium

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27
Q

Function of semicircular canals: Hyperpolarization occurs when the stereocilium bend ______________ from the kinocilium.

A

away

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28
Q

Function of semicircular canals: Either an increase or a decrease in the firing of the already tonically active nerve therefore signals the direction of rotation. For example, with rotation around the body axis to the left, the hair cells in the left horizontal canal become ________________________________________________________.

A

more depolarized resulting in an increase in frequency of action potentials along the left vestibular nerve.

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29
Q

Function of semicircular canals: This left turning will also result in the hair cells in the right horizontal canal to become more ________________________________________________________________________

A

hyperpolarized resulting in a decrease in the frequency of action potentials along the right vestibular nerve.

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30
Q

Function of semicircular canals: The signal from the hair cells is temporary because of a __________________ action of the cupula, which restores it to its resting position. Therefore, the semicircular canals are ______________ receptors, with a response lasting 20 sec. or less.

A

spring-like

rapidly adapting

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31
Q

Function of semicircular canals: The semicircular canals are ___________ threshold (___________sensitive receptors), responding to very ______________ angular changes

A

low (HIGHLY sensitive receptors)

small

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32
Q

Function of semicircular canals: The response from the receptor is _____________.

A

graded

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33
Q

Graded =

A

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

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34
Q

Otolithic organs =

A

The utricle and the saccule make up the otolithic organ.

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35
Q

The function of the otoliths is to detect linear _______________________________________ of the head as well as encoding the ______________________ of the head with respect to gravity.

A

acceleration and deceleration

static position

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36
Q

The important role of the utricle and saccule then is to maintain the head ______________ in space and to modulate postural ________________ relative to the position of the ______________.

A

upright

muscle tone

head

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37
Q

Structurally, the utricle and saccule are two large chambers located between the _____________________ and _____________________.

A

semicircular canals and the cochlear duct.

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38
Q

Both ends of the semicircular canals are continuous with the ___________.

A

utricle

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39
Q

The utricle and saccule are also filled with _______________.

A

endolymph

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40
Q

Overproduction of endolymph results in:

A
  • auditory disturbances
  • severe vertigo
  • nausea and
  • nystagmus
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41
Q

nystagmus is also know as:

A

a condition known as Meniere’s disease

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42
Q

What is the sensory organ on the wall of the utricle and saccule is called?

A

macula

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43
Q

The macula is covered with a _______________ layer with embedded small crystals of calcium carbonate called _______________.

A

gelatinous

otoconia

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44
Q

Hair cells project into the _____________________.

A

gelatinous layer

45
Q

As with the hair cells in the ampulla of the semicircular canals, these hair cells synapse at their __________ with the _______________________________.

A

base

sensory axons of the vestibular nerve

46
Q

The macula of the utricle is positioned in the __________________ plane when the head is upright, while the macula of the saccule is ________________.

A

horizontal

vertical

47
Q

The hair cells in both organs (utricle and saccule) are arranged such that head tilt will result in _______________ discharge from specific parts of the _____________ and ______________ discharge from other parts of the ____________________________.

A

increased

macula

decreased

same macula

48
Q

This complex arrangement allows for the utricle and saccule to be sensitive to _______________________. Therefore, these receptors are _____________________ and continue to respond at all times.

A

static head tilt in multiple planes

nonadapting

49
Q

The anatomical relationship between the utricle, the macula, and the semicircular canals is clinically significant in a condition called:

A

benign paroxysmal positional vertigo (BPPV).

50
Q

In BPPV, otoconia from the macular organs ______________________ into the semicircular canals, most commonly the ____________ canal.

A

break loose and float

posterior

51
Q

With specific head motions, this “debris” stimulates (______________________________) the hair cells in the _____________ and produces symptoms of ______________.

A

(increases the inertia of the cupula)

ampulla

vertigo [characteristic nystagmus (see below), and may also be accompanied by nausea]

52
Q

The vestibular portion of the 8th cranial nerve is a ___________ nerve with the cell bodies forming ________________ near the ____________ auditory meatus.

A

bipolar

Scarpa’s ganglion

internal

53
Q

After leaving the ganglion, the central processes of the vestibular nerve fibers join with ______________ fibers and travel in the internal auditory canal, along with the ____________ nerve, passing through ________________ bone into the posterior fossa, entering the brainstem at the ____________________ junction.

A

cochlear

facial

temporal

pontomedullary

54
Q

Primary vestibular afferents synapse on _________________________ in the vestibular nuclei of the brainstem and in the ____________________.

A

second order neurons

cerebellum

55
Q

The vestibular nuclei form a ________________ shaped complex located in each side of the brainstem in the _________________________.

