Week 4 Flashcards
WIT: Allows for rapid change of eye position; fastest speed om eye movement system
Saccade
A saccade is a ___ ___ process
Gaze Shifting
What are the 3 eye movements to change the angle of gaze?
- Saccade
- Pursuits
- Vergence
What area of the brain is for more voluntary forms of saccades?
Frontal Cortical
What area of the brain is for more involuntary/reflexive forms of saccade?
Parietal cortical
What higher cortical level makes the decision to make saccades?
Cortex
What makes the decision to generate pulse and step?
Premotor neurons
What higher cortical levels structures are involved in saccades?
- Frontal Cortex
- Parietal Cortex
- Thalamus
- Superior Colliculus
- Basal Ganglia
Lesions of the superior collicculus cause?
- increased saccadic latency
- hypometria
- abnormal saccades
- decreased saccadic speed
- can’t make express saccades
This provides the decision to generate saccades made to novel stimuli which catches one’s attention in periphery
Parietal Cortex
What are the 3 premotor neurons?
- Burst
- Tonic
- Pause
WIT: Projects to oculomotor neurons causing a phasic contraction of EOMs to moves eyes quickly to new angle
Burst Neurons - sends pulse signal
Horizontal EBN are where?
Paramedian Pontine Reticular Formation (PPRF)
Horizontal IBN are where?
Medullary Reticular Formation (MRF) in rostral medulla
Vertical EBN are where?
Rostral Interstitial Nucleus of MLF (riMLF)
Vertical IBN are where?
INC and riMLF
Unilateral lesion of the PPRF leads to deficit of saccade to the ______ side.
ipsilateral
Vertical saccade palsy is caused by a lesion where?
riMLF
Slow horizontal saccade is caused by a lesion where?
in the PPRF
Niemann-Pick type C disease is due to an impaired _____, causing a curved trajectory
Vertical Saccade
Tonic step command sends a step signal to do what?
hold the eye in position after the burst
NPH and MVN as horizontal neural integrators, integrate the __ signal to a ___ signal.
burst signal into a step signal
Where are the omni pause neurons located?
Nucleus raphe interpositus
WIT: Pauses to allow saccade to occur; only after inhibited can burst neurons be activated to produce the pulse signal
Omni Pause Neurons
When are pause neurons fired?
During fixation (we don’t want the eye to move during this time)
Lesions involving pause nerons lead to what?
- Saccadic intrusions/inappropriate saccades
What controls saccadic accuracy, the dynamics and initiation of saccades and saccadic adaptation?
Cerebellum
What 2 things calibrate saccadic amplitude?
- Dorsal Vermis
- Fastigial Nucleus
- tells how far to move the eye
What calibrates the pulse-step match?
Flocculus
What 5 things do you look for when clinically examining saccades?
- Latency
- Velocity
- Trajectory
- Accuracy
- Conjugacy
Saccades are slower if made in the darkness. What two types of saccades are the slowest?
- Anti-saccades
2. Memory guided
Saccades of the ____ eye tend to be larger faster and more skewed than saccades of the ____ eye.
abducting
adducting
Saccades usually begin within ___ msecs
200 msecs
Express saccades ONLY occur in which paradigm?
gap paradigm
~100msecs
What is the speed-accuracy trade off?
Latency increases if accuracy is desired
When you make a saccade, your vision is not blurred due to?
Saccadic Omission
What are the 2 types of saccadic omission that prevent blurring of the vision?
- Saccadic Suppression
2. Saccadic Masking
WIT: Reduction in visual sensitivity during eye movement
Saccadic suppression
WIT: Reduction in ability to detect blur because multiple images are experienced within a short time, creating “noise”.
Saccadic Masking
What is the role of saccadic omission in reading?
Prevent blur & incoherent sentences
Normometria = ?
Accurate Saccade
Hypermetria = ?
Overshoot
Hypometria = ?
Undershoot
What are the non-pathologic factors that affect saccadic accuracy?
- Size/Brightness of Target
- Tiredness (glissades are found)
- Age - usually undershoot
WIT: Anomalies in muscular activity in which errors of accuracy or force occur
Saccadic Dysmetria
What are the 3 types of saccadic dysmetria?
- Static
- Glissadic
- Post-saccadic drift
- Dynamic overshoot
In hypometria, what is too small? Is this normal?
The step signal.
Yes. 10% is normal
In hypermetria, what is too large? is this normal?
Step signal is too large.
No this is not normal
Glissadic hypometria is caused by what? What disease is an example?
- Error in the pulse signal, pulse is too small to move the eyes toward target
- INO - adduction deficit
Glissadic hypermetria is caused by what?
Error in pulse signal, pulse is too large
WIT: Inaccuracy in saccadic generator
post-saccadic drift
WIT: Reversal in central saccadic command
Dynamic overshoot
