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032508 - 2 topographic representation 3 Representation is...

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March 25, 2008 2: topographic representation 3: Representation is unique bc of distortions Under and over rep in relation to importance to somatosensory Dense packing of receptors on hand than arm; more inputs from per unit area 4: Minimum distance in mm that two points have to be in order to discriminate from a single point. Fingers discrim well but in other parts, distance much larger. Related to density of sensory receptors 5: Cross from one side of body to other side of brain at medulla. This is called contralateral lateral composition. 6: Nervous sys co-registers info from diff sensory receptors at a given location in the body. At level of cortex, you want incorp of sensory modalities- pain, temp, mechano, etc. Diff paths but end up in same place to be processed (?) 8: Either directly innervate motor or indirectly innervate interneurons which will innervate motor neurons. 9: Map for motor and fine control. Vocal cords don’t have much for sensory map but for motor, much representation. 10: Crossed at medulla from one side to other- contralateral 12: Maps not as fixed as ppl thought previously. The maps are adjustable. Thin electrical wires to record, find receptive fields. 13: Each neuron has portion of skin to which it is sensitive. Only touch w/I this portion is activates response in this particular neuron. At level of cortex, receives input from many sensory fibers (convergence). At level of cortex, receptive fields are “larger.” Scientists mapped portion of skin (perimeter) that related to response? Change in receptive field to expand to respond to larger region than before. Waited a few weeks, more expansion. Immediate compensation after seconds. 14:
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Neuron receives dominant input and neighboring weak input. Neighboring by themselves cannot cause neuron to fire, but if you cut dominant nerves, nerve senses main input is gone and somehow amplifies the weaker ones and starts to respond. Cortex in region is still not receiving full response, sends signal to nearby receptors, sprouting of axons (couple weeks) to territory where silent connections and even where no receptors were before. 15: Instead of cutting nerve, change way animal interacts w/ environment, does representation change?
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