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INTRODUCTION TO SENSORY PHYSIOLOGY Specialized sensory organs and free nerve endings in the skin provide four modalities of cutaneous sensation. The modality and location of each sensation is determined by the specific sensory pathways and frequency patterns in the brain; the threshold and intensity of the sensation depend partially on the density of the receptors. In this exercise we will: 1) Describe the distribution of cutaneous receptors; 2) Determine the two-point threshold in different regions of the skin: 3) Define and demonstrate sensory adaptation; and 4) Determine the ability to localize a cutaneous sensation in different regions. Four independent modalities of cutaneous sensation have traditionally been recognized-warmth. cold. touch, and pain. (pressure is excluded because it is mediated by receptors deep in the dermis. and the sensations of itch and tickle are usually exduded because of the mysterious origin.) Mapping of these sensations on the surface of the skin has revealed that the receptors are not generalized throughout the skin but are clustered at different points, (i.e. . have a punctuate distribution. Since the punctuate distribution is different for each of the four sensory modalities, earlier physiologists believed that each sensation was mediated by a different sensory receptor, and this view was supported by the histological identification of different cutaneous receptors. Excision of areas of the skin from different sensory maps, however, failed to reveal a different distribution of receptors, and more recent experiments have suggested that the four sensations may arise from an analysis of complex patterns of sensory (afferent) impulses in the brain. Experimental procedure 1. Mapping the Density of Temperature and Touch-Sensitive Spots of the Skin Divide into pairs. Each of you take turns being the toucher and the touchee. A. Procedure
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This note was uploaded on 04/22/2008 for the course PHPR 101 taught by Professor Smith during the Summer '08 term at Ohio Northern University.

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