Control of Eye Movements Flashcards
1
Q
- What do normal eye movements require?
A
- Head movements (vestibular information)
- Visual objects
- Proprioceptive info (LMNs)
- Selection of a visual target (brainstem and cortical area)
2
Q
- What are saccades?
- What type of movement are they
A
- Rapid eye movements
- Bring image of object onto the fovea
3
Q
- What is a smooth pursuit movement?
- What type of movement is this?
A
- Keeps moving image centered on the fovea
- Conjugate
4
Q
- What is a vestibular-ocular movement?
- What type of movement is this?
A
- Holds image steady on the fovea during head movements
- Conjugate
5
Q
- What is vergence?
- What type of movement is this?
A
- Keep image on the fovea when an object is moved near
- Disconjugate (eyes are crossing-not moving in same direction to focus on target)
6
Q
Summary of the types of eye movements and their control mechanisms
A
7
Q
- What are the three types of neurons that are important in saccadic eye movements?
- Where are these neurons located?
A
- Excitatory/Burst neurons-move eyes towards target
- Tonic neurons-keep eyes locked on final target
- Pause neurons-inhibit burst neurons so no further movement occurs
8
Q
- Describe the horizontal saccade system
A
- KEY POINT WITH HORIZONTAL SACCADE: Stimulate right frontal eye field, eyes move to the left (and vice versa)
- Steps
- Frontal eye field stimulated
- Sends axons to PPRF/Horizontal Gaze Center of CONTRALATERAL Side
- Axons project to ABDUCENS nuclei on same side of PPRF
- Axons from abducens nuclei can go to
- Lateral rectus m (on same side)
- OR
- via MLF to CN III nucleus to innervate medial rectus of opposite side
- Axons from abducens nuclei can go to
9
Q
- Describe the vertical saccade system
A
- Axons from frontal eye field travel to riMLF (Vertical Gaze Center)
- These axons travel to
- CN IV nucleus (Trochlear) to innervate superior oblique m
- or
- CN III nucleus (Oculomotor) to innervate inferior oblique m
10
Q
- What will happen if there is a tumor of the superior mudbrain/pineal gland/ or posterior commissure?
A
- Selective palsies of vertical gaze (can’t look up)
11
Q
- What will happen if there is a tumor in the red nucleus?
A
- Selective palsies of vertical gaze
- Cant look down
12
Q
- How can you test saccadic eye movements?
-
What will happen if there is a pathology of the frontal gaze center
- Destructive lesion
- Seizure activite
A
- Ask the patient to visually jump from one object to another (Basically ask them to scan the room)
- Destructive lesion-eyes will deviate towards side of lesion (if there is a car accident you’re driving by, your eyes will look towards it)
- Seizure activity/Irritation to the frontal eye field-eyes will deviate away (look away from something if irritated)
13
Q
- Describe the smooth pursuit pathway
- What is different about smooth pursuit and saccadic movements (besides speed?)
A
- Smooth pursuit pathway-if the parieto-occipital junction is stimulated, the eyes will move to the same side (unlike saccadic movements where if frontal eye field is stimulated and eyes look to contralateral side)
- STEPS
- Parieto-occipital junction is stimulated
- Axons relayed to pontine nuclei (IPSILATERAL side)
- Axons from pontine nuclei sent to CONTRALATERAL vestibulocerebellum/flocculonodular lobe
- Axons from vestibulocerebellum sent to the CONTRALATERAL ABducens nucleus
- Axons sent to Lateral rectus m
- or
- via MLF to CN III to innervate medial rectus m
14
Q
- How do you test for smooth pursuit movements?
- Pathology-lesion of parietal lobe causes loss of smooth pursuit movements to which side?
A
- Test
- H Test
- Optokinetic . tape
- Pathology
- Lesion of the parietal lobe will cause loss of smooth pursuit movements TOWARDS side of lesion
- No optokinetic nystagmus when tape is moved toward damaged lobe
15
Q
- Describe the optokinetic reflex
A
- Holds image of target steady on retina during sustained head rotation
- Smooth pursuit pathway and nuclei of accessory optic system
- Visual target broken when the target reaches the limit of visual field (can’t look any further in that direction)
- Eyes make quick move in opposite direction (optokinetic nystagmus)
- Requires intact parieto-occipital eye fields
16
Q
- Describe the vestibulo-ocular system
A
- KEY CONCEPT: Head turned to right-eyes go to left (and vice versa, similar to the saccadic eye movements)
- STEPS
- Head turned to right (as an example)
- Right vestibular portion of CN VIII activated
- Sends projections to vestibular nuclei (cerebellum) of IPSILATERAL side
- Vestibular nuclei sends projections to CN VI of CONTRALATERAL side
- CN VI sends projections to
- Lateral rectus of same side of abducens nuclei
- OR
- via MLF to contralateral CN III nuclei to medial rectus m.
19
Q
- Internuclear opthalmoplegia (INO)
A
- Lesion in MLF (pons or midbrain)
- Patient cannot ADduct the affected eye
- ABduction nystagmus of normal eye
EX: Patient’s left MLF is damaged:
- Ask patient to look to the left( fine because the left abducens works fine and right MLF works fine)
- Ask patient to loo to the right (right eye will work fine, but since left MLF is damaged, patient cannot ADduct their left eye (or move it towards the right)
- Convergence is fine (also gives you hint that its INO)
20
Q
- Lesion summary slide
A
