11. Visual Pathways (Black)
agnosia (loss of memory of an object by sight) results from a lesion to what area?
"what" (parvocellular) stream, responsible for object recognition
activity in primary visual association areas depends on _____ while in visual association areas it depends on _____.
*light* (response is the same for normal vs. scrambled image as long as quantity of light is the same) *form* (more active when there is a known object to identify vs. a scrambled image)
blood supply of: optic nerve, retina, lateral geniculate nucleus (LGN), optic chiasm + optic tract, optical radiations, striate cortex?
*nerve*: ophthalmic artery (branch of internal carotid) *retina*: central retinal + posterior ciliary arteries (branches of ophthalmic a.) *LGN*: posterior cerebral a. *chiasm + tract*: from multiple neighboring arteries (ACA, MCA, + posterior communicating artery) *radiations*: MCA *striate*: PCA (some overlap w/ MCA)
what nuclei/areas in the cortex are responsible for: 1. conscious awareness of what you are seeing 2. pupillary light reflex
1. lateral geniculate nucleus 2. pretectal area
retrolenticular or sublenticular fibers: -superior retina (lower visual quadrant), contralateral visual field -inferior retina (upper visual quadrant)
1. retrolenticular 2. sublenticular
overview: visual fields what fibers cross?
B & C = binocular fields A & D = monocular fields nasal retina fibers cross, temporal retina fibers stay ipsilateral
Case: right homonymous hemianopsia (absence of visual field on the R side) How would the pupillary light reflex be affected?
B (I think?? <-- confirm with someone)
what areas of the brain are visual cortex areas? visual association areas?
V1 = visual cortex (either side of calarine sulus) VA (V2-V5) = visual association areas (more of occipital lobe) (remember: S1 = primary somatosensory cortex SA = somatosensory association areas, "where" pathway SII = secondary somatosensory cortex, "what" pathway)
pupillary light reflex: direct vs. indirect rxn? pathway?
direct: response in ipsilateral eye indirect: response in contralateral eye pathway: rods/cones --> (retinal ganglion cells via optic tract) --> prectecal area --> (CN 3) --> pupillary constrictor muscle
Self-study: which vision field lesions would cause these deficits?
image
overview: course of optic radiations focusing on an object in upper + lower R visual fields
image
what are optic radiations?
large bundle of fibers that originate in the lenticulate nuc + course through parietal (retrolenticular fibers) or temporal lobe (sublenticular fibers, Meyer's loop) note: in image, green circle = lenticular nuc
Case: right homonymous hemianopsia (absence of visual field on the R side) Where is the lesion?
left LGN, left visual cortex
T/F: The "what" and "where" streams of information remain separate from the retina to the primary visual cortex & beyond.
note: know visual association areas as a collective group (don't need to know difference btwn V2 & V4)
location of primary visual cortex
occipital lobe, portions of the cuneus (C) + lingual (L) gyri that border the *calcarine sulcus*
visual pathway (general)
optic nerves --> optic chaism --> optic tract --> lateral geniculate nucleus --> visual cortex in occipital lobe
define: striate cortex
same as visual cortex (walls of calcarine sulus in occipital lobe)
where are the pathways of: -"where" (magnocellular) stream of visual information -"what" (parvocellular) stream of visual information
where = location in space & movement, dorsal pathway to posterior parietal lobe what = color, form (object identification), ventral pathway to inferior aspect of temporal lobe