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Psych 260Psych 260

Kim SweeneyKim Sweeney

ksweeney@cogsci.ucsd.eduksweeney@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!