Study Guide Exam 2 Chapter 10—vision Fovea: center of focus of eyeball. The most precise vision. Lens: Helps focus an image on the retina. Ciliary Muscle: Pulls on lens and changes shape to focus light further back or forward. Cornea: clear tip of eye. Takes in light information and bends to be more focused for eye ball. Refracts light. Retina: the receptive surface inside the eye that contains photoreceptors and other neurons. Sclera: White of the eye. Iris: the colored part of eye. Restricts light Pupil: size change my moving iris Optic nerve: Take information from the eye to the brain Optic Disc: no sensory receptors, blind spot Photo receptors are located in the back of the eyeball. Rod: A class of lightsensitive receptor cells (photoreceptors) in the retina that are most active at low levels of light. Don’t care about wavelengths. Very sensitivity. Cone: A class of photoreceptor cells in the retina that are responsible for color vision. Photons: light energy or wave energy Amount of visible light is relatively small different wavelengths interpret different colors Motion: detect moving stimuli in visual field. Set of cells supersensitive to moving stimuli—direction and speed. Hue: color Saturation: deepness or richness of color The 3 basic dimensions of the perception of light are brightness, hue and saturation. Adaptation: sensory cells change responsiveness with environmental. Eyes adjustment to dark room to light vice versa. Lateral inhibition: the phenomenon by which interconnected neurons inhibit their neighbors, producing contrast at the edges of regions. brain doesn’t always correctly reproduce what we see some cells deal with high levels of light, others deal with low levels Photoreceptor: neural cells in the retina that respond to light. During Darkness photoreceptors constantly release glutamate (since ion channels open for Na+) the constant release hyperpolarizes (inhibits) bipolar cells Bipolar cellas are unable to excite ganglion cells fire. Presence of Light rhodopisn(photopigment) is broken down a cascade of chemical reaction close ion channels reduce glutamate release depolarize bipolar cells (then it releases more neurotransmitters)bipolar cells depolarize ganglion cells (then produce action potentials)
Bipolar cells: A class of interneurons of the retina that receive information from rods and cones and pass the information to retinal ganglion cells Ganglion Cells: A class of cells in the retina whose axons form the optic nerve. *Photoreceptors (rod/cone)Bipolar cellsganglion cells Amacrine cells: specialized retinal cells that contact both the bipolar cells and the ganglion cells, and are especially significant in inhibitory interactions within the retina. Photopigmants: rhodopsin more rods than cones.
Light stimulation of a molecule of rhodopsin activates about 500 molecules of G proteins transducin. This activation causes a GTP moleculeto replace the GDP molecules that to binds to a subunit of transducin. the activated G protein activates a phosphodiesterase (PDE) Each PDE molecules hydrolyzes more than 2000 molecules of cGMP, reducing its concentration. The reduction in cGMP leads to closure of Na+ channels and hyperpolarization of the receptor. No light= depolarization Hyperpolarized= decreased transmitter release Depolarized = increased transmitter release stimulation of one photoreceptor may increase the firing of one ganglion cell and reduce firing of another. Vision Pathway! density of cones higher in fovea information from each retina goes to each side of the brain. Visual Pathway Optic nerve optic chiasm LGN V1 Superior colliculous: guides eye movements Lateral geniculate nucleus (LGN): receives sensory information, sends to information to occipital lobe.
Spacial Frequency filter theory: a pattern of light and dark alternating in a field. high frequency: important for detailed vision low frequency: general light images are formed by taking activity of different cells and combining activity. Cortical Organization both sides of the brain are getting information from both eyes. Ocular dominance columns: clear columns of cells. A region of cortex in which one eye or the other provides a greater degree of synaptic input.
Ocular Dominance Columns of cells that respond from one eye or the other. Subcolumnsorientation columns Different columns are differently sensitive to different frequencies. Dorsal Stream: vision for movement, location (detect where) Ventral stream: vision for recognition (what am I looking at?) Frontal lobe: planning movements based on what you see. Previsual parallel processing pathway in the visual system. Color Vision 3 classes of cones: L (long wavelengths), m (medium), s (short). – different ranges in sensitivity not color. Each pigment has a peak sensitivity but responds to a wide range of wavelengths.