Physiology: pain Flashcards
what is the definition of pain
an unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage
what are the 4 distinct processes in the physiology of pain
transduction, transmission, modulation, perception
describe what the transduction process of pain involves
translation of noxious stimulus into electrical activity at the peripheral nociceptor
describe what the transmission process of pain involves
propagation of pain signals as nerve impulses through the nervous system
describe what the modulation process of pain involves
modification/hindering of pain transmission in the nervous system
(eg by inhibitory neurotransmitters)
describe what the perception process of pain involves
conscious experience of pain, causes physiological and behavioural responses
describe what a nociceptor is
specific primary sensory afferent neurones
how are nociceptors activated
normally activated by intense noxious stimuli, can be mechanical, thermal or chemical
what neurons are first order neurones
nociceptors
describe the action of first order neurones
relay info. to second order neurones in the CNS by chemical synaptic transmission
what neurotransmitters are involved in nociceptor pathway
glutamate and peptides(eg neurokinin A)
where are second order neurones found
ascend spinal cord along anterolateral system(terminate in thalamus)
what are the second order neurones mainly comprised of
the spinothalamic tract(STT) and the spinoreticular tract(SRT)
describe the role of the spinothalamic tract(STT) in pain
involved in pain perception(location + intensity)
describe the role of the spinoreticular tract(STR) in pain
involved in autonomic response to pain, arousal, emotional responses, fear of pain
describe the role of third order neurones in pain physiology
relay sensory info. from the thalamus to the primary sensory cortex
what are the subtypes of nociceptor
A-gamma fibres and C-fibres
describe the myelination of the A-gamma and C-fibres types of nociceptor
A-gamma fibre = thinly myelinated
C-fibre = no myelin
describe what stimulus A-gamma and C fibre subtypes of nociceptor respond to
A-gamma fibre = noxious mechanical + thermal
C-fibre = all noxious stimuli
describe the type of pain mediated by A-gamma fibre nociceptors
‘first’, or fast, pain
lancinating, stabbing, pricking sensations
describe the type of pain mediated by C-fibre nociceptors
‘second’, or slow, pain
burning, throbbing, cramping, aching sensations
what different ways is pain classified
mechanism, time course, severity, origin
what types of pain are adaptive
nociceptive pain and inflammatory pain
what is nociceptive pain stimulated by
intense stimulation of nociceptors by noxious stimuli, mechanical, chemical or thermal
what is the function of nociceptive pain
early warning physiological protective system to detect + avoid noxious stimuli(therefore adaptive)
what is inflammatory pain activated by
variety mediators released form site of infection, by leucocytes, vascular endothelium and resident mast cells
inflammatory pain causes hyperalgesia and allodynia, describe what these are
hyperalgesia = heightened pain sensitivity to noxious stimuli allodynia = pain sensitivity to innocuous stimuli
describe how inflammatory pain is adaptive
promotes repair until healing occurs
what is neuropathic pain(pathological) pain caused by
damage to neural tissue
what different ways can neuropathic pain be perceived
burning, shooting, numbness, pins and needles
may be less localised
what is dysfunctional pain(pathological)
pain with no identifiable damage and no inflammation
what different types of pain are pathological, and are they adaptive
neuropathic and dysfunctional are patholgical
maladaptive
describe what referred pain is
feeling of pain in the skin distant to the internal organ it originates
what types of pain can be felt as referred pain
deep pain or visceral pain
what is referred pain caused by
convergence of nociceptive visceral and skin afferents upon same spinothalamic tract neurones
what are some sites of referred pain
gall bladder = right shoulder
heart = left arm, jaw
liver = right base of neck
