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Touch 1: Introduction to S omatosensation

Touch 1: Introduction to S omatosensation. Pick a sense to loose. Which sense would you prefer to loose? Vision? Hearing? Touch?. Ian Waterman. Auto-immune disease eliminated neurons transmitting sensory messages from body – could move but could not feel

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Touch 1: Introduction to S omatosensation

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  1. Touch 1: Introduction to Somatosensation

  2. Pick a sense to loose • Which sense would you prefer to loose? • Vision? • Hearing? • Touch? PSY 295 - Fall 2012 - Grinnell College

  3. Ian Waterman • Auto-immune disease eliminated neurons transmitting sensory messages from body – could move but could not feel • Could not feel the positions of his limbs (proprioception) • Could not feel the bed – floating sensation • Could not grip things with appropriate force • Could not stand safely Learned to overcome his disability by substituting visual feedback for proprioception and consciously plotting every step he took PSY 295 - Fall 2012 - Grinnell College

  4. Somatosensation • Cutaneous senses – touch and pain from skin • Proprioception – position of body and limbs • Kinesthesis – movement of body and limbs we will focus on the cutaneous senses PSY 295 - Fall 2012 - Grinnell College

  5. Somatosensory receptor neurons • Neurons that live in the dorsal root ganglion • Specialized peripheral terminal in skin which transduces touch signals into electrical signals (action potentials) PSY 295 - Fall 2012 - Grinnell College

  6. Encapsulated or bare • Dorsal root ganglion neurons with encapsulated receptors mediate touch and proprioception • Bare nerve endings mediate thermal sensations and pain PSY 295 - Fall 2012 - Grinnell College

  7. Skin • Largest sense organ (4 kg, 1.8 square meters) • Divided into dermis and epidermis PSY 295 - Fall 2012 - Grinnell College

  8. Two types of skin • Hairy and glabrous (hairless) • Tactile sensitivity is greatest on the glabrous skin on the hand, fingers, feet and lips PSY 295 - Fall 2012 - Grinnell College

  9. Touch receptors PSY 295 - Fall 2012 - Grinnell College

  10. Mechanoreceptors PSY 295 - Fall 2012 - Grinnell College

  11. Mechanorceptors PSY 295 - Fall 2012 - Grinnell College

  12. Mechanoreceptors • Both deep and superficial skin layers have slowly adapting receptors that respond to sustained stimulation and rapidly adapting receptors which respond to transient stimulation • Superficial • merkel: Slowly adapting (fine details) • messiner: Rapidly adapting (vibration) • Deep • ruffini: Slowly adapting (lateral skin stretch) • pacinian: Rapidly adapting (high frequency vibration) PSY 295 - Fall 2012 - Grinnell College

  13. Receptive fields • The receptive field of a somatosensory neuron is the region of skin where applying stimulation influences its firing rate • Receptors of different kinds have different size receptive fields • Superficial receptors have smaller receptive fields • Deep receptors have larger receptive fields PSY 295 - Fall 2012 - Grinnell College

  14. Receptive fields receptive field size varies as a function of body area PSY 295 - Fall 2012 - Grinnell College

  15. Receptive fields PSY 295 - Fall 2012 - Grinnell College

  16. Receptive fields PSY 295 - Fall 2012 - Grinnell College

  17. PSY 295 - Fall 2012 - Grinnell College

  18. PSY 295 - Fall 2012 - Grinnell College

  19. Web activity • http://sites.sinauer.com/wolfe3e/chap13/ssreceptorsF.htm PSY 295 - Fall 2012 - Grinnell College

  20. Other somatosensory receptors PSY 295 - Fall 2012 - Grinnell College

  21. Kinesthetic receptors • Mechanoreceptors in muscles, tendons and joints • Tell you where your limbs are and how they are moving • In the reflex arc they encode muscle stretch PSY 295 - Fall 2012 - Grinnell College

  22. Muscle spindle • Signal tension in the muscles • This signal is useful for determining limb position PSY 295 - Fall 2012 - Grinnell College

  23. Kinesthetic receptors are important • Ian waterman lost his kinesthetic sensation and could not determine the position of his limbs • Had to use visual feedback instead of just feeling where his limbs are like we do PSY 295 - Fall 2012 - Grinnell College

  24. Thermal receptors • Skin temperature is encoded by two populations of receptors • Cold and warmth fibers PSY 295 - Fall 2012 - Grinnell College

  25. Response of a cold fiber PSY 295 - Fall 2012 - Grinnell College

  26. Nociceptors • Bare nerve endings in skin sensitive to harmful stimuli • Pressure, burns, chemicals, etc… PSY 295 - Fall 2012 - Grinnell College

  27. Nociception is important • Woman born lacking ability to feel pain • Burned herself, bit her tongue, joint problems • Died at age 29 from infections PSY 295 - Fall 2012 - Grinnell College

  28. Somatosensory pathways PSY 295 - Fall 2012 - Grinnell College

  29. From skin to brain • How do dorsal root ganglion cells get information to the brain? PSY 295 - Fall 2012 - Grinnell College

  30. Two pathways • Spinothalamic pathway – slower, older pathway which carries signals from nociceptor and thermoreceptors • Dorsal column-medial leminiscal (DCML) pathway – faster, newer pathway which carries touch and kinesthetic signals PSY 295 - Fall 2012 - Grinnell College

  31. Spinothalamic pathway Left side of body is represented on right side of brain and vice versa PSY 295 - Fall 2012 - Grinnell College

  32. DCML pathway Left side of body is represented on right side of brain and vice versa PSY 295 - Fall 2012 - Grinnell College

  33. Somatosensory cortex • Information arrives in the somatosensory cortex • S1 receives information from ascending pathway PSY 295 - Fall 2012 - Grinnell College

  34. Columnar topographic organization • Neurons in same cortical column respond to nearby skin regions • Nearby cortical columns respond to nearby skin regions PSY 295 - Fall 2012 - Grinnell College

  35. Mapping somatosensory cortex • Canadian neurosurgeon Wilder Penfield • Stimulated S1 cortex while subjects undergoing neurosurgery • Found stimulating different areas of S1 gave different body sensations PSY 295 - Fall 2012 - Grinnell College

  36. Topographic body maps in S1 PSY 295 - Fall 2012 - Grinnell College

  37. Multiple maps in S1 • Different maps get input from different classes of receptors (3b gets input from cutaneous touch receptors) PSY 295 - Fall 2012 - Grinnell College

  38. Columnar organization of modality PSY 295 - Fall 2012 - Grinnell College

  39. Somatosensory homunculus PSY 295 - Fall 2012 - Grinnell College

  40. Web activity • http://sites.sinauer.com/wolfe3e/chap13/homunculusF.htm PSY 295 - Fall 2012 - Grinnell College

  41. Receptor spacing and two-point thresholds PSY 295 - Fall 2012 - Grinnell College

  42. Two-point touch discrimination PSY 295 - Fall 2012 - Grinnell College

  43. Demonstration PSY 295 - Fall 2012 - Grinnell College

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