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NPB+112+11+somatosensory+lecture+notes

NPB+112+11+somatosensory+lecture+notes - NPB 112 Winter...

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1 NPB 112, Winter 2011: 1/18/11- 1/20/11 Outline: I. Sensory physiology: overview (Ch. 9) II. Skin mechanoreceptor types A. Mechanoreceptor B. thermoreceptors 1. Warm receptors 2. Cold receptors C. Nociceptors (pain) (Ch. 10) 1. A-delta mechanical nociceptor 2. polymodal nociceptor I. OVERVIEW: sensory physiology, A. TUNING: Of adaptive value to detect certain forms of energy (e.g. withdrawal of limb from potentially injurious stimulus). B. FILTERING: need not detect ALL forms of energy, only those significant for survival. Most energy impinging upon an animal is filtered out. C. 5 basic senses or MODALITIES (Aristotle) and discriminable qualities: Sensory Modality Quality (sub-modality) vision color, motion hearing pitch smell ~400 functional odorant receptors taste sweet, sour, salt, bitter, "umami" (MSG, other amino acids) somatic touch-pressure, warm-cold, pain, itch, tickle, flutter-vibration, pleasurable touch (?) 1. qualitative discriminability suggests existence of specific sensory RECEPTORS connected to a neural pathway specific for that sensory quality. a. Johannes Muller (1800s) "law of specific nerve energies". b. Today called "labeled line" coding or "specificity".
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2 2. Sensory systems form "windows" on the world, filtering energy and letting through relevant information that is pieced together by the brain to form perceptions. D. STIMULUS TRANSDUCTION: transformation of stimulus energy into information (action potentials) that the brain can use. 1. RECEPTORS capture and transform energy. 2. TRANSDUCTION: process by which stimulus energy is transformed into electrical signal (e.g., depolarization of receptor) 3. ADEQUATE (APPROPRIATE) STIMULUS: Type of energy (electromagnetic, chemical, physical, thermal) that excites the receptor at the lowest relative intensity a. visible light for photoreceptors b. intense pressure on eye also activates photoreceptors (seeing stars) 4. Receptors are grouped on the sensory receptive tissue (skin for touch, retina for vision, cochlea for hearing, etc.). a. Part of receptor where energy is transduced is analogous to a dendrite, except it interfaces with the environment b. In touch (mechano-) receptor, stretch-activated channels open when the cell membrane is mechanically deformed, resulting in depolarization ( inward positive current) c. Depolarization is called RECEPTOR POTENTIAL (also GENERATOR POTENTIAL), much like an EPSP. (1) Spreads passively across membrane to axon hillock (2) Voltage-sensitive Na+ channels open if depolarization is big enough. E. GENERAL PLAN OF SENSORY SYSTEMS 1. After transduction, information is transmitted to the brain as action potentials. Sensory systems all have same basic plan.
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3 2. Receptor synapses with a series of relay neurons. Relays form the sensory pathway, including a synapse in sensory thalamus on the way to a specific sensory cortical area.
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