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39 Cards in this Set
- Front
- Back
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Eye movements are made in order to
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Maintain objects of interest in the centre of gaze
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Saccades ?
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-Rapid eye mvts (upto 900 degrees/s) that can be made voluntarily to change direction of gaze.
-Used to track rapidly moving targets. |
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Smooth pursuit mvts?
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Used to track slowly moving objects(upto 100 degree/s)-require a MOVING target.
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What happens during periods of fixation in smooth pursuit mvts?
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Eyes relatively stationary-most visual processing occurs then.
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How many extraoccular muscles ?
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6--> 4 rectus muscles + 2 obliques muscles.
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4 rectus muscles arise at
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Apex of orbit
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4 rectus muscles insert
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Into the sclera in front of the equator.
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Superior oblique ?
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Travels anteriorly and passes over bony trochlea.
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Obliques insert ?
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behind equator.
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Motor neurons of the Superior Oblique found in
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Trochlear nucleus
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Mtor neurons of the Lateral rectus found in
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Abducens nucleus
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How many types of neurons feed directly or indirectly onto motor neurons?
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3
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Name them.
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-Tonic neurons
-Burst neurons -Omnipause neurons |
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Tonic neurons do what ?
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Maintain static position of eyeball-->greater firing rate-->increased contraction of corresponding muscle--> greater deviation of eye.
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Tonic neurons excite
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Motor neurons that innervate eye muscles.
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Do burst neurons fire all the time?
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NO-only during a saccade ensuring rapid acc. of the eye during movement.
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Omnipause neurons?
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Interneurons in brainstem(Pons)
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Role of omnipause neurons?
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-Inhibit neurons during fixation preventing unwanted saccades
-during saccades,they stop firing--> release inhibition on burst neurons. |
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Tonic neurons ?
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Interneurons in medulla
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If left eye moves to left,
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Right eye moves to left,by same amount.
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Pt with lesions in pons cant make mvts in ispsilateral side but
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can make mvts to contralateral side.
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What happens during a horizontal saccade to the left in both eyes?
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-Both burst & toic neurons excite left lateral rectus and right medial rectus muscles.
-Left medial rectus & right lateral rectus motor neurons inhibited. |
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What is a central structure in brainstem involved in eye mvts ?
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Paramedian pontine reticular formation.
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Lesion in region of pons will
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disrupt HORIZ. mvts to the ipsilateral side
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Lesion to corresponding MIDBRAIN region will disrupt ?
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Vertical eye mvts
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A lesion to the MEDIAL LONGITUDINAL FASCICULUS will disrupt
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Coordination of 2 eyes.
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Load conditions for the oculomotor control system are
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Constant
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Feedback is provided by ?
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Retinal image displacement(saccades) and velocity(smooth pursuit).
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What does the inner ear contains ?
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-->Sensory apparatus that signals
-linear and angular acceleration of the head -angle of head wrt gravity |
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Otolith organs ?
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-Utricle
-Saccule |
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Membranous labyrinth is filled with ?
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-Endolymph
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Membranous labyrinth consists ?
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-3 semicircular ducts(mutually orthogonal)
-2 chambers(utricle & saccule) |
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Where does sensory transduction occur in the vestibular system?
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-Ampullae and Maculae
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Ampullae and Maculae contain
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Hair cells that protrude into jelly(excited when stereocilia bend twd kinocilium)
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Hair cells in the utricle and saccule respond to
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-Linear acceleration in horiz./vertical plane
-Angle of head wrt gravity |
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Hair cells in utricle and saccule important for ?
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Posture and movement control.
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Hair cells in semicircular ducts respond to
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Angular acc. of head abt their axes.(ducts on left and right sides of head act in differential pairs)
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Connections between afferents from semicircular ducts and oculomotor system ensure that
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Head mvts are accompanied by equal and opposite eye mvts so that eyes remain fixed in space ,avoiding BLURRED vision.
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Nystagmus
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Alternating slow and rapid eye mvts elicited in normal subjects by rotating them in a chair.
-maybe present in pt with lesions of vestibular system,oculomotor,cerebellar pathways. |