A

diamond

floor of fourth ventricle

56
Q

The vestibular nuclei are surrounded by the ___________________ laterally, the ____________________ medially, the _______________________ rostrally, and the _________________________________ ventrally.

A

inferior cerebellar peduncle

pontine reticular formation

middle cerebellar peduncle

nucleus and spinal tract of the trigeminal nerve

57
Q

The four main vestibular nuclei are the: .

A

SUPERIOR, LATERAL, MEDIAL, and DESCENDING (inferior or spinal) nuclei.

58
Q

Nucleus Y is important from an _________________ point of view. There are actually a number of others we won’t deal with. There is ____________________ of sensory input from multiple vestibular receptors (e.g. canals and otolith) onto __________________ order neurons in some areas of the nuclei, while in other locations there is clear _________________ organization of input from specific endorgans to specific nuclear areas.

A

integrative

convergence

second

topographic

59
Q

For example, the projections to the superior nucleus are primarily from the _______________________ and terminate in the _______________ in a topography specific to the canals.

A

semicircular canals

nucleus

60
Q

Surrounding brainstem areas support the vestibular nuclei in the task of controlling:

A

eye movements in the horizontal and vertical planes

61
Q

For the most part, each nucleus receives input from both the __________________________________.
The exception is the lateral nucleus that receives the majority of its vestibular input from the _____________.

A

semicircular canals and the otoliths.

utricle

62
Q

Fibers from the cerebellar ________________ lobe and ________________ nucleus (discussed with Cerebellum) terminate in _________________________.

A

floculonodular lobe and
fastigial nucleus

all four vestibular nuclei

63
Q

Afferents to the vestibular nuclei from the eyes as well as from the neck and limbs are relayed through the _________________ and help modulate _______________________________________ reflexes.

A

cerebellum

vestibulo-OCULAR, vestibuloCOLLIC and vestibuloSPINAL

64
Q

For example, the cerebellum exerts influence on limb extensor tone ________________ through tonic inhibition of the _________________

A

indirectly

lateral vestibular nucleus.

65
Q

The vestibular nuclei are extensively connected to each other and to adjacent and distant structures along the ______________.

A

neuraxis

66
Q

Ascending projections to the motor nuclei of the extraocular eye muscles in the ___________ and ___________ travel ______________________________ that runs in the floor of the fourth ventricle.

A

pons and midbrain

via the medial longitudinal fasciculus (MLF

67
Q

Projections also descend in the MLF, as well as in the lateral vestibulospinal tract _________________, and in the medial vestibulospinal tract to _______________________ of the spinal cord.

A

IPSILATERALLY

BOTH SIDES

68
Q

The fastigial nuclei and flocculonodular lobe of the cerebellum _________________ extensive input from the vestibular nuclei. The entire _________________, receives input from the vestibular nuclei where it is integrated with somatosensory mapping from the _______________________.

A

receive

vermis

limbs and trunk

69
Q

What is the vermis?

A

a principal region of the spinocerebellum

70
Q

Ascending vestibulo-thalamo-cortical projections serves the third function of the vestibular system involving ___________________________.

A

perception of self in space

71
Q

Traveling in the reticular formation adjacent to the MLF and the __________________ (auditory pathway), _____________ fibers from the lateral and superior vestibular nuclei terminate in the thalamus.

A

lateral lemniscus

secondary

72
Q

Thalamocortical projections to regions of the parietal lobe (association areas) produce a __________________________________________. This does not project to _________________________cortex therefore there is no perception of specific location in space (proprioception).

A

subjective sensation of rotation and body displacement.

primary somatosensory

73
Q

The peripheral vestibular endorgan is supplied by the ________________ artery, which most often is a branch of the ___________________________________, but occasionally branches directly off of the basilar artery.

A

labyrinthine

anterior inferior cerebellar artery (AICA)

74
Q

The labyrinthine a. has no anastomotic network and is highly susceptible to ________________.

A

ischemia

75
Q

Ischemia of the labyrinthine a. results in:

A

hearing loss and sudden onset of vertigo.

76
Q

The area of the brainstem containing the vestibular nuclei is supplied by the:

A

posterior inferior cerebellar artery (PICA) (caudal aspects) and the anterior inferior cerebellar artery (AICA) (rostral aspects).

77
Q

Specific clinical syndromes with symptoms of vestibular system involvement occur with occlusions of the _______________ artery, the ________________ artery, AICA and PICA.

A

basilar, labyrinthine and AICA, PICA

78
Q

The purpose of the vestibulo-ocular reflex (VOR) is to:

A

maintain stable vision during head motion

79
Q

When the head is turned to the left, the _____________ vestibular nerve ______________ firing and the ________________________ firing (as explained above).

