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Neuroanatomy > 10. Vestibular system > Flashcards

10. Vestibular system Flashcards

1
Q

Describe the relationship between components of the membranous labyrinth (utricle, saccule, semi-circular canals, cochlea) (slide 9)

A
  • 3 SEMI-CIRCULAR CANALS: anterior, posterior, lateral. Each has an ampulla with a crista ampullaris.
  • UTRICLE: connected with semi-circular canals. Has 1 macula
  • SACCULE: connected with cochlear duct. Has 1 macula.
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2
Q

Two types sensory receptors of the vestibular systems

A
  • 3 Crista ampullaris (in the ampulla) - ANGULAR acceledation
  • 2 Macula (in the utricle and saccule) - LINEAR acceledation + gravity
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3
Q

Crista ampularis - structure

Slide 10

A
  • 1 per ampulla/horizontal canal
  • Columnar neuroepithelial cells (hair cells + supportive cells)
  • HAIR CELLS have stereocilia + one kinocilium
  • Embedded in CUPULA - gelatinous structure, which project in the ampulla
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4
Q

Macula - structure

Slide 11

A
  • 1 per utricle (horizontal) and saccule (vertical)
  • Columnar neuroepithelial cells (hair cells and supportive cells)
  • HAIR CELLS have strereocilia + 1 kinocilium
  • Embedded in STATOCONIORUM - gelatinous structure, covered by otoliths (statocconia)
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5
Q

In the hair cells of macula and crista…
* Bending of sterocilia TOWARDS kinocilium causes ENTRY of K+ –> ____ polarization
* Bending of sterocilia AWAY from kinocilium causes EXIT of K+ at the basolateral portion –> ____polaraization

A
  • Towards kinocilium = DEpolarization
  • AWAY from kinocilium = HYPERpolarization

Endolymph is K+ rich, Na poor

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6
Q

Describe steps of vestibular receptor transduction

Slide 16

A
  • Stereocilia bent towards kinocilium
  • stretches tip link
  • opens K+ channels
  • K+ entry -> DEPOlarization
  • Activation of Ca+ channels
  • NT release on vestibular nerve dendrites
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7
Q

Describe the orientation of semi-circular canals

Slide 17

A
  • Anterior & posterior: vertical plane
  • Lateral: horizontal plane
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8
Q

How are semi-circular canals paired

A
  • R+L lateral
  • R anterior + L posterior
  • L anterior + R anterior
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9
Q

Crista (angular acceleration) - how does it work

A

Head still: equal firing R/L (vestibular nerve always fires)
Head movement to the L:
* L Cupula deflected towards utricle = increase firing
* R Cupula deflected away from utricle = decrease firing
* Causes jerk nystagmus to L (fast phase)

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10
Q

Macula (linear acceleration) - how does it work (slide 23)

A

(idem crista…)

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11
Q

Components of the peripheral vestibular pathway

A
  • 5 receptors (2 macula, 3 crista) containing sensory hair cells
  • Dendrites of bipolar neurons synapse with base of hair cells
  • Cell bodies form vestibular ganglion
  • Axons form vestibular nerve
  • Leave bony labyringht through internal acoustic meatus, along with cochlear nerve
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12
Q

Describe the central vestibular pathways

A

Axons of the vestibular nerve….:
* Most synapse on VN (lateral to 4th ventricle)
* Others reach cerebellum via caudal c.p. (to flocculonodular lobe + fastigial nucoeus)

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13
Q

Name the 4 VN

Slide 27

A
  • Rostral
  • Medial
  • Lateral
  • Caudal
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14
Q

The macula and crista reach which VN?

A

Crista: R + M
Macula: C + L

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15
Q

How does the cerebellum influence VN

A
  • Inhibitory purkinje fibers from flocculonodular lobe directly synapse on VN, which are facilitatory to ipsilateral extensors
  • Lx to the flocculonodular lobe therefore frees VN from cerebellar inhibition = controlateral head tilt = paradoxical vestibular syndrome
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16
Q

Name the two DESCENDING VESTIBULAR TRACTS. Where do they travel? Impact on LMN?

A
  • MEDIAL VESTIBULOSPINAL TRACT (to motor CNXI + cervical SC; involved in vestibulospinal reflex)
  • LATERAL VESTIBULOSPINAL TRACT (to entire SC; limbs + trunk)
  • Ventral funiculus
  • Facilitatory to ipsilateral EXTENSORS (inhibits flexors)

See extrapyramidal lecture for more details

17
Q

Name one ascending vestibular tract

Slide 35

A

Medial longitudinal fasciculus
* in dorsomedial tegmentum
* adjacent to motor nuclei of CN III, IV, VI
* Involved in vestibulo-ocular reflex

Pathway from vestibular nuclei to cortex not well understood

18
Q

Which vestibular structures are responsible for
* Horizontal eye movement
* vertical eye movement
* torsional eye movement

A
  • Horizontal: horizontal semi-circular ducts (lateral) + utricle
  • Vertical: vertical semi-circular ducts (anterior & posterior) + saccule
  • Torsiona: vertical ‘’ + utricle
19
Q

2 phases of vestibulo-ocular reflex

A
  1. Slow in opposite direction of head (as head starts moving)
  2. Fast in same direction as head (as head reaches end of visual field)
20
Q

Nystagmus

  • Draw the elements of the physiologic nystagmus (horizontal vestibuloocular reflex)

Slide 40

A

On both sides (R/L)
* Crista ampullaris (always fire, and firing increase when head moves ipsilateral)
* Motor nucleus VI - innervates lateral rectus
* Adjacent PARAbducent nucleus
* Motor nucleus III - innervates medial rectus
* Eyes with medial and lateral rectus
* MLF interconnects VN, III, VI nuclei

21
Q

Nystagmus

Describe the SLOW PHASE of nystagmus as head turns to the L

Slide 41

A
  • L vestibular nerve fires more
  • Activates R nucleus VI (R lateral rectus)
  • Activates L nucleus III (L medial rectus)
  • = conjugate eye movement to the R
22
Q

Nystagmus

Describe the FAST PHASE of nystagmus as head turns to the L

A
  • Excitatory burst cells of the L parabducen nucleus are eventually activated
  • Activates L nucleus VI (L lateral rectus)
  • Activates R nucleus III (R medial rectus)
  • = jerk eye movement to the L
23
Q

Nystagmus

Understand impact of a unilateral lx (pathologic nystagmus) to
* Peripheral vestibular system
* flocculonodular lobe

A

Peripheral vestibular sys :
* Fast phase AWAY from lx (as if opposite vestibular N is activated)
* Head tilt TOWARD lx (ipsilateral reduced extensor tone to CNXI and cervical SC)

Flocculonodular lobe
* Fast phase TOWARD lx (ipsi VN over-stimulated)
* Head tilt AWAY from lx (ipsi excessive extensor tone)

Neuroanatomy (20 decks)

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