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Psych 260Psych 260
Kim SweeneyKim Sweeney
[email protected]@cogsci.ucsd.edu
cogsci.ucsd.educogsci.ucsd.edu/~/~ksweeneyksweeney/psy260.htm/psy260.htm
Introduction to Introduction to
Physiological PsychologyPhysiological Psychology
The cutaneous sensesThe cutaneous senses
�� What kinds of things can we feel with our What kinds of
things can we feel with our
skin?skin?
�� Pressure, vibration, heat, cold, painPressure, vibration,
heat, cold, pain
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Transduction!Transduction!
� In the visual system, rods and cones transduce
light to neural signals…
� In the auditory system, hair cells transduce
sound waves to neural signals…
� In the olfactory and gustatory systems,
receptors transduce chemicals into neural
signals
� In the somatosensory system, sensory neurons
in skin, joints, organs transduce pressure (or
heat, or pain, or…) into neural signals…
Receptor cells Receptor cells transducetransduce stimuli
stimuli
into neural activityinto neural activity
Stimulus
Receptor Cell
Response
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Sensing and Moving/Responding Sensing and Moving/Responding
�� The two most basic nervous system functions!The two most
basic nervous system functions!
–– Even single cell organisms can sense nutrients and Even
single cell organisms can sense nutrients and
toxins, and respond by moving towards or awaytoxins, and respond
by moving towards or away
�� Complex organisms have specialized cells and Complex
organisms have specialized cells and
systems to carry out these functionssystems to carry out these
functions
–– our simplest but most crucial behaviors involve our simplest
but most crucial behaviors involve
reflexive responses to sensory stimulireflexive responses to
sensory stimuli
�� pain reflex to avoid damagepain reflex to avoid damage
�� increased breathing stimulated by blood CO2increased
breathing stimulated by blood CO2
Different modalities are encoded Different modalities are
encoded
by different receptor typesby different receptor types
Somatosensation
Proprioception
Olfaction
Gustation
Audition
Vision
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Sensation and PerceptionSensation and Perception
�� Generally speaking, the brain is sensitive to Generally
speaking, the brain is sensitive to
to change to change –– when there is no change, no when there is
no change, no
sensation sensation
Somatosensation: Touch and PainSomatosensation: Touch and
Pain
� Somatosensory system is three separate and interacting
systems:
– Exteroceptive – external stimuli
– Proprioceptive and kinesthetic – body position and motion
– Interoceptive – body conditions (e.g., temperature and blood
pressure)
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Somatosensation: Touch and PainSomatosensation: Touch and
Pain
��Exteroceptive SystemExteroceptive System-- specialized
specialized
receptors respond to various stimulireceptors respond to various
stimuli
–– Touch (mechanical stimuli)Touch (mechanical stimuli)
–– Temperature (thermal stimuli)Temperature (thermal
stimuli)
–– Pain (nociceptive stimuli)Pain (nociceptive stimuli)
A sensory stimulus presents A sensory stimulus presents
different kinds of informationdifferent kinds of information
�� ModalityModality
–– What kind?What kind?
�� IntensityIntensity
–– How much?How much?
�� DurationDuration
–– How long?How long?
�� LocationLocation
–– Where?Where?
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Your skinYour skin
�� Skin is the largest, heaviest organ of the Skin is the
largest, heaviest organ of the
bodybody
�� Humans have both hairy and Humans have both hairy and
glabrousglabrous
(hairless) skin.(hairless) skin.
Hairy and GlabrousHairy and Glabrous
�� Hairy skinHairy skin–– Free nerve endings Free nerve endings
––painful stimuli, changes in painful stimuli, changes in
temperaturetemperature
–– Ruffini corpusclesRuffini corpuscles ––indentation of
skinindentation of skin
–– Pacinian corpusclesPacinian corpuscles ––rapid
vibrationsrapid vibrations
–– (Hair Follicles)(Hair Follicles)
�� Glabrous skinGlabrous skin–– Free nerve endings, Ruffini and
Pacinian corpusclesFree nerve endings, Ruffini and Pacinian
corpuscles
–– MeissnerMeissner’’s corpuscless corpuscles –– stroking,
fluttering, small bumpsstroking, fluttering, small bumps
–– MerkelMerkel’’s disks disk –– compressioncompression
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Touch and Touch and
PainPain
Five cutaneousreceptors that occurin the human skin
Somatosensation: Touch and PainSomatosensation: Touch and
Pain
��Cutaneous Receptors:Cutaneous Receptors:–– Free nerve
endingsFree nerve endings
�� temperature and paintemperature and pain
–– MerkelMerkel’’s diskss disks�� gradual skin
indentationgradual skin indentation
–– MeissnerMeissner corpusclescorpuscles�� low frequency
vibrationlow frequency vibration
–– PacinianPacinian corpusclescorpuscles�� sudden displacements
of the skinsudden displacements of the skin
–– RuffiniRuffini corpusclescorpuscles�� gradual skin
stretchgradual skin stretch
unmyelinated
myelinated
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Somatosensory ReceptorsSomatosensory Receptors
�� Deep receptors: large receptive fields (big Deep receptors:
large receptive fields (big
patches of skin); patches of skin); -- low spatial
resolution.low spatial resolution.