A

When the head is turned to the left, the LEFT vestibular nerve INCREASES firing and the RIGHT DECREASES firing (as explained above).

80
Q

These changes in firing rates influence discharge from the medial vestibular nuclei, which in turn sends signals via the __________ to activate RIGHT _____________________ (right lateral rectus) and LEFT _______________________ (left medial rectus).

A

MLF

abducens nucleus

oculomotor nucleus

81
Q

Inhibitory impulses are sent to nuclei that control the antagonistic muscles that result in a lateral __________________ eye movement towards the right called nystagmus.

A

compensatory

82
Q

Nystagmus is characterized by:

A

a slow phase away from midline (caused by the vestibular input) and a fast phase (as the eyes rebound towards midline).

83
Q

The direction of nystagmus is named by the direction of the _______ phase because it is more readily identified.

A

fast

84
Q

For example, in the above case, nystagmus would be called left beating.

A

For example, in the above case, nystagmus would be called left beating.

85
Q

Eye movements are parallel to the plane of the _________ that has been stimulated.

A

canal

86
Q

Nystagmus is a normal response to ______________ head velocity. However there are also a whole host of nystagmus responses that are considered pathologic and relate to lesions either in the _________________ vestibular organ or the ______________ vestibular nuclei or pathways.

A

rotatory

peripheral

central

87
Q

The vestibulo-spinal reflex Influences ____________ extensors, primarily of the ________________ musculature and the ___________________.

A

ipsilateral

axial

lower extremities

88
Q

What give rise to the lateral vestibulospinal pathway?

A

Output of the lateral vestibular nucleus gives rise to the lateral vestibulospinal pathway.

89
Q

Axons of vestibulospinal pathway are seen in cross section as they pass through the ____________________ nucleus.

A

inferior vestibular

90
Q

Where does the vestibulocollic reflex get its name from?

A

the musculature of the neck.

91
Q

Remember identifying longus colli muscles on the anterior surface of the cervical vertebrae. This is a _________________ pathway that is most active through the __________________________ regions of the spine.

A

bilateral

cervical AND thoracic

92
Q

The primary source of these fibers is from the ________________________ of both sides.

A

medial vestibular nuclei

93
Q

When considering the bilateral nature of this pathway, consider that while one side of the system is sending excitatory signals to the ______________ of the __________________________________ on both sides, the other side is carrying signals that are decreasing, but are also going to both sides. This is an important concept since the control of axial musculature is dependent on this balance of increasing and decreasing signals.

A

extensors

upper extremity and axial musculature

94
Q

Major Inputs of superior vestibular nuclei =

A

semicircular canals

cerebellum

contralateral v. nuclei

95
Q

Major Inputs of lateral (Deiter’s) vestibular nuclei =

A

cerebellum

utricle and saccule

semicircular canals
(minimal)

96
Q

Major Inputs of medial vestibular nuclei =

A

semicircular canals
1o horizontal

utricle and saccule

cerebellum

contralateral v. nuclei

reticular formation

97
Q

Major Inputs of inferior (spinal or descending) vestibular nuclei =

A

utricle and saccule

cerebellum

98
Q

Major Inputs of Nucleus Y vestibular nuclei =

A

utricle and saccule

99
Q

Major outputs of superior vestibular nuclei =

A

MLF to oculomotor nuclei

Cerebellum

dorsal pontine RF

adjacent RF

thalamus

100
Q

Major outputs of lateral (Deiter’s) vestibular nuclei =

A

ipsilateral lateral vestibulo-spinal tract

thalamus

101
Q

Major outputs of medial vestibular nuclei =

A

bilateral medial vestibulo-spinal tract

MLF to oculomotor nuclei

Cerebellum

adjacent RF

102
Q

Major outputs of inferior (spinal or descending) vestibular nuclei =

A

Cerebellum

RF

contralateral v. nuclei

103
Q

Major outputs of Nucleus Y vestibular nuclei =

A

RF

contralateral v. nuclei

104
Q

Function of superior vestibular nuclei =

A

maintain eye position during head movement

arousal

conscious awareness of spatial orientation

105
Q

Function of lateral (Deiter’s) vestibular nuclei =

A

facilitates antigravity limb tone through vestibulospinal reflexes

spatial orientation

106
Q

Function of medial vestibular nuclei =

A

coordination of eye, head and neck movements

gaze holding in the horizontal plane

head control & stability – head turning and righting

107
Q

Function of inferior (spinal or descending) vestibular nuclei =

A

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

108
Q

Function of Nucleus Y vestibular nuclei =

A

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

704 (22 decks)

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