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Neurobiology II > Vestibular Pathway > Flashcards

Vestibular Pathway Flashcards

1
Q

What structures make up the outer ear/ external ear?

A
  • Auricle/Pinna (external ear)
  • Auditory canal – ends at tympanic membrane
  • Tympanic Membrane (Boundary between outer & middle ear)
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2
Q

What makes up the middle ear?

A

Ossicles
- Malleus
- Incus
- Stapes

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3
Q

What makes up the inner ear?

A
  • Cochlea
  • Labyrinth
  • Vestibule – utricle & saccule
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4
Q

What are the 3 functions of the peripheral vestibular system?

A
  • Maintain postural stability
  • Stabilizing visual images during head movement to allow clear vision
  • Provide information used for spatial orientation (head position relative to gravity)
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5
Q

What sensory input does the peripheral vestibular system receive?

A
  • Vestibular
  • Somatosensation
  • Vision
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6
Q

What is the central processor of the peripheral vestibular system?

A
  • Vestibular Nuclei
  • Cerebellum (calibrates)
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7
Q

What is the motor output of the peripheral vestibular system?

A
  • Postural reflexes
  • Eye movement
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8
Q

What is the Bony Labyrinth filled with?

A

Compact bone filled with perilymph (fluid similar to CSF)

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9
Q

What is inside a membranous labyrinth?

A
  • Suspended within bony labyrinth
  • Filled with endolymph (fluid similar to intracellular fluid)
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10
Q

What are the 5 neural structures of the membranous labyrinth?

A
  • 3 semi circular canals
    1. Horizontal semi-circular canal
    2. Posterior Semi Circular Canal
    3. Anterior Semi-Circular Canal
  • 2 otolith organs
    1. Saccule
    2. Utricle
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11
Q

What does the semi circular canals detect?

A
  • Detect angular acceleration around 3 axes
  • Each canal paired with canal on opposite side (Anterior canal to opposite posterior canal)
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12
Q

What is the posterior semi circular canal innervated by?

A

inferior vestibular nerve

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13
Q

What is the anterior semi circular canal innervated by?

A

Superior vestibular nerve

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14
Q

What is the horizontal semi circular canal innervated by?

A

Superior vestibular nerve

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15
Q

How does the endolymph in the semi circular canals move and in response to what?

A

Freely in response to head angular movement (opposite the perilymph)

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16
Q

The semi circular canals are enlarged at one end to form what?

A

Ampulla

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17
Q

What does the Ampulla contain?

A

Gelatinous cupula (flexible membrane)

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18
Q

What does the cupula contain and where do they sit?

A
  • Sensory hair cells (stereo cilia & kinocilia)
  • Hair cells sit in the Crista ampullaris
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19
Q

When you turn your head the endolymph in the semi circular canals move (BLANK) direction of perilymph. This cause the (BLANK) to move and thus (BLANK) move.

A
  • opposite
  • cupula
  • hair cells
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20
Q

When stereo cilia cells are deflected towards kinocilia does that cause excitation or inhibition?

A

excitation

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21
Q

When stereocilia cells are deflected away from kinocilia does this cause excitation or inhibition?

A

Inhibition

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22
Q

When you turn your head to the right the right horizontal canal is (BLANK) and the left horizontal canal is (BLANK)

A
  • Right is excited (increase firing rate)
  • Left is inhibited (decrease firing rate)
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23
Q

At rest how do we know our head is still and balanced?

A
  • Tonic Firing Rate: Head is stationary
  • The labyrinth is always firing action potentials at a constant rate down the vestibular nuclei
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24
Q

Healthy vestibular system have a resting firing rate at what?

A

70-100 spikes/sec

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25
Q

What does the otolith organs detect? and which specific axis does the utricle and saccule detect this on?

A
  • Detect Linear Acceleration
    1. Utricle: Horizontal Axis (Also detects head tilt)
    2. Saccule: Vertical Axis
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26
Q

What does the otolith organs contain?

A

Maculae (resemble cristae ampullaris)

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27
Q

What does the maculae contain and what is it?

A
  • Contain Otoconia
  • Calcium carbonate crystals within otolithic membrane (Sit on gelatinous layer)
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28
Q

Hair cells are embedded within gelatinous layer in the Maculae.
- What are the hair cells?
- The hair cells that sit on medial wall of saccule detect what?
- The hair cells that sit on the floor of utricle detect what?

A
  • Sit on Medial wall of saccule: Vertical acceleration
  • Sit on Floor of utricle: Horizontal Acceleration
  • Hair Cells= stereocilia and kinocilia
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29
Q

In the otoliths, with head tilt or acceleration, gravity/other acceleration pulling on crystals. What does this activate?

