VF - Eye Movements 3 - Saccades/Pursuit - Week 6 Flashcards
Name three subsystems of gaze shifting, and two subsystems of gaze holding.
Gaze shifting
- Saccade
- Pursuit
- Vergence
Gaze holding
- Vestibular
- Optokinetic
Define the following in terms of oculomotor computation:
Saccade
Pursuit
Vergence
Vestibular
Optokinetic
List them in order of firing rate (highest to lowest).
Saccade - distance of target image from fovea
Vergence - location of target in depth
Pursuit - target velocity
Optokinetic - speed and direction of full-field image motion
Vestibular - rotation or translation of head and body
Name the nerve of the final common pathway for each of the following extraocular muscles: Medial rectus Lateral rectus Superior rectus Inferior rectus Superior oblique Inferior oblique Name where in the brain the nuclei are.
CNIII oculomotor - midbrain Medial rectus Superior rectus Inferior rectus Inferior oblique
CNIV trochlear - midbrain
Superior oblique
CNVI abducens - pons
Lateral rectus
Describe cortical and brainstem control of eye movements early on in phyla vs how humans are today. Name one advantage that modern structures have over earlier ones.
Early phyla used largely brainstem control alone.
In humans, these pathways still exist, but have been overlaid with newer ones under cortical control.
This provides redundancy in case of damage.
What is neiman-pick type c disease caused by, and which saccadic movement does it attack first?
Caused by impaired cholesterol transport.
Attacks vertical saccades first, then horizontal.
Explain what neiman-pick type c disease can be misdiagnosed as, and why this can occur, and how to avoid this situation.
Misdiagnosed for psychosis/schizophrenia and other psychiatric disorders.
Issues arise when smooth movements are tested only. Saccades arent often tested, hence the misdiagnosis.
Name 5 key brainstem structures associated with eye movement pathways.
Thalamus Superior colliculus Inferior colliculus Cerebellum Pons
How are key brain structures arranged in the brainstem?
They are laterally paired.
How is a clear impression of the world maintained with only 1 degree of high foveal acuity?
On average, 3 saccades are made per second.
Describe why bursts of innervation is required to generate a saccade, and why it is important. Relate this to viscosity, and how it impacts this.
Extrocular muscles face high viscosity, and this is a major hindrance to saccades.
Moving a high viscosity system requires high force, hence the need for bursts of innervation.
When a saccade is generated, does the eye drift back to the centre due to elastic forces of muscles? Explain why/why not.
It remains fixated if everything is normal. Antagonistic muscles are switched off through tonic innervation to keep the eye in place.
Describe how OPNs and EBNs are involved in generating bursts of innervation.
-OPNs in the PPRF inhibit EBNs. When no longer driven by fixation cells in the SC, OPNs become less active, and EBNs fire a burst of innervation.
When a burst of innervation is released to induce a saccade, where does it eventually end up, and what happens to it? Give an example with leftward saccades.
The signal travels to both the nuclei associated with the muscle to be innervated (ie. abducens), and to key brainstem structures to be integrated into a tonic step of innervation.
This integrated innervation travels to the nuclei (abducens).
Here the tonic and burst are combined into a pulse-step of innervation.
Define what is meant by a pulse-step innervation.
The pulse gets the eye onto its target quickly.
The step keeps the eye in place.
On what side of the brain are saccadic bursts generated, and on which side of the saccadic movement?
What side is the step signal produced on?
Saccadic bursts originate ipsilaterally to the direction of the saccade.
Step signal also produced on the same side.
