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| High acuity vision relies on images staying on the... |
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Saccades are rapid eye movements (up to 900º/s) that can be made voluntarily to change the direction of gaze.
They are also used to....
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| track rapidly moving targets |
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| At the fovea there are all ... and no ... |
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| If object goes left right it is known as.... |
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| If object goes closer or further is known as |
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| Version and vergence mean... |
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| Version is when eyes move in same direction and verasion is when eyes move in opposite directions. |
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Smooth pursuit movements are used to track slowly moving objects (up to ...) – they require .... |
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From the geometry of the 6 extraocular muscles (...) it is simple to work out the major action of each muscle. For version movements, ...must be coordinated with the opposite .... |
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| (4 rectus and 2 oblique muscles), lateral recti , medial recti |
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| The trochlear nerve (the fourth cranial nerve, also called the fourth nerve, IV) is a motor nerve (a “somatic efferent” nerve) that innervates a single muscle: the ... muscle of the eye. |
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| The abducens nerve or abducent nerve (the sixth cranial nerve, also called the sixth nerve or simply VI) is a “somatic efferent” nerve that controls the movement of a single muscle, the ... of the eye |
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| The oculomotor nucleus originates at the level of the superior colliculus. The muscles it controls are the striated muscle in levator palpebrae superioris and all extraocular muscles except for the superior oblique muscle and the lateral rectus muscle |
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Firing patterns of brainstem neurons
Three types of neurons feed directly or indirectly onto the motorneurons. ... maintain the static position of the eyeball; a greater firing rate results in increased contraction of the corresponding muscle and thus greater deviation of the eye. ... fire only during a saccade ensuring rapid acceleration of the eye during the movement. ... inhibit burst neurons during fixation preventing unwanted saccades; during saccades they stop firing, releasing the inhibition on burst neurons.
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| Tonic neurons ,Burst neurons , Omnipause neurons |
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Brainstem circuitry
The figures show the connections, in the pons, mediating a horizontal saccade to the right in both eyes. Note that both burst and tonic neurons excite the right lateral rectus and left medial rectus muscles. Similar circuitry in the midbrain mediates vertical saccades. A lesion in the region of the pons shown will disrupt horizontal movements to the ipsilateral side. A lesion of the corresponding midbrain region will disrupt vertical eye movements. A lesion to the medial longitudinal fasciculus will disrupt coordination of the two eyes.
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6. Cortical pathways
There is a direct pathway from the frontal eye field to the paramedian pontine reticular formation and an indirect pathway through the superior colliculus. The upper layers of the colliculus are visual, with input from the retina, and the lower layers are motor, producing eye movments. Cells in the upper and lower layers have spatially corresponding receptive fields and motor fields. Implicated in visual attention.
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