Cranial Nerves - Oculomotor Flashcards
For the visual system to work efficiently, both eyes
must focus and remain focused on an object so the information can reach cortex in a form that can result in vision.
While we can detect objects over a large range extending into the periphery, we “see” objects only when
they are focused on the fovea
The oculomotor system works primarily
control the movement of our eyes
The oculomotor system works primarily to control the movement of our eyes, and is designed to (2)
- bring targets onto the fovea
2. keep them there
Historically five movement systems have been identified that put the fovea on a target (both eyes in a conjugate manner; foveation) and keep it there. (5)
- Vestibulo-ocular
- Optokinetic
- Saccade
- Smooth pursuit
- Vergence
Systems that stabilize the eye when the head moves (2)
- Vestibulo-ocular
2. Optokinetic
How does Vestibulo-ocular stabilize the eye when the head moves?
Vestibular input holds images stable on retina during head and body movement; gaze stabilization
How does Optokinetic stabilize the eye when the head moves?
visual input holds image stale on retina during sustained or slow head rotation
Systems that keep the fovea on a visual target (3)
- Saccade
- Smooth pursuit
- Vergence
How does Saccade keep the fovea on a visual target?
brings new object of interest onto fovea
How does Smooth Pursuit keep the fovea on a visual target?
holds image of a moving target on the fovea
How does Vergence keep the fovea on a visual target?
adjusts the eyes for viewing different distances in depth
In an oculomotor system that is functioning normally, the two eyes are “locked together which allows
for both eyes to be focused on an object
What is retinal disparity?
If the oculomotor system becomes “unlocked” and the eyes focus on different targets.
What happens to vision if retinal disparity occurs?
diplopia or double vision occurs.
Vestibulo-ocular, Optokinetic, Saccade, and Smooth pursuit allow for
a. conjugate movements
b. disconjugate movements
a. conjugate movements of the eyes for foveation
Vergence allows for
a. conjugate movements
b. disconjugate movements
b. disconjugate movements, convergence and divergence
The ___ system is used to quickly reposition the eyes (fovea) to focus on an image that has suddently been moved from the fovea.
Saccade System
T/F: Saccades can be horizontal or vertical.
True
The rapid eye movement required to bring the image back into focus is a
saccade
Reading a neuro handout is done by a series of
conjugate saccadic eye movements
Saccadic eye movements can be elicited by
visual input, as well as other stimuli, such as auditory stimuli, memories of locations, or verbal commands
With saccadic eye movements, both eyes move in a conjugate manner, in terms of
velocity, amplitude, and direction, for reestablishment of the image on the fovea.
The conjuage saccade system is directed through a
horizontal gaze center
the horizontal gaze center is located in the
pontine reticular formation (paramedian pontine reticular formation; PPRF) adjacent to the abducens nucleus.
The saccade system UMN control is a complicated system of interneurons, that involves a part of the
middle frontral gyrus termed the Frontal Eye Fields (FEF; area 8) and the Superior Colliculus.
The middle frontal gyrus termed the Frontal Eye Fields (FEF; area 8) and the Superior Colliculus is represented on both hemispheres and contains specific regions termed
horizontal gaze center, vertical gaze center, and vergence center. (these are separate and distinct regions within area 8.
