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Chapter 8

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Zachariah Campbell

General Principles of SensorySystem FunctionA Sensory receptorsspecialized cells that transduceconvert sensory energy into neural activity6 common properties of sensory receptorsReceptors are energy filtersdesigned to respond only to a narrow band of energy within each modalitys energy spectrumeg visual system can only detect visible light out of the whole electromagnetic spectrumcolordeficientcolorblind people lack receptors for parts of the usual visual spectrumReceptors transduce energyeach sensory system receptors specialized to filter a different form of energyvision light energy chemical energy photoreceptors of retina APaudition airpressure waves a few forms of mechanical energy last one activates auditory receptors APsomatosensory mechanical energy activates mechanoreceptors cells sensitive to touchpain etcAPtasteolfaction chemical molecules in airfood fit to receptors APpain tissue damage release chemicals acting like NT activate pain fibres APeg when hair is displaced via touch dendrite of somatosensory neuron around hair base trechdendrite has stretch sensitive Na channels that open and cause Na influx and APReceptive fields locate sensory eventsevery receptor organ and cell has a receptive field specific part of the world to which it respondseg in the retina each photoreceptor rods and cones points in a slightly different direction so has a unique receptive field each receptors special view is its receptive field fields sample sensory info and locate sensory events in spacefields of adjacent receptors may overlaprelatively different responses help localize sensationspatial dimensions of sensory info produce cortical patterns and map of sensory world to form sensory reality Receptors identify change and constancyrapidly adapting receptors detect the presence of somethingeasy to activate stop responding after a short timedetects movement of objectseg light touch on the arm quickly fades if kept stillslowly adapting receptors adapt more slowly to stimulationeg pressuresensitive receptors in skineg visual system rapidlyadapting rods respond to visible light of any wavelength vs slowlyadapting cones sensitive to colorpositionReceptors distinguish self from otherexteroceptive receptors that respond to external stimulieg objects in the world that we touchseeinteroceptive receptors that respond to our own activity eg optic flow streaming of visual stimuli when we move auditory flowchanges in sound intensity when we movetell us the positionmovement of our bodies interpret meaning of external stimulieg auditory flow tells us how fast we are moving whether we or the object is the one movingdifficulty in distinguishing self from other hallucinations OCDReceptor density determines sensitivitydifferent receptor density explains sensitivity in fingers vs armtwopoint sensitivity highest in body parts with the most sensitivity sensory systems use different receptors to enhance sensitivity under different conditionsvisual system fovea receptors cones are densely packed for sensitive color discrimination in bright light peripheral retina receptors rods are larger and more scattered for blackandwhite vision but highly sensitive to darklight discriminationB Neural relaysreceptors connect to cortex via sequence of intervening neuronsthree stages in somatosensory and visual system four in auditory mediate different responsesallow sensory systems to interactrelays determine hierarchy of motor responses some of the relay stages are in the brainstem spinal cord or cortexat each level relay allows sensory system to produce relevant actions that define hierarchy of motor behavioreg 1st relay for pain receptors in spinal cord related to reflexes that produce withdrawal of body part from stimulus pain pathway relays in brainstem especially midbrain periaqueductal grey matter surrounding cerebral aqueduct responsible for for complex response to pain stimulieg behavioural activation and emotional response in neocortex pain relays localize pain identify kind of pain external cause of pain potential remediesmessage modification takes place at relays
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