The Eye
Order by
69 terms
Terms | Definitions |
|---|---|
 optic chiasm | -part of brain where some optic nerves cross -60% cross -40% continue to thalamus/midbrain -located beneath hypothalamus -at the base of the diencephalon |
| suprchiasmatic nucleus | in the hypothalamus, one of the targets of retinal ganglion cell axons, |
| 3 layers of tissue in the eye | 1) retina 2) uveal tract 3) cornea |
| retina | innermost, sensitive to light, can transmit visual signals to central target |
| cornea | outer layer, transparent tissue that permits light rays to enter the eye -contributes most of the refraction in the eye |
| Optic disk | retinal axons leave the eye and travel trought the optic nerve and reach the thalamus and midbrain |
| 5 neurons of the retina | photoreceptors, bipolar cells, ganglion cells, horizontal cells, amacrine cells |
| Rods | -high sensitivity -low acuity -not really used in the dark -at the peripherary of the retina -better peripheral vision at night b/c of location of the rods in the retina -present at high density in most of the retina |
| Cones | -Color resolution -low sensitivity -high acuity -used during the day -high density in the fovea -types: red, green, blue |
| pathway from photoreceptor to optic nerve | photoreceptor to bipolar cells to ganglion cells |
| Phototransduction | absorption of light by photopigment in outersegment of photoreceptor initiates cascade that changes membrane potential and therefore, the amount of nt released |
| horizontal cells | in retina, allow lateral interactions btween photoreceptors and bipolar cells -maintain sensitivty to contrast |
| amacrine cells | postynaptic to bipolar cells, presynaptic to dendriate or gnaglion cells |
| shining light on a photoreceptor leads to | hyperpolarization |
| in the dark | depolarized, more (+), many Ca2+ channels in the synaptic terminal are open, lots of nt released, -Na+ and Ca2+ influx -K+ efflux |
| in the light | hyperpolarized, more (-), few Ca2+ channels open, rate of neurotransmitters released is reduced, |
| retinal photopigment | 11-cis-retinal + opsin, undergoes cis to trans conformational change when in captures a photon of light |
| scotopic vision | (dark), rod mediated, low level of illumination so uses rods only, spatial discrimination is poor b/c rod system has lower resolution |
| photopic vision | (light), cones are dominant, rods do not contribute |
| mesotopic vision | both contribute, in the moonlight |
| bipolar cells | transmit passivly, |
| major target of the optic tract | LGN |
| sclera | outermost tissue layer of the eye, composed of white fibrous tissue |
| primary function of the eye | achieve focused image on the surface of the retina |
| refraction in the eye | -bending of light necessary in the formation of focused images on the photoreceptors of the retina -cornea and lens are primarily responsible |
| Lens | -contributes to refraction in the eye -refraction of the lens is adjustable - |
| choroid | -largest component of the uveal tract -composed of a rich capillary bed and light absorbing pigment: melanin |
| melanin | light abosorbing pigment |
| Lens : when viewing distant objects | -relativly thin and flat -less refractive power |
| Lens: near vision | -lens becomes thicker and rounder -more refractive power |
| ciliary muscle | -surrounds the lens -activity changes the shape of the lens to adjust refraction |
| Pupil | -contractile aperture in the iris of the eye -pupil size can be adjusted to contribute to the clarity of images on the retina |
| Optic disk | -blood vessels enter eye through optic disk -site where retinal axons leave the eye and travel through the optic nerve to reach sites in the thalamus and midbrain |
| two types of photoreceptors in the retina | rods and cones |
| shining light on photoreceptor leads to | membrane hyperpolarization, |
| in the dark, membrane is | depolarized with a membrane potential of about -40mV |
| Cyclic cGMP-gated channels | -in the outer segment of the membrane -responsible for light induced changes in the electrical activity of photoreceptors |
| cGMP levels in the DARK | -cGMP level in the outer segment are HIGH -cGMP binds to Na+ permeable channels in the membrane to keep them open and allow Na+ to enter and DEPOLARIZE the cell |
| cGMP levels in the light | -absorption of a photon leads to decreace in cGMP levels, closing cation channesl and resulting in recepter HYPERPOLARIZATION |
| Steps of Phototransduction | ... |
| Rhodopsin | -photopigment in rods - |
| Opsin | -has 7 transmembrane proteins -opsin is coupled with retinal |
| Cis-Trans conformational change leads to | -activation of transducin, which in turn activates PDE -PDE hydrolyzes cGMP, which reduces its concentration in the outer segment and leads to closure of the channels in the outer segment |
| Transducin | -activated by change in opsin conformation -activates a PDE that hydrolyzes cGMP |
| hydrolysis of PDE | -hydrolyzes and lowers concentration of cGMP and reduces the number of cGMP molecules available -leads to channel closure |
| Fovea | -highly specialized region in the center of the macula -1.2 millimeters in diameter -increased cone density -decreased density of rods -mediates highest levels of visual acuity -has to retinal blood vessels |
| Foveola | -center of the fovea -cones only -completly rod- free |
| Blue | -short wavelength |
| Green | -medium wavelength |
| Red | -long wavelength |
| ON-center ganglion cells | -turning on a light in the receptive field of an ON-center ganglion cell produces a burst of action potentials |
| OFF-center ganglion cells | -turning on a light in the receptive field of an OFF-center ganglion cell reduces the rate of discharge -when the light is turned off, the cell responds with a burst of action potentials |
| 2 classes of ganglion cells | -ON center and OFF center |
| On and Off center ganglion cells | -present in roughly equal numbers -rcptive fields have overlapping distribution |
| Optic Tract | -formed by ganglion cell axons on each side -contains fibers from both eyes |
| target of ganglion cells in the optic tract | -diencephalon and midbrain |
| Target of ganglion cells in the optic tract in the diecephalon | -dorsal lateral geniculate nuclues of the thalamus |
| Primary Visual Cortex - V1 | -aka striate cortex -aka Brodman's area 17 -first binocular cells -first major processing center |
| Primary visual pathway | -pathway from retina via LGN of the thalamus to the primary visual cortex -carries info that allows concious visual perception |
| Pretectum | -second major target of ganglion cell axons -collection of neurons that lies between thalamus and midbrian |
| Edinger-Westphal Nucleus | -prectecal neurons project here -nerve cells near the nuclues of the oculomotor nerve, -located close to the visual center of the midbrain allows for control of pupil size according to light level |
| Suprachiasmatic nucleus | -in the hypothalamus -small group of neurons at the base of the diencephalon -a target of retinal ganglion cell axons -input from the retina -can detect if there is or is not natural light -biological clock of night and day -no suprachiasmitc nuclues=no bio clock |
| Superior Colliculus | -structure on the dorsal surface of the midbrain -target of retinal ganglion cell axons -coordinates head and eye movements to visual targets |
| input in the LGN | -inputs from both eyes are present but geniculate neurons are still monoculuar |
| Ocular dominance columns | -in cortical layer 4 -columns in visual cortex -devoted to input from left or right eye -important for binocular interaction and depth perception -beyond OCD, vision is binocular |
| magnocellular layers | -2 ventral layers og LG -composed of large neurons |
| Parvoceulluar layers | -more dorsal layers of LG -composed of smaller neurons |
| M ganglion cells | -terminate in magnocellular layer -have larger cell bodies -larger receptive fields than P cells -cannot transmit color information -faster conduction velocties -sensitive to depth |
| P ganglion cells | -smaller then M cells -can transmit information about color |
First Time Here?
Welcome to Quizlet, a fun, free place to study. Try these flashcards, find others to study, or make your own.