A

Pull of crystals activate hair cells – some maximally excited and some maximally inhibited

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30
Q

Why is there an increased sensitivity to gravity & linear acceleration?

A

Otolith membrane has more mass than cupula

31
Q

Describe utricle response to acceleration if the head moves forward

A
  • Calcium Carbonate crystals(otoconia) pull gelatinous membrane forward
  • Causes stereocilia to move towards Kinocilia
  • excitation
32
Q

Describe saccule response to feeling your head moving up

A

Calcium carbonate crystals (otoconia) move up
- Cause hair cells to move up
- stereocilia move towards kinocilia
- excitation!

33
Q

Describe the Vestibular Ocular Reflex

A
  • Maintains Stability of an image on the fovea of the retina during rapid head movements
  • Eyes move opposite the head!
  • Peripheral Vestibular system connects to central vestibular pathways
34
Q

In regards to SCC commincation with eye muscles:
For the Horizontal (left) what is the
Secondary nucleus?
Extraocular Motor Neuron?
Muscle?

A
  • Secondary Nucleus: Medial vestibular nucleus
  • Extraocular Motor Neuon: Left oculomotor nucleus & right abducens nucleus
  • Muscle: Left medial rectus & right lateral rectus
35
Q

For Posterior (left) what is the:
Secondary nucleus?
Extraocular Motor Neuron?
Muscle?

A
  • Secondary nucleus: Medial vestibular nucleus
  • Extraocular Motor Neuron: Right trochlear nucleus & right oculomotor nucleus
  • Muscle: left superior oblique & right inferior rectus
36
Q

For anterior/superior (left) what is the:
Secondary nucleus?
Extraocular Motor Neuron?
Muscle?

A
  • Secondary nucleus: Lateral vestibular nucleus
  • Extraocular Motor Neuron: right oculomotor nucleus
    Muscle: Left superior rectus & right inferior oblique
37
Q

What extra- ocular eye muscles does CN III innervate and what are their actions?

A
  • Medial rectus: Rotates Eye Horizontally In
  • Superior and Inferior Rectus mm: Rotates eye Vertically
  • Inferior Oblique: rotates the eye upward and away from the nose
38
Q

What extra-ocular eye muscle is innervated by CN IV and what is the action?

A

Superior Oblique: rotates the eye downward and toward the nose

39
Q

What extra-ocular eye muscle is innervated by CN VI and what is the action?

A

lateral rectus muscles: rotate the eyes horizontally out

40
Q

The relationship of eye velocity to head velocity is known as?

A

VOR Gain

41
Q

When the head is moving below 60 degrees/sec what does this do the gaze?

A
  • Gaze is maintained very well
  • Gaze stability with smooth pursuits using eye muscle movements
  • the ability to move the eyes with smooth, continuous motions in order to follow the movement of a target of interest and maintain the moving image on the fovea
42
Q

What is solely responsible when the head is moved very fast (>60 deg/sec)?

A

VOR is solely responsible

43
Q

What is inhibitory cut off?

A
  • Excitation can be recorded as up to 400 spikes/sec
  • Inhibition can only be recorded to a firing rate of 0 = inhibitory cut-off
  • When there is a lesion in one side, the imbalance may be seen
44
Q

What is VOR phase?

A

Relationship of amplitude between the eyes and the head

45
Q

If the head moves 10 degrees to the right and eyes move 10 degrees to left what does this mean?

A

zero phase shift

46
Q

How do hair cells of semi-circular canals and otoliths transmit neural discharge to vestibular nuclei?

A

Via the Vestibular Nerve (CN VIII)

47
Q

Where does the superior vestibule nerve receive inout from?

A
  • Utricle
  • Anterior & lateral semicircular canals
48
Q

Where does the inferior vestibular nerve receive input from?

A
  • Saccule
  • Posterior semicircular canal
49
Q

How does primary sensory neurons convey angular & linear acceleration information?

A

Through vestibular division of CN VIII to vestibular nuclei

50
Q

What are the 4 major nuclei in the pons/rostral medulla and what is the function?

A
  • Superior – relay for VOR (through Medial Longitudinal Fasciculus)
  • Medial – largest of the nuclei; relay forVOR (through MLF); medial vestibulospinal tract
  • Lateral – principal nucleus for lateral vestibulospinal reflex
  • Inferior – connected to all nuclei &cerebellum (lateral nucleus fibers run over it)
51
Q

What are the vestibular nuclei connections?

