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Vestibular Flashcards

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1
Q

When does the vestibular system mature in size?

A

By 17 to 19 weeks of gestation

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2
Q

What are the two sections of the vestibular system within the Bony and membranous labyrinths?

A

SCC

vestibule

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3
Q

Where is the vestibular apparatus located?

A

posterior to the cochlea in the petrous portion of the temporal bone

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4
Q

Provide information regarding the fluid found in the membranous labyrinth.

A

Endolymph

Created by the stria vasculairs (continuous with the scala media) and transmitted to the vestibular system by the ductus reuniens of the Hensen

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5
Q

The perilymph fills what area of the labyrinth? What is its function?

A

Fills the space b/t the membranous and bony labyrinth.

Works to provide a cushion between the two areas.

Supplied by the subarachnoid space via the perilymphatic duct.

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6
Q

What type of motion do the SCCs detect?

A

Angular motion

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7
Q

RALP regarding the excitatory/inhibitory relation for SCC?

A

right anterior
left posterior

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8
Q

If the left anterior is excited, what happens to its pair?

A

right posterior is inhibited

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9
Q

LARP regarding the excitatory/inhibitory relation for SCC?

A

left anterior
right posterior

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10
Q

What are the sensory organ for the SCC?

A

Crista ampullaris

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11
Q

Where does the crista ampullaris sit?

A

perpendicular to each other and are in the enlargement at the base of the canal called ampulla

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12
Q

How would you describe the ampulla?

A

It is the enlargement at the base of the canal that houses the crist ampullaris

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13
Q

Describe the cupula

A

Has the same specific gravity as the surrounding endolymph

gelatinous composition

extends to the “roof” of the SCC and separates the endolymph of SCC from the endolymph of the utricle

*Function:
Prevents endolymph from moving freely in the canal, but is elastic, so it will bend slightly in either direction

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14
Q

Type I and II HCs

A

Resting charge of -40 mV

Stereocilia contain tiplinks

Calcium and K+ channels

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15
Q

Type I HCs

A

more responsive within a small area of sensory epithelium

flask-shaped

Crest of crist ampullaris and striola of macula

Calyx to afferent

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16
Q

Type II HCs

A

react to stronger stimuli over the sensory epithelium

cylindrical shaped

Small bouton afferent
Efferents synapse directly to cells

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17
Q

What are the four parts of the crista ampullaris?

A

Cupulla

Type I and II HCs

Stereocilia and Kinocilium
*Project through the crista and embedded in the cupula
*Formed like haystacks

Afferent nerve endings
*projecting to the vestibular nuclei in the brainstem

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18
Q

What motion does the vestibule detect?

A

Linear

up/down, front/back, head tilt, gravity

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19
Q

What two organs are found in the vestibule?