�� Superficial receptors: small receptive fields Superficial
receptors: small receptive fields
(small patches of skin). (small patches of skin). –– high
spatial high spatial
resolution: e.g. for reading Braille.resolution: e.g. for
reading Braille.
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Deep ReceptorsDeep Receptors
� (subcutaneous) (large RF):
– Pacinian corpuscles:
� Rapidly adapting
� responds to rapid indentation of skin; vibration;
motion (of object across skin).
– Ruffini endings:
� Slowly adapting
� sense stretch of skin or bending of fingernails:
this compresses the nerve endings. Perception of
shape of objects.
Different receptors adapt at Different receptors adapt at
different ratesdifferent rates
Rapid SlowSlow Very Rapid
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Shallow receptorsShallow receptors
� (in superficial layers of skin) (small RF):
– Meissner’s corpuscles:
� Rapidly adapting
� stroking, fluttering; detecting small bumps
– Merkel disks:
� Slowly adapting
� give sustained responses to skin compression;
pressure
Different receptors adapt at Different receptors adapt at
different ratesdifferent rates
Rapid SlowSlow Very Rapid
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Different receptors adapt at Different receptors adapt at
different ratesdifferent rates
Rapid
Slow
Slow
Very Rapid
Receptive fields and adaptation Receptive fields and
adaptation
of mechanoreceptorsof mechanoreceptors
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The intensity of a stimulus is The intensity of a stimulus
is
transmitted by the frequency of transmitted by the frequency
of
the neural responsethe neural responseFiring Rate
Stimulus Intensity
Sigmoidal response function/curve
Threshold
Maximum response (Saturation)
Characteristics of sensory Characteristics of sensory
receptors in the skinreceptors in the skin
Receptor Stimulus Sensation Adaptation Location
Merkel's diskSteady
indentationPressure Slow Shallow
Meissner's
corpuscle
Low frequency
vibrationGentle fluttering Rapid Shallow
Ruffini's
corpuscle
Rapid
indentationStretch Slow Deep
Pacinian
corpuscleVibration Vibration Rapid Deep
Hair receptor Hair deflection Brushing Rapid or Slow Shallow
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In the human hand…In the human hand…
�� MeissnerMeissner’’s s -- 40% of mechanoreceptors40% of
mechanoreceptors–– Low frequency vibrations, movement of textures
Low frequency vibrations, movement of textures
across skinacross skin
�� Pacinian Pacinian -- ~15% of mechanoreceptors~15% of
mechanoreceptors–– Sense of vibration, discrimination of
texturesSense of vibration, discrimination of textures
�� RuffiniRuffini’’s s -- ~20% of mechanoreceptors~20% of
mechanoreceptors–– Cutaneous stretchingCutaneous stretching
�� MerkelMerkel’’s diskss disks-- 25% of mechanoreceptors25% of
mechanoreceptors–– Abundant in finger tips, lips, genitaliaAbundant
in finger tips, lips, genitalia
–– Feelings of light pressureFeelings of light pressure
The Pacinian Corpuscle is a rapidly The Pacinian Corpuscle is a
rapidly
adapting receptor celladapting receptor cell
on off
Capsule
Rebound
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The capsule of the Pacinian corpuscle The capsule of the
Pacinian corpuscle
is responsible for its rapid adaptationis responsible for its
rapid adaptation
Rebound
Ruffini corpuscles and Merkel’s disks don’t have capsules, so
are continuously responsive!
The Pacinian Corpuscle responds to The Pacinian Corpuscle
responds to
vibrations on the skinvibrations on the skin
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The receptive field of a receptor cell The receptive field of a
receptor cell
is determined by its morphologyis determined by its
morphology
Two point discriminationTwo point discrimination
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Lateral inhibition Lateral inhibition refines the receptive
refines the receptive
fieldfield of higherof higher--order sensory cellsorder sensory
cells
Lateral inhibition Lateral inhibition improves precisionimproves
precision
in higherin higher--order sensory cellsorder sensory cells
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Lateral inhibition Lateral inhibition improves
discriminationimproves discrimination
Neurons in the somatosensory cortex have Neurons in the
somatosensory cortex have
centercenter--on, surroundon, surround--off receptive fields…
off receptive fields…
of different sizesof different sizes
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How do the neural messages How do the neural messages
get to the brain?get to the brain?
