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Neuro Exam 3 > 2. Vestibular System > Flashcards

2. Vestibular System Flashcards

1
Q

Our vestibular system is important to produce motor responses necessary for daily function.

What are the components of our vestibular system?

A

Our vestibular system can be divided into 5 parts:

  • 1. Peripheral receptors apparatus
  • 2. Central vestibular nuclei (brainstem)
  • 3. Vestibuloocular network (vestibular nuclei)
  • 4. Vestibulospinal network
  • 5. Vestibulothalamocortical network
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2
Q

what is the Peripheral receptor apparatus?

A

It is located in the inner ear and responsible for causing head motion / position

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3
Q

what is the Central vestibular nuclei (brainstem)?

A

integrates and distributes information that controls motor activities and spatial orientation.

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4
Q

what is the Vestibuloocular network (vestibular nuclei)?

A

helps to control eye movements

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5
Q

what is the Vestibulospinal network?

A

coordinates head movements, axial muscles and postural reflexes

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6
Q

what is the Vestibulothalamocortical network?

A

perception of movement and spatial orientation

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7
Q

Our vestibular labyrinth is made up of what?

A
  • Bony labyrinth: protective shell (cochlea, vesitbule and 3 semi-circular canals) that houses the membranous labyrinth and contain perilymph.
  • Membranous labyrinth (utricle, saccule and semi-circular ducts) that filled with endolymph and contain the receptors for the senses of equilibrium and hearing.
    *
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8
Q

Are the ionic concentrations of the perilymph and endolymph similar_?_

A

No. They have different ionic concentartions and if disturbed, can lead to vestibular disease.

Secretory cells in the _______and _______ maintain the balance of ions.

  • membranous labyrinth
  • endolymphatic sac
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9
Q

What are the roles of our vesibular receptor organs?

A
  1. Semicircular canals (anterior, posterior and horizontal) detect angular accerleration (rotation of head)
  2. Otolith organs (utricle and saccule) detect translational head movements (linear acceleration)
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10
Q

The afferent fibers to these vestibular receptor organs come from the ___________ and head where?

A

Vestibular ganglion (scarpas ganglion);

central processes then enter the brainstem and synapse in the IPSILATERAL [vestibular nuclei and cerebellum].

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11
Q

The blood supply to the vestibular system is from

A

1. Labyrinthine artery, off of AICA; enters the temporal bone via the internal acoustic meatus.

  1. Stylomastoid artery is a second source mainly to the semicircular canals.
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12
Q

Interruptions in blood flow can cause

A
  1. vertigo,
  2. nystagmus,
  3. unstable gait.
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13
Q

What is the arrangement of our membranous labyrinth?

A
  • Semi-circular ducts are connected to the utricle. Each duct ends in a enlargement called the ampulla, which houses the sensory receptors embedded in the crista that extends across the ampulla
  • Saccule is also connected to the cochlea by the ductus reuniens.
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14
Q

Where are the sensory receptors in the utricle and saccule?

A

Utricle and saccule have sensory epithelium (macula) with hair cells embedded in them.

Utricle-> longitdunally along base with stereocilia pointing up.

Saccule-> vertically on medial wall, with sterocilia pointing out.

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15
Q

How do we drain endolymph from the membranous labyrinth?

A

Drained into the endolymphatic sinus -> endolymphatic sac via the endolymphatic duct .

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16
Q

What causes Meineires disease?

A
  • Too much endolymph in the membranous labyrinth, causing “hydrops” (abnormal distension of the labyrinth).
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17
Q

Symptoms of Meineres disesae?

Tx?

A
  1. Fluctuating hearing loss
  2. Tinnitus
  3. Vomitting
  4. Nystagmus
  5. vertigo (cant stand or move head)

Tx: diuretics (salt-restricted diet) and place shunt into swollen endolymphatic sac.

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18
Q

Describe our vestibular sensory receptors

A

Vestibular sensory receptors are hair cells with several stereocilia and 1 kinocilium that project from the apical surface.

  • When the stereocilia bend TOWARDS the kinocilium-> activating signal
  • When the stereocilia bend AWAY from the kinocilium-> inhibitory signal

There are two types:

  1. Type 1: Bulbous-shaped surrounded by a (calyx-shaped afferent neuron) located more centrally on the crista ampullaris.
  2. Type 2: Cylinders and innervated by afferent synaptic boutons located more laterally on the crista ampullaris.
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19
Q

Both Type 1 and Type 2 hair cells are innervated by what?

