302 Physiology of pain Flashcards
What are different types of pain?
- Nociceptive (somatic or visceral)
- Inflammatory
- Neuropathic
What is nociceptive pain?
A physiological response to real or threatened non-neural tissue damage
-Threat is thermal, chemical, or mechanical
-Reversible pain once the insult is removed
Which fibres are stimulated in nociceptive pain?
C fibres and Aδ fibres on peripheral nerves
What is somatic nociception?
Activation of nociceptors in skin, muscles, bones, joints, and connective tissues
Transmitted along A-delta and C fibres
Somatic pain – sharp or dull pain. Exacerbated by movement.
What is visceral nociception?
-Activation of nociceptors in internal organs
-Transmitted along autonomic fibres
Visceral pain – poorly localised, deep, squeezing, cramping pain, dull, sickening.
Associated autonomic symptoms – nausea, vomiting, sweating
What is inflammatory pain?
-Response of the somatosensory nervous system to tissue damage and inflammation.
In the periphery, increased inflammatory mediators (cytokines and chemokines) sensitize local nociceptors:
Lowers threshold for responsiveness (peripheral sensitization).
Results in activation of pathways after innocuous input and in exaggerated responses to noxious stimulation.
The plasticity that underpins these changes is rapid (occurring in minutes).
Inevitable consequence of surgery and tissue trauma.
Upregulation of nociception normally resolves as wound healing occurs.
What is neuropathic pain?
A lesion or disease of the somatosensory nervous system.
Impacts on function and causes structure changes in the somatosensory nervous system.
The result is a combination of sensory loss and increased responsiveness to both noxious and innocuous stimuli.
What is allodynia?
Pain after non-painful stimuli
What is hyperalgesia?
Heightened pain after painful stimuli
What is hyperpathia?
An eruptive pain extending beyond the duration of a stimulus
What does neuropathic pain feel like?
Electric shock
Burning
Cramping
Constant
Fleeting
Provoked
Name some nociceptors
Free nerve ending
Merkel disk
Meissner’s corpuscle
Pacinian corpuscle
Hair follicle receptor
What does a Merkel disk detect?
Gentle touch
What do Meissner’s corpuscles detect?
Vibrations
Most sensitive to low frequency vibrations
What do Pacinian corpuscles detect?
Vibrations transmitted to the skeleton
What does a free nerve ending detect?
Temperature, mechanical stimuli (touch, pressure, stretch) or danger (nociception)
What is the difference between nociception and pain?
Nociception: how signals about possible tissue damage get from the site of injury to the brain.
Pain: an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such.
What factors feed in to create pain from nociception?
Beliefs
Psychological factors
Cultural issues
Other illnesses
Personality
Social factors
Describe the nociceptive pathway
4 steps:
Periphery
Spinal cord
Brain
Modulation
What happens physiologically in tissue injury?
-Release of chemicals soup
-Stimulates nociceptors.
-Sensitizes nociceptors.
-Signal travels in Aδ or C nerve to spinal cord
What does ‘group A-C’ nerve fibre classification refer to?
(The level of myelination)
Group A – heavily myelinated. Carry quick, sharp pain
Group B – moderately myelinated
Usually general visceral afferent fibres and preganglionic nerve fibres of the autonomic nervous system
Group C – unmyelinated. Carry slow, achy pain
What is the effect of myelin on nerves?
Myelination allows the formation of nodes of ranvier that speeds up the activity along the axon via saltatory conduction
What happens when the pain signal reaches the spinal cord?
- Dorsal horn is the first relay station.
- Aδ or C nerve synapses with second order neurone.
- Second order neurone travels up opposite side of spinal cord
What is the tract of lissauer for?
Afferent fibres reach the spinal cord and use it to ascend or descend
