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85 Cards in this Set

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  • Back
What muscles control movement of the eyes?
Extra-ocular muscles
How many extra-ocular muscles are there?
Six
What muscles control accomodation and pupillary responses?
Intraocular muscles
What condition can cause rapid, randomly moving eyes? What is the problem and what is it usually caused by?
1. Saccadomania or Opsoclonus
2. Control system is messed up
3. Virus
What are rapid back and forth eye movements called?
Saccades
What muscle mediates intorsion?
Superior oblique
What muscle mediates extorsion?
Inferior oblique
What does the cilary muscle do? What is unique about this muscle?
1. Positive accomodation
2. It has no antagonistic muscle. Instead the suspensory ligaments act as the antagonist.
What causes pupil dilation? What ANS system causes this?
1. Dilator pupillae
2. Sympathetic
What causes pupil constriction? What ANS system causes this?
1. Sphincter pupillae
2. Parasympathetic
What reflex is absent in the eyes?
Stretch reflex
How does one keep track of eye position?
Create a corollary discharge/efference copy which is a copy of the signal sent to the muscles.
What is used to keep spatial constancy?
The corollary discharge.
What is spatial constancy?
The fact that as you move your eyes back and forth, the world doesn't seem to move even though the image is being projected on different parts of the retina.
Where does the corollary discharge signal come from?
The parietal complex
What is a property of eye movements in relation to one another?
Almost every eye movement is yolked.
Which eye movement is not yolked?
Changes in viewing distance.
Rule number seven states "Eye movements are controlled by __________"
Distinct neurological subsystems
What holds images of the seen world steady during sustained head rotation of the head?
Optokinetic system
What holds images of the seen world steady during brief heard rotation?
Vestibular system
What holds moving targets on the fovea?
Smooth pursuit
What is the quick eye movement from one location to another called?
Saccades
How long should it take you to go from looking at one side of the computer screen to the other?
30-40 milliseconds
What type of movement moves the eyes in different directions so one can see something at the same distance?
Vergence
At what speed does smooth puruit fail?
100 degress per second
What is it called when the eye has a distinct movement when the fluid in the semicircular canal is sloshing around?
After-nystagmus
What does the pupillary reflex control?
The amount of light that illuminates the retina.
What is the vestibular ocular reflex?
Where your head moves in one direction while your eyes move in the opposite direction to keep their gaze in the same position.
Describe what happens in the VOR.
1. You have a transient movement of the head and the eyes.
2. A neural signal then maintains the contraction of the muscles to hold the eye position against the elastic forces of that try to return the eye to its primary position.
What is a method for measuring eye velocity?
Using a contact lens with wires in it that produce a magnetic field that tracks eye movements.
At what frequencies does the gain of the VOR not come very close to one?
Less than 1 Hz
Describe the mechanism of the horizontal VOR.
1. Head moves to the right
2. Right semicircular canals pick the movement up
3. They transmit a signal to the medial vestibular nuclei
4. The MVN sends a signal to the contralateral VI that causes the left eye to abduct
5. The contralateral VI transmits a signal to the III that is contralateral (ipselateral to the head movement)
6. III now causes medial movement which results in that that eye looking left as well
7. Signals from the left semicircular canal also inhibit the opposite III and VI so the eyes may look left easier
What type of movements is the PPRF involved in?
Horizontal eye movements
Where are vertical eye movements organized?
The rostral interstitial nucleus of the MLF in the mesencephalic reticular formation
The vestibular system operates better at (higher/lower) frequencies?
Higher
What system is used at lower frequencies?
Optokinetic
Optokinetic movements are activated by what type of movements in our visual field?
Large movements (like the imax theater)
How do your eyes tend to move when large sections of the eye field move?
They tend to track the whole movement.
What part of the brain is sensitive to large eye field movement signals sent by the retinal ganglion cells?
Archaic part of the brain in the pretectum.
If you break nystagmus into a quick phase and a slow phase, what would happen during each phase?
1. Quick phase - return
2. Slow phase - following
Experimentation has shown what in regards to the function of the optokinetic system when spinning in the light?
