Study Guide for PSB2000 Exam 3 Vision Audition Mechanical Senses and Chemical Senses Chapter 6 Study Hints Law of specific nerve energies activity by a particular nerve always conveys the same type of information to the brain Anatomy of the eye and functions of the labeled parts Cornea where light enters highly curve light refracted as it passes through it Choloid responsible for absorbing excess light with darkly pigmented cells Retina where light entering eye is focused contains photoreceptors that convert light into electrical impulses Iris colored part of eye Pupil opening in iris Lens helps control further refraction of incoming light Ciliary body tissue that produces aqueous humor the liquid that bathes the front part of eye before it drains into the canal of Schlemm Ciliary Muscle part of ciliary body that changes the shape of lens via parasympathetic movements of the suspensory ligaments Cones photoreceptor perceive colors and fine detail Absorb blue green and red wavelengths Rods allow for perception of light and dark Macula central section of retina contains a high conc of cones Fovea central point of macular no rods are present For the picture to the right above When light enters through the pupil and strikes the retinal neurons it passes through the layers of cells pictured above and acts at the RECEPTORS they do the receiving on the far outside first First to visual receptors in the back of the eye Those send messages to neurons called bipolar cells located closer to the center of the eye Bipolar cells send messages to ganglion cells that are even closer to the center of the eye The axons of ganglion cells join one another to form the optic nerve that travels to the brain How photons stimulate action potentials without light receptors inhibit bipolar cells Light hyperpolarizes receptors Receptors stop N T release bipolar cells are disinhibited A P down optic nerve bipolar cells stimulate ganglion cells by releasing excitatory N T Rods and Cones and their difference in foveal and peripheral vision table 6 1 Rods abundant in the periphery best for dim light see black white receptors share line with many others so bad detail vision good sensitivity Cones abundant in the fovea best for bright light see color Acuity Sensitivity Tradeoff own line to brain so good detail vision bad sensitivity acuity fovea acuity rods off fovea can be a one to one relationship between receptors and bipolar ganglion cells which gives good also can use many to one receptors to ganglion bipolar cells convergence good sensitivity poor Photopigments chemicals contained by both rods and cones that release energy when struck consist of proteins called opsins wavelength red light medium wavelength green light short wavelength blue light exact structure of opsin molecule determines maximal sensitivity to wavelengths of light Long Trichromatic Theory of color vision three kinds of receptors for human vision color cones determine by a particular opsin within a photoreceptor each cone maximally sensitive to different set of wavelengths color perceived through relative rates of response of each cones Retinex Theory area Opponent Process Theory cortex compares information from various parts of retina to determine the brightness and color for each perceive color in terms of paired opposites brain has mechanism that perceives color on a continuum from red to green and another from yellow to blue bipolar cells are excited by one set of wavelengths and inhibited by another Color Constancy ability to recognize color despite changes in lighting Lateral Inhibition reduction of activity in one neuron by activity in neighboring neurons Retina s way of sharpening contrasts to emphasize the borders of objects What causes color vision deficiency impairment in perceiving color differences gene located on X caused by either lack of a type of cone or a cone that has abnormal properties most common is red green long and medium wavelength have same photopigment Protanopia deuteranopia red green color blindness Tritanopia blue color blindness Receptive field refers to part of visual field that either excites or inhibits a cell in the visual system of the brain The receptive field of a receptor is the point in space from which light strikes the cell The receptive field of the ganglion cell is the combined receptive fields of those receptors Brain regions involved in vision and the visual pathways through to the cortex The ganglion axons exit the as the optic nerve and then go to the optic chiasm place where two optic Most ganglion cell axons go to Lateral Geniculate Nucleus some to Superior Colliculus some to other nerves meet areas Lateral Geniculate Nucleus part of thalamus specialized for visual perception sends axons to other parts of thalamus and to visual areas of occipital cortex cortex and thalamus feed info back and forward Superior Colliculus reflexes and orientation There are correlations between cones rods and magno parvocellular cells Ganglion Cells Parvocellular Neurons most located in or near fovea have smaller cell bodies and receptive fields connect only to LGN highly sensitive to detect color and visual detail related to cones Magnocellular Neurons distributed evenly throughout retina larger cell bodies and visual fields mostly connect to LGN but also other visual areas of thalamus highly sensitive to large overall pattern and moving stimuli related to rods Pathways in brain The where pathway of vision is the dorsal stream Primary visual cortex Secondary visual cortex Association cortex to posterior parietal cortex important for things like maze learning ability to perceive movement find objects and move toward them The what pathway of vision is the ventral stream Primary visual cortex Secondary visual cortex Association cortex to inferior temporal cortex Important for things like object perception and recognition Shape pathway Simple Cells fixed excitatory and inhibitory zones the more light that shines in excitatory zone the more the cell responds the more in inhibitory zone the less the cell responds diagonal ones bar shaped or edge shaped receptive fields with vertical and horizontal orientations outnumbering Complex Cells located in V1 or V2 perpendicular to its access Hypercomplex Cells extend past a certain point Organization have large receptive fields with no excitatory or inhibitory zones respond to a pattern of light in a particular orientation and most strongly to stimulus moving similar to
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