Broadly Speaking… Broadly Speaking…
Sensory information
travels through the spinal
cord and thalamus to the
sensory cortex.
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Somatosensory CortexSomatosensory Cortex
Cortical Areas of SomatosensationCortical Areas of
Somatosensation
�� Primary somatosensory cortex (SI)Primary somatosensory cortex
(SI)–– Postcentral gyrus Postcentral gyrus
–– Somatotopic organization (somatosensory Somatotopic
organization (somatosensory homunculus) homunculus) –– more
sensitive, more cortexmore sensitive, more cortex
–– Input largely contralateralInput largely contralateral
�� SII SII –– mainly input from SImainly input from SI––
Somatotopic; input from both sides of the Somatotopic; input from
both sides of the bodybody
�� Much of the output from SI and SII goes to Much of the output
from SI and SII goes to association cortex in posterior parietal
association cortex in posterior parietal lobelobe
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Sensory HomunclulusSensory Homunclulus
� Receptive fields in
the somatosensory
cortex comprise a
somatotopic map of
the body
The The ““homunculushomunculus”” reflects the reflects the
density of receptor cellsdensity of receptor cells
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Neural plasticityNeural plasticity
Merzenich et al.
Neural plasticityNeural plasticity
Merzenich et al.
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Two Major Somatosensory PathwaysTwo Major Somatosensory
Pathways
�� DorsalDorsal--column medialcolumn medial--lemniscuslemniscus
systemsystem– Mainly touch and proprioception
– Stays ipsilateral until medulla
– First synapse in the dorsal column nuclei of the medulla…
– then decussate and go to ventral posterior nucleus…
– then (generally) head to primary somatosensory cortex
Two Major Somatosensory PathwaysTwo Major Somatosensory
Pathways
�� Anterolateral systemAnterolateral system– Mainly pain and
temperature
– Becomes contralateral in spinal cord.
– First synapse upon entering the spinal cord!
– all tracts head (generally) to primary somatosensory
cortex
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What could possibly go wrong?What could possibly go wrong?
�� Brown Brown SequardSequard SyndromeSyndrome
–– Because of the two separate Because of the two separate
tracts, damage to half the tracts, damage to half the
spinal cord results in:spinal cord results in:
�� Loss of Loss of movementmovement in the in the
ipsilateralipsilateral side of lesion side of lesion (dorsal
column medial (dorsal column medial lemniscuslemniscus))
�� Loss of Loss of pain and pain and
temperaturetemperature in in
contralateral side contralateral side
(anterolateral)(anterolateral)
What can possibly go wrong?What can possibly go wrong?
�� Somatosensory AgnosiasSomatosensory Agnosias
�� AstereognosiaAstereognosia –– inability to recognize
inability to recognize
objects by touchobjects by touch
–– pure cases are rare pure cases are rare –– other sensory
deficits other sensory deficits
are usually presentare usually present
�� AsomatognosiaAsomatognosia –– the failure to recognize the
failure to recognize
parts of oneparts of one’’s own bodys own body
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Perception of PainPerception of Pain
�� Pain appears to have three different Pain appears to have
three different
perceptual and behavioral effects:perceptual and behavioral
effects:
–– First is the sensory componentFirst is the sensory
component
�� Pure perception of intensity of painful stimulusPure
perception of intensity of painful stimulus
–– Second is immediate emotional consequencesSecond is immediate
emotional consequences
�� Unpleasantness or degree to which individual is
Unpleasantness or degree to which individual is
bothered by painful stimulusbothered by painful stimulus
–– Third is longThird is long--term emotional consequencesterm
emotional consequences
�� Threat that pain represents to Threat that pain represents to
one’s one’s future comfort future comfort
and welland well--beingbeing
Phantom Limbs, Phantom PainPhantom Limbs, Phantom Pain
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The Perception of PainThe Perception of Pain
Paradoxes of PainParadoxes of Pain�� Despite its unpleasantness,
pain is adaptive Despite its unpleasantness, pain is adaptive and
neededand needed
�� No obvious cortical representation (although No obvious
cortical representation (although the anterior cingulate gyrus
appears involved the anterior cingulate gyrus appears involved in
the emotional component of pain)in the emotional component of
pain)
�� Descending pain control Descending pain control –– pain can
be pain can be suppressed by cognitive and emotional suppressed by
cognitive and emotional factorsfactors
Pain PerceptionPain Perception
�� Anterior Cingulate Anterior Cingulate
CortexCortex
–– Mediates the emotional Mediates the emotional
component of paincomponent of pain
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Next time…Next time…
�� Sleep! Sleep!