Week 2 Flashcards
What are the 2 phases of pain and what fibres are responsible?
Quick and sharp - Aδ
Slow and dull - C
What sensory receptors are associated with Aα fibres?
Proprioceptors of skeletal muscle
What sensory receptors are associated with Aβ fibres?
Mechanoreceptors of skin
What sensory receptors are associated with Aδ fibres?
Pain and temperature
What sensory receptors are associated with C fibres?
Pain, temperature and itch
What is nociceptive pain?
Normal pain elicited only when a noxious stimulus which threatens to damage tissue is evoked
Protective/adaptive
High threshold, limited duration
Transmitted by Aδ and C fibres
What is chronic/clinical pain?
Evoked or spontaneous sustained sensory abnormality/peripheral pathology - stimulated by normally innocuous sensation
Maladaptive
Transmitted by Aβ, Aδ and C fibres
What is allodynia?
Normally innocuous stimuli perceived as noxious
What do hair follicle afferent receptors respond to?
Gentle brushing
What is dermatographia?
Condition in which light scratching of the skin causes intense reddening and raising - skin writing
What does the white reaction and triple response demonstrate?
Local effects of mild tissue damage
What is the white reaction and triple response?
White reaction - initial area of blanching on either side of scratch
Triple response - red reaction, wheal and flare
What is the red reaction, wheal and flare of the triple response?
Red reaction - red line at site of injury due to direct vasodilation mediated by histamine (primary hyperalgesia)
Wheal - slight oedema at site around red reaction, mediated by histamine
Flare - surrounding ill-defined erythema due to axon reflex (secondary hyperalgesia)
What mediators are released when tissue is damaged and where from?
Tissue damage - K+, prostaglandins
Plasma - bradykinin
Platelets - 5-HT
What mediators are released from axons at the site of tissue damage?
Substance P and CGRP which activate mast cells to release histamine
What role do substance P and CGRP play in tissue damage?
Substance P - plasma extravasation, oedema, bradykinin release
CGRP - vasodilation
What is ischaemic pain?
Pain associated with inadequate blood (and therefore oxygen) supply to active tissues (e.g. angina)
Where does referred pain from the heart radiate?
Left shoulder and arm
What laminae do Aδ and C-fibres terminate at in the spinal cord?
Laminae I and II
What laminae do Aβ (cutaneous) fibres terminate at in the spinal cord?
Laminae III-V
How does the supraspinal loop contribute to the modulation of nociceptive afferent input?
Serotonergic and
noradrenergic descending
projections from the periaqueductal grey matter
and medullary raphe nuclei directly inhibit projection of neurons and/or activate enkephalin containing interneurons to reduce nociceptive activity
What are the 2 explanations for how TENS machines work?
1 - stimulating large diameter axons of other sensory receptors, a jamming effect is created in the dorsal horn of the spinal cord (pain perception reduced/abolished by interference with pathway transmission)
2 - stimulation releases endorphins from the brainstem which activates descending pathways and suppresses pain pathway
What conditions are TENS machines used for?
RA, sciatica, sports injuries, MS, phantom-limb pain
What results should a cold-pressor test give?
Increased HR and BP as the sympathetic system is activated; will plateau/decrease eventually as parasympathetic is activated to maintain homeostasis