Study Guide for PSB2000 Exam 3 Vision Audition Mechanical Senses and Chemical Senses It is always advisable to know the key terms introduced in each section However the study hints listed here by chapter will also help you focus on other important concepts for the exam Chapter 6 Study Hints What is the law of specific nerve energies Law of specific nerve energies states that activity by a particular nerve always conveys the same type of information to the brain Example impulses in one neuron indicate light impulses in another neuron indicate sound The brain does not duplicate what we see Which neurons respond the amount of response and the timing of response influence what we perceive Know the anatomy of the eye What are the functions of the labeled parts in the image included here QuickTime and a decompressor are needed to see this picture Pupil Hole in the center of the eye where light passes through light enters the eye through an opening in the center of the iris called the pupil Size dilated or constricted determines how much light can pass Iris circular band of muscles that controls the size of the pupil therefore controls light entry Dilates with dilator and constricts with sphincter Also pigmentation complex pattern Whytt s reflex red eye Lens bends light to focus image on retina passing through the eye How By bending itself Ciliary muscles control its curvature lens The cornea also focuses light Fovea point of central focus most detailed vision happens here Retina rods and cones tissue with nerve cells and photoreceptors like an outgrowth of the brain same embryonic tissue Blind spot hole in retina where optic nerve exits eye no photoreceptors here blind spot Cranial Nerve CN II sensory information from photoreceptors to brain Optic nerve consists of the axons of ganglion cells that band together and exit through the back of the eye and travel to the brain The point at which the optic nerve leaves the back of the eye is called the blind spot because it contains no receptors Macula the center of the human retina The center portion of the macula is the fovea and allows for acute and detailed vision Vitreous humor QuickTime and a decompressor are needed to see this picture For the picture to the right above When light enters through the pupil and strikes the retinal neurons in what order Remember that it passes through the layers of cells pictured above and acts at the RECEPTORS they do the receiving on the far outside first In other words know the retinal circuitry pictured above and how photons stimulate action potentials Route within the Retina 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 Amacrine cells are additional cells that receive information from bipolar cells and send it to other bipolar ganglion or other amacrine cells Amacrine cells control the ability of the ganglion cells to respond to shapes movements or other specific aspects of virtual stimuli Retinal circuitry the optic nerve consists of the axons of ganglion cells that band together and exit through the back of the eye and travel to the brain The point at which the optic nerve leaves the back of the eye is called the blind spot because it contains no receptors How photons stimulate action potentials Without light receptors inhibit bipolar cells Light hyperpolarizes receptors Receptors stop NT release Bipolar cells are disinhibited Bipolar cells stimulate ganglion cells By releasing an excitatory NT AP down optic nerve We talked a lot about rods and cones and their difference in foveal and peripheral vision table 6 1 Also understand the Acuity Sensitivity Tradeoff QuickTime and a decompressor are needed to see this picture Acuity Sensitivity Tradeoff QuickTime and a decompressor are needed to see this picture While you don t need to know 11 cis retinal or all trans retinal you should know that there are photopigments comprised of retinal and opsins in rods and cones that respond to different wavelengths The exact structure of opsin molecule determines maximal sensitivity to wavelengths of light Long wavelength red light medium wavelength green light short wavelength blue light What is the Trichromatic Theory of color vision What is the Retinex Theory Opponent Process Theory Trichromatic Theory of color vision Three kinds of receptors for human color vision color cones Determined by the particular opsin within a photoreceptor Each cone is maximally sensitive to a different set of wavelengths short medium long wavelengths Color is perceived through the relative rates of response of each cones Any response by any one cone is ambiguous CNS must process relative activity across all cones Retina contains equal numbers of red and green cones much smaller number of blue cones 8 Remember Trichromatic theory 3 cones RGB Additive Color Mixing Perception of colors results when lights of various wavelengths are combined in the visual system Example yellow patch on TV is actually many tiny red and green dots white is equal amount of red green and blue These are the primary colors of light Retinix Theory suggests the cortex compares information from various parts of the retina to determine the brightness and color for each area Better explains color constancy Opponent Process Theory suggests that we perceive color in terms of paired opposites The brain has a mechanism that perceives color on a continuum from red to green and another from yellow to blue A possible mechanism for the theory is that bipolar cells are excited by one set of wavelengths and inhibited by another QuickTime and a decompressor are needed to see this picture Understand color and contrast constancy lateral inhibition Color Constancy the ability to recognize color despite changes in lighting is not easily explained by these theories Contrast Constancy lateral inhibition Lateral inhibition is the reduction of activity in one neuron by activity in neighboring neurons The response of cells in the visual system depends upon the net result of excitatory and inhibitory messages it receives Lateral inhibition is the retina s way responsible of sharpening contrasts to emphasize the borders of objects What causes color vision deficiency Color vision deficiency is impairment in
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