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FN Unit 2 > 15 - Vestibular System > Flashcards

15 - Vestibular System Flashcards

1
Q

Endolymph Composition, Location

A

High K+ (+80 mV)

In membranous vestibular system

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2
Q

Perilymph Composition, Location

A

High Na+, like CSF

Bathes membraneous vestibular system in bony labrynth of inner ear (scala vestibuli, scala tympani)

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3
Q

Vestibular System output

A
  1. Eye position 2. Axial posture
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4
Q

Components of Vestibular System

A
  1. Peripheral apparatus (static & kinetic labryinths)
  2. Vestibular (Scarpa’s) ganglion and nerve (CN 8)
  3. Vestibular Nuclei Complex in brainstem
  4. Outputs to cerebellum, SC, and brainstem motor neurons AND cortex
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5
Q

Vestibular Hair Cell stereocilia organization

A

Arranged by increasing length with a single tall kinocilium

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6
Q

Vestibular Hair Cell depolarization

A

When stereocilia are deflected toward the kinocilium

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7
Q

Vestibular Hair Cell hyperpolarization

A

When stereocilia are deflected away from the kinocilium

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8
Q

Peripheral Apparatus of Vestibular System

A

Sensory hair cells are found in 5 regions of the membranous labyrinth

  1. Utricle (linear acceleration)
    • Static labrynth/otolith organs
  2. Saccule (linear acceleration)
    • Static labrynth/otolith organs
  3. 3 ducts of semicurcular canals
    • Kinetic labyrinth
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9
Q

Static Labyrinth

A
  1. Utircle
  2. Saccule
  • Detect linear accelerations of the head
  • AKA otolith organs
  • Major component is otolithic maculae
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10
Q

Ampulla Anatomy

A
  • Raised, dilated region at base of semicircular canal
  • Contains crista: a patch of hair cells
  • Cilia from the crista project into cupula, a gelatinous matrix that spans the ampulla, interrupting endolymphatic space
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11
Q

Vestibular (Scarpa’s) Ganglion

A
  • Peripheral processes of the bipolar cells
  • Located in internal acoustic meatus
  • Central process forms the vestibular component of cranial nerve VIII
  • Efferent component of vestibular nerve (small number of axons from the vicinity of the lateral vestibular nucleus) innervate the hair cells.
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12
Q

4 Main Vestibular Nuclei and their Vasculature

A
  1. Lateral vestibular nucleus: AICA
  2. Medial vestibular nucleus: PICA
  3. Superior vestibular nucleus: AICA
  4. Inferior vestibular nucleus: PICA

All 4 cannot be seen in the same cross section; they are present for significant rostrocaudal distance from rostral medulla to middle of pons

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13
Q

Output of Vestibular Nuceli

A

Main:

  • Spinal cord (medial and lateral vestibulospinal tracts)
    • LVN, MVN
  • Oculomotor system (medial longitudinal fasiculus)
    • MVN, SVN
  • Cerebellum

Minor:

  • Travel via thalamus to parietal cortex, where balance reaches conscious perception
    • MVN
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14
Q

3 Vestibular Reflexes

A
  1. Vestibulo-spinal reflexes (VSR)
    • Act to stabilize the limbs and body when perturbed
  2. Vestibulo-collic reflexes (VCR)
    • Act on neck musculature to stabilize the head
  3. Vestibulo-ocular reflexes (VOR)
    • Act to maintain stable vision during head motion
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15
Q

Lateral Vestibular Nucleus

A
  • Main source of information going into cerebellum
  • NOTE: the cerebellum also just gets into from the vestibular nerve itself!
  • Generates lateral vestibulo-spinal tract which controls the vestibulo-spinal reflex (VSR)
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16
Q

Inferior Vestibular Nucleus

A

Only communicates with other side

17
Q

Medial Vestibular Nucleus

A
  • Generates the medial vestibulo-spinal tract which drives the vestibulo-collic reflex (VCR)
  • Project up to extraocular motor nuclei, axons get to targets via medial longitudinal fasciculus
  • Projects to the ventral posterior intermediate nucleus of the thalamus
  • Feeling of being dizzy/out of balance
18
Q

Medial Longitudinal Fasciculus

A
  • Midline fiber bundle that connects CN 3, 4, and 6 with themselves AND with the vestibular nuclei inferiorly
  • Important tract that “yolks” together nuclei that drive eyeball movement
  • Important for vestibulo-ocular reflex (VOR)
  • Vasculature = basilar paramedians
19
Q

Superior Vestibular Nucleus

A

Project up to extraocular motor nuclei, axons get to targets via medial longitudinal fasciculus

