Ch. 16: Vestibular and Visual System

Question 1

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

Answer 1

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

Question 2

What is the function of the semicircular canals?

Answer 2

Keeps eyes focused on the world around you

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

Question 3

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

Answer 3

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

Question 4

What is “paired activity” of the semicirular canals?

Answer 4

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)

Question 5

Why are the semicircular canals important?

Answer 5

stabilize VISION when HEAD is moving

Question 6

What is inside the Otolithic Organs?

Answer 6

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

Question 7

How do the Otolithic Organs generate AP’s?

Answer 7

• 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

Question 8

How many Otolithic Organs do you have?

Answer 8

2 per side

Question 9

Otolithic Organs respond to what type of movement?

Answer 9

• Linear acceleration/deceleration
• Chang in pull of gravity

Question 10

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

Answer 10

• 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

Question 11

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

Answer 11

• 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

Question 12

What are the Nasal Retina?

Answer 12

• Half of retina closest to nose
• “temporal” visual field

Question 13

What are the Temporal Retina?

Answer 13

• Closest to temple
• “Nasal” visual field

Question 14

What light info does the Optic Nerve Receive?

Answer 14

info from ALL visual space

Question 15

What light info does the Optic Tract Receive?

Answer 15

Only one field of vision

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

Question 16

What is the purpose of the Optic Chiasm?

Answer 16

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

Question 17

What is the Action Stream (dorsal)?

Answer 17

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

Question 18

What is the Preception Stream (ventral)?

Answer 18

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

Question 19

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

Answer 19

• 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

Question 20

What is Gaze Stabilization?

Answer 20

Keep eyes focused on object when head is moving

Question 21

What is Direction of Gaze?

Answer 21

Move eyes to focus on an object of interest

Question 22

What is Conjugate movement?

Answer 22

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

Question 23

What is Disconjugate movement?

Answer 23

Eyes moving in different directions (ex: cross eyes)

Question 24

What 2 reflexes help with Gaze Stabilization?

Answer 24

• 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

Question 25

What 4 things help with Direction of Gaze?

Answer 25

• 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

Question 26

What is Nystagmus?

Answer 26

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

Question 27

When is Nystagmus Physiologic?

Answer 27

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

Question 28

When is Nystagmus Pathologic?

Answer 28

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