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Published byFrancine Evans Modified over 9 years ago
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Sensory Systems 1. Visual 2. Auditory 3. Somatosensory 4. Gustatory 5. Olfactory acoustic vestibular cutaneous proprioceptive chemical (flavor) Distal senses Proximal senses
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Somatosensory Systems cutaneous proprioceptive
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Adequate Stimulus A stimulus of a quality and of sufficient intensity to excite a sensory receptor.
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Adequate Stimuli for Somatosensation Thermal (infrared radiation, contact) Touch (light touch, pressure, vibration) Pain and Itch (chemical, thermal, mechanical) Proprioception (mechanical; stretch or pressure)
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epicritic location vibration texture shape protopathic pain temperature itch and tickle Cutaneous subsystems
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Receptive field That part of the periphery to which a cell responds.
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Meissner’sMerkel’s PacinianRuffini’sFree nerve ending 60 hz vibration Stretch 200 hz vibration Pressure Pain
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Summation of responses of different receptors (spatial summation).
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Coding of intensity by increased rate (temporal summation).
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Epricritic, or non-pain Somatosensation
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As in the retina, receptive fields vary in size. Smaller receptive fields = greater acuity two-point discrimination
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Center-surround organization of cutaneous receptive fields results in lateral inhibition. Serves to enhance contrast
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Protopathic, or pain Somatosensation
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Free nerve endings that respond to: mechanical stimuli thermal stimuli chemical stimuli, or all three (polymodal receptors) Pain Receptors Called Nociceptors
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Free nerve endings of unmyelinated C fibers or thinly myelinated A δ fibers
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Cutaneous classified by conduction velocity Proprioceptive classified by axon diameter
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SubstanceEffect Potassiumactivation Bradykininactivation Histamineactivation Prostaglandinssensitization Substance Psensitization
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Gate control theory of pain control Transcutaneous electrical nerve stimulation may act via gate control
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Referred Pain
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CN V and VII
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Parallel Processing in the Somatosensory System Lemniscal System (non-pain; epicritic) Extralemniscal System (pain; protopathic) Spinothalamic pathways Neospinothalamic Paleospinothalamic Spinomesencephalic
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Neospinothalamic PaleospinothalamicSpinomesencephalic
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Neospinothalamic Pathway
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Paleospinothalamic Pathway
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Spinomesencephalic Pathway
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Descending control of pain
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Sensory System Summary 1. Sensory systems detect change over space (lateral inhibition to enhance contrast) over time (rapidly adapting) 2. Detect “features” 4. Parallel pathways 5. Hierarchical processing 6. Topographical organization 7. Non-uniform receptive fields 8. Extreme sensitivity, wide dynamic range 9. Non-linear response 3. Structures are laminated (cells in layers)
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