Vision Flashcards
Optic tract brings axons to three targets: lateral geniculate nucleus (LGN), pretectal nucleus, rostral colliculus.
Cortical projections in the LGN
optic tract->LGN->VI (primary visual cortex)
optic tract->LGN->brachium of rostral colliculus->rostral colliculus and pretectal area
Direct light reflex
Pupil constriction in illuminated eye
Nyastagmus
Periodic back and forth or up and down eye movement
Vestibular (prolonged angular acceleration of head) or Opticokinetic (passage of series of objects through the visual fields)
Eye movement control
Motorneurons to extra ocular eye muscles (3, 4, 6)
Gaze centers of brainstem (movement horizontal and vertical)
Cortex and brainstem (initiate particular types of movements)
Eye movements
Maintain visual fixation on a visual target already in view and reorient eyes toward a new target
Retino-tectal system
Characterized as reflex visuomotor system, controlling such reflex unconscious activities as pupillary dilation and constriction, head and eye orientation to visual stimuli
Axons pass directly to pretectum and rostral colliculus without synapsing in lateral geniculate body
Lateral geniculate nucleus (LGN)
Visual cortex for form vision (discriminative: what, where, color, motion)
Retinal field
Retinal area upon which light falls
Light that originates in temporal visual field strikes the nasal retinal field
Optic tract brings axons to:
Lateral geniculate nucleus (LGN), pretectal nucleus, and rostral colliculus
Horizontal gaze center
PPRF, activation leads to conjugate gaze shifts toward ipsilateral side
MLF interconnects motor nuclei of CN III and VI, coordinates horizontal conjugate eye movements
Visual field
Location in space from which light originates
Rounding of lens
Contraction of ciliary muscle to relax tension on lens, allowing it to round and increase optical power -> focuses eye on near object
Constriction of pupil
Improvement of visions through limiting entrance of stray light
Reflex orienting of the eyes
tecto-oculomotor system, CN III nucleus, CN IV nucleus, N VI nucleus
Tecto-oculomotor system
Rostral colliculus exercises control over eye movement
Convergence of eyes
Co-contraction of medial rectus muscles to align eyes with near object
Startle and orienting of head and neck
Tectospinal tract, cervical spinal cord motorneurons
Tectospinal tract
Originates from rostral colliculus
Descends with medal longitudinal fasiculus (MLF)
Subserves head reflex and upper extremity movement to photic stimuli
Conjugate gaze and pursuit
Frontal eye fields and parietal-occipital cortex, paramedic pontine reticular formation (PPRF), MLF, motor nuclei of III and VI
Pretectal nucleus
Pupillary light reflexes
Acuity
Minimum size of visual targets that can be detected
Fovea
Center of macula, area of pure cones
Macula
Location of majority of the cones where visual is normally centered
Rostral colliculus
Visual orienting response via tectospinal tract
Consensual reflex
Pupil constriction upon illumination of the other eye, mediated by caudal commissure which connects the two pretectal nuclei
Convergence
CN III nucleus, medial rectus muscles
Near triad
Accomplishment of focused vision upon attention to a near object, 3 integrated motor elements
Accommodation
Optic tract, pretectal nucleus, Ed West nucleus, ciliary ganglion, ciliary muscle
Postganglionic fibers from ciliary ganglion terminate in ciliary muscle (allow lens to round and focus eye near vision)
Decrease pupil size
Caused by postganlionic fibers from ciliary ganglion terminating in sphincter muscle of iris
Pupillary Light Reflexes
Optic tract, pretectal nucleus, Ed West nucleus, ciliary ganglion, pupil
Pretectal nuclei
Right and left connected by caudal commissure, output pathways go to both ipsilateral and contralateral Edinger-Westphal nuclei (PS portion of CN III)
