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