20
Q

Vestibulo-ocular Reflex (VOR)

A
  • Serves to maintain a stable image on the retina during rapid head rotation when the eyes are fixed on a target
  • VOR constitutes the direct control system
  • VOR is a 3-neuron reflex arc:
    • Primary afferent neuron
    • Vestibular nuclear neuron
    • Oculomotor (3, 4, and 6) motoneuron
21
Q

Medial Vestibulospinal Tract

A
  • Used in VCR
  • Descending pathway
  • BEGINS IN THE MEDULLA
  • Supplied by ASA
  • Arises mostly from the medial vestibular nucleus on both sides
    • Each tract contains both crossed and uncrossed fibers (decussate immediately)
  • Fibers descend bilaterally in the midline, supplying the medial (axial) lower motor neurons in the ventral horn of the cervical and upper thoracic spinal cord
  • Main function: adjust position of the head in response to changes in posture (VCR)
22
Q

Lateral Vestibulospinal Tract

A
  • VSR
  • Vasculature: AICA > PICA > ASA
  • Arises mostly from the lateral vestibular nucleus on the same side (this is an uncrossed tract)
  • Travel from LVN, descend through IVN to the end, then “pop up” ventrally at motor decussation in pyramids, then through ventral funiculus of SC.
  • Descends the full length of the spinal cord, innervating lower motor neurons in both medial (majority) and lateral (small number) groups in the ventral horn
  • Activation of this pathway facilitates axial extensor muscles and inhibits axial and appendicular flexors
  • Primary function is to maintain upright and balanced posture in response to inputs from the static and kinetic labyrinths (VSR)
23
Q

Clinical Signs Associated with Damage to Vestibular System

A
  • Vertigo: a sensation of motion when one is stationary, a type of “dizziness”
  • Ataxia: truncal ataxia (body position is difficult to maintain)
  • Nystagmus: rapid, oscillating conjugate eye movements, generally horizontal
  • Nausea & vomiting: other automatic signs may also include sweating, excessive salivation, etc.
24
Q

Benign paroxysmal positional vertigo (BPPV)

A
  • BPPV
  • Most common cause of vertigo
  • Caused by otoconia (ear crystal) displaced from the otolithic membrane in the utricle, drifting into the semicircular ducts (the posterior duct is most commonly affected)
  • Benign: not life-threatening
  • Paroxysmal: comes in sudden, brief spells
  • Positional: triggered by certain head positions or movements specific to directional sensitivity of the effected canal
  • Vertigo: false sense of rotational movement
  • Two forms:
    • Canalithiasis (most common)
      • Otoconia are moving within semicircular duct
      • Vertigo, nystagmus resolve within 1 min
    • Cupulothiasis
      • Occurs when otoconia adhere to cupula
      • Vertigo, nystagmus persist for longer periods
25
Q

Canalithiasis

A
  • Most common type of BBPV
  • Occurs when otoconia are moving within the semicircular duct
  • Vertigo and nystagmus resolve within 1 min
26
Q

Cupulolithiasis

A
  • Less common form of BPPV
  • Occurs when otoconia adhere to the cupula
  • Vertigo and nystagmus persist for longer periods
27
Q

Kinetic Labyrinth

A
  • Semicircular ducts
28
Q
A

A. Utricle

B. Saccule

C. Otolith organs

D. Vestibule

E. Semicurcular ducts

29
Q

Linear Accesleration of Head centers

A

Utricle, saccule (otolith organs, static labyrinth)

30
Q

Angular acceleration of head center

A

3 ducts of semicircular canal (kinetic labyrinth)

31
Q

Gravito-interal acceleration

A
  • Otolithic (utricle, saccule) maculae (patches of hair cells) detect static head position relative to gravity
  • Mass of otoliths above the hair cell-containing gelatinous layer shears the stereocilia.
  • Detects linear movement of the head
32
Q

Otoliths

A
  • Calcium carbonate crystals
  • Mass of otoliths above the hair cell-containing gelatinous layer shears the stereocilia forthe deteciton of linear accerelation
33
Q

What is this?

A

Kinetic Labyrinth

A. Ampulla

B. Utricle

C. Vestibular nerve fibers

D. Semicircular canal

E. Endolymph

F. Hair cells of crista

G. Cupula

34
Q

Cranial Nerve 3 Function

A

Medial Rectus

35
Q

Cranial Nerve 6 Function

A

Lateral Rectus

36
Q

Cristae

A

Patch of hair cells; considered a sensory receptor

FN Unit 2 (11 decks)

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