Physiology of Pain Flashcards
what is pain
an unpleasant sensory and emotional experience, associated with actual tissue damage or describe in terms of such damage
what are the four processes of pain
transduction, transmission, modulation, perception
what is transduction
translation of noxious stimulus into electrical activity at the peripheral nociceptor
what is transmission
propagation of pain signals as nerve impulses through the nervous system
what is modulation
modification/ hindering of pain transmission in the nervous system (e.g. by inhibitory neurotransmitters like endogenous opioids
what is perception
conscious experience of pain, causes physiological and behavioural responses
what are nociceptors and what activates them
specific primary sensory afferent neurones normally activated by intense noxious stimuli (mechanical, thermal or chemical)
what is a soma
nerve cell body
what is the path of pain in nerve
nociceptor (free nerve ending)- axon of nociceptor- soma- central terminal in CNS (dorsal posterior horn of spinal chord)- axon of projection (second order neurone)- spinothalamic and spinoreticulothalamic tracts
what does the central terminal do
releases neurotransmitters that excite second order neurones
what order of neurones are nociceptors
first order (relay information to second order neurones in CNS by chemical synaptic transmission)
where are nociceptor soma
within dorsal (posterior) root ganglion (DRG) (or terminal ganglion)
what are the neurotransmitters release by central terminal nociceptors
glutamate and peptides
what is the path of second order neurones
ascend the spinal chord in the anterolateral system to terminate in the thalamus
what tracts mainly make up the anterolateral system of the spinal chord and what do they do
the spinothalamic tract (STT) - involved in pain perception (intensity and location)
spinoreticular tract (SRT)- involved in automated response to pain, arousal, emotional response, fear of pain
what do third order neurons do
replay sensory information from the thalamus to the primary sensory cortex
what fibres make up nociceptors
Aδ and C fibres
describe Aδ fibres
mechanical/thermal nociceptors that are thinly myelinated
respond to noxious mechanical and thermal stimuli
conduct fast (lancinating, stabbing, prickling sensations)
describe C fibres
nociceptors that are unmyelinated
respond to all stimuli (are polymodal)
slow conduction (burning, throbbing, cramping, aching)
how can you classify pain
mechanisms (e.g. nociceptive, inflammatory, pathological
time course (acute, chronic, breakthrough pain)
severity
source of origin (somatic- skin, muscle, joints or visceral- internal organs)
what is nociceptive pain
normal response to injury of tissues by noxious damaging stimuli
only provoked by intense stimulation of nociceptors by noxious stimuli (chemical, mechanical, thermal)
why is nociceptive pain adaptive
is protective- acts as early warning physiological protection system to detect and avoid noxious stimuli
what causes inflammatory pain
activation of the immune system by tissue injury of infection
pain activates by variety of mediators released at the site of inflammation by leukocytes, vascular endothelium and tissue resident mast cells
how is inflammatory pain characterised
heightened sensitivity to noxious stimuli (hyperalgesia) and pain sensitivity to innoculus (non harmful) stimuli (allodynia)
