Flashcards in Eye and Head Movements Deck (55):
What are the two components for the control of gaze?
What does the oculomotor system control?
Moves eyes in orbit while head is still
What structures does the oculomotor system include?
Neural pathways coordinating movement of each eye
What does the head-movement system control?
Moves eye sockets as a whole while head moves
What structures does the head-movement system include?
What are saccadic eye movements?
Shifts fovea rapidly to new visual target
What are smooth pursuits?
Keeps image of moving target on fovea
What is vergence?
Moves eyes in opposite directions
- Convergence = going cross-eyed
- Divergence impossible
What are vestibular ocular movements?
Holds image still on retina during brief head movements
What are optokinetic movements?
Holds image stationary during sustained head rotation/translation
How many extraocular muscles are there?
What are the rectus muscles?
What are the oblique muscles?
Which muscle does superior oblique go underneath?
Which muscle does inferior oblique go near?
What kinds of actions do extraocular muscles have?
What is the primary action of superior rectus?
What is the primary action of inferior rectus?
What is the primary action of medial rectus?
What is the primary action of lateral rectus?
Where do the rectus muscles insert?
Where does the superior oblique insert?
Well behind equator at oblique angle close to lateral rectus
Through which structure does the tendon of the superior oblique run?
What is the primary action of superior oblique?
Torsion - down and in
Where does the inferior oblique insert?
Behind equator close to lateral rectus
What is the primary action of inferior oblique?
Torsion - up and out
Which muscles elevate and depress the eye when it is adducted?
Elevate = inferior oblique
Depress = superior oblique
Which muscles elevate and depress the eye when it is abducted?
Elevate = superior rectus
Depress = inferior rectus
What does the hierarchical control of eye movements involv?
LMNs = cranial nerves
Brainstem eye movement centres = reticular formation
Higher cortical area = frontal eye fields
Where are the frontal eye fields?
Near motor cortex
Which muscles are innervated by the oculomotor nerve?
Which muscles are innervated by the trochlear nerve?
Which muscles are innervated by the abducens nerve?
What is the medial longitudinal fasciculus (MLF)?
White matter tract > connects various cranial nerve nuclei
Which cranial nerve nuclei does the MLF especially connect?
What is the reticular formation?
Coordinates action of nuclei controlling eye movements
What are the two reticular formations?
Pontine paramedian reticular formation
Mesencephalic paramedian reticular formation
What does the pontine paramedian reticular formation control?
Horizontal gaze centre
Coordination of medial rectus and lateral rectus of each eye
Coordination of CN III and CN VI
What does the mesencephalic paramedian reticular formation control?
Vertical gaze centre
Coordination of superior oblique and superior rectus of each eye
Coordination of CN III and CN IV
What are burst neurons?
Fire at high frequency just before movement
Excitatory connections with ipsilateral abducens
Inhibitory connections suppress activity of contralateral abducens
What are omnipause neurons?
Fire continuously except during saccade
Project to contralateral abducens nucleus
What is needed for neural control of saccades?
Simultaneous excitation of burst neurons and inhibition of omnipause neurons
What is the sequence of events for the horizontal neural control of saccades?
1. Frontal eye fields send signal
2. Ipsilateral excitatory burst neurons in PPRF depolarises
3. Excitatory synapse in ipsilateral abducens nucleus
4. Ipsilateral CN VI sends signal
5. Lateral rectus contracts
6. MLF sends signal from ipsilateral abducens nucleus to contralateral oculomotor nucleus
7. Contralateral CN III sends signal
8. Medial rectus contracts
9. Ipsilateral inhibitory burst neurons in PPRF send signal
10. Contralateral abducens nucleus inhibited
11. Contralateral CN VI inhibited
13. Contralateral lateral rectus relaxes
14. MLF sends signal from contralateral abducens nucleus to ipsilateral oculomotor nucleus
15. Ipsilateral oculomotor nucleus inhibited
16. Ipsilateral oculomotor nerve inhibited
17. Ipsilateral medial rectus relaxes
What are eye movements ultimately driven by?
Which upper motor neurons drive brainstem gaze centres?
Frontal eye fields
Posterior parietal cortex
In which direction do frontal eye fields control saccades?
What happens when there is a lesion in the medial longitudinal fasciculus?
What provides information about the position of the head in space?
What is the role of the vestibular system in controlling eye movements?
Coordinates position of head and eyes
What structure gives information about head position?
What structure gives information about linear acceleration?
How do the vestibular sensory receptors work?
Crystals and fluid inside vestibule over hair cells
Hair cells have cilia
Move head > move fluid > move cilia
Hair cells depolarise or hyperpolarise
With which cranial nerves does the vestibulocochlear nerve communicate to coordinate eye movements when the head moves in the horizontal plane?
CN III and VI
Which nucleus receives vestibular information?
Vestibular nuclei in medulla