1. It replaces the vestibular system after it decays continuing the compensatory eye movements
2. It prevents after-nystagmus upon completion of spinning
Why does the brain compensate for the whole world moving?
Becaue it isn't supposed to be moving...you are!
What are voluntary eye movements used to look at objects of interest?
1. Saccades
2. Smooth pursuit
3. Vergence
How many saccades do we have per second when just sitting around?
2-4
How fast can your eyes move during a saccade? Accelerate?
1. 600 degrees per second
2. 10000 degrees per second squared
Is the system for controlling saccades usually on or off?
On, you have to turn it off to look at something of interest.
Where is the premotor cicuitry for saccade movements usually located?
In the PPRF
What is the nature of the muscles firing during a saccade?
1. First you have a transient burst of large force to move the eye intially
2. Then you have muscles fire to hold it in place tonically
Motor neurons have to have what in order to cause a saccade?
High spontaneous firing rate
Ocular movement is one of the last movements to go in what disease?
ALS
Where are the signals that develop the tonic eye position located?
Nucleus prepositus hypoglossi
What inhibits burst neurons?
Omnipause neurons
What are the two steps in having an eye movement?
1. The trigger
2. The size of the eye movement
What determines the size of an eye movement?
Superior colliculi
What must be shut down to have an eye movement?
The OPN
What do burst sizes correlate to?
Saccade sizes
How does a burst get transformed into a saccade movement?
The nucleus prepositis integrates the signal and turns it into a sustained firing rate.
What has to shut down in order for burst and tonic firing to proceed
OPN activity
What sort of relationship does sccade size have with burst size?
Linear
How does the saccade know where it needs to stop?
It compares known eye position to the target eye position.
When a saccade is taking place, what are the inhibitory burst neurons inhibiting?
The omnipause nucleus so tha the saccade can take place.
In the feedback mechanism for saccades, how long is the delay when sending position information back to the EBN?
5 ms
What happens in the saccade feedback mechanism when the eye position matches up?
The IBN is inhibited and it now is no longer inhibiting the OPN which then inhibits the EBN.
Where does the signal that tells where the eye should be orginate?
1. Frontal eye fields
2. Superior colliculis
It was originally thought that the signal coded for desired eye position but now it thinks what?
It codes for changes in eye position.
Where is a 2D motor-map that allows you to orient quickly to differently stimuli?
The superior colliculus
Where in the superior colliculus is the area for large saccades? Small saccades? Vertical downward? Vertical upward?
1. Caudally
2. Rostrally
3. Laterally
4. Medially
A shift in activity in the superior colliculus shifts in what direction?
In the direct of the activity
What ar ethe two cortical areas needed in eye movements?
1. Frontal eye fields
2. Parietal eye fields
What type of movement is impaired with damage to the frontal eye fields?
Memory guided saccades
Schizophrenics have problems with what kind of eye movements?
Anti-saccades
How do the parietal eye fields help in controlling the saccades?
They relay information directly to the superior colliculus. They determine the relationship between an object and the individual in the extrapersonal space.
What is intimately involved in motor learning and therefore involved in saccades over time?
Cerebellum
Where is eye movement calibrated?
The cerebellum
What happens if the signal to the EBN is insufficient?
You get long drawn out, slow eye movements.
What happens if the tonic activity in a saccade is affected?
The eye will drift back to its original position instead of being held in the new position.
What is the visual cue for tracking?
Velocity
When an object is moving too quickly to be tracked, what happens?
Saccades predominate
Where does information for smooth tracking originate? Where is it sent next and where does it end up?
1. The retina
2. The lateral geniculate
3. The striate cortex
What role do the frontal eye fields play in smooth tracking?
Predicting where an object will come out after passing behind an obstruction.
The information for smooth tracking goes through what steps in its pathway?
Dorsolateral pontine nuclei, relaying in the cerebellum, impinging on the medial vestibular nuceli and sent to the occulomotor nuclei
Where is it believed that signals for smooth pursuit, vestibular signals and optokinetics are integrated?
Medial vestibular nucleus and then passed on to occulomotor nuclei
When does smooth pursuit develop?
6 to 9 months
Which eye movements are not yoked?
Vergence
What two things make up the near response?
Congvergence and accomodation