375 Touch

somatosensation

body senses

3 somatosensation systems

exteroception: sensory info from the outside world

proprioception: info on body position

interoception: info we gather from our internal bodily functions (ex. breathing)

5 exteroception skin receptors

Meissner’s corpuscles

Pacinian corpuscles

Merkel cells

Ruffini endings

free nerve endings

Meissner’s corpuscles

location: closest to outer layer of skin

function: registers when something rubs skin

RF size: small

AR: fast

Pacinian corpuscles

location: bottom-most in skin

function: respond to sudden displacements of the skin

RF: large

AR: fast

Merkel cells

location: below Meissner’s corpuscles

function: respond to steady pressure or steady skin indentation

RF size: small

AR: slow

Ruffini endings

location: dermis

function: detects skin stretching

RF size: large

AR: slow

nociceptors

pain receptors with free nerve endings

two groups:

A-delta: myelinated for heat and pressure

C-fiber: unmyelinated for heat/cold, pressure, and noxious chemicals

2 exteroception brain pathways

dorsal column pathway: touch and proprioception pathway, high cross pathway (crossover occurs in the medial lemiscus, which is higher in the brain stem)

spinothalamic pathway: pain and temperature pathway, low cross pathway (crossover occurs low in brainstem in the spinal cord)

pain and touch sensations utilize

different brain pathways

somatosensory cortex

located directly behind the central sulcus in the parietal lobe

two parts: S1 and S2

somatosensory homunculus

maps parts of the cortical structure which represent each part of the body

general rule: size matters, the bigger the area, the more sensitive that part of the body will be

mostly dedicated to hand, face, and mouth perception

anterior to posterior: we get different responses for the same body part for a given body part

asomatognosia

inability to feel, recognize, or be conscious of one’s own specific body parts

ex. inability to recognize one’s hand as their own

asterognosis

inability to identify an object by active touch of the hands without other sensory input, also occurs from dorsal column damage

ex. inability to recognize a key as a key when eyes are closed, solely relying on touch

pain

exaggeration of normal stimulus

4 pain thresholds

lower threshold: aka sensation threshold, when the first report of a sensation occurs (ex. place hand on hot plate and it is then turned on and warmth is felt)

pain perception threshold: when stimulus becomes painful

pain tolerance: being able to withstand pain even if it hurts

encouraged pain tolerance: painfully enduring pain for a period of time

6 factors that influence pain perception

individual experience

familial responses

cultural responses

gender differences

level of attention/anticipation

control of the pain

3 main issues of measuring pain perception

pain is good

no cortical center

top-down control of pain

pain is good

pain is informative, adaptive, and tells us that something is wrong

episodic analgesia

temporary/transient pain relief

congenital analgesia

chronic condition of the inability to perceive pain

no cortical center

temporary, chronic, and emotional components of pain involve numerous parts of the brain

top-down control of pain

pain is controlled from our CNS

Melzack/Wall gate control theory

a “gate” in the spinal cord can regulate the transmission of pain signals to the brain

large diameter mechanoreceptors receive input from: light touch, fast fibers, low threshold

small diameter nociceptors receive input from: intense stimulation, slow fibers, high threshold

SG = substantial gelatinosia

T = transmission cells

function of mechanoreceptors in the GCT: keep the gate closed and inhibit pain

function of nociceptors in the GCT: opens the gate to cause pain

mechanoreceptors stimulate the SG, which causes the SG to: inhibit T cells which are transmitting the pain signal

nociceptors stimulate the SG, which causes the SG to: override inhibition, opening the gate which causes pain

a little stimulation is okay, a lot of stimulation is bad!

in short, mechanoreceptors can inhibit the transmission of pain signals from nociceptors at the spinal cord level by “closing a gate”, reducing pain perception

endorphins

neurotransmitters produced to decrease pain and stress

released when pain and stress are experienced to reduce pain

haptic perception

active touch, person initiates the activity

humans are good at using it to distinguish objects

principle exploratory procedures (Lederman/Klatzky)

watched people’s movements during haptic touch and categorized these movements

8 principle explanatory procedures

lateral motion: moving fingers across object, gets info on texture

pressure: pushing into an object, gets info on hardness

static contact: tapping object, gets info on temperature

function test: feeling multiple parts of object, gets info on specific function

unsupported holding: movement while holding object up or down, gets info on weight

enclosure: encompassing an object in hand, info on global shape and volume

contour following: tracing finger around shape, gets info on exact shape and global shape

part motion test: moving parts of an object, gets info on part motion