vision 1 Flashcards
what is the visual pathway of light within the eye
light enters the cornea where most refraction occurs, it goes through the aqueous humor, pupil, lens, vitreous humour, then hits retina
explain the pupiliary reflex
the retina projects to the pretectum, edinger westphal nucleus, ciliary ganglion, then innervates the ciliary muscle of the iris
-reflex in both eyes
how does accomodation of the lens occur for near focus
the cilliary muscle is stimulated/contracts, the zonule fibers lessen tension, and the lens becomes rounder/thicker
how does accomodation of the lens occur for far focus
the cilliary muscle does not contract, the zonule fibers have high tension, and the lens is flat
myopia
when you cannot see far away, corrected with a concave lens
hyperopia
cannot see near/hyperfocusing on far away objects, corrected with convex lens
what part of the visual field do the left temporal retinal ganglion cells see
right nasal visual field
what part of the visual field do the right nasal retinal ganglion cells see
the left temporal visual field
what part of the total visual field can be seen by one eye
one eye can see 90 degrees of its ipsilateral visual field and 60 degrees of the contralateral visual field
describe the laminar organization of the retinal ganglion cells
pigment epithelium, outer segment layer (contains photoreceptor cell bodies), outer plexiform layer (where horizontal cells synapse with photoreceptor cells and bipolar cells), inner nuclear layer(bipolar cell bodies), inner plexiform layer (where amacrine cells, bipolar cells, and ganglion cells synapse), ganglion cell layer, and nerve fiber layer
what are the two main functions of the pigment epithelium layer
-the pigment epithelium plays a big role in phagocytosis of the discs in the photoreceptors
-it absorbs excess light
scotopic
primarily rod cell vision, poor acuity,
mesotopic
rod and cone cell vision, moonlight/starlight
phototopic
rod saturation begins, mostly cone cell vision, high acuity
indoor lighting, sunlight
what happens at the optic disk
ganglion cell axons exit the eye to the optic nerve, no photoreceptors, blind spot
fovea
receives input when you intentionally focus on something, one to one cone cell and ganglion cell ratio gives you incredibly high acuity,
do you understand how transducin and phosphodiesterase recover once we return to dark from light
if not, watch that part of the lecture again!
wavelength of blue, green, and red cones
short, medium, long
what two cones are both on the X chromosome
red and green, explains why red/green colorblindness is so common
protanopia
no absorption of red
deuteranopia
no absorption of green
what mechanisms allow for dark adaptation to occur faster than light adaptation
IS THIS TRUEpupilliary reflex, R regeneration, and the outnumbering of rods to retinal ganglion cells
how does calcium contribute to decreasing the sensitivity to light at greater luminances
-by decreasing inhibition of guanylate cyclase which hydrolyzes cGMP
-by decreasing inhibition of rhodopsin kinase which normally promotes arrestin
-affinity for cGMP receptors/driving force tapers off as more calcium comes into the cell
describe stimulation of receptive fields and transduction in bipolar cells
receptive fields are stimulated by their centers and surrounds by light, send graded potentials
rg9 bind to transducin alpha to stimulate gtpase activity, transducin alpha gtp dissociates from pde, transducin alpha gdp binds to transducin beta and gamma, pde now has inhibitory gamma subunit and is inhibited
what does calcium inhibit
rhodopsin kinase and guanylate cyclase
where does phototransduction take place
in the disc membranes/rods
why do we need red and green cones
to provide information about color, and also visual high def image information, shapes, and edges(most of them)
