L45 - Eye movement Flashcards
Importance of eye movement?
- Highvisualacuityisrestrictedtothefovea
2. Eyemovementscandirectthefovea to newobjectsofinterest-“foveation”
Pathways for pupillary constriction and dilation?
In bright light:
- parasympathetic stimulation on circular (constrictor) muscle of iris runs circularly
- pupillary constriction
In dim light,
- sympathetic stimulation on radial (dilator) muscle of iris runs radially
- pupillary dilation
List the 5 types of eye movements? Classify into 2 categories?
Gaze-shifting movements (voluntary/ attention)
(1)Saccades (2)Smoothpursuit (3)Vergence
Gaze‐stabilizing movements (Reflexive)
(4)Vestibulo‐ocularreflex (5)Optokineticreflex
Innervation of the extraocular muscles?
Superior oblique = CN IV Trochlear
Lateral rectus = CN VI Abducens
All the rest: Superior rectus,Inferior rectus, Medial rectus, Inferior oblique = CN III Oculomotor
Describe saccadic eye movement? Is it voluntary or not?
Voluntary Rapidmovements ofbotheyes in the same direction betweentwophasesof fixation(conjugateeyemovement)
+
Verysmallmicro‐saccades(involuntary) to prevent fading
Drivenmainlybypositionsignals
Time course of saccadic eye movement?
Timecourse:200‐250ms
Describe smooth pursuit movement? Is it voluntary or not?
Slow,smootheyemovementsusedtotrackmoving objectsoncefoveation isachieved
Quasi-voluntary:
Can choose whether or not to track a moving stimulus, but
Cannot voluntarily generate smooth pursuit in the absence of a moving target
2 basic response phases of smooth pursuit eye movement?
- Pursuit initiation (= open-loop phase ~0.1s: catchup saccade)
- Pursuit maintenance (driven by velocity error / retinal slip: alternative focus + out-of-focus)
Describe Vergence eye movement? Is it voluntary?
disconjugate movements used to converge the eyes onto targets at different distances
Reflexive + voluntary components
- Convergence of lines of sight of each eye to see an object that is nearer
- Divergence of lines of sight of each eye to see an object that is father away
What drives vergence eye movements?
binocular disparity of a target to be fixed
> > align the fovea of each eye with targets located at different distance
Which of the gaze-shifting eye movements are opposite in action?
Vergence = Disconjugate eye movement
Saccadic = conjugate eye movement
Function of vestibular-ocular reflex?
stabilize the eyes on a target during rapid head movements
Describe the eye movements in vestibular-ocular reflex?
Vestibular system detects brief, transient changes in head position
> > Eye moves in opposite direction to head
> > preserves image on the center of visual field
> > physiologic nystagmus
What are the 2 forms of vestibular-ocular reflex and which organs are involved?
- Rotational VOR: driven by signals from the semi-circular canals which sense head rotations
- Translational VOR: driven by signals from the otolith organs which sense linear head acceleration
Describe the reflex arc in vestibulo-ocular reflex?
- Stimulus = head movement
- Afferent = vestibular nerve
- Center = vestibular nucleus
- Efferent = oculomotor nerves, abducens nerves
- Effector = extra-ocular muscles
Describe the neuronal control pathways in the right semi-circular canal when the head turns right?
endolymph turns from right to left due to inertia
> > depolarize hair cells
action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
medial longitudinal fasciculus:
Contralateral abducens nucleus (VI) = stimulate contralateral lateral rectus
Ipsilateral oculomotor nucleus (III) = stimulate ipsilateral medial rectus
> > > > > Eyes focus on left
Describe the neuronal control pathways in the left semi-circular canal when the head turns right?
endolymph turns from right to left due to inertia
> > hyperpolarize hair cells
less action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
through medial longitudinal fasciculus
Contralateral abducens nucleus (VI) = inhibit contralateral lateral rectus
Ipsilateral oculomotor nucleus (III) = inhibit ipsilateral medial rectus
> > > > > Eyes focus on left
Describe the VOR suppression test?
Visual fixation on outstretched hands + rotate chair from side-to-side
Normal = eyes remain fixed on outstretched hands
Abnormal = eyes move in opposite direction to rotation with catch-up saccades to re-fix gaze on outstretched hands
Describe the Caloric reflex test for comatose patients?
Head tilted back 60o
horizontal canals of reclining patient are nearly vertical
Warm water on right causes ampullofugal flow in right horizontal duct = action potential
Cold water on left causes ampullopetal flow in left horizontal duct = less action potential
Function of Optokinetic eye response? Is it voluntary?
stabilizetheeyesduringheadmovements
Drivenbyretinaslip(likepursuit)but reflexiveandinvoluntary.
