NSCI 110 1st Edition Lecture 20 Outline of Last Lecture I There are a variety of ways to assess degrees of wakefulness a Glasgow coma scale measures eye opening motor response verbal response b A person in a vegetative state may exhibit signs of wakefulness without awareness i Persistent vegetative state II Our perceptions of the visual world are based on environment internal state and experience III Anatomy of the human eye allows photons of light to be converted into action potentials a Optic disk is our blind spot b Light is bent when traveling from the air to the aqueous environment in the eye Outline of Current Lecture I The retina is responsible for relaying detailed images to the cortex a Consists of layers photoreceptors at the back bipolar cells ganglion cells b Contains the fovea where there are only cones II There are two types of photoreceptors in the visual system a Rods vision at night or in dim lighting b Cones color perception and fine details III Light hyperpolarizes receptors a Reduces the amount of glutamate released by photoreceptors IV Lateral interactions also occur among retinal cells surround inhibition a Horizontal cells inhibit nearby bipolar cells b Amicrine cells inhibit nearby ganglion cells V Retinotopic organization exists among both optic pathways Current Lecture What is projected onto the retinal surface is an inverted image but the brain corrects this o For the best visual acuity seeing fine details the image must be projected onto the retina Light must travel through neurons in the retina to reach receptors at the back of the eye Retina consists of layers of cells o Ganglion cells are the outermost layer light hits here first Have synapses with the optic disk that exits as the optic nerve o There is a fovial pit that is free of any rods These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Cones are most dense here Lack of ganglion cells Foveal pit in the middle Two types of receptors o Cones Color and form perception Red cones green cones and blue cones long middle and short wavelengths Each is responsive to a respective wavelength of light Each sends distinct signals to the cortex where the color is interpreted o Rods Long cylindrical Sensitivity to light night vision Maximally sensitive in a dark environment When light strikes rodoxin bleaching occurs Becomes clear in color When light is removed it is reconstituted back into a purple o Each has a chemical layer that is responsible for converting light to chemical energy Activated when light is projected onto the molecules Molecule changes shape and usually activates a second messenger pathway Glutamate is released when in the dark cells are most depolarized in the dark Light hyperpolarizes both of these receptors So light reduces the amount of glutamate being released Results in differential signaling in the ganglion and bipolar cells Retina and receptors o Highest density of ones is in the foveal region mostly foveal pit Peripherally the density of rods increases greatly then slowly drops off further away Where it intersects with the optic disc lacks any receptors Constitutes the blind spot Blue cones more densely populated around the foveal pit o Cones are much larger than rods in diameter Receptors and neurons in the retina o MACULA directly surrounding the fovea Photons hit rods or cones first in the back of the retina releasing a certain amount of glutamate where they synapse with bipolar cells Bipolar cells synapse with ganglion cells Basic pathway designed for maximum acuity because each pathway consists of single bipolar and ganglion cells signals are not lost remain specific o Convergence occurs in the PERIPHERY Not as strong visual acuity but increased sensitivity Multiple rods cones may synapse on a single bipolar cell Multiple bipolar cells may synapse on a single ganglion cell o Lateral interactions occur among horizontal cells A horizontal cell also receives the signals from a rod cone and inhibits neighboring synapses Sharpens that specific signal Called surround inhibition Amicrine cells perform the same exact lateral functions as horizontal cells but between bipolar and ganglion cells o Retinotopic organization of optic pathways your visual field is represented in a specific manner There is overlap between the two eyes Some portions of the visual field are picked up by specifically the left or right eye Images on the temporal side of the eye stay on the same side of the optic pathway Those on the nasal side of the eye travel to the opposite side Left side images end up in the right occipital lobe and vice versa Fovea constitutes a large area of the occipital lobe