T2 L12: Physiology of pain 2 Flashcards
What is the definition of acute and chronic pain?
Acute <3months
Chronic >3 months
What causes acute pain
Tissue injury or inflammation. When the injury site recovers, the pain stops
Eg. following surgery, musculoskeletal injury, burn, headache, visceral pain
Which type of pain is caused by excitation of nociceptors?
Acute pain
What is the effect of bradykinin and NGF on pain?
They reduce the threshold of heat-activated channels (TRPV1) so cause pain
What is the effect of prostaglandins on pain?
They reduce the threshold of sodium channels so cause pain
What is hyperalgesia?
An increased sensitivity to feeling pain and an extreme response to pain
What are the sites of action of acute pain treatment?
PNS (at the site of injury)
CNS
Both
What is the drug Lidocaine for?
Also known as Lignocaine
It is applied to the skin to reduce pain
How does Lidocaine work?
It prevents nociceptors firing by blocking sodium channels
How do NSAID’s work?
They reduce the inflammatory response by inhibiting prostaglandin synthesis so that the sodium channel threshold can’t decrease
How does paracetamol work?
It exact mechanism in not known
It inhibits COX enzymes enzymes in the CNS so there is no prostaglandin formation. It acts on the serotonergic pathway
How do topical capsasin treatments work on reducing pain?
They are TRPV1 agonists so they persist opening of the TRPV1 channels causing a calcium overload so the nociceptor stops working
Too much calcium causes mitochondrial overload
How do opioids work to reduce pain?
They agonise the endogenous opioid system
They work on the spinal cord, disinhibit the brainstem, and inhibit nociceptor channels peripherally
What type of drug is Tramadol?
An opioid
What is the gate control theory of pain?
The pain cause by nociceptors can be reduced by the simultaneous activation of low threshold mechanoreceptors (alpha/beta fibres)
Rubbing or blowing on the pain will reduce it
It’s modulation of pain at the spinal cord level
What is the mechanism of gate theory?
Stimulation of alpha/beta fibres at injury site activates interneurons in the dorsal horn, which inhibit spinothalamic neurones
The C fibres inhibit inhibitory interneurons (opening of the gate)
Alpha/beta fibres activate inhibitory interneurons (closes gate)
What % of population does chronic pain affect?
20-50%
Which type of pain is both nociceptive and neurpathic?
Chronic pain
What are some causes of neuropathic pain?
Compression Traction Sever Hypoxia Demyelination Tumour Neuroinflammation
How may patients describe neuropathic pain?
Burning Numbness Shooting pains Pins and needles Aching Hypersensitivity
What happens to nerve at the site of injury?
The damaged nociceptor tips fire spontaneously because there is an accumulation of transported ion channels at the site
What is central sensitisation?
Increase in responsiveness of nociceptors withing the CNS
Normal inputs begin to produce abnormal responses due to reduced threshold for activation
What is the mechanism behind reduced threshold for activation in the CNS?
There is alteration of channels and causes insertion of more channels so neurones fire more easily
What is Allodynia?
Extreme sensitivity to touch