A

Vestibular efferents that control their sensitivity when activated by [stimuli or stimilation of CN 5]

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20
Q

The hair cells of the semicircular canals are protected in a gelatinous ________ that does what?

A

Cupula, that will push the stereocilia to or away from kinocilia.

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21
Q

Explain what happens to hair cells when you have rotational head movement?

A

Rotational head movement (angular acceleration) -> displaces endolymph -> pushes cupula to one side or another -> displaces sterocilia in the SAME DIRECTION.

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22
Q

What is the macula?

A

Macula sensory epithelium that contains hair cells receptors in the utricle and saccule.

Hai

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23
Q

What is the arrangement of the macula?

A

Sterocilia of the macula extend into the otolith membrane, which is covered by Ca2+ carbonate crystals called otoconia.

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24
Q

How does the Sterocilia extend into the otolith membrane respond to endolymph?

A

It DOES NOT; because it is more dense than the endolymph.

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25
Q

What does the macula respond to?

A

Changes in gravity or linear accelerations (forward-backward/up-down) will displace the otoconia, bending the sterocilia that are below it.

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26
Q

Afferent fibers from the otolithic organs and semicircular canals target a variety of locations, like…

A

Vestibular nuclei.

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27
Q

What are our vestibular nuclei?

A
  • 1. Superior vestibular nucleus
  • 2. Medial vestibular nucleus
  • 3. Lateral vestibular nucleus
  • 4. Inferior vestibular nucleus
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28
Q

Where are our vesitbular nuclei located?

A
  1. Superior vestibular nucleus- superolaterally in central pons, bordered by restiform body and 4th ventricle
  2. Medial vestibular nucleus- lateral floor of the 4th ventricle -> rostrocaudal
  3. Lateral vestibular nucleus- lateral to medial vestibular nucleus
  4. Inferior vestibular nucleus- lateral to medial vestibular nucleus and extends through the medulla.
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29
Q

Describe vesitbular afferents

A
  1. Primary afferent fibers from the hair cells (utricles, saccules or semicircular ducts) enter at pontomedullary junction
    1. CB: Scarpas ganglion
  2. Go through restiform body of the inferior cerebellar peducle & branch into ascending & descending fibers
  3. Otolith organs (maculae) go to lateral, medial, & inferior vestibular nuclei •
  4. Those from semicular canals ->
    1. Mainly superior and medial vestibular nuclei
  5. Afferents from the saccule also to to contralateral oculomotor nucleus & influence vertical eye movements
  6. From here; fibers can go down, back, up and ALL the way up.
30
Q

From the vestibular nucleus, EFFERENT fibers can then go to the cerebellum, describe this pathway.

CEREBELLAR CONNECTIONS

A
  1. Primary vestibulocerebellar fibers (from fastigial) do not synapse at vestibular nuclei -> go through the juxtarestiform body (inferior cerebellar peduncle) -> vestibulocerebellum -> target dendate and fastigial nuclei
  2. Secondary vestibulocerebellar fibers: Fibers from CN VIII -> synapse at vestibular nuclei -> 2nd order neurons travel to the cerebellum -> fastigial and dendate nuclei
31
Q

____________ is the only sensory organ that sends direct primary afferents to the cerebellum.

A

vestibular system

32
Q

What are other afferent fibers?

A
  1. Vestibulovestibular fibers- 2nd order neurons that originate on ipsilateral vestibular nuclei (usually superior and medial vestibular nuclei) and then send go to the same nuclei on the contralateral side for coordination.
  2. Spinovestibular fibers: fibers from the spinal cord which synapse on the vestibular nuclei (mainly medial and lateral) - providing proprioceptive input.
33
Q

Also, the vestibular system receives input from the

A
  • 1. reticular formation
  • 2. raphe nuclei
  • 3. thalamus
  • 4. other cortical regions
34
Q

What is the vestibuloocular network?

A

Helps to keep a fixed gaze while our head is moving. For example: reading a sign while we are walking.

35
Q

How does the vestibuloocular network help us to keep a fixed gaze while our head is moving?

A

Vestibuloocular reflex- a reflex of stabilizing eye movements that occurs in multiple directions (horizontal, vertical and torisional), which can be suppressed to focus on a moving target

36
Q

Is the vestibuloocular reflex compensatory?

A

Yes, because they are equal in magnitude & opposite in direction to the head movement perceived

Meaning that when you look to the L, to keep the object of interest on your fovea your eyes will move to the R

37
Q

One example of horizontal reflexes is?

A

Rotational vestibuloocular reflex

38
Q

What structures are involved in horizontal movements?

