1. Psychology 355 05 The Somatosensory System

2. Psychology 3552 Introduction Somatic Sensation A.Touch, sharp pain, ache, chill/burn B.Proprioception: Body position, location of limbs. Interacts with vestibular sense and vision; interacts with touch for “haptics”. Baroreceptors. C.Somatic sensory system: Different from other systems: several sense systems 1.Receptors: Distributed throughout body 2.Responds to widest variety of stimulus types

3. Psychology 3553 Touch Types and layers of skin A.Hairy and glabrous (hairless) B.Epidermis (outer) and dermis (inner) I.Functions of skin A.Protective function B.Prevents evaporation of body fluids C.Provides direct contact with world II.Mechanoreceptors A.Most somatosensory receptors are mechanoreceptors

4. Psychology 3554 Touch Mechanoreceptors A.Pacinian corpuscles B.Ruffini's endings C.Meissner's corpuscles D.Merkel's disks Free nerve endings Krause end bulbs

5. Psychology 3555 Touch

6. Psychology 3556 Touch Mechanoreceptors Åke Vallbo and colleagues

7. Psychology 3557 Touch Mechanoreceptors A.Åke Vallbo and colleagues

8. Psychology 3558 Touch Mechanoreceptors Two Point Threshold Braille letters consist of dots 2.5 mm apart and can be read at ~600 characters / minute.

9. Psychology 3559 Touch Mechanoreceptors I.Rapidly Adapting (RA) -respond to changes in stimulation, but do not continue to respond to constant stimulation II.Slowly Adapting (SA) -respond to constant stimulation III.Punctate - small receptive fields with distinct boundaries IV.Diffuse - large receptive fields with non-distinct boundaries PunctateDiffuse RARA-Punctate Meissner Corpuscles RA-Diffuse Pacinian Corpuscles SASA-Punctate Merkel Disks SA-Diffuse Ruffini Endings

10. Psychology 35510 Touch Mechanoreceptors I.Meissner Corpuscles (RA-punctate) responds best to active touch involved in object exploration; texture II.Pacinian Corpuscles (RA-diffuse) extremely sensitive over a large receptive field to high frequency changes in pressure; its membrane is deformed – e.g., a breeze on the palm of your hand; vibrations III.Merkel Disks (SA-punctate) constant sources of stimulation over a small area – e.g., carrying a pebble IV.Ruffini Endings (SA-diffuse) constant stimulation over a larger area – e.g., the feeling of clothing; skin stretch V.Free nerve endings - pain fibers & thermal conductance fibers

11. Psychology 35511 Touch Mechanoreceptors Receptive field size and adaptation rate

12. Psychology 35512 Touch Mechanoreceptors adaptation rate: Pacinian Corpuscle

13. Psychology 35513 Touch Primary Afferent Axons A.A Proprioception B.A  Touch C.A  Fast Pain, temperature D.C, Slow Pain, Temperature, Itch

14. Psychology 35514 Touch Primary Afferent Axons Enter spinal cord through the dorsal root Dorsal Root Dorsal Root Ganglion Cell

15. Psychology 35515 Touch I.The Spinal cord A.Spinal segments (30)- spinal nerves within 4 divisions of spinal cord B.Dermatomes- 1-to-1 correspondence with segments with overlap. What happens when a dorsal root is cut? Shingles

16. Psychology 35516 Touch The Spinal cord Sensory Organization I.Cervical (C) II.Thoracic (T) III.Lumbar (L) IV.Sacral (S)

17. Psychology 35517 Touch The Spinal cord Sensory Organization I.Cervical (C) II.Thoracic (T) III.Lumbar (L) IV.Sacral (S)

18. Psychology 35518 Touch The Spinal cord Sensory Organization I.Cervical (C) II.Thoracic (T) III.Lumbar (L) IV.Sacral (S)

19. Psychology 35519 Touch Division of spinal gray matter: 1.Dorsal horn Myelinated A axons (mechano) 2.Intermediate zone 3.Ventral horn

20. Psychology 35520 Touch Dorsal Column– Medial Lemniscal Pathway Ipsilateral without synapses along spinal cord Touch information ascends through dorsal column, dorsal nuclei, medial lemniscus, and ventral posterior nucleus to primary somatosensory cortex Cerebral Cortex

21. Psychology 35521 Touch Dorsal Column– Medial Lemniscal Pathway dorsal column, dorsal nuclei, medial lemniscus, and ventral posterior nucleus to primary somatosensory cortex

22. Psychology 35522 Touch The Trigeminal Touch Pathway A.Trigeminal nerves: Face, mouth, tongue (cranial V) B.Other cranial nerves (throat and abdominal cavity: cranial IX, X)

23. Psychology 35523 Touch Somatosensory Cortex A.Primary: BA 3b B.Other areas 1.Postcentral gyrus BA 1, 2 2.Posterior Parietal Cortex

24. Psychology 35524 Touch Somatosensory Cortex A.Brodmann’s Area 3b (or S1): Primary somatosensory cortex 1.Receives dense input from VP nucleus of the thalamus 2.Neurons: Responsive to stimuli 3.Lesions impair somatic sensations 4.Electrical stimulation evokes sensory experiences

25. Psychology 35525 Touch Somatosensory Cortex : 3b Columnar Organization Somatotopic Organization

26. Psychology 35526 Touch Somatosensory Cortex Cortical Somatotopy 1.Homunculus 2.Importance of mouth i.Tactile sensations: Important for speech ii.Lips and tongue: Last line of defense iii.Infants and non-primate mammals touch primarily with their mouths 3.Fingers and Thumb

