PSY280 - 9. Cutaneous Senses Flashcards
somatosensation
umbrella term for sensory signals from the body.
3 major components: proprioception, kinesthesis + cutaneous senses
Ian Waterman: Loss of proprioception
forge new link between mind and body
planned movement - think it thoroughly
no movement is automatic - would have to be plotted
use of visualization - eyes have to tell mind what they were doing, control them
look at them to control them
other senses to tell brain what our body is doing
Proprioception
position of the body & limbs
Kinethesis
movement of body & limbs
The cutaneous senses
refers to touch, temperature & pain
tactile perception - most commonly think of in terms of touch
tactile: mechanical displacement of skin
touch is a near senses - have to be in direct contact
we have to act, not a passive sense
Skin
heaviest & one of the largest organs in the body
varies over various parts of body
2 basic layers: epidermis (outer) +
dermis (inner) - connective + nutritive tissue
Skin
receptors within 2 layers
multiple channels of processing - diff receptors have diff functions: tell you about shape, temperature + texture
Mechanoreceptors
tactile receptors - responsive to mechanical stimulation
each type of tactile receptor has an axon
each axon encapsulated - specialized nerve ending where transduction takes place
specialized endings give each type of tactile receptor their specialization
Mechanoreceptors
Each type is characterized by:
kind of stimulation: pressure, vibration, movement - diff preference
size of RF: area of the skin where you touch affects firing rate of that perception
Mechanoreceptors
rate of adaptation: reduced firing in response to continuous stimulation, diff than habituation
Mechanoreceptors
slow adapting - response huge increase at onset, some decrement, but still see continuous firing for duration
fast adapting - spike at onset, rapid adaptation so total silence until the offset
slow adapting - prefer continuous
fast adapting - prefer change
Mechanoreceptors: SA1 Merkel - epidermis
sustained pressure, very low frequency (<5 Hz) spatial deformation, low vibration detection
slow adapting, continuously fire with presence, small RF
texture perception pattern/form detection
Mechanoreceptors: RA1 Meissner - epidermis
temporal changes in skin deformation (~5-50 Hz), fast adapting - burst at onset + offset
detecting changes - slightly higher in frequency in changes across skin
low frequency vibration detectable - slipping heavy object
at start + end where most problematic
low frequency changes for both
Mechanoreceptors: SA2 Ruffini - dermis
sustained downward pressure, lateral skin stretch - tells us about form (grip), skin slip - eraser moving across skin
finger position, stable grasp, large RF
Ruffini cylinders - small encapsulation
Mechanoreceptors RA2 Pacinian - dermis
temporal changes in skin deformation (~50-700 Hz)
preference for change in high frequency vibrations + large RF = sensitive to small light changes
holding something in contact with something else - writing with 1 piece of paper on a desk
Kinesthetic
receptors help us determine where our limbs are & what movements they’re making:
muscle spindles: wrap around muscle fibres to detect length + shape + rate at which changing angle of limbs
either contracted + fat/long + slim which determines angle of limb
Kinesthetic
receptors in tendons: muscle tension, muscle to bone
receptors on joints: active when joint is bent beyond normal limit - when it’s about to break
Thermoreceptors
Warmth fibers fire when skin temp of surrounding skin rises
Cold fibers fire in response to decreases in skin temp
both are free nerving - no specialized capsules
Thermoreceptors
37 degrees - neither cold/warm receptors fire that much
range is betw 10-50
colder than 17 and warmer than 47, properly retained by pain receptors
body keeps it at survivable temp
Nociceptors
free nerve endings
A-delta fibers respond to strong pressure or heat: myelinated (fast) - initial sharp pain
Nociceptors
C-fibers respond to intense stimulation of various sorts: unmyelinated (slow) - responsible for throbbing pain
pressure, heat, cold, chemicals
capsaicin - spicy - slow build
Spinothalamic pathway
•evolutionarily older, slower, more synapses - slower because there’s more info exchange points
carries info from thermoreceptors & nociceptors
similar to Parvo + magno: concerned with diff kinds of info influences where they end up
Medial lemniscal pathway
wider axons, fewer synapses, faster
tactile & kinesthetic information: pressure, vibrations, positional info
info necessary for execution of planned action sequences - so needs to be carried quickly to brain, important to get frequent feedback
Medial lemniscal pathway
myelination within each, mostly in lemniscal
both go to spinal cord to maintain contralateral organization - happens earlier in Spinothalamic
both stop first at ventral posterior nucleus thalamus - up to cortex to S1
cortex is somatotopically organized
spatial events on skin spatially mapped in somatosensory cortex
need back + forth to be effective
neurons in S1 + S2 have lots of crosstalk + with other cortical areas
cortex is somatotopically organized
S1 - original perceptual work
S2 - more complex analysis
generally areas of skin adjacent to each other are adjacantly organized in cortex
cortical magnification
Areas devoted to highly sensitive areas occupy more cortex in the brain than less sensitive areas
somatosensory homunculus: hands, tongue, lips are huge
cortical magnification
good at tactile perception, more representation
cortical magnification in vision: massive amount of space devoted to tiny fovea
more space = more detail
two-point discrimination
threshold: minimum distance necessary to determine there are 2 separate stimuli
poor discrimination - feels like 1 stimulus
75% or greater at the trial, distance is threshold
plasticity
Experience improves discrimination.
