Physiology and Pathophysiology of Pain Flashcards
What is pain?
Pain is an unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of such damage or both
Is not a stimulus
Final product of complex-information processing network
What are the steps in the pain pathway?
Step 1. Periphery
- Detection
- Transmission to spinal cord (first order neurons)
Step 2. Spinal cord
- Processing
- Transmission to brain (Thalamus) (second order neurons)
Step 3. Brain
• Perception, learning, response
Step 4. Modulation
• Descending tracts
What does the thalamus do?
Recieves all sensory information then sends it to all different parts of the brain
What is nociception?
The detection of tissue damage by specialized transducers connected to A-delta and C fibers
What are nociceptors and what do they respond to?
Free nerve endings of A delta and C-fibres
Respond to thermal, chemical, mechanical noxious stimuli
Where is the cell body of primary afferents/1st order neurons located and where do they synapse?
Cell body in Dorsal root ganglion
First order neurons
Synapse at spinal cord
Describe the features of the different types of fibres
Are C fibres myleinated and therefroe do they conduct fast or slow?
non-myelinated
conduct slowly
What do axons entering the spinal dorsal horn continue as?
tracts
What is the spinothalamic tract?
Major ascending tract for nociception
Arises in Rexed Lamina 2 & 5
Forms the lateral spinothalamic tract
Ends in:
Ventroposterior thalamic nuclei
Medial thalamus
Thalamus is the second ___________
Thalamus is the second relay station
Where does the thalamus have connections with?
cortex
limbic system
brain stem
Where is the main area in the thalamus that spinothalamic tracts go?
Ventroposterior thalamic nuclei
Medial thalamus
Pain perception occurs in ________________
Pain perception occurs in somatosensory cortex
Why does the thalamus send information about pain to the limbic system?
to help form memories, learning and emotion
Descending pathways come form the brain to ______
dorsal horn
What do the descending pathways do to the pain signal
usually decrease it
What is allodynia?
Allodynia refers to central pain sensitization (increased response of neurons) following normally non-painful, often repetitive, stimulation. Allodynia can lead to the triggering of a pain response from stimuli which do not normally provoke pain
What is A?
Defnition of Allodynia
Decreased threshold for response
What is B?
Definition of Hyperalgesia
Exaggerated response to normal and supranormal stimuli
What is C?
Definition of Spontaneous Pain
Spontaneous activity in nerve fibres
What is Central sensitization?
Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain
It is the response of second order neurons in the CNS to normal input both noxious & non-noxious
What are the 3 main components of Central sensitization?
wind-up
classical
long-term potentiation
What is wind up central sensitisation?
Involves only activated synapses
Homosynaptic activity dependent progressive increase in response of the neurons
Manifests over the course of stimuli & terminates with stimuli
Wind-up is literally winding up the response to the input. So the wind-up happens only in neurons taking part in the synapses with primary afferent input. It is activity dependent; progressively increases the response of the neurons
What is classic central sensitisation?
Involves opening up of new synapses (silent nociceptors)
the new synapses, which were silent till then, will start to receive input and record the nociception
Heterosynaptic activity dependent plasticity
Immediate onset with appropriate stimuli
Outlast the initial stimuli duration
Can be maintained even at low levels of ongoing stimuli
What is long-term potentiation central sensitisation?
Involves mainly the activated synapses
Occurs primarily for very intense stimuli
a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons
What are the features of acute pain?
<1 month
Usually obvious tissue damage
Increased nervous system activity
Pain resolves upon healing
Serves a protective function
What are the features of chronic pain?
>3-6 months
Pain for 3–6 months or more
Pain beyond expected period of healing
Usually has no protective function
Degrades health and function
Differences between acute and chronic pain:
pathological or physiological?
acute - physiological
chronic - pathological
Differences between acute and chronic pain:
presence of noxious stimuli or not
acute - Presence of noxious stimuli
chronic - Presence of noxious stimuli is not essential
Differences between acute and chronic pain:
what is the purpose?
acute - Serves protective function
chronic - Does not serve any purpose
Differences between acute and chronic pain:
what controls it?
acute - Usually nociceptive
chronic - Nociceptive, neuropathic or mixed
What is nociceptive pain?
A sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli
Painful region is typically localised at the _______ -often described as throbbing, aching or stiffness
site of injury
Nociceptive pain is usually ______ limited and resolves when ___________ heals (e.g. bone fractures, burns and bruises)
Can also be _______ (e.g. osteoarthritis)
Usually time limited and resolves when damaged tissue heals (e.g. bone fractures, burns and bruises)
Can also be chronic (e.g. osteoarthritis)
What does nociceptive pain tend to respond to?
Tends to respond to conventional analgesics
What is neuropathic pain?
Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system
Where is neuropathetic pain felt?
The painful region may not necessarily be the same as the site of injury - pain occurs in the neurological territory of the affected structure (nerve, root, spinal cord, brain)
Does neuropathic pain tend to be a chronic or an acute condition?
Almost always a chronic condition (e.g. postherpetic neuralgia [PHN], poststroke pain)
How does neuropathic pain respond to conventional analgesics?
Responds poorly to conventional analgesics
What is nociplastic pain?
Pain that arises form altered nociception despite no clear evidence of actual or threated tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain
Does nociplastic pain depend on a stimulus?
no
stimulus independent
In nociplastic pain is there any injury or structural neuronal damage?
No inflammation/injury
No structural neuronal damage
What is nociplastic pain due to?
due to central plasticity - Neural plasticity refers to the ability of neurons to change in form and function in response to alterations in their environment
Does nociplastic pain have any function?
serves no protective or adaptive function
Is nociplastic pain pathological or physiologic pain?
pathological
What can be used in the management of transduction of pain?
NSAIDs
Ice
Rest
LA blocks
Nerve blocks
Drugs e.g. opioids
Surgery
What is the gate control theory?
The gate control theory of pain asserts that non-painful input closes the nerve “gates” to painful input, which prevents pain sensation from traveling to the central nervous system. Gate Control Theory of Pain describes how non-painful sensations can override and reduce painful sensations
What is used in the management of perception of pain?
Education
Cognitive behavioural therapy
Distraction
Relaxation
Graded motor imagery
Mirror box therapy - helps allivate phantom limb pain
a box with a mirror down the center, patient places the good limb into one side and the residual limb into the other and patient then looks into the mirror on the side with the good limb and makes “mirror symmetric” movements. Because the subject is seeing the reflected image of the good hand moving, it appears as if the phantom limb is also moving
What can be used in the management of descending modulation in pain?
(if the input of pain cant be contorlled then this is how pain would be contorlled)
Placebos
Drugs - Opioids, Antidepressants
Surgery - Spinal cord stimulation
Pain is a _________ phenomena while nociception is the _________ process
Pain is a subjective phenomena while nociception is the physiologic process
Pain is subjected to ___________at every stage of transmission (this can be used to our advantage)
Pain is subjected to modulation at every stage of transmission (this can be used to our advantage)
Does chronic pain serve any protective function?
no
