6.5 Pain physiology and pharmacology Flashcards
What are the two types of peripheral nerves?
A delta fibres: lightly myleinated, relatively fast, high threshold mechanoreceptors
C fibres: non myelinated, slow, specific nociceptors
Where do A delta and C fibres enter the spinal cord and what kind of pain do they transmit?
A: lamina V - acute pain and temperature
C: Lamina II substantia gelatinosa - slow burning pain
What are the ascending pain and temperature fibres?
Spinothalamic
Lateral: paleospinothalamic
Anterior: neospinothalamic
Where do the paleospinothalamic and neospinothalamic project?
Paleo:post central gyrus
Neo:post central gyrus, reticular formation, medulla, limbic system
What are the targets for the descending pathways of pain?
inflammation, conduction, synapse and central perception and descending pathways
Where are opiod receptors located?
Brain, brainstem, spinal cord, peripheral neurons and intestine
How do opioids work?
They work on opioid receptors which are G coupled receptors - Inhibit this which leads to inhibition of voltage gated Ca channels and reduced NT release presypatically
Increase in potassium conductance an membrane hyperpolarisation post synaptically
What effect do opioids have on brain receptors?
Decrease firing of GABAergic neurons leading to disinhibition of descending pathways which inhibits spinal pain transmission
What are the CNS and GIT side effects of opioids?
CNS: sedation, euphoria, respiratory depression
GIT: nausea, vomiting, constipation
What is the role of the COX enzyme?
Convert arachidonic acid to prostaglandins
How can pain be assessed?
Pain score
Functional pain assessment
Physiological assessmnet
What are the two principles of biological pain treatment?
Treat reversible physiology
Provide pharmacological analgesia both systemic and regional
What is the holy trinity of pain management?
Paracetamol, NSAIDs and opioids
What are the 3 tiers of analgesia?
1: paracetamol, NSAIDs, opioids
2: ketamine, tramadol, clonidine, gabapentinoids
3: local anaesthetics