27. Psychology 35527 Touch Somatosensory Cortex Cortical Somatotopy

28. Psychology 35528 Touch Somatosensory Cortex Cortical Magnification The receptive fields and cortical representations give more acuity to fingers, mouth, nose and tongue

29. Psychology 35529 Touch Somatosensory Cortex S1: Rat 1.Vibrissae 2.“Barrel cortex”

30. Psychology 35530 Touch Somatosensory Cortex S1: Rat 1.Vibrissae 2.“Barrel cortex”

31. Psychology 35531 Touch Somatosensory Cortex S1 – Owl monkey

32. Psychology 35532 Touch Somatosensory Cortex A.Cortical Map Plasticity B.Remove digits or overstimulate – examine somatotopy before and after 1.Conclusions of experiments Reorganization of cortical maps a.Dynamic b.Adjust depending on the amount of sensory experience

33. Psychology 35533 Touch Somatosensory Cortex A.Cortical Map Plasticity B.Remove digits or overstimulate – examine somatotopy before and after 1.Conclusions of experiments Reorganization of cortical maps a.Dynamic b.Adjust depending on the amount of sensory experience

34. Psychology 35534 Touch Somatosensory Cortex Squirrel Monkey Cortical Map Plasticity

35. Psychology 35535 Touch The Posterior Parietal Cortex 1.Involved in somatic sensation, visual stimuli, and movement planning 2.Astereoagnosia 3.Neglect syndrome

36. Psychology 35536 Pain Nociception: No pain, no gain? Hansen’s Disease. A.Pain - feeling of sore, aching, throbbing B.Nociception - sensory process, provides signals that trigger pain 1.Mechanical 2.Thermal 3.Chemical 4.Polymodal

37. Psychology 35537 Pain Transduction of Pain A.Mechanically-gated ion channels B.Damage to cells release proteases (an enzyme which digests proteins) which cause kaninogen to break down to form bradykinin which binds to certain nociceptors: Hyperaglesia: Bradykinin – increases the sensitivity of nociceptors and thermoreceptors Prostaglandins – caused by enzymatic breakdown of membrane lipids – cause increased sensitivity of nociceptors Substance P – Released by nociceptors - Causes swelling & Mast cell activation: release of histamine

38. Psychology 35538 Pain I.Primary Afferents and Spinal mechanisms A.First pain and second pain B.Referred pain: Angina

39. Psychology 35539 Pain Ascending Pain Pathways Differences between touch and pain pathway 1.Nerve endings in the skin 2.Diameter of axons 3.Connections in spinal cord i.Touch – Ascends Ipsilaterally ii.Pain – Ascends Contralaterally

40. Psychology 35540 Pain Ascending Pain Pathways Spinothalamic Pain Pathway Dorsal Root – immediactly decussates Spinothalamic Tract Spinothalamic tract

41. Psychology 35541 Pain Spinothalamic tract Ascending Pain Pathways Spinothalamic Pain Pathway Dorsal Root – immediactly decussates Spinothalamic Tract

42. Psychology 35542 Pain Comparing Pathways

43. Psychology 35543 Pain Reflex Arc

44. Psychology 35544 Pain I.The Regulation of Pain A.Afferent Regulation B.Descending Regulation C.The endogenuos opiates 1.Opioids and endomorphins

45. Psychology 35545 Pain The Regulation of Pain Descending regulation Periaquaductal gray matter

46. Psychology 35546 Phantom Pain I.After surgical removal of a limb, sensations resume in the limb II.In 90% of patients, the sensations are very painful III.In 60% the pain is excruciating: described sometimes as an arm on fire, being torn or punctured, great pressure

47. Psychology 35547 Phantom Pain: Strange Facts I.Stimulating certain areas of skin (e.g., face) may aggrevate phantom pain. II.Severing the nerve doesn’t help. Blocking the nerve doesn’t help. Removing the portion of the thalamus that relays the information to the brain doesn’t help III.Stimulating the nerve does help. Electric or manual stimulation of the stump helps tremendously electric more so).

48. Psychology 35548 Phantom Pain: A Theory I.Recall that the cortex is plastic and may reorganize. II.Normally this involves annexing juvenile or unused neurons (indicated by low activity level) III.In amputation the entire area of say an arm is no longer active in the brain IV.Other areas attempt to annex these neurons V.Because the neurons already had a specialization (e.g., sharp pain) and are no being stimulated by adjacent areas of cortex, the subject feels pain.

49. Psychology 35549 The cortical areas for the face annex the cortical areas for the arm and fingers. Some of those neurons were previously specialized for pain. Phantom Pain

50. Psychology 35550 Temperature Thermoreceptors I.A uniquely tactile object property II.The rate at which heat is gained or lost between the skin and an object - we do not detect absolute temperature III.Metal objects, fluids etc. create a more extreme sensation of temperature than do other objects (despite no differences in absolute temperature) because heat energy is transferred more easily to and from them IV.If a metal and a wooden block are both 150°, the metal block will feel hotter than the wooden block.Likewise for the same blocks at 0° the metal block will feel colder

51. Psychology 35551 Temperature The Temperature Pathway A.Organization of temperature pathway Identical to pain pathway B.Cold receptors coupled to A and C C.Hot receptors coupled to C

52. Psychology 35552 Concluding Remarks I.Sensory systems exhibit similar organization and function II.Sensory types are segregated within the spinal cord and cerebral cortex III.Repeated themes Parallel processing of information Columnar Organization Cortical Magnification IV.Perception of objects (haptics) involves the seamless coordination of somatic sensory information

53. Psychology 355 End of Presentation