Lab 9 Structures Flashcards
what is the visual field? what are the 2 parts?
what we “see”
* right/left fields for each eye
what is the retinal field? what are the 2 parts?
“flipped” version of what we see that’s projected onto retina of eye
* temporal field → lateral
* nasal field → medial
how does the information that falls on top/bottom of visual field reflect onto the retinal field?
- objects within bottom of visual field fall on top of retinal field
- objects within top of visual field fall on bottom of retinal field
how does info that falls on retinal field land on the primary visual cortex?
- objects within bottom of retinal field will remain on bottom throughout course to visual cortex
- objects within top of retinal field will remain on top throughout course to visual cortex
what information does optic nerve carry?
all visual field information from single eye
what happens if optic nerve is lesioned?
monocular info loss (all info from ipsilateral eye)
where does info go after optic nerve? what info does it carry at this point?
optic chiasm
* visual info from nasal retina only crosses to other side
what happens if optic chiasm is lesioned?
heteronymous hemianopsia (bitemporal hemianopsia)
where does the info go after the optic chiasm? what type of info does it carry at this point?
optic tract
* same visual field of each eye travels together via optic tract
* (ex.) left optic tract carries right sided visual field info from BOTH eyes
* (ex.) right optic tract carries left sided visual field info from BOTH eyes
what happens if optic tract is lesioned?
homonymous hemianopsia
* same visual field is affected for BOTH eyes
where does the info go after the optic tract?
lateral geniculate nucleus (LGN)
what happens if optic radiation (LGN → primary visual cortex) is lesioned?
homonymous quadrantnopsia
parietal lobe → inferior quadrantnopsia
temporal lobe → superior quadrantnopsia (Meyer’s loop)
lesion in upper loop → lower visual field info from BOTH eyes lost
lesion in lower loop → upper visual field info from BOTH eyes lost
what visual info terminates in upper portion of LGN?
visual field info carried from upper retina
what visual info terminates in lower portion of LGN?
visual field info carried from lower retina
what info is carried within given tract that travels between optic chiasm to LGN?
all aspects of visual info (peripheral, central, upper, lower)
* (ex.) left optic tract carries central vision, peripheral vision, upper and lower visual field info of right visual field of BOTH eyes
* (ex.) right optic tract carries central vision, peripheral vision, upper and lower visual field info of left visual field of BOTH eyes
where does info go after LGN?
visual info splits to take an upper and lower visual pathway to primary visual cortex in occipital lobe
where do the upper loop fibers travel? what info does it carry?
travels through parietal lobe → terminate in upper primary visual cortex (above calcarine sulcus)
* fibers carrying visual field info from upper RETINAL field (lower VISUAL field)
where do the lower loop fibers travel? what info does it carry?
travels through temporal lobe → terminate in lower primary visual cortex (below calcarine sulcus)
* fibers carrying visual field info from lower RETINAL field (upper VISUAL field)
how is visual info organized in primary visual cortex?
peripheral and central vision are represented in separate regions
* central vision dispersed over relatively large region
what is central vision sparing?
- caused by focal/localized lesions in the visual cortex
- since most of cortex associated with central vision is likely spared
what happens if occipital lobe is lesioned?
homonymous quadrantnopsia with central vision spared
eye movement of CN III? if lesioned, what position does eye rest at?
- up, down, in, up/in
- if lesioned → out/down
eye movement of CN IV? if lesioned, what position does eye rest at?
- down/in
- if lesioned → up/out
eye movement of CN VI? if lesioned, what position does eye rest at?
- lateral
- if lesioned → medially
lesion of eye movement cranial nerves leads to what type of vision?
double vision
what is the name of the center that coordinates activation of conjugate gaze? what 2 main structures are included in it?
horizontal/pontine gaze center = abducnes nucleus + PPRF
which gaze center is stimulated for the side you want to look at?
ipsilateral
* (ex.) left pontine gaze center activated → eyes move left
which abducens nucleus is stimulated by the horizontal gaze center?
ipsilateral
what happens once abducens nucleus is stimulated?
CN VI controls lateral rectus to move eye laterally
which oculomotor nucleus is stimulated by the horizontal gaze center?
contralateral
what happens once oculomotor nucleus is stimulated?
CN III controls medial rectus to move eye medially
medial longitudinal fasciculus (MLF) connects what 2 structures?
highway for communication from abducens nucleus → contralateral oculomotor nucleus
which way do eyes move in relation to gaze center?
eyes move toward activated gaze center (abducens nucleus)
what 3 things can elicit conjugate gaze?
- voluntary tracking (vision/interest) via cerebral cortex → smooth pursuit
- head movement (vestibulo-ocular reflex)
- moving object in visual field (optokinetic reflex) → finding/tracking
how does voluntary tracking elicit conjugate gaze?
activation of frontal eye fields (Area 8) → stimulate contralateral abducens nucleus (PPRF) → conjugate gaze for voluntary tracking
how does head movement elicit conjugate gaze?
- semicircular canals elicits involuntary movement of eyes
- semicircular canals stimulated → sends signals to medial/superior vestibular nucleus → stimulates contralateral abducens nucleus → involuntary conjugate gaze
- vestibulo-ocular reflex stabilizes eyes for rapid turning/onset of head motion
how does moving object in visual field elicit conjugate gaze?
- optic nerve → optic tract → pretectal nucleus → medial vestibular nucleus → contralateral abducens nucleus
- neurons in LGN, Area 17, middle/med sup temporal cortex can also be involved
- optokinetic reflex: slower effect than vestibulo-ocular reflex but sustains stabilizing objects on retina for longer duration of head movement → picks up where vestibular system leaves off
lesion of MLF
- dysconjugate gaze: 2 eyes don’t move together
- CN III and CN VI function intact
lesion of CN III, CN VI, occulomotor nucleus
- dysconjugate gaze: 2 eyes don’t move together
what is the pupillary light reflex?
results in reflexive constriction of both pupils when light falls on one eye
* parasympathetic
* 2 pathways
what is the pathway of the afferent limb of pupillary light reflex?
light enters eye → travels in optic nerve → ipsilateral pretectal nuclei → posterior commissure → connection to contralateral pretectal nuclei → Edinger-Westphal nuclei → bilateral response
what is the pathway of the efferent limb of pupillary light reflex?
neurons exit Edinger-Westphal nuclei → travels towards eye alongside oculomotor nerve → ciliary ganglion (pre-ganglionic parasympathetics) → leaves ganglion → terminates in pupillary constrictor muscles of pupil (post-ganglionic parasympathetics)
direct response to pupillary light reflex
constriction of pupil ipsilateral to pupil exposed to light
consensual response to pupillary light reflex
constriction of pupil contralateral to pupil exposed to light
what is the pupillary dilation (ciliospinal) reflex?
individual pupil dilation in darkened environment
* sympathetic
* separate pathway for each eye
descending path of pupillary dilation reflex
light reduction signal → hypothalamic neuron → hypothalamus → intermediolateral cell column T1 segment → preganglionic sympathetic neuron → superior cervical ganglion
ascending path of pupillary dilation reflex
post-ganglionc neuron from superior cervical ganglion (travels with internal carotid artery) → dilator muscle of pupil AND smooth muscle (Mueller’s muscle) of upper eyelid
what is Horner’s Syndrome?
lesion of sympathetic path to head/neck
what are the 3 signs/symptoms of Horner’s Syndrome?
- persistent pupillary constriction
- ptosis of upper eyelid
- loss of sweating on involved side of face
