Ch 15: The cutaneous senses Flashcards
What are the somatosenses and the cutaneous senses?
somatosenses:
-cutaneous senses: everything we feel through the skin (touch and pain)
-proprioceptive: body orientation
-kinesthesis: orientation of movement
-haptic: coordinate touch and movement
-vestibular: balance/spatial orientation
-see notes for more detail
What are two neural pathways?
- SPINOTHALAMIC PATHWAY:
-small bb nerves synapse in spinal cord
-spinal cord to brainstem to thalamus (VPN)
-then to cortex: anterior cingulate cortex (pain), insular cortex (emotion), primary somatosensory cortex
-carries primary temp and pain info - MEDIAL LEMNISCAL PATHWAY:
-larger longer nerve fibres synapse in the medulla
-ascends via media lemniscus to thalamus
-then to primary somatosensory cortex
-touch and proprioceptive info
How is tactile information processed? What is the two-point threshold?
-touch = constant pressure, vibe = changing pressure
-stimulus containing kinetic energy (movement) = abrupt change in skin tension
-soft touch signals go to insula (emotion)
-development, social cooperation, affiliation, maybe evolutionary
-oxytocin = positive emotion = release during soft touch
What is J.J. Gibson’s idea of active touch?
-active touch = self directed, aids in accuracy of IDing objects
-the way that an object is handled is diff depending on what ur trying to find out about the object
How is temperature perceived?
-warm and cold are separate
-warm fibres vs cold fibres
-b/c thermal grill illusion: simultaneously activates both and confuses brain
-paradoxical cold: hot stimulus produces sensation of cold; maybe b/c activation of cold fibres
THERMAL ADAPTATION:
physiological zero: temp where receptors have become adapted: don’t feel hot or cold just normal
-perception of temp is relative to physiological zero. there is never an absolute lack of temperature
-takes 20 mins, only truly occurs between 29-37 degrees C
How is pain perceived?
nociception = neural encoding of impeding or actual tissue dammage
-once thought excess of intensity, actually more complex tho
-evolutionarily adaptive
-tissue damage = intense pain = motivation to end pain
-affected by nonphysical factors including culture
What is synesthesia, and what are two theoretical explanations of it?
-blend of the 2 senses
1.
2.
skin
-glabrous = hairy
-epidermis = outer layer
-surface = corner (ded)
-inner layer = dermis
-neural systems @ epi/dermal boundary, receptors believed to exist there
Specificity theory
(INTUITIVE AND SIMPLISTIC, BUT WRONG)
-one mechanoreceptor per each basic sense
-warmth = Ruffini
-cold = Krause and bulbs
-touch = Meissner corpuscles
-pain = free nerve endings
-complex sensation is blends of these
punctate sensitivity: if there’s a receptor under the skin at a location, there must be sensitivity to the associated location
VIA self dissection: stimulate a nerve fibre and see which type of stimulus activates it
problems:
-no correlation for self dissection
-u feel sensation past where the actual nerve is (kinetic and thermal energy felt over distance past where it is stimulated)
-cornea has all sensations and only one type of nerve ending
-thermal grill illusion: cold + warm = painfully hot
pattern theory
(SEEN AS THE MORE CORRECT THEORY)
-pattern of multiple neutron fire = perception of a certain sensation
-receptors differ in structure (lots of diff types of mechanoreceptors) but not in function (they all do the same shit)
-same receptor can yield multiple types of sensations, depending on intensity of activation
-why diff types then ?
…
-each type has is tuned to prefer a certain stimulus
-ex. corpuscle likes vibes. tuned for onset and offset of pressure
-fibres relatively specialized but also respond to diff sensations too
diff types of mechanoreceptors (15.1)
receptors close to skins surface:
MERKEL (slowly adapting)
MEISSNER CORPUSCLE (rapidly adapting
(cutaneous receptive field = fire neutron in area of skin)
FIBRES:
SA1 fibres: slowly adapting, fires constantly
-associated w/merkel
RA2 fibres: rapidly adapting, fires only when stimulus first applied
-associated w/meisner corpuscle
receptors deep in skin:
Ruffini cylinder: -SA2 fibre, slowly adapt, responds to continuous stim, ex. stretching skin
pacinian corpuscle: Ra2/PC, slowly adapt, responds when stim applied/removed ex. vibration and fine texture
and how are the cutaneous senses represented in the cortex?
-both pathways end in the somatosensory cortex
-2 areas receive signal from cortex:
1. primary somatosensory cx (S1)
2. secondary somatosensory cx (S2)
-signals between S1 and S2 via insult (emotion) and anterior cingulate cortex (pain)
HOMUNCULUS: - (AKA somatotropic organization)
-somatosensory cx organized maps correspond to loc on body. disproportionate. places that are more sensitive receive more neural representation (larger brain area)
-amount of cortical area changed via experience dependent plasticity
MEASURED VIA:
-evoked potential method: electrode on scalp
-direct stimulation:stimulate neutron directly during surgery to see what happen (allowed for mapping cortical areas that correspond to body loc)
measuring thresholds for touch (2 types of thresholds)
- absolute threshold: via von Frey hairs what can u feel vs can’t feel push into ur skin
- difference threshold: -touch 2 points what’s the minimum distance that still feels like 2 points
What is Gate Control Theory?
-see diagram in notes…
Specificity theory approach to pain perception
-one type of neutron per type of pain…
-sharp pain for one receptor (A8)
-burning/throbbing for other receptor (C)
-double pain = sharp then dull
evidence: lack of pain in a disease = complete lack of these receptors (a8 and C)
