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, controlling the movement of our eyes, is designed to (2 functions):
1) bring targets onto the fovea, and 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. They are as follows:
- movements that stabilize the eye when the head moves
2. movements that keep the fovea on a visual target
Movements that stabilize the eye when the head moves are classified as ___________________ and ____________________.
• vestibulo-ocular
and
• optokinetic
Movements that keep the fovea on a visual target are classified as ___________________, ___________________ and ____________________.
- saccade
- smooth pursuit
- vergence
vestibulo-ocular =
vestibular input holds images stable on retina during head and body movement; gaze stabilization
optokinetic =
visual input holds images stable on retina during sustained or slow head rotation
saccade =
brings new objects of interest onto fovea
smooth pursuit =
holds image of a moving target on the fovea
vergence =
adjusts eyes for viewing different distances in depth
In an oculomotor system that is functioning normally, the two eyes are:
“locked” together.
This allows both eyes to be focused on an object.
If the system becomes “unlocked” and the eyes focus on different targets (retinal disparity), what occurs?
diplopia or double vision occurs.
While the first four systems allow for the conjugate movements of the eyes for foveation, the vergence system allows for:
convergence or divergence (disconjugate movements)
What is diplopia?
the subjective complaint of seeing 2 images instead of one and is often referred to as double-vision.
The Saccade System is used to quickly:
reposition the eyes (fovea) to focus on an image that has suddenly been moved from the fovea.
Saccades can be ________________ or _________________.
horizontal or vertical
with the horizontal being the best understood from a neuronal pathway point of view.
What is the rapid eye movement required to bring the image back into focus?
saccade
Reading this card is done by a series of ________________ saccadic eye movements.
conjugate
Saccadic eye movements can be elicited by what types of inputs?
Visual input, auditory stimuli, memories of locations, or verbal commands.
Both eyes move in conjugate manner, in terms of ______________, _______________ and _____________ for reestablishment of the image on the fovea
velocity, amplitude and direction for reestablishment of the image on the fovea
This movement (reestablishment of image on fovea) is similar to the quick or saccade phase of _________________________.
vestibular nystagmus
This conjugate system is directed through a horizontal gaze center located in the ________________________________________,
pontine reticular formation (paramedian pontine reticular formation; PPRF)
Where is the PPRF located?
adjacent to the abducens nucleus.