Optokinetic eye response work with which other eye movement?
TheVORandoptokineticsystems actinacomplementary.
Operateeffectivelyinresponsetoslow (below1Hz)headmovements,wheretheVORhaslowgain.
Together,theykeepthe eyesontarget
Describe optokinetic nystagmus?
alternatingslowandfastmovement oftheeyesinresponsetoanystimuli
Which side of the cortex processes which side of the visual field?
Left half of visual cortex receives information from the right half of the visual field/ left half of retinal yield of both eyes
Right half of the cortex receives information from the left half of the visual field/ right half of retinal field of both eyes
Describe the motor neuronal activity in saccadic eye movement? (think is the AP constant?)
‘Burst-tonic’ neuronal firing pattern
Abducens neuron fires a burst of activity that precedes the movement > move eye into position
In between saccades, these neurons have tonic firing > maintain static eye position
Which 3mainbrainareasare involvedinselectingvisual targetsforsaccadesand planningthemovements?
(a)Superiorcolliculus (b)Frontaleyefields (c)Lateralintraparietalarea
What are the 2 ‘fields’ processed in the visual pathway brain regions?
spatially overlapping:
(a) Visual receptive field: region of space in which visual stimuli activate cell
(b) Movement field: a region of the visual field for which the neuron responds BEFORE execution of a saccadic eye movement
Compare the brain areas that modulate visual signals vs sensory and attentional signals?
- Visualsignals = dorsalspatialvisionpathway in occipital lobe
- Sensoryandattentionalsignals = frontaleyefield near frontal lobe
- Initiation andcoordinationofeyemovement = superiorcolliculus + oculomotorcentersinreticular formation +vestibularnuclei
Describe the place code for saccade vectors and the 3 types of neuronal response to onset of visual target?
InSC,FEF,thesaccadevectorproducedbymicrostimulation
=sameindependentof startingeyeposition
3typesofresponsesofneuronsinallthreeareas
(a)Visualneurons: respondbrisklytoonset
(b) Visual/movementneurons: brisk responsetovisualtarget+burstof activitybeginningrightbeforesaccade
(c) Movementneurons: novisualresponsebut clearburstofactivityaroundsaccade
Describe the visual neuron response to onset of visual target? Activity before saccadic eye movement?
respondbrisklytoonsetof visualtargetinreceptivefield
Noburstofactivityaroundtimeofsaccade
Describe the visual/ movement neuron response to onset of visual target? Activity before saccadic eye movement?
brisk responsetovisualtargetandalsoburstof activitybeginningrightbeforesaccade
Describe the movement neuron response to onset of movement target? Activity before saccadic eye movement?
novisualresponsebut clearburstofactivityaroundsaccade
Relate the layers of the superior colliculus to the neurons involved in saccadic eye movement
Superficial = visual neurons Intermediate = Visual/ movement neuron Deep = movement neuron
Which brain area do saccade planning and generation?
Superior colliculus = planning the particular metrics (amplitude, direction)of a saccade.
Frontal eye field = higher level role in target selection for saccade
Damage to one of SC or FEF causes permanent loss of saccadic eye movement. T or F?
False
Lesions made to the SC alone or the FEF alone cause transient deficits with saccades, but these largely recover
lesions are made to both SC and FEF = permanent loss
Frontal eye field send signals to which brain region for processing horizontal movement?
Horizontalmovement–ParamedianPontine ReticularFormation(PPRF)
2 pathways:
1) Indirect:byprojectionstotheipsilateral SuperiorColliculus,whichinturnprojectsto thecontralateralPPRF.
2)Direct:byprojectionstothecontralateral PPRF
Describe outflow tracts of the Paramedian Pontine Reticular Formation. (For horizontal eye movement)
1) Ipsilateral Lateral rectus (abducen)
2) Medial longitudinal fascilulus > Contralateral oculomotor nucleus > Contralateral Medial rectus
Part of brain affected: Gazetotheright impaired.
Lesion upstream to right abducens nucleus
Part of brain affected: Impairedadductionof lefteye.
Lesion in left medial longitudinal fasciculus
Part of brain affected: Impairedadductionof lefteyeandptosis.
oculomotor nerve palsy (common)
Part of brain affected: Eyescannotbemovedto right.Intactleftpontine centermoveseyestoleft
Lesion upstream to right pontine gaze center
Which brain area integrates sensory input (sound, vision)?
Angular gyrus of parietal-temporal-occipital association cortex
