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34 Cards in this Set
- Front
- Back
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What role does CN VII play in oculomotor control?
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Efferent limb of corneal/blink reflex
(parasympathetic innervation of lacrimal gland) |
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What are eye movements in the same direction? different?
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Conjugate
Convergence (or Vergence) ... medial only |
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What are the six eye movements? (directionally)
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elevation, depression, abduction, adduction, intorsion, extorsion
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Where is the fovea in relation to the optic nerve?
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lateral (see relationship of visual axis to orbit)
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What CN would making a pt look down and in test? How?
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CN IV; by making sup. oblique a pure depressor --> weakness will be evidenced by vertical diplopia
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What eye movements are carried out by the S.O.? I.O?
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Superior O.:Depression, Abduction, Intorsion
Inferior O.: Elevation, Abduction, Extorsion recall: both attach medially and at ~45 degrees to eyeball |
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What would a left head tilt possibly represent? explain
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Damage to the right CN IV.
Right S.O. paralyzed --> chronic extorsion --> left head tilt initiates vestibular system causing: left eye intorsion (now lined up with right eye) |
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What are the three inputs to extra-ocular eye movements?
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Vestibular
Visual Voluntary |
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What eye movements rely on the MLF? (Medial Longitudinal Fasiculus)
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horizontal
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What two nuclei does the MLF connect?
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CN VI (Abducens) (Lat. rectus) and CN III (Med. rectus)
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How are the eyes affected by a lesion on one side of the MLF (intranuclear)?
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Failure of adduction on affected side (medial rectus)
Nystagmus in abducting eye (lateral rectus) --> there is believed to be some cross-inhibition of the medial rectus (CN III) from the MLF interneuron to allow for smooth horizontal movements, which is knocked out by the lesion |
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Why can someone with an MLF lesion still have convergence?
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vergence movements are organized in the rostral midbrain and do not require the circuitry of the MLF
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What type of lesion would cause 1 and 1/2 syndrome? how?
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a lesion on the CN VI nucleus (Abducens) that also inhibits the MLF going to the other side.
this knocks out the signal to both eyes to look to the side of the lesion and also blocks the incoming signal from the CN VI nucleus (Abducens) on the other side coming to the CN III nucleus on the lesioned side |
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What does an electro-oculogram test?
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Eye movement
using the +6 mV resting potential of the retina |
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What is required for smooth pursuit? what is happening?
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visual target (moving)
the image stays "fixed" on the retina |
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What are quick eye movements that serve to move an image across a retina?
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saccades
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What stabilizes the retinal image despite movements of the head? which system controls this?
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Vestibulo-ocular Reflex (VOR)
completely vestibular, occurs even when eyes closed |
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If the head moves right, what direction do the eyes move in the VOR?
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left
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Which movements stabilize the image of the "background"?
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Optokinetic movements
(synergistic with VOR) |
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What are the two phases of Optokinetics?
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optokinetic phase (slow; stabilizes retinal image) and
quick reset phase (resets the eye's position in the orbit) |
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Where is the "control" for vertical eye movements? horizontal?
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Vertical = Rostral Midbrain Reticular Formation (ventral to superior colliculus, near CN III nucleus)
Horizontal = Paramedian Pontine Reticular Formation (just ventral to CN VI nucleus) |
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What is the disease with paralysis of upward gaze? what would cause this?
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Parinaud's syndrome
compression of Rostral Midbrain Reticular formation (controls vertical eye movements), possibly from pinealoma |
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* What are the different paths for quick and slow eye movements starting in the Cerebral cortex (frontal, parietal or occipital lobes)
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Slow = cerebral cortex --> Pontine Nuclei + Vestibular Nuclei (Medulla) --> Cerebellum (flocculus) --> Oculomotor Nerves
Fast = cerebral cortex --> Superior Colliculus (Midbrain) --> Reticular Formation of pons and midbrain (esp. Paramedian pontine reticular formation - PPRF) --> Oculomotor Nerves |
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What is common in tonic lesions?
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"look to the lesion"
If lesion on right, motor on left is unopposed and can push eyes right |
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Which two eye muscles have contralateral sources of their axons? what does this mean for the side lesions affect?
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superior rectus and superior oblique receive axons that cross after exiting their nucleus
However, since the longest part of the axon is ipsilateral, weakness or paralysis usually indicates an ipsilateral lesion. |
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what is the large myelinated tract of the brainstem that provides coordinated circuitry?
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Medial Longitudinal Fasiculus (MLF)
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* what are the principle functions of Fast and slow eye movements?
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Fast: displace an image from one part of the retina to another
Slow: prevent an image from moving on the retina (making it stick) |
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Note:
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Quick eye movements are ALWAYS conjugate (same direction)
slow movements can be conjugate or vergent |
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do quick and slow movements originate from the same parts of the brain?
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no, separate in higher, premotor parts of the system and converge in the final pathway, the oculomotor neurons themselves
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Which organs are sensitive to linear accelerations? angular rotation?
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otolith organs
semicircular canals |
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Do the eyes need to be open for optokinetic movements? VOR?
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optokinetics: Yes
VOR: No |
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What is the residual jitter of the eye?
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physiological nystagmus
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How do we know higher cortical areas are involved in smooth pursuit?
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it uses a predictive strategy, generating and internal replica of the target velocity and matching eye velocity to this
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Which cranial nerves are responsible for vertical movement and vergence?
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CN III and CN IV
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