skin senses - henderson state universityfac.hsu.edu/ahmada/3 courses/3 physiological/1...
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Touch and PainTouch and Pain
Chapter 8Chapter 8
Majority of illustrations in this presentation are from Biological Psychology4th edition (© Sinuer Publications)
Majority of illustrations in this presentation are from Biological Psychology4th edition (© Sinuer Publications)
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Skin SensesSkin Senses
Human skin is the largest sensory organ (10‐20 sq.
ft.) and can be stimulated by a number of physical stimuli. These
include:
1. Mechanical Stimuli2. Thermal Stimuli3. Chemical Stimuli
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Skin SensesSkin Senses
Touch Mechanical
Pressure Mechanical
Vibration Mechanical
Tickle Mechanical
Pins and needles Mechanical
Wetness Chemical
Smoothness Mechanical
Cold Thermal
Warm Thermal
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Distribution of ReceptorsDistribution of Receptors
Five different kinds of receptors are embedded in two layers of the skin. Some are close (epidermis) to the surface of the skin and others are deeper (dermis) in
the skin.
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Merkel’s DisksMerkel’s Disks
Merkel’s disks have small receptive fields with
antagonistic surrounds making them responsive to edges and points (Braille
characters).
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Meissner’s CorpusclesMeissner’s Corpuscles
Meissner’s corpuscles closer to epidermis have small receptive fields and respond to changes in
stimuli giving information about texture.
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Pacinian CorpusclesPacinian Corpuscles
Pacinian corpuscles deep in the skin, respond to
stimuli vibrating at 200Hz or more, giving texture
information.
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Ruffini’s CorpusclesRuffini’s Corpuscles
Ruffini Corpuscles are sensitive to stretching of skin when fingers and limbs are moved.
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SummarySummary
Surface Receptor
(Small RF)
Deep Receptor
(Large RF)
RapidAdaptation
Meissner's Corpuscles (Texture)
Pacinian Corpuscles (Vibration)
SlowAdaptation
Merkel’s Disk (Edges)
Ruffini’s Corpuscles (Stretch)
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Receptor ResponseReceptor Response
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Touch, Vibration and StretchTouch, Vibration and Stretch
Touch (and pain) are close to the surface of the skin and vibration and stretch are deep in the skin.
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Hot, Cold and PainHot, Cold and Pain
Free nerve endings are sensitive to hot, cold and pain. The are close to the surface of the skin.
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Axon Size, Touch, Pain and TemperatureAxon Size, Touch, Pain and Temperature
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Touch PathwayTouch Pathway
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DermatomesDermatomesSkin surface can be divided into patches (dermatomes),
innervated by spinal nerves.
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Body Surface RepresentationBody Surface Representation
Spinal and facial nerves innervate S1 and S2
somatosensory cortices. Skin in S1 cortex is
topographically mapped four times (Areas 1, 2, 3a
and 3b). As seen homunculus represents different parts of the skin
disproportionately.
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Columnar OrganizationColumnar Organization
Fingers 2,3 & 4 are represented on the somatosensory
cortex. Each finger is represented in a
different column and within each column different touch sensations.
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Plasticity in Sensory MapsPlasticity in Sensory Maps
Sensory maps can change with experience even in adulthood. Three experiments with monkeys show
such plasticity.
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DenervationDenervation
In experiment 1, nerves from the thumb and the forefinger were severed. Maps of the thumb and
forefingers shrunk and were taken over by the back of the hand (dorsal surface) after a few weeks.
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Finger RemovedFinger Removed
In experiment 2, middle digit was surgically removed, leading to reorganizing of the second and fourth
digit’s sensory map.
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ExperienceExperience
In experiment 3, monkey was trained to keep his second and third digits in contact with a rotating disk in order to obtain food rewards. Maps of these digits
increased.
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Cortical LesionsCortical Lesions
Specific cortical lesions in area 3b can impair animal’s ability to sense texture (fast adapting, purple) or
edges (slow adapting, dark blue).
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PET ScansPET Scans
PET scans require measuring brain activity during control and experimental conditions and finding their difference. Averaging PET scans across participants
gives us a composite picture.
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Posterior Parietal CortexPosterior Parietal Cortex
In humans, posterior part of the parietal cortex
activates during exploration of solid objects
by touch (Roland and Larson, 1976).
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PainPain
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PainPain
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or
described in terms of such damage.
Pain experience is adaptive in nature. Gives us clues about bodily and mental suffering. What if there was no
pain?
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Congenital Insensitivity to PainCongenital Insensitivity to Pain
Ashley Blocker (right) feels neither painnor extreme hot or cold. Human pincushion
In a rare congenital disease (congenital analgesia) a person may feel no pain. Such people die young,
because of trauma to the body.
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Purposes of PainPurposes of Pain
1. Short‐term pain leads to quick withdrawal from the source escaping further damage.
2. Long‐lasting pain results in inactivity, grooming, feeding, drinking that promotes recuperation.
3. The expression of pain serves as a social signal to others – elicits caregiving behavior from others.
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Measurement of PainMeasurement of Pain
McGill Pain Questionnaire (Melzak, 1984) outlines sensory, motivational and cognitive components of
pain, and measure it quantitatively.
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Pain Due to InjuryPain Due to Injury
Pain caused by injury to the skin causes release of chemicals which affect receptors in free nerve endings
to relay pain messages to the brain.
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CapsaicinCapsaicin
Best evidence about pain receptors come from
capsaicin (vanilloid) found in chili peppers. Vanilloid receptor 1 (VR1) and vanilloid receptor‐like protein 1 (VRL1) bind
capsaicin to register pain.
C‐fibers Aδ‐fibers
VR‐1 receptors
VRL1 receptors
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Cool ReceptorsCool Receptors
Cool‐menthol receptor 1 (CMR1) was likewise
discovered that registered “coldness” on the skin. These receptor also
connect to small C‐fibers.
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Pain PathwayPain Pathway
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Pain ReliefPain Relief
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Pain ReliefPain Relief