TIMS VISION Flashcards
what is the predominant sensory input regarding the external environment?
vision
what does vision require?
transduction of photon energy into a frequency of action potentials in the retina of the eye
where are the action potentials conducted?
primary visual cortex of the brain
optic nerve becomes what after it crosses the optic chiasm?
optic tract
left and right visual field in relation to the LGN of the right hemisphere
left visual field projects medially and the right visual field projects laterally
the retina contains what kind of cells?
photosensitive cells of the eye
what structure of the eye bends incident light? what about the fine tuning and focus?
cornea and lens with the cornea doing most of the bending
lens
T/F, light passing through the midline is bent by the cornea or lens?
F, it tis not
what helps us accommodate for near or far objects?
circular and meridional fibers attached to suspensory ligaments
this type of focus is accomplished by relaxing the fibers, which tightens the ligaments and elongating the lens and results in less bending of light
distant focus
affect of suspensory ligaments relaxed?
no pulling and lens are more spherical, more bending of light
affect of suspensory ligaments contracted?
pulling and so lens ends up in a more elongated or contracted state, less bending of light
normal vision?
emmetropia
near sighted? lens to treat?
myopia
concave lens
far sighted? lens to treat?
hypermetropia
convex lens
this disorder of the lens results from a bulge developing one axis along the lens and is corrected by placing a lens with a concavity along the same axis in front of the eye?
astigmatism
what cells are involved in the encoding of incoming light?
why are the axons of the ganglion cells significant?
rods and cones for transduction
horizontal, bipolar and amacrine cells for processing
ganglion cells for transmission of the action potentials to the brain
*they become the optic nerves
these cells are used for white and black vision?
rod cells
these cells are used for color vision?
cone cells
where are the cones concentrated?
behind the pupil in an area called the macula
this is the region of greatest visual acuity and is predominantly comprised of cone cell transducers?
fovea, located in the center of the macula
this is what we have in our vision which results from the location where the ganglion cell axons congregate and lead the eye to form the optic nerve?
blind spot
T/F, rods and cones are located in the optic disk and so light striking the area can be transduced?
F, the cannot and so light cannot be transduced
what is the purpose of the pigment epithelium?
the pigment absorbs photons which manages to pass by the ads and cones without being absorbed
storage for vitamin A
this is needed for rhodopsin synthesis by rod cells?
retinol
this type of vitamin deficiency will result in rods not being as effective leading to night blindness
vitamin A
what is the chemical responsible for light transduction?
rhodopsin
what are the three photopsins the cones are sensitive too? shortest waveleght to longest?
blue, green, red
blue
green
red
what colors are the most common forms of color blindness?
red
green
red-green
briefly describe the mechanism of light transduction?
photon strikes rhodopsin, retinal is converted from cis to trans producing metarhodopsin II and so the trans-retinal dissociates and detaches from scotopsin by the rhodopsin kinase
the trans retinal is converted back to cis retinal by retinal isomerase and also have the formation of the rhodopsin
*constant illumination causes a decrease in rhodopsin
what happens when the metarhodopsin is activated?
transducin is activated with activates phosphodiestreae molecules which catabolizes cAMP, cGMP to GMP an inactivating mechanism decreasing Na conductance therefore causing the membrane potential to hyper polarize leading to the inactivation of the metarhodopsin by the rhodopsin kinase
what is the effect of the hyperpolarization on the rod cells?
increase in frequency of APs in the ganglion cells and so these depolarize affecting the ganglion cells via bipolar cells that result an inhibitory NT, but the ganglions cells are further depolarized
keep in mind that ganglion cells receive information from both cones and rods
how are images pieced together?
picture is associated by modality and cannot be reassembled except by the visual association cortex which helps us put it into a picture
