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any energy capable of exciting a receptor (mechanical, chemical, thermal, photic) |
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to convert energy into a different type of energy (ie: light --> a pattern of action potentials) |
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| specialized nerve cells that transduce energy |
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| Receptors are ________ specific |
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receptors respond to/detect a a. wide or b. narrow range of stimuli |
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b. narrow - only detect a small range of energy levels ie: eye: 400-700 nM ear: 20-20,000 Hz taste buds: specific chemicals |
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those attributes of a stimulus that will alter the firing rate of a sensory cell -can measure RF at each level of sensory system -there are as many RF's as there are cells in a sensory system |
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-how many synapses (order of system) -degree of decussation (crossover) -projects to which area of the thalamus? -projects to which area of the cortex? -does corgex show "topical" organization -modification of sensory coding (experience, hormones?) |
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| Function of visual systems is to detect: |
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| Electromagnetic Radiation emitted by objects |
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1- locate figure vs. ground (ie: recognize figure) 2- detect movement (predator/prey?) 3- detect color (adaptive value of color) |
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2nd cranial nerve conveys visual information to the brain |
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| 3 layers of cells in the retina |
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photoreceptors - 1st order bipolar - 2nd order ganglion cell - 3rd order |
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-120 million -light sensitive (NOT color) found in periphery of retina consist of stacked protein disks low activation threshold |
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6 million are color sensitive found mostly in fovea (it's hard to see color when there's not much light) they require a high level of luminosity |
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| consist of opsin (protein) and retinal (lipid from vitamin A) |
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Ganglion cells exhibit low baseline firing rates -receptive fields: circular in shape with ring-shaped surrounding -"ON-Cell": light placed on center (the "on-area" increases firing -light placed on surrounding area decreases firing |
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| Hubel (California) and Wiesel (Sweden) |
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| wrote a paper about what the eye sends to the brain (of a frog) |
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ganglion cell ->through optic chiasm --> lateral geniculate --> primary visual cortex (striate) [mesial aspect of occiptal lobe (Brodmann 17)] |
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| in animals without a cortex (ie: reptiles), visual information goes to the: |
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| superior colliculi in the midbrain |
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| A minor percentage of visual information does not go to the primary visual area. Instead, this small percentage goes to... |
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From striate cortex (V1) circulates in 2 streams/directions |
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1-Dorsal: spatial location of the object. "where" an object is -projects to pos. parietal association cortex 2-Ventral: Recognition of complex patterns - "what" an object is (v2, V3, V4, V5) -and to inferior temporal cortex (Temp/Occipit, Temporal) |
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disturbances in vision -apperceptive visual agnosia -associative visual agnosia -prosopagnosia (inability to recognize faces) -pure alexia (without agraphia) |
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| damage before the optic chiasm in one eye results in |
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| complete blindness in that eye |
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| damage in the optic chaism (pituitary adenoma - common tumor there) |
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causes a bitemporal hemianopia (or heminopsia - aka cannot see half) lose peripheral vision but are usually unaware |
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| damage at the level of the primary of the visual cortext you lose |
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half the visual field - you can't see half.. if you have left damage, you have a right hemianopia.. aka can't see right visual field |
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| a quarter of the visual field is gone |
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| a small area you can't see |
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| the afferences (over-represented) |
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| in motor cortex, layer ___ is over represented |
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| eyes are directed to those areas that convey the most |
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| information (ie: on a face... the eyes and nose) |
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inability to open the eyelid (due to 3rd optical nerve damage) |
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