Transcript 12 Touch - pantherFILE

TOUCH, HAPTICS &
PROPRIOCEPTION
Touch
The oldest perceptual modality
The most social sense
The most closely linked to motion and action
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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
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Receptive
Field
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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
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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
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Types of Fibers
Punctate
Diffuse
RA
SA
RA-Punctate
RA-Diffuse
SA-Punctate
SA-Diffuse
• 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
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The nerve fibers enervate four
receptor types
Receptors
1. Meissner Corpuscles (RA-punctate) responds best to
active touch involved in object exploration
2. Pacinian Corpuscles (RA-diffuse) extremely sensitive
over a large receptive field -- blow gently on the palm of
your hand
3. Merkel Disks (SA-punctate) constant sources of
stimulation over a small area, such as if you were
carrying a pebble
4. Ruffini Endings (SA-diffuse)constant stimulation over a
larger area - also detects skin stretch
•
Free nerve endings - pain fibers & thermal conductance
fibers
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Four Receptor Types
a) Merkel Receptor
SA Punctate
b) Meissner Corpuscle
RA Punctate
c) Ruffini Ending
SA Diffuse
d) Pacinian Corpuscle
RA Diffuse
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Cross
Section of
the Skin
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Peripheral Pathways of Touch
•
•
•
Proprioceptors
Mechanoreceptors
Two pathways for pain (both of which are
independent from other tactile or proprioceptive
pathways) –
1. one fast pathway for sharp pain,
2. one slow pathway for dull pain
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Peripheral Pathways for Touch
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Peripheral
Pathways
For Touch
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Cortical Pathways of Touch
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Sensation of Touch
• Adjacent portions of skin surface tend to be represented by
adjacent portions of cortex
• Cortical magnification for lips, nose and fingers
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Cortical Magnification
• The receptive fields
and cortical
representations
give more acuity to
fingers, mouth,
nose and tongue
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Cortical
Magnification
corresponds to
greater acuity
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Cortical Plasticity for Touch
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Faculties of Touch
1) Object identification
2) Proprioception
3) Object localization
4) Detection of tissue damage
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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
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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,
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Haptics
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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
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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.
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Proprioception
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Prioprioception Includes
The Vestibular Sense
Ocular Motor
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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
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Interactions
of Touch
& Vision
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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
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Pain
Pain Pathway
Somatosensory Cortex
Thalamus
Spinal Cord
Dorsal Horn
Nerve
Free Nerve Ending
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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
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Pain:
The
Reflex
Arc
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Gaiting Pain
Cortex
• 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
Thalamus
Spinal Cord
Dorsal Horn
Nerve
Free Nerve Ending
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Gating
Pain:
Dorsal
Horn
(Root)
Back
Chest
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Spino-Thalamic Pathway:
Temperature & Pain
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Medial Lemniscal Pathway:
Mechanoreceptors & Proprioception
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Phantom Pain
1. After surgical removal of a limb,
sensations resume in the limb
2. In 90% of patients, the sensations are very
painful
3. In 60% the pain is excruciating: described
sometimes as an arm on fire, being torn or
punctured, great pressure
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Phantom Pain: Strange Facts
1.Stimulating certain areas of skin (e.g., face)
may aggrevate phantom pain.
2.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!
3.Stimulating the nerve does help. Electric or
manual stimulation of the stump helps
tremendously electric more so).
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Phantom Pain: A Theory
1. Recall that the cortex is plastic and may
reorganize.
2. Normally this involves annexing juvenile or
unused neurons (indicated by low activity level)
3. In amputation the entire area of say an arm is no
longer active in the brain
4. Other areas attempt to annex these neurons
5. 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.
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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.
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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
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