1. Sensory Systems 1. Visual Distal senses 2. Auditory Proximal senses acoustic vestibular 3. Somatosensory cutaneous proprioceptive 4. Gustatory chemical (flavor) 5. Olfactory

2. Somatosensory Systems cutaneous proprioceptive

3. Adequate Stimulus A stimulus of a quality and of sufficient intensity to excite a sensory receptor.

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

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

7. Receptive field That part of the periphery to which a cell responds.

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

14. Summation of responses of different receptors (spatial summation).

15. Coding of intensity by increased rate (temporal summation).

16. Epricritic, or non-pain Somatosensation

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

18. Center-surround organization of cutaneous receptive fields results in lateral inhibition. Serves to enhance contrast

19. Protopathic, or pain Somatosensation

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

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

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

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

27. Gate control theory of pain control Transcutaneous electrical nerve stimulation may act via gate control

28. Referred Pain

31. CN V and VII

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

37. Neospinothalamic Paleospinothalamic Spinomesencephalic

38. Neospinothalamic Pathway

39. Paleospinothalamic Pathway

40. Spinomesencephalic Pathway

41. Descending control of pain

45. 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