Chapter 10
The Ocular Motor System:Gaze Disorders
optic nerve fibers
transmittingimpulses
from the rightvisual fieldstravel in left
optic tract
the visual fields areprojected onto the
retina both inverted and reversed
optic nervefiberstransmittingimpulsesfrom the leftvisual fieldstravel in rightoptic tract
the eyes must move so that the object is
focused on the visualreceptors in thebinocular zone
Types of eye movements:
1. Vergence movements eyes shift between distant and near objects
divergence vs.
convergence
(controlled by brainstem gaze centers and cortical gaze centers)
Types of eye movements:
2. Conjugate movements both eyes move in the same direction
up or downleft or right
saccadicsmooth pursuit
optokineticvestibulo-ocular
(controlled by brainstem gaze centers and cortical gaze centers)
Types of Conjugate movements:
Saccadic - voluntary rapidly moving from one target to another - reflexive nystagmus (ocular ataxia)
rhythmic oscillation of the eyeballs REM sleep
Smooth pursuit - reflex movements that keep the image of a moving target fixed on the retinae
Types of Conjugate movements:
Optokinetic - keep a visual field that is moving past the eyes fixed on the retinae as long as possible, then the eyes quickly fix on the next upcoming visual field
Vestibulo-ocular (ch. 13) - keep targets fixed on the retinae during brief movements of the head
left eye movements:
medial rectus lateral rectus
superior oblique
inferior oblique
inferior rectus
superior rectus
Brainstem gaze centers:
1. Horizontal gaze center in the paramedian pontine reticular formation (PPRF)
2. Vertical gaze center in the accessory oculomotor nuclei of the midbrain (in the periaqueductual gray matter) at the rostral end of the MLF
3. Vergence center in the rostral midbrain (near the oculomotor nuclei)
horizontalgaze center
Fig. 10-2
controlsconjugatemovementstoward theipsilateral side
rightipsilateralcontralateral
MLF
interneurons from the abducens nucleus ascend in the contralateral MLF
right
Horizontal Gaze Center
ipsilateral abducens nucleus
contralateral oculomotor nucleus
rightfrontal
loberight eye left eye
lefthorizontalgazecenter
result of a lesion of the right HGC
result of a lesion of the left MLF
*note - the affected eyewill still adduct
during convergence
right internuclear ophthalmoparesis (INO) upon attempted gaze to the left
T2-weighted axial MRI showing the responsible lesion involving the right pontine tegmentum (arrow).
location of the accessory oculomotor nuclei (vertical center) & vergence centers
In rostral midbrain:
Vertical gaze centers
neurons for upward gazeare more dorsal thanthose for downward gaze
Vergence gaze centers
control convergenceand divergence
(interconnected by the posterior commissure)
posterior commissure
midbrain gaze centers are affected by: pineal gland tumors dilation of cerebral aqueduct
Cortical gaze centers:
projects to the vertical and horizontalgaze centers and the superior colliculus
left
right
(to the contralateral side)
there is also (transient) conjugate deviation of the eyes to the side of the lesion
L Frontal eye field R Frontal eye field
L Horizontal gaze center R Horizontal gaze center
Bilateralism of cortical connections with the brainstem gaze centers:
dominant connectionnon-dominant connection
Fig. 16-6b
parietal association areas: 5, 7, 39, 40process tactile and
visual info.
area 7 has widespreadconnections with the visual
and motor areas of the cortex
affects saccadic eye movements
and visual attention
lesion difficulty moving eyes toward same side, neglect of objects on the opposite side
lesion loss of smooth pursuit & optokinetic movements (when targets are moving toward the side of the lesion)
smooth pursuit movements
& optokinetic nystagmus (slow drift and fast return)
vergencecenters
abducens nuclei
somatic oculomotor neurons medial rectus mm.
(visceromotor) parasympathetic neurons ciliary and pupillary constrictor mm.
temporal eye field
(convergence) (divergence)
Fig. 10-6
Superior Colliculus: involved in reflex turning of head and eyes in response to startling pain or auditory orvisual stimuli
lesion does not result in major eye movement abnormalities
(pain and auditory)
Fig. 10-5 fast
igia
l nuc
lei
the cerebellumhelps with coordination ofeye movements
FEF, prefrontal cortex, and posterior parietal cortex basal ganglia basal ganglia and thalamus FEF and adjacent prefrontal cortex
Parkinson’s disease: seldom or lacking spontaneous ocular movements infrequent blinking (staring appearance)
Flocculonodular lobe fastigial nucleus vestibular nuclei vestibulo-ocular connections to the ocular motor nerves
Unilateral cerebellum lesions: nystagmus (especially when the eyes are directed toward side of lesion)
Chapter 10know the difference between the two types of vergence eye movements know the difference between saccadic and smooth pursuit eye movementsknow the difference between optokinetic and vestibulo-ocular eye movementsknow the cranial nerves that control eye movements and the muscles they innervateknow the locations and functions of the brainstem gaze centersknow the result of a lesion of the horizontal gaze centerknow the result of a unilateral lesion of the medial longitudinal fasciculusknow the two conditions that can affect the vertical and vergence gaze centersknow the locations and functions of the cortical gaze centersknow the result of a lesion of the frontal eye field and whyknow which cortical eye field is associated with contralateral neglectknow the three components of the near response that occur during convergenceknow the function of the superior colliculusknow how basal ganglia and cerebellar disorders affect eye movements
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