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