Touch and Pain

sensory transduction

translation to language the brain can understand - electrical

receptive field

windows through which neurons sense the world

place code

topographical maps — how the brain represents sensory inputs

parallel pathways

processing multiple aspect of input in different pathways

cutaneous senses

provide info from surface of body

proprioception

perception of body position and posture

• submodality of cutaneous sense

• provide info about location of body in space

kinesthesia

submodality of cutaneous sense; provide info about movement of body through space

organic senses

provide info from, in, and around internal organs

cutaneous senses stimuli

• pressure

• vibration

• heating

• cooling

• tissue damage (pain)

coding touch

receptive fields — basis of a place code

• the locations on the skin to which a somatosensory neuron responds to

coding touch ex.

put recording device in somatosensory neuron, and touch diff parts of the body, trying to see which body part will get the neuron to fire

receptive field — resolution of the senses

the two point threshold for any part of the body is determined by the size of the receptive fields and the extent of overlap

• taking a paper clip and bending to make two points that are close together; will feel the two points on the fingers, but not on the shoulder

sensory transduction

mechanoreceptors

mechanoreceptors

neurons that convert mechanical stimulus into ‘receptor potentials’

• mechanically gated ion channels (mechanical stimulation opens the channel, causing a change in membrane potential)

• detect stimuli that cause vibration or changes in pressure (tactile stimuli) [also detected by free nerve endings]

four types of somatosensory receptors/mechanoreceptors

• ruffini corpuscles

• pacinian corpuscles

• meissner’s corpuscles

• merkel’s disks

ruffini corpuscles

vibration sensitive, large receptive fields, slow adapting

pacinian corpuscles

detects mechanical stimuli, especially vibrations, large receptive fields, fast adapting

meissner’s corpuscles

touch sensitive, small receptive fields, fast adapting

merkel’s disks

touch sensitive, small receptive fields, slow adapting

glabrous skin

hairless skin of palms and soles of feet

• contains dense complex mixture of receptors (reflecting how we use palms and inside of fingers to explore world)

skin consists of…

subcutaneous tissue, dermis, epidermis, receptors

mechanism of mechanoreceptors

movement of dendrites of mechanoreceptors causes ion channels to open, and the flow of ions into or out of the dendrite causes a change in the membrane potential

size and nature of receptive field of merkel’s disk

small, sharp borders

size and nature of receptive field of ruffini corpuscles

large, diffuse borders

size and nature of receptive field of meissner’s corpuscles

small, sharp borders

size and nature of receptive field of pacinian corpuscles

large, diffuse borders

location of receptor for merkel’s disk

hairy and glabrous skin

location of receptor for ruffini corpuscles

hairy and glabrous skin

location of receptor for meissner’s corpuscles

glabrous skin

location of receptor for pacinian corpuscles

hairy and glabrous skin

location of receptor for hair follicle ending

base of hair follicle

location of receptor for free nerve ending

hairy and glabrous skin

function of receptor merkel’s disk

detection of form and roughness, especially by fingertips

function of receptor of ruffini corpuscles

detection of static force against skin; skin stretching; proprioception

function of receptor of meissner’s corpuscles

detection of edge contours; braille like stimuli, especially by fingertips

function of receptor for pacinian corpuscles

detection of vibration; information from end of elongated object being held, such as a tool

function of receptor of hair follicle ending

detection of movement of hair

function of receptor of free nerve ending

detection of thermal stimuli, noxious stimuli (pain), tickling, pleasurable touch from gentle stroking with a soft object