Ch. 16: Vestibular and Visual System Flashcards Preview

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Flashcards in Ch. 16: Vestibular and Visual System Deck (29):

How many semicircular canals are there in the inner ear? What angles do they face?

  • 3 per side of the body
    • Anterior: 45º forward
    • Posterior: 45º deg backward
    • Horizontal: tilted 30º off horizontal

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What is the function of the semicircular canals?

Keeps eyes focused on the world around you

(All 3 together can detect any direction your head moves)


What is the purpose of the hair cells in the inner ear and where are they located?

  • Provide Baseline activity and when moving
  • Located at one end of each semi circle in fluid
    • bend of hair cells → creates AP's


What is "paired activity" of the semicirular canals?

AP's inc on side toward rotation and dec proportionally on side away from rotation.

(Anterior semicircle or right is in line with posterior semicircle on left)


Why are the semicircular canals important?

stabilize VISION when HEAD is moving


What is inside the Otolithic Organs?

Have hair cells that are anchored in jelly with rocks on top.


How do the Otolithic Organs generate AP's?

  • Respond to pull of gravity (helps w/postural stabilty - connected to vestibulospinal tract (keep you upright).
  • Gravity pulls hair cells → they bend → generate AP's


How many Otolithic Organs do you have?

2 per side


Otolithic Organs respond to what type of movement?

  • Linear acceleration/deceleration
  • Chang in pull of gravity


What are the inputs to the vestibular nuclei (CN VIII)?

  • Vestibular Information - head movement & pull of gravity
  • Visual Information - light information - can see relative position
  • Unconscious proprioceptive info - position of body and joints in space
  • Tactile Info - pressure sensors in skin
  • Auditory info - change of sound detects movement


What are the outputs from the vestibular nuclei (CN VIII)?

  • Cerebral Cortex - "I'm dizzy"
  • Med Longitudinal Fasciculus/Extraocular (CN II, IV, VI) nuclei - eyes controlled relative to head movement
  • Superior Colliculus/Accessory N - contract muscles to keep you up right
  • Med vestibulospinal tract - posture of head & upper body - maintain equillibrium
  • Lat vestibulospinal tract - posture of trunk & lower body - maintain equillibrium
  • Reticular Formation - affect consciousness = nausea & vomitting
  • Cerebellum - Can influence posture & eye movements

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What are the Nasal Retina?

  • Half of retina closest to nose
  • "temporal" visual field

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What are the Temporal Retina?

  • Closest to temple
  • "Nasal" visual field

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What light info does the Optic Nerve Receive?

info from ALL visual space

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What light info does the Optic Tract Receive?

Only one field of vision

(ex: pulls right visual field from both eyes to left side of brain through chiasm)

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What is the purpose of the Optic Chiasm?

Allows nasal retina information to switch sides of the brain so all info in optic tract reflects one visual field

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What is the Action Stream (dorsal)?

  • From occipital to motor planning cortex
    • Motor plan to get what you see
    • characterize things by colors, shapes, contours

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What is the Preception Stream (ventral)?

  • Occipital cortex to temporal lobe
    • Recognize & name what you see

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Visual information diverges in the optic tract and goes to what 3 routes?

  • Conscious sight: Thalamus → Occipital Cortex
    • Action stream (dorsal)
    • Perception stream (ventral)
  • Orientation & visually guided eye movments: Superior Colliculus
    • Reflex movement of head and eyes when something thrown at you
  • Midbrain connection of pupillary reflexes: Pretectal Area
    • Adjust pupils & curvature of eye


What is Gaze Stabilization?

Keep eyes focused on object when head is moving


What is Direction of Gaze?

Move eyes to focus on an object of interest


What is Conjugate movement?

Both eyes moving in the same direction (ex: tracking side to side)


What is Disconjugate movement?

Eyes moving in different directions (ex: cross eyes)


What 2 reflexes help with Gaze Stabilization?

  • Vestibulo-Ocular Reflex (VOR) - fast head movements
    • Eyes stay steady while head moves
  • Optokinetic Reflex - Slow head movements
    • Eyes stay focused on object when head moving slow


What 4 things help with Direction of Gaze?

  • Smoot Pursuit: consciouly contract muscles to move the eyes while head is still
  • Saccades: Jumps in eye movement. Normal when scanning
    • Voluntary: look from one person to another
    • Reflexive: Catch something in periphery and look to see what it is
  • Vergence: Looking cross eyed (very near objects)
  • VOR suppression/cancellation:consciously move eyes WITH head - conscious override of VOR


What is Nystagmus?

  • Involuntary back and forth movements of eye → keep world steady when moving (ex: spinning really fast)


When is Nystagmus Physiologic?

  • During acceleration/deceleration of head (ex: spinning)
    • Combo of
      • VOR (slow - eyes lag behind)
      • Saccade (fast - eys catch up)


When is Nystagmus Pathologic?

When there is no appropriate stimulus (ex: simply laying down)