Flashcards in Physiology of Pain Deck (28):
What are nociceptors?
Nociceptors are specific peripheral primary sensory afferent neurones normally activated preferentially by intense stimuli (e.g. thermal, mechanical, chemical) that are noxious
Comprose Adelta and C-fibres.
what type of neurones are nociceptors?
First order neurones
What are the 3 forms of pain? Are they adaptive or maladaptive?
Nociceptive pain - adaptive
Inflammatory pain - adaptive
Pathological pain - maladaptive
Why is pain essential to the protection of the organsim?
Discourages physical contact and movement thus promoting tissue repair
Describe first and second pain noting the nociceptors involved in these processes.
First pain - immediately after the insult – know exactly where it’s coming from – lancinating, stabbing, pricking
Second pain - throbbing, cramping, aching, burning, not as well localised - mediated by C-fibres
Describe the nociceptive pathway from a peripheral site to the dorsal horn of the spinal cord and the projection pathways from the spinal cord to the brain
- Free nerve ending is stimulated by noxious componeent
- Axon of nociceptor (1st order neurone)
- dorsal (posterior) horn of spinal cord
!Crosses over spinal cord!
- Axon of projection (2nd order) neurone
- Anterior (neo)- and posterior (paleo)-spinothalamic and spinoreticulothalamic tracts on opposite side of body – contra-laterally
What kind of functions do peptidergic C-fibres have?
efferent and afferent functions
Describe the development of neurogenic inflammation
CGRP released from branches of free nerve endings can propagate around other free nerve endings giving efferent signal away from CNS – sets up special kind of inflammation = neurogenic inflammation
Give examples of stimuli that can cause nociceptor sensitization.
What is hyperalgesia? Primary and secondary
Increased sensitivity to pain caused by damage to nociceptors or peripheral nerves
Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues.
Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues.
What is allodynia?
innoculus stimuli now elici pain
What is pain hypersensitivity?
heightened sensitivity to noxious stimuli
What causes inflammatory pain?
activation of the immune system to injury or infectop
What causes pathological pain?
results from abnormal nervous system function - may be neuropathic or dysfunctional.
Does pathological pain have a protective function?
what is the purpose of nociceptive pain?
Serves as an early warning system to detect and minimise contact with damaged stimuli (noxious events)
Why is nociceptive pain high threshold?
It is provoked only by intense stimuli that activate nociceptors
How does nociceptive pain override most other ongoing activities of the nervous system?
- initiates a withdrawl reflex
- extremely unpleasant
- engages adverse emotional components
- serves to inscribe memories that allow avoidance of harm in the future
What happens in the absence of pain?
Gross damage to the body occurs and goes undetected
What are Adelta fibres?
mechanical/thermal nociceptors that are thinly myelinated (conduction velocity of 6 – 30 ms-1 ) - respond to noxious mechanical and thermal stimuli. Mediate ‘first pain’
What are C-fibres?
nociceptors that are unmyelinated (conduction velocity of 0.5 – 2.0 ms-1) – collectively they respond to all noxious stimuli (e.g. they are polymodal). Mediate ‘second pain’
Where do dorsal root ganglia lie?
Lateral to the spinal column – project centrally to the dorsal horn of the spinal cord and peripherally to the skin, muscle, tendons, joints, internal organs
Where do Trigeminal ganglia project?
centrally to brainstem trigeminal nucleus
Where do Nodose (iferior vagal) ganglia go?
Project centraly to the floor of the 4th ventricle to innervate the viscera
What do selective NSAIDs inhibit?
COX2 (to inhibit the synthesis and accumulation of prostaglandins)
Give examples of non-selective NSAIDs.
aspirin, ibuprofen, indometacin, naproxen and diclofenac – prescription drugs not OTC drugs
Peptidergic Polymodal Nociceptors are what and have what?
Subset of C-fibres
afferent and efferent functions