12 touch
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12 touch






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12 touch 12 touch Presentation Transcript

  • Touch
    • The oldest perceptual modality
    • The most social sense
    • The most closely linked to motion and action
  • 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
  • Receptive Field
  • 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
  • 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
  • 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
  • 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
  • Four Receptor Types
    • Merkel Receptor SA Punctate
    • Meissner Corpuscle RA Punctate
    • Ruffini Ending SA Diffuse
    • Pacinian Corpuscle RA Diffuse
  • Cross Section of the Skin
  • 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
  • Peripheral Pathways for Touch
  • Peripheral Pathways For Touch
  • Cortical Pathways of Touch
  • Sensation of Touch
    • Adjacent portions of skin surface tend to be represented by adjacent portions of cortex
    • Cortical magnification for lips, nose and fingers
  • Cortical Magnification
    • The receptive fields and cortical representations give more acuity to fingers, mouth, nose and tongue
  • Cortical Magnification corresponds to greater acuity
  • Cortical Plasticity for Touch
  • Faculties of Touch
    • 1) Object identification
    • 2) Proprioception
    • 3) Object localization
    • 4) Detection of tissue damage
  • 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
  • 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,
  • Haptics
  • 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
  • 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.
  • Proprioception
  • Prioprioception Includes The Vestibular Sense Ocular Motor
  • 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
  • Interactions of Touch & Vision
  • 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
  • Pain
    • Pain Pathway
    Somatosensory Cortex Thalamus Spinal Cord Dorsal Horn Nerve Free Nerve Ending
  • 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
  • Pain: The Reflex Arc
  • 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
  • Gating Pain: Dorsal Horn (Root) Back Chest
  • Spino-Thalamic Pathway: Temperature & Pain
  • Medial Lemniscal Pathway: Mechanoreceptors & Proprioception
  • 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
  • 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).
  • 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.
  • 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.
  • 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