A

utricle

saccule

*Neither is sensitive to constant velocities

Both otolithic organs

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20
Q

Describe the utricle

A

oriented horizontally

superior to the saccule, anterior to the SCCs

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21
Q

Describe the saccule

A

oriented vertically

inferior to the utricle

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22
Q

Each organ (utricle & saccule) contains a ____

A

macula

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23
Q

The utricular macula detects ____

A

linear horizontal acceleration

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24
Q

The saccular macula detects ____

A

linear vertical acceleration

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25
Describe the macula
Similar to cupula (tectorial membrane of the cochlea) Has otoliths/otoconia that sit on the top of the macula
26
Otoliths
Provide a weight-bearing system Calcium carbonate crystals Sit on top of the gelatinous material of the macula Gravity causes displacement, which causes deflection of HCs which provides signals to the brain
27
What are the otolithic organs?
Utricle and saccule
28
Otolithic organ function when the head accelerates
The lower part of the utricular or succular (basement) membrane immediately follows otoconia lags, deflects stereocilia toward/ away from the kinocilium HCs de- or hyperpolarize (depending on direction of deflection)
29
Otolith organs detect ___ movements
Forward and backward movements head tilt, up/down, and gravity
30
Anterior SCC detects
Nodding up and down
31
Posterior SCC detects
Moving head side to side
32
Horizontal SCC detects
Moving head left and right
33
Describe what happens when the one of the SCCs are activated.
When there is a movement in the SCC, the ampulla is in the same plane of motion, but the endolymph lags, which pushes/pulls the cupula, bending the HCs to send sensory information to the brain
33
When the HCs bend towards the kinocilium, is this excitatory/inhibitory?
excitatory
34
When the HCs bend away from the kinocilium, is this excitatory/inhibitory?
inhibitory
35
The otolith organs are oriented with HCs in their respective position, and ___ resting on top of the gelatinous membrane.
otoconia
36
With acceleration, the utricle HCs and otoconia __
lag *basically in the opposite direction
37
With head deceleration to stopping
The basement membrane decelerates to stop Otoconia remain in motion, deflecting the stereocilia in the opposite direction HCs de- or hyperpolarize (depending on direction of deflection)
38
The peripheral vestibular system is first supplied by the ____ then to ____, then to
The AICA (or basilar artery), which then branches to the labyrinthine artery This divides into the anterior vestibular artery and the common cochlear artery which then branches into the posterior vestibular artery's
39
The anterior vestibular artery supplies blood to _____
utricle, ampullae of the horizontal and anterior SCC, and some to saccule
40
The posterior vestibular artery supplies blood to ____
inferior saccule and the ampullae of the posterior SCC
41
What are the two branches of the vestibular portion of CN 8?
inferior superior
42
The inferior vestibular nerve carries input from the
Saccule and posterior SCC
43
The superior vestibular nerve carries input from the
horizontal and anterior SCC, utricle, and some of the saccule
44
What are the four primary vestibular nuclei
superior *SCC, commisural fibers from contr. superior vestibular nuclei inferior *saccule, cerebellum, contra. vestibular nuclei medial *SCC, reticular formation, contra. medial vestibular nucleus, cerebellum, spinal cord **send efferent to oculomotor, abducens, MLF lateral *utricel, cerebellum, spinal cords
45
The central vestibular system is responsible for
communicating with the central visual and proprioceptive systems makes motor controls based on head's mvt in space
46
What are the three main outputs for the vestibular nuclei
1. CN III and VI: main routes *MLF: direct pathway good for quick communication **Reticular formation: maintains spontaneous activity, responsible for compensatory eye mvts 2. Spinal cord: reticulospinal or vestibulospinal pathways 3. cerebellum: vestibulocerebellar pathway
47
What are the four main reflexes
Vestibulo-ocular reflex (VOR) Vestibulo-spinal reflex (VSR) Vestibulo-collic reflex (VCR) Cervico-ocular reflex (COR)
48
What is the foveal reflex
When the visual and vestibular systems act together to keep a target steadily focused on the fovea (back portion) of the eye *However, head mvts can be fast while the "recording" of the foveal image can be slow..creating blurred/unfocused images to be perceived Hence, this is when the vestibular system comes into play
49
What are the vestibular end organs?
SCC, and otolith organs (urticle, and saccule)
50
What is nystagmus, and when is it initiated?
compensatory eye mvts involuntary eye mvts with clearly defined slow and fast components initiated by a stimulus exciting the vestibular end organs, which triggers a response in the VOR arc. normally occurs when the head is rotating (visually evoked, under caloric, or when gaze is focused at the extreme lateral like endpoint nystagmus
51
What is the slow component of nystagmus?
tracking/ pursuit compensatory mvt
52
What is the fast component of nystagmus?
generated by the CNS direction of the fast component (saccades) ex: when the RB nystagmus is when the fast phase is the to the right
53
When the head is turning to the left, the slow phase of nystagmus will be to the ____as the eyes try to keep the visual target centered on the fovea. When this is no longer possible, the eyes will snap back to ___, moving quickly to ____
right center left **This is the fast phase of nystagmus, which is LB in this case***
54
It is pathological when this nystagmus occurs ____, resulting from ___
spontaneously ex: changes in head position, or results from changes in gaze position
55
What are the following types of nystagmus that are considered abnormal?
Positional, Hallpike, fistual, vestibular type (spontaneous), and central type
56
Describe what happens when you turn your head to the left
Excitatory: left SCC left medial vestibular nuclei right ispilateral abducen (CN 6) sending info using MLF to left medial rectus (CN 3) Inhibitory: right SCC right medial vestibular nuclei left ipsilateral abducen (CN 6) sending info using MLF to left medial rectus CN 3
56
What are the extraocular muscles that are included in VOR?
medial rectus (adduction) *exc: ipsilateral horizontal SCC *inhib: contralateral horizontal SCC lateral rectus (abduction) *exc: contralateral horizontal SCC *inhib: ipsilateral horizontal SCC superior rectus (elevation) *exc: ipsi. anterior SCC *inhib: contra. posterior SCC inferior rectus (depression) *exc: contra. posterior SCC *inhib: ipsil. anterior SCC superior oblique (extorsion) *exc: ipsi. posterior SCC *inhib: contra. anterior SCC inferior oblique (intorsion) *excit: contra. anterior SCC *inhib: ipsilateral posterior SCC
57
How can the VOR be evaluated clinically
oVEMPs vHIT
58
Vestibulospinal reflex (VSR)
responsible for maintaining head and body posture during daily activities stabilizes the head in space, which allows us to move our head in the opposite direction of the existing head-in-space velocity **posture think VSR, for maintain head and body posture**
59
What are the three neuron arcs involved in VSR?
vestibular afferents vestibular nuclei cervical spinal cord
60
How is the VSR clinically evaluated?
Posturography using the sensory organization test (SOT)
61
Vestibulocollic Reflex (VCR)
maintains head position and horizontal gaze relative to gravity
62
How is VCR evaluated?
cVEMP
63
Cervico-ocular reflex
responsible for eye mvts in relation to head or torso mvts comes in play when there is a disturbance to VOR function **There are no clinical test for COR**
64
What are the five main areas on how the cerebellum receives vestibular input?
1. Lobules I to V of anterior lobe 2. Deep cerebellar nuclei *communication point and tract for VSR 3. Lobules VI to VII 4. Lobules IX and X 5. Central paraflocculus and flocculus
65
What are the projections for vestibular system after the cerebellum
Cerebellum and vestibular nuclei -->thalamus and cortex----->temporal and partial lobe
66
What areas of the brain receive and integrate visual, vestibular, and somatosensory systems?
thalamus and cortex *cortex has projections to the frontal eye field
67
What important role does the dorsal medial superior temporal cortex (MSTd) play?
processing optic flow information (smooth pursuit) and head direction
68
What does true vertigo mean??
the sensation of movement either of the individual or their surroundings, when no mvt is occuring
69
What does unsteadiness mean>
what precedes falls, or the sensation that one is going to gall
70
What are the differences between/t peripheral and central symptoms?
Peripheral: -severe nausea/vomiting -mild imbalance -mild oscillopsia (unstable vision) -hearing loss -generally recovers with tx or compensated for with time Central: -rarely includes hearing loss -severe imbalance and oscillopsia (unstable vision with mvt) -neurological symptoms -some nausea and vomiting (but not to the extent of peripheral) -compensation is quite slow

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