Quiz 6 Study Guide What is lateral inhibition What is its function Lateral inhibition Each cell inhibits its neighbors Interconnections between cells of the visual system alter the apparent brightness of visual objects and also enhance boundaries by means of a process known as lateral inhibition What are the functions of the cornea lens and ciliary muscles Cornea Focus light Bending light which forms the image Lens Focus light Shape changes in order to focus on objects at different distances from the eye Horizontal amacrine cells provide lateral connections across the retina axons of ganglion cells carry information out of the eye to the brain Ciliary muscles adjust the focus by changing the shape of the lens What are the bipolar cells and ganglion cells What makes up the optic nerve Bipolar cells Receive input from rods cones Process and report light stimulation to ganglion cells Ganglion cells Produce action potentials that travel along their axons to the brain Information from many photoreceptors converges on each ganglion cell Ganglion axons form the optic nerve What is the optic chiasm and what happens there Site where the two optic nerves leaving the eye meet In humans half of the axons from each eye cross to the other side After passing the optic chiasm the axons are called the optic tract Describe the path of light from the cornea to the place where it activates a photoreceptor Light from the cornea projects to the retina there bipolar cells receive input from the rods and cones then they synapse on ganglion cells What are horizontal and amacrine cells Horizontal cells contact photoreceptors and bipolar cells Amacrine cells contact bipolar and ganglion cells Which cells in the retina generate only graded potentials and which generate action potentials All cell except ganglion cells generate only graded potentials Ganglion cells generate action potentials What are the photopic and scotopic systems and when is each active Photopic system relies on cones requires more light and allows color vision sensitive to wavelength Scotopic system relies on rods works in dim light relatively insensitive to wavelength What is the relationship of RETINAL and opsin in rhodopsin What does light do When activated by light rhodopsin rod pigment dissociates into retinal and opsin catalyzing an intracellular second messenger cascade that results in the closing of many sodium channels The resultant graded hyperpolarization leads to a decrease in glutamate release from tonic levels signaling a change in illumination What are 11 cis RETINAL and all trans RETINAL In the dark retinal is bent at carbon 11 11 cis retinal it fits into a pocket in the big opsin protein When light strikes it the long hydrocarbon chain straightens all trans retinal can no longer fit in the pocket What type of electrophysiological response occurs in the rods cones when phototransduction occurs When activated by light rhodopsin the rod pigment dissociates into retinal and opsin catalyzing an intracellular second messenger cascade that results in the closing of many sodium channels The resultant graded hyperpolarization leads to a decrease in glutamate release from tonic levels signaling a change in illumination Describe the responses of on center and off center bipolar and ganglion cells Illumination of the center of an on center off surround cell results in an increase in firing and illumination of the surround results in a decrease in firing The reverse pattern holds for off center on surround cells Bipolar and ganglion cells have concentric receptive fields Off center bipolar cells excite off center ganglion cells when light is turned off On center bipolar cells excite on center ganglion cells when light is turned on Bipolar cells release glutamate which always depolarizes ganglion cells What transmitter is released by all rods cones What are its effects on on center off center bipolar cells What transmitter is released by bipolar cells What is its effect on ganglion cells Rods and cones release glutamate On center bipolar cells turning on light excites them they receive less glutamate which normally inhibits on center bipolar cells Off center bipolar cells turning off light in the center of the field excites the cells they receive more glutamate and are depolarized Bipolar cells release glutamate always depolarizes ganglion cells What is the relationship between on center bipolar cells and on center ganglion cells How about off center bipolar and off center ganglion cells On center bipolar cells excite on center ganglion cells when light is turned on Off center bipolar cells excite off center ganglion cells when light is turned off How did the fovea get its name What kinds of photoreceptors are located there Latin for pit Cones Why is the blind spot blind Why is this not a problem for our vision No blood vessels or axons in the front cones No receptors ganglion cell axons exit through blind spot Where in the retina do we have greatest sensitivity to dim light Why 20 degrees from the center where rods are most concentrated Where in the retina do we have greatest visual acuity Why Fovea contains highest density of cones Where do most ganglion cell axons terminate Where else do some of them terminate Most ganglion cell axons go to the lateral geniculate nucleus LGN Some go to the superior colliculus Where is the primary visual cortex V1 What is another name for that area Occipital lobe Striate Cortex area 17 Describe the receptive fields of simple and complex cells in the visual cortex What may provide the input to simple cells How about complex cells Simple cells bar or edge detectors respond to an edge or bar of a particular width orientation and location 3 on center LGN cells provides input to simple cells Complex cells also respond to a bar of a particular width and orientation but may be located anywhere in the visual field Several simple cells provide input to complex cells What are the contributions of V4 and V5 to visual perception V4 color perception perception of form V5 specialized for motion perception Where is inferotemporal IT cortex and what does it contribute Where do IT axons project Where are faces recognized On inferior convexity of temporal lobe Cells in inferotemporal IT cortex respond to complex forms including forms that the subject has learned to recognize Receptive fields in IT cortex probably develop through experience and learning Prefrontal cortex in both monkeys and humans responds to faces