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Somatosensory Systems

Somatosensory Systems. cutaneous proprioceptive. Adequate Stimuli. Thermal (infrared radiation, contact). Touch (light touch, pressure, vibration). Pain and Itch (chemical, thermal, mechanical). Proprioception (mechanical; stretch or pressure). Cutaneous subsystems. epicritic

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Somatosensory Systems

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  1. Somatosensory Systems cutaneous proprioceptive

  2. Adequate Stimuli Thermal (infrared radiation, contact) Touch (light touch, pressure, vibration) Pain and Itch (chemical, thermal, mechanical) Proprioception (mechanical; stretch or pressure)

  3. Cutaneous subsystems epicritic location vibration texture shape protopathic pain temperature itch and tickle

  4. Epricritic, or non-pain Somatosensation

  5. Meissner’s Merkel’s 60 hz vibration Pressure Riffini’s Free nerve ending Pacinian Pain Stretch 200 hz vibration

  6. As in the retina, receptive fields vary in size. Smaller receptive fields = greater acuity two-point discrimination

  7. Center-surround organization of cutaneous receptive fields results in lateral inhibition, as in retina Serves to enhance contrast

  8. Protopathic, or pain Somatosensation

  9. Pain Receptors Called Nociceptors • Free nerve endings that respond to: • mechanical stimuli • thermal stimuli • chemical stimuli, or • all three • (polymodal receptors)

  10. Free nerve endings of unmyelinated C fibers or thinly myelinated Aδ fibers

  11. Cutaneous classified by conduction velocity Proprioceptive classified by axon diameter

  12. SubstanceEffect Potassium activation Bradykinin activation Histamine activation Prostaglandins sensitization Substance P sensitization

  13. Gate control theory of pain control

  14. Referred Pain

  15. CN V and VII

  16. Parallel Processing in the Somatosensory System Lemniscal System (non-pain; epicritic) Extralemniscal System (pain; protopathic) Spinothalamic pathways Neospinothalamic Paleospinothalamic Spinomesencephalic

  17. Neospinothalamic Paleospinothalamic Spinomesencephalic

  18. Neospinothalamic Pathway

  19. Paleospinothalamic Pathway

  20. Spinomesencephalic Pathway

  21. Descending control of pain

  22. Sensory System Summary 1. Sensory systems detect change over space (lateral inhibition to enhance contrast) over time (rapidly adapting) 2. Detect “features” 3. Structures are laminated (cells in layers) 4. Parallel pathways 5. Hierarchical processing 6. Topographical organization 7. Non-uniform receptive fields 8. Extreme sensitivity, wide dynamic range 9. Non-linear response

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