Touch is the oldest sense and involves mechanoreceptors in the skin that detect deformations. There are four main receptor types - Meissner corpuscles, Pacinian corpuscles, Merkel disks, and Ruffini endings. Tactile information is processed in the peripheral and central nervous systems, with different cortical areas representing information from different body parts. Proprioception provides information about body position and movement through receptors in the muscles and joints. Haptics and proprioception together allow us to identify objects and perceive their location through active touch.

1. TOUCH, HAPTICS & PROPRIOCEPTION

2. Touch The oldest perceptual modality The most social sense The most closely linked to motion and action

3. Receptive Field Mechanoreceptors detect skin deformations Tactile acuity is determined by how close the mechanoreceptors are to each other and by the size of the receptive field

4. Receptive Field

5. Receptive Field The two-point threshold for any part of the body is determined by the size of the receptive fields and the extent of overlap

6. Receptive Field The two-point threshold for any part of the body is determined by the size of the receptive fields and the extent of overlap

7. Types of Fibers Rapidly Adapting (RA) -respond to changes in stimulation, but do not continue to respond to constant stimulation Slowly Adapting (SA) -respond to constant stimulation Punctate - small receptive fields with distinct boundaries Diffuse - large receptive fields with non-distinct boundaries

8. The nerve fibers enervate four receptor types Receptors Meissner Corpuscles (RA-punctate) responds best to active touch involved in object exploration Pacinian Corpuscles (RA-diffuse) extremely sensitive over a large receptive field -- blow gently on the palm of your hand Merkel Disks (SA-punctate) constant sources of stimulation over a small area, such as if you were carrying a pebble Ruffini Endings (SA-diffuse)constant stimulation over a larger area - also detects skin stretch Free nerve endings - pain fibers & thermal conductance fibers

9. Four Receptor Types Merkel Receptor SA Punctate Meissner Corpuscle RA Punctate Ruffini Ending SA Diffuse Pacinian Corpuscle RA Diffuse

10. Cross Section of the Skin

11. Peripheral Pathways of Touch Proprioceptors Mechanoreceptors Two pathways for pain (both of which are independent from other tactile or proprioceptive pathways) – one fast pathway for sharp pain, one slow pathway for dull pain

12. Peripheral Pathways for Touch

13. Peripheral Pathways For Touch

14. Cortical Pathways of Touch

15. Sensation of Touch Adjacent portions of skin surface tend to be represented by adjacent portions of cortex Cortical magnification for lips, nose and fingers

16. Cortical Magnification The receptive fields and cortical representations give more acuity to fingers, mouth, nose and tongue

17. Cortical Magnification corresponds to greater acuity

18. Cortical Plasticity for Touch

19. Faculties of Touch 1) Object identification 2) Proprioception 3) Object localization 4) Detection of tissue damage

20. Object Identification Haptics provide abstract, 3-D information about object form Spatial Frequency Analysis of Skin Deformations provides information about local form texture, density, mass and torque Thermal conductance gives information about object material properties

21. Haptics Active touch is a mode of perceptual explorarion (c.f., visual search) Haptics can detect gross features of objects form, mass, weight distribution, torque,

22. Haptics

23. Spatial Frequencies Spatial frequencies correspond to the rate of minute deformation which determine texture (i.e. coarse, smooth etc.) Larger deformations correspond to object features Active touch ( Haptics ) allows us to determine the position of tactile features on an object relative to each other These features corresponds to visual information about texture, shape and form and relative position Sensory Substitution --Braille

24. Proprioception All muscles have nerve fibers which detect the amount the muscle is stretched All joints have fibers which detect the relative position of each bone Together these allow you to determine the position of every part of your body.

25. Proprioception

26. Prioprioception Includes The Vestibular Sense Ocular Motor

27. Haptics, Proprioception and Object Location Prioprioceptors allow you to determine the position of every part of your body. Haptic touch is the interaction of proprioceptive and mechanoreceptive information Object location is determined (within a narrow range) by the position of the object relative to the body

28. Interactions of Touch & Vision

30. Thermal Conductance A uniquely tactile object property The rate at which heat is gained or lost between the skin and an object - we do not detect absolute temperature 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 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

31. Pain Pain Pathway Somatosensory Cortex Thalamus Spinal Cord Dorsal Horn Nerve Free Nerve Ending

32. Pain Sharp Pain Reflex Limb is pulled toward the body out of harms way Normal pain information continues to brain for more considered action Somatosensory Cortex Thalamus Spinal Cord Dorsal Horn Nerve Muscle Free Nerve Ending

33. Pain: The Reflex Arc

34. Gaiting Pain Gate control theory of pain - pain is actively suppressed in emergency situations by messages sent from the brain to the Dorsal Horn This allows you to escape on a broken limb or with a gash Pain resumes when emergency is over Cortex Thalamus Spinal Cord Dorsal Horn Nerve Free Nerve Ending

35. Gating Pain: Dorsal Horn (Root) Back Chest

36. Spino-Thalamic Pathway: Temperature & Pain

37. Medial Lemniscal Pathway: Mechanoreceptors & Proprioception

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

39. Phantom Pain: Strange Facts Stimulating certain areas of skin (e.g., face) may aggrevate phantom pain. 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! Stimulating the nerve does help. Electric or manual stimulation of the stump helps tremendously electric more so).

40. Phantom Pain: A Theory Recall that the cortex is plastic and may reorganize. Normally this involves annexing juvenile or unused neurons (indicated by low activity level) In amputation the entire area of say an arm is no longer active in the brain Other areas attempt to annex these neurons 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.

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

42. Phantom Pain TENS (transcutaneous electrical stimulation) uses tiny electrical pulses, delivered through the skin to nerve fibers, to directly stimulate nerves in the stump that formerly enervated the limb. Spinal cord stimulation uses electrodes surgically inserted within the epidural space of the spinal cord. Deep brain or intracerebral stimulation is considered an extreme treatment and involves surgical stimulation of the brain. These treatments all create activity in the cortical region associated with the former limb, which prevents adjacent neurons from annexing