The Somatosensory System June 5, 2014

1. The Somatosensory SystemJune 5, 2014

2. The Exteroceptive System

3. Somatosensory Information

4. Just a Touch • Somatosensation – sensations from body • Exteroceptive (skin) • Interoceptive – internal, proprioceptive • Less tangible/obvious

5. The Use of Bodily Sensations How do you use exteroceptive cues? Communication Safety Social bonding Guidance of motor reflexes

6. The Use of Bodily Sensations What is out there, how should I interact with it? Identify objects & their properties Texture, temperature, malleability, etc.

7. The Use of Bodily Sensations Each sense -- unique “perspective” Identify (or guess) properties w/ high accuracy Soft or hard Sharp or dull Rough or smooth Wet or dry Sticky or non-adhesive Hot or cold

8. Somatosensory Receptors • Different types in and under skin – aspects of stimuli • Mechanical stimulation (pressure, vibration) • Thermal (temperature) • Nociceptive (pain) • Combination of activation • Size, strength, constancy

9. Somatosensory Receptors Pacinian corpuscles (deep, quickly adapt) Mechanical pressure Large receptive field Ruffini endings (deep, slowly adapt) Pressure, stretch

10. Somatosensory Receptors Meissner’s corpuscles (surface, rapidly adapt) Light touch, vibration Merkel’s disks (surface, slowly adapting) Pressure Free nerve endings Temperature Pain

12. Somatosensory Receptors • Stimuli alters membrane permeability, fires • Temperature, pain, itch – myelinated & unmyelinated • Fast detection - location, severity • Slow - lingering, reminder Perception – how the brain interprets this info

13. Identifying Objects Identify object by tactile properties… • Manipulation - change pattern of stimulation • Identify what is constant or changing

14. Why can’t you tickle yourself?

15. Identifying Objects Two point discrimination… • Higher conc. receptors – more sensitivity • Smaller receptive fields Where is this most likely?

16. Processing at the Cortex

17. From Skin to CNS • Each receptor type has own “line” to cortex • Spinal nerves at dorsal spinal cord • Dermatomes • Cranial nerves at brainstem • Trigeminal nerve – face sensation

18. Information to Cortex Dorsal column medial-lemniscussystem • Primarily touch • Dorsal root  medulla • Crossover • Joins trigeminal nerve •  ventral posterior thalamus  cortex • Primary, secondary, association

20. Information to Cortex Anterolateral system • Pain, temperature • Dorsal root • Crossover • Multiple pathways

21. Information to Cortex • Reticular formation (alertness) • Tectum (eye movements) • Thalamus  cortex (w/ trigeminal)

24. Cortical Processing 10 somatosensory cortex in post-central gyrus (parietal) • Somatotopic arrangement • Homunculus – representation of body in cortex Secondary/association streams

26. Review / Critical Thinking What areas of the rat somatosensory cortex might be most highly represented? (Highest sensitivity)?

27. Pain

28. The Experience of Pain Why is pain important? • Current or impending danger • Acids, extreme temperatures, tissue damage Can also be internal (organ damage, etc.)

29. What is Special about Pain? • Cognitive, emotional factors • Not “one to one” • Variability • Experience • No real “site” for cortical processing

30. What is Special about Pain? • Absence of stimuli • Chronic, residual • CNS plasticity • Lack of sensitization – respond if something “there”

31. Analgesics Substance P – intense pain, vomiting Receptors in periaqueductal gray (tegmentum) Endorphins regulate/block input • “Endogenous morphine”

32. Analgesics Placebo effect - cognitive • Incr./decr. perception of pain w/out physical change Sensitization may occur w/ damaged tissue

33. Somatosensory Disorders

34. Sensory Deficits Paraesthesia – tickling, burning, numbness W/out cause Pins and needles Level of receptors, spinal cord

35. Cortical Deficits • Usually subtle • Tactile location difficulties • Astereognosia– cannot recognize by touch • Phantom limbs – sensation in absence of receptor • How might this occur?

36. Pain Disorders • Hypersensitivity • Inability to feel pain Both can have serious consequences

37. Insensitivity to Pain Congenital insensitivity to pain (CIP) - congenital analgesia Extremely rare Lack pain, temperature sensation Pressure intact Improper formation of nerve cells CIPA – CIP w/ anhydrosis (lack of sweating)

38. Insensitivity to Pain No aversion to painful stimuli – effects? • Hyperthermia (due to lack of sweating) • Infections, damage to mouth (biting lips, tongue) • Joint problems (improper postures) • Eye damage (scratching, rubbing) • Can lack gag reflex, coughing and sneezing Injury/death

39. Importance for Attachment The Importance of Touch in the Development of Attachment Lenora Duhn, “Advances in Neonatal Care”

40. Chemical Senses & Multimodal Processing

41. The Chemical Senses

42. Use of Chemical Signals Monitor molecular content of environment • Olfaction – smell • Gustation – taste

43. Use of Chemical Signals Which sense could you live without? • Humans likely choose taste or smell • Impact on assessment/interaction w/ environment • Influences on behavior

44. The Olfactory System

45. Olfactory Receptors • Airborne chemicals inhaled • Receptors in nasal passages on olfactory mucosa (mucus-covered tissue) • Millions of receptors • Each contains 1 of ~1000 different receptor proteins

47. Olfactory Receptors • Axons synapse in clusters in olfactory glomeruli • Similar protein – convergence • Glomeruli w/in the olfactory bulb • Base of brain

48. Processing Olfactory Information Olfactory tract: Olfactory bulb…  medial temporal lobe/limbic • Amygdala • Fear, emotion processing  orbitofrontal cortex (cognitive processing)

50. Processing Olfactory Information Unlike other senses so far… • Not directly filtered through thalamus • No real “primary cortex” • No consistent topographic arrangement Evidence for symmetry (L/R), consistency