Anatomy and Physiology of Pain Flashcards
What are the four physiological mechanisms of pain?
Transduction
Transmission
Perception
Modulation
Define pain
Unpleasant sensation and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What is nociceptive pain?
Normal, acute pain resulting from nociceptor activity
Which is the fastest nociceptor sensory neurone?
Ad
Which is the slowest nociceptor fibre?
C
Which is the second fastest nociceptor fibre?
Ab
What are in the membrane of nociceptors which allow responses to tissue damaging stimuli
receptor proteins
Which receptor detects pH changes in skeletal and cardiac muscle relating to ischaemia?
ASIC3
Why is there sometimes lack of pain fibres?
Shortened life span
Which nociceptors produce sharp, fast pain?
Ad (+ some Ab)
Where are nociceptors present?
Thermal + Mechanical
Provides precise location
Where do Ad fibres synapse?
laminae I and V
What type of pain do C fibres produce?
slow, burning
What are the two types of C fibres?
Peptidergic fibres
Peptide poor fibres
What do peptidergic fibres do?
Release peptides to produce inflammatory responses + healing
What do peptide poor fibres do?
Have distinct receptors which provides mechanical nociception
Where do C fibres synapse?
laminae I and II
Where do C fibres also innervate through interneurons?
lamina V
What does the spinothalamic tract pathway start + finish?
Sensory pathway from skin to thalamus
Where is information from Ventral Posterolateral (VPL) of the thalamus relayed to?
somatosensory cortex of brain?
Where does spinothalamic tract decussate at?
Level of spinal cord
What does the lateral spinothalamic tract modulate?
Pain + Temperature
Where does the lateral spinothalamic tract end?
Different sites of the brainstem
What are the primary afferents of lateral spinothalamic tract?
C fibres and some Ad fibres
Where are projection neurones found in lateral spinothalamic tract?
laminae I
What does the lateral tract innervate?
more posterior and medial parts of the thalamus; MDvc, POm and VMpo
Where does MDvc project to?
Anterior cingulate cortex
What is anterior cingulate cortex responsible for?
emotion and motivation
Where does posterior thalamus project to?
anterior/rostral insula
What does lateral STT sub serve as?
Punishing aspects of pain
What does the anterior tract modulate?
Pressure and touch
What are primary afferents of Ad of anterior tract?
Ad fibres and some Ab and C fibres
Where are projection neurones found for anterior tract?
laminae V
What does anterior tract innervate?
VPL and VPM (mainly project to primary somatosensory cortex)
What does anterior STT sub serve as?
Fast, discriminative aspects of pain
What are inflammation signs of normal acute pain?
Heat
Redness
Pain
Swelling
What is peripheral sensitisation?
Increased sensitivity to afferent nerve stimuli
How does peripheral sensitisation work?
Inflammatory mediators impact nociceptors by reducing activation threshold and increasing responsiveness
Where does increased pain sensitivity occur?
directly in damaged tissue
Where do prostaglandins work?
key role in inflammatory pain
What do phospholipase A2 release and where?
Arachidonic acid from cell membranes
What uses arachidonic acid as a substrate for PG synthesis?
COX 1 + COX 2
Where is COX 1 found?
low levels tonically
Where is COX 2 found?
Induced by inflammation
How do PGs sensitise C fibres?
Increase number of open Na+ channels
What do PGs also cause?
central sensitising effects
What can target PGs?
Analgesics
NSAIDs
(for pain reduction)
What is released in central sensitisation?
glutamate + peptides
What releases glutamate + peptides in central sensitisation?
Nociceptor afferents
What causes central sensitisation?
Prolonged nociceptor input
Where does prolonged nociceptor input work on in central sensitisation?
dorsal horn neurones
What is an effect of central sensitisation?
Increased sensitivity of dorsal horn nociceptive 2nd order neurones to inputs
What does increased sensitivity of dorsal horn cause?
allodynia or secondary hyperalgesia (pain occuring in the region surrounding the damage)
Define allodynia
pain from things which are not painful
define hyperalgesia
heightened response
Define chronic pain
Pain > 12 weeks
What can be a characteristic of chronic pain?
maladaptive
Why does chronic pain occur?
abnormal activity in the neural system
What is the difference between neuropathic pain vs dysfunctional pain?
Neuropathic = injury or dysfunctional in neural system Dysfunctional = no known lesion or inflammation
How do you deal with peripheral nociceptors?
Local anaesthetics + anti-inflammatory drugs
How do you deal with peripheral nerves
Local anaesthetics
How do you deal with dorsal root?
Local anaesthetics
opioids
A2 agonist
How do you modulate pain in brain?
Opioids
A2 agonists
What does acupuncture do?
Activate Ad fibres so stimulates primary pain modulation centre (PAG)
What does PAG mediate?
Diffuse Noxious Inhibitory Control (DNIC) so pain inhibits pain