A

1. Horizontal canals

2. Utricle

39
Q

BIG PICTURE:

R head rotation:

  • ___ head turn
    • ____ horizontal semicircular canal
    • ______ medial and lateral vesibular nuclei
    • _______ abducens nucleus
        • ______ lateral rectus m.
        • _____ oculomotor nucleus
            • _____ medial rectus m.
  • Eyes will move to the ______ side.
A
  • right head turn
    • right horizontal semicircular canal
    • right medial and lateral vesibular nuclei
    • left abducens nucleus
        • left lateral rectus m.
        • right oculomotor nucleus
            • right medial rectus m.
  • Eyes will move to the left side.
40
Q

Rotational Vestibuloocular Reflex

A

information from the vestibular system influences the muscles of eye movements.

HEAD TURN IS LEFT

    1. Primary afferents from the L horizontal semicircular canals -> + neurons in the left medial & lateral vestibular nuclei
      * Commisural fibers then project to the same contralateral nuclei to decrease inhibitory signals.
    1. Axons from the L vestibular nuclei ->
      * medial longitudinal fasciculus (MLF) to + contralateral abducens nucleus
      • Inhibitory signals -> ipsilateral abducens nucleus
      • Excitatory signals -> ipsilateral oculomotor nucleus (+ medial rectus m)
    1. Axons from contralateral abduncens nucleus -> R lateral rectus m (turns the R eye right) via CN 6
      * AT THE SAME TIME: Abducens send excitatory impulses to contralateral oculomotor nucleus via MLF-> innervate the control innervates th_e contralateral medial rectus m_ -> innervates the L medial rectus (turning the L eye right).
41
Q

When you have a rotation of the head to the L and you stay fixated on a object, what do you eyes do?

A

L medial rectus is + -> L eye moves medially

R lateral rectus is activated -> R eye moves latearlly.

Eyes will move to the R

42
Q

When you look to the L

Matching bilateral connections do what?

A

Keep the L lateral rectus inhibited and the R medial rectus inhibited

43
Q

A leftward head turn

  • +_____ horizontal semicircular canal -> + _____ vestibular nuclei
    • ___________ abducens motor neurons -> producing contraction in the ______ lateral rectus and ______ medial rectus
  • Compensatory __________ eye movement keeps the object of interest on the fovea
A
    • left horizontal semicircular canal -> + left vestibular nuclei
    • contralateral abducens motor neurons -> producing contraction in the R lateral rectus and L medial rectus
  • Compensatory rightward eye movement keeps the object of interest on the fovea
44
Q

What is the linear vestibuloocular reflex?

A

Occurs similarly to rotational reflexes and involves extraoccular muscles and neurons.

45
Q

What is an example of the linear vestibuloroccular reflex?

A
  1. Moving head side to side results in eyes moving opposite to head movement
  2. Vertical movment of head (when jogging) cause an opposite directed vertical gaze to stabilize your eyes.
46
Q

What are involved in vertical movments?

A
  1. Vertical semicircular canals
  2. saccule
47
Q

What is nystagmus?

and what is it named for?

A

A combination of slow phases and fast-return phases of the eye.

The nystagmus is named for the direction of the fast retun phase (direction you are moving your head)

48
Q

What is left-beating/right-beating?

A

Left beating nystagmus: fast-return phase occurs to the left

Right beating nystagmus: fast return phase occurs to the R

49
Q

Describe the process of nystagmus.

A

When we have a large head rotation( move out body 360 degrees)

    1. Vestibuloocular reflex moves our eyes slowly in a direction OPPOSITE to our head motion.
    1. However, eyes will reach a limit of how far they can turn
    1. Eyes will rapidly spring back to the central position, moving in the SAME direction as the rotation of our head.
    1. Another slow phase beings.
50
Q

How do we test the vestibular labyrinth in paitents who have

[dizziness and vertigo problems]?

A

CALORIC TEST

COWS

  1. Put cold/warm water into the external auditory canal.
  2. Cold water induces nystagmus that beats towards the Opposite side
    1. ​(Cold water in L ear should produce a right-beating nystagmus)
  3. Warm water beats towards the Same side.
    1. Warm water in L ear should produce a L-beating nystagmus.

Both ears should give equal responses, but unilateral lesion of the vestibular pathway causes absence of this reflex.

51
Q

unilateral lesion of the vestibular pathway affects caloric test how?

A

Reduced or absent nystagmus IPSILATERALLY

52
Q

vestibulospinal system- infleunces what?

