2 - pathophysiology of pain and pain management lectures Flashcards
what are nociceptors?
high-threshold sensory neurons of the peripheral somatosensory nervous system capable of transducing a range of noxious stimuli
nociceptors are equipped with receptors sensitive to what types of stimuli?
mechanical, thermal and chemical
what are high threshold noxious stimuli transduced into?
an electrical action potential
what is TRPM8 activated by?
noxious cold temps
what is TRPV1 activated by?
noxious heat
how can a nocicpetor be activated?
- DIRECTLY — through painful stimuli
- INDIRECTLY — through activation and release of stimulatory molecules from neighbouring cells (eg. keratinocytes)
what does the activation of a nociceptor lead to?
generation of an AP —> transmission of info to spinal cord
nocicpetors are glutamatergic and some are also peptidergic. explain.
- release glutamate and neuropeptides (eg. substance P, calcitonin gene related peptide - CGRP) to the 2nd order neurons in the dorsal horn of the spinal cord
- this info is then transmitted
where do pain pathways cross the midline?
spinal cord
where do proprioceptive pathways cross the midline?
medulla
where do 2nd order neurons synapse in pain processing?
thalamus
what do nocicpetors detect?
pain, temperature, course touch
sensory neurons are pseudo-unipolar. what does this mean?
- put out 1 axon which branches into 2:
- 1 branch goes centrally to SC
- 1 goes peripherally out to innervate target tissues
where do cell bodies of sensory neurons reside within?
dorsal root ganglia
Aa/Ab vs. Ad vs. C fibres
- Aa/Ab = largest, myelinated, fastest conduction
- C = smallest, not myelinated, slowest conduction
what is rexed laminae?
- describes the organisation of the spinal cord grey matter based on size and packing density of neurons
what are the 4 types of pain?
1) nociceptive
2) inflammatory
3) neuropathic
4) nociplastic
what is nociceptive pain?
pain that arises from actual or threatened damage to non-neural tissue and is due to the activation of nociceptors
what are the characteristics of nociceptive pain?
= good pain
- high-threshold stimulus-dependent pain
- thermal, mechanical or chemical stimuli
- pain evoked in a graded response by appropriate high intensity (noxious) stimuli
- adaptive and serves a purpose
- more noxious = more pain
what are the characteristics of inflammatory pain?
= still good pain
- active inflammation
- sensitisation
- evoked by low and high threshold stimuli
- adaptive, protective during the healing response and reversible
what is inflammatory pain?
the spontaneous hypersensitivity to pain that occurs in response to tissue damage and inflammation
what is neuropathic pain?
pain caused by a lesion or disease of the somatosensory nervous system
give some examples of neuropathic pain
what are the characteristics of neuropathic pain?
= bad pain
- marked neuroimmune component
- sensitisation
- spontaneous and evoked by low and high intensity stimuli
- maladaptive and persistent
- abnormal amplification of all stimuli
- serves no useful purpose
- not well-managed
- spontaneous pain — no stimuli
describe sensitisation
= increased responsiveness of nociceptive neurons to their normal inputs, and/or recruitment of a response to normally subthreshold inputs
- can include a drop in threshold and an increase in suprathreshold response — doesn’t take as much to activat nocicpetors and they respond greater
- spontaneous discharges and increases in receptive field size may also occur
- clinically, sensitisation may only be inferred indirectly from phenomena such as hyperalgesia or allodynia
what is hyperalgesia?
increased pain from a stimulus that normally provokes pain
what is allodynia?
pain due to a stimulus that does not normally provoke pain
what does spontaneous pain feel like and what is it accompanied with?
often described as burning, tightness accompanied with parasthesia, tingling, shooting or stabbing pains
what co-morbidities is neuropathic pain associated with?
anxiety, depression and sleep-disturbance
what is nociplastic pain?
pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain
what is post-hepatic neuralgia (PHN)?
the pain that persists after shingles has cleared
what is mechanical allodynia?
sensitivity to clothes, bedsheets etc
what are 4 mechanisms of neuropathic pain?
- increased inflammatory cells and mediators
- altered nociceptor activity (receptor/ion channel expression) peripheral sensitisation
- altered spinal processing, central sensitisation, synaptic reorganisation
- altered central processing, descending inhibition
how do mast cells cause AP generation?
- release histamine and cytokines
- these stimulate receptors on primary sensory afferent terminals to generate an AP
what does antidromic stimulation of afferent terminals lead to?
release of neuropeptides from these terminals — binds to receptors on mast cells — more degranulation, release of histamine — therefore larger area perceived as being painful
—> increased blood flow and vascular permeability
what are the first inflammatory cells to infiltrate damaged tissue?
neutrophils