passive exposure - track 2 point discrimination on index finger - 1.1 mm
plasticity
passively experiences 2 points at varying distances
threshold decreased to .9 mm
without continued exposure, improvement disappears
finger specific
test left index, no diff
Are receptive fields getting larger or smaller?
Behavioral changes accompany changes in cortical organization: more cortex becomes dedicated to the finger tips
cortical reorganization to represent long term improvement in discrimination
correlated with expanded cortical representation for that area
Are receptive fields getting larger or smaller?
mapping out cortical area for each of 5 digits, map out specific area being trained
3 months training to pay attention to stimuli at tip area
are dedicated to fingertip expanded + invaded into adjacent areas
smaller: better for detail - HD - but need more
phantom limb
sensation perceived from physically amputated
if nerve fibers are severed because limb is gone, experience of touch + pain has to be happening in brain
touches to face and upper arm can be translated to senses of missing limb
homunculus: area of cortex dedicated to missing limb, neurons are being coopted
phantom limb
areas that process face + upper arm start to invade, but not complete
cortical reorganization based on experience can lead to somatosensory confusion - face processing starting to happen in that area
rehab: mirrors to help resolve confusion
tactile acuity
Neurons in the somatosensory cortex have different sized receptive fields, depending on how important tactile sensitivity is for body part to function efficiently.
stimulate area, anywhere on the large RF
tactile acuity: two point discrimination
track mean threshold as a function of body part
hands + fingers, face: high acuity, low threshold
calves to chest: high threshold
feet: medium, low threshold, high acuity
evolutionary in nature
tactile acuity: grating sensitivity
reflected in firing
ability to detect orientation of grating
merkel cells: response as function of grating
as you pass stimulus over receptive field, stimuli correspond to activity in receptor
tactile acuity: grating sensitivity
preference for narrow bars with wide gaps
small gaps are detectible, but not good representation, for detecting large detain
Pacinian: continuous firing, not high frequency enough to detect changes
Haptic perception
knowledge derived from sensory receptors in skin, muscles, tendons & joints
active info seeking: explore tactile stimuli to understand specific characteristics of stimuli
Haptic perception
inform object identification/material properties
blindfolded: 100 common everyday objects
accuracy near 100% around 2-3 seconds
Haptic perception
ppl engage in stereotypical set of hand movements to discover specific properties
paired each procedure with types of info best at identifying
Lateral motion: texture
pressure: hard or soft
Haptic perception
static contact: temperature
unsupported holding: weight
enclosure: shape, volume
contour following: global + exact shape, details
Pattern of firing
pattern of firing of different receptors code features
specific shape represented by pattern of firing
pattern mirrors curvature of balls
larger: high activity at contact + decreasing activity as you move away from point
ventrolateral nucleus
processes kinesthetic information
similar to visual + auditory
ventral posterior nucleus
processes tactile information
both much larger
both first go to posterior but kinesthetic goes to ventrolateral
MGN: centre surround organization to receptive field
still fairly simple organization - ON/OFF signal
physiology of haptic perception: cortex
Neurons in cortex prefer simple features (orientation, direction of movement, shape).
