Lec22_Touch_Chap12b - Somatosensation Part 2(Chap 12...

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Somatosensation, Part 2 (Chap 12) Dr. Jonathan Pillow Perception (PSY 323) The University of Texas at Austin Lecture 21
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The Physiological Mechanisms of the Somatosensory System
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Touch receptors : Embedded on outer layer (epidermis) and underlying layer (dermis) of skin Categorized by: 1. Type of stimulation to which it responds 2. Size of the receptive field 3. Rate of adaptation (fast versus slow)
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Tactile receptors Called “ mechanoreceptors ” because they respond to mechanical stimulation: pressure, vibration, or movement 4 types, defined by: 1 . Receptive field size (type I vs. II) big II I small
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Tactile receptors Called “ mechanoreceptors ” because they respond to mechanical stimulation: pressure, vibration, or movement 4 types, defined by: Touch Stimulus Fast Adapting (FA) Slow Adapting (SA) 2. Response properties (FA vs. SA)
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• Merkel cell neurite complexes (SA I) • Meissner corpuscles (FA I) • Ruffini endings (SA II) • Pacinian corpuscles (FA II) small } large }
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Cross section of the human hand illustrating locations of the four types of mechanoreceptors and the two major layers of skin (SA1) (SA2) (FA1) (FA2)
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high-freq vibration, light touch; “buzz” (diffuse) texture / form perception; “pressure” low-freq vibration, slip; “wobble”, flutter (localized) finger position, grasp; (no sensation reported)
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Other type of mechanoreceptors: Kinesthetic receptors : sense of where limbs are, what kinds of movements are made, - found within muscles, tendons, and joints Types: Muscle spindle : located in a muscle, senses its tension (also known as a “stretch receptor”) Receptors in tendons signal tension in muscles Receptors in joints signal when joint is bent
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A muscle spindle
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Importance of kinesthetic receptors: Strange case of neurological patient Ian Waterman: Cutaneous nerves connecting kinesthetic mechanoreceptors to brain destroyed by viral infection Lacks kinesthetic senses, dependent on vision to tell limb positions
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