A

tone and postural adjustments via the lateral and medial vestibulospinal tracts

53
Q

Lateral Vestibulospinal Tract

A
    1. Neurons in the lateral and inferior vestibular nuclei -> all levels of ipsilateral SC.
      * Neurons located
      • Anterorostral areas -> cervical SC.
      • Posterocaudal regions -> lumbosacral cord.
    1. -> Lateral medulla -> anterior funiculus of the spinal cord
    1. -> synapse on alpha and y motor neurons and interneuons laminae 7 to 9 at all levels of ipsilateral SC.

Collaterals communicate at each segment for better coordination of posture.

54
Q

Medial Vestibulospinal Tract

Fx:

Pathway:

A

Primary fx: vestibular stimulation of neck muscles

    1. Afferent fibers from [vestibular receptors, cerebellum and DCML from SC] synapse on
  • 2. Medial vestibular nucleus (and some input from lateral and inferior as well)
    1. -> fibers decend bilaterally through MLF
    1. -> synapse in lamina 7-9 of cervical SC onto neck flexor and extensor MN.
55
Q

Vestibular information can also enter the THALAMUS ________, but most fibers terminate in the ________ thalamic nuclei.

A
  • Vestibular information can also enter the THALAMUS bilaterally, but most fibers terminate in the contralateral thalamic nuclei.
  • Specifically, mostly VPL and some in the VPI.
56
Q

Vestibular information is ALSO sent to the cortex.

What areas?

A

1. Areas 2v and 3a (primary somatosensory cortex)

2. _Area 7 (_parietal cortex)

3. Insular areas of the lateral sulcus and p_arietoinsular vestibular cortex (PIVC_)

4. Prefrontal cortex and superior frontal gyrus

57
Q

Vestibular information to

  1. Areas 2v and 3a (primary somatosensory cortex)
  2. Area 7 (parietal cortex)

does what?

A
  1. 2v -> sensation of motion of the whole body
  2. 3a -> integrated motor control of HEAD and body
  3. 7 (parietal CTX)-> spatial awaress.
58
Q

Vestibular information to

  1. Insular areas of the lateral sulcus and parietoinsular vestibular cortex (PIVC)
  2. Prefrontal cortex and superior frontal gyrus

does waht?

A
  • 3. Insular areas of the lateral sulcus and parietoinsular vestibular cortex (PIVC): body motion, proptioception and stimuli in motion
  • 4. Prefrontal cortex and superior frontal gyrus: receives information about frontal eye field; control saccades and smooth eye movement
59
Q

Lesions to Area 7 (parietal cortex) cause what?

A

Confusion in spatial awareness

60
Q

Lesions to Insular areas of the lateral sulcus and parietoinsular vestibular cortex (PIVC) cause what?

A
  1. Vertigo
  2. loss of perception for visual vertical
61
Q

What is dizziness?

A
  • a non-speicific term that means spatial disorientation that may or may not involve feelings of moving.
    • can be accompanied with nasaeu or postural instability
62
Q

Is dizziness a problem with the vestibular system?

A

Not always

63
Q

What is vertigo?

A

you think your body is in motion, often spinning or turning, when there is no motion at all. There are two kinds: subjective and objective

64
Q

Subjective vertigo:

A

patient experiences the sensation of spinning while things in the environment are not moving

65
Q

Objective vertigo

A

objects are spinning while the patient is not moving

66
Q

What will a nystagmus during objective vertigo look like?

A

nystagmus moves in the OPPSITE direction to the original direction of rotation

67
Q

Benign Paroxysmal Positional Vertigo (BPPV)

what is it and what is d/t?

A
  • Common vestibular disorder: brief episodes of vertigo caused by changed in body position (such as turning over in bed, getting up in the morning, rising)
  • D/t: Otoliths dissociate from otholith membrane and get stuck in cupula of semicircular canal (cuplothiasis), bending stereocilia abnormally.
68
Q

Vestibular schwannoma can compress what?

A

CN 7, 8 and labrynthine arter:

  1. hearing loss
  2. problems walking
  3. tinnius
69
Q

What is vestibular neurtis?

A

Swelling around the vestibular N -> N/V/vertigo, no hearing loss or CNS problems

70
Q
  1. Identify the clinical implications of the findings on Doll’s Eyes Maneuver and oculoclonic testing.
A

Doll’s eye maneuver is something you can do in a comatose patient to test for brainstem lesions.

  • If the vestibular system is intact: the eyes will move left if you move their head right and vice versa.

Neuro Exam 3 (18 decks)

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