Lecture - 06 - Vestibular Systems Flashcards Preview

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Flashcards in Lecture - 06 - Vestibular Systems Deck (15)
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1
Q

Vestibular system

A

sense head motion

  • output to cerebral cortex, 3 reflex paths, cerebellum
  • visual system helps
  • visuo-vestibular conflict causes dizziness/nausea
  • peripheral and brainstem vestibular dysfunction causes pathological sense of self-motion due to visuo-vestibular conflict
2
Q

semicircular canals

A

sense head angular acceleration (rotation)

  • ampulla inside has tissue ridge (crista) with hair cells embedded in gelatinous mass called cupula
  • hair cells bent by fluid moving cupula
  • vestibular nerves have constant spontaneous spike rate, head moving to left increases firing and moving to right decreases firing (towards kinocilia = excite)
  • compares with inputs from other ear
  • horizontal canals on both sides work as team (one side excites, one side inhibits)
  • send input to brain via MEDIAL vestibulospinal tract
  • vestibulo-cervical reflex
3
Q

otoliths

A

sense linear acceleration and gravity

  • hair cells sit in utricle and saccule in macula and are embedded in gelatinous otolithic membrane
  • topped with Ca carbonate crystals (otoliths)
  • tilt head backward/forward, gravity causes heavy otoliths to bend hair cilia to either excite or inhibit
  • same with acceleration
  • utricle macula: horizontal plane (forward/backward, side to side acceleration, head tilts)
  • saccule macula: vertically oriented (up/down)
  • movements in all directions are covered
  • send input to brain via LATERAL vestobulospinal tract
  • vestibulo-spinal reflex
4
Q

Vestibulo-ocular reflex

A

oculomotor system for gaze stabilization
3 sets of semicircular canals lie in 3 orthogonal planes and sense rotation by working in pairs
-each pair of canals use extraocular muscles that move the eyes in the same plane
-horizontal canals = medial rectus and lateral rectus
-eye movement: synapse on abducens to stim MR and LR, inhibit medial longitudinal fasciculus to inhibit CN3 movement of other MR and LR pair

5
Q

Vestibulo-cervical (collic) reflex

A

vestibulospinal system to control head stabilization during movement and head “posture”

6
Q

Vestibular-spinal reflex

A

to vestibulospinal systems to control body stabilization during movement and limb movement

7
Q

Vestibular organ

A

vestibular part of inner ear

  • hair cells are sensory receptors
  • sit in membranous labyrinth at 5 locations
  • 3 ampulla at ends of semicircular canals, 2 otoliths (utricle and saccule)
  • membranous labyrinth pasted up against bony walls of bony labyrinth so sound vibrations don’t cause hair cell vibration
8
Q

Blood supply

A

basilar –> AICA –> int. auditory artery

9
Q

Vestibular hair cell function

A

activated/excited by bending of cilia

  • K rushes in to depolarize, causing Ca channels to open and come in to release transmitter and activate vestibular nerve
  • at “rest” many vestibular neurons are spontaneously active, so bending hair cell cilia signals CNS to increase or decrease firing
  • signals from vestibular apparati bilaterally compared by brain
10
Q

Input to brain

A

several subdivision of vestibular nuclei

  • pons/medulla border
  • vestibular hair cells –> vestibular nuclei via CN8
11
Q

Vestibulocortical

A

consciously sensing motion

  • bilaterally (but more IPSI) from nuclei to posterolateral thalamus
  • insula and somatosensory cortex light up
  • parietal operculum
12
Q

Vestibulocerebellar

A

cerebellum gets info about motor plan, compare with muscles present situation, then send corrective info back to motor cortex

  • cerebellum does this for reflex pathways of vestibular system
  • cerebellum gets info from hair cells
  • reflexes work without cerebellum but not as well
  • vestibular input to cerebellum goes to flocculonodular lobe
13
Q

Optokinetic Nystagmus

A

if head is fixed in position, eyes will follow an object until they can’t go any further then they rapidly snap back and look for something else to focus on
-snapback direction = nystagmus direction

14
Q

Caloric testing

A

tests integrity of vestibular apparatus of each ear independently
-perfuse warm/cold water into ear
Warm Same, Cold Opposite

Also tests brainstem/cortex integrity

  • fast eye movements occur due to cerebral cortex whereas slow movements do not
  • no beating = cortical/corticobulbar issue
  • slow phase changes - brainstem problem
15
Q

Benign paroxysmal vertigo (BPPV)

A

normally hair cells in canals only sense head turning

  • sometimes otoconia fall off utricle’s otolithic membrane and get into canal –> cause hair cells in cupola to sense gravity
  • misplaced otoconia activate canal hair cells –> vertigo