12. Eye movement Flashcards
What are the 2 gaze shifting classes?
Saccades and Vergence
What is saccades?
Brings objects of interest onto the fovea
e.g looking between your two fingers very quickly
What is vergence?
Moves the eyes in equal and opposite directions. Between near and far gaze.
What are the 4 classes for gaze holding?
- Vestibular
- Optokinetic
- Smooth pursuit
- Fixation
Vestibular and optokinetic work together
What is vestibular class?
Holds retinal image steady during brief head rotation
What is optokinetic class?
Holds retinal image steady during sustained head rotation
What is smooth pursuit class?
Holds the image of a small moving target on the fovea.
e.g looking at a plane in the sky and tracking it.
What is fixation class?
Holds eyes in primary position
Explain neural control of eye movements
Frontal lobe, parietal lobe, occipital lobe (high cognitive areas) send info the the brain stem. To the pons where cranial nerves are.
Input from the high cognitive areas will arrive at excitatory burst neurons (horizontal and vertical). This then stimulates the III, IV and VI nerves to send signal to eye muscles.
If these were constantly firing our eyes would be jumping all over the place so are kept in check by omnipause neurons. The omnipause neurons turn off when Input from the high cognitive areas will arrive at excitatory burst neurons
How are saccades generated?
Info processed in frontal eye field. This sends the info to:
1. The cerebellum which helps to compute the size and control the movement
2. The superior colliculus. This contains lots of cells to help dictate whereabouts in your visual field you will move your eyes to.
2a. The parietal cortex. Shifts out attention to a new area. and then sends to superior colliculus.
All of these signals then sent to brainstem nuclei.
