Lecture 11 Flashcards
what are the 2 systems needed for clear and stable vision?
eye movement system (stabilize image on fovea) and accommodative system (clear image)
what is a saccadic eye movement?
brings the image of an object of interest rapidly onto the fovea
what is a smooth pursuit eye movement?
holds the image of a small moving target on the fovea
what is a vergence eye movement?
moves the eyes in an opposite direction so that images of a single object are held simultaneously on both fovea
what are 3 eye movements that direct the fovea to an object of interest?
saccades, smooth pursuits and vergences
what are 3 eye movements that hold images steady on the retina?
fixation, vestibular (VOR) and optokinetic
what is a fixation eye movement?
holds the image of a stationary object on the fovea when head is immobile
what is a vestibular (VOR) eye movement?
holds the image steady on the retina during brief head movements
what is an optokinetic eye movement?
holds image steady on the retina during sustained head movements or when the environment moves around the head
what are monocular eye movements called?
ductions
what are versions?
conjugate eye movements - 2 eyes move in the same direction by the same amount
what are vergences?
disjugate eye movements - 2 eyes move in opposite directions
what are the movements called for ductions in the z, y, and x-axis?
z = abduction and adduction y = elevation (supraduction) and depression (infraduction) x = incyclotorsion and excyclotorsion
what are the movements called for versions in the z, y and x-axis?
z = dextroversion and levoversion y = elevation and depression x = dextrocycloversion and levocycloversion
what are 4 types of version movements (conjugate)?
saccadic movement, smooth pursuit, vestibular (VOR) movement and optokinetic movement
what do conjugate eye movements control?
gaze control
what do disjugate eye movements control?
vergence control
what is the input to the frontal eye fields (FEF)? what is the output?
input = many cortical and subcortical areas output = superior colliculus and other gaze centers
what is the function of the frontal eye fields (FEF)?
voluntary eye movements (not guided by target) and scanning the visual field
where are the frontal eye fields located?
frontal lobe of cerebral cortex (brodmann’s area 8)
where is the superior colliculus (SC) located?
pair of nuclei located on the upper surface of the midbrain
what is the input to the superior colliculus (SC)?
retina, auditory system, somatosensory system and frontal eye fields
what is the output from the superior colliculus (SC)?
to other gaze control centers
what is the function of the superior colliculus (SC)?
controls the direction and magnitude of saccades
where is the horizontal gaze center (PPRF) located?
located in the reticular formation of the pons (known as the Paramedian Pontine Reticular Formation)
what is the input to the PPRF?
directly from the superior colliculus, FEF or cerebellum
what is the output from the PPRF?
to nuclei of motor nerves controlling horizontal eye movements (directly or crossing midline via MLF)
where is the vertical gaze center NIC located?
in the rostral part of the midbrain reticular formation (Interstitial Nucleus of Cajal)
what is the output from the NIC?
to nuclei of motor nerves controlling vertical eye movements (CN3 and CN4)
what is the medial longitudinal fasciculus (MLF)?
a midline tract in the medial midbrain and pons - connects the nuclei of the 3 eye movement motor nuclei
what is the input or stimulus for a saccade?
target position, angle in degrees
what is the input or stimulus for a pursuit?
target motion deg/sec
what is the input or stimulus for a vergence?
vergence stimulation from disparity
what is the input or stimulus for accommodation?
target distance in diopters
what is the input or stimulus for VOR/OKN?
target velocity and head velocity
what is the output in accommodation?
change in focus
what is the output in a saccade?
change in angle of the eye/position
what is the output in a pursuit?
change in velocity of the eye
what is the output in a vergence?
change in position of the eyes
what is the output in VOR/OKN?
change in velocity of the eyes
how does an open loop system work?
none of the output is fed back into the input (no fine-tuning of the response)
how does a closed loop system work?
all or part of the output is fed back into the input altering the final output