A
  • Distributes to other CN through Medial Longitudinal Fasciculus (MLF) (VOR)
  • Flocculonodular node (cerebellum)
  • Vestibulospinal tracts
  • Medial and Lateral
  • Cerebral cortex
  • Reticular formation for autonomic control and arousal
52
Q

What is the nucleus of origin of the Medial longitudinal fasciculus (MLF)?

A

Primarily medial vestibular nucleus and superior vestibular nucleus

53
Q

What is the projection of the medial longitudinal fasciculus?

A
  • The MLF connects the vestibular nuclei to ocular nuclei (III, IV, VI) for eye muscle control
  • MLF: heavily myelinated tract runs near midline bilaterally
54
Q

What is the function of the medial longitudinal fasciculus?

A

Vestibulo-ocular reflex (VOR) - Adjust eyes in response to head movement

55
Q

Where does the cerebellum project?

A
  • Vestibulocerebellum (through inferior nuclei or directly)
  • Flocculonodular lobes
  • Cerebellar vermis
56
Q

What is the function of the cerebellum?

A

Vestibulo-ocular reflex (VOR) – adjust eyes in response to head movements
- Contributes to posture control for balance
- Influences coordination of limb movements and magnitude of motor response based on vestibular stimul

57
Q

For the medial vestibulospinal tract what is the:
Nucleus of origin?
Projections?
Level of termination?
Function?

A
  • Nucleus of origin: Medial andInferior vestibular nucleus
  • Projection: Descends bilaterally in medial motor system
  • Level of Termination: Cervical and Upper Thoracic Cord
  • Function: Position of Head and Neck
58
Q

For the lateral vestibulospinal tract what is the:
Nucleus of origin?
Projections?
Level of termination?
Function?

A
  • Nucleus of origin: Lateral vestibular nucleus
  • Projection: Descends in medial motor system ipsilaterally
  • Level of termination: entire spinalcord – terminate in ventral horn
  • Function: Balance
59
Q

What is the specific part of the cortex has vestibular nuclei connections/ pathways?

A

Parietal association cortex and lateral temporoparietal junction

60
Q

In regards to the cortex, what is the projection, function and where does it give input to?

A
  • Projection: to ventral posteriornucleus of thalamus → cortex
  • Function: Control neck & headposition
  • Input to Corticospinal tracts
61
Q

What is the vascular supply to the peripheral vestibular system?

A

Labyrinthine artery (branch of AICA)
* Common cochlear artery
* Anterior vestibular artery

62
Q

What is the vascular supply to the central vestibular system?

A
  • PICA: inferior portion of cerebellar hemispheres, dorsolateral medulla
  • Basilar artery: pons
  • AICA: cerebellum, lower pons, peripheral vestibular system
63
Q

What are some examples of inner ear pathology?

A
  • Vestibular Neuritis (UVH)
  • Benign Paroxysmal Positional Vertigo
  • Meniere’s Disease
  • Unilateral or Bilateral vestibular hypo function
64
Q

What can central lesions be a result of?

A
  • Head Trauma
  • Meningitis
  • Brainstem or Cerebellar Stroke
  • Multiple Sclerosis
65
Q

What are some impairments that can be seen with vestibular pathology?

A
  • Vertigo
  • nystagmus
  • unsteadiness
  • postural instability
  • ataxia
  • nausea
  • vision blurring with head movements
66
Q

What is vertigo?

A

illusion of movement
- Room is spinning
- Most common cause is a Peripheral dysfunction

67
Q

What can lightheadedness be from?

A
  • Hypotension
  • Hypoglycemia
  • Anxiety
68
Q

What is disequilibrium and what can it be due to?

A
  • Disequilibrium: sense of being off balance
  • Could also be due to weakness and somatosensory dysfunction
69
Q

What is oscillopsia?

A

Motor of objects in the environment that are known to be stationary

70
Q

What can other dizziness be due to?

A

light-headedness/faintness, nausea, unsteadiness

71
Q

What are some common causes of central vestibular disorders?

A
  • Ischemia
  • tumors
  • cerebellar degeneration or hemorhage
  • brainstem stroke
  • Multiple Sclerosis
  • Arnold-Chiari malformation
72
Q

What are the signs and symptoms of central vestibular disorders?

A
  • Somatosensory and/or motor loss
  • double vision
  • Horner’s syndrome
  • ataxia
  • dysarthria
  • verticality
73
Q

Central vestibular disorder are caused by?

A

Damage to vestibular nuclei or to connections within the brain

Neurobiology II (14 decks)

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