PSIO 201 5th Edition Lecture 36Outline of Current Lecture I. Introduction to Sensory FunctionII. GustatoryIII. OlfactoryIV. General SensesV. Special SensesVI. Reception FieldVII. SpecificityVIII. Sensory TransductionCurrent LectureGeneral Senses – receptors distributed throughout body – not collected within specialized ‘senseorgans’4 Types:1. Pain receptors2. Temperature thermoreceptors3. Touch, pressure, body position mechanoreceptors4. Chemical stimuli chemoreceptors (-O2, CO2)General Senses – Somatic Senses vs. Visceral SensesSomatic = body surface ( surface temp, touch, pain and muscle soreness)Visceral = internal organs (stomach ache, gut cramps etc)Special Senses – receptors congregated in specialized ‘sense organs’5 Types:1. Smell (olfaction) – nose2. Taste (gustation) – tongue3. Sight (vision) – eye4. Balance/Equilibrium – ear5. Sound (hearing) – earSpecificity of Sensation:Regardless of stimulus modality all sensations is “read” in the CNS as electrical signals; we can discriminate between different types of stimuli because different receptor types respond preferentially to different stimuli. A mechanoreceptor is more sensitive to touch than to light; a photoreceptor is more sensitive to light than to touchReceptive Field – Discrimination between two similar stimuli (e.g. two points on the body surface, two sounds of similar pitch) is dependent on the number of receptors within an area of sensory surfaceSensory Transduction Common Steps 1. Stimulus arrives at receptor and alters membrane potential of receptors – “graded potential/ depolarizing or hyperpolarizing receptor potential2. Receptor potential influences (directly or indirectly) rate of AP production in a sensory neuron (the afferent pathway)3. Aps travel to CNS along afferent pathway4. CNS interprets/processes these incoming signalsSensory Transduction –Interpretation of afferent (sensory) input The brain assumed that any signals coming in along a sensory afferent from a particular receptor reflects stimulation by the appropriate stimulus (i.e. pressure, photon) - All other characteristics of the stimulus (e.g. intensity, duration) are conveyed by the prequency and pattern of the incoming signalsGeneral Senses 4 Types:1. Nociceptors (pain)2. Thermoreceptors (temperature)3. Chemoreceptors (e.g. O2, CO2, H+)4. Mechanoreceptors (touch, pressure, proprioception)Special Senses – generally show a greater degree of selectivity for specific stimuli – same principles of receptor function/sensory transduction
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