Pain pathways and central processes of pain

what are the 2 types of ion channels are found in receptors

• mechanically gated

• ligand gated (extracellular)

what chemicals are nociceptor stimulators

• bradykinin

• serotonin

• potassium

• histamine

• hydrogen ions

what chemicals are nociceptor sensitisers

• prostaglandins

• substance P

• nerve growth factor

what determines the initial frequency of action potential in nerve fibre

amplitude of generator potential in receptor

what happens in receptors that don’t display adaptation

• constant stimulus will produce constant generator potential

• = constant train of action potentials in nerve fibre leading from receptor

what happens in receptors with slow adaptation

• constant stimulus will produce generator potential that wanes over time= decreased frequency of action potentials in nerve fibre

what happens in receptor with rapid adaptation

• constant stimulus will produce generator potential that falls off very quickly= decreased frequency of action potentials in nerve fibre= loss of action potentials

why are receptors displaying rapid adaption a good thing

• if receptor is providing info about a not harmful stimulus and you’re more interested in rate of change in amplitude of stimulus rather than amplitude of stimulus

function of free nerve ending receptor

temperature or pain

threshold for free nerve ending temperature receptor

varies

adaptation rate for free nerve ending temperature receptor

rapid

threshold of free nerve ending pain receptor

high

adaptation rate of free nerve ending pain receptor

slow

function of meissner’s corpuscles

touch receptor

threshold of meissner’s corpuscles

low

adaptation of meissner’s corpuscles

rapid

function of merkel disks

touch receptor

threshol of merkel disk

low

adaptation rate of merkel disks

slow

function of ruffini endings

touch receptor

threshold of ruffini endings

low

adaptation rate of ruffini endings

slow

function of pacinian corpuscles

deep pressure receptor

threshold for pacinian corpuscles

low

adaptation rate for pacinian corpuscles

very rapid

what is a receptive field

• region of sensory surface that when stimulated causes change in firing of neuron

do primary afferent have large or small receptive fields

small

how do receptive fields of neighbouring neurons interact

overlap

what is convergence in respect to receptive fields

proximal sensory neurons have receptive fields that are composites of receptive fields of more distal neurons

if spatial resolution is high is convergence high or low

low

what does low convergence mean

a given primary afferent will only synapse with 1 or a few sets of higher order sensory neurons

what does high convergence mean

a given primary afferent may synapse with a large number of higher-order sensory neurons

in what circumstances can convergence be high

if spatial resolution isn’t so important

what is nociception

detection of harmful stimuli

steps of pain pathway

• sensory receptor in skin or a joint or a viscus activated by noxious stimulus

• axon of sensory neuron

• synapses with neuron in dorsal horn

• axon of neuron decussates within 1-2 spinal segments

• ascending fibre projects to thalamus in spinothalamic tracts

• synapses with neuron in thalamus

• axon of neurone projects to primary somatosensory cortex

why do you experience phantom limb pain

• absence of first order neuron following avulsion of dorsal root form spinal cord

describe gate-control theory of pain

• stimulation of large-diameter sensory neurons can block out message from pain fibres

what do interneurons modulate

transmission of impulses through pain pathway

what is activity of interneurons modulated by

input from small and large diameter afferents

where are interneurons found

in substantia gelatinosa of spinal cord

fibres from where can close the ‘gate’ in pain pathway

• periaqueductal grey matter

• raphe nuclei

• locus coeruleus

pharmacological treatment for neuropathic pain

• opioids

• anticonvulsants

• antidepressant

physical treatment for neuropathic pain

• TENS

• touch therapy

• acupuncture

• surgery