Eg touch pressure pain temperature vision hearing

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Eg. touch, pressure, pain temperature, vision, hearing, taste, smell etc Interceptors (visceroceptors) - inside body Respond to stimuli inside body Eg. chemical change, temperature, pain, discomfort, thrist, hunger etc We are often unaware of their workings Proprioceptors - also inside body Confined to muscles, tendons, joints, ligaments Monitor stretch, inform brain of body movement Receptor structure Five special senses Vision, hearing, equilibrium, smell, taste Housed in complex sense organs, eg. eyes General senses Overwhelming majority Monitor most types of sensory information Tactile (touch, pressure, stretch, vibration) Temperature Pain “Muscle sense” (proprioception) Not 1-to-1 1 receptor / several different kinds of stimuli 1 stimulus / different kinds of receptors +/- encapsulated by connective tissue Levels of sensory perception Sensation - awareness of internal/external environment Perception - conscious interpretation of stimuli Somatosensory system - three levels of neural integration: 1. Receptor level : input from extero/intero/proprioceptors 2. Circuit level : processing in ascending pathways 3. Perceptual level : processing in cortical sensory areas Sensory receptors detect stimuli and their nerves contain the afferent and efferent fibres that deliver impulses to and from the CNS Sensory perception - (1) Receptor level
Transduction: receptor converts the stimulus (eg. light, sound, odorant) into an electrical event (conversion to energy that brain can use) Stimulus energy —> graded potential If graded potential reaches threshold , an action potential (nerve impulse) propagated to CNS Strength, duration and pattern - but NOT type!!! Of stimulus encoded in nerve impulse frequency Stimulus must match receptor specificity and be in its receptive field More complex receptors are more specific; smaller receptive fields allow brain to better localize stimulus Receptors can produce two types of graded potentials Generator potential: receptor is part of general sensory neuron, eg on dendrite Receptor potential: separate receptor cell releases neurotransmitter to sensory neuron (most special senses) Adaption Response of sensory receptor to constant stimulus declines over time ( eg. sewage plant workers eat on job) 2 types of receptor response possible: Phasic: fast adapting Bursts of impulses at beginning/end of stimulus Report changes in environment Eg. lamellar, tactile corpuscles Tonic: slow/sustained response, little/no adaptation Eg. Nociceptors, proprioceptors, since protective Fast adaptation examples: initially dazzled by bright sunlight (seconds), loss of taste (minutes) Sensory perception - (2) Circuit level Impulses delivered along spinal cord to primary somatosensory cortex in brain Chain of 3 neurons: First order: link receptor with cell body in spinal cord
Second order: move up spinal cord to brain Third order: take message to cerebral somatosensory cortex Sensory perception - (3) perceptual level Sensory input is interpreted in the cerebral cortex

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