Download Objectives 31

1. Each retina  optic tract  optic chiasm (nasal fibers from ganglion cell axons decussate
across the midline and join undecussated fibers from temporal half of other retina in the optic
tract)  optic tract ends in lateral geniculate nucleus of thalamus  optic radiation
(retrolenticular and sublenticular parts of internal capsule)  primary visual cortex above and
below calcarine sulcus (striate cortex)
Retinotopic map – map of image falling on retina; large number of fibers representing fovea; in
visual cortex – retina represented right side up (superior fields below calcarine sulcus, inferior
fields above), fovea represented posteriorly at occipital pole (large), periphery anteriorly
2. Deficits in visual fields
- Fibers to upper back of calcarine sulcus go through retrolenticular part of internal capsule and
to occipital lobe
- Fibers to lower bank go through sublenticular part and loop out into temporal lobe (Meyer’s
loop) before turning posteriorly toward occipital lobe
- Damage in optic radiation or occipital lobe spares part of the large foveal representation (foveal
or macular sparing)
3. – Receptive fields of lateral geniculate neurons are similar to those of ganglion cells: input
from one eye, center-surround antagonism, some receptive fields are for color and others are
for black/white contrast, lot of representation of small foveal receptive fields, LGN neurons
project to striate cortex
- cortical cells for contrasts have a variety of receptive fields; cortical cells do not respond to
diffuse illuminate because there are excitatory and inhibitory regions in receptive fields that
cancel each other out; receptive fields are not circular which do not respond well to small spots
of light
- Cortical cells respond to stripes or edges with a particular orientation; simple cells have
excitatory and inhibitory regions in the shape of oriented bars; complex cells respond to oriented
lines of a particular length
-other neurons are more concerned with color than with black/white contrast; they have circular
receptive fields with antagonistic center-surround color properties
4. – visual cortex divided into hypercolumns; within hypercolumns all aspects of the
information coming from a particular part of the contralateral visual field are sorted (to
association areas); each hypercolumn includes two sets of orientation columns through which
all stimulus orientations are mapped out for both eyes; among orientation columns are colorsensitive neurons
- Foveal hypercolumns correspond to small areas of visual field and peripheral hypercolumns to
larger areas
- Form and color processed in ventral areas of occipital and temporal lobes
- processing of location and motion takes place in dorsal parts of occipital and parietal lobes
5. – Illumination of either retina causes both pupils to constrict
- Sphincter is strong; parasympathetic innervation from oculomotor nerve and ciliary ganglion;
activated during pupillary light reflex
- Dilator is weak; sympathetic innervation via intermediolateral cell column of spinal cord 
superior cervical ganglion; preganglionic sympathetics for dilator activated by long descending
pathways from ipsilateral half of hypothalamus
Pupillary light reflex
- Response of illuminated eye is direct reflex; equal response of unilluminated eye is consensual
reflex
- Afferent impulses travel over ganglion cells in optic nerve; half of them (nasal) cross in optic
chiasm
- Fibers bypass lateral geniculate nucleus and travel through superior brachium to pretectal
area (rostral to superior colliculus at midbrain-diencephalon junction; adjacent to posterior
commissure
- Pretectal area projects bilaterally to Edinger-Westphal nucleus of oculomotor nucleus
(preganglionic parasympathetics neurons reside there)  oculomotor nerve  ciliary ganglion
 sphincter