Eye and Head Movements Flashcards
which ocular system controls gaze while the head is still?
oculomotor system: extraocular muscles and neural pathways coordinating movement of each eye
which ocular system controls gaze while the head is moving?
head-movement system: moves the eye sockets as a whole while the head moves.
involving vestibular and oculomotor system.
what are saccadic eye movements?
shift fovea rapidly between new visual targets (when looking at different aspect of a painting)
describe smooth pursuit eye mvmts?
keeps the image of a moving target on the fovea
describe ocular vergence?
moves eyes in opposite directions towards the middle to focus on a near object. ie left eye moves right, right eye moves left.
vestibular ocular movements?
holds image still on the retina during brief head movements
optokinetic ocular movements?
holds image still during sustained head rotation or translation
what are the six extraocular muscles acting in 3 antagonist/agonist pairs?
lateral rectus/medial rectus,
superior rectus/inferior rectus,
inferior/superior oblique
where does the superior oblique insert? prime action?
runs through the trochlea (fibrocartilage pulley) and inserts behind the equator at an oblique angle close to the LR.
Acts in Torsion. Brings eye medially and inferiorly.
(opposite of what youd expect)
where does the inferior oblique insert? prime action?
inserts behind the equator close to the LR.
acts in torsion. moves eye medially and superiorly.
opposite of what you’d expect
how do you clinically test the superior rectus?
move eyes laterally and then upwards.
how do you clinically test the superior oblique?
move eyes medially and then inferiorly.
CASE: middle aged male presents with double vision when looking to the sides. Hx of multiple sclerosis. Possible cause?
inter nuclear ophthalmic lesion. medial rectus muscles are deficient bilaterally.
Which nerve innervates MR, SR, IR, IO
oculomotor nerve (III)
which nerve invervates LR?
abducens nerve (VI)
which nerve innervates SO?
trochlear nerve (IV)
explain the hierarchical control over eye movement?
–>controlled by lower motor neurons: oculomotor, abducens, and trochlear.
–>brainstem eye movement centre is in the reticular formation.
–>higher cortical areas (frontal eye fields)
which white matter tract connects cranial nerve nuclei and allows for coordination between eyes for gaze
medial longitudinal fasciculus (MLF)
Vertical gaze centre location and function?
In midbrain reticular formation.
- Coordinates superior oblique and superior rectus of each eye. (UP and DOWN movements=vertical gaze centre)
- coordinates CN III and IV (oculomotor and trochlear)
Horizontal gaze centre location and function?
pontine [paramedian] reticular formation.
- coordinates medial rectus and lateral rectus of each eye. (SIDE TO SIDE movements=horizontal gaze centre)
- coordinates CN III and VI (oculomotor and abducens)
how are burst neurons involved in horizontal saccades?
- fire at high frequency just before movement
- provide excitatory stimulation to ipsilateral abducens
- inhibitory burst neurons to the contralateral abducens nerve
How are omnipause neurons involved in horizontal saccades?
these are inhibitory GABAergic
- project to contralateral abducens
- fire continuously EXCEPT during a saccade
Which segment of reticular formation controls horizontal saccades?
Pontine paramedian reticular formation (PPRF)
–>Receives input from cortex frontal eye fields and posterior parietal cortex
Which UMN’s drive the brainstem gaze centres?
Frontal eye fields (FEF), and posterior parietal cortex
T/F the frontal eye field of the cerebrum controlls saccades in the ipsilateral direction?
FALSE. Controls saccades in the contralateral direction.
How does the vestibular system provide information about position of head in space?
semicircular canals (x3) sense head position otoliths organs (x2) sense linear acceleration
to control gaze when the head turns left, where does the left vestibular nucleus signal downstream?
to the CONTRALATERAL abducens nerve nucleus.
Describe the chain of events in maintaining gaze when the head turns left?
left horizontal semicircular canal signals to left vestibular nucleus,
signals to right abducens nucleus AND to left oculomotor nucleus,
right abducens nucleus signals to lateral rectus muscle of right eye AND to left oculomotor nucleus,
lateral oculomotor nucleus signals to medial rectus of left eye.