neurons progressively more complex organization
S1: RF prefers horizontal align, silent for vertical orientation
S2: tip of index finger, prefers upward motion - direction + movement
physiology of haptic perception: cortex
larger receptive field: entire palm: more active for flat shape of ruler, no change in response to cylinder
ares of temporal cortex important for object identification: preference for shape
physiology of haptic perception: cortex
object identification is often multisensory in nature
both receptor types in epidermis have small RF, in dermis have large RF
thing detection - need to be in epidermis so not much penetration of skin is necessary
pain perception
can experience injury without experiencing pain
can experience pain without stimulation
realization where you start to feel pain
phantom limb is opposite - no limb, but pain
cortex is obviously involved in pain receptors
Pain
somewhat subjective with distinguishable components:
sensory, cognitive, emotional
separate components to whole experience
gate control model
t-cell - activity determines intensity of pain based on relative activity (transmission of pain to brain)
activity dictated by s + l fibers - nociception
S-fibers - nociception; increases t-cell activity - small, slow transmission, synapse with neurons that activate t cell that open pain gate
gate control model
L-fibers - non-painful tactile perception; large, can convey info fasterinhibits activity of t- cell
gate control model
SG- gate closes
central control - cognitive influence on nociception
model of pain perception
through ganglion dorsal root to dorsal horn
afferent (approaching) + efferent (existing)
gate control model
l-fibers:, inhibitory - decrease overall firing in t-cell that close the gate
rubbing area to stimulate l-fibers
get to interneuron first which will close the gate - overall perception of pain
cognitive affects - top down - to influence perception
Attention
increase sensory-specific cortical activation
attending to identity of object - increased activity in temporal
attention increases neural response
Attention
somatosensory info - increase in activity that process
V1: tactile attention condition: had to do something with condition - visual task
in both cases experienced raised letters
Attention
virtual reality games to draw attention away from pain.
how to treat burn patients - changing of bandages
virtual reality games - snow world - immersive reality where they have snowball fight
immersive nature of VR showed dramatic improvements, lower levels of pain
Placebo Effect
If you expect something to hurt, it will hurt more.
experience of relief from symptoms resulting from a substance that has no pharmacological effect
placebo influences expectations of pain
Placebo Effect
experience less pain when they don’t expect no pain
not ethical to give placebos when they’re in real pain
make analegesics more effective - by telling them you are giving them
Placebo Effect
giving them shot more effective than pills - assume that more effective in delivery + serious
more pills, larger pills
blue pills: soothing
red pills: danger connotations
Co-occurring emotional
emotional experiences can modulate experience of pain
fight or flight - processing pain less efficiently
sympathetic - don’t have time to deal with pain
in dangerous situation, pain is not helpful
positive emotion make pain less painful
emotion & pain
Emotion can increase or decrease the experience of pain.
images normed for valence
lots of proportion of images that lots of people have rated
normed according to intensity level
emotion & pain
high intensity not suitable to show - dead bodies + porn
passively viewed images for international affective picture system
cold pressor method: correlated with kind of images ppl viewed
avg duration correlation with emotional valence
sensory component
sensory component:
• thalamus
• somatosensory cortices
• insula
sensory component
sensory: describing type + intensity of pain
burning, sharp, throbing - perceptual qualities
insula: tucked in behind temporal lobe + parts of frontal lobe
last place that dictates pain intensity
sensory component
affect/emotional processing: how unpleasant
torturous, annoying - how we feel about it
amygdala processes emotion
cingulate: + orbito in particular
orbito: modulates feelings for wide variety of stimulus
affective component
- thalamus
- amygdala
- anterior cingulate
- prefrontal & orbitofrontal cortex
multimodal nature of pain
Suggestion can affect unpleasantness without affective intensity, indicating the two components are separable at the subjective level of experience.
painful sitmulus: rate subjective pain intensity + unpleasant
hypnotic suggestion: huge diff
for unpleasantness: same
multimodal nature of pain
Increased unpleasantness ratings elicited changes in ACC, but not in S1, demonstrating the two components are separable in the brain.
PET: low intensity suggestions accompany decrease in S1
lower unpleasantness suggestions accompany decrease in cingulate
cingulate produce emotional response
Pleasant touch
separate component of
our experience of touch
Pleasant touch
Emotional properties of non-painful touch are mediated by C-tactile afferent fibers (CT afferents):
•located in hairy skin
•preference for slow-moving, lightly applied force
Pleasant touch
hairy skin: not purpose for manipulation
development of emotional connection
hormonal changes due to skin to skin contact
slow moving lightly applied force - petting
release of endorphins
Opioids
analgesics, reducing pain & inducing euphoria.
endogenous analog was described.
known power of opioids for a long time
endogenous opioids: endorphins
pitutitary gland in response to stress + painful stimulation + high intensity exercise + sex
Opioid receptors
binding site for opioids & endorphins
Naloxone is a powerful opioid antagonist.
prefered agent over both opioids like heroin or endorphins, but does nothing
Naloxone
can be used to treat opiate overdoses & can be used to identify conditions under which endorphins are released: • pain • placebo • pleasant touch • exercise • capsaicin
Naloxone
immediate effect - treat overdose pain - triggers endorphins - pain is more painful placebos less effective pleasant touch not nearly as pleasant exercise no longer euphoria capsaicin - myth
