Case 2 - Overview of Pain Flashcards
what is pain
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
what is nociception
noxious (toxic) stimulus that can become noxious with prolonged exposure. process though which peripheral pain receptors transit information about current tissue damage centrally as pain.
what is a nociceptor
receptor in end organ that detects biochemical changes associated with current or potential tissue damage
what is hyperalgesia
exaggerated response to noxious stimuli
what is allodynia
sensation of pain in response to an innocuous stimulus
what is nociceptive pain
pain in response to actual or potentially harmful stimulation. often described as aching and localised. aggravated by movement
what is neuropathic pain
nerve injury or impairment that is associated with allodynia. often described as shooting or radiating. independent of movement
diagram showing types of pain
when do free nerve endings develop
7 weeks
when is the hormonal stress response to pain developed
18 weeks
when are thalamic projections into the somatosensory cortex developed
23-30 weeks
when are haemodynamic and behavioural reactions to painful stimuli developed
26 weeks
what are the 4 phases of pain pathways
- transduction
- transmission
- modulation
- central perception
what is the first step in the nociceptive process
thermal, mechanische or chemical stimuli of noxious intensity come into contact with a tissue
examples of inflammatory mediators from injured tissues
- globulin
- protein kinases
- arachniodonic acid
- nerve growth factor
- histamine
- substance P
what is transduction
when the inflammatory mediators stimulate transducer channels which leads to initiation of receptor potentials
what do receptor potentials evoke
action potentials in sensory nerve fibres
what is transmission
when action potentials are carried as affect signals via sensory nerve fibres to the dorsal root ganglia and dorsal horn of the spinal cord
what is modulation
when the signal is transmitted up the spinal cord to the brain stem and thalamus where significant processing may occur
what is central perception
the signal finally reaches the somatosensory cortex.
what is the amygdala involved in
the emotional and affective response to pain and pain modulation
what is the hypothalamus involved in
the neuroendocrine corticotropin response to pain
what is the periaqueductal gray matter involved in
key centre for pain modulation, involved in aversive and defensive pain behaviours
what is the basal ganglia involved in
the cognitive, affective and discriminative aspects of pain perception
what is the cerebral cortex involved in
it is the ultimate site of pain perception, potential for conscious activation of descending pathways for pain modulation.
what are pain signals modulated by
endogenous opuoid peptides - endophines
where are these pain signals modulated
- spinal cord
- dorsal root ganglia
- midbrain periaqueductal gray
where does the mechanism of the modulation of pain occur
the descending inhibitory pathways
what are the mechanisms of action of endogenous opioid peptides:
- activation of mu, kappa and delta opioid receptors leading to decreased presynaptic calcium influx which leads to decreased release of glutamate and SP
- increased K+ conductance in dorsal horn neurones
diagram showing the pathway of pain
what are the three types of afferent nerve fibres
Type A, Type B, Type C
describe type A fibres
large and myelinated
fast conducting
what are A-alpha fibres
primary receptors of the muscle spindle and Golgi tendon organ
what are A-beta fibres
afferent axon with largest diameter. secondary receptors of the muscle spindle that contribute to cutaneous mechanoreceptors
perceive light touch and or moving stimuli
what are A-delta fibres
free nerve endings that conduct stimuli related to pressure and temperature
what is the conduction speed of A-delta fibres
20m/sec
describe type B fibres
midsized, thinly myelinated fibres
responsible for autonomic information
describe C fibres
unmyelinated nociceptor slow fibres
conduction speed is approx 2m/sec
repsons to combinations of thermal, mechanical and chemical stimuli
what is rexed laminae
organised somatosensory and motor map laid out in the spinal cord of each spinal segment. different types of sensory nerves and the corresponding information they carry are organised so as to synapse in specific territories in the dorsal horn known as laminae
what are the 10 different laminae
Receives and relays noxious and thermal stimuli
Receives and relays noxious and non noxious physical stimuli and is involved In pain modulation
Receives and relays physical stimuli related to light touch and proprioception
Receive and relays non noxious physical stimuli
Receives and relays noxious stimuli and is involved in pain modulation
Received and relays information involved in spinal reflexes and proprioception
Receives and relays information related to visceral function and noxious stimuli
Receives and relays information related to visceral function and noxious stimuli
Receives and relays information relayed to motor control
Centrally located; where sensory and motor neurones cross before ascending/descending and where some degree of interneuronal cross-talk takes place
what happens with these laminae in pathologic conditions
there can be abnormal rearrangement of sensory inputs that contributes to the development of central sensitisation and other manifestations of chronic pain
ascending pathway of pain neurones
- nociceptors
- neurone cell bodies
- 2nd order neurones
- thalamus
describe nociceptors
receptors in the periphery respond to heat, intense cold, mechanical distortion, changes in pH and chemical irritants
describe neurone cell bodies:
the cell bodies are first order neurones located in the dorsal horn and dorsal root ganglia of the spinal grey matter.
what are the main neurotransmitters released by primary afferents
glutamate, SP and CGRP
describe the 2nd order neurones
after synapsing in the spinal cord, the 1st order neurones project to 2nd order neurones
2nd order neurones cross the midline at the anterior white commissure
These neurones then ascend to the thalamus via the contralateral spinothalamic tract, carrying both pain and temperature sensations
describe the thalamus
from the thalamus, the stimulus is sent to the somatosensory cerebral cortex via fibres in the posterior limb of the internal capsule
Other thalamic neurones project to areas of the cortex associated with emotional responses
what is the descending pathway of pain
the hypothalamus and cortical regions proves painful stimuli and signals for the release of inhibitory mediators and hormones that make pain suppression more effective = pain modulation.
