Pain mechanisms Flashcards
(36 cards)
What are the 3 forms of pain?
Nociceptive, inflammatory and pathological pain
What is nociceptive pain?
Adaptive - an immediate protective response, short lived
What is inflammatory pain?
Adaptive - assists in healing, persists over days, possibly weeks
What is pathological pain?
Maladaptive - no physiological purpose, persists over months, years or even a lifetime
How is acute pain normally managed?
Generally effectively controlled by NSAIDs, paracetamol and in moderate/severe cases the addition of opioids of several classes
Chronic pain can sometimes be managed by a number of alternative classes of drug such as?
Antidepressants
Anticonvulsants
Local anaesthetics
What kind of pain is not managed well by opioids?
Neuropathic pain
How is pain originating from the skin typically described?
Well localised
Pricking, stabbing, burning
How is pain originating from muscle typically described?
Poorly localised
Aching, soreness, tenderness, cramping, stabbing, burning
How is pain originating from viscera typically described?
Poorly localised
Dullness, vagueness, fullness, nausea
Somatosensory pathways often comprise three neurons in series. Where is the cell body location of the 1st order neuron?
Dorsal root ganglia (innervation of limbs, trunk, posterior head) or cranial ganglia (innervation of anterior head)
Somatosensory pathways often comprise three neurons in series. Where is the cell body location of the 2nd order neuron?
Dorsal horn of spinal cord or brainstem nuclei
Somatosensory pathways often comprise three neurons in series. Where is the cell body location of the 3rd order neuron?
Thalamic nuclei
What are nociceptors?
Specific peripheral primary sensory afferent neurons normally activated preferentially by intense stimuli (e.g. thermal, mechanical, chemical) that are noxious
Nociceptors are first order neurons that relay information to 2nd order neurons in the CNS by chemical synaptic transmission
Nociceptive pain is adaptive and high threshold. What does this mean?
Adaptive - an early warning system to detect and minimise contact with damaging stimuli
High threshold - generally provoked only by intense stimuli that active nociceptors
How does nociceptive pain override most other ongoing activities of the nervous system?
Initiates a withdrawal reflex
Is extremely unpleasant
Engages adverse emotional components
Serves to inscribe memories that allow avoidance of harm in the future
Inflammatory pain is adaptive and protective. What does this mean?
Adaptive and protective - caused by activation of the immune system in injury or infection
Causes pain hypersensitivity (heightened sensitivity to noxious stimuli) and allodynia (innocuous stimuli now elicit pain)
Assists in healing of a damaged body part - pain recedes once this has occurred
Pathological pain is maladaptive. What does this mean?
Results from abnormal nervous system function - may be neuropathic or dysfunctional
What are the subtypes of nociceptor?
A delta fibres
C fibres
What are A delta fibres?
Mechanical/thermal nociceptors that are thinly myelinated - respond to noxious mechanical and thermal stimuli
Mediate first or fast pain
What are C fibres?
Nociceptors that are unmyelinated - collectively they respond to all noxious stimuli
Mediate second or slow pain
What is frequency coding?
The rate of action potential discharge correlates with the intensity of the applied stimulus
What do C-MH fibres respond to?
Noxious mechanical stimuli, activated by noxious heat, sensitive to capsaicin
Shows sensitisation to repeated stimuli
Contributes to heat pain and location of the stimulus
What do C-M fibres respond to?
Noxious mechanical stimuli, insensitive to heat and capsaicin