Physiology of pain Flashcards
What are the three categories of pain? Which are adaptive and maladaptive?
- Nociceptive (adaptive)
- Inflammatory (adaptive)
- Pathological (maladaptive)
What are nociceptors?
Peripheral sensory afferents activated by noxious stimuli (chemical, thermal and mechanical)
How is inflammatory pain adaptive and protective?
Causes hypersensitivity and allodynia which serves to protect against further injury
What are the two main subtypes of nociceptor? What types of stimuli do they respond to?
A-delta (mechanical and thermal) and C-fibres (polymodal)
What is first and second pain?
First- stabbing, lancing sensation (A-delta)
Second- throbbing sensation (C-fibre)
Where are the nociceptive cell bodies located for:
a) skin, muscles, tendons, joints, organs
b) head, oral cavity and neck
c) the viscera
a) dorsal root ganglia
b) trigeminal ganglia
c) nodose ganglia (inferior ganglion of vagus nerve)
Describe the path taken by signals in nociceptor afferents.
First order neurone; enter and synapse within the dorsal root of the spinal cord; ascend the anterior/posterior spinothalamic and spinoreticulothalamic tracts in the second order neurone (axon of projection)
Describe the afferent and efferent functions of peptidergic C-fibres.
Afferent- transmit pain information to CNS via release of glutamate/substance P/neurokinin A in the dorsal horn
Efferent- release pro-inflammatory mediators from peripheral terminals contributing to neurogenic inflammation
What are the two main peptides released in neurogenic inflammation by C-fibres?
Substance P and calcitonin-gene related peptide (CGRP)
What overall effect does neurogenic inflammation have?
Increases nociceptor activation and sensitivity causing hyperalgesia and allodynia
What do prostaglandins do?
Sensitive/activate nociceptive neurones
How do NSAIDs work?
COX inhibitors- stop prostaglandin synthesis
Why are specific COX-2 inhibitors limited in their use?
Prothrombotic
