Two types of nociceptive pain
- Normal
- Inflammatory
What is inflammatory pain?
- nociceptors activated by inflammatory mediators that arise from tissue damage/disease
What stage of nociceptive pain differs with inflammatory pain?
- transduction
What happens during transduction to lead to inflammatory pain?
- nociceptors activated by endogenous (vs exogenous) chemical stimuli
Types of nociceptive pain
- Normal
- Inflammatory
What is inflammatory pain?
- nociceptors activated by inflammatory mediators that arise from tissue damage/disease
Which stage of nociception differs with inflammatory pain?
- transduction
What happens during transduction to lead to inflammatory pain?
- nociceptors activated by endogenous stimuli rather than exogenous
- inflammatory mediators released in response to tissue injury
Types of inflammatory mediators
- neurotransmitters
- peptides
- ATP
- protons
- lipids
- chemokines
- cytokines
- neurotrophins
Sources of inflammation
- Acute: tissue damage
- Chronic: chronic disease
- Neurogenic: in response to activation of nociceptive neurons
Which peptides are released by nociceptive neurons during neurogenic inflammation?
- substance P
- gene-related peptide (CGRP)
What is it called when peptides are released during neurogenic inflammation?
- axon reflex
- in response to depolarization with transduction in nociceptive neurons
What do substance P and CGRP trigger?
- infiltration of more immune cells in the area through vasodilation and enhancing vascular permeability and vascular leakiness
What else happens to nociceptive neurons to lead to inflammatory pain?
- structure and function of nociceptive neurons is altered by inflammation making nociceptors more susceptive to activation by all stimuli (chemical, thermal, mechanical)
3 main changes to nociceptive neurons due to inflammation
- more ion channels
- ion channels have increased response to noxious stimuli
- ion channels have lower threshold and will respond to less noxious stimuli
Peripheral sensitization
- increased responsiveness and reduced threshold of nociceptive neurons in periphery to the stimulation of their receptive fields
What does increased responsiveness mean?
- more frequent firing and longer duration
What does lower threshold mean?
- things that dont normally cause pain will cause pain
Central sensitization
- increased responsiveness of nociceptive neurons in the CNS to their normal or sub-threshold afferent input
- not related to inflammatory pain
Clinical features of sensitization sensory changes
- allodynia
- hyperalgesia
Allodynia
- pain due to a stimulus that does not normally provoke pain
- reduced threshold of NNs
Hyperalgesia
- increased pain from a stimulus that normally provokes pain
- increased responsiveness of NNs
What can the location of pain tell us?
- the physiological mechanism
What are the sensory signs of inflammatory pain?
- sensory signs correspond to areas of edema (blue/black area)
