Physiology and Pathophysiology of Pain Flashcards
What is pain?
Unpleasant sensory and emotional experience associated with, or resembling, actual/potential tissue damage.
Are pain and nociception the same?
No
What is nociception?
The physiological process by which noxious stimulation is communicated through the peripheral and central nervous system
Where does the perception of pain occur?
Somatosensory cortex
What detects pain in the periphery?
Nociceptors
Which neurons transmit the pain from the periphery to the spinal cord?
First order neurons
Which type of neurons transmits from the spinal cord to the thalamus?
Second order neurons
What happens when the pain information reaches the thalamus?
Perception, learning, response
Nociceptors are free nerve endings of which types of fibres?
A delta and C fibres
At which temperature does it become known as noxious stimuli range?
Above 42 degrees.
Which type of things do nociceptors respond to?
Thermal, chemical and mechanical noxious stimuli
The first order neurons carry fibres to which part of the spinal cord?
Cell body in dorsal root ganglion
Which fibres transmit fast, sharp pain?
A delta fibres
Which types of fibre transmits dull pain?
C fibres
Where in the dorsal root ganglion do the first order neurons synapse?
Rexed lamina 1 and 2
Give three characteristics of the neurons which receive the input from primary afferents.
- Nociceptive specific
- Low threshold mechanoreceptive
- Wide dynamic range
Which tract in the main ascending tract for nociception?
Spinothalamic tract
Which rexed lamina does the spinothalamic tract arise from?
Rexed lamina 1, 2 & 5
What is allodynia?
Pain due to a stimulus which does not usually provoke pain
What changes are seen in the nociceptor in response to allodynia?
Decreased threshold for response
What is hyperalgesia?
Abnormally heightened sensitivity to pain
What changes are seen in the nociceptor in response to hyperalgesia?
Exaggerated response to normal and supranormal stimuli
What changes are seen in the nociceptor in response to spontaneous pain?
Spontaneous activity in nerve fibres
What is central sensitization?
Response of second order neurons in the CNS to both noxious and non-noxious stimuli
There are three components of central sensitization; wind-up, classical and long-term potentiation.
What is meant by wind-up?
Homosynaptic activity is dependant on the progressive increase in neuron response
Which type of synapses does wind-up involve?
Only activated synapses
Name the neurotransmitters involved in the process of wind-up.
Substance P
CGRP
What happens in classical central sensitization?
Involves opening up of new synapses and is responsible for a lot of pathophysiology
Which synapses are involved in long-term potentiation?
Mainly activated synapses
Which two things can pain be based on?
Duration e.g. chronic or acute
Mechanism
What are three mechanisms of pain?
Nociceptive
Neuropathic
Nociplastic
Is acute pain physiological or pathological?
Physiological
Is chronic pain physiological or pathological?
Pathological
Which type of pain serves as a protective function?
Acute pain
Which type of pain is nociceptive?
Acute
Which type of pain can be nociceptive, neuropathic or neoplastic?
Chronic
What is nociceptive pain?
A sensory experience that occurs when nociceptors respond to noxious stimuli
Describe nociceptive pain.
-Pain usually localised to site of injury
-Usually time limited
-Tends to respond to conventional analgesics
What is neuropathic pain?
Pain caused by a lesion or disease of the somato-sensory NS
Describe neuropathic pain.
-Painful region may not necessarily be the same of the affected site
-Predominantly chronic
-Poor response to analgesics
What is nociplastic pain?
Pain that arises from altered nociception despite no clear evidence of tissue damage, lesion or disease affecting the somatosensory system.
Describe nociplastic pain.
-Stimulus independent
-No inflammation/injury
-No structural neuronal damage
-Pathological
-No protective or adaptive function
-Due to central plasticity
