Physiology and Pathophysiology of Pain Flashcards
What is nociception?
Detection of tissue damage by specialized transducers connected to A(delta) and C fibres
Where are the cell bodies of primary afferent nerves located? Where do these nerves synapse?
Cell bodies in the dorsal root ganglion
Synapse at the spinal cord
Which nerve fibres are responsible for detecting fast/sharp pain? Which fibres sense secondary slow/dull pain? Why?
- A(delta) fibres detect first/sharp pain because they are myelinated with medium diameter
- C fibres detect slow/dull pain because they are unmyelinated with small diameter
Cell bodies of spinothalamic tract neurones mostly located in which rexed lamina? What is a rexed lamina?
rexed lamina 1, 2 & 5
Rexed laminae is a system of labelling portions of grey matter in the SC according to their cellular composition. Similar to Brodmann areas
Which nuclei of the thalamus is involved in the relay of nociceptive information?
Ventroposterior thalamic nuclei and the medial dorsal nucleus
To what parts of the brain does the thalamus relay pain information?
- Cortex
- Limbic System
- Brainstem
What is the primary control centre for descending pain modulation?
PAG
Periaqueductal grey matter (located around the cerebral aqueduct)
What is hyperalgesia and when does it occur?
It is increased perception of pain or even perception of non-noxious stimuli as noxious
Occurs whenever there is tissue injury or inflammation
Difference between primary and secondary hyperalgasia?
Primary: hyperalgesia at the site of injury
Secondary: hyperalgesia in the surrounding tissue
What is allodynia?
Reduction in the threshold at which stimuli becomes noxious, often following non-painful stimulation
Examples of peripheral sensitization?
- Allodynia: reduced threshold
- Hyperalgesia: exaggerated responses
- Spontaneous pain: often without stimuli
What is central sensitization?
When the second order neurones in the CNS start inputting noxious and non-noxious stimuli as pain
3 Main components of central sensitization?
- Wind up
- Classical
- Long-term potentiation
What is wind up? When does it manifest?
Winding up the response to input
Smaller inputs create larger responses due to wound up system, manifests over the course of the stimulus and terminates with the stimulus
What is classical central sensitization? How long does it last in relation to the activating stimulus?
- New synapses are opened up in the dorsal horn, only respond to significant stimuli
- When significant stimuli activates new pathways, pain response tends to outlast the stimuli and can be maintained at even low levels of ongoing stimuli
How is long term potentiation central sensitization activated?
- Involves mainly the activated synapses, occurs primarily for very intense stimuli
Differences between segmental and suprasegmental central sensitization?
Segmental - nerve injury in SC, pain response is segmented/localized
Suprasegmental - nerve injury in brain, pain is felt all over the body (fibromyalgia/chronic widespread pain)
Differences between acute and chronic pain?
- Acute lasts for <1 month, chronic for >3-6 months
- Acute pain resolves upon healing
- Chronic pain doesn’t usually serve a protective function like acute pain
- Acute pain occurs in presence of noxious stimuli, chronic pain doesn’t require stimuli
What is nociceptive pain?
Sensory experience in response to specific peripheral sensory neurones respond to noxious stimuli
Can nociceptive pain be chronic?
- Usually time limited and resolves
- Can be chronic, but still in response to valid stimuli (eg. osteoarthritis)
What is neuropathic pain?
Pain caused by a primary lesion or dysfunction in the somato-sensory nervous system
Usually chronic, painful region may not be the same as site of injury
How do neuropathic and nociceptive pain tend to respond to analgesics?
- Nociceptive tends to respond to conventional analgesics
- Neuropathic does not
Four phases at which you can attempt to treat pain?
- Transduction (NSAIDS/Ice)
- Transmission (opiods/surgery)
- Perception (Behavioural therapy)
- Descending modulation (opiods/spinal cord stimulation)
What is a cordotomy?
- Surgical procedure that disables selected pain conducting tracts in the spinal cord
(stops pain at transmission stage)