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 I Chapter 6 Study Hints A What is the law of specific nerve energies 1 Activity by a particular nerve always conveys the same type of information to the brain a Example impulses in one neuron indicate light impulses in another neuron indicate sound 2 The brain does not duplicate what we see perceive 3 Which neurons respond the amount of response and the timing of response influence what we B Know the anatomy of the eye What are the functions of the labeled parts in the image included here 1 Iris Circular band of muscles that controls the size of the pupil therefore controls light entry a Dilates with dilator b Constricts with sphincter c Also Pigmentation complex pattern Whytt s reflex Red eye 2 Pupil Hole in the center of the eye where light passes through a Size dilated or constricted determines how much light can pass 3 Lens Bends light to focus image on retina passing through the eye a How By bending itself 4 Ciliary muscle controls the curvature 5 Cornea focuses light 6 Fovea Point of central focus a Most detailed vision 7 Retina Tissue with nerve cells and photoreceptors a Like an outgrowth of the brain same embryonic tissue 8 Blind Spot Hole in retina where optic nerve exits eye a No photoreceptors here 9 Optic Nerve a Cranial Nerve CN II b Sensory info from photoreceptors to brain c c C For the picture above When light enters through the pupil and strikes the retinal neurons in what order 1 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 a First to visual receptors in the back of the eye b Those send messages to neurons called bipolar cells located closer to the center of the eye c Bipolar cells send messages to ganglion cells that are even closer to the center of the eye i The axons of ganglion cells join one another to form the optic nerve that travels to the brain 2 Retinal Circuitry a 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 b The point at which the optic nerve leaves the back of the eye is called the blind spot because it contains no receptors Retinal Circuitry Receptors rods and cones Horizontal cells Amacrine cells Ganglion cells Outer segment Inner segment Bipolar cells Optic nerve fibers Light 3 How photons stimulate action potentials a Without light receptors inhibit bipolar cells b Light hyperpolarizes receptors c Receptors stop neurotransmitter release d Bipolar cells are disinhibited e Bipolar cells stimulate ganglion cells i By releasing an excitatory NT f AP down optic nerve D We talked a lot about rods and cones and their difference in foveal and peripheral vision table 6 1 2 Rods most abundant in the periphery of the eye and respond to faint light 120 million per 1 Table 6 1 retina a Best for dim light b See black white c Receptors share line with many others d So bad detail vision good sensitivity 3 Cones most abundant in and around the fovea 6 million per retina a Essential for color vision more useful in bright light b Own line to brain c So good detail vision bad sensitivity E Acuity Sensitivity Tradeoff Acuity Sensitivity Trade off Spatial summation Stimulus Receptors Less spatial summation Bipolar Cells Ganglion Cells One to one good acuity fovea Many to one convergence good sensitivity poor acuity rods off fovea 1 Pool info from many receptors decrease percent info from any one receptor F While you don t need to know 11 cis retinal or all trans retinal know 1 Photopigments comprised of retinal and opsins in rods and cones that respond to different wavelengths a Release energy when struck by light b Retinal responsible for activation of 2nd messenger system c Opsin makes the photopigment sensitive to particular wavelength of light 2 The exact structure of opsin molecule determines maximal sensitivity to wavelengths of light a Long wavelength red light b Medium wavelength green light c Short wavelength blue light G Trichromatic Theory of color vision 1 Three kinds of receptors for human color vision color cones 2 Determined by the particular opsin within a photoreceptor 3 Each cone is maximally sensitive to a different set of wavelengths a Short medium long wavelengths 4 Color is perceived through the relative rates of response of each cones 5 Any response by any one cone is ambiguous CNS must process relative activity across all cones 6 Retina contains equal numbers of red and green cones much smaller number of blue cones 8 H Additive Color Mixing 1 Perception of colors results when lights of various wavelengths are combined in the visual system 2 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 I What is the Retinex Theory the cortex compares information from various parts of the retina to determine the brightness and color for each area 1 Better explains color constancy J Opponent Process Theory We perceive color in terms of paired opposites 1 The brain has a mechanism that perceives color on a continuum from red to green and another from yellow to blue inhibited by another by these theories of size or distance 2 A possible mechanism for the theory is that bipolar cells are excited by one set of wavelengths and K Understand color and contrast constancy lateral inhibition 1 Color constancy the ability to recognize color despite changes in lighting is not easily explained 2 Contrast constancy the ability to perceive objects as maintaining a constant contrast independent L What causes color vision deficiency 1 Color vision deficiency impairment in perceiving color differences a Gene responsible is contained on the X chromosome b Caused by either the lack of a type of cone or a cone has abnormal properties c Most common form is difficulty distinguishing between red and green d Results from the long and medium wavelength cones having the same photopigment M Receptive fields 1 The receptive field of a receptor is the point in space from which light strikes the cell 2 The receptive field of the ganglion cell is the combined receptive fields of those receptors N The ganglion axons exit as the optic nerve
View Full Document
Unlocking...